Sol-gel processed fluorite-structured PrOy-ZrO2 mixed oxides deposited on alumina

Abstract

Preparation of PrO _y (Pr ₆ O ₁₁ ) or single-phase fluorite-structured PrO _y -ZrO ₂ 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 C ₃ H ₇ ) ₃ or a mixture of Pr(O ⁱ C ₃ H ₇ ) ₃ and Zr(O ⁱ C ₃ H ₇ ) ₄ · ⁱ C ₃ H ₇ OH and calcination at 600 °C. Subsequent calcination at 900 °C caused partial transformation of Pr ₆ O ₁₁ to PrAlO ₃ but only improved the crystallinity of the mixed oxide. Further calcination at 1200 °C led to complete transformation of Pr ₆ O ₁₁ but only partial disproportionation of PrO _y -ZrO ₂ to PrAlO ₃ and ZrO ₂ ; 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 -ZrO ₂ , 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.