In situ Raman spectroscopy of adsorbed dioxygen was used to characterize electron defects on the surface of nanocrystalline cerium oxide that was partially reduced with H 2 and CO. Via 16 O/ 18 O 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 CeO 2 surface to form superoxide (O 2 -) and peroxide (O 2 2-) species, respectively. A band at 357 cm -1 was attributed to the cerium-oxygen vibration of the adsorbed superoxides, O 2 -, whereas the bands at 538 and 340 cm -1 were assigned to the asymmetric and symmetric cerium-oxygen vibrations of the surface peroxides, O 2 2-, 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.

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The redox behavior of CuZSM-5 was investigated by flow microbalance and FTIR measurements using CO and NO as probe molecules. The weight change resulting from switching the flow of 10% O2 in He to pure He corresponded to the removal of extralattice oxygen and approximately 20% autoreduction of total copper ion by one electron. FTIR absorption spectra of CO over CuZSM-5 showed that the concentration of the Cu+ sites changed reversibly upon switching the pretreatment gas from He to O2. The combined experiments (flow microbalance and CO adsorption) proved that CuZSM-5 has a redox function at 500 °C. Continuous measurement of NO adsorption spectra using the same wafer, following a pretreatment in flowing He at 500 °C, also demonstrated the redox properties of CuZSM-5. During the early stage of NO adsorption, a sharp band at 2295 cm-1 appeared that could be assigned in several different ways. Changes occurring as NO underwent reaction on the surface were recorded.

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