Photocatalytic Reduction of Carbon Dioxide to Methane at the Pd-Supported TiO2 Interface: Mechanistic Insights from Theoretical Studies

Photocatalytic conversion of CO2 into value-added solar fuels is a promising solution for energy crisis and global warming. Recent experimental studies show that the Pd nanoparticle-supported TiO2 surface has excellent photocatalytic performances for CO2 transformation. However, the mechanism is still ambiguous. In this work, we have explored the detailed mechanism of photocatalytic reduction of CO2 to CH4 at the interface of the anatase TiO2(101) surface with a 13-atom Pd nanocluster (referred to as Pd-13@TiO2) using periodic density functional calculations. Our results demonstrate that the adsorption and initial activation of CO2 and the hydrogenation of CO toward CH4 are all contributed by the marriage of the Pd-13 cluster and the TiO2(101) support. Benefiting from the favorable geometric and electronic structures at the interface, the highest energy barrier among all the studied processes is reduced to 1.16 eV, which makes the overall CO2 photocatalytic reduction proceed efficiently. The present first-principles insights provide important mechanistic implications for designing superior metal/semiconductor photocatalysts for converting CO2 to carbon-neutral fuels.