Effect of the preparation method on the properties of zirconia-ceria materials

Zirconium-cerium mixed oxides were prepared by two methods: (i) sol-gel hyd rolysis of alcoholic solutions of zirconium alkoxides (n-propoxide and n-bu toxide) in the presence of aqueous solutions of cerium nitrate (method SG) or (ii) coprecipitation of aqueous solutions of zirconyl and cerium-nitrate s by ammonia (method NP). Dried Or calcined solids were characterized by XR D, DTA, BET and oxygen storage capacity (OSC) measurements, O-2 adsorption was monitored by infrared spectroscopy. Regardless of the zirconium precurs or, SG samples calcined at 900 degrees C have a fluorite-type structure wit h BET surface areas Varying between 35 and 45 m(2) g(-1); Cerium-rich sampl es (0.85 less than or equal to x less than or equal to 0.90), with excellen t OSC properties and high thermal stability can be prepared by the sol-gel method. FTIR studies of O-2 adsorption reveal the presence of stable supero xide species whose concentration strongly depends on the cerium content and the method of preparation. A good correlation between the relative amount of O-2(-) species and OSC values was observed. Superoxide ions may be forme d at the same anionic vacancies as those involved in oxygen storage.