Molecular adsorption and dissociation of CO on TiO anatase (001) activated by oxygen vacancies.

A study on the influence of oxygen vacancies on the anatase (001) surface on the CO adsorption process is presented. For its realization, density functional theory (DFT) was used under the Perdew-Burke-Ernzerhof (PBE) generalized gradient and the spin-polarized approximations. Hubbard-U corrections and van der Waals interactions were also included. Three different types of oxygen vacancies were investigated at different sites on the anatase (001) surface; the formation energies in each case were 67.05, 113.84, and 93.16 kcal/mol, respectively. We identified a type of oxygen vacancy that could favor both the CO adsorption and dissociation. The differences on CO adsorption properties are due to electronic and structural causes, such as midgap states (Ti polarons species) and changes in the structural properties on the TiO surface, generated upon the introduction of an oxygen vacancy. It is concluded that oxygen vacancies can play an important role in both CO adsorption and dissociation.