Product speciation during regeneration of lean NOx traps

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 is based on a series of flow reactor temperature ramp experiments performed on a core sample from a fully formulated lean NOx trap catalyst. The experiments used simultaneous flow of NOx and reductant species (H2 and CO) to decouple the reduction reactions from the NOx storage and release processes. The mechanism accounts for the observed product distribution (including NH3 and N2O) 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 the experiments. 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.