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

Abstract

Zirconium-cerium mixed oxides were prepared by two methods: (i) sol-gel hydrolysis of alcoholic solutions of zirconium alkoxides (n-propoxide and n-butoxide) in the presence of aqueous solutions of cerium nitrate (method SG) or (ii) coprecipitation of aqueous solutions of zirconyl and cerium nitrates by ammonia (method NP). Dried or calcined solids were characterized by XRD, DTA, BET and oxygen storage capacity (OSC) measurements, O ₂ adsorption was monitored by infrared spectroscopy. Regardless of the zirconium precursor, SG samples calcined at 900 °C have a fluorite-type structure with BET surface areas varying between 35 and 45 m ² g ^–1 . Cerium-rich samples (0.85≤x≤0.90), with excellent 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 superoxide 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 formed at the same anionic vacancies as those involved in oxygen storage.