Surface oxygen species over cerium oxide and their reactivities with methane and ethane by means of in situ confocal microprobe Raman spectroscopy

The activation of molecular oxygen on the surface of cerium oxide and the reactivities of surface oxygen species with methane and ethane were studied by means ofin situconfocal microprobe Raman spectroscopy in the temperature range 298–1023 K. The results showed that O22-, O2- and O2δ- (0<δ<1) adspecies formed on the surface of an oxygen-pretreated cerium oxide sample when the temperature was below 423 K. As the temperature was increased, some oxygen species desorbed from the sample surface. At 1023 K, only the CeO2F2gpeak (at 449 cm-1) and O2- species (at 1159 cm-1) were observed on the CeO2 surface. In the absence of gaseous oxygen, ethane reacted with lattice oxygen species and diatomic oxygen adspecies, including O22-, O2- and O2δ- (0<δ<1) below 373 K. In contrast, the reactions of methane with superoxide and lattice oxygen species apparently did not take place until the temperature was increased to 1023 K. © 1997 by John Wiley & Sons, Ltd.