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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.

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.

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.