Adsorption and reaction of CO on a ceria–Rh(1 1 1) “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(1 1 1)2 × 1-O surface and on ceria–Rh(1 1 1) “inverse model catalyst” surfaces using C 1s and O 1s core level and valence band photoelectron spectroscopy with synchrotron radiation. The adsorption of CO on the oxygen-precovered (2 × 1)-O surface was found to proceed slower than on the clean Rh(1 1 1) surface, because of a kinetic limitation which is introduced by the O + 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(1 1 1) surfaces the O + CO oxidation reaction is much faster than on the Rh(1 1 1)2 × 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(1 1 1) surface, which might be located at the oxide–metal interface. No CO dissociation has been detected on the Rh(1 1 1) 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(1 1 1) as indicated by the reduced CO saturation coverage.