Phase analysis and oxygen storage capacity of ceria-lanthana-based TWC promoters prepared by sol-gel routes

Ceria-lanthana-based promoters of three-way catalysts are synthesized by two different sol-gel routes, involving nitrate precursors. The oxygen uptake ability of these compounds is measured by O-2 chemisorption. The specific surface area is determined by N-2 adsorption (BET). X-ray diffraction data are analyzed by Rietveld refinement, demonstrating that lanthanum forms solid solution with CeO2; its total amount in ceria depends on the competitive formation of La-Al mixed oxides and on the synthetic method. The O-2 uptake ability is essentially determined by the La content in the ceria-lanthana solid solution, while it is independent on the surface area and on the CeO2 particle size. The 0, uptake ability increases with the La: Cc relative, amount in the ceria-lanthana solid solution, but decreases beyond a La:Ce molar ratio greater than approximate to 0.18. This behavior is ascribed to the stable association of vacancy-vacancy or vacancy-dopant cation. (C) 2002 Elsevier Science.