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Dual-brick catalyst systems containing Pd-only catalysts followed by Pt/Rh three-way catalysts (TWCs) are effective emission solutions for both close-coupled and underfloor LEV/ULEV applications due to optimal hydrocarbon light-off, NOx control, and balance of precious metal (PGM) usage. Dual-brick [Pd +Pt/Rh] systems on 3.8L V-6 LEV-calibrated vehicles were characterized as a function of PGM loading, catalyst technology, converter volumes, and substrate cell density. While hydrocarbon emissions improve with increasing Pd loading, decreasing the front catalyst volume at constant Pd content (resulting in higher Pd density) improved light-off emissions. Use of 600cpsi substrates improved underfloor NMHC emissions on a 3.8L vehicle by ∼ 6-10mg/mi compared to 400cpsi catalysts, and thus allowing reduction of catalyst volume while achieving ULEV emission levels without air addition.

The performance data for monolithic ceramic converters, to date, shows that fuel management, engine characteristics, substrate design, catalyst formulation, substrate/coating interaction, and packaging design have a profound influence on converter durability and sustained activity and that certain trade-offs are necessary to optimize the overall performance of the converter system. This paper concentrates on the effect of the catalyst system on light-off performance, steady state conversion efficiency, pressure drop, high temperature strength, and thermal shock resistance. The physical properties and engine test data for Corning's EX-20, 400/6 square cell substrate with two different catalyst formulations, production high-tech vs advanced high-tech, show that the advanced catalyst results in marked improvement in mechanical durability and catalytic activity over that achievable with the production catalyst due to improved substrate/coating interaction.