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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.