How Oxygen Vacancies Activate CO₂ Dissociation on TiO₂ Anatase (001)

Abstract

The adsorption, dissociation, and diffusion of CO2 on the anatase (001) surface was studied using DFT by means of the generalized gradient approximation using the Perdew–Burcke–Ernzerhof (PBE)-functional and applying corrections for long-range dispersion interactions. Different stable adsorption configurations were identified for the fully oxidized surface. The most stable adsorption configuration is the monodentated carbonate-like structure. Small energy barriers were identified for the conversion of a physisorbed to a chemisorbed configuration. CO2 dissociation is found to be unfeasible on the stoichiometric surface. The introduction of oxygen vacancy defects gives rise to new highly stable adsorption configurations with a stronger activation of the C–O bonds. This leads to the possibility of exothermic dissociation of CO2 with barriers up to 22.2 kcal/mol, corresponding to chemical lifetimes of less than 4 s at 300 K. These reactions cause a CO molecule to be formed, which will easily desorb, and the reduced surface to become oxidized. It is clear that oxygen vacancy defects play a key role in the catalytic activity of an anatase (001) surface. Oxygen vacancies play an important role in the dissociation of CO2 on the anatase (001) surface, and will play a significant role in complex problems, such as the catalytic conversion of CO2 to value-added chemicals.