Abstract
X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) have been used to follow the effect of calcination temperature on CeO 2 particle size, relative CeO 2 concentration, and cerium oxidation state for CeO 2 supported on γ- Al 2 O 3. When the calcination temperature was increased from 500 to 900°C, XRD results indicated a decrease in the relative concentration of CeO 2 at the highest loading (15 wt%), while XPS results reflected an apparent reduction of Ce 4+ to Ce 3+ at the lowest loading (5 wt%). Together these results suggest a transformation of a portion of the CeO 2 particles to a more dispersed Ce 3+-like species following high-temperature calcination. The reduction of ceria under these conditions is thermodynamically unfavorable. The apparent reduction of Ce 4+ to Ce 3+ upon calcination may be the result of an electronic effect, rather than a true reduction of the ceria.
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