Insights into the methanol synthesis mechanism via CO2 hydrogenation over Cu-ZnO-ZrO2 catalysts: Effects of surfactant/Cu-Zn-Zr molar ratio

In this study, we evaluated aspects of the CO2 hydrogenation mechanism, correlating structure-activity relationships of Cu-ZnO-ZrO2 catalysts prepared by one-pot surfactant-assisted co-precipitation with different surfactant ratios. Identifying the CO2 hydrogenation pathway intermediates is key to controlling the reaction selectivity. Experimental evidence shows that the CO2 is dissociating into CO* and O* onto the surface of the CuZnO-ZrO2 catalyst. The adsorption and dissociation of CO2 were evidenced by a combination of in situ ambient pressure X-ray Photoelectron Spectroscopy (AP-XPS) and Fourier Transform Infrared Spectroscopy (FTIR) with a transmission cell. AP-XPS showed that the catalysts are composed of a Cu2+, Zr3+, and Zr4+ mixture and two kinds of Zn2+ species. After the H-2 reduction process, only Cu2+ was reduced to Cu-0. The Zn and Zr species were oxidized by the dissociated O* species. In situ transmission FTIR showed that CO was adsorbed onto the Cu+/0 sites. The catalyst with the higher surfactant molar ratio exhibited the highest CO2 conversion close to the equilibrium conversion, as well as a good methanol formation rate.