Dr Melis S. Duyar


Senior Lecturer in Chemical and Process Engineering

About

Areas of specialism

Heterogeneous catalysis; Carbon dioxide capture and utilisation

My qualifications

2012
BSc in Chemical and Biological Engineering
Koc University
2013
MS in Earth and Environmental Engineering
Columbia University
2015
PhD in Earth and Environmental Engineering
Columbia University

Research

Research interests

Teaching

Publications

Loukia-Pantzechroula Merkouri, Huseyin B. Ahmet, Tomás Ramirez Reina, Melis Duyar (2022)The direct synthesis of dimethyl ether (DME) from landfill gas: A techno-economic investigation, In: Fuel 319123741 Elsevier

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.

Loukia-Pantzechroula Merkouri, Tomás Ramirez Reina, Melis Duyar (2022)Feasibility of switchable dual function materials as a flexible technology for CO2 capture and utilisation and evidence of passive direct air capture, In: Nanoscale14(35)pp. 12620-12637 Royal Society of Chemistry

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. 

C. Janke, M.S. Duyar, M. Hoskins, R. Farrauto (2014)Catalytic and adsorption studies for the hydrogenation of CO₂ to methane, In: Applied Catalysis B: Environmental152pp. 184-191 Elsevier

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.

I.C. ten Have, E. Valle, A. Gallo, J.L. Snider, Melis S. Duyar, T.F. Jaramillo (2019)Development of Molybdenum Phosphide Catalysts for Higher Alcohol Synthesis from Syngas by Exploiting Support and Promoter Effects, In: Energy Technology7(5)1801102pp. 1-14 Wiley-VCH Verlag

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.

R. Matthew Bown, M Joyce, QI ZHANG, TOMAS RAMIREZ REINA, MELIS DUYAR (2021)Identifying Commercial Opportunities for the Reverse Water Gas Shift Reaction, In: Energy Technology9(11)2100554 Wiley

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.

M.S. Duyar, C. Tsai, J.L. Snider, J.A. Singh, A. Gallo, J.S. Yoo, A.J. Medford, F. Abild-Pedersen, F. Studt, J. Kibsgaard, S.F. Bent, J.K. Nørskov, T.F. Jaramillo (2018)A Highly Active Molybdenum Phosphide Catalyst for Methanol Synthesis from CO and CO2, In: Angewandte Chemie - International Edition57(46)pp. 15045-15050 Wiley-VCH Verlag

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.

Melis S. Duyar, M.A.A. Treviño, R.J. Farrauto (2015)Dual function materials for CO₂ capture and conversion using renewable H₂, In: Applied Catalysis B: Environmental168pp. 370-376 Elsevier

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.

R. Farrauto, M. Duyar (2014)Direct hydrogenation of CO₂ to synthetic natural gas over Ru/γ-Al₂O₃ catalysts, In: Proceedings of the 38th International Precious Metals Institute Annual Conference (IPMI 2014): Precious Metals 2014: Back to the Future or Back to the Pastpp. 551-555 International Precious Metals Institute
M.S. Duyar, R. Farrauto (2014)Synthetic natural gas production by catalytic hydrogenation of CO₂ over a Ru/y-Al₂O₃ catalyst for renewable energy storage, In: Proceedings of the 2014 AIChE Annual Meeting1 AIChE
Loukia-Pantzechroula Merkouri, Tomas Ramirez Reina, Melis Duyar (2021)Closing the Carbon Cycle with Dual Function Materials, In: Energy & Fuels American Chemical Society

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.

Loukia-Pantzechroula Merkouri, Estelle Le Saché, Laura Pastor-Pérez, Melis Duyar, Tomas Ramirez Reina (2022)Versatile Ni-Ru catalysts for gas phase CO2 conversion: Bringing closer dry reforming, reverse water gas shift and methanation to enable end-products flexibility, In: Fuel315123097 Elsevier

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.

Eduardo Valle, Melis Duyar, Jonathan Snider, Samuel Regli, Magnus Ronning, Alessandro Gallo, Thomas Jaramillo (2022)In situ studies of the formation of MoP catalysts and their structure under reaction conditions for higher alcohol synthesis: The role of promoters and mesoporous supports, In: Journal of Physical Chemistry C American Chemical Society

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.

QI ZHANG, LAURA PASTOR PEREZ, J.J. Villora-Pico, M Joyce, A. Sepúlveda-Escribano, MELIS DUYAR, TOMAS RAMIREZ REINA (2022)Ni-Phosphide catalysts as versatile systems for gas-phase CO2 conversion: Impact of the support and evidences of structure-sensitivity, In: Fuel323124301 Elsevier

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.

Melis S. Duyar (2018)Engineering catalytic interfaces for the sustainable production of fuels and chemicals, In: Proceedings of the 2018 AIChE Annual Meetingpp. 86-87 AIChE
Melis S. Duyar, Alessandro Gallo, Samuel K. Regli, Jonathan L. Snider, Joseph A. Singh, Eduardo Valle, Joshua McEnaney, Stacey F. Bent, Magnus Rønning, Thomas F. Jaramillo (2021)Understanding Selectivity in CO2 Hydrogenation to Methanol for MoP Nanoparticle Catalysts Using In Situ Techniques, In: Catalysts11(1)143 MDPI AG

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.

Melis S. Duyar, S. Wang, M.A. Arellano-Treviño, R.J. Farrauto (2016)CO₂ utilization with a novel dual function material (DFM) for capture and catalytic conversion to synthetic natural gas: An update, In: Journal of CO2 Utilization15pp. 65-71 Elsevier

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.

Zhengbin Tian, Chao Dong, Qun Yu, Run-Ping Ye, Melis S Duyar, Jian Liu, Heqing Jiang, Guang-Hui Wang (2020)A universal nanoreactor strategy for scalable supported ultrafine bimetallic nanoparticles synthesis, In: Materials today (Kidlington, England)40pp. 72-81 Elsevier Ltd

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.

J.L. Snider, V. Streibel, M.A. Hubert, T.S. Choksi, E. Valle, D.C. Upham, J. Schumann, Melis S. Duyar, A. Gallo, F. Abild-Pedersen, T.F. Jaramillo (2019)Revealing the Synergy between Oxide and Alloy Phases on the Performance of Bimetallic In-Pd Catalysts for CO₂ Hydrogenation to Methanol, In: ACS Catalysis9(4)pp. 3399-3412 American Chemical Society

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.

John Buckingham, TOMAS RAMIREZ REINA, MELIS DUYAR (2022)Recent advances in carbon dioxide capture for process intensification, In: Carbon Capture Science & Technology2100031 Elsevier Ltd

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.

Michael North, Melis Duyar, Shuoxun Wang, Martha A. Arellano-Treviño, Robert J. Farrauto, Peter Styring (2020)CO2 capture and catalytic conversion using solids, In: Michael North, Peter Styring (eds.), Fundamentals1pp. 127-136 De Gruyter
Alessandro Gallo, Jonathan L. Snider, Dimosthenis Sokaras, Dennis Nordlund, Thomas Kroll, Hirohito Ogasawara, Libor Kovarik, Melis S. Duyar, Thomas F. Jaramillo (2019)Ni5Ga3 catalysts for CO2 reduction to methanol: Exploring the role of Ga surface oxidation/reduction on catalytic activity, In: Applied Catalysis B: Environmental118369 Elsevier

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.

Melis S. Duyar, A. Ramachandran, C. Wang, R.J. Farrauto (2015)Kinetics of CO₂ methanation over Ru/γ-Al₂O₃ and implications for renewable energy storage applications, In: Journal of CO2 Utilization12pp. 27-33 Elsevier

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.

Melis S. Duyar, R.J. Farrauto, M.J. Castaldi, T.M. Yegulalp (2014)In situ CO2 capture using CaO/γ-Al₂O₃ washcoated monoliths for sorption enhanced water gas shift reaction, In: Industrial and Engineering Chemistry Research53(3)pp. 1064-1072 American Chemical Society

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.

Xinyao Wang, Runping Ye, MELIS DUYAR, CAMERON ALEXANDER PRICE, Hao Tian, Yanping Chen, Na Ta, Hao Liu, JIAN LIU (2021)Design of mesoporous ZnCoSiOx hollow nanoreactors with specific spatial distribution of metal species for selective CO2 hydrogenation, In: Nano Research Springer

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.

Serdar Yilmaz, Aynur Gürbüz, Pelin Guler, MELIS DUYAR (2022)Single step synthesis and heat effect on structure of new type nanostructured zirconia based solid electrolyte, In: Chemical papers76(3)pp. 1803-1814 Springer

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.

Melis S Duyar, Alessandro Gallo, Jonathan L Snider, Thomas F Jaramillo (2020)Low-pressure methanol synthesis from CO2 over metal-promoted Ni-Ga intermetallic catalysts, In: Journal of CO2 utilization39101151 Elsevier Ltd

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.

M.S. Duyar, R. Farrauto (2014)Synthetic natural gas production by catalytic hydrogenation of CO₂ over a Ru/γ-Al₂O₃ catalyst for renewable energy storage, In: Proceedings of the International Congress on Energy 2014, ICE 2014 - Topical Conference at the 2014 AIChE Annual Meeting1 AIChE