Search Results

Conventional Three-way catalysts consist of precious metals and metal oxide supports. The sintering of precious metals is known to cause a decrease in the catalytic activity. Recently, we discovered that Pt/Ce-based oxide catalysts have high durability compared to Pt/Al2O3 following aging treatment. Using X-ray absorption analysis, we found that the Pt-O-Ce bond, that is, the Pt-support interaction, inhibits the sintering of Pt particles.

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.

A new 3-way catalyst with NOx conversion performance for lean-burn engines has been developed. The catalyst oxidizes NOx and stores the resulting nitrate, which is then reduced by HC and CO during engine operation around the stoichiometric air/fuel ratio. Both the composition of the storage component and the particle sizes of the noble metal were optimized. In addition, a special air fuel mixture control has been developed to make the best of the NOx storage-reduction function. The present catalyst showed 90% conversion efficiency and improved fuel economy by 4% in the Japanese 10-15 mode test cycle. The efficiency remained at 60% or more after durability test.