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.