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Dual-monolith converters containing Pd-only catalysts followed by Pt/Rh three-way catalysts (TWCs) provide effective emission solutions for NLEV and Tier IIa close-coupled dual-bank V-8 applications due to optimal hydrocarbon and NOx light-off, transient NOx control, and balance of precious metal (PGM) usage. Dual-catalyst [Pd +Pt/Rh] systems on a 5.3L V-8 LEV light truck vehicle were characterized as a function of PGM loading, catalyst technology, and substrate cell density. NLEV hydrocarbon emission control of the 6500 lb vehicle was optimal using dual 1.2L converters with each containing front ceria-free Pd catalysts coupled with rear Pt/Rh TWCs. Advanced non-air prototype calibrations coupled with reduced catalyst washcoat mass on 600cpsi/4mil substrate resulted in minimal Pd usage of ∼0.02 toz/vehicle due to achieving catalyst inlet temperatures of 350-400°C in <10 sec on both banks of the V-8 engine.

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.

Palladium-rhodium three-way catalysts (Pd/Rh TWCs) demonstrate the most versatile capability in achieving California LEV/ULEV emission standards for various applications ranging from thermally severe high-temperature close-coupled locations to thermally limited cooler underfloor environments. Engine aged dual-brick converters consisting of front Pd catalysts followed by rear Pd/Rh TWCs met ULEV emission standards for a high-temperature close-coupled 4.3L medium-duty truck and LEV standards for a much cooler underfloor 3. IL passenger car location, as well as intermediate environments experienced by a 3.8L vehicle. The Pd + Pd/Rh TWC systems have performance advantages and are more cost effective compared to Pd-only or trimetal (Pt/Pd/Rh) systems. For thermally limited systems such as the 3. IL system, addition of air to the Pd + Pd/Rh system was necessary.

While often treated as separate entities, there is a significant interaction between engine operating parameters and the catalytic aftertreatment system in determining overall performance. The impressive gains in vehicle emissions and durability required for such marketplaces, as California and Europe provide excellent examples of this interrelationship. Similarly, the Indian marketplace can expect to follow these technology progressions in engine as well as catalyst application design. To progress from an unregulated emissions environment to the first level of catalyzed aftertreatment of relatively simply designed carbureted engines, and then to more sophisticated engines with fuel injection, India can take advantage of what has been learned in other marketplaces worldwide.

Scooters and motorcycles are favoured as economical forms of transportation throughout much of Asia. This is particularly true of vehicles with 2-stroke powerplants, thanks to the high specific output produced by this simpler, less costly engine. However, a serious disadvantage of these vehicles is that they emit considerably higher volumes of gaseous pollutants per driven kilometer than do other automobiles. Reductions of greater than 50% in these gaseous emissions can be effected through the use of catalysts to treat the exhaust from these engines. In this paper, important aspects of the operating conditions and durability requirements which must be factored into the design of durable, active catalyst formulations for these vehicles will be described.

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.

Both laboratory and engine dynamometer testing were used to characterize the relative activity of Pt, Pd and Rh supported on Ce and/or La stabilized supports. In the laboratory studies performance was measured after laboratory aging under conditions designed to simulate severe engine aging. The impact of Pt-Rh and Pd-Rh alloying on performance was examined as well as the cumulative effect of both metals on overall activity. The performance of laboratory aged non-alloyed Pt-Rh and Pd-Rh catalysts was dominated by the Rh function. For Pt-Rh the overall performance features for CO and NOx conversion were very similar over the Rh-only, Pt + Rh (separated metals) and alloyed Pt-Rh catalysts. Pt-Rh alloying was found to have a detrimental impact on high temperature HC performance.