(429c) Aerobic Reduction of NOx in the Sequential LNT-SCR Catalytic Reactor

The effect of key parameters on the DeNO_x performance of the sequential LNT-SCR catalyst under non-isothermal operation is investigated in detail. The model simulates the cyclic operation of the sequential catalyst with lean NO_x storage, aerobic reduction of the stored NO_x using H₂ in the LNT and selective reduction of NO_x with NH₃ in the SCR. Global kinetics with fast and slow sites are used to account for the storage and regeneration reactions in the LNT and the reduction of NO_x due to NH₃ in the SCR catalyst. H₂ oxidation and H₂-NO reactions are described using micro-kinetic mechanism to predict the experimentally observed selectivities. The transient simulations reveal traveling concentration and temperature fronts along the length of the catalyst. The effect of various parameters like the precious metal loading, space velocity, inlet and initial temperature of the catalyst, number of sequential bricks and the total cycle time on the formation and speed of the traveling fronts are studied to determine the optimal operating conditions of the sequential catalyst. H₂ oxidation exotherm resulted in enhanced reaction rates and selectivities during non-isothermal operation. Consequently significant DeNOx activity is observed even with the Pt loading as low as 0.1wt%. However, from the ignition point of view too low Pt loading resulted in decrease in the DeNOx activity. The performance of the sequential LNT-SCR catalyst under cold start conditions is studied and the results are compared to those observed in the literature.