Lean NOx Trap System Design for Cost Reduction and Performance Improvement

The effects of PGM zoning and washcoat staging have been investigated as a means to lower the cost and simultaneously improve the performance of a lean NO_x trap system. It is shown that reverse PGM zoning can be used to reduce the cost of the LNT while essentially maintaining the NO_x performance of a similarly-sized trap with a uniformly high PGM loading. In addition, the effective temperature window of the trap can be expanded by staging different NO_x trap formulations that are optimized for different temperature ranges. Alternatively, LNT washcoat staging can be used to improve the hydrocarbon conversion of the trap while maintaining good NO_x performance. Laboratory data and vehicle data are presented for several NO_x trap system combinations that demonstrate the improved performance that can be obtained from a combination of reverse PGM zoning and washcoat staging.