Abstract
CeO 2–Al 2O 3 mixed oxides with different CeO 2 loading (in the range of 0.5–12 wt.%) were prepared by wetness impregnation of alumina with aqueous solution of di-ammonium hexanitrate cerate (NH 4) 2[Ce(NO 3) 6]. The samples after calcination at 773 and 1073 K were characterized by different techniques, using X-ray diffraction (XRD), UV–VIS diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR). It is shown that different types of cerium oxide species are formed on the surface depending on the amount of CeO 2 and temperature of calcination of the samples. XRD showed the formation of nanocrystallites of ceria on alumina surface when the amount of CeO 2 is higher than 6 wt.%; at lower concentrations ceria was found to be amorphous. The ceria loading lower than 6 wt.% stabilizes the textural properties of alumina. At loading of 1 wt.% of CeO 2 XPS spectra reveals the presence of a strong interaction between ceria and alumina leading to a formation of superficial CeAlO 3-like phase. TPR results show that well dispersed CeO 2 particles present on the surface of alumina form CeAlO 3 at temperature of reduction in the range of 873–993 K, while for the reduction of CeO 2 crystallites, a higher temperature of reduction of 1190 K is needed.
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