Dr Tomas Ramirez Reina

The catalytic oxidation of aqueous crystal violet (CV) solutions was investigated using Ni and Fe catalysts supported over Mg–Al oxides synthesized by the autocombustion method. The influence of temperature, loading, and selectivity were studied in the catalytic wet air oxidation (CWAO) of CV. The kind of metal had an important contribution in the redox process as significant differences were observed between Fe, Ni, and their mixtures. The catalysts with only Fe as active phase were more efficient for the oxidation of CV under normal conditions (T = 25 °C and atmospheric pressure) compared to those containing Ni, revealing the influence of the transition metal on catalytic properties. It was found that iron-containing materials displayed enhanced textural properties. The synthesis of Fe/MgAl catalysts by the autocombustion method led to solids with excellent catalytic behavior, 100% CV degradation in eight hours of reaction, 68% selectivity to CO₂, and significant reduction of chemical oxygen demand (COD).

The catalytic oxidation of aqueous Crystal Violet (CV) solutions has been investigated using Ni and Fe catalysts supported over Mg-Al oxides synthetized by the auto-combustion method. The influence of temperature, loading and selectivity were studied in the catalytic wet air oxidation (CWAO) of CV. The kind of metal had an important contribution in the redox process, since significant differences between Fe, Ni and their mixtures were observed. The catalysts with only Fe as active phase were more efficient for the oxidation of CV under normal conditions (T = 25 °C and atmospheric pressure) compared to those containing Ni, revealing the influence of the transition metal on catalytic properties. It was found that iron containing materials displayed enhanced textural properties. The synthesis of Fe/MgAl catalysts by the auto-combustion method, leads to solids with excellent catalytic behavior, CV degradation of 100% in eight hours of reaction, 68% of selectivity to CO2 and significant reduction of COD (Chemical oxygen demand)

The development of catalytic materials for the recycling CO₂ through a myriad of available processes is an attractive field, especially given the current climate change. While there is increasing publication in this field, the reported catalysts rarely deviate from the traditionally supported metal nanoparticle morphology, with the most simplistic method of enhancement being the addition of more metals to an already complex composition. Encapsulated catalysts, especially yolk@shell catalysts with hollow voids, offer answers to the most prominent issues faced by this field, coking and sintering, and further potential for more advanced phenomena, for example, the confinement effect, to promote selectivity or offer greater protection against coking and sintering. This work serves to demonstrate the current position of catalyst development in the fields of thermal CO₂ reforming and hydrogenation, summarizing the most recent work available and most common metals used for these reactions, and how yolk@shell catalysts can offer superior performance and survivability in thermal CO₂ reforming and hydrogenation to the more traditional structure. Furthermore, this work will briefly demonstrate the bespoke nature and highly variable yolk@shell structure. Moreover, this review aims to illuminate the spatial confinement effect and how it enhances yolk@shell structured nanoreactors is presented.

Increasing demand for CO2 utilization reactions and the stable character of CO2 have motivated the interest in developing highly active, selective and stable catalysts. Precious metal catalysts have been studied extensively due to their high activities, but their implementation for industrial applications is hindered due to their elevated cost. Among the materials which have comparatively low prices, transition metal carbides (TMCs) are deemed to display catalytic properties similar to Pt-group metals (Ru, Rh, Pd, Ir, Pt) in several reactions such as hydrogenation and dehydrogenation processes. In addition, they are excellent substrates to disperse metallic particles. Hence, the unique properties of TMCs make them ideal substitutes for precious metals resulting in promising catalysts for CO2 utilization reactions. This work aims to provide a comprehensive overview of recent advances on TMCs catalysts towards gas phase CO2 utilization processes, such as CO2 methanation, reverse water gas shift (rWGS) and dry reforming of methane (DRM). We have carefully analyzed synthesis procedures, performances and limitations of different TMCs catalysts. Insights on material characteristics such as crystal structure and surface chemistry and their connection with the catalytic activity are also critically reviewed.

Washing synthetic textile fibers releases micro/nano plastics, endangering the environment. As new filters and associated regulations are developed to prevent fiber release from washing machines, there emerges a need to manage the collected waste, for which the only current options are combustion or landfill. Herein we show for the first time the application of a catalytic pyrolysis approach to upcycle textile derived fibrous micro/nano plastics waste, with the aim of keeping carbon in the solid phase and preventing its release as a greenhouse gas. Herein, we demonstrate the co-production of hydrogen and carbon nanomaterials from the two most prevalent global textile microfiber wastes: cotton and polyester. Our results pave a way forward to a realistic process design for upcycling mixed micro/nano fiber waste collected from laundering, drying, vacuuming, and environmental cleanup.

Summary This work reports the synthesis and characterisation of a core‐shell n‐octacosane@silica nanoencapsulated phase‐change material obtained via interfacial hydrolysis and polycondensation of tetraethyl orthosilicate in miniemulsion. Silica has been used as the encapsulating material because of its thermal advantages relative to synthesised polymers. The material presents excellent heat storage potential, with a measured melting latent heat varying between 57.1 and 89.0 kJ kg−1 (melting point between 58.2°C and 59.9°C) and a small particle size (between 565 and 227 nm). Degradation of the n‐octacosane core starts between 150°C and 180°C. Also, the use of silica as shell material gives way to a heat conductivity of 0.796 W m−1 K−1 (greater than that of nanoencapsulated materials with polymeric shell). Charge/discharge cycles have been successfully simulated at low pressure to prove the suitability of the nanopowder as phase‐change material. Further research will be carried out in the future regarding the use of the synthesised material in thermal applications involving nanofluids.

Catalytic hydrodeoxygenation (HDO) is a critical technique for upgrading biomass derivatives to deoxygenated fuels or other high-value compounds. Phenol, guaiacol, anisole, p-cresol, m-cresol and vanillin are all monomeric phenolics produced from lignin. Guaiacol is often utilised as a model lignin compound to deduce mechanistic information about the bio-oil upgrading process. Typically, a source of H2 is supplied as reactant for the HDO reaction. However, the H2 supply, due to the high cost of production and additional safety precautions needed for storage and transportation, imposes significant economic infeasibilities on the HDO process's scaling up. We investigated a novel H2-free hydrodeoxygenation (HDO) reaction of guaiacol at low temperatures and pressures, using water as both a reaction medium and hydrogen source. A variety of Ni catalysts supported on zirconia/graphene/with/without nitrogen doping were synthesised and evaluated at 250 °C and 300 °C in a batch reactor, with the goal of performing a multi-step tandem reaction including water splitting followed by HDO. The catalysts were characterised using H2-TPR, XRD, TEM and XPS to better understand the physicochemical properties and their correlation with catalytic performance of the samples in the HDO process. Indeed, our NiZr2O/Gr-n present the best activity/selectivity balance and it is deemed as a promising catalyst to conduct the H2-free HDO reaction. The catalyst reached commendable conversion levels and selectivity to mono-oxygenated compounds considering the very challenging reaction conditions. This innovative HDO approach provides a new avenue for cost-effective biomass upgrading. [Display omitted] •Innovative in-situ HDO approach with H2O as the source of hydrogen.•Polymers containing nitrogen as precursors for N-doped carbon supports.•Addition of Zr2O to the catalyst as a promoter.•Advanced Ni-based N-doped carbon supported catalysts for "H2-free" HDO of guaiacol synthesis.•NiZr2O/Gr-n has the most favourable activity/selectivity ratio for the “H2-free” HDO reaction.

Here we present a comprehensive study on the effect of reaction parameters on the upgrade of an acetone, butanol and ethanol mixture – key molecules and platform products of great interest within the chemical sector. Using a selected high performing catalyst, Fe/MgO-Al2O3, the variation of temperature, reaction time, catalytic loading and reactant molar ratio have been examined in this reaction. This work is aiming to not only optimise the reaction conditions previously used, but to step towards using less energy, time and material by testing those conditions and analysing the sufficiency of the results. Herein we demonstrate that this reaction is favored at higher temperatures and longer reaction time. Also, we observe that increasing the catalyst loading had a positive effect on the product yields, while reactant ratios have shown to produce varied results due to the role of each reactant in the complex reaction network. In line with the aim of reducing energy and costs, this work showcases that the products from the upgrading route have significantly higher market value than the reactants, highlighting this process represents an appealing route to be implemented in modern biorefineries.

MAX phases are layered ternary carbides or nitrides that are attractive for catalysis applications due to their unusual set of properties. They show high thermal stability like ceramics, but they are also tough, ductile, and good conductors of heat and electricity like metals. Here, we study the potential of the Ti 3 AlC 2 MAX phase as a support for molybdenum oxide for the reverse water–gas shift (RWGS) reaction, comparing this new catalyst to more traditional materials. The catalyst showed higher turnover frequency values than MoO 3 /TiO 2 and MoO 3 /Al 2 O 3 catalysts, due to the outstanding electronic properties of the Ti 3 AlC 2 support. We observed a charge transfer effect from the electronically rich Ti 3 AlC 2 MAX phase to the catalyst surface, which in turn enhances the reducibility of MoO 3 species during reaction. The redox properties of the MoO 3 /Ti 3 AlC 2 catalyst improve its RWGS intrinsic activity compared to TiO 2 - and Al 2 O 3 -based catalysts. MAXimize your conversion! The hydrogenation of CO 2 via reverse water−gas shift can be catalyzed efficiently by molybdenum oxide supported on a MAX phase.

This work showcases cost-effective elemental mercury capture strategy enabled by bamboo saw dust and bromine flame retardant (BFR) derived sorbent prepared by a novel hydrothermal-pyrolysis method. The hydrothermal treatment of bamboo and BFR blend was conducted in subcritical water resulting in a hydrothermal char. Subsequently, the hydrothermal char was pyrolyzed in nitrogen atmosphere leading to an improved pore architecture. The resulting biomaterials were proven highly effective for Hg removal. A thorough analysis of the physicochemical properties of the samples was conducted by means of BET, SEM, XRD, XPS and FT-IR. Key parameters such as bamboo/BFR ratio, hydrothermal temperatures and pyrolysis temperatures influence Hg0 removal capacity of our bio-sorbents. Overall, the optimal bamboo/BFR ratio, hydrothermal temperature and pyrolysis temperature are 2:1, 320 °C and 800 °C, respectively. Under these optimized conditions, a very promising elemental mercury removal efficiency of 99% is attained. The kinetics and mechanism of Hg0 removal are also proposed. The experimental data fit well with a pseudo-second-order model, indicating that Hg0 adsorption over sorbents was dominated by chemisorption. Our results indicate that the C–Br groups in sorbents provide active sites for oxidizing Hg0 into HgBr2. [Display omitted] •Bamboo and BFR were used to prepare sorbents for Hg0 removal.•A novel hydrothermal-pyrolysis method was proposed.•The optimal preparation parameters were determined.•Hg0 adsorption over sorbents was dominated by chemisorption.•C-Br groups were dominated active sites for oxidizing Hg0 into HgBr2.

Time-resolved operando DRIFTS-MS was performed to elucidate the CO2 capture and conversion mechanisms of a NiRuNa/CeAl DFM in CO2 methanation, reverse water-gas shift, and dry reforming of methane. CO2 was captured mainly in the form of carbonyls and bidentate carbonates, and a spillover mechanism occurred to obtain the desired products.

The CO₂ methanation is an important process in coal-to-gas, power-to-gas and CO₂ removal for spacecraft. Recently, metal-organic framework (MOF) derivatives have been demonstrated as high-performance catalysts for CO₂ upgrading processes. However, due to the high costs and low stability of MOF derivatives, it still remains challenge for the development of alternative synthesis methods avoiding MOF precursors. In this work, we present the sol-gel method for loading Ni-MOF to silica support in two-steps. Upon modifying the procedure, a more simplified one-step sol-gel method has been developed. Furthermore, the obtained Ni/SiO₂ catalyst still exhibits great catalytic performance with a CO₂ conversion of 77.2% and considerable CH4 selectivity of ~100% during a stability test for 52 h under a low temperature of 310 °C and high GHSV of 20,000 mL·g−1·h−1. Therefore, this work provides a ground-breaking direct strategy for loading MOF derived catalysts, and might shed a light on the preparation of highly dispersed Ni/SiO₂ catalyst.

With the aim of moving towards sustainability and renewable energy sources, we have studied the production of long chain hydrocarbons from a renewable source of biomass to reduce negative impacts of greenhouse gas emissions while providing a suitable alternative for fossil fuel-based processes. Herein we report a catalytic strategy for Acetone, Butanol and Ethanol (ABE) upgrading using economically viable catalysts with potential impact in modern bio-refineries. Our catalysts based on transition metals such as Ni, Fe and Cu supported on MgO-Al2O3 have been proven to perform exceptionally with outstanding conversions towards the production of a broad range of added value chemicals from C2 to C15. Although all catalysts displayed meritorious performance, the Fe catalyst has shown the best results in terms conversion (89%). Interestingly, the Cu catalyst displays the highest selectivity towards long chain hydrocarbons (14%). Very importantly, our approach suppresses the utilization of solvents and additives resulting directly in upgraded hydrocarbons that are of use in the chemical and/ or the transportation industry. Overall, this seminal work opens the possibility to consider ABE upgrading as a viable route in bio-refineries to produce renewably sourced added value products in an economically favorable way. In addition, the described process can be envisaged as a cross-link stream among bio and traditional refineries aiming to reduce fossil fuel sources involved and incorporate “greener” solutions.

Carbon dioxide (CO2) is one of the most harmful greenhouse gases and it is the main contributor to climate change. Its emissions have been constantly increasing over the years due to anthropogenic activities. Therefore, efforts are being made to mitigate emissions through carbon capture and storage (CCS). An alternative solution is to close the carbon cycle by utilising the carbon in CO2 as a building block for chemicals synthesis in a CO2 recycling approach that is called carbon capture and utilisation (CCU). Dual Function Materials (DFMs) are combinations of adsorbent and catalyst capable of both capturing CO2 and converting it to fuels and chemicals, in the same reactor with the help of a co-reactant. This innovative strategy has attracted attention in the past few years given its potential to lead to more efficient synthesis through the direct conversion of adsorbed CO2. DFM applications for both post combustion CCU and direct air capture (DAC) and utilisation have been demonstrated to date. In this review, we present the unique role DFMs can play in a net zero future by first providing background on types of CCU methods of varying technological maturity. Then, we present the developed applications of DFMs such as the synthesis of methane and syngas. To better guide future research efforts, we place an emphasis on the connection between DFM physiochemical properties and performance. Lastly, we discuss the challenges and opportunities of DFM development and recommend research directions for taking advantage of their unique advantages in a low-carbon circular economy.

Nowadays, global climate change is likely the most compelling problem mankind is facing. In this scenario, decarbonisation of the chemical industry is one of the global challenges that the scientific community needs to address in the immediate future. Catalysis and catalytic processes are called to play a decisive role in the transition to a more sustainable and low-carbon future. This critical review analyses the unique advantages of structured reactors (isothermicity, a wide range of residence times availability, complex geometries) with the multifunctional design of efficient catalysts to synthesise chemicals using CO2 and renewable H-2 in a Power-to-X (PTX) strategy. Fine-chemistry synthetic methods and advanced in situ/operando techniques are essential to elucidate the changes of the catalysts during the studied reaction, thus gathering fundamental information about the active species and reaction mechanisms. Such information becomes crucial to refine the catalyst's formulation and boost the reaction's performance. On the other hand, reactors architecture allows flow pattern and temperature control, the management of strong thermal effects and the incorporation of specifically designed materials as catalytically active phases are expected to significantly contribute to the advance in the valorisation of CO2 in the form of high added-value products. From a general perspective, this paper aims to update the state of the art in Carbon Capture and Utilisation (CCU) and PTX concepts with emphasis on processes involving the transformation of CO2 into targeted fuels and platform chemicals, combining innovation from the point of view of both structured reactor design and multifunctional catalysts development.

[Display omitted] •Economically viable catalysts for gas phase CO2 upgrading.•Ni promoted active phases supported on saponite clay as nature inspired catalysts.•Advantageous bimetallic Ni-Cu formulation to suppress methanation.•Remarkable selectivity for low temperature RWGS using Ni-Cu/Saponite. Chemical CO2 upgrading via reverse water gas shift (RWGS) represents an interesting route for gas phase CO2 conversion. Herein, nature inspired clay-based catalysts are used to design highly effective materials, which could make this route viable for practical applications. Ni and transition metal promoted Ni saponite clays has been developed as highly effective catalysts for the RWGS. Saponite supported NiCu catalyst displayed a remarkable preference for the formation of CO over CH4 across the entire temperature range compared to the saponite supported NiCo and Ni catalysts. The NiCu sample is also highly stable maintaining ∼ 55% CO2 conversion and ∼ 80% selectivity for CO for long terms runs. Very importantly, when compared with reference catalysts our materials display significantly higher levels of CO2 conversion and CO selectivity. This confirmed the suitability of these catalysts to upgrade CO2-rich streams under continuous operation conditions.

This paper deals with the development and potential application of a novel mixed ionic-electronic conductive anode composite comprised of copper and iron oxide based on gadolinium-doped ceria (CuO–Fe2O3/GDC) for solid-oxide fuel cell (SOFC). Synthesis of the nanocrystalline CuO–Fe2O3/GDC powders was carried out using a novel co-precipitation method based on ammonium tartrate as the precipitant in a mixed-cationic solution composed of Cu2+, Fe3+, Gd3+, and Ce3+. Thermal decomposition of the resultant precipitate after drying (at 55 °C) was investigated in a wide range of temperature (25–900 °C) using simultaneous DSC/TGA technique in air. The DSC/TGA results suggested the optimal calcination temperature of 500 °C for obtaining the nanocrystalline anode composite from the resultant precipitate. The synthesised CuO–Fe2O3/GDC samples were further characterised using XRD, dilatometry, FESEM, and EDX. Several single cells of SOFCs were fabricated in the anode-supported geometry using the synthesised CuO–Fe2O3/GDC composite as the anode, GDC/CuO composite as the electrolyte, and LSCF/GDC composite as the cathode layer. The fabricated cells were analysed using FESEM imaging and EIS analysis, where an equivalent circuit containing five R-CPE terms was used to interpret the EIS data. The module fitted well the impedance data and allowed for a detailed deconvolution of the total impedance spectra. The catalytic activity and uniformity of the synthesised nanocomposites was further evaluated using TPR analysis, demonstrating excellent activity at temperatures as low as 200 °C.

In this work, the use of biomethane produced from local biogas plants is proposed as renewable fuel for light marine transport. A profitability analysis is performed for three real biogas production plants located in Cornwall (United Kingdom), considering a total of 66 different scenarios where critical parameters such as distance from production point to gas grid, subsidies, etcetera, were evaluated. Even though the idea is promising to decarbonize the marine transport sector, under the current conditions, the approach is not profitable. The results show that profitability depends on the size of the biogas plant. The largest biogas plant studied can be profitable if feed-in tariffs subsidies between 36.6 and 45.7 €/MWh are reached, while for the smallest plant, subsidies should range between 65 and 82.7 €/MWh. The tax to be paid per ton of CO2 emitted by the shipping owner, was also examined given its impact in this green route profitability. Values seven times greater than current taxes are needed to reach profitability, revealing the lack of competitiveness of renewable fuels vs traditional fuels in this application. Subsidies to make up a percentage of the investment are also proposed, revealing that even at 100% of investment subsidized, this green approach is still not profitable. The results highlight the need for further ambitious political actions in the pursuit of sustainable societies.

[Display omitted] •Novel in-situ HDO strategy with H2O as hydrogen source.•N-doped reduced graphene oxide (RGO) advanced supports.•Comparison among Pt-based and Ni N-doped RGO supported catalysts for ‘H2-free’ HDO of guaiacol.•Innovate route for economically viable biomass upgrading. Herein we present an innovative route for model biomass compounds upgrading via “H2-free” hydrodeoxygenation (HDO) reactions. The underlaying idea is to implement a multifunctional catalyst able to activate water and subsequently use in-situ generated hydrogen for the HDO process. In this sense we have developed a series of effective Ni and Pt based catalysts supported on N-promoted graphene decorated with ceria. The catalyst reached commendable conversion levels and selectivity to mono-oxygenated compounds considering the very challenging reaction conditions. Pt outperforms Ni when the samples are tested as-prepared. However, Ni performance is remarkably boosted upon applying a pre-conditioning reductive treatment. Indeed, our NiCeO2/GOr-N present the best activity/selectivity balance and it is deemed as a promising catalyst to conduct the H2-free HDO reaction. Overall, this “proof-concept” showcases an economically appealing route for bio-compounds upgrading evidencing the key role of advanced catalysts for a low carbon future.

The RWGS reaction represents a direct approach for gas-phase CO2 upgrading. This work showcases the efficiency of Fe/CeO2-Al2O3 catalysts for this process, and the effect of selected transition metal promoters such as Cu, Ni and Mo. Our results demonstrated that both Ni and Cu remarkably improved the performance of the monometallic Fe-catalyst. The competition Reverse Water-Gas Shift (RWGS) reaction/CO2 methanation reaction was evident particularly for the Ni-catalyst, which displayed high selectivity to methane in the low-temperature range. Among the studied catalysts the Cu promoted sample represented the best choice, exhibiting the best activity/selectivity balance. In addition, the Cu-doped catalyst was very stable for long-term runs – an essential requisite for its implementation in flue gas upgrading units. This material can effectively catalyse the RWGS reaction at medium-low temperatures, providing the possibility to couple the RWGS reactor with a syngas conversion reaction. Such an integrated unit opens the horizons for a direct CO2 to fuels/chemicals approach.

BACKGROUND Control of greenhouse gas emissions has become one of the most important challenges faced by humanity. Among the various approaches to mitigating CO2 emissions, carbon capture and storage (CCS) is considered one of the most promising clean coal options for the future because it can be implemented in the short and medium terms at the industrial scale. Among CCS techniques, oxy‐combustion offers advantages in using pure oxygen (O2) as a comburent, where in a flue gas composed mainly of CO2 and water vapor is generated. Cryogenic air separation is the only available technology that can provide the required amount of O2, but this process requires large amounts of energy and is costly, which make its large‐scales implementation difficult. RESULTS In this framework, oxygen transport membranes are being researched as an O2 supplier unit because they offer advantages from a techno‐economic view point. In the present work, the thermochemical stabilities of La0.6Sr0.4Co0.2Fe0.8O3 and Cobalt‐doped Ce0.9Gd0.1O were evaluated to obtain information on their behavior in oxy‐combustion atmospheres. Experiments were performed in a circulating fluidized bed boiler of a pilot plant using an experimental sampling train. Samples of the two materials were characterized by X‐ray diffraction, X‐ray fluorescence, infrared spectroscopy, Raman spectroscopy, scanning electron microscopy with energy‐dispersive X‐ray spectroscopy, and Brunauer–Emmett–Teller analysis. CONCLUSIONS The results revealed that both materials were susceptible to the presence of species that originated from flue gas, materials comprising the boiler and ducts, and coal ash, and that the CGO_Co material showed better performance than the other studied material. © 2020 Society of Chemical Industry

Since climate change keeps escalating, it is imperative that the increasing CO2 emissions be combated. Over recent years, research efforts have been aiming for the design and optimization of materials for CO2 capture and conversion to enable a circular economy. The uncertainties in the energy sector and the variations in supply and demand place an additional burden on the commercialization and implementation of these carbon capture and utilization technologies. Therefore, the scientific community needs to think out of the box if it is to find solutions to mitigate the effects of climate change. Flexible chemical synthesis can pave the way for tackling market uncertainties. The materials for flexible chemical synthesis function under a dynamic operation, and thus, they need to be studied as such. Dual-function materials are an emerging group of dynamic catalytic materials that integrate the CO2 capture and conversion steps. Hence, they can be used to allow some flexibility in the production of chemicals as a response to the changing energy sector. This Perspective highlights the necessity of flexible chemical synthesis by focusing on understanding the catalytic characteristics under a dynamic operation and by discussing the requirements for the optimization of materials at the nanoscale.

Herein a novel process to synergize biogas upgrading, CO2 utilization and waste recycling is proposed. Our study emerges as a promising strategy within the circular economy. In this work, the technical feasibility of Flue-Gas Desulfurization Gypsum as precipitant for definitely CO2 storage is studied. The precipitation stage is evaluated through two key factors: the quality of the carbonate product and the precipitation efficiency obtained. The physicochemical characterization of the solid carbonate product was analysed by means of Raman, X-Ray diffraction and scanning electron microscopy. The precipitation efficiency is evaluated through the variation of the main precipitation parameters (temperature, molar ratio and time). For this purpose, two groups of experiments were performed. The first group was aimed to model the precipitation system through experiments designed with DesignExpert vs.12 software. The second group of experiments allows to compare our results with pure species as precipitants, as well as to validate the model designed. The physicochemical characterization performed reveals high purity calcite as product. Encouraging precipitation efficiencies were obtained, ranging from 53.09–80.09% (66 % average). Furthermore, the model reveals a high influence of the molar ratio (3–5 times higher impact than other parameters) and low influence of temperature, which evidences the low energy consumption of the proposal. To optimize energy consumption, the model suggests 33 sets of parameters values. Examples of these values are 20 °C, 1.5 mol/mol, and 30 min, which allow to obtain a 72.57 % precipitation efficiency. Overall, this study confirms the technical feasibility of this circular economy approach.

Converting CO2 to methane via catalytic routes is an effective way to control the CO2 content released in the atmosphere while producing value-added fuels and chemicals. In this study, the CO2 methanation performance of highly dispersed Ni-based catalysts derived from aqueous miscible organic layered double hydroxides (AMO-LDHs) was investigated. The activity of the catalyst was found to be largely influenced by the chemical composition of Ni metal precursor and loading. A Ni-based catalyst derived from AMO-Ni3Al1-CO3 LDH exhibited a maximum CO2 conversion of 87.9% and 100% CH4 selectivity ascribed to both the lamellar catalyst structure and the high Ni metal dispersion achieved. Moreover, due to the strong Ni metal–support interactions and abundant oxygen vacancy concentration developed, this catalyst also showed excellent resistance to carbon deposition and metal sintering. In particular, high stability was observed after 19 h in CO2/H2 reaction at 360 °C.

Understanding the viability of the RWGS from a thermodynamic and techno-economic angle opens new horizons within CO2 conversion technologies. Unfortunately, profitability studies of this technology are scarce in literature and mainly focused on overall conversion and selectivity trends with tangential remarks on energy demands and process costs. To address this research gap, herein we present a comprehensive techno-economic study of the RWGS reaction when coupling with Fischer-Tropsch synthesis is envisaged to produced fuels and chemicals using CO2 as building block. We showcase a remarkable impact of operating conditions in the final syngas product and both CAPEX and OPEX. From a capital investment perspective, optimal situations involve RWGS unit running at low temperatures and high pressures as evidenced by our results. However, from the running cost angle, operating at 4 bar is the most favorable alternative within the studied scenarios. Our findings showcase that, no matter the selected temperature the RWGS unit should be preferentially run at intermediate pressures. Ultimately, our work maps out multiple operating scenarios in terms of energy demand and process cost serving as guideline to set optimal reaction conditions to unlock the potential of the RWGS for chemical CO2 recycling. [Display omitted] •Techno-economic study of the RWGS as CO2 conversion process.•Impact of methanation as competitive route to RWGS.•Analysis of multiples scenarios including energy demands and auxiliary equipment.•Technology comparison in terms of energy requirement, CAPEX and OPEX.

The excessive CO 2 emissions in the atmosphere and the consequent climate change have motivated the interest in studying CO 2 utilization processes. Among these CO 2 upgrading reactions, reverse water gas shift (rWGS), CO 2 methanation, and dry reforming of methane (DRM) have been studied widely because the concentration of CO 2 in air could be reduced by running the above reactions and their products can be used as fuel. However, the large‐scale industrial application for these CO 2 utilization processes has been hindered by the side reactions and the vast input of heat. Therefore, developing highly active, selective, and s catalysts is of importance. This chapter aims to provide a comprehensive overview of recent advances on catalysts toward the above three CO 2 utilization processes; synthesis methods, catalytic performances, and limitations of different catalysts have been carefully analyzed. In addition, the backgrounds and fundamentals of these reactions are also critically reviewed.

Designing an economically viable catalyst that maintains high catalytic activity and stability is the key to unlock dry reforming of methane (DRM) as a primary strategy for biogas valorization. Ni/Al 2 O 3 catalysts have been widely used for this purpose; however, several modifications have been reported in the last years in order to prevent coke deposition and deactivation of the samples. Modification of the acidity of the support and the addition of noble metal promoters are between the most reported strategies. Nevertheless, in the task of designing an active and stable catalyst for DRM, the selection of an appropriate noble metal promoter is turning more challenging owing to the lack of homogeneity of the different studies. Therefore, this research aims to compare Ru (0.50 and 2.0%) and Re (0.50 and 2.0%) as noble metal promoters for a Ni/MgAl 2 O 4 catalyst under the same synthesis and reaction conditions. Catalysts were characterized by XRF, BET, XRD, TPR, hydrogen chemisorption (H 2 -TPD), and dry reforming reaction tests. Results show that both promoters increase Ni reducibility and dispersion. However, Ru seems a better promoter for DRM since 0.50% of Ru increases the catalytic activity in 10% and leads to less coke deposition.

Biomass resources have the potential to become a viable renewable technology and play a key role within the future renewable energy paradigm. Since CO2 generated in bio-energy production is equal to the CO2 absorbed during the growth of the biomass, this renewable energy is a net zero emissions resource. Biomass gasification is a versatile method for transforming waste into energy in which biomass material is thermochemically converted within a reactor. Gasification's superior flexibility, including both in terms of biomass type and heat generation or energy production alternatives, is what stimulates biomass gasification scientific and industrial potential. Downdraft gasifiers seem to be well for small-scale generation of heat along with energy, whereas fluidised bed and entrained flow gasifiers currently attain significant economies of scale for fuel production. The operation of gasifiers is influenced by several factors, including operational parameters, feedstock types, and reactor design. Modelling is a valuable tool for building a unit based on the results of model prediction with different operational parameters and feedstock in such scenarios. Once verified, a suitable model may be used to assess the sensitivity of a gasifier's performance to changes in various operational and design factors. Effective models may help designers to theorise and predict the impacts of a variety of characteristics without the need for further empirical observations, which can help in the design and implementation of this technology. This work provides an overview of gasification technologies and a succinct guidance to the modelling decisions and modelling strategies for biomass gasification to enable a successful biomass to fuel conversion. A technical description and critical analysis of thermodynamic, stoichiometric, computational fluid dynamic and data-driven approaches is provided, including crucial modelling considerations that have not been explored in earlier studies. The review aims to aid researchers in the field to select the appropriate approach and guide future work.

The exponential growth of greenhouse gas emissions and their associated climate change problems have motivated the development of strategies to reduce CO2 levels via CO2 capture and conversion. Reverse water gas shift (RWGS) reaction has been targeted as a promising pathway to convert CO2 into syngas which is the primary reactive in several reactions to obtain high-value chemicals. Among the different catalysts reported for RWGS, the nickel-based catalyst has been proposed as an alternative to the expensive noble metal catalyst. However, Ni-based catalysts tend to be less active in RWGS reaction conditions due to preference to CO2 methanation reaction and to the sintering and coke formation. Due to this, the aim of this work is to study the effect of the potassium (K) in Ni/CeO2 catalyst seeking the optimal catalyst for low-temperature RWGS reaction. We synthesised Ni-based catalyst with different amounts of K:Ni ratio (0.5:10, 1:10, and 2:10) and fully characterised using different physicochemical techniques where was observed the modification on the surface characteristics as a function of the amount of K. Furthermore, it was observed an improvement in the CO selectivity at a lower temperature as a result of the K-Ni-support interactions but also a decrease on the CO2 conversion. The 1K catalyst presented the best compromise between CO2 conversion, suppression of CO2 methanation and enhancing CO selectivity. Finally, the experimental results were contrasted with the trends obtained from the thermodynamics process modelling observing that the result follows in good agreement with the modelling trends giving evidence of the promising behaviour of the designed catalysts in CO2 high-scale units.

This work reports the successful and simplistic synthesis of highly uniform NiCo@SiO₂ yolk@shell catalysts, with their effectiveness towards CO₂ recycling investigated within the RWGS reaction. The engineered microstructure catalysts display high CO₂ conversion levels and a remarkable selectivity for CO as main reaction product across the whole examined temperatures. Interestingly, the selectivity is affected by Ni loading reflecting a close correlation catalytic performance/material structure-composition. Further to this behaviour, the designed nanoreactor exhibits considerable deactivation resistance and performance under reaction cycling conditions and appears to demonstrate the production of larger organic molecules after qualitative analysis of the product gas by mass spectrometry. These results demonstrate the effectiveness of the spatial confinement effect, imbued to the material from its advanced morphology, through its influence of deactivation resistance and control of reactive selectivity.

Micro/nanoplastics have sparked attention in recent years due to their widespread presence in the environment. Currently, several waste valorization approaches are under development in order to upcycle micro/nanoplastics. Thermal conversion technologies such as pyrolysis, gasification, liquefaction, or hydrothermal carbonization can yield high-value solid products, oil, and gases from plastics waste. The common thermal conversion technologies investigated focus on maximizing the production of oil and gases (such as H2 and CH4) for use as fuel. Except for hydrogen, when these products are used to generate energy, the carbon emissions generated are comparable to those produced by traditional fossil fuels. Herein, we present a review of the current efforts to capture and convert plastic waste into valuable products with an emphasis on identifying the need to develop processes specifically for micro/nanoplastics while also preventing the release of CO2 emissions. We identify the development of efficient catalytic materials as a critical research need for achieving economically viable thermochemical conversion of micro/nanoplastics. [Display omitted] •When evaluating upcycling techniques for existing plastics waste, it is essential to consider the full life cycle of products, minimizing CO2 emissions of these processes.•Conversion of micro/nanoplastics waste to carbon nanomaterials and energy vectors can be a sustainable solution.•The development of economical catalysts materials for upcycling plastics is essential for the application and feasibility of the technologies at an industrial scale.

The catalytic performance of a series of bimetallic Ni-Co/CeO2-Al2O3 catalysts were evaluated within the dry reforming of methane (DRM) reaction, commonly used for upgrading biogas. The study focused on the variation of CeO2 weight loadings between 0, 10, 20 and 30%. It was found that the addition of CeO2 promoted CH4 and CO2 conversion across the temperature range and increased H2/CO ratio for the “low temperature” DRM. X-Ray Diffraction (XRD), H2-Temperature Programmed Reduction (H2-TPR) and X-Ray Photoelectron Spectroscopy (XPS) analysis revealed the formation of Ce4+ during activation of the 30% sample, resulted in excessive carbon deposition during reaction. The lowest CeO2 weight loadings exhibited softer carbon formation and limited increased chemical stability during reaction at the expense of activity. Of the tested weight loadings, 20 wt% CeO2 exhibited the best balance of catalytic activity, chemical stability and deactivation resistance in the DRM reaction. Hence this catalyst can be considered a promising system for syngas production from biogas at relatively low temperatures evidencing the pivotal role of catalysts design to develop economically viable processes for bioresources valorisation.

Chemical CO2 recycling in the gas phase constitutes a straightforward approach for effective CO2 conversion to added-value products like syngas or synthetic methane. In this scenario, some traditional processes such as the dry and bi-reforming of methane, the CO2 methanation and the reverse water-gas shift have gained a renewed interest from the CO2 utilisation perspective. Indeed, these reactions represent flexible routes to upgrade CO2 and their application at an industrial scale could substantially reduce CO2 emissions. The bottleneck for the implementation of these processes at the commercial level is the development of highly active and robust heterogeneous catalysts able to overcome CO2 activation and deliver sufficient amounts of the upgrading products (i.e. syngas or synthetic natural gas) at the desired operating conditions. This review paper gathers the most recent advances in the design of new catalytic formulations for chemical CO2 recycling in the gas phase and constitutes an overview for experts and newcomers in the field to get fundamental insights into this emerging branch of low-carbon technologies.

The reverse water gas shift reaction (RWGS) has attracted much attention as a potential means to widespread utilization of CO2 through the production of synthesis gas. However, for commercial implementation of RWGS at the scales needed to replace fossil feedstocks with CO2, new catalysts must be developed using earth abundant materials, and these catalysts must suppress the competing methanation reaction completely while maintaining stable performance at elevated temperatures and high conversions producing large quantities of water. Herein we identify molybdenum phosphide (MoP) as a nonprecious metal catalyst that satisfies these requirements. Supported MoP catalysts completely suppress methana-tion while undergoing minimal deactivation, opening up possibilities for their use in CO2 utilization.

Biomass gasification streams typically contain a mixture of CO, H₂, CH₄, and CO₂ as the majority components and frequently require conditioning for downstream processes. Herein, we investigate the catalytic upgrading of surrogate biomass gasifiers through the generation of syngas. Seeking a bifunctional system capable of converting CO₂ and CH₄ to CO, a reverse water gas shift (RWGS) catalyst based on Fe/MgAl₂O₄ was decorated with an increasing content of Ni metal and evaluated for producing syngas using different feedstock compositions. This approach proved efficient for gas upgrading, and the incorporation of adequate Ni content increased the CO content by promoting the RWGS and dry reforming of methane (DRM) reactions. The larger CO productivity attained at high temperatures was intimately associated with the generation of FeNi₃ alloys. Among the catalysts’ series, Ni-rich catalysts favored the CO productivity in the presence of CH₄, but important carbon deposition processes were noticed. On the contrary, 2Ni-Fe/MgAl₂O₄ resulted in a competitive and cost-effective system delivering large amounts of CO with almost no coke deposits. Overall, the incorporation of a suitable realistic application for valorization of variable composition of biomass-gasification derived mixtures obtaining a syngas-rich stream thus opens new routes for biosyngas production and upgrading.

For the rWGS reaction, Fe5C2 (Hagg’s carbide) catalyst exhibits superior CO2 activity and α-Fe catalyst shows higher CO selectivity. Fe3C is the less efficient phase compared to Fe5C2/α-Fe. [Display omitted] Fe-based catalysts are efficient systems for CO2 conversion via reverse water-gas shift (rWGS) reaction. Nevertheless, the nature of the active phase, namely metallic iron, iron oxide or iron carbide remains a subject of debate which our paper is meant to close. Fe0 is a much better catalyst for the rWGS than Fe3C. The activity of Fe0 can be promoted by the addition of Cs and Cu whose presence hinders iron carburisation while favouring both higher conversion and enhanced selectivity. When the samples are aged in the rWGS reaction mixture during stability test a new phase appear: Fe5C2, resulting in a more active but less selective catalysts than Fe0 for the rWGS reaction. Hence our results indicate that we could potentially achieve an optimal activity/selective balance upon finely tuning the proportion Fe/Fe5C2. Beyond the fundamental information concerning active phase we have observed the presence of advanced Fischer-Tropsch-like products at ambient pressure opening new opportunities for the design of hybrid rWGS/Fischer-Tropsch systems.

Biogas is defined as the mixture of CH 4 and CO 2 produced by the anaerobic digestion of biomass. This particular mixture can be transformed in high valuable intermediates such as syngas through a process known as dry reforming (DRM). The reaction involved is highly endothermic, and catalysts capable to endure carbon deposition and metal particle sintering are required. Ni-pyrochlore catalysts have shown outstanding results in the DRM. However, most reported data deals with CH 4 /CO 2 stoichiometric ratios resulting is a very narrow picture of the overall biogas upgrading via DRM. Therefore, this study explores the performance of an optimized Ni-doped pyrochlore, and Ni-impregnated pyrochlore catalysts in the dry reforming of methane, under different CH 4 /CO 2 ratios, in order to simulate various representatives waste biomass feedstocks. Long-term stability tests showed that the ratio CH 4 /CO 2 in the feed gas stream has an important influence in the catalysts' deactivation. Ni doped pyrochlore catalyst, presents less deactivation than the Ni-impregnated pyrochlore. However, biogas mixtures with a CH 4 content higher than 60%, lead to a stronger deactivation in both Ni-catalysts. These results were in agreement with the thermogravimetric analysis (TGA) of the post reacted samples that showed a very limited carbon formation when using biogas mixtures with CH 4 content

Mitigation of anthropogenic CO2 emissions possess a major global challenge for modern societies. Herein, catalytic solutions are meant to play a key role. Among the different catalysts for CO2 conversion, Cu supported molybdenum carbide is receiving increasing attention. Hence, in the present communication, we show the activity, selectivity and stability of fresh-prepared β-Mo2C catalysts and compare the results with those of Cu/Mo2C, Cs/Mo2C and Cu/Cs/Mo2C in CO2 hydrogenation reactions. The results show that all the catalysts were active, and the main reaction product was methanol. Copper, cesium and molybdenum interaction is observed, and cesium promoted the formation of metallic Mo on the fresh catalyst. The incorporation of copper is positive and improves the activity and selectivity to methanol. Additionally, the addition of cesium favored the formation of Mo0 phase, which for the catalysts Cs/Mo2C seemed to be detrimental for the conversion and selectivity. Moreover, the catalysts promoted by copper and/or cesium underwent redox surface transformations during the reaction, these were more obvious for cesium doped catalysts, which diminished their catalytic performance.

This paper demonstrates the benefits of incorporating CO2 utilisation through methanation in the steel industry. This approach allows to produce synthetic methane, which can be recycled back into the steel manufacturing process as fuel and hence saving the consumption of natural gas. To this end, we propose a combined steel-making and CO2 utilisation prototype whose key units (shaft furnace, reformer and methanation unit) have been modelled in Aspen Plus V8.8. Particularly, the results showed an optimal performance of the shaft furnace at 800 °C and 6 bar, as well as 1050 °C and atmospheric pressure for the reformer unit. Optimal results for the methanation reactor were observed at 350 °C. Under these optimal conditions, 97.8% of the total CO2 emissions could be mitigated from a simplified steel manufacturing scenario and 89.4% of the natural gas used in the process could be saved. A light economic approach is also presented, revealing that the process could be profitable with future technologic developments, natural gas prices and forthcoming increases of CO2 emissions taxes. Indeed, the cash-flow can be profitable (325 k€) under the future costs: methanation operational cost at 0.105 €/Nm3; electrolysis operational cost at 0.04 €kWh, natural gas price at 32 €/MWh; and CO2 penalty at 55€/MWh. Hence this strategy is not only environmentally advantageous but also economically appealing and could represent an interesting route to contribute towards steel-making decarbonisation. [Display omitted] •Engineering solutions to curb CO2 emissions in steel-making processes•Advantages of a methanation unit for a greener steel production•Profitability analysis of a CO2 conversion•Optimisation of key parameters to showcase the benefits of the methanation process

Production of fuels and targeted chemicals from biomass represents a current challenge. Pyrolysis of biomass generates liquid bio-oils but these are highly complex mixtures. In order to obtain the desired products, optimized reaction conditions are required and this, in turn, drives the need for a fundamental understanding of the complex reaction network. Bio-oils are a complex mixture of thousands of individual molecular compositions, with differing numbers of carbon, hydrogen, nitrogen, and oxygen atoms (c, h, n, and o, respectively). The compositional spaces of such complex mixtures with high oxygen contents are commonly plotted using van Krevelen diagrams, where the H/C versus O/C ratios are displayed. For a bio-oil to be effectively used in engines, further upgrading is necessary to drive the compositions towards low oxygen and high hydrogen content (thus, low O/C and high H/C values). Here, we propose reaction vectors in van Krevelen diagrams to outline the possible reaction routes that favour the production of molecules with increased energy density, using examples of bio-oils produced from citrus waste (lemon and orange peel) and olive pulp. When reactions such as the addition or loss of CO, CO2, CH4, and H2O occur, a displacement of the compositions of molecules in terms of H/C and O/C coordinates is observed. The direction and magnitude of the displacement along each axis in van Krevelen diagrams depends upon the specific reaction route and the elemental content of each molecule. As a consequence of the wide diversity of compositions, different reaction routes are suggested that include multi-step upgrading processes, including hydrogenation and the elimination of oxygen in the form of CO and CO2. The detailed molecular composition of the starting material, plotted in van Krevelen diagrams for visualization, paves the way for greater insight into potential reaction pathways for components within these highly complex mixtures. In turn, the equations proposed hold potential to inform future production strategies, increasing the energy density of bio-oils whilst also reducing the undesirable char formation.

[Display omitted] •Local electron density of metal Ni could be regulated by the crystal phase of ZrO2 support.•Ni/m-ZrO2 presented faster CO2 methanation at low-temperature than Ni/c-ZrO2.•Ni/m-ZrO2 exhibited high oxygen vacancies and strong electronic metal-support interactions.•The formate is the key intermediate for CO2 methanation over Ni/ZrO2.•Both the experiments and DFT calculation determine the structure–activity relationship. CO2 methanation is a promising route for converting CO2 into a marketable natural gas. The major challenge of this process is to enhance CO2 methanation catalytic activity at low temperature. This work showcases a supported-catalysts phase engineering strategy to overcome the challenge. We report a ∼ 24% decrease in the activation energy of methanation reaction over Ni/monoclinic-ZrO2 due to the optimization of ZrO2 crystal phases and thus turnover frequency of CO2 methanation at 240 °C increases by ∼ 116% than Ni/cubic-ZrO2. Both experimental characterizations and theoretical calculations confirm the high local electron density of Ni over Ni/monoclinic-ZrO2, a key factor to present superior performance for CO2 methanation, resulting from its high oxygen vacancies and electronic metal-support interactions. This is beneficial to the adsorption and dissociation of H2 and the hydrogenation of formate intermediate. Hence our work might open an avenue for rational design of advanced low-temperature CO2 hydrogenation catalysts via a phase engineering strategy.

The conversion of biogas, mainly formed of CO2 and CH4, into high-value platform chemicals is increasing attention in a context of low-carbon societies. In this new paradigm, acetic acid (AA) is deemed as an interesting product for the chemical industry. Herein we present a fresh overview of the current manufacturing approaches, compared to potential low-carbon alternatives. The use of biogas as primary feedstock to produce acetic acid is an auspicious alternative, representing a step-ahead on carbon-neutral industrial processes. Within the spirit of a circular economy, we propose and analyse a new BIO-strategy with two noteworthy pathways to potentially lower the environmental impact. The generation of syngas via dry reforming (DRM) combined with CO2 utilisation offers a way to produce acetic acid in a two-step approach (BIO-Indirect route), replacing the conventional, petroleum-derived steam reforming process. The most recent advances on catalyst design and technology are discussed. On the other hand, the BIO-Direct route offers a ground-breaking, atom-efficient way to directly generate acetic acid from biogas. Nevertheless, due to thermodynamic restrictions, the use of plasma technology is needed to directly produce acetic acid. This very promising approach is still in an early stage. Particularly, progress in catalyst design is mandatory to enable low-carbon routes for acetic acid production. [Display omitted] •Biogas conversion to acetic acid represents a circular economy route for chemicals manufacturing.•Two new BIO-strategies are proposed to obtain acetic acid from CO2 and CH4.•The implementation of plasma technology in dry reforming represents a step-ahead on carbon-neutral processes.•The state-of-the-art of lab-scale non-thermal plasma dry reforming to value-added products has been reviewed.

The reverse water gas shift (RWGS) reaction is a promising technology for introducing carbon dioxide as feedstock to the broader chemical industry through syngas production. While this reaction has attracted significant attention recently for catalyst and process development, there is a need to quantify the net CO2 consumption of RWGS schemes, while taking into account parameters such as thermodynamics, alongside technoeconomic constraints for feasible process development. Also of particular importance is the consideration of the cost and carbon footprint of hydrogen production. Herein, research needs to enable net carbon‐consuming, economically feasible RWGS processes are identified. By considering the scenarios of hydrogen with varying carbon footprints (gray, blue, and green) as well as analyzing the sensitivity to process heating method, it is proposed that the biggest enabling development for RWGS commercial implementation as a CO2 utilization technology will be the availability of low‐cost and low‐carbon sources of hydrogen. RWGS catalyst improvements alone will not be sufficient for economic feasibility but are necessary given the prospect of dropping hydrogen prices.

Dry reforming of methane is a very appealing catalytic route biogas (mainly composed by greenhouse gases: carbon dioxide and methane) conversion into added value syngas, which could be further upgraded to produce liquid fuels and added value chemicals. However, the major culprits of this reaction are coking and active phase sintering that result in catalysts deactivation. Herein we have developed a highly stable bimetallic Ni–Rh catalyst supported on mixed CeO2–Al2O3 oxide using low-noble metal loadings. The addition of small amounts of rhodium to nickel catalysts prevents coke formation and improves sintering resistance, achieving high conversions over extended reaction times hence resulting in promising catalysts for biogas upgrading. [Display omitted] •H2-rich syngas can be obtained efficiently from biogas reforming.•Ni-based catalysts are deactivated by metal sintering and coke deposition.•Doping with low Rh loadings deactivation can be successfully prevented.

The work in this paper evidences the viability of producing synthetic natural gas (SNG) via the methanation reaction tackling two fundamental challenges on methanation catalysis (i) the development of advanced catalysts able to achieve high CO2 conversion and high methane yields and (ii) the unexplored effect of residual methane on the methanation stream. Both challenges have been successfully addressed using Ni/CeO2-ZrO2 catalysts promoted with Mn and Co. Mn does not seem to be a good promoter while Co prevents carbon deposition and secondary reactions. In fact, our Co-doped sample reached high levels of CO2 conversion and CH4 selectivity, especially at low reaction temperatures. In addition, this catalyst exhibits excellent catalytic behaviour when methane is introduced into the gas mixture, indicating its feasibility for further study to be conducted in realistic flue gases environments and methanation units with recycling loops. Furthermore, when methane is introduced in the reactant mixture, the Ni-Co/CeO2-ZrO2 sample is very stable maintaining high levels of conversion and selectivity. Overall our Co-doped catalyst can deliver high purity synthetic natural gas for long-term runs, promising results for gas-phase CO2 conversion units.

KNaTiO3 is a novel type of solid CO2 sorbents with strong sorption capacity and excellent regenerability at high temperatures. However, the expensive titanium precursor hampers its implementation for industrial applications. Herein, advanced KNaTiO3 based CO2 sorbents were first fabricated directly from high titanate slag (HTS). Elemental mapping analysis reveals high dispersion of KNaTiO3 and the crystal structure of KNaTiO3 in KNaTiO3HTS-3 almost unchanged even after 15 cycles. The carbonation conversion of KNaTiO3-HTS-3 preserved a highly commendable value even after 100 sorption/desorption cycles, outperforming pure KNaTiO3. In addition, this sorbent exhibited faster sorption rate at 700 degrees C. Dynamic simulation demonstrated that the sorption constants k(1) and k(2) are higher and the activation energy is lower than those of conventional high-temperature sorbents. The CO2 sorption capacity of KNaTiO3-HTS-3 only met a slight decrease from 15.7 to 14.6 wt% with the decreasing CO2 concentration from 100 to 10 vol%. Compared with traditional high temperature CO2 sorbents, KNaTiO3HTS-3 shows a slower breakthrough time. The reaction mechanism process for the promising sorbent is proposed. The HTS-derived KNaTiO3-based high-temperature CO2 sorbent has outstanding CO2 uptake, excellent regenerability, fast reaction kinetics as well as low cost, offering bright prospects in practical applications.

Transition to low carbon societies requires advanced catalysis and reaction engineering to pursue green routes for fuels and chemicals production as well as CO2 conversion. This comprehensive review provides a fresh perspective on the dry reforming of methane reaction (DRM) which constitutes a straightforward approach for effective CO2 conversion to added value syngas. The bottleneck for the implementation of this process at industrial scale is the development of highly active and robust heterogeneous catalysts able to overcome the CO2 activation barrier and deliver sufficient amount of the upgrading products at the desired operation conditions. Also, its high energy demand due to the endothermic nature of the reaction imposes extra difficulties. This review critically discusses the recent progresses on catalysts design ranging from traditional metal-supported catalysts to advanced structured and nanostructured systems with promising performance. The main advantages and culprits of the different catalytic systems are introduced aiming to inspire the catalysis community to further refine these formulations towards the development of “supercatalysts” for DRM. Besides the design of increasingly complex catalyst morphologies as well as other promising alternatives aiming at reducing the energy consumption of the process or tackle deactivation through reactor design are introduced.

The UK faces unprecedented environmental challenges which require urgent action. The promotion of renewable energy sources is a promising solution to tackle these challenges. Among the renewable options, syngas production from biogas via dry reforming of methane shows great potential as a green alternative to meet global environmental goals. The purpose of this work is to estimate the potential of syngas production from biogas in the UK and its profitability. To estimate the syngas production, we present an overview of methane dry reforming to syngas. This analysis reveals that nickel/alumina catalysts are the most popular choice for the mentioned reaction. Afterwards, the potential biogas production in the UK is obtained. Both set of data are subsequently combined to estimate the potential for syngas production from biomass in the UK. A techno-economic analysis is performed to estimate the syngas price to reach profitability. This analysis reveals syngas prices ranging from 1.154 to 1.564 €/m3 to overcome production costs, which is higher than producing syngas from traditional fossil fuels. Further analysis has also been conducted to estimate the production of different utilisation routes for said syngas including biofuel, methanol and electricity.

CO2 emissions in the atmosphere have been increasing rapidly in recent years, causing global warming. CO2 methanation reaction is deemed to be a way to combat these emissions by converting CO2 into synthetic natural gas, i.e., CH4. NiRu/CeAl and NiRu/CeZr both demonstrated favourable activity for CO2 methanation, with NiRu/CeAl approaching equilibrium conversion at 350 °C with 100% CH4 selectivity. Its stability under high space velocity (400 L·g−1·h−1) was also commendable. By adding an adsorbent, potassium, the CO2 adsorption capability of NiRu/CeAl was boosted, allowing it to function as a dual-function material (DFM) for integrated CO2 capture and utilisation, producing 0.264 mol of CH4/kg of sample from captured CO2. Furthermore, time-resolved operando DRIFTS-MS measurements were performed to gain insights into the process mechanism. The obtained results demonstrate that CO2 was captured on basic sites and was also dissociated on metallic sites in such a way that during the reduction step, methane was produced by two different pathways. This study reveals that by adding an adsorbent to the formulation of an effective NiRu methanation catalyst, advanced dual-function materials can be designed.

The use of fossil fuels is primarily responsible for the increasing amounts of greenhouse gas emissions in the atmosphere and, unless this issue is quickly addressed, the effects of global warming will worsen. Synthesis gas (syngas) is an attractive target chemical for carbon capture and utilisation and dry reforming of methane (DRM) enables the conversion of methane (CH4) and CO2, the two most abundant greenhouse gases, to syngas. This paper presents a techno-economic analysis of a syngas-to-dimethyl ether (DME) process, by utilising landfill gas as feedstock. The process developed herein produces DME, methanol and high-pressure steam as products, resulting in an annual income of €3.49 m and annual operating expenses of €1.012 m. Operating profit was calculated to be €2.317 m per year and the net present value (NPV) was €11.70 m at the end of the project’s 20-year lifespan with a profitability index of 0.83€/€. The process was expected to have a payback time of approximately 10 years and an internal rate of return of 12.47%. A key aspect of this process was CO2 utilisation, which consumed 196,387 tonnes of CO2 annually. The techno-economic analysis conducted in this paper illustrates that greenhouse gas utilisation processes are currently feasible both in terms of CO2 consumption and profitability.

In this paper we present a techno-economic analysis of a novel route for biomethane – urea co-production from biogas. The idea emerges as an alternative path for improving the profitability of biogas upgrading plants. The profitability of four different biogas plant sizes (100, 250, 500, and 1000 m3/h) in four European countries (Spain, Italy, United Kingdom and Germany) is studied under the current policy schemes for biomethane production of each country. Our study evidences that with the present policy schemes for biomethane production, only medium and large scale plants (500 and 1000 m3/h) in Italy would be profitable. The reason is the current strong support for biomethane production in Italy through feed-in tariffs subsidies. In this sense, we analysed the potential benefits of governmental incentives through bio-methane subsidies (feed-in tariffs and investment percentage). Feed-in tariffs proved to be a worthwhile solution for large plants. Indeed, profitability is reached under subsidies of 30-48 €/MWh. Overall, plants located in southern EU countries are more likely to reach profitability with lower subsidies. The potential of costs reduction (i.e. ammonia price) was also analysed, showing that cutting-down production costs is essential to reduce the amount of subsidies received. In summary, our study shows the challenge that European policies face in the path towards a bio-based economy using biogas upgrading as reference case.

The European Union has set an ambitious plan for addressing the Global Challanges in the coming years. One of these challenges is the use of biomass and the production of biomass-derived products following the spirit of a circular economy. Biogas obtained from biomass anaerobic digestion could play a pivotal role in this strategy. Herein an innovative strategy for synergizing biogas upgrading to biomethane and formic acid production from CO2 is presented. A profitability analysis of the combined biogas upgrading – CO2 utilization process was conducted to assess the economic viability of this novel approach. The profitability study focuses mainly on net present value and profitability index. Even though the process is environmentally favourable, negative profitability results are obtained. To revert the negative outputs, out of the market formic acid prices (1767–3135 €/t) would be needed to achieve a net present value equal to zero. The alternative of feed-in tariffs biomethane subsidies needs high values (121.1–269.4 €/MW) to reach profitable scenarios. These unsuccessful profitability results are ascribed to high consumables costs, mainly associated with the catalytic conversion of a CO2-rich feedstock. A 80% reduction of catalysts costs can considerably improve net present value up to 50%. This result indicates that further research is needed to find econimocally appealing catalysts to perform this process. The effect of biomethane subsidies as percentage of investment was also considered, evidencing encouraging results for small scale plants.

We report for the first time the support dependent activity and selectivity of Ni-rich nickel phosphide catalysts for CO2 hydrogenation. New catalysts for CO2 hydrogenation are needed to commercialise the reverse water–gas shift reaction (RWGS) which can feed captured carbon as feedstock for traditionally fossil fuel-based processes, as well as to develop flexible power-to-gas schemes that can synthesise chemicals on demand using surplus renewable energy and captured CO2. Here we show that Ni2P/SiO2 is a highly selective catalyst for RWGS, producing over 80% CO in the full temperature range of 350–750 °C. This indicates a high degree of suppression of the methanation reaction by phosphide formation, as Ni catalysts are known for their high methanation activity. This is shown to not simply be a site blocking effect, but to arise from the formation of a new more active site for RWGS. When supported on Al2O3 or CeAl, the dominant phase of as synthesized catalysts is Ni12P5. These Ni12P5 catalysts behave very differently compared to Ni2P/SiO2, and show activity for methanation at low temperatures with a switchover to RWGS at higher temperatures (reaching or approaching thermodynamic equilibrium behaviour). This switchable activity is interesting for applications where flexibility in distributed chemicals production from captured CO2 can be desirable. Both Ni12P5/Al2O3 and Ni12P5/CeAl show excellent stability over 100 h on stream, where they switch between methanation and RWGS reactions at 50–70% conversion. Catalysts are characterized before and after reactions via X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), temperature-programmed reduction and oxidation (TPR, TPO), Transmission Electron Microscopy (TEM), and BET surface area measurement. After reaction, Ni2P/SiO2 shows the emergence of a crystalline Ni12P5 phase while Ni12P5/Al2O3 and Ni12P5/CeAl both show the crystalline Ni3P phase. While stable activity of the latter catalysts is demonstrated via extended testing, this Ni enrichment in all phosphide catalysts shows the dynamic nature of the catalysts during operation. Moreover, it demonstrates that both the support and the phosphide phase play a key role in determining selectivity towards CO or CH4.

[Display omitted] •New electro-catalyst ER-Cu5-LDH/rGO was designed from Cu5Al-CO3 hybrid LDH/GO precursor.•The catalyst exhibited high C2H4 faradaic efficiency and C2H4 partial current density.•Introduction of rGO significantly increase the electric conductivity of ER-Cu5-LDH/rGO.•LDHs precursor can lead to a high dispersion of active copper species.•ER-Cu5-LDH/rGO is promising for electrochemical conversion of CO2 into C2H4. Electrochemical CO2 conversion to value-added fuels and chemicals enabled by suitable heterogeneous catalysts has attained great attention given its economic viability and overall process efficiency. Herein, we have designed a new electro-catalyst ER-Cu5-LDH/rGO using electro-reduction method from Cu5Al-CO3 hybrid LDH/GO precursor for efficient CO2 reduction reaction (CO2RR). Interestingly, the ER-Cu5-LDH/rGO catalyst presented a higher C2H4 production selectivity than the ER-Cu5-LDH catalyst without rGO. The obtained ER-Cu5-LDH/rGO exhibited a high C2H4 faradaic efficiency (FE) up to 54 % and a high C2H4 partial current density of ‒11.64 mA/cm2 at ‒1.2 V vs. RHE. It also exhibited excellent stability up to 50 h. The total FE of gaseous and liquid products for ER-Cu5-LDH/rGO is closed to 100 %. The morphological changes during CO2RR were monitored using SEM analyses for catalyst stability examination. The influence of electrolyte or pH on the electro-catalytic performance of ER-Cu5-LDH/rGO were studied. In order to reflect the superiority of LDH precursors, a control catalyst containing Cu2O supported on rGO (ER-Cu2O/rGO) was prepared and comparatively studied. Overall, our hybrid catalyst system ER-Cu5-LDH/rGO is very promising materials for CO2 conversion to C2H4, displaying remarkable FE, high C2H4 partial current density, and the excellent stability. Such a commendable behavior is ascribed to the excellent dispersion of active copper species as well as the superior electric conductivity of rGO.

The bi-reforming of methane (BRM) has the advantage of utilising greenhouse gases and producing H2 rich syngas. In this work Ni stabilised in a pyrochlore-double perovskite structure is reported as a viable catalyst for both Dry Reforming of Methane (DRM) and BRM. A 10 wt.% Ni-doped La2Zr2O7 pyrochlore catalyst was synthesised, characterised and tested under both reaction conditions and its performance was compared to a supported Ni/La2Zr2O7. In particular the effect of steam addition is investigated revealing that steam increases the H2 content in the syngas but limits reactants conversions. The effect of temperature, space velocity and time on stream was studied under BRM conditions and brought out the performance of the material in terms of activity and stability. No deactivation was observed, in fact the addition of steam helped to mitigate carbon deposition. Small and well dispersed Ni clusters, possibly resulting from the progressive exsolution of Ni from the mixed oxide structure could explain the enhanced performance of the catalyst.

"H-2-free" HDO is a revolutionary route to circumvent the limitations of H-2-fed HDO reactors for biomass upgrading. This work demonstrates the viability of this economically appealing route when an adequate catalyst is implemented. Herein, we have developed a new family of Pt catalysts supported on N-doped activated carbons for the H2-free HDO process of guaiacol. Several N-donors have been used to tune the catalyst's structural and electronic properties. As a general trend, the N-promoted samples are more selective towards oxygen-depleted products. The best performing material, namely Pt/PANI-AC, reached outstanding guaiacol conversion values - ca. 75% at 300 degrees C while displaying reasonable stability for multiple recycling operations. The advanced performance is ascribed to the modified electronic and acid-base properties which favor guaiacol activation and C-O cleavage, as well as the excellent dispersion of the Pt nanoparticles. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Herein a potential synergy between biogas upgrading and CO2 conversion to bio-methanol is investigated. This novel idea arises as an alternative path to the traditional biogas – to – bio-methane route which involves CO2 separation. In this work a techno-economic analysis of the process was performed to study the profitability for potential investors. A total of 15 scenarios were analysed. Different biogas plant sizes were examined as baseline scenarios: 100, 250, 500, and 1000 m³/h. Furthermore the potential effect of governmental incentives through bio-methane subsidies (feed-in tariffs and investment percentage) was studied. Finally a sensitivity analysis was developed to study the effect of key parameters. The results of the baseline scenarios demonstrated that not profitable results can be obtained without subsidies. Bio-methane subsidies as feed-in tariffs proved to be effective for the 500 and 1000 m³/h plant sizes. For a feed-in tariff subsidy of 40 €/MW, 500 m³/h biogas production plants are remarkably profitable (net present value equal to 3106 k€). Concerning 1000 m³/h biogas production plants, 20 €/MW of subsidies as feed-in tariffs gives similar net present value result. Our results point out that only big biogas production can produce bio-methanol at profitable margins under 90–100% of investment subsidied. The sensitivity analysis showed that electricity, natural gas and bio-methanol price can affect considerably to the overall profitability, converting predicted positive cases in negative scenarios.

The feasibility of a Dual Function Material (DFM) with a versatile catalyst offering switchable chemical synthesis from carbon dioxide (CO2), was demonstrated for the first time, showing evidence of the ability of these DFMs to passively capture CO2 directly from the air as well. These DFMs open up possibilities in flexible chemical production from dilute sources of CO2, through a combination of CO2 adsorption and subsequent chemical transformation (methanation, reverse water gas shift or dry reforming of methane). Combinations of Ni Ru bimetallic catalyst with Na2O, K2O or CaO adsorbent were supported on CeO2 – Al2O3 to develop flexible DFMs. The designed multicomponent materials were shown to reversibly adsorb CO2 between the 350 and 650oC temperature range and were easily regenerated by an inert gas purge stream. The components of the flexible DFMs showed a high degree of interaction with each other, which evidently enhanced their CO2 capture performance ranging from 0.14 to 0.49 mol/kg. It was shown that captured CO2 could be converted into useful products through either CO2 methanation, reverse water-gas shift (RWGS) or dry reforming of methane (DRM), which provides flexibility in terms of co-reactant (hydrogen vs methane) and end product (synthetic natural gas, syngas or CO) by adjusting reaction conditions. The best DFM was the one containing CaO, producing 104 μmol of CH4/kgDFM in CO2 methanation, 58 μmol of CO/kgDFM in RWGS and 338 μmol of CO/kgDFM in DRM. 

Global warming caused by increasing CO(2)atmospheric levels is calling for sustainable fuels. For instance, biomethane produced by biogas upgrading is a promising source of green energy. Technologies to upgrade biogas include chemical absorption, water scrubbing, physical absorption, adsorption, cryogenic separation and membrane separation. Historically, water scrubbing was preferred because of the simplicity of this operation. However, during the last decade, membrane separation stood out due to its promising economic viability with investment costs of 3500-7500 euro/(m(3)/h) and operational costs of 7.5-12.5 euro/(m(3)/h). Here we review biogas upgrading by membrane separation. We discuss gas permeation, membrane materials, membrane modules, process configurations and commercial biogas plants. Polymeric materials appear as most adequate for membranes aimed to upgrade biogas. Concerning membrane modules, hollow fibers are the cheapest (1.5-9 euro/m(2)). Multistage configurations provide high methane recovery, of 99%, and purity, of 95-99%, compared to single-stage configurations.

The increasing anthropogenic emissions of greenhouse gases (GHG) is encouraging extensive research in CO2 utilisation. Dry reforming of methane (DRM) depicts a viable strategy to convert both CO2 and CH4 into syngas, a worthwhile chemical intermediate. Among the different active phases for DRM, the use of nickel as catalyst is economically favourable, but typically deactivates due to sintering and carbon deposition. The stabilisation of Ni at different loadings in cerium zirconate inorganic complex structures is investigated in this work as strategy to develop robust Ni-based DRM catalysts. XRD and TPR-H2 analyses confirmed the existence of different phases according to the Ni loading in these materials. Besides, superficial Ni is observed as well as the existence of a CeNiO3 perovskite structure. The catalytic activity was tested, proving that 10 wt.% Ni loading is the optimum which maximises conversion. This catalyst was also tested in long-term stability experiments at 600 and 800°C in order to study the potential deactivation issues at two different temperatures. At 600°C, carbon formation is the main cause of catalytic deactivation, whereas a robust stability is shown at 800°C, observing no sintering of the active phase evidencing the success of this strategy rendering a new family of economically appealing CO2 and biogas mixtures upgrading catalysts. [Display omitted]

The synthesis of effective heterogeneous catalysts is one of the main challenges toward hydrothermal processing of wood-derived biomass into marketable sustainable chemicals. Many of these catalysts are based on noble metals and are normally synthesized using multiple steps in time-consuming processes. Here, we have developed a one-pot catalyst synthesis method for Ni-CeO2-x supported on carbon nanofibers. In situ H-2 production through formic acid decomposition enabled the synthesis of catalysts in their reduced form, with ceria as Ce3+ and presence of metallic Ni. This catalyst promoted Kraft lignin conversion in supercritical water at short reaction times with a 79 wt % yield of a bio-oil composed of nearly 69 wt % of monoaromatics. Thus, lignin breakdown was achieved without resourcing to noble metal catalysts, molecular H-2, or cosolvents, with a decrease in catalyst synthesis time and unit operations and with an attractive yield of a chemically uniform product fraction.

The reverse water-gas shift reaction (RWGS) reaction represents a direct route for CO2 conversion whose selectivity significantly depends on the selected catalyst. In this work, a new family of bimetallic iron-copper oxide catalysts supported on ceria-alumina with various Fe/Cu oxides ratios were investigated for the RWGS reaction. Additionally, bare Fe-based and Bare Cubased catalysts were synthesized for comparison. Our results demonstrate that the developed bimetallic Fe-Cu catalysts present a remarkable enhancement of catalytic performance when compared to monometallic systems, especially at the so-called "low-temperature range" for RWGS. Characterization results evidence that Cu species undergo different states on the catalytic surface during the reaction, wherein the formed metallic Cu is linked to the catalytic activity via the strength of the interaction with the multioxide phases, such as Fe3O4/CeO2, while the copper-dopped ceria could contribute to the promotion of CO selectivity. Besides, we identify that the Fe/Cu oxides mass ratio of 0.25/0.75 is an optimal formulation rendering highly commendable CO2 conversion levels at 450 degrees C with excellent selectivity and stability for long-term runs. Very importantly, without preactivation, our multicomponent materials still display an optimum performance which have a potential realistic application from cost perspective than other Cu-based catalysts. Overall, this work showcases a strategy to design highly effective multicomponent Fe-Cu catalysts for CO2 conversion via RWGS.

Herein a novel process for CO₂ capture and utilization suitable for small-medium scale applications is presented. The use of potassium and calcium wastes is proposed as an alternative low-energy path to CO₂ capture and waste valorization. In our work, CaCO₃ precipitation studies were performed to corroborate the feasibility of the novel process described. Reaction time, reaction temperature, molar ratio, and K₂CO₃ initial concentration were varied to analyse their effects on the precipitation efficiency. The purity and main characteristics of the obtained product were physicochemically characterized to evaluate the potential cost of the final solid product by means of Raman spectroscopy, X-ray diffraction, FTIR, and scanning electron microscopy. Results show that promising precipitation efficiencies are obtained in comparison with other waste-valorization and CO₂ capture process, even at room temperatures. High quality calcite was obtained as solid product. Overall our work confirms the technical viability of the proposed route to synergize CO₂ capture and saline waste utilization.

Advanced catalytic materials able to catalyse more than one reaction efficiently are needed within the CO2 utilisation schemes to benefit from end-products flexibility. In this study, the combination of Ni and Ru (15 and 1 wt%, respectively) was tested in three reactions, i.e. dry reforming of methane (DRM), reverse water-gas shift (RWGS) and CO2 methanation. A stability experiment with one cycle of CO2 methanation-RWGS-DRM was carried out. Outstanding stability was revealed for the CO2 hydrogenation reactions and as regards the DRM, coke formation started after 10 h on stream. Overall, this research showcases that a multicomponent Ni-Ru/CeO2 -Al2O3 catalyst is an unprecedent versatile system for gas phase CO2 recycling. Beyond its excellent performance, our switchable catalyst allows a fine control of end-products selectivity.

Optimization of MgO adsorbents is predominantly focused on the regulation of appropriate adsorption sites for CO2 associated with Mg2+-O2- sites of low coordination. Here, for the first time, we conducted transient kinetic experiments to identify and characterize changes of the CO2 molecular path in MgO-based CO2 adsorbents upon the addition of molten salt modifiers. Among the optimized samples, addition of 10 mol % NaNO2 on the surface of MgO exhibited the highest CO2 uptake (15.7 mmol g(-1)) at 350 degrees C compared to less than 0.1 mmol g(-1) for the unpromoted MgO. Kinetic modeling showed that the interaction of molten salt-promoted MgO with CO2 at 300 degrees C involves three different processes, namely, fast surface adsorption associated with surface-active basic sites, chemical reaction associated with MgCO3 formation, and a slow diffusion step being the rate-limiting step of the carbonation process. Furthermore, transient kinetic studies coupled with mass spectrometry under low CO2 partial pressure agreed well with the kinetic simulation results based on TGA measurements, demonstrating an in-depth understanding of the CO2-capturing performance gained and its considerable significance for future practical designs of precombustion CO2 capture.

This chapter introduces several key concepts of the hierarchical yolk@shell morphology before considering the applications of these versatile encapsulated materials toward the chemical and photochemical conversion of CO 2 . The most prominent methods of synthesis for these materials will also be discussed, noting the degree of control available to each.

Advanced catalytic technologies are crucial to enable the transition toward a low-carbon industry with minimized CO2 emissions. This paper showcases the application of highly effective Ru-promoted Ni-based catalysts for gas-phase CO2 upgrading: CO2 methanation and reverse water-gas shift. The addition of small amounts of Ru results in a remarkable enhancement of CO2 conversion and selectivity. The bimetallic Ru-Ni catalyst displays greater metallic dispersion, tuned electronic properties and outstanding stability for long-term runs, a mandatory requisite for its implementation in actual CO2 conversion units. The singularity of our advanced catalyst lays on its capacity to work effectively for both the CO2 methanation and the reverse water-gas shift, allowing end-product flexibility by adjusting the reactor temperature. Such versatility opens a big range of possibilities to adapt this technology in heavy carbon industries whose net CO2 emissions represent a big share in the global greenhouse gases emissions.

Nickel phosphide catalysts show a high level of selectivity for the reverse water-gas shift (RWGS) reaction, inhibiting the competing methanation reaction. This work investigates the extent to which suppression of methanation can be controlled by phosphidation and tests the stability of phosphide phases over 24-hour time on stream. Herein the synthesis of different phosphide crystal structures by varying Ni/P atomic ratios (from 0.5 to 2.4) is shown to affect the selectivity to CO over CH 4 in a significant way. We also show that the activity of these catalysts can be fine-tuned by the synthesis Ni/P ratio and identify suitable catalysts for low temperature RWGS process. Ni 12 P 5-SiO 2 showed 80–100% selectivity over the full temperature range (i.e., 300–800 • C) tested, reaching 73% CO 2 conversion at 800 • C. Ni 2 P-SiO 2 exhibited CO selectivity of 93–100% over a full temperature range, and 70% CO 2 conversion at 800 • C. The highest CO 2 conversions for Ni 12 P 5-SiO 2 at all temperatures among all catalysts showed its promising nature for CO 2 capture and utilisation. The methanation reaction was suppressed in addition to RWGS activity improvement through the formation of nickel phosphide phases, and the crystal structure was found to determine CO selectivity, with the following order Ni 12 P 5 >Ni 2 P > Ni 3 P. Based on the activity of the studied catalysts, the catalysts were ranked in order of suitability for the RWGS reaction as follows: Ni 12 P 5-SiO 2 (Ni/P = 2.4) > Ni 2 P-SiO 2 (Ni/P = 2) > NiP-SiO 2 (Ni/P = 1) > NiP 2-SiO 2 (Ni/P = 0.5). Two catalysts with Ni/P atomic ratios; 2.4 and 2, were selected for stability testing. The catalyst with Ni/P ratio = 2.4 (i.e., Ni 12 P 5-SiO 2) was found to be more stable in terms of CO 2 conversion and CO yield over the 24-hour duration at 550 • C. Using the phosphidation strategy to tune both selectivity and activity of Ni catalysts for RWGS, methanation as a competing reaction is shown to be no longer a critical issue in the RWGS process for catalysts with high Ni/P atomic ratios (2.4 and 2) even at lower temperatures (300–500 • C). This opens up potential low temperature RWGS opportunities, especially coupled to downstream or tandem lower temperature processes to produce liquid fuels.

Herein we analyze the profitability of a novel regenerative process to synergize biogas upgrading and carbon dioxide utilization. Our proposal is a promising alternative which allows to obtain calcium carbonate as added value product while going beyond traditional biogas upgrading methods with high thermal energy consumption. Recently we have demonstrated the experimental viability of this route. In this work, both the scale-up and the profitability of the process are presented. Furthermore, we analyze three representative scenarios to undertake a techno-economic study of the proposed circular economy process. The scale-up results demonstrate the technical viability of our proposal. The precipitation efficiency and the product quality are still remarkable with the increase of the reactor size. The techno-economic analysis reveals that the implementation of this circular economy strategy is unprofitable without subsidies. Nonetheless, the results are somehow encouraging as the subsides needed to reach profitability are lower than in other biogas upgrading and carbon dioxide utilization proposals. Indeed, for the best-case scenario, a feed-in tariff incentive of 4.3 €/MWh makes the approach profitable. A sensitivity study through tornado analysis is also presented, revealing the importance of reducing bipolar membrane electrodialysis energy consumption. Overall our study envisages the big challenge that the EU faces during the forthcoming years. The evolution towards bio-based and circular economies requires the availability of economic resources and progress on engineering technologies. [Display omitted] •Novel strategy for synergizing biogas upgrading & carbon capture and utilization•Scaling-up experiments and profitability analysis are performed.•Three scenarios are defined to analyze the implementation of circular economy.•Precipitation efficiency and product quality are not affected by reactor size.•Profitability analysis confirms the need of subsidies to promote circular economy.

Herein a novel path is analysed for its economic viability to synergize the production of biomethane and dimethyl ether from biogas. We conduct a profitability analysis based on the discounted cash flow method. The results revealed an unprofitable process with high cost/revenues ratios. Profitable scenarios would be reached by setting prohibitive DME prices (1983–5566 €/t) or very high feed-in tariffs subsidies (95.22 €/MWh in the best case scenario). From the cost reduction side, the analysis revealed the need of reducing investment costs. For this purpose, we propose a percentage of investment as incentive scheme. Although the size increase benefits cost/revenues ratio, only the 1000 m3/h biogas plant size will reach profitability if 90% of the investment is subsidized. A sensitivity analysis to check the influence of some important economical parameters is also included. Overall this study evidences the big challenge that our society faces in the way towards a circular economy. •Novel alternative for synergizing bio-methane and dimethyl ether production.•Profitability analysis for four different plant sizes.•The effect of dimethyl ether price and subsidies is studied.•The analysis revealed a technically viable but financially unprofitable process.•Evidence of the need of a strong green policy-making strategy.

This work establishes the primordial role played by the support’s nature when aimed at the constitution of Ni2P active phases for supported catalysts. Thus, carbon dioxide reforming of methane was studied over three novel Ni2P catalysts supported on Al2O3, CeO2 and SiO2-Al2O3 oxides. The catalytic performance, shown by the catalysts’ series, decreased according to the sequence: Ni2P/Al2O3 > Ni2P/CeO2 > Ni2P/SiO2-Al2O3. The depleted CO2 conversion rates discerned for the Ni2P/SiO2-Al2O3 sample were associated to the high sintering rates, large amounts of coke deposits and lower fractions of Ni2P constituted in the catalyst surface. The strong deactivation issues found for the Ni2P/CeO2 catalyst, which also exhibited small amounts of Ni2P species, were majorly associated to Ni oxidation issues. Along with lower surface areas, oxidation reactions might also affect the catalytic behaviour exhibited by the Ni2P/CeO2 sample. With the highest conversion rate and optimal stabilities, the excellent performance depicted by the Ni2P/Al2O3 catalyst was mostly related to the noticeable larger fractions of Ni2P species established.

Solid oxide fuel cells can operate with carbonaceous fuels, such as syngas, biogas, and methane, using either internal or external reforming, and they represent a more efficient alternative to internal combustion engines. In this work, we explore, for the first time, an alumina membrane containing straight, highly packed (461,289 cpsi), parallel channels of a few micrometers (21 mm) in diameter as a microreformer. As a model reaction to test the performance of this membrane, the dry reforming of methane was carried out using nickel metal and a composite nickel/ceria as catalysts. The samples with intact microchannels were more resistant to carbon deposition than those with a powdered sample, highlighting the deactivation mitigation effect of the microchannel structure. The coke content in the microchannel membrane was one order of magnitude lower than in the powder catalyst. Overall, this work is a proof of concept on the use of composite alumina membrane as microchannel reactors for high temperature reactions.

Reverse water gas shift (RWGS) competes with methanation as a direct pathway in the CO2 recycling route, with methanation being a dominant process in the low-temperature window and RWGS at higher temperatures. This work showcases the design of multi-component catalysts for a full-temperature-range RWGS behavior by suppressing the methanation reaction at low temperatures. The addition of alkali promoters (Na, K, and Cs) to the reference Ni/CeO2 catalyst allows identifying a clear trend in RWGS activation promotion in both low- and high-temperature ranges. Our characterization data evidence changes in the electronic, structural, and textural properties of the reference catalyst when promoted with selected dopants. Such modifications are crucial to displaying an advanced RWGS performance. Among the studied promoters, Cs leads to a more substantial impact on the catalytic activity. Beyond the improved CO selectivity, our best performing catalyst maintains high conversion levels for long-term runs in cyclable temperature ranges, showcasing the versatility of this catalyst for different operating conditions. All in all, this work provides an illustrative example of the impact of promoters on fine-tuning the selectivity of a CO2 conversion process, opening new opportunities for CO2 utilization strategies enabled by multi-component catalysts.

•Profitability analysis of green hydrogen production from biogas.•Prices could be competitive versus electrolysis hydrogen production.•Subsidies could boost the hydrogen market in the short-medium term.•Costs reduction strategies are envisaged. Hydrogen is not only considered as a cornerstone within renewable energy portfolio but it is also a key enabler for CO2 valorisation being a central resource for industrial decarbonization. This work evaluates the profitability of hydrogen production via combined biogas reforming and water–gas shift reaction, based on a real case scenario for landfill biogas plant in Seville (Spain). A techno-economic model was developed based on a process model and the discounted cash-flow method. A biogas flow of 700 m3/h (input given by the landfill biogas plant) was used as plant size and the analysis was carried out for two different cases: (1) use of already available energy sources at the industrial plant, and (2) solar energy generation to power the process. The economic outputs obtained showed that under the current circumstances, this hydrogen production route is not profitable. The main reason is the relatively low current hydrogen prices which comes from fossil fuels. A revenues analysis indicates that hydrogen from biogas selling prices between 2.9 and 5.7 €/kg would be needed to reach profitability, which are considerably higher than the current hydrogen cost (1.7 €/kg). A subsidy scheme is suggested to improve the competitiveness of this hydrogen production process in the short-medium term. A cost analysis is also performed, revealing that electricity prices and investment costs have a high impact on the total share (23–40% and 8–22%, respectively). Other potential costs reduction such as catalyst, labour and manteinance & overhead are also evaluated, showing that cutting-down production costs is mandatory to unlock the potential of hydrogen generation from biogas. Our work showcases the techno-economic challenge that green energy policies face in the path toward sustainable societies.

Introduction: Innovating technologies to efficiently reduce carbon dioxide (CO2) emission or covert it into useful products has never been more crucial in light of the urgent need to transition to a net-zero economy by 2050. The design of efficient catalysts that can make the above a viable solution is of essence. Many noble metal catalysts already display high activity, but are usually expensive. Thus, alternative methods for their production are necessary to ensure more efficient use of noble metals. Methods: Exsolution has been shown to be an approach to produce strained nanoparticles, stable against agglomeration while displaying enhanced activity. Here we explore the effect of a low level of substitution of Ni into a Rh based A-site deficienttitanate aiming to investigate the formation of more efficient, low loading noblemetal catalysts. Results: We find that with the addition of Ni in a Rh based titanate exsolution is increased by up to ∼4 times in terms of particle population which in turn results in up to 50% increase in its catalytic activity for CO2 conversion. Discussion: We show that this design principle not only fulfills a major research need in the conversion of CO2 but also provides a step-change advancement in the design and synthesis of tandem catalysts by the formation of distinct catalytically active sites.

Rising carbon dioxide (CO2) levels in the atmosphere from anthropogenic sources have led to the development of carbon capture, utilisation and storage (CCUS) technologies. In order to decarbonise chemical synthesis, a process intensification approach can be employed, wherein CO2 capture is coupled to a chemical reaction in a way that improves energy efficiency and product yields. In this review paper, we present advances in CO2 adsorbent development for process intensification, focusing on applications that have achieved a synergistic effect between CO2 adsorption and catalytic reactions that either consume or generate CO2. Firstly, we present a range of solid CO2 adsorbents of varying capability to capture CO2. Then we present a short introduction to the importance of developing CO2 adsorbents for process intensification. In order to improve the direction of research in the future, we emphasise the importance of developing compatible adsorbents and catalysts that operate synergistically and discuss the importance of cross cutting themes in process intensification and research opportunities for the future.

The rapid economic and societal development have led to unprecedented energy demand and consumption resulting in the harmful emission of pollutants. Hence, the conversion of greenhouse gases into valuable chemicals and fuels has become an urgent challenge for the scientific community. In recent decades, perovskite-type mixed oxide-based catalysts have attracted significant attention as efficient CO2 conversion catalysts due to the characteristics of both reversible oxygen storage capacity and stable structure compared to traditional oxide-supported catalysts. In this review, we hand over a comprehensive overview of the research for CO2 conversion by these emerging perovskite-type mixed oxide-based catalysts. Three main CO2 conversions, namely reverse water gas shift reaction, CO2 methanation, and CO2 reforming of methane have been introduced over perovskite-type mixed oxide-based catalysts and their reaction mechanisms. Different approaches for promoting activity and resisting carbon deposition have also been discussed, involving increased oxygen vacancies, enhanced dispersion of active metal, and fine-tuning strong metal-support interactions. Finally, the current challenges are mooted, and we have proposed future research prospects in this field to inspire more sensational breakthroughs in the material and environment fields.

CO2 hydrogenation to CH3OH via heterogeneous catalysis is one of the most promising and available approaches for mitigation of anthropogenic CO2 issues. In this work, thermodynamic equilibria of CO2 to methanol were compared with experimental results at given conditions using a commercial Cu/ZnO/Al2O3 catalyst for CO hydrogenation to methanol. It was found that, the high pressure, low temperature, and high H-2/CO2 ratio are favorable to methanol synthesis from CO2. Furthermore, the kinetic data were measured with an isothermal integral reactor under temperature between 160 and 240 degrees C, lower than that for CO hydrogenation to methanol reaction. Based on the single-active site and dual-active site LH mechanisms, both kinetic models can achieve full illustration of the influence of the operating conditions and the mechanisms. According to comparative analysis of the error variances of model correlations and the adsorbate coverages on the active sites, the dual-site mechanism identified to be superior to the single-site one for methanol synthesis from CO2 feedstock. Overall, this paper provides fundamental understanding of the thermodynamic and kinetic aspects of a central route for CO2 Valorisation. [GRAPHICS] .

•Non-precious catalysts for production of syngas from CO2 dry reforming of methane.•Extensive review of Ni-based bimetallic and transition metal phosphides.•Fundamental mechanisms of anti-coking and stability of catalysts in DRM reactions.•Recommendation of future research directions in non-precious catalysts for DRM. It is worthwhile to invest in the development of CO2 reforming of methane, as it presents a promising alternative for transforming two global warming gases into a very versatile product such as syngas. A syngas rich feed gas presents extensive prospects for existing downstream industrial processes for producing valuable fuels and chemicals. The commercialization of the DRM process greatly depends upon the development of low cost, non-precious transition metal-based catalysts, to provide a desirable balance between catalytic activity and stability. In this review, the progress in the advancements of non-precious catalytic materials have been discussed from a theoretical point of view. A theoretical perspective gives an opportunity to gain fundamental information at the atomic level, such as the interaction of reaction intermediates with particular crystal facets (typically active sites in the reaction), combined with electronic structure insights, directly influencing the kinetic behaviour of the catalyst system. Theoretical insights into the DRM reaction mechanisms on non-precious Ni-based bimetallic and transition metal phosphide catalysts are extensively discussed, together with the mitigation mechanisms to avoid carbon deposition and catalyst deactivation under DRM reaction conditions. Prospects of future development of DRM are also provided, highlighting the importance of computational chemistry studies in the development of the next-generation advanced DRM catalysts.

The rapid increase in the concentration of atmospheric carbon dioxide is one of the most pressing problems facing our planet. This challenge has motivated the development of different strategies not only in the reduction of CO2 concentrations via green energy alternatives but also in the capture and conversion of CO2 into value-added products. Metal-organic frameworks (MOFs) are a relatively new class of porous materials with unique structural characteristics such as high surface areas, chemical tunability and stability, and have been extensively studied as promising materials to address this challenge. This comprehensive review identifies the specific structural and chemical properties of MOFs that result in advanced CO2 capture capacities and fairly encouraging catalytic CO2 conversion behaviour. More importantly, we describe an interconnection among the unique properties of MOFs and the engineering aspects of these intriguing materials towards CO2 capture and conversion processes.

Kraft lignin (KL) is a by-product from cellulose production typically treated as a waste or used as a low-value fuel in heat and power generation in the pulp and paper industry. This study explores KL upgrading to monoaromatic compounds using supercritical water (SCW) as reaction medium. The effect of Ni–CeO2 catalysts supported on carbon nanofibers (CNF) and activated carbon (AC) on the product distribution was investigated. These catalysts were prepared by a wet-impregnation method with acetone, and reduced Ni was observed without the use of H2. CNF presented a high degree of stability in SCW. Ni in its reduced state was still present in all spent catalysts, mainly when CNF were the support. While catalysts supported in AC led to high yields of char and gas, a 56 wt% yield of a light liquid fraction, recovered as dichloromethane (DCM)-soluble product and consisting mainly of (methoxy)phenols (>80 mol%), was obtained in a batch reactor at 400 °C, 230 bar, with Ni–CeO2/CNF as a catalyst. A short reaction time was key to avoid the formation of gas and char. This study demonstrates that high yields of DCM-soluble products from KL and low char formation can be obtained by using only SCW and catalysts, an alternative to widely reported approaches like the addition of organic co-solvents (e.g., phenol) and/or H2.

This contribution presents a kinetic study for the identification of the complex reaction mechanism occurring during the ABE upgrading, and the development of a kinetic model. Employing graph theory analysis, a directed bipartite graph is constructed to reduce the complexity of the reaction network, and the reaction rate constants and reaction orders are calculated using the initial rate method, followed by the calculation of the activation energy and frequency factor for an Arrhenius-type law. Subsequently, using general mass balancing a proposed mathematical model is produced to determine the apparent reaction rates, which are successfully in line with the experimental results.

Herein we study the economic performance of hydrochar and synthetic natural gas co-production from olive tree pruning. The process entails a combination of hydrothermal carbonization and methanation. In a previous work, we evidenced that standalone hydrochar production via HTC results unprofitable. Hence, we propose a step forward on the process design by implementing a methanation, adding value to the gas effluent in an attempt to boost the overall process techno-economic aspects. Three different plant capacities were analyzed (312.5, 625 and 1250 kg/hr). The baseline scenarios showed that, under the current circumstances, our circular economy strategy in unprofitable. An analysis of the revenues shows that hydrochar selling price have a high impact on NPV and subsidies for renewable coal production could help to boost the profitability of the process. On the contrary, the analysis for natural gas prices reveals that prices 8 times higher than the current ones in Spain must be achieved to reach profitability. This seems unlikely even under the presence of a strong subsidy scheme. The costs analysis suggests that a remarkable electricity cost reduction or electricity consumption of the HTC stage could be a potential strategy to reach profitability scenarios. Furthermore, significant reduction of green hydrogen production costs is deemed instrumental to improve the economic performance of the process. These results show the formidable techno-economic challenge that our society faces in the path towards circular economy societies.

Here, we report the synthesis of mesoporous ZnO/Ni@m-SiO2 yolk-shell particles. The unique ZnO/Ni@m-SiO2 catalysts demonstrate impressive resistance to sintering and coking for dry reforming of methane (DRM). They also display long term stability with high levels of conversion and selectivity, making this catalyst promising for chemical CO2 upgrading.

Once considered an inert element, gold has recently gained attention as a catalyst. This book presents a comprehensive review of this rapidly-evolving field. It provides readers with a thorough background to the use of gold in catalysis, as well as the latest methods for the preparation of gold catalysts. Written to be accessible by postgraduates and newcomers to the field, this book is also beneficial to experienced researchers and is an essential reference in the laboratory.

This chapter presents the current state of the art in the development of mechanically and chemically robust perovskite-based membranes for industrial applications. Without providing an exhaustive picture of all developments in the field, the principal points of interest are discussed and the most recent concepts summarized. Finally, brief guidelines for possible future studies are proposed.

In this work the influence of the lanthanide series oxide addition to gold supported alumina catalyst is discussed. A clear promoting effect was observed no matter the employed reaction. Nevertheless, the presence of hydrogen in the oxidation mixture reveals interesting dissimilarities within the series of studied oxides. The differences in the catalytic behaviour of the samples are correlated to the crystal structure variations, oxygen sub-lattice disorder, gold presence and oxide's ability to undergo hydration/dehydration reactions.

Catalytic hydrodeoxygenation (HDO) is a fundamental and promising route for bio-oil upgrading to produce petroleum-like hydrocarbon fuels or chemical building blocks. One of the main challenges of this technology is the demand of high-pressure H2, which poses high costs and safety concerns. Accordingly, developing cost-effective routes for biomass or bio-oil upgrading without the supply of commercial H2 is essential to implement the HDO at commercial scale. This paper critically reviewed the very recent studies relating to the novel strategies for upgrading the bio-feedstocks with ‘green’ H2 generated from renewable sources. More precisely, catalytic transfer hydrogenation/hydrogenolysis (CTH), combined reforming and HDO, combined metal hydrolysis and HDO, water-assisted in-situ HDO and non-thermal plasma (NTP) technology and self-supported hydrogenolysis (SSH) are reviewed herein. Current challenges and research trends of each strategy are also proposed aiming to motivate further improvement of these novel routes to become competitive alternatives to conventional HDO technology.

Bio-hydrogenated diesel (BHD), derived from vegetable oil via hydrotreating technology, is a promising alternative transportation fuel to replace nonsustainable petroleum diesel. In this work, a novel Pt-based catalyst supported on N-doped activated carbon prepared from polypyrrole as the nitrogen source (Pt/N-AC) was developed and applied in the palm oil deoxygenation process to produce BHD in a fixed bed reactor system. High conversion rates of triglycerides (conversion of TG > 90%) and high deoxygenation percentage (DeCOx% = 76% and HDO% = 7%) were obtained for the palm oil deoxygenation over Pt/N-AC catalyst at optimised reaction conditions: T = 300 ◦C, 30 bar of H2, and LHSV = 1.5 h−1 . In addition to the excellent performance, the Pt/N-AC catalyst is highly stable in the deoxygenation reaction, as confirmed by the XRD and TEM analyses of the spent sample. The incorporation of N atoms in the carbon structure alters the electronic density of the catalyst, favouring the interaction with electrophilic groups such as carbonyls, and thus boosting the DeCOx route over the HDO pathway. Overall, this work showcases a promising route to produce added value bio-fuels from bio-compounds using advanced N-doped catalysts.

Silica-supported nickel phosphide catalysts with varying Ni/P atomic ratios (12/5, 2, 1, and 0.5) and 15 wt.% Ni-loading are synthesized. The synthesized catalysts are calcined and subjected to Temperature Programmed Reduction (TPR) analysis to evaluate Hydrogen consumption. Pre-reaction X-ray diffraction (XRD) analysis is performed on all calcined samples after reduction and passivation. The reduced catalysts are tested for the reverse water-gas shift reaction and post-reaction XRD analysis is performed on them. Stability tests are conducted on catalysts with Ni/P atomic ratios of 12/5 and 2, followed by XRD analysis of post-stability samples. The elemental composition of the catalysts at each stage is evaluated via inductively coupled plasma mass spectroscopy (ICP-MS) analysis. All experimental data is made available for re-use through this platform.

It still remains challenge for expanding the photo-response range of TiO2 with dominant {0 0 1} facets due to the hardly achieving modification of the electronic structure without destroying the formation of TiO2 high energy facets. Herein, we report the construction of carboxylate species modified TiO2 nanosheets with dominant {0 0 1} facets by employing ethanol as a carbon source through a low-temperature (300 degrees C) carbonization method. The as-obtained samples were investigated in detail by using various characterization techniques. The results indicate that the carboxylate species derived from the oxidation and carbonization of ethanol are coordinated to the {0 0 1} facets in a bidentate bridging mode. The electron-withdrawing carboxylate species induce TiO2 to form a lower valence band edge and a narrower bandgap, which enhances the oxidation ability of photogenerated holes and expands the photo-response range. The partially carbonized carboxylate species can also act as a photosensitizer to induce visible-light photocatalytic activity of TiO2 nanosheets. In addition, the carboxylate species can further promote the separation of photogenerated charge carriers. The findings of this work may provide a new perspective for tuning the band structure of TiO2 with dominant {0 0 1} facets and improving its photocatalytic performance. (C) 2020 Elsevier Inc. All rights reserved.

The aim of this study is to evaluate comprehensively the effect of spray angle, spray distance and gun traverse speed on the microstructure and phase composition of HVOF sprayed WC-17 coatings. An experimental setup that enables the isolation of each one of the kinematic parameters and the systemic study of their interplay is employed. A mechanism of particle partition and WC-cluster rebounding at short distances and oblique spray angles is proposed. It is revealed that small angle inclinations benefit notably the WC distribution in the coatings sprayed at long stand-off distances. Gun traverse speed, affects the oxygen content in the coating via cumulative superficial oxide scales formed on the as-sprayed coating surface during deposition. Metallic W continuous rims are seen to engulf small splats, suggesting crystallization that occurred in-flight.

•Primary product distribution from fast pyrolysis of torrefied biomass was determined.•High heating rate of 1000 °C s−1 with minimised secondary reaction was used.•Significantly larger volatile yields obtained due to fast heating.•Heavier tars were obtained from samples torrefied at higher temperatures.•Significant reduction in the extent of gasification with torrefaction temperatures caused by chemical not physical changes. Torrefaction is a key process for biomass energy densification ahead of its utilisation in pyrolysis, gasification or combustion, and therefore the changes it originates have been the subject of multiple studies. Most of them employ low heating rates, in the range of thermogravimetric analysers (TGA), typically below 1 °C s−1 or high rates (100–1000 °C s−1) in reactors where tars undergo considerable secondary reactions following release from a particle and the temperature history of the sample is not well defined, such as entrained flow or fluidised beds. This study aims to analyse the behaviour of torrefied lignocellulosic biomass (oak) under fast pyrolysis in with very controlled temperature history and absence of secondary reactions between evolving volatiles and chars in a wire mesh reactor (WMR), which allows determination of primary products. To this end, oak was firstly torrefied in a grey-King reactor to provide samples from mild to severe torrefaction (210–300 °C). The raw and torrefied oaks were pyrolyzed/gasified, at 1000 °C s−1 and 850 °C in the WMR using He and CO2 atmospheres. All samples showed high volatile production, in excess of 80 wt.%, but with a clear drop with increasing torrefaction temperature. The char yields from the WMR in CO2 were lower than in He, reflecting a degree of char gasification. However, char deactivation at the higher torrefaction temperatures caused a sharp decrease in the extent of gasification from 32 wt.% for Raw Oak to 6 wt.% for oak torrefied at 300 °C (Oak-300). This is a consequence of the predominance of chemical effects such as enrichment of carbon, which increased from 46.5 wt.% for Raw Oak to 54.3 wt.% in Oak-300 and depletion of oxygen, which led to greater aromaticity and structural order in the char with torrefaction temperature, over physical changes observed by scanning electron microscopy (SEM) revealing increasing porosity.

This paper reveals the effect of calcium and magnesium ions in carbonation experiments carried out to regenerate sodium hydroxide from a biogas upgrading unit. This novel study arises as an alternative to standard physical process whose elevated energy consumption imposes economic restrictions. Previous works employed alkaline waste to turn them into value added product. Nevertheless, no attractive economical results were obtained due to the low regeneration efficiencies. Our hypothesis is that both calcium and magnesium waste composition percentages have an impact in the result, hence this work propose an isolated study aiming to determine the of each one in the global performance. To this end, the operational parameters (reaction time, reaction temperature and molar ratio) were tuned as well as physicochemical properties of the final solid samples were analysed by several techniques. The results indicate that calcium is much more prone than magnesium to reach high efficiencies in aqueous carbonation experiments. Additionally, higher quality products were achieved with calcium. The results of this study suppose an important step for understanding the aqueous carbonation through waste in the path to achieve a more sustainable city and society.

In this work the development of a series of gold catalysts, essentially based on γ-alumina promoted with a small superficial fraction of Ce–Fe mixed oxides, is reported. The catalytic behaviour is evaluated in the water gas shift reaction. The formation of a Ce–Fe solid solution is evidenced by XRD and related to the catalytic activity where the importance of the Ce–Fe interaction is demonstrated. The best catalyst reached CO conversions very close to the equilibrium limit. A long-term stability test is performed and the loss of activity is observed and attributed to reaction intermediates. Almost complete recovery of the initial conversion is achieved after oxidation treatment, suggesting that the problem of stability could be overcome by a suitable change in the reaction parameters thus leading to a highly efficient catalyst for future applications in H2 production and clean-up

In this work an in situ XRD and XANES study of two gold catalysts supported on iron-promoted ceria-alumina carriers was carried out during the water-gas shift reaction (WGS). The first catalyst, Au/CeO2-FeO x/Al2O3, was prepared using a commercial alumina support in order to obtain a Ce-Fe oxide solid solution and in the second one, Au/FeOx/CeO2-Al2O3, an iron oxide monolayer was deposited onto a ceria-alumina commercial support to promote its redox properties. Catalytic activities in the WGS were remarkably different for both systems. The catalytic activity of the Au/CeO 2-FeOx/Al2O3 catalyst was higher than the one shown by the Au/FeOx/CeO2-Al 2O3 catalyst that resulted active at much higher temperatures. In situ XRD demonstrates the formation of magnetite (Fe 3O4) during the WGS reaction and the presence of big gold particles, ca. 21 nm in diameter, in the low-activity system. This in contrast to the high-activity system that shows undetectable gold nanoparticles and the absence of diffraction peaks corresponding to magnetite during the WGS. The data obtained using in situ XANES states that Ce4+ species undergo reduction to Ce3+during the WGS for both catalysts, and also confirms that in the high-activity catalyst iron is just present as Fe3+ species while in the low-activity catalyst Fe3+ and Fe2+ coexist, resulting in iron spinel observed by XRD. These results allow us conclude that the Au/CeO2-Fe2O3/Al 2O3 catalyst is a suitable catalyst for WGS when avoiding the formation of magnetite, in such a case Fe3+ species favors reduction and water splitting increasing the catalytic activity in the WGS reaction

This work presents an evaluation of a high performance series of water gas shift (WGS) catalysts in the preferential CO oxidation reaction (PrOx) in order to examine the applicability of the same catalyst for both processes as a first step for coupling both reactions in a single process. Gold based catalysts are applied in an extensive study of the CO-PrOx reaction parameters, such as λ, WHSV, CO concentration and [H2O]/[CO2] ratio in order to obtain the best activity/selectivity balance. CO and H2 oxidation reactions were treated separately in order to establish the degree of CO/H2 oxidation competition. Additionally the catalysts behavior in the CO-PrOx parallel reactions such a WGS and RWGS have been also carried out to analyze their effect on product composition.

Rivulet instabilities appear in many engineering applications. In absorption equipment, they affect the interface area available for mass transfer, and thus, reducing the efficiency. Here, computational fluid dynamics are used to reproduce the meanders and braids in rivulets flowing down an inclined channel. Fast oscillations of the meander (f = 5.6 Hz) are observed at low flow rates. At greater flow rates, an analysis of the transversal velocity in the retraction waves shows the effect of the surface tension, which causes the braiding phenomenon, and thus, the reduction in gas-liquid interface area.

Herein a strategy for biogas upgrading in a continuous flow absorption unit using CaCl2 as capturing agent is reported. This process is presented as an alternative to the standard physical regeneration processes to capture carbon dioxide (CO2) from biogas effluents with inherent high energy penalties. This work showcases a systematic study of the main parameters (reaction time, reaction temperature, and molar ratio reactant/precipitator) affecting calcium carbonate (CaCO3) precipitation efficiency in a reaction between sodium carbonate (Na2CO3) and CaCl2. In addition, the purity and main characteristics of the obtained product were carefully analysed via in a combined characterization study using Raman, XRD, and SEM. Our results indicate that acceptable precipitation efficiencies between 62 and 93% can be reached by fine tuning the studied parameters. The characterization techniques evidence pure CaCO3 in a calcite structure. These results confirmed the technical feasibility of this alternative biogas upgrading process through CaCO3 production.

In this work the development of gold catalysts, essentially based on γ-alumina with small superficial fraction of Ce-Fe mixed oxides as support for the low temperature CO oxidation is proposed. Characterization results obtained by means of TEM, OSC, XPS, UV-Vis spectroscopy and H2-TPR are employed to correlate the activity data with the catalysts composition. The bare γ-alumina supported gold catalyst demonstrates the poorest activity within the series. The addition of CeO2 or FeOX improves the catalytic performance, especially observed for the CeO2-FeOx mixed oxide doped samples. This enhanced CO oxidation activity was related to the Ce-Fe interaction producing materials with promoted redox properties and therefore oxidation activity.

The aim of this study is to evaluate comprehensively the effect of spray angle, spray distance and gun traverse speed on the microstructure and phase composition of HVOF sprayed WC-17 coatings. An experimental setup that enables the isolation of each one of the kinematic parameters and the systemic study of their interplay is employed. A mechanism of particle partition and WC-cluster rebounding at short distances and oblique spray angles is proposed. It is revealed that small angle inclinations benefit notably the WC distribution in the coatings sprayed at long stand-off distances. Gun traverse speed, affects the oxygen content in the coating via cumulative superficial oxide scales formed on the as-sprayed coating surface during deposition. Metallic W continuous rims are seen to engulf small splats, suggesting crystallization that occurred in-flight.

This paper evidences the viability of chemical recycling of CO2 via reverse water-gas shift reaction using advanced heterogeneous catalysts. In particular, we have developed a multicomponent Fe-Cu-Cs/Al2O3 catalyst able to reach high levels of CO2 conversions and complete selectivity to CO at various reaction conditions (temperature and space velocities). In addition, to the excellent activity, the novel-Cs doped catalyst is fairly stable for continuous operation which suggests its viability for deeper studies in the reverse water-gas shift reaction. The catalytic activity and selectivity of this new material have been carefully compared to that of Fe/Al2O3, Fe-Cu/Al2O3 and Fe-Cs/Al2O3 in order to understand each active component’s contribution to the catalyst’s performance. This comparison provides some clues to explain the superiority of the multicomponent Fe-Cu-Cs/Al2O3 catalyst

This paper reveals a regeneration method for a carbonate compound after carbon dioxide (CO2) absorption in a biogas upgrading unit run with caustic mixtures, obtaining precipitated calcium carbonate (PCC) as valuable by-product. This process arises as an alternative to physical regeneration, which is highly energy intensive. This work provides novel insights on the regeneration efficiency of carbonates to hydroxides while also studying the influence of K+ or Na+ in the caustic CO2-trapping solution. The compared parameters were the reaction time, temperature and molar ratio. Moreover, psychochemical characterization of solids was obtained by means of Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray powder diffraction (XRD) and Scanning Electron Microscopy (SEM) images. The results indicate that regeneration efficiencies are slightly lower when potassium is used instead of sodium, but quite acceptable for both of them. The chemical characterization experiments showed the predominance of calcium carbonate. Overall, the results obtained in this study proved that this process is feasible to upgrade biogas through PCC precipitation, which appears to be a promising economically viable process to synergise CCS and CCU.

Biogas is a renewable, as well as abundant, fuel source which can be utilised in the production of heat and electricity as an alternative to fossil fuels. Biogas can additionally be upgraded via the dry reforming reactions into high value syngas. Nickel-based catalysts are well studied for this purpose but have shown little resilience to deactivation caused by carbon deposition. The use of bi-metallic formulations, as well as the introduction of promoters, are hence required to improve catalytic performance. In this study, the effect of varying compositions of model biogas (CH4/CO2 mixtures) on a promising multicomponent Ni-Sn/CeO2-Al2O3 catalyst was investigated. For intermediate temperatures (650 °C), the catalyst displayed good levels of conversions in a surrogate sewage biogas (CH4/CO2 molar ratio of 1.5). Little deactivation was observed over a 20 h stability run, and greater coke resistance was achieved, related to a reference catalyst. Hence, this research confirms that biogas can suitably be used to generate H2-rich syngas at intermediate temperatures provided a suitable catalyst is employed in the reaction.

Mo2C is an effective catalyst for chemical CO2 upgrading via reverse water-gas shift (RWGS). In this work, we demonstrate that the activity and selectivity of this system can be boosted by the addition of promoters such as Cu and Cs. The addition of Cu incorporates extra active sites such as Cu+ and Cu0 which are essential for the reaction. Cs is an underexplored dopant whose marked electropositive character generates electronic perturbations on the catalyst’s surface leading to enhanced catalytic performance. Also, the Cs-doped catalyst seems to be in-situ activated due to a re-carburization phenomenon which results in fairly stable catalysts for continuous operations. Overall, this work showcases a strategy to design highly efficient catalysts based on promoted β-Mo2C for CO2 recycling via RWGS.

CO2 utilisation is becoming an appealing topic in catalysis science due to the urgent need to deal with greenhouse gases (GHG) emissions. Herein, the dry reforming of methane (DRM) represents a viable route to convert CO2 and CH4 (two of the major GHG) into syngas, a highly valuable intermediate in chemical synthesis. Nickel-based catalysts are economically viable materials for this reaction, however they show inevitable signs of deactivation. In this work stabilisation of Ni in a pyrochlore-perovskite structure is reported as a viable method to prevent fast deactivation. Substitution of Zirconium by Ni at various loadings in the lanthanum zirconate pyrochlore La2Zr2O7 is investigated in terms of reactant conversions under various reaction conditions (temperature and space velocity). XRD analysis of the calcined and reduced catalysts showed the formation of crystalline phases corresponding to the pyrochlore structure La2Zr2-xNixO7-δ and an additional La2NiZrO6 perovskite phase at high Ni loadings. Carbon formation is limited using this formulation strategy and, as a consequence, our best catalyst shows excellent activity for DRM at temperatures as low as 600 °C and displays great stability over 350 hours of continuous operation. Exsolution of Ni from the oxide structure, leading to small and well dispersed Ni clusters, could explain the enhanced performance.

Carbon formation and sintering remain the main culprits regarding catalyst deactivation in the dry and bi-reforming of methane reactions (DRM and BRM, respectively). Nickel based catalysts (10 wt.%) supported on alumina (Al2O3) have shown no exception in this study, but can be improved by the addition of tin and ceria. The effect of two different Sn loadings on this base have been examined for the DRM reaction over 20 h, before selecting the most appropriate Sn/Ni ratio and promoting the alumina base with 20 wt.% of CeO2. This catalyst then underwent activity measurements over a range of temperatures and space velocities, before undergoing experimentation in BRM. It not only showed good levels of conversions for DRM, but exhibited stable conversions towards BRM, reaching an equilibrium H2/CO product ratio in the process. In fact, this work reveals how multicomponent Ni catalysts can be effectively utilised to produce flexible syngas streams from CO2/CH4 mixtures as an efficient route for CO2 utilisation.

Clean hydrogen production via WGS is a key step in the development of hydrogen fuel processors. Herein, we have designed a new family of highly effective catalysts for low-temperature WGS reaction based on gold modified copper-zinc mixed oxides. Their performance was controlled by catalysts’ composition and the Au-Cu synergy. The utilization of hydrotalcite precursors leads to an optimal microstructure that ensures excellent Au and Cu dispersion and favors their strong interaction. From the application perspective these materials succeed to overcome the major drawback of the commercial WGS catalysts: resistance towards start/stop operations, a mandatory requisite for H2-powered mobile devices.

This work showcases an innovative route for biocompound upgrading via hydrodeoxygenation (HDO) reactions, eliminating the need for external high-pressure hydrogen supply. We propose the use of water as reaction media and the utilization of multifunctional catalysts that are able to conduct multiple steps such as water activation and HDO. In this study, we validate our hypothesis in a high-pressure batch reactor process using guaiacol as a model compound and multicomponent Ni-based catalysts. In particular, a comparison between ceria-supported and carbon/ceria-supported samples is established, the carbon-based materials being the suitable choice for this reaction. The physicochemical study by X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction, and temperature-programmed reduction reveals the greater dispersion of Ni clusters and the strong metal-support interaction in the carbon/ceria-based samples accounting for the enhanced performance. In addition, the characterization of the spent samples points out the resistance of our catalysts toward sintering and coking. Overall, the novel catalytic approach proposed in this paper opens new research possibilities to achieve low-cost bio-oil upgrading processes.

The present work showcases the versatility of nanogold systems supported on Zn-doped ceria when applied in two important environmental processes, the total CO oxidation, and the liquid phase oxidation of glucose to gluconic acid. In the CO oxidation the suitability of these materials is clearly demonstrated achieving full conversions even at sub-ambient conditions. Regarding the glucose oxidation our materials display high conversion values (always over 50%) and very importantly full or almost full selectivity toward gluconic acid—an added value platform chemical in the context of biomass upgrading routes. The key factors controlling the successful performance on both reactions are carefully discussed and compared to previous studies in literature. To our knowledge this is one of the very few works in catalysis by gold combining liquid and gas phase reactions and represents a step forward in the flexible behavior of nano gold catalysts.

In this comprehensive review, the main aspects of using Au/CeO2 catalysts in oxidation reactions are considered. The influence of the preparation methods and synthetic parameters, as well as the characteristics of the ceria support (presence of doping cations, oxygen vacancies concentration, surface area, redox properties, etc.) in the dispersion and chemical state of gold are revised. The proposed review provides a detailed analysis of the literature data concerning the state of the art and the applications of gold–ceria systems in oxidation reactions.

Selective conversion of CO2 to CO via the reverse water gas shift (RWGS) reaction is an attractive CO2 conversion process, which may be integrated with many industrial catalytic processes such as Fischer−Tropsch synthesis to generate added value products. The development of active and cost friendly catalysts is of paramount importance. Among the available catalyst materials, transition metal phosphides (TMPs) such as MoP and Ni2P have remained unexplored in the context of the RWGS reaction. In the present work, we have employed density functional theory (DFT) to first investigate the stability and geometries of selected RWGS intermediates on the MoP (0001) surface, in comparison to the Ni2P (0001) surface. Higher adsorption energies and Bader charges are observed on MoP (0001), indicating better stability of intermediates on the MoP (0001) surface. Furthermore, mechanistic investigation using potential energy surface (PES) profiles showcased that both MoP and Ni2P were active toward RWGS reaction with the direct path (CO2* → CO* + O*) favorable on MoP (0001), whereas the COOH-mediated path (CO2* + H* → COOH*) favors Ni2P (0001) for product (CO and H2O) gas generation. Additionally, PES profiles of initial steps to CO activation revealed that direct CO decomposition to C* and O* is favored only on MoP (0001), while H-assisted CO activation is more favorable on Ni2P (0001) but could also occur on MoP (0001). Furthermore, our DFT calculations also ascertained the possibility of methane formation on Ni2P (0001) during the RWGS process, while MoP (0001) remained more selective toward CO generation.

The catalytic performance of a series of bimetallic Ni-Co/CeO2-Al2O3 catalysts were evaluated within the dry reforming of methane (DRM) reaction, commonly used for upgrading biogas. The study focused on the variation of CeO2 weight loadings between 0, 10, 20 and 30%. It was found that the addition of CeO2 promoted CH4 and CO2 conversion across the temperature range and increased H2/CO ratio for the “low temperature” DRM. X-Ray Diffraction (XRD), H2-Temperature Programmed Reduction (H2-TPR) and X-Ray Photoelectron Spectroscopy (XPS) analysis revealed the formation of Ce4+ during activation of the 30% sample, resulted in excessive carbon deposition during reaction. The lowest CeO2 weight loadings exhibited softer carbon formation and limited increased chemical stability during reaction at the expense of activity. Of the tested weight loadings, 20 wt% CeO2 exhibited the best balance of catalytic activity, chemical stability and deactivation resistance in the DRM reaction. Hence this catalyst can be considered a promising system for syngas production from biogas at relatively low temperatures evidencing the pivotal role of catalysts design to develop economically viable processes for bioresources valorisation.

A series of effective NiMo/SiO2 catalysts for heavy oil upgrading in supercritical water have been developed. Experimental results with anthracene as model compound resembling structures present in heavy oils showed that the catalytic activity as well as the liquid and gas product distributions are governed by catalyst composition. In particular by adjusting the Ni/Mo ratio different physicochemical properties (crystalline phase composition, particle size and catalysts reducibility) are obtained, which have influence on catalytic behavior. A variety of liquid products together with a valuable gas (rich in H2) are produced in this process, which takes place with remarkably low coke deposition on the catalysts. Overall, the results derived from this work confirm the viability of upgrading polyaromatic structures in supercritical water using Ni-Mo catalysts and provides an insight on the main parameters to control in catalyst design.

In this work, the WGS performance of a conventional Ni/CeO2 bulk catalyst is compared to that of a carbon-supported Ni-CeO2 catalyst. The carbon-supported sample resulted to be much more active than the bulk one. The higher activity of the Ni-CeO2/C catalyst is associated to its oxygen storage capacity, a parameter that strongly influences the WGS behavior. The stability of the carbon-supported catalyst under realistic operation conditions is also a subject of this paper. In summary, our study represents an approach towards a new generation of Ni-ceria based catalyst for the pure hydrogen production via WGS. The dispersion of ceria nanoparticles on an activated carbon support drives to improved catalytic skills with a considerable reduction of the amount of ceria in the catalyst formulation

A copper-ceria bulk catalyst has been compared to a series of catalysts designed according to the as called “supported approach”, corresponding to the dispersion of low content mixed copper-ceria oxide on alumina matrix. The principal characteristics of both types of catalysts are contemplated and the differences in their electronic and redox properties discussed in details. As a plus, the gold metal promotion of the catalysts is also envisaged. The advantages of the systems in the CO clean up reactions, WGS and CO-PrOx are commented. While the WGS activity appears to be ruled especially by the Cu/Ce surface to volume ratio, the CO-PrOx reaction is governed by the CuO loading. Gold addition provides benefits only at the low temperature WGS regime. Very importantly, the supported systems are always superior to the bulk configuration in terms of specific activity, a key factor from the catalyst’s design perspective.

Self-standing, planar dual-phase oxygen transport membranes consisting of 70 vol.% (ZrO2)0.89(Y2O3)0.01(Sc2O3)0.10 (10Sc1YSZ) and 30 vol.% LaCr0.85Cu0.10Ni0.05O3-δ (LCCN) were successfully developed and tested. The stability of the composite membrane was studied in simulated oxy-fuel power plant flue-gas conditions (CO2, SO2, H2O). The analyses of the exposed composites by X-ray diffraction (XRD), X-ray fluorescence (XRF), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and Raman spectroscopy revealed an excellent stability. Oxygen permeation fluxes were measured across 1000 µm thick and 110 µm thick self-supported 10Sc1YSZ-LCCN (70-30 vol.%) membranes from 700 °C to 950 °C using air as the feed gas and N2 or CO2 as the sweep gas. The 110 µm thick membrane, prepared by tape-casting and lamination processes, showed oxygen fluxes up to 1.02 mLN cm-2 min-1 (950 °C, air/N2). Both membranes demonstrated stable performances over long-term stability tests (250-300 h) performed at 850 °C using pure CO2 as the sweep gas.

An innovative route for bio‐compounds upgrading via “hydrogen‐free” hydrodeoxygenation (HDO) is proposed and evaluated using guaiacol as a model compound in a high‐pressure batch reactor. Experimental results showed that noble metal supported on activated carbon catalysts are able to conduct tandem multiple steps including water splitting and subsequent HDO. The activity of Ru/C catalyst is superior to other studied catalysts (i.e. Au/C, Pd/C and Rh/C) in our water‐only HDO reaction system. The greater dispersion and smaller metal particle size confirmed by the TEM micrographs accounts for the better performance of Ru/C. This material also presents excellent levels of stability as demonstrated in multiple reciclabylity runs. Overall, the proposed novel approach confirmed the viability of oxygenated bio‐compounds upgrading in a water‐only reaction system suppressing the need of external H2 supply and can be rendered as a fundamental finding for the economical biomass valorisation to produce added value bio‐fuels.

Solid oxide fuel cells (SOFCs) are a rapidly emerging energy technology for a low carbon world, providing high efficiency, potential to use carbonaceous fuels and compatibility with carbon capture and storage. However, current state-of-the-art materials have low tolerance to sulfur, a common contaminant of many fuels, and are vulnerable to deactivation due to carbon deposition when using carbon-containing compounds. In this review we first study the theoretical basis behind carbon and sulfur poisoning, before examining the strategies towards carbon and sulfur tolerance used so far in the SOFC literature. We then study the more extensive relevant heterogeneous catalysis literature for strategies and materials which could be incorporated into carbon and sulfur tolerant fuel cells.

O transport membranes (OTM) are a promising alternative to conventional systems of air separation based on cryogenic distillation for oxy-fuel combustion power plants. In this work, a systematic study of the thermochemical stability of La0.6Sr0.4Co0.2 Fe0.8O3 (perovskite-type) and cobalt doped Ce0.9Gd0.1O (fluorite-type) is proposed. The experiments were developed in a laboratory scale facility, which is able to mimic realistic oxy-fuel combustion flue gas containing SOx, NOx, H2O and CO2. In order to understand the thermochemical behavior of this type of materials, a full characterization analysis of the tested samples using a wide portfolio of analytical techniques such as X-ray diffraction (XRD), X-ray fluorescence (XRF), infrared spectroscopy (ATR-FTIR), Raman spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and Brunauer−Emmett−Teller analysis (BET) has been carefully discussed. Our data revealed the superior stability of the CGO samples in comparison with the LSCF at all the test conditions studied in this work. The formation of crystalline and amorphous sulphates and carbonates are evident for the LSCF while for the CGO samples do not react with SOX and barely form carbonates. The presence of silicon species – typically ignored in academic works – has been detected, pointing its relevance for real applications.

Dual-phase composite oxygen transport membranes consisting of 50 vol% Al0.02Zn0.98O1.01 and 50 vol% (ZrO2)0.89(Y2O3)0.01(Sc2O3)0.10 were successfully developed and tested. The applicability of the membrane in oxy-fuel power plants schemes involving direct exposure to flue gas was evaluated by exposing the membrane to gas streams containing CO2, SO2, H2O and investigating possible reactions between the membrane material and these gases. The analyses of the exposed composites by x-ray diffraction (XRD), x-ray fluorescence (XRF), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and Raman spectroscopy revealed excellent stability. Additionally, an electrical conductivity measurement over 900 h confirmed that the composite is stable under prolonged exposure to CO2. However, an instability of the dual-phase membrane under oxygen partial pressures below PO2~10−4 atm. was found. Oxygen permeation tests on a 1 mm thick self-standing membrane resulted in an oxygen flux of 0.33 mLN min−1 cm−2 at 925 °C in air/N2. Stability tests in CO2 with 3 vol% O2 demonstrated the potential for the use of 10Sc1YSZ-AZO dual-phase membranes in oxy-combustion processes involving direct exposure to flue gas.

Abstract: The conversion of CO2 into CO via the Reverse Water-Gas Shift (RWGS) reaction is a suitable route for CO2 valorisation. Fe-based catalysts are highly active for this reaction but their activity and selectivity can be substantially boosted by adding Cs as a promoter. In this work we demonstrate that Cs modifies the redox behaviour and the surface chemistry of the iron based materials. The metallic dispersion and the amount of metallic Fe centres available for the reaction depends on Cs loading. 5 wt.% of Cs is an optimum amount of dopant to achieve a fair activity/selective balance. Nevertheless, depending on the RWGS reactor operational temperature, lower concentrations of Cs also lead to acceptable catalytic performance. Along with the excellent activity of the prepared materials this work showcases their robustness for long-term runs and the strong impact of H2/CO ratio in the overall catalytic performance.

Catalytic hydrodeoxygenation (HDO) is a fundamental process for bio-resources upgrading to produce transportation fuels or added value chemicals. The bottleneck of this technology to be implemented at commercial scale is its dependence on high pressure hydrogen, an expensive resource which utilization also poses safety concerns. In this scenario, the development of hydrogen-free alternatives to facilitate oxygen removal in biomass derived compounds is a major challenge for catalysis science but at the same time it could revolutionize biomass processing technologies. In this review we have analyzed several novel approaches, including catalytic transfer hydrogenation (CTH), combined reforming and hydrodeoxygenation, metal hydrolysis and subsequent hydrodeoxygenation along with non-thermal plasma (NTP) in order to avoid the supply of external H2. The knowledge accumulated from traditional HDO sets the grounds for catalysts and processes development among the hydrogen alternatives. In this sense, mechanistic aspects for HDO and the proposed alternatives are carefully analyzed in this work. Biomass model compounds are selected aiming to provide an indepth description of the different processes and stablish solid correlations catalysts composition-catalytic performance which can be further extrapolated to more complex biomass feedstocks. Moreover, the current challenges and research trends of novel hydrodeoxygenation strategies are also presented aiming to spark inspiration among the broad community of scientists working towards a low carbon society where bio-resources will play a major role.

This work addresses the thermochemical stability of ceramic materials –typically used in oxygen transport membranes– under the harsh gas environments found in oxyfuel combustion processes. Specifically, a dual-phase NiFe2O4-Ce0.8Tb0.2O2-δ (NFO-CTO) composite and a single-phase La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) were studied. The effect of the main contaminants present in this kind of processes (CO2, SO2 and H2O) has been tested. NFO-CTO composite remains stable under all the conditions studied whereas LSCF presents a poor stability in the presence of CO2 and SO2. Regardless of the treatment, NFO-CTO conserves its crystalline structure, without giving rise to new species due to segregation or incorporation of sulphur and/or carbon. On the contrary, LSCF is prone to degradation in contact with CO2 and SO2, segregating Sr in the form of SrCO3 and SrSO4 and Co and Fe in the form of CoO and Fe3O4. It is also shown that SO2 interaction with LSCF is stronger than in the case of CO2. A concentration of just 2000 ppm of SO2 in CO2 is enough to subdue the formation of SrCO3, promoting the segregation of Sr only in the form of SrSO4. With the results presented in this work, it is possible to conclude that the NFO-CTO is a suitable candidate from the thermochemical viewpoint to be used as membrane material in 4-end modules for oxygen generation integrated into oxyfuel combustion processes whereas the use of LSCF should be dismissed.

Cu-ZnO based catalysts are the benchmark materials for the low-temperature WGS reaction. However, they present a crucial drawback which limits their application in portable devices: they only work under very low space velocities. In this study, we have developed a series of multicomponent Cu-ZnO catalysts able to work at relatively high space velocities with outstanding activity and stability. Different reference supports have been utilised with CeO2-Al2O3 being the most promising system. Overall, this work describes a strategy to design advanced Cu-based catalysts that can overcome the residence time restrictions in the WGS reaction.

The dry reforming of methane with CO2 is a common route to transform CO2/CH4 mixtures into added value syngas. Ni based catalysts are highly active for this goal but suffer from deactivation, as such promoters need to be introduced to counteract this, and improve performance. In this study, mono- and bi-metallic formulations based on 10 wt.% Ni/CeO2-Al2O3 are explored and compared to a reference 10 wt.% Ni/γ-Al2O3. The effect of Sn and Pt as promoters of Ni/CeO2-Al2O3 was also investigated. The formulation promoted with Sn looked especially promising, showing CO2 conversions stabilising at 65% after highs of 95%. Its increased performance is attributed to the additional dispersion Sn promotion causes. Changes in the reaction conditions (space velocity and temperature) cement this idea, with the Ni-Sn/CeAl material performing superiorly to the mono-metallic material, showing less deactivation. However, in the long run it is noted that the mono-metallic Ni/CeAl performs better. As such the application is key when deciding which catalyst to employ in the dry reforming process.

The water-gas shift (WGS) reaction over structured Cu, Ni, and bimetallic Cu-Ni supported on active carbon (AC) catalysts was investigated. The structured catalysts were prepared in pellets form and applied in the medium range WGS reaction. A good activity in the 180–350 °C temperature range was registered being the bimetallic Cu-Ni:2-1/AC catalyst the best catalyst. The presence of Cu mitigates the methanation activity of Ni favoring the shift process. In addition the active carbon gasification reaction was not observed for the Cu-containing catalyst converting the active carbon in a very convenient support for the WGS reaction. The stability of the bimetallic Cu-Ni:2-1/AC catalyst under continuous operation conditions, as well as its tolerance towards start/stop cycles was also evaluated.

Conversion of agro-wastes into energy can be key to a circular-driven economy that could lead tomodels for sustainable production. Thermochemical processing is an interesting alternative for the upgrading of agro-wastes to energy. However, owing to the complex and largely unknown set of reactions occurring during thermal breakdown, to ensuring consistent quality of the final products is still a goal to achieve at industrial level. The present study investigates the evolution of solid products of pyrolysis, to gain some insights in these complexities. Chars derived fromslowpyrolysis (200–650 °C) of citrus pulp in a horizontal reactor have been characterized bymeans of Fourier Transform Infrared spectroscopy (FT-IR), X-Ray Diffraction (XRD), ThermoGravimetric Analysis (TGA) and Scanning Electron Microscopy (SEM). Results are discussed also in light of similarities with coal thermal breakdown. At temperatures below 300 °C, changes in solid matrix are mainly due to breaking of aliphatic compounds. Significant changes in char structure and behavior then occur between 300 °C and 500 °C mainly related to secondary char-tar reactions. Above 500 °C, changes appear to occur mainly due to recombination reactions within matrix, which thereby becomes progressively less reactive.

In this work a novel strategy for bio-methane production and magnesium chloride waste valorization is addressed. The proposed process is a potential alternative path to the already existing biogas upgrading technologies by carbon dioxide mineralization into valuable magnesium carbonate. The main parameters affecting the precipitation efficiency (reaction time, reaction temperature, and molar ratio reactant/precipitator) are studied, leading to promising results which spark further investigation in this innovative route. Additionally the purity and the morphology of the obtained solid product was accurately analysed through different physicochemical characterization techniques such as Raman, X-Ray diffraction and Scanning electron microscope. The characterisation study reveals a mixture of Nesqueonite and Dypingite carbonate phases obtained in the process being the later the dominant phase in the resulting precipitate. Overall, the results discussed herein confirmed the technical feasibility of this innovative strategy for synergizing carbon dioxide mineralization and renewable energy production.

In this work, a series of Au/CeO2-MOx/Al2O3 catalysts has been prepared and evaluated in the PrOx reaction. Within the series of dopants Fe and Cu containing samples enhanced the catalytic performance of the parent Au/CeO2/Al2O3 catalyst being copper the most efficient promoter. For both samples an enhanced oxygen storage capacity (OSC) is registered and accounts for the high CO oxidation activity. More particularly, the Au/CeO2-CuOx/Al2O3 catalyst successfully withstands the inclusion of water in the PrOx stream and presents good results in terms of CO elimination. However to achieve a good selectivity toward CO2 formation properly adjusting of the reaction parameters, such as oxygen concentration and space velocity is needed. Within the whole screened series the Cu-containing catalyst can be considered as the most interesting alternative for H2 clean-up applications.

Outstanding catalysts for the water was shift reaction are reported in this work. The combination of gold nanoparticles with Cu/ZnO/Al2O3 prepared from hydrotalcite-like precursors leads to very promising systems for pure hydrogen production. Full CO conversion is reached at temperatures as low as 180 °C. The key point seems to be the cooperation of Au and Cu and the optimal metal-oxide contact derived from the synthesis method. The high activity of gold for low temperature CO oxidation and the suitability of copper for the WGS results in a perfect synergy. Moreover the materials developed in this work present good stability and tolerance towards start/stop cycles an indispensable requisite for a realistic application in an integrated hydrogen fuel processor.

CO2 reforming of methane is an effective route for carbon dioxide recycling to valuable syngas. However conventional catalysts based on Ni fail to overcome the stability requisites in terms of resistance to coking and sintering. In this scenario, the use of Sn as promoter of Ni leads to more powerful bimetallic catalysts with enhanced stability which could result in a viable implementation of the reforming technology at commercial scale. This paper uses a combined computational (DFT) and experimental approach, to address the fundamental aspects of mitigation of coke formation on the catalyst’s surface during dry reforming of methane (DRM). The DFT calculation provides fundamental insights into the DRM mechanism over the mono and bimetallic periodic model surfaces. Such information is then used to guide the design of real powder catalysts. The behaviour of the real catalysts mirrors the trends predicted by DFT. Overall the bimetallic catalysts are superior to the monometallic one in terms of long-term stability and carbon tolerance. In particular, low Sn concentration on Ni surface effectively mitigate carbon formation without compromising the CO2 conversion and the syngas production thus leading to excellent DRM catalysts. The bimetallic systems also presents higher selectivity towards syngas as reflected by both DFT and experimental data. However, Sn loading has to be carefully optimized since a relatively high amount of Sn can severely deter the catalytic performance.

Herein a strategy to design highly efficient Au/CeO2/Al2O3 based WGS catalysts is proposed. The inclusion of transition metals, namely Fe, Cu and Zn as CeO2 dopant is considered. All the promoters successfully increased the WGS performance of the undoped sample. The activity improvement can be correlated to structural and/or redox features induced by the dopants. The comparative characterization of the doped samples by means of XRD, Raman spectroscopy and OSC evaluation permits an accurate understanding of the boosted WGS activity arising from the Ce-promoter interaction. This study establishes distinction among both, structural and redox sources of promotion and provides a useful strategy to develop highly active Au/CeO2 based catalysts for the WGS reaction.

This paper has described the application of nickel-doped catalytic constituents based on gadolinium-doped ceria (GDC) for fabrication of the solid-oxide fuel cell (SOFC) anode layer integrated with an in-situ methane-reforming layer (MRL). Nanocrystalline powders of Ni1-xCo3xO1+3x/GDC and Ni1-xCuxO/GDC with various compositions (x = 0.3, 0.5, 0.7) were synthesised using an ultrasound-assisted method followed by a thermal treatment to be applied for fabrication of the integrated MRL and the SOFC anode layer, respectively. Thermogravimetric analysis showed that the synthesized powders should be optimally calcined at 700 °C to exhibit improved crystallinity and catalytic activity. The morphological analysis showed the formation of nanocrystalline powders with particle size ranging from 4-86 nm that was confirmed by the crystal size analysis using XRD results. The elemental analysis by EDX indicated a successful distribution of the constituent ceramic and bimetallic phases after the addition of a sonication stage. The results of FT-IR and Raman spectroscopy confirmed lack of solvents residual after calcination that was in agreement with residual moisture content values obtained from TGA data. The fabricated anode-MRL bilayers had an adequate porosity (36.7%) and shrinkage (33.5%) after adding carbon particles as a pore former (at a loading fraction of 5.9 wt.%). The catalytic performance measurements of the MRL showed a methane conversion of 13% at maximum activity with a weight hour space velocity (WHSV) of 60 L/gh that was mainly due to carbon deposition in the reaction condition.

This work presents a comparison of the gold- and platinum-based catalysts behavior in the water-gas shift (WGS) reaction. The influence of the support, e.g., its composition and electronic properties, studied in detail by means of UV-Vis spectroscopy, of the metal nature and dispersion and of the stream composition has been evaluated. The catalytic performance of the samples is directly correlated with the electronic properties modification as a function of metal and/or support. Both metals present high activity in the selected reaction although in a different operation temperature window.

The production of H2 pure enough for use in fuel cells requires the development of very efficient catalysts for the water–gas shift reaction. Herein, a series of gold catalysts supported on ZnO-promoted CeO2–Al2O3 are presented as interesting systems for the purification of H2 streams through the water–gas shift reaction. The addition of ZnO remarkably promotes the activity of an Au/CeO2/Al2O3 catalyst. This increase in activity is mainly associated with the enhanced oxygen storage capacity exhibited for the Zn-containing solids. High activity and good stability and resistance towards start-up–shut-down situations was found, which makes these catalysts a promising alternative for CO clean-up applications.

BACKGROUND This paper presents a physicochemical comparison of the solid products obtained from two alternative processes that recycle waste sodium carbonate (Na2CO3) solution, which is produced following the absorption of CO2 in a biogas‐upgrading unit. Chemical regeneration processes offer an attractive alternative to the energetically demanding standard physical methods. In the first process, sodium hydroxide (NaOH) is regenerated as a precipitate from the chemical reaction of Na2CO3 with calcium hydroxide (Ca(OH)2). The second process shows a path to obtain a valuable sodium chloride (NaCl) and Calcium carbonate (CaCO3) rich brine from calcium chloride (CaCl2) acting as a precipitant agent. In both processes, Precipitated Calcium Carbonate (PCC) is obtained as the most valuable by‐product, but with varying properties due to the different origin. RESULTS The purpose of this work is to analyse physicochemically both variations of PCCs obtained and examining the differences between these solid samples in order to determine which method produces more desirable characteristics in the final product. To this end, FTIR, Raman, XRD and SEM were employed as characterization methods. The results reflect that both PCCs have a calcite crystal structure, or morph, being as both PCC products originate from CaCl2 that is more similar to commercial calcium carbonate calcite. CONCLUSION These results confirmed that a pure CaCO3 valuable by‐product can be obtained from a biogas upgrading unit with several industrial applications.

Platinum and gold structured catalysts were compared as active phases in classical and O2-assisted Water Gas Shift (WGS) reaction. Both metals were supported on iron-doped ceria mixed oxide and then, structured on metallic micromonolithic devices. As expected the WGS activity of both micromonoliths is conditioned by the nature of the noble metals being Pt the most active metal in traditional conditions. However, the addition of oxygen to the classical water gas feed turns the balance in favor of the gold based catalysts, being the presence of gold responsible for an excessive improvement of the catalytic activity

This article presents a regeneration method of a sodium hydroxide (NaOH) solution from a biogas upgrading unit through calcium carbonate (CaCO3) precipitation as a valuable by-product, as an alternative to the elevated energy consumption employed via the physical regeneration process. The purpose of this work was to study the main parameters that may affect NaOH regeneration using an aqueous sodium carbonate (Na2CO3) solution and calcium hydroxide (Ca(OH)2) as reactive agent for regeneration and carbonate slurry production, in order to outperform the regeneration efficiencies reported in earlier works. Moreover, Raman spectroscopy and Scanning Electron Microscopy (SEM) were employed to characterize the solid obtained. The studied parameters were reaction time, reaction temperature, and molar ratio between Ca(OH)2 and Na2CO3. In addition, the influence of small quantities of NaOH at the beginning of the precipitation process was studied. The results indicate that regeneration efficiencies between 53%–97% can be obtained varying the main parameters mentioned above, and also both Raman spectroscopy and SEM images reveal the formation of a carbonate phase in the obtained solid. These results confirmed the technical feasibility of this biogas upgrading process through CaCO3 production.

Herein, the production of synthetic natural gas is proposed as an effective route for CO2 conversion. Typical catalysts for this reaction are based on Ni. In this study, we demonstrated that the addition of promoters such as iron and cobalt can greatly benefit the activity of standard Ni methanation catalysts. In particular cobalt seems to be a very efficient promoter. Our Co doped material is an outstanding catalysts for the CO2 methanation leading to high levels of CO2 conversion with selectivities close to 100%. Additionally, this catalyst is able to preserve excellent performance at relatively high space velocity which allows flexibility in the reactor design making easier the development of compact CO2 utilisation units. As an additional advantage, the Co-promoted catalysts is exceptionally stable conserving high levels of CO2 conversion under continuous operations in long terms runs.

The development of novel fabrication methods to produce ceria catalysts with good high-temperature stability is critical for their implementation across a range of different applications. Herein, graphene oxide flakes are used as a sacrificial template in the synthesis of ceria particles to replicate the graphene oxide’s two-dimensionality. While performing the synthesis without graphene oxide results in large agglomerations of ceria crystallites, the addition of graphene oxide during the synthesis results in ceria nanoflakes (< 10 nm) replicating the graphene oxide morphology. This novel shape limits the diffusion of atoms at high temperature to a two-dimensional plane which is translated into a low sintering degree and consequently, an enhanced thermal stability. In this way, the ceria flakes are capable of maintaining high surface areas after calcination at high temperatures (> 400 °C) which results in improved catalytic performance for the oxidation of carbon monoxide. This resistance versus sintering has also a beneficial effect when ceria flakes are used as catalytic support of nickel particles. Improved metal dispersion and high metal-support interaction leads to lower sintering during the dry reforming of methane than similarly prepared un-templated ceria nickel catalysts. These results demonstrate the advantage of using graphene oxide as a sacrificial template for the production of sintering-resistant catalysts with good catalytic performance at high temperatures.

The hydrogenation of levulinic acid to γ-valerolactone with water as solvent is a crucial reaction for producing fine chemicals. However, the development of highly stable catalysts is still a major challenge. Here, we prepared a Ru nanoparticles incorporated in mesoporous-carbon (Ru-MC) catalyst to achieve high stability in acidic aqueous medium. The Ru-MC showed excellent catalytic performance (12024h-1 turnover frequency) in the hydrogenation of LA-to3 GVL. Compared with Ru supported on mesoporous carbon catalyst (Ru/MC) prepared by conventional wet impregnation method, the Ru-MC showed excellent reusability (more than 6 times) and thermal stability (up to 600 oC). Based on H2-TPR-MS characterization, it was proposed that the incorporated structure significantly increased the interaction between Ru nanoparticles and carbon support, which effectively prevent the leaching and sintering of Ru nanoparticles and contributed to increased high reusability and thermal stability of the Ru-MC.

This study reports the potential application of Ni2P as highly effective catalyst for chemical CO2 recycling via dry reforming of methane (DRM). Our DFT calculations reveal that the Ni2P (0001) surface is active towards adsorption of the DRM species, with the Ni hollow site being the most energetically stable site and Ni-P and P contributes as co-adsorption sites in DRM reaction steps. Free energy analysis at 1000 K found CH-O to be the main pathway for CO formation. The competition of DRM and reverse water gas shift (RWGS) is also evidenced with the latter becoming important at relatively low reforming temperatures. Very interestingly oxygen seems to play a key role in making this surface resistant towards coking. From microkinetic analysis we have found greater oxygen surface coverage than that of carbon at high temperatures which may help to oxidize carbon deposits in continuous runs. The tolerance of Ni2P towards carbon deposition was further corroborated by DFT and micro kinetic analysis. Along with the higher probability of C oxidation we identify poor capacity of carbon diffusion on the Ni2P (0001) surface with very limited availability of C nucleation sites. Overall, this study opens new avenues for research in metal-phosphide catalysis and expands the application of these materials to CO2 conversion reactions.

A new approach for understanding PrOx reaction over gold catalysts is proposed in this work. The competition between H2 and CO oxidation has been studied over a series of Au/MOx/Al2O3 (M = Ce and Co) catalysts in simulated post-reforming gas stream, containing H2O and CO2 for H2 cleanup goals. The catalysts' behavior is correlated to their oxygen storage capacity, redox behavior, and oxidation ability. The estimation of the reaction rates reveals that in these solids the H2 combustion, the selectivity limiting factor in the PrOx process, is mainly controlled by the support and not by the gold presence. The possible use of the hydrogen oxidation reaction as a catalyst selection criterion is discussed

Dry reforming of ethanol and glycerol using CO2 are promising technologies for H2 production while mitigating CO2 emission. Current studies mainly focused on steam reforming technology, while dry reforming has been typically less studied. Nevertheless, the urgent problem of CO2 emissions directly linked to global warming has sparked a renewed interest on the catalysis community to pursue dry reforming routes. Indeed, dry reforming represents a straightforward route to utilize CO2 while producing added value products such as syngas or hydrogen. In the absence of catalysts, the direct decomposition for H2 production is less efficient. In this mini-review, ethanol and glycerol dry reforming processes have been discussed including their mechanistic aspects and strategies for catalysts successful design. The effect of support and promoters is addressed for better elucidating the catalytic mechanism of dry reforming of ethanol and glycerol. Activity and stability of state-of-the-art catalysts are comprehensively discussed in this review along with challenges and future opportunities to further develop the dry reforming routes as viable CO2 utilization alternatives.

In the context of Carbon Capture and Utilisation (CCU), the catalytic reduction of CO2 to CO via reverse water-gas shift (RWGS) reaction is a desirable route for CO2 valorisation. Herein, we have developed highly effective Ni-based catalysts for this reaction. Our study reveals that CeO2-Al2O3 is an excellent support for this process helping to achieve high degrees of CO2 conversions. Interestingly, FeOx and CrOx, which are well-known active components for the forward shift reaction, have opposite effects when used as promoters in the RWGS reaction. The use of iron remarkably boosts the activity, selectivity and stability of the Ni-based catalysts, while adding chromium results detrimental to the overall catalytic performance. In fact, the iron-doped material was tested under extreme conditions (in terms of space velocity) displaying fairly good activity/stability results. This indicates that this sort of catalysts could be potentially used to design compact RWGS reactors for flexible CO2 utilisation units.

A series of V2O5- and Co3O4-modified ceria/alumina supports and their corresponding gold catalysts were synthesized and their catalytic activities evaluated in the CO oxidation reaction. V2O5-doped solids demonstrated a poor capacity to abate CO, even lower than that of the original ceria/alumina support, owing to the formation of CeVO4. XRD, Raman spectroscopy, and H2-temperature programmed reduction studies confirmed the presence of this stoichiometric compound, in which cerium was present as Ce3+ and its redox properties were avoided. Co3O4-doped supports showed a high activity in CO oxidation at subambient temperatures. The vanadium oxide-doped gold catalysts were not efficient because of gold particle agglomeration and CeVO4 formation. However, the gold–cobalt oxide–ceria/alumina catalysts demonstrated a high capacity to abate CO at and below room temperature. Total conversion was achieved at −70 °C. The calculated apparent activation energy values revealed a theoretical optimum loading of a half-monolayer.

Encapsulation of metal nanoparticles is a leading technique used to inhibit the main deactivation mechanisms in dry reforming of methane reaction (DRM): Carbon formation and Sintering. Ni catalysts (15%) supported on alumina (Al2O3) and ceria (CeO2) have shown they are no exception to this analysis. The alumina supported catalysts experienced graphitic carbonaceous deposits, whilst the ceria showed considerable sintering over 15 h of DRM reaction. The effect of encapsulation compared to that of the performance of uncoated catalysts for DRM reaction has been examined at different temperatures, before conducting longer stability tests. The encapsulation of Ni/ZnO cores in silica (SiO2) leads to advantageous conversion of both CO2 and CH4 at high temperatures compared to its uncoated alternatives. This work showcases the significance of the encapsulation process and its overall effects on the catalytic performance in chemical CO2 recycling via DRM.

Herein, a series of highly efficient gold based catalysts supported on mesoporous CeO2-Fe2O3 mixed oxides for CO elimination reactions have been developed. The materials have been fully characterized by means of XRD, Raman and UV-vis spectroscopies among other techniques. We identify the Ce-Fe synergism as a fundamental factor controlling the catalytic performance. Our data clearly reveal that the CO oxidation activity is maximized when the electronic and structural properties of the support are carefully controlled. In this situation, fairly good catalysts for environmental applications as for example H2 streams purification for fuel cell goals or CO abatement at room temperature can be designed

A series of NiMo/SiO2 catalysts was synthesized by sol-gel method for heavy oil upgrading in supercritical water (SCW). Phenanthrene was used as substrate as it represents polyaromatic structures present in asphaltenes. No phenanthrene conversion was observed in a blank (non-catalytic) experiment. However, phenanthrene conversions up to 24 % after 1 h of reaction in SCW at 425 °C and 230 bar were observed in the presence of NiMo/SiO2, underlining the role of the catalysts in the process. Conversion was found to be dependent mainly on Ni content and the Ni/Mo ratio in the catalysts. The liquid products obtained are thought to be the result of both oxidation and hydrogenation processes. Characterization of the fresh and spent catalysts using X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) was performed. It was revealed that catalysts are not completely stable in SCW, showing that NiMo intermetallic compounds formed the initial catalysts were decomposed, Mo0 and Ni0 were oxidised and the latter formed Ni2SiO4. In addition, MoO2 phase domain size in the catalysts increased and the surface of the spent catalysts appeared to be enriched with Ni and depleted with Mo.

The WGS reaction over multicomponent Au/Ce1-xCuxO2/Al2O3 catalysts is studied in this work. The systems are carefully designed aiming to take advantage of every active phase included in the formulation: gold, ceria and copper. Special emphasis is given to the CeO2-CuO synergy and its influence on the displayed catalytic performance with and without gold. To this aim a meaningful correlation between the physicochemical properties of the mixed materials and their activity/stability is proposed. In general terms the developed catalysts present high activity under realistic WGS reaction conditions, with fairly good long term stability. In addition, the systems successfully withstand start-up/shut-downs situations, indispensable requisite for real applications in the field of pure hydrogen production for fuel cell goals

A series of ZnO and Fe2O3 modified ceria/alumina supports and their corresponding gold catalyst were prepared and studied in the CO oxidation reaction. ZnO-doped solids show a superior catalytic activity compared to the bare CeO2-Al2O3, which is attributed to the intimate contact of the ZnO and CeO2 phases, since an exchange of the lattice oxygen occurs at the interface. In a similar way, Fe2O3-modified supports increase the ability of the CeO2-Al2O3 solids to eliminate CO caused by both the existence of Ce–Fe contact surface and the Fe2O3 intrinsic activity. All of the gold catalysts were very efficient in oxidising CO irrespective of the doping metal oxide or loading, with the ZnO containing systems better than the others. The majority of the systems reached total CO conversion below room temperature with the ZnO and Fe2O3 monolayer loaded systems the most efficient within the series.

In this work, bimetallic Cu–Ni catalysts have been studied in the water-gas shift (WGS) reaction, and they have shown different levels of synergy and anti-synergy in terms of catalytic activity and selectivity to the desired products. Cu–Ni interactions alter the physicochemical properties of the prepared materials (i.e. surface chemistry, redox behaviour, etc.) and as a result, the catalytic trends are influenced by the catalysts' composition. Our study reveals that Cu enhances Ni selectivity to CO2 and H2 by preventing CO/CO2 methanation, while Ni does not help to improve Cu catalytic performance by any means. Indeed, the monometallic Cu formulation has shown the best results in this study, yielding high levels of reactants conversion and excellent long-term stability. Interestingly, for medium-high temperatures, the bimetallic 1Cu–1Ni outperforms the stability levels reached with the monometallic formulation and becomes an interesting choice even when start-up/shutdowns operations are considered during the catalytic experiments.

Historically, the emission of particles from clinker kiln stacks has been one of the main environmental concerns in cement manufacturing processes. Up to now, environmental regulations have only focused on determining and controlling filterable particulate matter (FPM) in industrial emission sources. However, in recent years a growing interest in determining and analysing condensable particulate matter (CPM) has been evidenced due to the significant and established contribution of CPM to total emissions of particulate matter (PM). In this work, total PM (FPM + CPM) emissions from a clinker kiln in a cement manufacturing process have been characterized. A series of tests were performed to simultaneously collect FPM and CPM using a sampling train patented by University of Seville. The results showed very low level of emissions compared to regulatory limits. The average FPM and CPM concentrations obtained in the kiln were in the same order of magnitude, at 3.4 mg/Nm3 and 2.8 mg/Nm3, respectively. The CPM analysed was predominantly inorganic and represented 46% of total PM emissions. In addition, a microscopic morphological analysis was carried out on the samples and confirmed the presence of CPM with a size of less than 2 μm, as well as establishing the principal constituent elements of the same. The main element components were Al, Ca, Fe, Si, C and O. Compounds such as CaCO3, alite, ferrite and dolomite were detected with analytical characterization techniques, such as infrared spectroscopy (FTIR) analysis and X-ray diffraction (XRD), providing a better understanding of the sources of contamination within CPM. [Display omitted] •Understanding the physical-chemical nature of CPM from a clinker•Multi-technique analytic approach including SEM-EDX, FITR and XRD•The CPM was predominantly inorganic and represented 46% of total PM emissions.•CaCO3, alite, ferrite and dolomite were detected in the composition of the CPM.

The catalytic performance is highly related to the catalyst structure. Herein, a series of Ni nanoparticles supported on Y2O3 with different morphologies were successfully synthesized via hydrothermal process screening different pH environments. These Ni/Y2O3 catalysts were applied to efficiently produce COx-free H-2 through ammonia decomposition. We identify a significant impact of Y2O3 supports on nickel nanoclusters sizes and dispersion. The experimental results show that Ni/Y11 catalyst achieves 100% ammonia decomposition conversion under a gas hour space velocity (GHSV) of 12,000 ml.h(-1).g(cat)(-1) and temperature of 650 degrees C. Such a high level of activity over Ni/Y11 catalyst was attributed to a large specific surface area, appropriate alkalinity, and small Ni nanoparticles diameter with high dispersion.

In this work, the evolution of pyrolytic products of nature rubber (NR) and vulcanized NR were studied by performing a series of ReaxFF molecular dynamics simulations. The simulations under different temperatures (2400, 2600, 2800, 3000 K) were performed to investigate the influence of temperature on the distribution and characterization of product. The effect of water on product distribution and sulfur evolution during vulcanized NR pyrolysis were investigated by adding different amount of water molecules (50 and 200) into reaction sys-tems. The mechanism of water molecules promoting the decomposition of vulcanized NR was discussed and proposed. The results show that vulcanized cross-linked structure promotes the decomposition of carbon chains resulting more gas product at low temperature. Water can promote the further decomposition of heavy and light tars into gas product and inhibit the secondary formation of heavy tar. Moreover, water also facilitate the transfer of sulfur atoms to H2S and reduce the content of thiophene compounds at high temperature. Results indicate that water condition can provide a stronger cracking environment by generating OH radicals and reacting with in-termediate products of vulcanized NR pyrolysis forming R-C-OH radicals, which are the main precursors of CO and other oxygen-containing products.

In this work, an integration systems approach connecting an oil refinery and a bio-refinery is proposed. These plants can be connected through various pathways such as on-site power generation, utility systems and syngas production with the feed of refinery residue, bio-oil and other streams. One important pathway that is the focus in this work represents the production of chemicals produced via biomass sources into the petrochemical and transportation industry as valuable products. Focusing on the latter route of integration, the upgrading of Acetone, Butanol and Ethanol produced by sugar fermentation via bacterial species, has been chosen as a pathway to produce valuable products that could be utilised in both the chemical sector and the transportation industry. There is little current literature regarding this upgrading process, making it a relatively novel option of producing valuable products. The reaction systems studied consist of the self-condensation of the alcohols and cross condensation of alcohols and acetone using active metals supported on basic supports as catalysts at high temperatures and pressure in a batch reactor. Moreover, catalysts syntheses were conducted successfully to verify the proposed integration approach. The results have shown an outstanding performance for the catalysts in terms of conversion and selectivity, having conversions as high as 90%. The catalysts have also proven to yield valuable products with broad market options in the chemical Industry. In conclusion, this route has shown promising results in terms of providing valuable C-2-C-15 products, useful for both the petrochemical industry and the transportation sector while using economically favourable catalysts in comparison with previous studies.

The active forms of Au and Pt in CeO2-based catalysts for the water-gas shift (WGS) reaction are an issue that remains unclear, although it has been widely studied. On one hand, ionic species might be responsible for weakening the Ce-O bonds, thus increasing the oxygen mobility and WGS activity. On the other hand, the close contact of Au or Pt atoms with CeO2 oxygen vacancies at the metal-CeO2 interface might provide the active sites for an efficient reaction. In this work, using in situ X-ray absorption spectroscopy, we demonstrate that both Au and Pt remain unoxidized during the reaction. Remarkable differences involving the dynamics established by both species under WGS atmospheres were recognized. For the prereduced Pt catalyst, the increase of the conversion coincided with a restructuration of the Pt atoms into cuboctahedrical metallic particles without significant variations on the overall particle size. Contrary to the relatively static behavior of Pt-0, Au-0 nanoparticles exhibited a sequence of particle splitting and agglomeration while maintaining a zero oxidation state despite not being located in a metallic environment during the process. High WGS activity was obtained when Au atoms were surrounded by oxygen. The fact that Au preserves its unoxidized state indicates that the chemical interaction between Au and oxygen must be necessarily electrostatic and that such an electrostatic interaction is fundamental for a top performance in the WGS process.

This work is a detailed study on how to optimize gold colloids preparation and their deposition to very different in nature carbon materials. The change of the continuous phase and its dielectric constant is used to assure the good dispersion of the hydrophilic/hydrophobic carbons and the successful transfer of the preformed small size colloids to their surface. The sintering behavior of the particles during the calcination step is also studied and the optimal conditions to reduce to a minimum the particle size increase during the protecting agent removal phase are found. The as prepared catalysts have been tested in a relevant reaction in the field of environmental catalysis such as the reduction of 4-nitrophenol leading to promising results. Overall, this work proposes an important methodology to follow when a carbonaceous material are selected as catalyst supports for green chemistry reactions.

This study proposes various routes to integrate a fossil fuel-based system, such as an oil-refinery, with bio-refining processes aiming to enhance industry productivity. This is particularly relevant due to the lack of adaptation of existing refineries to diminishing oil supply. Moreover, the integration of oil and bio-refineries has a massively positive effect on the reduction of CO2 emissions. The proposed integration structure connects the industries through routes such as on-site power generation, syngas production using refinery residue and bio-oil and other waste streams, utility systems, and utilising chemicals produced via biomass sources into the petrochemical and transportation industry as valuable products. Focusing on the latter route of integration, the upgrade of Acetone, Butanol and Ethanol (produced by sugar fermentation via bacterial species) has been chosen as a pathway to produce valuable products that could be used in both the chemical sector and the transportation industry. The reaction system consists of the self-condensation and cross condensation of alcohols and acetone using active metals on their corresponding basic supports as catalysts at high temperatures and pressure in a batch reactor. The proposed approach has resulted in the production of long-chain hydrocarbons suitable for the chemicals or transportation industry. (C) 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

This works aims to provide an understanding on basic chemical kinetics pertaining to three-way catalytic (TWC) converters from an educational perspective, aimed at those novel readers in this field. Rate of reactions and its factors are explained, showcasing that the chosen catalyst is the main factor affecting the overall rate of reaction. Furthermore, this overview revisit insights of the catalytic converter structure and the environmental issues that come along with it. Lastly, the chemical and physical properties of the reactants and products-pollutant and less-toxic gases—are discussed, in order to gather a better understanding of the reactants and products that enters a catalytic converter.

Gold has long held the fascination of mankind. For millennia it has found use in art, cosmetic metallurgy and architecture; this element is seen as the ultimate statement of prosperity and beauty. This myriad of uses is made possible by the characteristic inertness of bulk gold; allowing it to appear long lasting and above the tarnishing experienced by other metals, in part providing its status as the most noble metal.

Pyrolysis provides an attractive alternative for the upgrading of agro-wastes to energy and chemicals. However, consistent quality of the final products is still a goal to be achieved at industrial level. The present study aims at complementing existing results recently published by the authors and investigating the physico-chemical evolution and oxidative reactivity of solid products of pyrolysis of citrus waste. Chars derived from slow pyrolysis (50 degrees C min(-1), 200-650 degrees C peak temperature) of orange and lemon pulp (OP and LP) in a horizontal batch reactor were characterized by means of Thermo-Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Electron Paramagnetic Resonance (EPR) and Raman spectroscopy. Results show how the onset of breaking of covalent bonds in matrix is triggered by reaching pyrolysis temperatures of 330-350 degrees C. Around those temperatures, the population of free-radicals significantly increases on solids and chars become more reactive, thereby favoring retrogressive, recombination and secondary solid-vapor reactions. Results also show that the higher content of lignin on LP may facilitate the formation of aromatic networks via lignin fragmentation and condensation above 500 degrees C. This trend is also confirmed by DSC patterns in which, above 500 degrees C, significantly more endothermic reactions occur in LP as a comparison to OP. This conclusion is further corroborated by more pronounced G-band Raman shifts shown for LP as a comparison to OP. The present results shed new light on the thermochemical breakdown of solid agro-wastes and provide insights for development of slow pyrolysis technology toward the production of valuable renewable carbonaceous materials.

The signal crosstalk and electromagnetic interference (EMI) problems direly need to be resolved in the rapid development of modern microwave communication technology for a better working frequency and transmission power of electronic systems. Where the new absorbing materials such as molybdenum disulfide (MoS2)/titania (TiO2)/Ti2CTx and MoS2/Ti2CTx composites could meet the requirement of "thin, strong, light weight, and wide band" for excellent absorbing performance. In this work, a lighter Ti2CTx material was selected as the matrix, and MoS2 was in-situ grown on Ti2CTx matrix by traditional hydrothermal method and microwave solvothermal method. The fabricated composite exhibited synergic effect of two-dimensional heterostructural interface and double dielectric elements, where a small amount of TiO2 and a certain proportion of MoS2 jointly improve the impedance matching of the composite material. In here, the extreme reflection loss (RLmin) can reach - 54.70 dB (with a frequency of 7.59 GHz, 3.39 mm thickness), and the maximum effective absorption bandwidth (EAB(max)) can reach 4 GHz. Polyethylene glycol 200 was used as the solvent instead of water to make Ti2CTx less oxidized during the composite process, where the microwave heating would attain fast speed, short time, high efficiency, and uniform product. Since, the MoS2/Ti2CTx composite without oxidizing possessed a wider effective absorption bandwidth (EAB) at a thinner thickness, thus resulting in the excellent microwave absorption performance and confirming the validity and rationality of new microwave absorption materials.

In-situ hydrodeoxygenation of guaiacol over Ni-based nitrogen-doped activated carbon supported catalysts is presented in this paper as an economically viable route for bio-resources upgrading. The overriding concept of this paper is to use water as hydrogen donor for the HDO reaction, suppressing the input of external high-pressure hydrogen. The effect of nitrogen sources, including polypyrrole (PPy), polyaniline (PANI) and melamine (Mel) on the structural, electronic and ultimately of catalytic features of the designed materials have been addressed. Nitrogen-doped samples are more active than the undoped counterparts in the “H2-free” HDO process. For instance, the conversion of guaiacol increased by 8 % for Ni/PANI-AC compared to that of Ni/AC catalysts. The superior performance of Ni/NC can be attributed to the acid-base properties and modified electronic properties, which favours the C-O cleavage and water activation as well as enhances dispersion of Ni particles on the catalysts’ surface.

Innovating technologies to efficiently reduce carbon dioxide (CO2) emission or covert it into useful products has never been more crucial in light of the urgent need to transition to a net-zero economy by 2050. The design of efficient catalysts that can make the above a viable solution is of essence. Many noble metal catalysts already display high activity, but are usually expensive. Thus alternative methods for their production are necessary to ensure more efficient use of noble metals. Exsolution has been shown to be an approach to produce strained nanoparticles, stable against agglomeration while displaying enhanced activity. Here we explore the effect of a low level of substitution of Ni into a Rh based A-site deficient titanate aiming to investigate the formation of more efficient, low loading noble metal catalysts. We show that this design principle not only fulfils a major research need in the conversion of CO2 but also provides a step-change advancement in the design and synthesis of tandem catalysts by the formation of distinct catalytically active sites.    

Ethylene is the world’s largest commodity chemical and a fundamental building block molecule in the chemical industry. Oxidative coupling of methane (OCM) is considered a promising route to obtain ethylene due to the potential of natural gas as a relatively economical feedstock. In a recent work, this route has been integrated by Godini et al (2013) with methane dry reforming (DRM) in a dual membrane reactor, allowing an improved thermal performance. In this work, we have explored a more ambitious integrated system by coupling the production of methane and carbon dioxide via coal gasification with the DRMOCM unit. Briefly, our process utilises coal to generate value-added methane and ethylene. In addition, CO2 management is achieved through CO2 methanation and dry methane reforming. Potential mass and energy integration between two systems is proposed as well as the optimum conditions for synthetic natural gas production. The upstream gasification process is modelled to determine the influence of temperature, pressure, and feed composition in the methane yield. The results suggest that the key variables are temperature and hydrogen concentration, as both parameters significantly affect the methane and CO2 levels in the linking stream. This study reports for the first time the linking stream between the two systems with a high methane concentration and the appropriate amount of CO2 for downstream processing.

In this work, the systematic integration of bio-refineries within oil refineries is considered. This is particularly relevant due to the lack of adaptation of existing refineries to diminishing oil supply. Moreover, the integration of oil and bio-refineries has a massively positive effect on the reduction of CO2 emissions. For instance, the biodiesel produced in bio-refineries could be integrated with conventional oil refinery processes to produce fuel, thusly reducing the dependence on crude oil. This represents a suitable alternative for increasing profit margins while being increasingly environmentally friendly. The identified possible routes of integration will be discussed in this contribution. For this purpose, the different proposed alternatives and their configurations were simulated and analysed. The developed models simulated key integrations e.g. a gasification unit that is fed from pyrolysis oil, biodiesel, and refinery residue, before being combined into one system involving all three. Varying forms of synthesis for these three feeds were also considered, focusing on novel techniques as well as environmentally friendly options that made use of waste products from other processes. The simulations revealed valuable gas stream rich in H2, with some CO2 and with a slight excess of CO resulting from the gasification unit. Further upgrading of these products was achieved by coupling the gasifier with a water gas shift (WGS) unit. This allowed a fine tune of the H2:CO ratio in the gas stream which can be further processed to obtain liquid hydrocarbons via Fischer-Tropsch (FT) synthesis or alternatively, clean hydrogen for fuel cells applications.

The present invention relates to a substrate for a gold catalyst, of formula CeO2 - ΜΟχ/ΑΙ2O3, wherein the substrate comprises between 60 and 90% w/w of Al2O3 and a percentage of CeO2 between 10 and 40% w/w, optionally doped with MOx oxide, with M selected from Fe, Zn, Co and Ni, Zr or mixtures thereof. The present invention relates to the use of the catalyst for the water-gas shift reaction and, more particularly, the use thereof in fuel cells.

This work reports the synthesis and characterisation of a core-shell n-octacosane@silica nano-encapsulated phase-change material obtained via interfacial hydrolysis and poly-condensation of tetraethyl orthosilicate in mini-emulsion. Silica has been used as the encapsulating material because of its thermal advantages relative to synthesised polymers. The material presents excellent heat storage potential, with a measured latent heat varying between 57.1 and 89 kJ∙kg-1 (melting point between 58 and 64°C) and a small particle size (between ~565 and ~227 nm). Degradation of the n-octacosane core starts between 150 and 180°C. Also, the use of silica as shell material gives way to a heat conductivity of 0.796 W∙m-1∙K-1 (greater than that of nano-encapsulated materials with polymeric shell). Charge/discharge cycles have been successfully simulated at low pressure to prove the suitability of the nano-powder as phase-change material. Further investigations will be carried out in the future regarding the use of the synthesised material in thermal applications involving nanofluids.

Hydrogen-alimented fuel cells (FC) have a strong potential to play a decisive role in the new energy system for the coming years. The production of H2 pure enough to use it in fuel cells requires the development of very efficient catalysts for the WGS reaction. In our group several gold-ceria based catalysts have been developed presenting very promising results in this process [1,2]. The successful catalytic design makes mandatory an accurate knowledge about the reaction mechanism and the active species involved in the process. In order to address these issues a combination of several in-situ/operando characterization techniques is performed in this work using an optimized Au/CeO2-FeOx/Al2O3 catalyst. Synchrotron-based in-situ time-resolved Xray absorption spectroscopy (TR-XAS) and operando DRIFTS during the WGS reaction are employed with the ultimate goal to establish structure-activity relations and to propose the most likely reaction pathways.

The current status of world oil reserves is a contentious matter, but it is widely accepted that conventional resources are dwindling and their reserves are less easily accessible [1]. Therefore, the production of heavy crude oil (HCO), which is the remnant of conventional oil has become more relevant and will remain so in the foreseeable future [2]. In this sense, there is a need for more efficient refining processes to transform HCO into lighter fuels. Conventional processes for increasing the value of heavy oil fractions aim to increase the H/C ratio of fuel, generating lighter fractions. However, this implies either rejecting a large amount of the carbon in the feed as in thermal and catalytic cracking processes, or using high pressure hydrogen, an expensive gas, in hydrocracking processes [3].