Mechanism of Oxygen Exchange between CO₂ and TiO₂(101) Anatase

The mechanism of oxygen exchange between CO 2 and a defective anatase (101) surface was investigated by density functional theory calculations including corrections for long-range dispersion interactions and for on-site Coulomb interactions. The calculations identify a carbonate-like configuration at a surface oxygen defect site as the key intermediate species responsible for the oxygen exchange. The stability of this species, its vibrational frequencies, and the reaction barriers involved in the oxygen exchange mechanism are found to be highly dependent on the specific value of the Hubbard U correction used to describe the on-site Coulomb interactions within the GGA+U procedure. U parameter values that result in CO 2 adsorption energies and reaction barriers for oxygen exchange consistent with the results of room-temperature experiments are smaller ( U ≤ 2.5 eV) than those that reproduce the experimental band gap or location of defect states in the band gap of the reduced TiO 2 crystal.