Development, validation and application of a model for an SCR catalyst coated diesel particulate filter

There is a lot of interest in combining aftertreatment system components to reduce packaging volume and cost. One example of this is the SCRF®, which consists of an NH3 Selective Catalytic Reduction (SCR) catalyst coated on a diesel particulate filter (DPF). In this work, a one-dimensional model for an SCRF® has been developed. The model was produced by combining kinetics for either a Cu-zeolite or an Fe-zeolite SCR catalyst, originally developed for a flow-through monolith, with a physical model for a coated DPF. The kinetics for the various NH3single bondNOX reactions, as well as for NH3 oxidation, were developed from laboratory microreactor data. The model is capable of predicting the conversion of NO and NO2, NH3 slip and the formation of N2O, as well as effects associated with NH3 storage and desorption. In the model, reactants can diffuse to the catalytic coating both from the gas flowing along the coated channel (as in a flow-through monolith) and from the gas flowing through the filter wall. The model has been validated against engine data for both light- and heavy-duty diesel conditions. In general, good agreement between model prediction and the experimental data was achieved for both Cu- and Fe-zeolite SCRF®s. It is demonstrated that SCR kinetics developed for a flow-through monolith are capable of giving a good prediction when the same coating is applied to a wall-flow filter in the SCRF®. The model has been applied to investigate the interaction between SCR and DPF functionality. The presence of soot on the SCRF® is predicted to have no significant impact on NOX conversion. Conversely, SCR activity (NOX reduction) is predicted to significantly retard the rate of soot removal by oxidation with NO2. Both predictions are in agreement with experimental results.