The low-temperature performance of NOx storage and reduction catalyst

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 NO 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 degrees C, while the former was greater than the latter below the temperature of 400 degrees C. This indicated that when the temperature was below 400 degrees 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 H-2 > CO > C3H6 below 400 degrees 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 H-2 was supplied. We also verified that the H-2 generation more favorably occurred through the water gas shift reaction than through the steam reforming reaction. This difference in the H-2 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 H-2 generation reaction. (c) 2006 Elsevier B.V. All rights reserved.