Mechanistic investigation into influence of adsorbed H and H2O on In-Rh alloy during CO2 hydrogenation to methanol

Abstract

In our study, DFT calculations were employed to study the influence of both adsorbed H₂ and H₂O upon the catalysis reactivity of CO₂ hydrogenation to methanol over two exposed planes of In-Rh alloy. For InRh(011), CH₃OH formation is not viable from both “Formate” and “RWGS+CO-Hydro” mechanisms owing to the substantial kinetic barrier encountered. For In3Rh(212), the activated H* prefers to adsorb at surface Rh atoms from the first layer and thereby generates three potentially reactive sites (Rh_I, Rh_II and Rh_III), from which methanol is produced through the “Formate” pathway. Based on the microkinetic model, methanol is selectively produced from Rh_III while CO is the favorable product from the other two. Methanol formation from both Rh_I and Rh_II is substantially limited by the rate-determining step (RDS) owing to the bridging configuration of H* being too stable. As a major side product of CO₂ hydrogenation, H₂O introduction could lower the RDS of the “Formate” pathway from Rh_III and thereby substantially improve its production rate of methanol. Overall, our calculation determines the reactive site of In-Rh alloy and explains the way how H₂ and H₂O influence the reaction mechanism and catalysis performance of the bimetallic system.