Preparation of alumina supported ceria. I: Selective measurement of the surface area of ceria and free alumina

Abstract

In a general study of the role played by each component of three-way catalysts, a selective measurement of alumina and ceria surfaces area has been developed on model ceria-alumina supports. Three CeO 2 /Al 2 O 3 solids (6.5, 13.4, 21 wt.% CeO 2 ) were prepared by grafting Ce acetylacetonate on the surface of an alumina and calcination at 673 K. They were characterized by BET and X-ray diffraction measurements. The hydrogen temperature-programmed reduction (TPR) resulted in profiles similar to those of unsupported cerias, thus allowing an estimation of the equivalent surface area of ceria alone from the hydrogen uptake at low temperature. By adsorbing CO 2 on the OH groups of the alumina surface, hydrogenocarbonates species were formed and the IR band at 1235 cm −1 was selected to determine quantitatively the unpertubed alumina surface. In that case, by comparison with the BET surface area, it was possible to deduce an other value of the ceria surface area. The two sets of values obtained by these independent methods were found in good agreement, thus giving a good support for the reliability of each method. They show that the unpertubed alumina surface decreases when increasing the cerium content. Only 20% of the original alumina surface is preserved in the support containing 21 wt.% CeO 2 .