Regeneration of palladium subsequent to solid solution and segregation in a perovskite catalyst: an intelligent catalyst

The object of this study was to provide a function for self-regeneration of precious metals in a usage ambience without auxiliary treatment. The strat egy was to control the catalytic active site of those crystalline ceramics known as perovskite-type oxides at the atomic level in order to create the new, needed function. Three series of Pol-containing perovskite catalyst sy stems were prepared by coprecipitation of Pd with La, Fe, and Co using the alkoxide method. It was confirmed that Pd formed a solid solution of the pe rovskite-type oxide. And Pd in the perovskite crystal structure exhibited a n abnormal oxidation number or higher binding energy than the normal bivale nce, and it was presumed to be the reason for increasing the catalytic acti vity. The results of dissolution analysis for the aged Pd-perovskite cataly st suggested that Pol was not only dispersed on the surface of the perovski te crystal, but was present also in the solid solution of the perovskite cr ystal. The formation of a solid solution in this Pol-perovskite crystal was affected by the B site elements. And Pd in LaFe0.54Co0.36Pd0.10O3 system w as more durable than in LaCo0.90Pd0.10O3 or in LaFe0.90Pd0.10O3. Furthermor e, the formation of Pd solid solution into these perovskite crystals also d epended on atmospheres and temperatures. It appeared that a high state of d ispersion was maintained as I'd repeatedly forms solid solutions in the per ovskite crystal or segregates out from the crystal depending on the fluctua tion of redox conditions and temperatures in automotive catalyst ambience. We named such a catalyst, wherein a precious metal regenerates itself while in operation and remains highly active without requiring any auxiliary tre atment, "an intelligent catalyst".