Kinetic modeling analysis of selective reduction reaction for NO{sub}x in diesel exhaust by HC

摘要

The three-way catalysts employed in gasoline engines cannot be used in diesel exhaust gas atmosphere. This causes one of the various difficult problems in decreasing NO{sub}x emissions. As one of technologies for addressing this problem, attention has been focused on selective reduction catalysts capable of converting NO{sub}x by using HC contained in exhaust gas as a reducing agent. There have been several reports dealing with the catalysts. Nevertheless, a mechanism of NO{sub}x conversion reaction of NO{sub}x catalysts has not been clarified sufficiently. Additionally, the number of attempts to predict the NO{sub}x conversion efficiency of the NO{sub}x catalysts with exhaust gas condition is still small. On this paper, Pt-loaded zeolite, which is one of the NO{sub}x catalysts, was taken up and the reaction mechanism of it was examined by the prediction model of conversion reaction of it. Two models, the model based on the direct reaction between HC and NO{sub}x and the model based on the reaction, which permits HC reaction intermediate produced by HC oxidation to purify NO{sub}x, were investigated. The conversion efficiencies of HC and NO{sub}x for exhaust gas simulating the conditions in the vehicle were predicted with the later model more accurately than the former model. It is presumed that the reaction, in which HC reaction intermediate was involved, occurred on the condition. Additionally, it is also presumed that the reaction occurred in the conversion reaction on a prototype.