EFFECT OF CALCINATION TEMPERATURE ON AL2O3-SUPPORTED CEO2 - COMPLEMENTARY RESULTS FROM XRD AND XPS

X-ray diffraction (XRD) and X-my photoelectron spectroscopy (XPS) have been used to follow the effect of calcination temperature on CeO2 par ticle size, relative CeO2 concentration, and cerium oxidation state fo r CeO2 supported on gamma-Al2O3. When the calcination temperature was increased from 500 to 900-degrees-C, XRD results indicated a decrease in the relative concentration Of CeO2 at the highest loading (15 wt%), while XPS results reflected an apparent reduction of Ce4+ to Ce3+ at the lowest loading (5 wt%). Together these results suggest a transform ation of a portion of the CeO2 particles to a more dispersed Ce3+-like species following high-temperature calcination. The reduction of ceri a under these conditions is thermodynamically unfavorable. The apparen t reduction of Ce4+ to Ce3+ upon calcination may be the result of an e lectronic effect, rather than a true reduction of the ceria.