The mechanism of the water-gas shift reaction on Cu/TiO₂(110) elucidated from application of density-functional theory

The Cu/TiO₂(110) surface displays a great catalytic activity toward the water-gas shift reaction (WGSR), for which Cu is considered to be the most active metal on a TiO₂(110)-supported surface. Experiments revealed that Cu nanoparticles bind preferentially to the terrace and steps of the TiO₂(110) surface, which would not only affect the growth mode of the surface cluster but also enhance the catalytic activity, unlike Au nanoparticles for which occupancy of surface vacancies is favored, resulting in poorer catalytic performance than Cu. With density-functional theory we calculated some possible potential-energy surfaces for the carboxyl and redox mechanisms of the WGSR at the interface between the Cu cluster and the TiO ₂ support. Our results show that the redox mechanism would be the dominant path; the resident Cu clusters greatly diminish the barrier for CO oxidation (22.49 and 108.68 kJ mol^-1, with and without Cu clusters, respectively). When adsorbed CO is catalytically oxidized by the bridging oxygen of the Cu/TiO₂(110) surface to form CO₂, the release of CO₂ from the surface would result in the formation of an oxygen vacancy on the surface to facilitate the ensuing water splitting (barrier 34.90 vs. 50.49 kJ mol^-1, with and without the aid of a surface vacancy).