Selectivity of NO_x storage catalyst regeneration in automotive applications

The selectivity of NO_x reduction products during the catalyst regeneration was studied. When reductants reacted with NO_x over an incompletely reduced Pt surface, N₂O was more likely to form, but this likelihood decreased with progressive reduction of the surface. When the surface became more fully reduced, the reduction products were mainly N₂ and NH₃. The latter could further react with remaining NO_x stored further downstream. During H₂ regeneration, two regeneration fronts (H₂, NH₃) could develop and, combined with spatial distribution of stored NO_x, could affect the global selectivity. Integrating these assumptions into a global NSRC model led to reasonable prediction of the observed N₂O formation. Adding C₃H₆ or C₃H₈ to the feed (10% more reductant) raised N₂O selectivity significantly at 200°-350°C. Considering the increased total reductant, the higher N₂O could not be readily explained by Pt redox state changes alone. Instead, additional hydrocarbon regeneration fronts were involved. These multiple reduction fronts and the individual light-off characteristics of H₂, NH₃, C₃H₆, and C₃H₈ combined to determine the global selectivity of NO_x reduction over NO_x storage and reduction catalyst. This is an abstract of a paper presented at the CHISA 2012 - 20th International Congress of Chemical and Process Engineering and PRES 2012 - 15th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction (Prague, Czech Republic 8/25-29/2012).