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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.