Sulfur poisoning and regeneration of bimetallic Pd-Pt methane oxidation catalysts

The influence of SO2 on the total oxidation of methane over Pd-Pt/Al2O3 and Pd-Pt/La2O3-Y2O3-CeO2-ZrO2 catalysts under typical lean burn gas engine conditions was investigated and compared to engine-aged samples. Differences in deactivation rate and in stability of poisoning species were identified at 400 degrees C and 450 degrees C. A positive effect of higher pressure, related to pre-turbo positioning of the catalyst, on the activity was observed. Realistic pre- turbo conditions including high temperature (600 degrees C) and high pressure (4 bar) were found to favor methane conversion but even under these conditions some deactivation took place due to formation of strongly bound sulfur species and probably due to sintering of the noble metal particles. Engine aged samples were obtained after 60 h on an SO2 containing exhaust-gas of a lean-burn gas engine at 450 degrees C. Laboratory tests with these samples revealed high accumulation of sulfur species with a higher concentration at the catalyst inlet than the outlet. Different regeneration strategies for SO2 poisoned catalysts were successfully applied. Rich conditions led to very pronounced regeneration at 550 degrees C of a poisoned Pd-Pt/La2O3-Y2O3-CeO2-ZrO2 catalyst. Short rich pulses were even able to regenerate the catalyst during operation at the gas engine. Periodic switches to lambda < 1 finally stabilized a methane conversion above 65% for several hours demonstrating the good transferability of lab test data to the engine tests. (C) 2017 Elsevier B.V. All rights reserved.