jp0311254_si_001.pdf (107.32 kB)
Probing Defect Sites on the CeO2 Surface with Dioxygen
journal contribution
posted on 2004-04-29, 00:00 authored by Vladimir V. Pushkarev, Vladimir I. Kovalchuk, Julie L. d'ItriIn situ Raman spectroscopy of adsorbed dioxygen was used to characterize electron defects on the surface of
nanocrystalline cerium oxide that was partially reduced with H2 and CO. Via 16O/18O isotope substitution,
the bands in the range of 1135−1127 and 877−831 cm-1 were assigned to the O−O stretching vibration of
dioxygen species bound to one- and two-electron defects on the CeO2 surface to form superoxide (O2-) and
peroxide (O22-) species, respectively. A band at 357 cm-1 was attributed to the cerium−oxygen vibration of
the adsorbed superoxides, O2-, whereas the bands at 538 and 340 cm-1 were assigned to the asymmetric and
symmetric cerium−oxygen vibrations of the surface peroxides, O22-, respectively. The dynamics of the defect
annihilation that results from surface reoxidation by adsorbed dioxygen species during temperature-programmed
experiments allowed peroxide species adsorbed on isolated and aggregated two-electron defects to be
distinguished. A general approach to investigate the reactivity of different surface dioxygen species toward
reductants was demonstrated using CO oxidation as a probe reaction.