A computational study of CO2 hydrogenation on single atoms of Pt, Pd, Ni and Rh on In2O3(111)

Abstract

Metal promoted indium oxide (In₂O₃) catalysts are promising materials for CO₂ hydrogenation to products such as methanol and carbon monoxide. The influence of the dispersion of the promoting metal on the methanol selectivity of In₂O₃ catalysts is a matter of debate, which centers around the role of atomically dispersed single metal atoms vs. metal clusters as catalysts for methanol formation. In this study, we used density functional theory calculations to compare the role of single atoms (SAs) of Ni, Pd, Pt and Rh placed on the In₂O₃(111) surface to study CO₂ hydrogenation to CO and methanol. Direct and hydrogen-assisted CO₂ dissociation pathways leading to CO as well as methanol formation via either formate or CO intermediates are explicitly considered. Microkinetic simulations show that all SA models mainly catalyze CO formation via a redox pathway involving oxygen vacancies where adsorbed CO₂ dissociates followed by CO desorption and water formation. The higher barriers for hydrogenation of formate intermediates compared to the overall barrier for the rWGS reaction explain the negligible CH₃OH selectivity.