Abstract
The cerium species have been characterized during the temperature-programmed reduction (TPR) process under H2 atmosphere by means of the X-ray absorption fine structure (XAFS) spectroscopy and the X-ray diffraction (XRD) method. The in-situ XAFS measurements revealed that the CeO2 species was finally reduced to Ce2O3 at 900 ºC with an intermediate state generated in the temperature rage of 550–750 ºC. The absorption edge shift of the X-ray absorption near edge structure (XANES) spectra indicated that the non-stoichiometric compound was formed as the intermediate species, and the estimated composition was CeO1.65. The in-situ XRD measurements during the TPR process showed the shift of the diffraction lines of CeO2 above 400 ºC, indicating the formation of the non-stoichiometric intermediate. The quantitative analysis of the lattice parameter demonstrated that the crystal plane spacing for the (111) plane of the non-stoichiometric intermediate was expanded by about 0.03 Å than the initial CeO2 phase.
