日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

From the points of lower CO₂ emission in the production of light oil and in driving cars than gasoline-cars, diesel cars are one of the most promising vehicles. However, it was likely that aftertreatment of exhaust gases from diesel-engine cars was more difficult than that of gasoline-engine cars. It was because the exhaust gases contain a lot of oxygen, resulting in a low reduction efficiency of NO_x. Then, two kinds of technologies of NO_x reduction in lean conditions have been investigated using a zeolite as a catalyst component. One is urea- SCR and the other is ammonia-storage NO_x reduction in rich/lean operations. In the two NO_x reduction technologies, the zeolite plays an important role as an ammonia adsorbent. Ammonia-storage NO_x reduction in rich/lean operations proceeds in the following steps: NO_x adsorption on OSC materials in the lean operation, reduction of the adsorbed NO_x on Pt and ammonia-storage on metal-zeolite and finally NO_x reduction on the catalyst using stored ammonia.