In situ NAP-XPS study of CO2 and H2O adsorption on cerium oxide thin films

Abstract

Insights of CO2 and H2O activation on cerium oxide based catalysts are of great interest to many important catalytic processes, which are widely studied in model systems under ultrahigh vacuum conditions. Here, in situ near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) was used to study CO2 and H2O adsorption on fully oxidized CeO2 and partially reduced CeO2−x surfaces. It is found that CO2 only weakly interacts with the stoichiometric CeO2 but strongly adsorbs on partially reduced CeO2−x surfaces with surface carbonate formation. H2O dissociatively adsorbs reversely on the CeO2 surface with H2O exposure pressure above 1 × 10−3 mbar, while H2O strongly dissociates on the partially reduced CeO2−x surfaces. The surface dissociated OH and H species are stable on the CeO2−x surface up to 600 K. Both CO2 and H2O adsorption cause clear reoxidation of partially reduced CeO2−x. This study provides new insights into CO2 and H2O interaction with cerium oxide surfaces at near ambient pressure conditions.