| Popis: |
Oxygen species adsorbed on the surface and in the bulk of a Pt/CeO2 catalyst have been investigated by FT-IR, ESR and FT-Raman spectroscopies. FT-IR and ESR spectra show that the dioxygen species, peroxide and superoxide, are easily formed on the CeO2 surface and are stable at temperatures below 373 K. For Pt/CeO2, the dioxygen species are formed at the very beginning of the admission of oxygen, but quickly disappear in a minute. FT-Raman spectra indicate that a partially reduced CeO2 can be fully reoxidized at temperatures above 573 K, while a partially reduced Pt/CeO2 can be easily reoxidized even at room temperature. The oxygen species on Pt/CeO2 catalyst are highly mobile: the dioxygen species formed on CeO2 surface of Pt/CeO2 can spillover onto Pt surface or the interface of Pt-CeO2 where they dissociate into monoxygen species. On the other hand, the monoxygen species formed on the Pt surface can migrate onto the CeO2 surface and reoxidize partially reduced CeO2. It is suggested that the mobility of oxygen may be one of the main reasons for the oxygen storage ability of CeO2 under working conditions. A schematic model is proposed to describe the spillover of oxygen species on Pt/CeO2 catalyst. |
