Understanding Sulfur Poisoning of Bimetallic Pd-Pt Methane Oxidation Catalysts and their Regeneration

Abstract Pd-Pt/Al2O3 and Pd-Pt/CeO2-ZrO2-Y2O3-La2O3 methane oxidation catalysts were investigated under typical lean-burn gas engine conditions with respect to sulfur poisoning and during reactivation, particularly under the most efficient rich conditions. Sulfation of the noble metal and the support material led to pronounced catalyst deactivation. A pronounced transfer of sulfates to the support, particularly alumina, only partially protects the noble metal. In situ X-ray absorption spectroscopy gave insight into the nature and evolution of Pd species during regenerative treatment. Although palladium sulfate that formed during poisoning is decomposed at approximately 200 °C in oxygen-free conditions, support regeneration requires higher temperatures, which result in PdS formation above 400 °C. Despite its high stability under rich conditions, PdS decomposition by oxidation in lean atmosphere leads to the recovery of the activity. In addition, water vapor that is present during the rich regeneration exhibited a beneficial effect on the regeneration with higher catalytic activity after regeneration.