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Various CTOs have been tested at inlet gas temperature of 600°C, nearly muximum output operation on Bench Engine Dynamometer Unit with 2.8 - 6.6 liter D.I. engine. Base metals promoted CTO are found to be deteriorated unexpectedly through the test conditions mentioned above. On the other hand, noble metal promoted CTO showed good durability against such full load operation condition. The problem arised from noble metal promoted CTO is evolution of sulfur trioxide at much higher concentration than from base metals promoted CTO. It is concluded that sulfur content in diesel fuel should be reduced as low as possible, such as to current gasoline level to use noble metal promoted CTO. Tow types of particulate trap structure, wall-flow monolith (WFM) and ceramic foam have been evaluated. These carriers have trapped ashes from lubricating oil in a comparable efficiency to their particulate trap efficiency.

A lean burn engine is effective in reducing fuel consumption. NOX storage-reduction catalysts (NSR catalyst) have been developed for these engines. In order to improve the performance of NSR catalysts, suppression of sulfur poisoning, which is one of the main causes of NSR catalyst deactivation, must be improved. In this paper, the sulfur desorption phenomenon has been analyzed from a novel point of view. Based on these results, an NSR catalyst with improved sulfur resistance has been developed by incorporation of highly dispersed titania, and use of a heat resistant zirconia with enhanced basicity.

It is an essential task for automobiles to reduce their fuel consumption. A direct injection gasoline engine (D-4 engine) is effective in reducing fuel consumption, but the reduction of NOx in the lean combustion region is impossible with a conventional three-way catalyst. The NOx storage-reduction three-way catalyst was put into practical use in 1994 for vehicles with lean-burn engines. This catalyst, however, is poisoned by SO2 caused by fuel sulfur, thus its activity is reduced. The conversion efficiency of this sulfur poisoned catalyst was not sufficient for reducing NOx in the exhaust gas of D-4 engine. We have, therefore, studied the mechanism of sulfur poisoning, and succeeded in improving the catalytic performance with the newly developed monolithic substrate and the newly developed additives.