In Situ Characterization of Cu/CeO2 Nanocatalysts for CO2 Hydrogenation: Morphological Effects of Nanostructured Ceria on the Catalytic Activity

A combination of time-resolved X-ray diffraction (TR-XRD), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), and diffuse reflectance infrared Fourier transform spectroscopy was used to carry out in situ characterization of Cu/CeO2 nanocatalysts during the hydrogenation of CO2. Morphological effects of the ceria supports on the catalytic performances were investigated by examining the behavior of copper/ceria nanorods (NR) and nanospheres. At atmospheric pressures, the hydrogenation of CO2 on the copper/ceria catalysts produced mainly CO through the reverse water gas shift (RWGS) reaction and a negligible amount of methanol. The Cu/CeO2-NR catalyst displayed the higher activity, which demonstrates that the RWGS is a structure-sensitive reaction. In situ TR-XRD and AP-XPS characterization showed significant changes in the chemical state of the catalysts under reaction conditions, with the copper being fully reduced and a partial Ce4+ -> Ce3+ transformation occurring. A more effective CO2 dissociative activation at high temperature and a preferential formation of active bidentate carbonate and formate intermediates over CeO2(110) terminations are probably the main reasons for the better performance of the Cu/CeO2-NR catalyst in the RWGS reaction.