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

Abstract

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 (S_CO = 0.0%–87.8%) from 200–300 °C, while the Cu–Ce–Zr catalyst with 8 wt% Ce loading presents higher CO₂ conversion ( X_{{\mathrm{C}\mathrm{O}}_2} = 5.4%–15.6%) and CH₃OH selectivity ( S_{{\mathrm{C}\mathrm{H}}_3\mathrm{O}\mathrm{H}} = 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.

Graphical abstract

Keywords

CO₂ hydrogenation / Cu–Ce–Zr / hydroxyls / CO/CH₃OH selectivity

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Higher Education Press