Regeneration of Sulfur Poisoned Pd–Pt/CeO2–ZrO2–Y2O3–La2O3 and Pd–Pt/Al2O3 Methane Oxidation Catalysts

Abstract

The poisoning of Pd–Pt/Al2O3 and Pd–Pt/CeO2–ZrO2–Y2O3–La2O3 methane oxidation catalysts by SO2 was studied under conditions typical for lean burn gas engines. Regeneration of sulfur-poisoned catalysts was achieved by applying rich conditions at 500 and 550 °C. The presence of NOx resulted in a slower deactivation rate. While Pd–Pt/CeO2–ZrO2–Y2O3–La2O3 showed a superior catalytic activity, durability and regeneration ability compared to Pd–Pt/Al2O3 under NOx-free reaction conditions, its reactivation by a rich treatment was strongly inhibited if NOx was present during the aging and regeneration process. Operando X-ray absorption spectroscopy (XAS) was used to monitor the evolution of Pd and Pt during poisoning and regeneration. The studies show the formation of PdS and metallic Pd during reactivation of Pd–Pt/Al2O3, followed by transition to PdO after changing to lean reaction gas mixture. On the other hand, Pd species supported on CeO2–ZrO2–Y2O3–La2O3 could not be reduced under rich conditions and no regeneration occurred.