Water interaction with CeO2(1 1 1)/Cu(1 1 1) model catalyst surface

Interaction of water with fully oxidized and partially reduced CeO2(1 1 1) thin film model catalyst grown on a Cu(1 1 1) surface was investigated by photoelectron spectroscopy (PES), scanning tunneling microscopy (STM) and temperature programmed desorption (TPD). On the stoichiometric surface water adsorbs molecularly at low temperatures (≤120 K) while on the reduced surface the adsorption is partially dissociative with formation of OH groups. STM indicates no morphology variation and a very sensitive Ce 4d–4f resonant photoelectron spectroscopy (RPES) no noticeable change of the oxidation state of ceria upon water adsorption and subsequent complete desorption. Formation of co-adsorbed phase of residual water with OH during molecular water desorption, on the other hand, leads to a substantial resonance of the Ce3+ photoemission state around 170 K. We propose that this behaviour indicating ceria reduction is in this case an electronic effect of the Ce 4f charge accumulation and Ce 5d charge depletion.