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 di4erent sol+gel routes, involving nitrate
precursors. The oxygen uptake ability of these compounds is
measured by O2 chemisorption. The speci5c surface area is
determined by N2 adsorption (BET). X-ray di4raction data are
analyzed by Rietveld re5nement, 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 O2 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 O2 uptake ability increases with the La:Ce relative amount
in the ceria+lanthana solid solution, but decreases beyond
a La:Ce molar ratio greater than +0.18. This behavior is ascribed
to the stable association of vacancy+vacancy or vacancy+
dopant cation.