The role of copper valence states in CuZnAl catalysts for CO₂-to-methanol conversion

CuZnAl (CZA) is a classic industrial catalyst widely used for the synthesis of methanol from syngas, but its catalytic performance is not optimal for the hydrogenation of CO2 to methanol. Meanwhile, understanding the catalytic mechanism of Cu species in the CZA catalyst remains a great challenge. In this study, we systematically investigated the valence state change of active Cu species in CZA catalyst and their influence on catalytic performance by modifying the catalysts with varying amounts of electron donor K, thus identifying the catalytic function of Cu species with different valence states. H2-TPR, XPS and HR-TEM characterizations reveal that the highly dispersed K species supported on CZA catalysts will inhibit the reduction of CuO, resulting in a small amount of Cu2O active species being produced under reaction conditions thus causing a decrease in catalytic activity. Furthermore, XRD and Cu LMM spectra show that the proportion of Cu0 in K-modified CZA catalysts increases with K loading, but a higher proportion of Cu0 species on the surface obviously promotes the reverse water gas shift (RWGS) reaction. According to the results of in situ infrared spectroscopy, CZA catalyst follows the reaction pathway mediated by HCOO* in the hydrogenation of CO2 to methanol.