Investigation of combined DOC and NSRC diesel car exhaust catalysts

The system of two monolithic catalytic reactors – diesel oxidation catalyst (DOC) and NOx storage and reduction catalyst (NSRC) – is studied. The catalysts are used in series for the conversion of exhaust gases from automobiles with Diesel engines (or other lean-burn engines). Several tens of catalytic reactions are considered in the description by a model based on a system of non-linear partial differential equations (mass and enthalpy ballances). A simulation study is performed to examine the effects of parameters determining the performance of the upstream-located DOC (size and effective heat capacity of the monolith, catalytic activity in individual reaction steps) on the performance of the NSRC in the European driving cycle (NEDC). Effective numerical methods used for the solution of the resulting non-linear PDEs are described. Results of the maximization of the overall NOx conversion over the NEDC for several DOC and NSRC reactor configurations and different regeneration strategies are presented. It is shown, that the DOC may have a positive effect on the overall NOx conversion over the NEDC. Regarding NOx conversion over the NEDC, the effect of the NOx storage capacity of the NSRC is significant.