A System(atic) Approach towards Low Precious Metal Three-Way Catalyst Application

Future three way catalyst systems are expected to consist of a relatively small start catalyst and a larger volume underfloor catalyst. The main role of the start catalyst is to provide rapid light off. For this purpose, the start catalyst requires relatively small volume with high precious metal loading. Computer simulation is employed to optimize the start catalyst volume with respect to light off performance and precious metal cost.

The main role of the underfloor catalyst is NOx removal at elevated temperatures and high space velocities. Due to its large volume, substantial precious metal savings can be realized by the design of a low precious metal underfloor catalyst. The present study focuses on a systematic understanding of NOx breakthrough in three-way catalysts. Special emphasis is on the interaction of the catalyst and the engine management system, especially the lambda control.

Based on the results of a detailed experimental and modelling investigation of dynamic catalyst operation, an optimized washcoat formulation for use in underfloor applications has been developed. Compared to current production type catalysts, more than 50 % reduction of precious metal loading without any loss in catalytic activity is achieved.