Global kinetic model for lean NOx traps

Modeling and flow reactor experiments are used to investigate the global kinetics for lean NOx traps (LNTs). Experiments were conducted with a Pt/Rh/BaO/Al2O3 model catalyst, and the inlet feed gas was switched between lean and rich periods. It has previously been observed that NO oxidation to NO2 is important for NOx storage, and therefore a global mechanism for NO oxidation on Pt/Al2O3 is developed. This is then used in the NOx trap model, after the parameters had been adjusted to match the NO and NO2 concentrations from experiments on the Pt/Rh/BaO/Al2O3 catalyst. The mass transport of NO and NO2 inside the particles is described by a shrinking-core model. Further, it is found that two global reaction steps are needed for storage in order to explain the experimental observations:  one step for the formation of barium nitrates and the other step for the formation of loosely bound barium nitrites. Reaction steps were added to the model for regeneration of the trap with C3H6. The model is tuned based on s...