Rational regulation of oxygen vacancies in high-entropy oxides to balance FeO and FeC phases for catalytic CO hydrogenation to light olefins.

Adjusting surface oxygen vacancies (O) is crucial for oxide catalysts. Doping spinel ZnFeO with elements of different valence states or atomic radio to obtain high-entropy oxides (HEOs) is a common method for creating O. Indeed, the formation of single-phase HEOs and the existence of lattice distortion were confirmed by X-ray diffraction and in-situ Raman, and the concentration of O in HEOs (O = 0.40-0.55) was higher compared to those of binary oxides (O = 0.21) by X-ray photoelectron spectroscopy of oxygen and oxygen temperature programmed desorption. Furthermore, analysis based on X-ray photoelectron spectroscopy of iron showed that the carburization ability of Fe atoms in HEOs with different O concentrations during the hydrogenation process exhibited significant differences. Finally, density functional theory further confirmed that an appropriate O concentration could promote CO adsorption and activation, inducing a balance between iron oxide (FeO) and iron carbide (FeC) during the reaction process, thereby enabling efficient synthesis of olefins through CO hydrogenation. The ZnFeCuZrMnO catalyst with the optimal O concentration achieved a CO conversion rate of 38.9 % and C2-4 olefins (C-C) selectivity of 40.7 %, outperforming the ZnFeO catalyst. This work provides a design strategy for high-entropy catalysts and serves as guidance for the rational design of spinel oxide-based catalysts with different O densities.