Dr. Melis Duyar is Senior Lecturer of Chemical and Process Engineering at the University of Surrey. She has a research background in heterogeneous catalysis for energy and environmental applications. Dr. Duyar received her B.Sc. (2012) in Chemical and Biological Engineering from Koç University in Istanbul, Turkey. She obtained her M.S. (2013) and Ph.D. (2015) in Earth and Environmental Engineering from Columbia University in the City of New York and conducted post-doctoral research (2015-2017) in the Chemical Engineering Department at Stanford University. Prior to her academic appointment at the University of Surrey, Dr. Duyar worked at the US Department of Energy’s SLAC National Accelerator Laboratory as Associate Staff Scientist in the SUNCAT Center for Interface Science and Catalysis and was also Lecturer of Chemical Engineering at Stanford University for 2 years (2017-2019).
Areas of specialism
Dr. Duyar’s research interests focus on the development of novel adsorbent materials for carbon dioxide capture and catalytic materials for the production of sustainable fuels and chemicals from carbon based feedstocks. Her research aims to establish rational design criteria for catalytically active materials for the following applications:
- Combined carbon dioxide capture and utilisation
- Thermochemical reduction of carbon dioxide
- Methanol synthesis
- Higher alcohol synthesis
- Fischer-Tropsch synthesis
Dr. Duyar’s research interests focus on the development of novel adsorbent materials for carbon dioxide capture and catalytic materials for the production of sustainable fuels and chemicals from carbon based feedstocks. Her research aims to establish rational design criteria for catalytically active materials for the following applications:
- Combined carbon dioxide capture and utilisation
- Thermochemical reduction of carbon dioxide
- Methanol synthesis
- Higher alcohol synthesis
- Fischer-Tropsch synthesis
ENG3190 PROCESS OPERATION AND MANAGEMENT
ENG2111: SEPARATION PROCESSES 1 & HYSYS
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.
Methanol is a major fuel and chemical feedstock currently produced from syngas, a CO/CO2/H2 mixture. Herein we identify formate binding strength as a key parameter limiting the activity and stability of known catalysts for methanol synthesis in the presence of CO2. We present a molybdenum phosphide catalyst for CO and CO2 reduction to methanol, which through a weaker interaction with formate, can improve the activity and stability of methanol synthesis catalysts in a wide range of CO/CO2/H2 feeds. MoP katalysiert die Hydrierung von CO und CO2 zu Methanol. Indem nur der einzähnige Koordinationsmodus von Formiat stabilisiert wird, umgeht das Phosphid den (sich verstärkenden) Effekt, der sich aus der notwendigen Voraussetzung, sauerstoffhaltige Intermediate zu binden, und der Desaktivierung des Katalysators durch hohe Formiat‐Bedeckungen in Gegenwart von CO2 ergibt.
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.
In a highly competitive retail market, many microbreweries have attempted to maximise profits and decrease energy consumption through retrofitting their operations with renewable energy. This paper develops an optimisation model to minimise investment and operation costs of a microbrewery meeting the dynamic energy demands, via an integrated photovoltaic (PV) system with energy storage and different boiler choices to lower carbon emissions. A microbrewery in UK has been used for the case study to demonstrate the approach on real data, with challenges in implementation and real-world constraints and considerations discussed. A set of rigorous multi-objective optimisation and sensitivity analyses are performed to analyse the resulting system. For the particular brewery, a modern electric boiler combined with photovoltaic system is an economic and sustainable choice, due to the cooling and other electric requirements in the brewery, leading to a 33 percent reduction in operational costs with a payback time of 2.6 years.
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.
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.
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.
In this study, Erbium and Ytterbium doped Bismuth based electrolyte was investigated for the solid oxide fuel cells. Yb 2 O 3 and Er 2 O 3 oxides were doped into the Bi 2 O 3 compound using solid-state reaction method in (Er 2 O 3 ) x (Yb 2 O 3 ) y (Bi 2 O 3 ) 1-x–y stoichiometric ratio ( x = 2, 4, 6, 8 mol% and y = 5, 10, 15, 20 mol%). Investigations were carried out for 700 °C, 750 °C, 800 °C sintering temperatures, respectively. Structural characterization was carried out using X-ray powder diffraction (XRD), and stable face-centred cubic crystal phase ( δ -phase) was successfully obtained in all samples containing more than 12 mol% dopant. When the variation of the lattice parameters according to the total addition rate is examined, it is observed that as the additive content increases, lattice parameters also become larger. Differential Thermal Analysis (DTA) showed that all samples were thermally stable and phase transformation was not observed below 1000 °C. The porosity of pellets was analysed from their surface images taken via Scanning Electron Microscopy (SEM), and these results showed an increase in porosity with increasing dopant content. Total conductivities of electrolytes were measured by Four-Point Probe technique (4PPT), and temperature dependency of conductivity was investigated. The single δ -phase ErYbSB-15 sample was found to have highest conductivity (~ 5 × 10 –2 Scm −1 at 560 °C). This conductivity value is higher than the conductivity of 20 mol% Erbium doped bismuth oxide previously known as the highest conductivity value of doped Bismuth oxide based electroceramics given in the literature. Graphical abstract Synthesising of Er and Yb Doped Bismuth Oxide Solid Electrolytes
Styrene is an important monomer for synthetic resins, ion exchange resins and synthetic rubber. Styrene polymerization requires the use of initiators to increase the reaction rate, with composite initiators showing promise for increased reaction rates. However, increased reaction rates in polymerization, if uncontrolled, can lead to thermal runaway with disastrous consequences. Numerous runaway incidents have been documented, indicating inadequate awareness of the thermal hazards of polymerization reactions. This study focuses on determining via calorimetric techniques the thermal hazards of styrene polymerization using azodiisobutyronitrile (AIBN) and tert-Butyl peroxybenzoate (TBPB) composite initiators. Differential scanning calorimetry (DSC) is employed to investigate the thermal decomposition properties of composite initiators with varying composition. Non-isothermal experiments and adiabatic experiments are used to determine the thermal hazard parameters including initial exothermic temperature and heat release of styrene polymerization. The risk of secondary reactions is evaluated by reaction calorimetry (RC1e) and product thermogravimetric analysis (TGA). Key safety parameters of the exothermic reaction, such as the onset temperature, heat release, time to maximum rate under adiabatic condition as well as activation energy, are presented. The results show that the thermal hazard of the polymerization reaction is lowest when the ratio of AIBN to TPPB in the composite initiator is 1:1. In this scenario, the temperature reached by the uncontrolled reaction does not provoke the decomposition of the products, yet the runaway consequences are still unacceptable. This work provides extensive data as a reference for the process optimization of styrene polymerization from the perspective of safety.
In situ capture of CO₂ allows the thermodynamically constrained water gas shift (WGS) process to operate at higher temperatures (i.e., 350 C) where reaction kinetics are more favorable. Dispersed CaO/γ-Al₂O₃ was investigated as a sorbent for in situ CO₂ capture for an enhanced water gas shift application. The CO₂ adsorbent (CaO/γ-Al₂O₃) and WGS catalyst (Pt/γ-Al₂O₃) were integrated as multiple layers of washcoats on a monolith structure. CO₂ capture experiments were performed using thermal gravimetric analysis (TGA) and a bench scale flow through reactor. Enhancement of the water gas shift (EWGS) reaction was demonstrated using monoliths (400 cells/in.2) washcoated with separate layers of dispersed CaO/γ-Al₂O₃ and Pt/γ-Al₂O₃ in a flow reactor. Capture experiments in a reactor using monoliths coated with CaO/γ-Al₂O₃ indicated that increased concentrations of steam in the reactant mixture increase the capture capacity of the CO₂ adsorbent as well as the extent of regeneration. A maximum capture capacity of 0.63 mol of CO₂/kg of sorbent (for 8.4% CaO on γ-Al₂O₃ washcoated with a loading of 3.45 g/in.3 on monolith) was observed at 350 C for a reactant mixture consisting of 10% CO₂, 28% steam, and balance N₂. Hydrogen production was enhanced in the presence of monoliths coated with a layer of 1% Pt/γ-Al2O₃ and a separate layer of 9.4% CaO/γ-Al₂O₃. A greater volume of hydrogen compared to the baseline WGS case was produced over a fixed amount of time for multiple cycles of EWGS. The CO conversion was enhanced beyond equilibrium during the period of rapid CO₂ capture by the nanodispersed adsorbent. Following saturation of the adsorbent, the monoliths were regenerated (CO₂ was released) in situ, at temperatures far below the temperature required for decomposition of bulk CaCO₃. It was demonstrated that the water gas shift reaction could be enhanced for at least nine cycles with in situ regeneration of adsorbent between cycles. Isothermal regeneration with only steam was shown to be a feasible method for developing a process.
CO₂ methanation has been evaluated as a means of storing intermittent renewable energy in the form of synthetic natural gas. A range of process parameters suitable for the target application (4720 h⁻¹ to 84,000 h⁻¹ and from 160 °C to 320 °C) have been investigated at 1 bar and H₂/CO₂ = 4 over a 10% Ru/γ-Al₂O₃ catalyst. Thermodynamic equilibrium was reached at T ≈ 280 °C at a GHSV of 4720 h⁻¹. Cyclic and thermal stability tests specific to a renewable energy storage application have also been conducted. The catalyst showed no sign of deactivation after 8 start-up/shut-down cycles (from 217 °C to RT) and for total time on stream of 72 h, respectively. In addition, TGA-DSC was employed to investigate adsorption of reactants and suggest implications on the mechanism of reaction. Cyclic TGA-DSC studies at 265 °C in CO₂ and H₂, being introduced consecutively, suggest a high degree of short term stability of the Ru catalyst, although it was found that CO₂ chemisorption and hydrogenation activity was lowered by a magnitude of 40% after the first cycle. Stable performance was achieved for the following 19 cycles. The CO₂ uptake after the first cycle was mostly restored when using a H₂-pre-treatment at 320 °C between each cycle, which indicated that the previous drop in performance was not linked to an irreversible form of deactivation (sintering, permanent poisoning, etc.). CO chemisorption on powder Ru/γ-Al₂O₃ was used to identify metal sintering as a mechanism of deactivation at temperatures higher than 320 °C. A 10% Ru/γ-Al₂O₃//monolith has been investigated as a model for the design of a catalytic heat exchanger. Excellent selectivity to methane and CO₂ conversions under low space-velocity conditions were achieved at low hydrogenation temperatures (T = 240 °C). The use of monoliths demonstrates the possibility for new reactor designs using wash-coated heat exchangers to manage the exotherm and prevent deactivation due to high temperatures.
The accumulation of CO₂ emissions in the atmosphere due to industrialization is being held responsible for climate change with increasing certainty by the scientific community. In order to prevent its further accumulation in the atmosphere, CO₂ must be captured for storage or converted to useful products. Current materials and processes for CO₂ capture are energy intensive. We report a feasibility study of dual function materials (DFM), which capture CO₂ from an emission source and at the same temperature (320 °C) in the same reactor convert it to synthetic natural gas, requiring no additional heat input. The DFM consists of Ru as methanation catalyst and nano dispersed CaO as CO₂ adsorbent, both supported on a porous γ-Al₂O₃ carrier. A spillover process drives CO₂ from the sorbent to the Ru sites where methanation occurs using stored H₂ from excess renewable power. This approach utilizes flue gas sensible heat and eliminates the current energy intensive and corrosive capture and storage processes without having to transport captured CO₂ or add external heat.
A δ-Ni5Ga3/SiO2 catalyst, which is highly active and stable for thermal CO2 hydrogenation to methanol, was investigated to understand its surface dynamics during reaction conditions. The catalyst was prepared, tested and characterized using a multitude of techniques, including ex-situ XRD (X-ray Diffraction), TEM (Transmission Electron Microscopy), H2-TPR (Temperature Programmed Reduction), CO chemisorption, along with in-situ ETEM (Environmental Transmission Electron Microscopy), APXPS (Ambient Pressure X-ray Photoelectron Spectroscopy) and HERFD-XAS (High Energy Resolution Fluorescence Detected X-Ray Absorption Spectroscopy). Upon air exposure Ga migrates from the subsurface region to the surface of the nanoparticles forming a Ga-oxide shell surrounding a metallic core. The oxide shell can be reduced completely only at high temperatures (above 600 °C); the temperature of the reducing activation treatment plays a crucial role on the catalytic activity. HERFD-XAS and APXPS measurements show that an amorphous Ga2O3 shell persists during catalysis after low temperature reductions, promoting methanol synthesis.
Kinetics of CO₂ hydrogenation over a 10% Ru/γ-Al₂O₃ catalyst were investigated using thermogravimetric analysis and a differential reactor approach at atmospheric pressure and 230–245 °C. The data is consistent with an Eley–Rideal mechanism where H2 gas reacts with adsorbed CO₂ species. Activation energy, pre-exponential factor and reaction orders with respect to CO₂, H₂, CH₄, and H₂O were determined to develop an empirical rate equation. Methane was the only hydrocarbon product observed during CO₂ hydrogenation. The activation energy was found to be 66.1 kJ/g-mole CH₄. The reaction order for H₂ was 0.88 and for CO₂ 0.34. Product reaction orders were essentially zero. This work is part of a larger study related to capture and conversion of CO₂ to synthetic natural gas.
Dual function materials (DFMs) for CO₂ capture and conversion couple the endothermic CO₂ desorption step of a traditional adsorbent with the exothermic hydrogenation of CO₂ over a catalyst in a unique way; a single reactor operating at an isothermal temperature (320 °C) and pressure (1atm) can capture CO₂ from flue gas, and release it as methane upon exposure to renewable hydrogen. This combined CO₂ capture and utilization eliminates the energy intensive CO₂ desorption step associated with conventional CO₂ capture systems as well as avoiding the problem of transporting concentrated CO₂ to another site for storage or utilization. Here DFMs containing Rh and dispersed CaO have been developed (˃1% Rh 10% CaO/γ-Al₂O₃) which have improved performance compared to the 5% Ru 10% CaO/γ-Al₂O₃ DFM (0.50 g-mol CH₄/kg DFM) developed previously. Ruthenium remains the catalyst of choice due to its lower price and excellent low temperature performance. The role of CO₂ adsorption capacity on the final methanation capacity of the DFM has also been investigated by testing several new sorbents. Two novel DFM compositions are reported here (5% Ru 10% K₂CO₃/Al₂O₃ and 5% Ru 10% Na₂CO₃/Al₂O₃) both of which have much greater methanation capacities (0.91 and 1.05 g-mol CH₄/kg DFM) compared to the previous 5% Ru 10% CaO/γ-Al₂O₃ DFM.
Methanol is a major fuel and chemical feedstock currently produced from syngas, a CO/CO2/H2 mixture. Herein we identify formate binding strength as a key parameter limiting the activity and stability of known catalysts for methanol synthesis in the presence of CO2. We present a molybdenum phosphide catalyst for CO and CO2 reduction to methanol, which through a weaker interaction with formate, can improve the activity and stability of methanol synthesis catalysts in a wide range of CO/CO2/H2 feeds.
Molybdenum phosphide (MoP) catalysts have recently attracted attention due to their robust methanol synthesis activity from CO/CO2. Synthesis strategies are used to steer MoP selectivity toward higher alcohols by investigating the promotion effects of alkali (K) and CO-dissociating (Co, Ni) and non-CO-dissociating (Pd) metals. A systematic study with transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy (XAS) showed that critical parameters governing the activity of MoP catalysts are P/Mo ratio and K loading, both facilitating MoP formation. The kinetic studies of mesoporous silica-supported MoP catalysts show a twofold role of K, which also acts as an electronic promoter by increasing the total alcohol selectivity and chain length. Palladium (Pd) increases CO conversion, but decreases alcohol chain length. The use of mesoporous carbon (MC) support has the most significant effect on catalyst performance and yields a KMoP/MC catalyst that ranks among the state-of-the-art in terms of selectivity to higher alcohols.
In2O3 has recently emerged as a promising catalyst for methanol synthesis from CO2. In this work, we present the promotional effect of Pd on this catalyst and investigate structure–performance relationships using in situ X-ray spectroscopy, ex situ characterization, and microkinetic modeling. Catalysts were synthesized with varying In:Pd ratios (1:0, 2:1, 1:1, 1:2, 0:1) and tested for methanol synthesis from CO₂/H₂ at 40 bar and 300 °C. In:Pd(2:1)/SiO₂ shows the highest activity (5.1 μmol MeOH/gInPds) and selectivity toward methanol (61%). While all bimetallic catalysts had enhanced catalytic performance, characterization reveals methanol synthesis was maximized when the catalyst contained both In–Pd intermetallic compounds and an indium oxide phase. Experimental results and density functional theory suggest the active phase arises from a synergy between the indium oxide phase and a bimetallic In–Pd particle with a surface enrichment of indium. We show that the promotion observed in the In–Pd system is extendable to non precious metal containing binary systems, in particular In–Ni, which displayed similar composition–activity trends to the In–Pd system. Both palladium and nickel were found to form bimetallic catalysts with enhanced methanol activity and selectivity relative to that of indium oxide.
Dry reforming of methane (DRM) is a promising technology to convert carbon dioxide (CO2) and methane (CH4), two major greenhouse gases into syngas (a mixture of carbon monoxide (CO) and hydrogen (H2)). A thermodynamic equilibrium analysis for DRM with a focus on carbon formation is carried out in Aspen Plus using the Gibbs free energy minimization method. The effects of feed CO2/CH4 ratio (0.5–3), reaction temperature (773–1373 K), and system pressure (0.1–10 atm) on the equilibrium conversion, product distribution, and solid carbon formation are investigated. From the analysis, it was found that the optimal operating conditions of 1 atm, 1123 K, and a feed ratio (CO2:CH4) of 1:1, minimized carbon formation, produced syngas at a H2/CO ratio of 1 (sufficient for downstream Fischer–Tropsch synthesis), while minimizing energy requirements. It is found that adding small amounts of oxygen or water significantly reduced carbon formation, minimized loss in syngas production, and reduced energy requirements. Three application scenarios were simulated to reflect the valorization of vented and flared natural gas and landfill gas (LFG). It was found that using captured CO2 with natural gas and LFG produced favorable results and therefore may be an opportunity for commercial DRM. Dry reforming of methane (DRM) utilizes two greenhouse gases, carbon dioxide and methane, to generate syngas which can be used as a building block in the chemical industry. Herein, thermodynamic baselines to underpin laboratory testing and development of catalysts for DRM are established, focusing on the valorisation of realistic waste gases such as vented or flared natural gas and landfill gas.
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.
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.
Fischer-Tropsch synthesis (FTS) is an essential approach to convert coal, biomass, and shale gas into fuels and chemicals, such as lower olefins, gasoline, diesel, and so on. In recent years, there has been increasing motivation to deploy FTS at commercial scales which has been boosting the discovery of high performance catalysts. In particular, the importance of support in modulating the activity of metals has been recognized and carbonaceous materials have attracted attention as supports for FTS. In this review, we summarised the substantial progress in the preparation of carbon-based catalysts for FTS by applying activated carbon (AC), carbon nanotubes (CNTs), carbon nanofibers (CNFs), carbon spheres (CSs), and metal-organic frameworks (MOFs) derived carbonaceous materials as supports. A general assessment of carbon-based catalysts for FTS, concerning the support and metal properties, activity and products selectivity, and their interactions is systematically discussed. Finally, current challenges and future trends in the development of carbon-based catalysts for commercial utilization in FTS are proposed.
More than 25% of chemical transformations involve at least one hydrogenation step. Selective hydrogenation of unsaturated aldehydes is an essential process in the industrial production of pesticides and pharmaceutical synthesis. Since CC hydrogenation with lower bond energy is thermodynamically favored over CO hydrogenation, the selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) is relatively challenging. Herein, we report a series of Pt-CeO2 nanoreactors with different spatial locations and microenvironments of Pt nanoparticles (NPs) on hollow CeO2 that are active for the selective hydrogenation of CAL to COL. We show the effects of active metal spatial location, microenvironment, metal–support interactions, and Fe doping on the activity and selectivity within Pt-CeO2 nanoreactors. Pt@Fe-CeO2 shows excellent catalytic performance with an 88.9% selectivity for COL at a CAL conversion of 97.2%. The variations of the electronic and crystal structure after Fe doping, simultaneously, and the linear adsorption of CAL on the CeO2 hollow structure contribute to the high performance of selective hydrogenation to COL. Our findings might shed light on the rational design of the nanoreactors for catalytic organic transformations with desired selectivity.
Electrochemical CO2 reduction simultaneously achieves conversion and storage of electrical energy as chemical energy through carbon recycling. Electrocatalysts with single-site and high efficiency for CO2 reduction have recently attracted much attention. In this review, the rational design strategies of single-site metal catalysts (SSMCs) for CO2 reduction are summarized. Particularly, we present the microenvironment engineering of SSMCs which entails atomic-scale design and nanoreactor construction. We further discuss the catalytic mechanisms, effects of the types, and coordination environments among metal species on tailoring catalytic activity and those nanoreactor features toward high-performance electrochemical CO2 reduction. Finally, we overview the current challenges and prospects of single-site metal catalysts for electrochemical CO2 reduction.
In this review, we summarized research efforts surrounding the synthesis, characterization of 2D MOFs nanosheets, main recommend the top-down methods and bottom-up methods. These strategies allow the fabrication of multifunctional materials and thus endow 2D MOFs nanosheets with very unique properties for a wide range of applications in catalysis, sensing, gas separations, storage energy and other fields. [Display omitted] •Profound and full-scale perspective on recent progress of 2D MOFs nanosheets.•Comprehensively summarized synthetic methods for 2D MOFs nanosheets.•Properties and applications of 2D MOFs nanosheets in various fields. Two-dimensional metal–organic frameworks (2D MOFs) have attracted intensive attention owing to tailorable composition and structures, unique dimension-dependent properties, and tunable surface chemistry. Therefore, applications of 2D MOFs have been explored widely in many fields. To make practical application of the 2D MOFs fast, it is of vital importance to develop low-cost, controllable and facile synthesis. In recent years, significant progresses have been achieved in the synthesis of 2D MOFs nanosheets. In this review, we summarize the effective synthetic strategies, dividing them into top-down and bottom-up methods. Subsequently, we discuss the applications of these 2D MOFs nanosheets in electrocatalysis, photocatalysis, energy conversion/storage, gas separation, sensing and adhesion, and share insights into the challenges and prospects in this field.
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.
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.
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.
Climate change is becoming increasingly more pronounced every day while the amount of greenhouse gases in the atmosphere continues to rise. CO2 reduction to valuable chemicals is an approach which has gathered substantial attention as a means to recycle these gases. Herein we explore some of the tandem catalysis approaches that can be used to achieve transformation of CO2 to C-C coupled products, focusing especially on tandem catalytic schemes where there is a big opportunity to improve performance by designing effective catalytic nanoreactors. Recent reviews have highlighted the technical challenges and opportunities for advancing tandem catalysis, especially highlighting the need for elucidating structure-activity relationships and mechanisms of reaction through theoretical and in situ/operando characterization techniques [1–3]. In this review, we focus on nanoreactor synthesis strategies as a critical research direction, and discuss these in the context of two main tandem pathways (CO-mediated pathway and Methanol-mediated pathway) to C-C coupled products.
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.
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.
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.
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.
Supported bimetallic catalysts have become an important class of catalysts in heterogeneous catalysis. Although well-defined bimetallic nanoparticles (BNPs) can be synthesized by seeded-growth in liquid phase, uniform deposition of these BNPs onto porous supports is very challenging. Here, we develop a universal nanoreactor strategy to directly fabricate the PdAu BNPs in the solid support of coral-like nitrogen-doped mesoporous polymer (NMP) with uniform dispersion in a large scale. This strategy is based on coordination chemistry to introduce the high-quality seeds of Pd nanoclusters and the Au ions into the NMP, and thus to be used as a nanoreactor for seeded growth of PdAu BNPs in solid state during thermal reduction. Many other supported Pd-based BNPs (diameters ranging from 2 to 3 nm) have also been successfully synthesized by adoption of this strategy, including PdRu, PdCo, PdNi, PdZn, PdAg and PdCu BNPs. As an example, the as-synthesized Pd1Au1/4 sample shows enhanced catalytic performance in formic acid (FA) dehydrogenation compared with the monometallic analogues, indicating the synergistic effect between Pd and Au. In addition, the Pd1Au1/4 product is molded into monolith without any binders due to its coral-like structure. The Pd1Au1/4 monolith shows considerable activity in FA dehydrogenation with a turnover frequency (TOF) value of 3684 h−1 at 333 K, which is recycled five times without changes in activity. We believe that the nanoreactor strategy provides an effective route to synthesize various supported bimetallic catalysts that have potential for applications in green and sustainable catalytic processes.
Ni-Ga and M-Ni-Ga (M = Au, Co, Cu) catalysts were evaluated for methanol synthesis from CO2 at 10 bar and 200−270 °C. The following trend in turnover frequency (TOF) for CO2 hydrogenation was observed: AuNiGa > CuNiGa > NiGa > CoNiGa, where TOF increased with decreasing catalyst affinity for CO. The presence of a third metal was found to influence both the formation of the Ni-Ga intermetallic phase as well as the number of available sites for CO chemisorption. Phase formation, catalyst composition and stability were evaluated using therm ogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning transmission electron microscopy and energy dispersive X-ray spectroscopy (STEM-EDX). Au-Ni-Ga, which showed a nearly 4-fold improvement in TOF at 263 °C and 10 bar compared to Ni-Ga, consisted of Ni3Ga particles decorated with Au, as evidenced by post catalysis characterization.
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.
In heterogeneous catalysis, the precise placement of active components to perform unique functions in cooperation with each other is a tremendous challenge. The migration of matter on micro/nano-scale caused by diffusion is a promising pathway for design of catalytic nanoreactors with precise active sites location and controllable microenvironment through compartmentalization and confinement effects. Herein, we report two categories of mesoporous ZnCoSiOx hollow nanoreactors with different metal distributions and microenvironment engineered by the diffusion behavior of metal species in confined nanospace. Double-shelled hollow structures with well-distributed metal species were obtained by adopting core@shell structured ZnCo-zeolitic imidazolate framework (ZIF)@SiO2 as a template and employing three stages of hydrothermal treatment including the decomposition of ZIF, diffusion of metal species into the silica shell, and Ostwald ripening. Additionally, the formation of yolk@shell structure with a collective (Zn-Co) metal oxide as the yolk was achieved by direct pyrolysis of ZnCo-ZIF@SiO2. In CO2 hydrogenation, ZnCoSiOx with double-shelled hollow structures and yolk@shell structures respectively afford CO and CH4 as main product, which is related with different dispersion and location of active sites in the two catalysts. This study provides an efficient method for the synthesis of catalytic nanoreactors on the basis of insights of the atomic diffusion in confined space at the mesoscale.
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.
Molybdenum phosphide (MoP) catalyzes the hydrogenation of CO, CO2, and their mixtures to methanol, and it is investigated as a high-activity catalyst that overcomes deactivation issues (e.g., formate poisoning) faced by conventional transition metal catalysts. MoP as a new catalyst for hydrogenating CO2 to methanol is particularly appealing for the use of CO2 as chemical feedstock. Herein, we use a colloidal synthesis technique that connects the presence of MoP to the formation of methanol from CO2, regardless of the support being used. By conducting a systematic support study, we see that zirconia (ZrO2) has the striking ability to shift the selectivity towards methanol by increasing the rate of methanol conversion by two orders of magnitude compared to other supports, at a CO2 conversion of 1.4% and methanol selectivity of 55.4%. In situ X-ray Absorption Spectroscopy (XAS) and in situ X-ray Diffraction (XRD) indicate that under reaction conditions the catalyst is pure MoP in a partially crystalline phase. Results from Diffuse Reflectance Infrared Fourier Transform Spectroscopy coupled with Temperature Programmed Surface Reaction (DRIFTS-TPSR) point towards a highly reactive monodentate formate intermediate stabilized by the strong interaction of MoP and ZrO2. This study definitively shows that the presence of a MoP phase leads to methanol formation from CO2, regardless of support and that the formate intermediate on MoP governs methanol formation rate.
Three formulations of a molybdenum phosphide (MoP) catalyst system were characterized for the higher alcohols synthesis (HAS) reaction using in situ x-ray absorption spectroscopy (XAS) and x-ray diffraction (XRD), monitoring the chemical phase evolution during activation and under reaction conditions. The in situ study herein provides important insights into the effect of the support and of K that lead to high performance in HAS for K-promoted MoP supported on carbon, as evidenced by previous studies (ethanol selectivity: 29%; conversion: 5%). During the activation process, XAS shows that the carbon supported samples reduce and reach a highly crystalline state at a lower temperature than the SBA-15 supported sample, indicating a substantial difference in catalyst activation. After activation, the samples are introduced to relevant reaction conditions resulting in spectra fairly similar to one another. XRD results corroborate the difference in degree of crystallinity of these samples, in alignment with the XAS, and reveal the formation of a crystalline potassium pyrophosphate (K4P2O7) during the activation period of the K-promoted samples. This K4P2O7 phase remains present under reaction conditions. Taken together, these results provide insight into the roles played by the carbon support and K promotion, connecting activity to electronic and crystal structure.
In this study, the new type solid electrolytes studied that can be an alternative to 8YSZ used in conventional Solid Oxide Fuel Cells while exhibiting the same ionic conductivity at lower temperatures. Cubic phase Zirconium Oxide stabilised with Ytterbium and Yttria doping (YbYSZ) have been synthesized with various doping fractions (only for certain amounts of Yb = 0.02, 0.04, 0.06, 0.08, 0.12, 0.16 mol% and Y = 0.02, 0.04, 0.06, 0.08, 0.16 mol%) by the Pechini method. The particle size distribution of the powder calcined at 900 °C for 24 h is examined by Field Emission Scanning Electron Microscope (SEM). The powder was pelletized and sintered to obtain a dense structure. Electrochemical Impedance Spectroscopy (EIS) was performed as a function of temperature. Highest ionic conductivity obtained in this study is 2.43 × 10 −1 Scm −1 at 800 °C for the 0.06 mol% Yb and 0.02 mol% Y doped ZrO 2 (6Yb2YSZ) electrolyte. The relationship between grain structure and conductivity is investigated using SEM and EIS. Grain size increases with dopant loading up to 0.12 mol% but degradation of microstructure is observed on higher dopant ratio. The power density of the produced single cell is measured 313.9 mW/cm 2 . It is concluded that the 6Yb2YSZ electrolyte material is a promising candidate for use as solid electrolyte.
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.