Surface conversion of CuO–ZnO to ZIF-8 to enhance CO2 adsorption for CO2 hydrogenation to methanol

Abstract

The catalytic conversion of CO₂ into value-added fuels is a promising strategy for mitigating energy crisis. Cu/ZnO is extensively used for CO₂ hydrogenation to methanol (CH₃OH) but still generally suffers from low conversion and selectivity. To enhance the conversion and selectivity, novel floral CuO–ZnO@ZIF-8 catalysts were prepared to form diamond-shaped particles ZIF-8 with abundant oxygen vacancies and CO₂ adsorption capacity on the surface of floral hydrothermal CuO–ZnO. The oxygen vacancies can provide sites for H* adspecies and CO₂ adsorption, which activate the reaction intermediate and reduce the whole energy barrier, thus enhancing the selectivity of CO₂ hydrogenation to CH₃OH. Moreover, because of the high porosity and high CO₂ adsorption capacity of ZIF-8 together with coordination between CuO–ZnO, the adsorption and activation of CO₂ over CuO–ZnO@ZIF-8 can be simultaneously enhanced. Among co-precipitated CuO–ZnO, hydrothermal CuO–ZnO, and CuO–ZnO@ZIF-8 (1 : 2, 1 : 4, 1 : 6) catalysts, CuO–ZnO@ZIF-8 (1 : 4) exhibits the best catalytic performance (CO₂ conversion 14.64% and CH₃OH selectivity 93.41%). This study provides a promising for combining metal–organic frameworks (MOFs) with metal catalysts in CO₂ hydrogenation to CH₃OH.