Carbon dioxide activation and dissociation on ceria (110): a density functional theory study

Ceria (CeO(2)) is a promising catalyst for the reduction of carbon dioxide (CO(2)) to liquid fuels and commodity chemicals, in part because of its high oxygen storage capacity, yet the fundamentals of CO(2) adsorption, activation, and reduction on ceria surfaces remain largely unknown. We use density functional theory, corrected for onsite Coulombic interactions (GGA+U), to explore various adsorption sites and configurations for CO(2) on stoichiometric and reduced ceria (110), the latter with either an in-plane oxygen vacancy or a split oxygen vacancy. We find that CO(2) adsorption on both reduced ceria (110) surfaces is thermodynamically favored over the corresponding adsorption on stoichiometric ceria (110), but the most stable adsorption configuration consists of CO(2) adsorbed parallel to the reduced ceria (110) surface at a split oxygen vacancy. Structural changes in the CO(2) molecule are also observed upon adsorption. At the split vacancy, the molecule bends out of plane to form a unidentate carbonate with the remaining oxygen anion at the surface; this is in stark contrast to the bridged carbonate observed for CO(2) adsorption at the in-plane vacancy. Also, we analyze the pathways for CO(2) conversion to CO on reduced ceria (110). The subtle difference in the energies of activation for the elementary steps suggest that CO(2) dissociation is favored on the split vacancy, while the reverse process of CO oxidation may favor the formation of the in-plane vacancy. We thus show how the structure and properties of the ceria catalyst govern the mechanism of CO(2) activation and reduction.