Uncovering the Crucial Role of Oxygen Vacancy in Altering Activity and Selectivity of CO₂ Hydrogenation on ZnGa₂O₄ Spinel Surfaces

While oxygen vacancies (V_Os) on metal oxides are widely reported to play important roles in CO₂ hydrogenation to methanol or other hydrocarbons by cooperating with zeolites, the underlying mechanisms are still far from well understood. Herein, we present a theoretical study to explore the formation mechanism and catalytic roles of V_O in the hydrogenation of CO₂ to methanol on ZnGa₂O₄(100). Our calculations manifest that surface oxygen vacancy generated by producing water can enhance activating both H₂ and CO₂, owing to the emergence of frustrated Lewis pair sites or coordinative unsaturated Zn cation in the sublayer. Moreover, the adsorbed hydride can be stabilized by the coordinative unsaturated Zn cation. Then, oxygen vacancies, together with the hydride, can alter the CO₂ adsorption structures to benefit the formation of *HCOO instead of *COOH, thereby turning the production selectivity from carbon monoxide to methanol. Interestingly, microkinetic modeling reflects that V_O monomer is more active in the methanol production rate (0.37 s^–1) than V_O dimer (6.64 × 10^–3 s^–1) at 643 K, suggesting keeping a high proportion of V_O monomers on the surface is important. Hence, our study provides important insights into the role of oxygen vacancies in altering the catalytic performance of CO₂ hydrogenation on spinel oxide surfaces.