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The emission and flow restriction characteristics of three different ceramic substrates with varying wall thickness and cell density (400 cpsi/6.5 mil, 600/4.3, and 600/3.5) are compared. These 106mm diameter substrates were catalyzed with similar amounts of washcoat and fabricated into catalytic converters having a total volume of 2.0 liters. A Pd/Rh catalyst technology was applied at a concentration of 6.65 g/l and a ratio of 20/1. Three sets of converters (two of each type) were aged for 100 hours on an engine dynamometer stand. After aging, the FTP performance of these converters were evaluated on an auto-driver FTP stand using a 2.4L, four-cylinder prototype engine and on a 2.4L, four-cylinder prototype vehicle. A third set of unaged converters was used for cold flow restriction measurements and vehicle acceleration tests.

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.

Palladium-rhodium catalyst technologies have been investigated to establish the relationship between emission performance and their oxygen storage capacity (OSC) or other physical properties. Catalyst performance was evaluated using stand dynamometer and FTP testing after both oven air aging and engine aging. Monolith catalysts were characterized for aged surface area and precious metal dispersion. Various components of the washcoat supports were characterized by surface area and X-ray diffraction (XRD) analysis for phase composition and CeO2-ZrO2 solid solution crystallite size. The correlation between OSC delay times and tailpipe emissions for NMHC, CO and NOx was highly nonlinear in these studies. Addition of CeO2-ZrO2 solid solution components to the washcoat significantly improved steady state activity after aging, but did not significantly affect the correlation between emissions and OSC.

FTP emissions from a 2.2L four cylinder vehicle are measured from six different converters. These converters have been designed to have both similar flow restriction and to have similar platinum group metals. The durability of these six converters is evaluated after dynamometer aging of both 125 and 250 hours of RATsm aging. These catalytic converters use various combinations of 400/3.5 (400 cells/in2/3.5mil wall), 400/4.5, 400/6.5, 600/3.5, 600/4.5, and 900/2.5 ceramic substrates in order to meet a restriction target and to maximize converter geometric surface area. Total catalyst volume of the converters varies from 1.9 to 0.82 liters. Catalyst frontal area varies from 68 cm2 to 88 cm2. Five of the six converters use two catalyst bricks. The front catalyst brick uses either a three-way Pd washcoat technology containing ceria or a non-ceria Pd washcoat technology. To minimize dependence on palladium the rear brick uses a Pt/Rh washcoat at a loading of 0.06 Toz and a ratio of 5/0/1.

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 successful commercialization of lean burn gasoline engines is dependent upon development of an effective emission aftertreatment system which can provide HC, CO, and NOx control not only under lean operating conditions, but also when the engine operates at the stoichiometric point under conditions of high engine speed and/or load. NOx adsorber catalysts (NOx traps) are capable of storing NOx under lean condition, and subsequently releasing and catalyzing its reduction under conditions rich of the stoichiometric point. Aftertreatment systems based on these types of catalysts show great potential for reaching current and future emission standards. Key to the successful application of NOx adsorber catalysts is the development of engine control strategies which maximize NOx conversion while minimizing the fuel economy penalty associated with adsorber regeneration. In this paper limitations associated with NOx trap adsorption and regeneration strategies are discussed.

Although improvements in NOx adsorber formulations are increasing the sulfur resistance of these materials, and legislation continues to further restrict sulfur levels in fuels, sulfur poisoning remains as one of the key issues associated with successful commercialization of NOx adsorber technology throughout the world. Because of the stability of the sulfate poisons, high temperatures which stress the thermal stability of some of the most efficient NOx adsorbents are required for desulfation. Additionally, the rich condition which favors sulfur release simultaneously increases the H2S content of the emission. Sulfur traps offer the potential for reducing the formation of poisoning sulfates on downstream NOx adsorbents. Results characterizing the sulfur scavenging efficiency of these materials, as well as the conditions required for their regeneration will be presented. Strategies for their successful application on motor vehicles will be discussed.

Regulations are being considered or have already been enacted to limit the exhaust emissions of hydrocarbons, CO and NOx from small engines, such as those used in the lawn and garden industry. One of the most promising ways for engine manufacturers to comply with current and future emission standards is through the use of catalysts. However, these small engines provide an environment with a number of challenges for emission catalyst activity and durability which are not found with automotive exhaust, which is traditionally where catalysts of this type have been used. Problems unique to the small engine can include extremely short catalyst residence times, high hydrocarbon and carbon monoxide to oxygen ratios, overall high levels of emissions leading to high reaction exotherms, and pertubated flow due to single cylinder operation. A number of catalyst variables were tested using 4-stroke engines.

FTP and ECE + EUDC emissions are measured from six converters having similar restriction and platinum group metals on two 1999 prototype engines/calibrations. A 2.2L four cylinder prototype vehicle is used to measure FTP emissions and an auto-driver dynamometer with a prototype 2.4L four cylinder engine is used to determine the ECE + EUDC emissions. The catalytic converters use various combinations of 400/3.5 (400cpsi/3.5mil wall), 400/4.5, 400/6.5, 600/3.5, 600/4.5, and 900/2.5 ceramic substrates in order to meet a restriction target and to maximize converter geometric surface area. Total catalyst volume of the converters varies from 1.9 to 0.82 liters. Catalyst frontal area varies from 68 cm2 to 88 cm2. Five of the six converters use two catalyst bricks. The front catalyst brick uses either a three-way Pd washcoat technology containing ceria or a non-ceria Pd washcoat technology. Pd loadings are 0.1 troy oz. of Pd.