Isao Tan

Design of the intelligent catalyst for Japan ULEV standard

We have reported the innovation of “An intelligent catalyst” which has the function for self-regeneration of Pd realized through the solid solution and segregation of Pd in a perovskite crystal. In this paper, the issues and the solutions for a practical perovskite catalyst for the Japan ULEV standards are discussed.

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 strategy 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 Pd-containing perovskite catalyst systems 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 perovskite-type oxide. And Pd in the perovskite crystal structure exhibited an abnormal oxidation number or higher binding energy than the normal bivalence, and it was presumed to be the reason for increasing the catalytic activity. The results of dissolution analysis for the aged Pd-perovskite catalyst suggested that Pd was not only dispersed on the surface of the perovskite crystal, but was present also in the solid solution of the perovskite crystal. The formation of a solid solution in this Pd-perovskite crystal was affected by the B site elements. And Pd in LaFe0.54Co0.36Pd0.10O3 system was more durable than in LaCo0.90Pd0.10O3 or in LaFe0.90Pd0.10O3. Furthermore, the formation of Pd solid solution into these perovskite crystals also depended on atmospheres and temperatures. It appeared that a high state of dispersion was maintained as Pd repeatedly forms solid solutions in the perovskite crystal or segregates out from the crystal depending on the fluctuation 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 treatment, “an intelligent catalyst”.

The Self-Regenerative "Intelligent" Catalyst for Automotive Emissions Control

Co-free LaFePdO3 perovskite catalyst with the self-regenerative function of Pd was developed. This technology was named the “intelligent catalyst”. Suppression capacity for Pd particle growth and catalytic activity of the Co-free perovskite LaFePdO3 were compared with those of LaFeCoPdO3. It was confirmed that Pd particles on LaFePdO3 maintained a nano-particle size by the results of XAFS analysis and TEM observation after aging in engine exhaust gas at 900 °C, and LaFePdO3 demonstrated an excellent light-off performance. Further, the design configuration for LaFePdO3 in the washcoat was investigated to maximize the self-regenerative function under practical conditions.

The Intelligent Catalyst: Pd-Perovskite Having the Self-Regenerative Function in a Wide Temperature Range

An innovative Pd-perovskite “Intelligent Catalyst”, which exhibits a greatly improved durability owing to the self-regeneration function of Pd nanoparticles, has been developed. The Pd-perovskite catalyst was prepared by the alkoxide method, and X-ray absorption fine structure (XAFS) measurements were carried out in SPring-8 using the 8-GeV synchrotron radiation. Pd occupied the B-site (6-fold coordination) of the perovskite lattice in the oxidative atmosphere, and segregated out to form metallic nanoparticles in the reductive atmosphere. The catalyst retained a predominantly perovskite structure throughout a redox cycle of the exhaust-gas, while the local structure around Pd could be changed in a completely reversible manner. The agglomeration and growth of the metal particles is suppressed as a result of the Pd movement between inside and outside the perovskite lattice. This function enables an automotive catalyst to regenerate itself into an active state in fluctuation typically encountered in the exhaust gas from the gasoline engine. And it is revealed, by in-situ and ex-situ XAFS analyses, that the self-regenerative function of Pd occurred in a wide temperature range from very low to high one. The intelligent catalyst is one solution for precious metals supply and demand problem, and is expected to become the global standard of the catalyst technology.

Intelligent catalysts with self-regenerative function

An “intelligent catalyst” that has the self-regenerative function of Pd (Palladium) achieved through solid solution and segregation of Pd in a perovskite crystal was first commercialised in 2002. Daihatsu has made attempts to apply this intelligent technology to other precious metals, such as Rh (Rhodium) and Pt (Platinum), and advanced intelligent catalysts with a self-regenerative function of Rh and Pt have been developed successfully.