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Hydrocarbon conversion across emission control catalysts is a strong function of inlet temperature. The bulk of unconverted hydrocarbon emissions arises in Bag 1 of the FTP-75 cycle before the emission control system goes closed-loop. A general strategy for improving converter hydrocarbon efficiency is to heat up the catalyst early in Bag 1. One strategy for doing this is to place a small catalytic converter near the engine manifold. This approach to hydrocarbon control is well established and represents a production feasible method. This paper explores the use of close-coupled catalysts in conjunction with conventional underfloor converters for achieving the California low emission vehicle standards. The paper identifies catalytic formulations for both converters that optimize emission system performance. The benefits of double wall exhaust pipe connecting the two converters and thin walled substrate for the light-off catalyst were also studied.

Various noble metal compositions are used for three-way catalyst applications. The most typical composition contains platinum and rhodium at various loadings and ratios. Recently palladium and rhodium compositions have received considerable attention by automobile companies. The strengths and weaknesses of the various noble metal use strategies have been widely discussed. Unfortunately, the content for much of the discussion has been based on information generated in the early to mid-1970s with catalysts of relatively simple formulation when compared to today's higher technology products. The present study compares the relative durability performance of modern platinum/rhodium and palladium/rhodium catalysts of identical loading under a variety of aging and evaluation conditions. These conditions were chosen to simulate some of the operating conditions encountered in U.S. and European driving applications.

Recent advances in three-way catalyst formulations have led to significant improvements in durability and performance. These advances for recent Pt/Rh catalyst formulations, for the most part/have been due to a reduction of thermal deactivation. Increased durability plays a critical role in the reducing noble metal usage/meeting tighter emission standards/and extending the durability warranty requirements. In reality, significant advances may be not be readily apparent because of the methods used to evaluate the technology. Some performance benefits may be transparent to particular durability and evaluation procedures, or certain vehicle emission systems. However, as part of an optimized vehicle/catalyst system, the performance benefits may be pronounced. This paper examines the benefits of improved three-way catalyst technologies in order to accelerate their application for tougher emission requirements.

The noble metal palladium (Pd) has the capability of simultaneously converting significant quantities of HC, CO and NOx in automotive exhaust. Primary interests in using palladium-containing TWC catalysts are overall noble metal cost reduction, reduction in rhodium usage and important performance advantages. Dynamometer aging experiments comparing palladium and platinum/rhodium catalysts were conducted under a variety of operating conditions. Vehicle evaluation of these aged catalysts under U.S. FTP-75, European ECE-15 and Japan 10-Mode conditions indicate that palladium-only TWC technology is viable for achieving high levels of three-way control. Vehicle aging studies (25K miles) were also conducted. They confirm the excellent durability results obtained from the dynamometer aging studies: the palladium-only TWC catalyst gave essentially equivalent U.S. FTP-75 and Japan 10-Mode performance to a high-tech platinum/rhodium catalyst.

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.

On a global basis there is a resurgence of interest in the use of palladium in automotive emission control catalysts because of cost, availability and performance advan­tages under certain operating con­ditions relative to more expensive noble metals. This paper reviews a variety of potential vehicle applic­ations for the use of palladium containing catalysts. Included in the study are for the replacement of platinum by palladium in conventional platinum/rhodium systems, palladium-only three-way catalysts, palladium-only dual bed catalysts and two-stroke and lean-burn engine applications.

Various catalytic control strategies must be carefully considered in order to make substantial progress towards meeting che more stringent NOx and hydrocarbon emission standards being proposed for the 1990s. In the development of newer catalyst technologies, this paper discusses the effects of noble metal loadings, catalyst volumes, improved washcoat technologies, base metal promoters/stabilizers, and air/fuel ratio operation on catalyst performance. The effect of various vehicle systems on FTP modal catalyst performance determined the factors influencing NOx control over selected vehicles. The results of these studies indicate that improvements in catalyst technologies will need to be systematically coupled with improvements in system control technology to simultaneously optimize the total emission system to achieve the more stringent standards being proposed.

Durability performance characteristics of copper-containing base metal catalysts and base metal/low noble metal catalysts have been determined in laboratory and engine aging conditions under well controlled stoichiometric closed-loop A/F operation. Cu-Cr base metal formulations yield significant HC and CO conversions under stoichiometric operation after aging at 620°C, but deteriorate rapidly at high-temperature (750°C inlet) stoichiometric operation. Incorporation of Rh into the base metal formulation substantially improved NOx performance, a major weakness of base metal catalysts. The addition of Cu-Cr base metals substantially improves CO oxidation over Pt, Pd, and Rh catalysts but was accompanied by some loss of HC conversion over Pt and Rh. A Cu-Cr/Pd catalyst, however, also had better HC conversions as well as significantly improved light-off performance when compared to a Pd-only catalyst.

The performance of potential sulfate sorbents was evaluated using an engine-dynamometer screening test procedure. Bulk and supported sorbents were tested. The two most promising sorbents were a bulk CaO preparation and alumina supported Na. The CaO sorbent appeared to be inherently non-selective between sulfates and SO2. Calcining this sorbent in a CO2 atmosphere resulted in increased pellet crush strength and reduced volume expansion upon use. The Na/Al2O3 sorbent had good activity and selectivity, but may lack capacity and be subject to leaching losses of Na-compounds. Vehicle and dynamometer durability testing of these two sorbents was conducted. From these preliminary tests, it was determined that neither met all the criteria of an ideal sorbent for vehicle use.

Platinum, palladium, and copper-chromium oxidation catalysts for exhaust emission control were exposed to exhaust gases from a steady-state engine dynamometer test in which the amount of oil consumed per unit volume of catalyst was high. When unleaded gasoline (0.004 Pb g/gal, 0.004 P g/gal) was used, conventional SE oil caused somewhat greater loss of catalyst activity than an ashless and phosphorus-free (“clean”) oil. Chemical analysis of the catalyst indicated that phosphorus from the conventional oil was probably responsible for the difference. However, a test run with low-lead (0.5 Pb g/gal, 0.004 P g/gal) gasoline and “clean” oil caused much greater catalyst activity deterioration than either of the tests with unleaded gasoline.