Synthesis, structure and catalytic properties of Zr-Ce-Pr-O mixed oxides

Zr-0.10(Ce1-xPrx)0.90 O-2 mixed oxides (x between 0 and 0.75) were prepared by coprecipitation (nitrates) or by the sol-gel route. Zirconium n-propoxide and cerium and/or praseodymium nitrates were used as precursors. "Sol-gel"oxides calcined at 900 degreesC were shown to be cubic with a fluorite-type structure. Coprecipated oxides could not be obtained as solid solutions. The BET surface area of these samples rapidly decreases when x>0.50. A Raman study confirmed that all oxides were cubic and evidenced the presence of oxygen vacancies. The optimum oxygen storage capacity (OSC) was obtained for Zr-0.10(Ce0.50Pr0.50)(0.90)O-2. It appears that the substitution of cerium by praseodymium in Zr0.10Ce0.90O2 mixed oxides leads to a material with improved redox properties. The presence of vacancies, associated with Pr3+/Pr4+ ions, is thought to be responsible for these enhanced OSCs.