CO2 activation on ultrathin ZrO2 film by H2O co-adsorption: In situ NAP-XPS and IRAS studies

Utilizing CO2 as sustainable carbon source requires its activation by catalytically active oxides on which CO2 can form different surface bound carbonaceous species. This may be promoted or even enabled by surface hydroxyl groups. We have investigated the interaction of CO2 with a ZrO2 model surface, i.e. a O-Zr-O trilayer grown on Pt3Zr(0001), in the absence and presence of H2O, employing in situ near ambient (atmospheric) pressure X-ray photoemission spectroscopy (NAP-XPS) and infrared reflection absorption spectroscopy (IRAS). Whereas room temperature exposure to pure CO2 up to 3 x 10(-2) mbar did not induce any interaction with the ZrO2 model surface, co-adsorption of CO2 + H2O resulted in the formation of various carbonaceous surface species. Apparently, in the presence of humidity (surface hydroxylation) CO2 was activated on ZrO2 at near ambient pressures. Combining NAP-XPS and IRAS allowed identifying the surface species, which were formate, dioxy-methylene, formaldehyde and carbon. These species may be intermediates of upconverting CO2 to methanol and highlight the ability of ZrO2 as active support.