DOC modeling combining kinetics and mass transfer using inert washcoat layers

• NO2 reacts preferentially with CO rather than C3H6 causing inhibition of NO oxidation.
• Inert washcoat layers provides conditions for estimating effective diffusivity.
• Effect of washcoat transport resistance most apparent for C3H6 and CO oxidation.
• Kinetic model performed well with O, CO and NO2 as the only surface species.
• Model developed resolving transport resistance, kinetics and inhibition effects.

The aim of this study was to develop a kinetic and transport model for diesel oxidation catalysts (DOC) with a satisfactory compromise between accuracy and computational demands for robust simulation of transient full-scale operation. Specifically the model accounts for surface concentrations of key species needed to capture transient features for typical lean exhaust conditions. In addition, the model accounts for transport limitations and distinguish them from reaction kinetics as well as apparent NO oxidation inhibition effects due to reactions. To achieve this, lab scale experiments were performed with DOCs with different platinum loadings and three different washcoat configurations of which two had an inert top layer. Both kinetic parameters for a detailed kinetic model and effective diffusivities were optimized for the experimental data using a single channel catalyst model. The experiments showed a clear effect of increased transport resistance for propene and CO and also that NO2 plays an important role as an oxidizing agent for preferentially CO at low temperature (<120 °C). The resulting model showed good agreement with measurement data using O, CO and NO2 as the only surface species. The use of different thicknesses of an inert washcoat layer closest to the gas bulk aided the resolution of kinetics from transport phenomena.

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