An investigation of the CH3OH and CO selectivity of CO2 hydrogenation over Cu−Ce−Zr catalysts

A series of Cu−Ce−Zr catalysts with different Ce contents are applied to the hydrogenation of CO2 to CO/CH3OH products. The Cu−Ce−Zr catalyst with 2 wt% Ce loading shows higher CO selectivity (SCO = 0.0%–87.8%) from 200–300 °C, while the Cu−Ce−Zr catalyst with 8 wt% Ce loading presents higher CO2 conversion \(({X_{{\rm{C}}{{\rm{O}}_2}}} = 5.4\% - 15.6\% )\) and CH3OH selectivity \(({S_{{\rm{C}}{{\rm{H}}_3}{\rm{OH}}}} = 97.8\% - 40.6\% )\). The number of hydroxyl groups and solid solution nature play a significant role in changing the reaction pathway. The solid solution enhances the CO2 adsorption ability. At the CO2 adsorption step, a larger number of hydroxyl groups over the Cu−Ce−Zr catalyst with 8 wt% Ce loading leads to the production of H-containing adsorption species. At the CO2 hydrogenation step, a larger number of hydroxyl groups assists in encouraging the further hydrogenation of intermediate species to CH3OH and improving the hydrogenation rate. Hence, the Cu−Ce−Zr catalyst with 8 wt% Ce loading favors CH3OH selectivity and CO2 activation, while CO is preferred on the Cu−Ce−Zr catalyst with 2 wt% Ce loading, a smaller number of hydroxyl groups and a solid solution nature. Additionally, high-pressure in situ diffuse reflectance infrared Fourier transform spectroscopy shows that CO is produced from formate decomposition and that both monodentate formate and bidentate formate are active intermediate species of CO2 hydrogenation to CH3OH.