(560bp) Influence of Coordination Environment Around Anchored Single-Site Cobalt Catalyst for CO2 Hydrogenation
In this study, cobalt single site catalyst supported on silica were explored due to their highly uniform active sites; allowing for definitive claims as to which surface species are responsible for specific reaction mechanisms. To characterize the structure and dispersion of the single-site catalysts, techniques such as UV-vis, XAFS, XPS, TPR, and Raman were utilized under ambient conditions as well as under reductive environments to simulate reaction conditions. This thorough understanding of the surface moieties under ambient and reductive environments coupled with their corresponding catalytic performance during CO2 hydrogenation allows us to discern how the transition between isolated atoms to small nanoparticles affects the reaction mechanism. To understand the surface under a reductive environment, we performed in situ XAFS, and pretreatment studies via XPS, using hydrogen as our reductant to elucidate the nature of the active site. We have found that under reductive environments below 500oC, the surface remains almost entirely in the Co2+ (Td) geometry. Our findings from our CO2 hydrogenation studies have shown that isolated atoms promote the preferential formation of CO via the RWGS reaction while small ensembles between Co2+(Td) and Co0 form both methane and CO, suggesting a change in reaction mechanism; which will ultimately be elucidated by this work.
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