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The FTP HC, CO, and especially NOx emissions of standard Pd Only three way catalysts have been demonstrated to be more sensitive to fuel sulfur content than Pt/Rh, Pd/Rh, and Pt/Pd/Rh catalysts. To understand the interaction between Pd Only three way catalysts and sulfur, a laboratory study was conducted to examine the relationships between washcoat composition, washcoat structure, and catalyst activity under various evaluation sulfur conditions. First, Pd promoters were examined for their ability to increase activity under both low and high sulfur test conditions. Second, an examination of catalyst structure demonstrated that control of the interaction between Pd and the stabilized ceria washcoat component is critical to achieving high catalyst activity under both low and high sulfur test conditions.

With the advent of stricter vehicle emission standards, the improvement of three way catalyst performance and durability remains a pressing issue. A critical consideration in catalyst design is the potential for variations in fuel sulfur levels to have a significant impact on the ability to reach TLEV, LEV, and ULEV emission levels. As a result, a better understanding of the role of PGM composition in the interplay between thermal durability and sulfur tolerance is required. Three way catalysts representative of standard Pd-only, Pd/Rh and Pt/Rh formulations were studied over a variety of aging and evaluation conditions. The parameters investigated included aging temperature, air fuel ratio and sulfur level. Evaluations were performed on a 1994 TLEV vehicle using different sulfur level fuels. The effect of PGM loading was also included within the study.