Spinel ZnFe<sub>2</sub>O<sub>4</sub> Regulates Copper Sites for CO<sub>2</sub> Hydrogenation to Methanol
Tangkang Liu, Di Xu, Dengdeng Wu, Guoliang Liu, Xinlin Hong
Abstract
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 °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/H2 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.