A Summary of Sulfur Deactivation, Desorption, and Regeneration Characteristics of Mono- and Bimetallic Pd-Pt Methane Oxidation Catalysts: Pd:Pt Mole Ratio and Particle Size Dependency

Abstract

Complete CH4 oxidation (combustion) studies were conducted with fresh (small particle size) and sintered (large particle size) Pd/Pt bimetallic, Al2O3 supported catalysts before and after exposure to SO2. Temperature-programmed oxidation, reduction, and desorption as models for potential catalyst regeneration were evaluated in terms of CH4 oxidation performance recovery. Temperature-programmed desorption studies show that Pd/Pt catalysts with little Pt substitution or small particle sizes tended to form aluminum sulfate species at low temperatures. Aluminum sulfate species thermally decompose at high temperatures, thus requiring high-temperature conditions to recover catalytic activity lost due to sulfate formation. In contrast, Pd/Pt catalysts with higher Pt content or larger particle sizes were less effective at sulfate formation at low temperatures. In this case, low-temperature decomposing sulfur species inhibited the CH4 oxidation reaction over a broader temperature range. For Pd/Pt catalysts with high Pt content and small particle size, the associated sintering effects from the temperature-programmed reduction and desorption methods were more detrimental to catalytic activity than the sulfur exposure used in this study. Sintering bimetallic samples increased the particle size and provided some resistance to further sintering. Sintered, SO2-exposed Pd/Pt catalysts with low Pt content recovered all activity via temperature-programmed desorption regeneration, whereas those with high Pt content catalysts only recovered some activity. Regardless of particle size, the effectiveness of the temperature-programmed desorption regeneration method decreased with increasing Pt content.