Rich oxygen vacancies in core–shell structured Co3O4-CuO-ZnO@ZIF-8 for boosting CO2 hydrogenation to methanol

Converting carbon dioxide (CO2) into high-quality methanol to alleviate the energy crisis is a promising strategy. However, as a traditional catalyst for CO2 hydrogenation to methanol, Cu/ZnO exhibits low CO2 conversion and low methanol selectivity at low temperature. In order to improve the catalytic performance of CO2 hydrogenation to methanol, Co3O4 was introduced to form Co3O4-CuO-ZnO with flower-like structure, and then diamond-shaped ZIF-8 particles with large specific surface area and rich oxygen vacancies were synthesized on the surface of Co3O4-CuO-ZnO by hydrothermal method. A series of characterizations showed that the synthesis of ZIF-8 greatly increased the specific surface area of the catalyst. The oxygen vacancy is the site of CO2 adsorption and activation, and stabilizes the reaction intermediate, which promotes the conversion of CO2 and the formation of methanol. The introduction of Co promotes the formation of the alloy phase, enhances the interaction between the metals, makes the active center more dispersed, reduces the sintering of the catalyst, and thus exhibits better catalytic performance. Among co-precipitated CuO-ZnO, hydrothermal CuO-ZnO, CuO-ZnO@ZIF-8, Co3O4-CuO-ZnO and Co3O4-CuO-ZnO@ZIF-8 catalysts, Co3O4-CuO-ZnO@ZIF-8 exhibits the best catalytic performance (CO2 conversion 16.06% and CH3OH selectivity 94.58%). Based on the above design, ZIF-8 and Co3O4 synergistic CuO-ZnO catalyst effectively improved CO2 conversion and CH3OH selectivity.