Zr-Ce-Pr-Cu-O 系酸化物の相平衡と酸素放出・吸収特性

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. A candidate for the high efficient OSC materials must lie in the composition of (Zr2/8Cex/8Pr(6-x)/8)O2-y (x=0~6), because the small amount of Ce addition stabilizes a single phase of λ-(Zr0.25Pr0.75)O2-y with wide oxygen nonstoichiometry. In addition, noble catalytic metal, e.g., copper must be investigated instead of platinum. In the present work, the (Zr2/8Cex/8Pr(6-x)/8)O2-y compositions (x=0~6) with the addition of Cu have been investigated for the phase relationship and OSC behavior. 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 the Ar+5% H2. When oxidized at 1473 K in air, the two-phases region between the λ-and C-phases, observed for (Zr2/8Cex/8Pr(6-x)/8)O2-y, disappeared and a pyrochlore-like phase appeared with the addition of Cu. That is, the addition of Cu led to the mutual solid solution of λ- and C-phases. When the samples (Zr2/8Cex/8Pr(6-x)/8)Cu0.5/8O2-y (x<3) were reduced at 1373 K in H2, C-rare earths-like phase appeared on (Zr2/8Cex/8Pr(6-x)/8)Cu0.5/8O2-y (x<3). With increasing the Ce content, the lattice parameter of the CaF2 unit varied continuously to those of λ- and C-phases. For the samples (Zr2/8Cex/8Pr(6-x)/8)Cu0.5/8O2-y (x=0∼6), the oxygen storage capacity was greatly improved at low temperatures as 573 K, probably due to the oxygen defect of pyrochlore-like phase.