Abstract
Abstract: The Pd-only catalyst has made a strong comeback in both TLEV and LEV applications. However, it has been found that Pd-only catalysts are susceptible to Pb poisoning, despite the high Pd loading thereon. Several commercially available Pd-only catalysts were evaluated in this study. After aging with leaded fuel, lead deposition was discovered on these catalysts. The lead appears to be front-loaded and concentrated on the surface of washcoat coatings. It can also penetrate into the washcoat. The impact on catalyst performance is mainly on NOx conversion reduction. TEM elemental mapping and XPS results suggest that Pb preferentially associates with Pd. The hypothesis is proposed that Pb deposition onto Pd occurs because the Pd is competing with Pb for sulfur. Rh-containing catalysts may prove to be strong candidates in compensating for the compromised NOx performance observed in Pd-only catalysts aged with leaded fuel.
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