Abstract
Abstract Temperature programmed desorption(TPD) measurements of CO and NO, flow reactor measurements, and XPS analysis were performed on Pt,Rh and Pt+Rh supported on alumina, alumina+ceria and ceria. Ceria induces significant modifications in the CO, NO TPD spectra and in the activity of the catalysts, indicating noble metal-ceria interaction but no evidence for charge transfer between Pt and ceria was found in the XPS spectra. Successive TPD runs of NO showed that ceria-containing samples maintained their capacity to dissociate NO for longer time periods than catalysts without ceria and also that there was a gradual decrease in the low temperature N2 desorption peak associated with noble metal-ceria interaction. The observed influence of ceria on the CO TPD spectra and on the steady-state CO oxidation activity vanishes for samples exposed to SO2 demonstrating that SO2 poisons the noble metal-ceria interaction. This is probably associated with the formation of Ce3-sulphate, as demonstrated by XPS spectra, which blocks double bonded CO and/or dicarbonyl sites. Under oscillating conditions the SO2 poisoning is less severe. The noble metal ceria interaction may be associated with oxygen vacancies in ceria adjacent to the noble metal particles.
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