Effects of surface oxygen vacancy on CO₂ adsorption and its activation towards C₂H₄ using metal (Cu, Pd, CuPd) cluster-loaded TiO₂ catalysts: a first principles study

The conversion of the highly selective CO₂ reduction reaction (CO₂RR) into desired value-added multicarbon compounds, like C₂H₄, is crucial, but it is mainly constrained by the high energy barrier for C-C coupling and the multi-electron transfer process. Herein, M/TiO₂ and M/TiO₂-V_O (M = Cu, Pd, CuPd, and V_O refers to the surface oxygen vacancy) catalysts were designed to study the CO₂RR towards C₂H₄ by using density functional theory (DFT). We found that the surface oxygen vacancy enhances the adsorption ability of studied catalysts. The CO₂ molecule is strongly adsorbed at the metal-surface interfaces of Cu/TiO₂-V_O, Pd/TiO₂-V_O and CuPd/TiO₂-V_O catalysts with adsorption energies of −1.79, −1.75 and −1.71 eV, respectively. Furthermore, the C-C coupling reaction does not occur on the Cu and PdCu cluster sites of the M/TiO₂-V_O catalysts, indicating the inactivity of these sites for C₂ products. However, Pd/TiO₂, CuPd/TiO₂ and M/TiO₂-V_O interfaces favor the C-C coupling reaction and therefore have the potential to reduce CO₂ to C₂ products. Additionally, the Gibbs free energy calculations reveal that the surface oxygen vacancy improves the OCCO hydrogenation to C₂H₄ at the CuPd/TiO₂-V_O interface.