Carbon Dioxide Adsorption on CeO (110): An XPS and NEXAFS Study.

The adsorption of CO on the surface of a CeO (110) bulk single crystal was studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The high-quality XPS and C K-edge NEXAFS data show that CO adsorbs as a carbonate species on both fully oxidized CeO (110) and partially reduced CeO (110). No evidence for the formation of a carboxylate (CO ) intermediate could be found. On the fully oxidized CeO (110) substrate, the carbonate decomposes upon heating to above 400 K, leading to the desorption of CO . The NEXAFS data reveal the presence of a minor amount of formate (or carboxylate) and bicarbonate species, which are related to reactions of CO with surface hydroxyl groups. In the case of reduced CeO (110), the carbonate species completely disappear upon heating to temperatures above 500 K. In contrast to conclusions presented in earlier works, the oxidation state of the surface is unchanged, that is, CO does not re-oxidize the reduced CeO (110) surface.