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A set of elementary surface reactions is proposed for modeling the chemistry in a lean NOx trap during regeneration (reduction of stored NOx). The proposed reaction mechanism can account for the observed product distribution from the trap over a range of temperatures and inlet gas compositions similar to those expected for realistic operation. The mechanism includes many reactions already discussed in the literature, together with some hypothesized reactions that are required to match observations from temperature programmed reactor experiments with a commercial lean NOx trap catalyst. Preliminary results indicate that the NOx trap regeneration and byproduct formation rates can be effectively captured by using a relatively compact set of elementary reactions.

We study the NOx storage process in lean NOx traps using bench-flow experiments and simulated diesel exhaust. Given that formulation alone is an inadequate indicator of performance (due to the effects of manufacturing processes) a minimal set of experiments is always needed to compare the performance of LNTs. We define simple performance measures based on such a set of experiments that can be used to compare lean phase operations of various LNTs under various conditions concisely. Though the noble metal sites are essential for storage, the benefits of increasing noble metal loading start to wane beyond a certain limit. Our experiments suggest a possibility that a lean NOx reduction reaction may be occuring in LNTs. If this reaction is confirmed further in future experiments, its products need to be identified. The sorbent shifts the equilibrium between NO and NO2 towards NO.