In situ FTIR and ex situ XPS/HS-LEIS study of supported Cu/Al2O3 and Cu/ZnO catalysts for CO2 hydrogenation

Cu-based catalysts are commonly used in industry for methanol synthesis. In this study, supported catalysts of 5 wt% Cu/Al2O3 and 5 wt% Cu/ZnO were prepared, and their surface characteristics during H2 reduction and CO2 hydrogenation were investigated using in situ Fourier transform infrared spectroscopy (FTIR), ex situ X-ray photoelectron spectroscopy, and high sensitivity low energy ion scattering spectroscopy. During the H2 reduction and CO2 hydrogenation processes, it was found that Al2O3 can stabilize Cu+. In situ FTIR spectra indicated that the 5 wt% Cu/Al2O3 can adsorb large amounts of bicarbonate and carbonate species, which then convert into formate during CO2 hydrogenation. For the 5 wt% Cu/ZnO, it was found that Cu nanoparticles were gradually covered by a highly defective ZnOx overlayer during H2 reduction, which can effectively dissociate H2. During CO2 hydrogenation, the adsorbed bicarbonate or carbonate species can convert into formate and then into a methoxy species. Using these surface sensitive methods, a more in-depth understanding of the synergistic effect among the Cu, Al2O3, and ZnO components of Cu-based catalysts was achieved.