Kinetic model for modern double-layered Pd/Rh TWC as a function of metal loadings and mileage

• Overall reaction kinetics for double-layered Pd/Rh monolith TWC was developed.
• 3D activity function was developed as a function of Rh loading and mileage.
• Overall kinetics was obtained by combining activity function and reference kinetics.
• Pd/Rh TWC performance may be well predicted with respect to metal loading and mileage.

The overall reaction kinetics for a modern double-layered Pd/Rh bimetallic TWC has been developed by combining the activity functions derived separately for the Pd-based (aPd) and Rh-based (aRh) TWCs with their respective reference reaction kinetics. A 3D activity function for the commercial Rh-based TWC (aRh) was developed on the basis of the metal surface area (MSA) of Rh, and subsequently used in combination with the detailed reaction kinetics of the Rh reference catalyst in predicting the catalytic performance variation with respect to the Rh loading from 2.5 to 15 g/ft3 and the catalyst mileage from 4 k to 100 k miles obtained from the laboratory aging program. Finally, the catalytic performance of a modern double-layered Pd80/Rh10 TWC monolith reactor was predicted with a reasonable accuracy over a wide range of the catalyst mileage from 4 k to 100 k by using the overall reaction kinetics for Rh developed in this work along with that for Pd developed previously. The excellent capability of the overall reaction kinetic model in predicting the catalytic performance of the Pd/Rh bimetallic TWC is attributable to the successful combination of the accurate initial activity profiles of Pd and Rh at 4 k miles, the accurate characterization of the deactivation kinetics of Pd and Rh, the detailed surface reaction kinetics employed, and the spatial separation of Pd and Rh particles in a double-layered catalyst configuration.