Mechanism of CO2 Photocatalytic Reduction to Methane and Methanol on Defected Anatase TiO2 (101): A Density Functional Theory Study

With rising emission of CO2 affecting human life, photocatalytic reduction of CO2 attracts substantial research interest. Anatase TiO2 is known to be one of the most promising catalysts of this process. Here, we adopted density functional theory calculations to systematically study the pathways of CO2 reduction on the defected anatase TiO2(101) surface. We find that oxygen vacancies play a critical role in promoting the reaction, as compared to the pristine surface. They help CO2 binding, activation, and dissociation and stabilize other reaction intermediates. The most feasible identified reaction mechanism proceeds through surface CO species, to CHO, CHOH, CH2OH or CHO, CH2O, and CH3O, to produce methane and methanol. In addition, there exists a carbene-like deoxygenation pathway to form the CH species on the vacancy, which can give rise to methane by binding protons successively.