The low-temperature performance of NOx storage and reduction catalyst

Abstract

The catalytic performance and the behavior of NOx storage and reduction (NSR) over a model catalyst for lean-burn gasoline engines have been mainly investigated and be discussed based on the temperature and reducing agents use in this study. The experimental results have shown that the NOx storage amount in the lean atmosphere was the same as the NOx reduction amount from the subsequent rich spike (RS) above the temperature of 400°C, while the former was greater than the latter below the temperature of 400°C. This indicated that when the temperature was below 400°C compared with the NOx storage stage, the reduction of the stored NOx is somehow restricted. We found that the reduction efficiencies with the reducing agents decrease in the order H2>CO>C3H6 below 400°C, thus not all of the NOx storage sites could be fully regenerated even using an excessive reducing agent of CO or C3H6, which was supplied to the NSR catalyst, while all the NOx storage sites could be fully regenerated if an adequate amount of H2 was supplied. We also verified that the H2 generation more favorably occurred through the water gas shift reaction than through the steam reforming reaction. This difference in the H2 generation could reasonably explain why CO was more efficient for the reduction of the stored NOx than C3H6, and hinted as a promising approach to enhance the low-temperature performance of the current NSR catalysts though promoting the H2 generation reaction.