Unraveling the evolution of oxygen vacancies in TiO_2−x/Cu and its role in CO₂ hydrogenation

The remarkable contribution of oxygen vacancies has been revealed by the operando spectroscopies for methanol synthesis from CO₂ hydrogeneration on the reducible metal oxide-supported copper catalysts. However, a challenge remains in the intrinsic understanding of the evolution and advantage of oxygen vacancies for methanol synthesis. Here we prepare the TiO_2−x/Cu with different oxygen vacancy densities by adjusting the ball-milling frequency. At the optimal condition, a TiO_2−x/Cu with more oxygen vacancies delivers an excellent methanol yield of 26.5 mmol g⁻¹ h⁻¹ at 300 °C with a selectivity of more than 70%. The combined analysis of experimental characterizations and theoretical calculations reveals that the mutual dispersions of TiO_2−x and Cu driven by mechanical energy induce the electron rearrangement in the d orbital of the Ti atom and relax the Ti–O binding at the interface, which facilitates the formation of oxygen vacancies that further reduce the barrier of CO₂ hydrogenation to *HCOO due to higher nucleophilicity of titanium ions.