Modelling of dynamic processes during the regeneration of NOx storage catalyst

Two kinetic models for the NOx reduction in periodically operated NOx storage catalyst are discussed-the simpler NH3-selectivity model, and the more complex NH3-dynamics model. They differ in the approach to the formation of the NH3 as a main by-product of the stored NOx reduction. The NH3-selectivity model assumes direct reduction of the stored NOx to nitrogen or ammonia with empirically obtained selectivity ratio, dependent on temperature and the reducing agent (CO, H-2 and HC). The more complex NH3-dynamics model considers both NH3 formation and NH3 decomposition reactions in the spatially distributed system, resulting in the evolution of moving NH3 peak on the reduction front boundary during the NSRC regeneration. The predictions of the two models are compared and confronted with experimental observations. For the estimation of integral component conversion (cumulative emissions) around the mean regeneration phase length the simpler NH3-selectivity model can be used. The more complex NH3-dynamics model is consistent with experimentally observed evolution of the outlet NH3 concentrations, and it is also more sensitive to operating conditions. On the other hand, the increased model complexity results in longer computation times.