Exafs study of ceria-lanthana-based TWC promoters prepared by sol-gel routes

Extended X-ray absorption fine structure (EXAFS) experiments at the Ce K- and La K-edges were performed on ceria–lanthana– alumina three-way catalysts promoters prepared by sol–gel routes, in order to investigate the effect of lanthanum doping on the ceria structure. The formation of Ce1-xLaxO2-x/2 solid solution, already observed by X-ray diffraction, was confirmed by EXAFS analysis, while no experimental evidence of a Ce–Al interaction was found. In presence of cerium and aluminum, lanthanum is involved in the formation of solid solution with CeO2 and of La–Al compounds. When the La:Al molar ratio is sufficiently high, the growth of a tridimensionally ordered LaAlO3 perovskite compound is observed. For increasing values of x/1-x in the solid solution Ce1-xLaxO2-x/2, the Ce–O distance decreases, while La–O distance remains nearly constant.