6 research outputs found
Using CoCuGa/SiO to identify stability-issues in ethanol-selective Co-Cu alloyed catalysts in carbon monoxide hydrogenation
Hydrogenation of CO to higher alcohols such as ethanol is an attractive pathway for industrial production while avoiding competition with food crops. However, thermocatalytic ethanol production from syngas is currently hindered by the lack of selective catalysts. The structural integrity of ternary-alloyed CoCu2Ga nanoparticles supported on silica was studied during thermo-catalytic CO hydrogenation. Catalysts of four different CoCuGa weight-loadings were tested catalytically under differential conversion, showing their different intrinsic selectivity during CO hydrogenation towards ethanol, methanol, and hydrocarbons. CoCuGa catalysts with 3.5 wt% and 17.8 wt% proved most and least selective towards ethanol formation, respectively. These two were studied in depth using STEM-EDX of fresh and spent samples showing different size distributions of the nanoparticles for all samples, and a change in the Co/Cu distribution of the nanoparticles from fresh to spent samples. In situ characterization using XRD, XANES, and EXAFS during CO hydrogenation supported the findings of the STEM-EDX and elucidated that the fresh more homogenous catalyst consisting of ternary CoCuGa nanoparticles de-alloyed into Cu-rich and CoGa-rich nanoparticles. This de-alloying was possibly driven by two factors: the metastable phase of CoCuGa decreasing its free energy by separating Cu and Co; and the strong interaction between Co and CO further driving a segregation. From a theoretical standpoint, Cu-Co intermetallics present the most selective catalyst to form ethanol over methane and methanol. The experimental findings presented here support the theory, although further efforts are needed to improve structural stability during the catalytic reaction
Grey-box Modeling of Reversible Solid Oxide Cell Stack’s Electrical Dynamics Based on Electrochemical Impedance Spectroscopy
This paper aims to design a lumped-capacity modelof a reversible solid oxide cell stack for hydrogen electrolysis.The lumped-capacity model needs to have an adequate representationof the electrical dynamics over a wide operatingrange and a model structure suitable for the design of a physicalemulator. The grey-box model is based on data obtained by electrochemicalimpedance spectroscopy conducted on a commercialsolid oxide cell stack for four different gas compositions at sixaging stages. In addition, a comparison of the experimental andsimulated voltage response of the reversible solid oxide cell stackin cyclic reversible operation mode was conducted at differentaging levels of the stack
Optimizing Ni-Fe-Ga alloys into NiFeGa for the hydrogenation of CO into methanol
A screening study of the catalytic performance of ternary alloy nanoparticles containing nickel, iron and gallium supported on silica for methanol synthesis from CO and H was performed. Catalysts were prepared by incipient wetness impregnation and subsequently reduced in H before catalytic testing. NiFeGa showed the best performance of the tested catalysts in terms of methanol yield. An optimization of the preparation was done to improve activity and selectivity, reaching a performance close to that of commercially available Cu/ZnO/AlO/MgO at low reaction temperatures and pressure. Extensive in situ characterisation using environmental TEM, in situ XRD and in situ EXAFS of the formation of the NiFeGa catalyst explains an optimal reduction temperature of 550 °C: warm enough that the three atomic species will form an alloy while cold enough to prevent the catalyst from sintering during the formation
Using CoCu<sub>2</sub>Ga/SiO<sub>2</sub> to identify stability-issues in ethanol-selective Co-Cu alloyed catalysts in carbon monoxide hydrogenation
Hydrogenation of CO to higher alcohols such as ethanol is an attractive pathway for industrial production while avoiding competition with food crops. However, thermocatalytic ethanol production from syngas is currently hindered by the lack of selective catalysts. The structural integrity of ternary-alloyed CoCu2Ga nanoparticles supported on silica was studied during thermo-catalytic CO hydrogenation. Catalysts of four different CoCu2Ga weight-loadings were tested catalytically under differential conversion, showing their different intrinsic selectivity during CO hydrogenation towards ethanol, methanol, and hydrocarbons. CoCu2Ga catalysts with 3.5 wt% and 17.8 wt% proved most and least selective towards ethanol formation, respectively. These two were studied in depth using STEM-EDX of fresh and spent samples showing different size distributions of the nanoparticles for all samples, and a change in the Co/Cu distribution of the nanoparticles from fresh to spent samples. In situ characterization using XRD, XANES, and EXAFS during CO hydrogenation supported the findings of the STEM-EDX and elucidated that the fresh more homogenous catalyst consisting of ternary CoCu2Ga nanoparticles de-alloyed into Cu-rich and CoGa-rich nanoparticles. This de-alloying was possibly driven by two factors: the metastable phase of CoCu2Ga decreasing its free energy by separating Cu and Co; and the strong interaction between Co and CO further driving a segregation. From a theoretical standpoint, Cu-Co intermetallics present the most selective catalyst to form ethanol over methane and methanol. The experimental findings presented here support the theory, although further efforts are needed to improve structural stability during the catalytic reaction.</p
Reversible Atomization and Nano-Clustering of Pt as a Strategy for Designing Ultra-Low-Metal-Loading Catalysts
Noble metal-based catalysts have numerous industrial uses, and maximum utilization of the precious metals by lowering the metal loading is of significant interest in heterogeneous catalysis research. However, lowering the metal loading could lead to single-atom metal species formation, which may not be active for important reactions like propylene oxidation. We report a way to drastically reduce precious metal loading of catalysts by judiciously choosing an active metal/support pair and using the reversible atomization-nanoparticulate formation of transition metal on a high-surface area support. Here, Pt and MgAl2O4 are used as the transition metal and high-surface area support, respectively. Through catalytic testing and characterization using scanning transmission electron microscopy and synchrotron X-ray absorption spectroscopy, a reversible change between atomization and nano-cluster formation under oxidizing and reducing conditions has been found. Via density functional theory, favorable sites for reversible Pt adsorption are identified, including ionic Pt4+ sites that can serve to nucleate nanoclusters. Catalytic reaction modeling also rationalizes the catalytic inertness of atomic Pt sites. Finally, a re-activation mechanism for the atomized Pt based on gases present during reaction has been formulated and demonstrated