Initial reduction of CO2 on perfect and O-defective CeO2 (111) surfaces: towards CO or COOH?

First-principle calculations were performed to explore the initial reduction of CO2 on perfect and O-defective CeO2 (111) surfaces via direct dissociation and hydrogenation, to elucidate the product selectivity towards CO, COOH, or HCOO. The results showed that CO2 prefers a bent configuration with the C atom of CO2 occupying the oxygen vacancy site. Reductive hydrogenation CO2 + H -> COOH* was more competitive than CO2 + H -> HCOO* on both perfect and O-defective CeO2 (111) surfaces. Comparatively, CO2 hydrogenation towards COOH was slightly more favorable on the perfect surface, whereas reductive dissociation of CO2 was predominant on the O-defective CeO2 (111) surface. Electronic localization function, charge density difference, and density of states were utilized to analyze the effect of charge accumulation and redistribution on the adsorption and reductive dissociation of CO2 caused by the presence of O vacancies. The results of this study provided detailed insight into the initial reduction mechanisms of CO2 towards different products on perfect and O-defective CeO2 (111) surfaces.