(405a) Lean NOx Reduction By H2/CO/C3H6 Using NSR and SCR Catalysts

Transient NO_x reduction performance of NSR and SCR catalysts is studied under adiabatic conditions using 1+1 dimensional two phase model. In the NSR catalyst, NO_x is stored under lean conditions on the model Pt/BaO/Al₂O₃ catalyst and subsequently regenerated by a rich mixture of H₂, CO and C₃H₆. A micro-kinetic reaction scheme is developed based on literature reported steady state and cyclic experimental studies of both NO_x Storage and Reduction (NSR), and Selective Catalytic Reduction (SCR) processes. The kinetic parameters are initially estimated for each reductant separately, and are then modified based on comparison with experimental results. Mechanistic analysis of the reaction scheme provides clear insights into the dependence of NO_x reduction efficiency on feed temperature and molar ratio of reducing agents. The model is able to reasonably accurately predict the NO_x conversion and selectivities observed during the experimental studies. The kinetic scheme is further used to investigate the behavior of coupled NSR-SCR catalysts and study the effects of various parameters like cycle time, rich feed ratio, feed temperature, precious metal loading and catalyst architecture on NO_x conversion under both aerobic and anaerobic conditions. Spatio-temporal concentration and temperature profiles are analyzed and used to determine the optimum operating conditions for the coupled catalysts, especially at low temperatures.