Spinel ZnFe2O4 Regulates Copper Sites for CO2 Hydrogenation to Methanol

Cu-ZnO catalysts are widely studied for the direct hydrogenation of CO2 to methanol for high activity. However, despite the widespread research, promoting the intrinsic activity of active sites remains a contentious topic. We here report a facile strategy to manufacture ZnFe2O4 spinel-supported Cu catalysts with a tuneable size of Cu nanoparticles for selective methanol synthesis from CO2 hydrogenation. The optimized 33Cu/ZnFe-0.5 catalyst exhibits a high methanol selectivity of 71.6% at a CO2 conversion of 9.4% at 260 degrees C and 4.5 MPa. Increasing the Zn/Fe ratio decreases the selectivity of methanol at the same CO2 conversion and especially at lower CO2 conversions. The generation of extra Cu+ sites at Cu-spinel interfaces instead of Cu-ZnOx interfaces markedly inhibits the reverse water gas shift reaction during CO2 hydrogenation. The roles of Cu sites in methanol synthesis from CO2/H-2 are that the Cu-ZnO interfaces act as the active sites for speeding up the production of methanol, while the Cu+ sites at the Cu-spinel interfaces act as synergy sites for improving the methanol selectivity and activity of each Cu-ZnO site.