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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 beneficial effects of CeO2/ZrO2 solid solutions on the performance of fully formulated Pt, Rh TWC (three-way-conversion) catalysts were measured using both stand dynamometer and FTP testing after severe engine aging. The performance advantages were consistent with an enhancement of the chemical promotional effects of CeO2. These included increased effectiveness for CO and NOx conversion and to a lesser extent for HC compared to catalysts prepared with the same loading of Ce and Zr but no solid solution formation. Higher performance could be achieved with the CeO2/ZrO2 solid solution catalysts having half the Ce loading of conventional catalysts prepared with pure CeO2. The physico-chemical properties of the catalysts were characterized using both XRD and TPR. XRD was used to determine the degree of solid solution formation between CeO2 and ZrO2 and TPR was used to characterize the redox properties/oxygen storage of the catalysts before and after aging.