Abstract
Oxide materials with high oxygen storage capacity (OSC) at low temperatures, possessing high thermal stability at high temperatures are indispensable for advanced automotive exhaust catalyst. We have recently discovered a single CaF2-type phase of λ-(Zr1/4Pr3/4)O2-y with wide oxygen nonstoichiometry, which can release oxygen at a low temperature as 573 K in Ar. In the present study, various (Zr2/8Cex/8Pr(6-x))O2-y(x=0~6) compositions were prepared by a coprecipitation method. The samples were first oxidized at 1473 K in air, reduced in H2 at 1373 K, and then oxidized again at 973 K in air. The oxide samples obtained in each situation were subjected to XRD, OSC analysis and TPD oxygen gas analysis by means of TG/DTA in Ar+5%H2. The single λ-phase with CaF2 structure appeared for x=0.5 and 1. The Ce addition stabilized the λ-phase, while a single C-phase with CaF2 structure appeared in the composition range of x=5 and 6. Two-phases region of the λ- and C-phases existed for the composition of 1<x<5, where the amount of oxygen released with fast rate decreased monotonously with decreasing the Pr composition. The oxygen release and OSC properties have been discussed in terms of phase relationship and Ce/Pr composition.
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