Uncovering the Crucial Role of Oxygen Vacancy in Altering Activity and Selectivity of CO<sub>2</sub> Hydrogenation on ZnGa<sub>2</sub>O<sub>4</sub> Spinel Surfaces
Mengjia Xi, Xi‐Yang Yu, Xue Su, Lei Xiong, Xiaogang Ning, Peng Gao, Zheng‐Qing Huang, Chun-Ran Chang
Abstract
While oxygen vacancies (V O s) on metal oxides are widely reported to play important roles in CO 2 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 CO 2 to methanol on ZnGa 2 O 4 (100). Our calculations manifest that surface oxygen vacancy generated by producing water can enhance activating both H 2 and CO 2, 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 CO 2 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 CO 2 hydrogenation on spinel oxide surfaces.