Sol-gel processed fluorite-structured PrO(y)-ZrO₂ mixed oxides deposited on alumina

Preparation of PrO(y) (Pr₆O₁₁) or single-phase fluorite-structured PrO(y)-ZrO₂ mixed oxide, supported on high-surface-area γ-alumina, was achieved for the first time by impregnation of γ-alumina powder with Pr(O(i)C₃H₇)₃ or a mixture of Pr(O(i)C₃H₇)₃ and Zr(O(i)C₃H₇)₄·(i)C₃H₇OH and calcination at 600°C. Subsequent calcination at 900°C caused partial transformation of Pr₆O₁₁ to PrAlO₃ but only improved the crystallinity of the mixed oxide. Further calcination at 1200°C led to complete transformation of Pr₆O₁₁ but only partial disproportionation of PrO(y)-ZrO₂ to PrAlO₃ and ZrO₂; transformation of γ- to α-alumina was also inhibited in the case of the mixed oxide. In contrast, there was no evidence of any crystalline phase containing praseodymium upon calcination of γ-alumina powder impregnated with a mixture of praseodymium nitrate and zirconium chloride in a 1:0 or 1:1 molar ratio. These results show that praseodymium oxide can be supported on alumina and stabilized against reaction with the alumina by the incorporation of zirconium in the form of the mixed oxide, PrO(y)-ZrO₂, provided it is deposited using alkoxide precursors. This stabilization should allow praseodymia to undergo redox processes and thus provide oxygen storage capacity when supported on alumina in a catalyst washcoat.