Adsorption and reaction of CO on a ceria-Rh(111) "inverse model catalyst" surface

The adsorption of CO and the reaction of CO with preadsorbed oxygen at room temperature has been studied on the Rh(I 11)2 x 1-O surface and on ceria-Rh(l 11) "inverse model catalyst" surfaces using C Is and 0 Is core level and valence band photoelectron spectroscopy with synchrotron radiation. The adsorption of CO on the oxygen-precovered (2 x l)-O surface was found to proceed slower than on the clean Rh(l 11) surface, because of a kinetic limitation which is introduced by the 0 + CO clean-off reaction. The latter removes adsorbed oxygen as CO2 at 300-320 K, which desorbs into the gas phase. On the ceria-Rh(l 11) surfaces the 0 + CO oxidation reaction is much faster than on the Rh(I 11)2 x 1-O surface suggesting a catalytically active role of the ceria-Rh interface. The XPS spectra indicate a preferential occupation of hollow-type CO adsorption sites on the ceria-Rh(I 11) surface, which might be located at the oxide-metal interface. No CO dissociation has been detected on the Rh(l 11) supported ceria inverse catalyst surfaces. On a CeRh3 alloy surface, prepared by thermal decomposition of the ceria in ultrahigh vacuum, the hollow-type CO adsorption sites are energetically favoured suppressing the on-top sites almost completely, but the global adsorption energy is lower than on Rh(I 11) as indicated by the reduced CO saturation coverage. (C) 2003 Elsevier Science B.V. All rights reserved.