Role of oxygen vacancy in high-entropy Cu1Zn1Al0.5Ce5Zr0.5Ox for CO2 hydrogenation reaction

High-entropy oxides (HEOs) have garnered significant attention in catalysis due to their excellent redox properties and superior stability. In this study, we prepared and investigated a high-entropy oxide, Cu₁Zn₁Al_0.5Ce₅Zr_0.5O_x, to elucidate the impact of oxygen vacancy density on the CO₂ hydrogenation reaction. Comparisons were made with binary or ternary solid solutions composed of the same cations present in this HEO, and possessing the same phase structure. The HEO exhibits a higher surface oxygen vacancy density as evidenced by Raman spectroscopy and XPS. The increased number of oxygen vacancies significantly increases the active sites and enhances the strength for CO₂ adsorption. Combined with kinetic analysis, it is suggested that the enhanced CO₂ adsorption leads to improved CO₂ conversion on the HEO. Moreover, the formation of oxygen vacancies facilitates H₂ dissociation and supply, which is pivotal for methanol formation on the HEO. The stability of the HEO Cu₁Zn₁Al_0.5Ce₅Zr_0.5O_x surpasses that of the medium entropy oxide, showing no significant deactivation after 100 hours of reaction.