摘要
Cu/ZnO/Al2O3 catalysts are the most well-known heterogeneous catalysts for the hydrogenation of CO and CO2 into methanol. Herein, density functional theory calculations were performed to investigate the mechanism of H-2 activation and the effects of hydrogen spillover on CO2 adsorption and activation at the interfacial site of the ZnO/Cu model catalyst, which was simulated by loading ZnO ribbons of different sizes on the Cu(111), Cu(100), and Cu(211) surfaces. The ZnO/Cu interface is found to facilitate the formation of H adsorbates from the dissociation of H-2 molecules, which promotes the facile formation of oxygen vacancy (V-O) sites in the ZnO component due to its reducibility and the hydrogen spillover effect. The resulting interfacial structure of the ZnO/Cu model catalyst can contain perfect, hydroxylated, and oxygen-vacancy-present ZnO sites, which may act as the adsorption and activation sites for CO2. Further calculations show that molecular CO2 adsorbed at the V-O site can be efficiently activated by direct dissociation or hydrogenation to the HCOO* species. In addition, the smaller ZnO structure and less exposure of the Cu(211) facet facilitate hydrogen spillover and the formation of the interfacial V-O site. This study provides important insights into the structure-activity relationship for the active sites of the ZnO/Cu model catalyst and the mechanisms of CO2 activation and hydrogenation.
