Advances in Pd Containing Three Way Catalyst Activity

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. Third, the stabilized ceria washcoat material was improved resulting in a formulation, which was not only more active under high sulfur test conditions, but recovered activity more quickly when sulfur was removed from the test reaction mixture.