11th July, 2002
World-Leading Development of a Self-Regenerating "Intelligent Catalyst"
Daihatsu has led the world in developing an "intelligent catalyst" for
automotive emissions control that regenerates its precious metals in reaction
to natural fluctuation of automotive exhaust gas, allowing it to suppress degradation
and maintain fresh catalytic activity. The new catalyst presents high performance
while dramatically reducing the large amount of precious metals, thus conserving
a valuable natural resource and lowering the cost of the catalyst.
Daihatsu is now working to commercialize the new product as a next-generation,
high-performance, low-cost automotive catalyst, following its successful introduction
of the TOPAZ catalyst last year.
All the conventional automotive catalysts disperse fine particles of a precious
metals such as palladium, platinum or rhodium, onto the surface of alumina or
another supporting materials. To achieve a long-term catalytic durability, the
conventional catalyst employs the excess amount of precious metals.
The amount of precious metals used in catalyst production has increased since
the early 1990's, when automotive emissions standards were strengthened in all
over the world. The use of palladium, however, which is able to effectively oxidize
the hydro-carbons at relatively low temperatures, has seen particularly rapid
growth. Because palladium is also widely used in other fields, including dentistry,
and electrochemistry, it is important to reduce the use in the automotive catalyst.
A state-of-the-art automotive petrol engine is operated close to the theoretical
air-to-fuel ratio by using oxygen sensors and a sophisticated feedback control
system linked to the catalyst, a natural fluctuation associated with adjusting
the air-to-fuel ratio occurs between excessive and insufficient oxygen states
(called "oxidative" and "reductive" atmospheres, respectively).
And the catalyst is constantly subjected to temperatures of 800°C or higher.
Heat exposure causes the fine particles of precious metals to agglomerate together
in a phenomenon known as "particle growth," thus reducing the catalyst's
overall surface area and its catalytic activity.
Palladium is also the most heat sensitive of the commonly applied precious metals.
It has been difficult, by conventional technologies, to reduce the amount of palladium
in the automotive catalyst.
Daihatsu has developed a nono-technology that uniformly layouts palladium ions, at the atomic level, into a special perovskite-type crystal. This allows the palladium to move into the perovskite crystal structure as metallic ions in the high-temperature oxidative atmosphere, then to segregate out of the crystal in the reductive atmosphere to form fine metallic particles. When the atmosphere again becomes oxidative, the palladium moves back into the crystal and repeats the cycle, effectively regenerating itself through a new function, without any auxiliary treatment, that suppresses particle growth.
The new technology greatly improves the heat resistance of palladium and boosts its catalytic activity and durability compared with conventional catalysts. Further, it can also be used with other precious metals, such as platinum and rhodium, to dramatically reduce the amounts of these vital natural resources required in catalyst production and lower catalyst costs accordingly.
In developing the new material, the Daihatsu team was aided by the co-operation
of Professor Dr. Makoto Misono of Kogakuin University and Professor Dr. Noritaka
Mizuno of The University of Tokyo. Analysis of the self-regenerating function
was conducted jointly by Daihatsu, the Japan Atomic Energy Research Institute,
Toyota Central R&D Labs., Inc., and Tokyo University of Science and was reported
in the July 11th edition of the prominent scientific journal "Nature"
in the United Kingdom as a new design concept for catalytic development.
(Complete document appears in Nature, Vol. 148 (2002) pp 164-167),
Terminology
[Reference information]
