Sol-gel precursors and the oxygen storage capacity of PrO_y-ZrO₂ materials

The gels derived from mixtures of Pr(OⁱC₃H₇)₃ and Zr(OⁱC₃H₇)₄·ⁱC₃H₇OH, upon hydrolysis and pyrolysis, furnish single-phase PrO_y-ZrO₂ materials crystallized in the fluorite structure. These materials can be coated onto high-surface-area γ-alumina powders or deposited onto dense α-alumina coupons in the form of thin films from a solution of parent alkoxides modified with 2,4-pentanedione in THF. The fluorite structure of the PrO_y-ZrO₂ in the films appears to be thermally stable in air up to 1200°C. Temperature-programmed-reduction (TPR) measurements show that the bulk PrO_y-ZrO₂ material with a Pr:Zr molar ratio of 1:1 can store and release oxygen while that with a molar ratio of 1:3 cannot. The precursors play an important role in determining phase composition of the resulting PrO_y-ZrO₂ material. A mixture of monoclinic and cubic or tetragonal phases was found in PrO_y-ZrO₂ prepared from a new single-source heterometallic alkoxide, Pr₂Zr₆(μ₄-O)₂(μ-OAc)₆ (μ-OⁱPr)₁₀(OⁱPr)₁₀, whereas a mixture of cubic and tetragonal phases was present in PrO_y-ZrO₂ made previously by coprecipitation from aqueous solutions of the metal nitrates.