First-principles study of CO2 hydrogenation to methanol on In-Ru alloys: Revealing the influence of surface In/Ru ratio on reaction mechanism and catalyst performance

Designing high-performance catalyst is vital in the field of CO2 methanolization. In this study, two In3Ru surfaces (In3Ru_i and In3Ru_r) were employed as computational models and the density functional theory was applied to study the influence of surface In/Ru ratio on their surface morphologies, reaction mechanisms and catalysis performance for methanol synthesis. Surface characterization reveals that In3Ru_i is higher in surface In/Ru ratio than In3Ru_r, and such difference facilitates CO2 adsorption on In3Ru_r. Being different in surface In/Ru ratio, two surfaces exhibit distinct variations in the reaction mechanism of methanol formation. For In3Ru_i, the "Formate" pathway dominates the first CO2 activation step which leads to methanol production. On the other hand, In3Ru_r prefers the "reverse water-gas shift" pathway (RWGS) in the initial step of CO2 activation, but this mechanism is unable to generate CH3OH due to the kinetic limitation of CO* hydrogenation. Based on the microkinetic modeling, In3Ru_i is superior in both CO2 production rate and CH3OH selectivity than the other one, suggesting higher surface In/Ru ratio benefits methanol formation, which complies well with the experiment. Overall, our study offers a new perspective with respect to how surface morphology of the bimetallic catalyst influences the reaction mechanisms of CO2 hydrogenation.