Mathematical modelling of precious metals catalytic converters for diesel NOx reduction

Precious metal catalysts for NOx reduction in lean diesel engine exhaust conditions are characterized by a narrow temperature range of efficient operation and require high availability of reducing species in significant concentration. Consequently, there exists a large optimization potential in the design and control of lean-NOx catalytic conversion systems. A mathematical model of the transport and chemical phenomena in platinum-based lean-NOx catalysts was formulated, based on the experience with analogous models for gasoline three-way catalysts. A simplified four-reaction scheme is employed, considering the oxidation of CO, H-2 and hydrocarbons (HCs), as well as the reaction between NOx and HCs. Results are compared with previously published laboratory and engine data in order to assess the capacity of this approach in representing real-world behaviour of Pt-based lean-NOx catalysts. Initial results illustrate the power and flexibility of the model, which is able to predict the NOx conversion characteristics in model gas tests as well as in full-scale engine tests with reasonable accuracy.