Due to their high catalytic activity for the complete CH4 oxidation reaction, there has been a substantial amount of research published on noble metal-based catalysts for natural gas engine emissions abatement. In terms of sulfur poisoning/deactivation, studies have shown that Pd-based catalysts are quite susceptible to sulfur poisoning and experience an abrupt decline in activity upon exposure whereas Pt-based catalysts only display gradual activity loss. Bimetallic Pt/Pd catalysts are attractive due to their potential resistance to sintering and improved activity. However, researchers found that these bimetallic benefits only held true in the absence of sulfur. Due to the high temperatures required for sulfate decomposition/sulfur regeneration, sintering and its potential to induce activity loss are a concern. Here, CH4 combustion studies were conducted with Pt/Pd mono- and bimetallic, γ-Al2O3 supported catalysts before and after exposure to SO2. CO and SO2 DRIFTS studies were used to identify sites impacted by SO2 exposure and evaluate the Pd:Pt mole ratio effect on sulfur surface species formation. Temperature-programmed oxidation, desorption, and reduction as models for possible catalyst regeneration were evaluated in terms of sulfur release and CH4 oxidation performance recovery. At low temperatures, Pd-rich bimetallic catalysts tended to form sulfate species, which could only be removed at high temperatures in an effort to recover catalytic activity. In contrast, catalysts with higher Pt content were less effective at low-temperature sulfate formation, resulting in molecular SO2 and surface sulfite species inhibiting the CH4 oxidation reaction over a broader temperature range. In general, for the bimetallic samples the effectiveness of SO2 regeneration methods decreased with increasing Pt content. Also, for bimetallic catalysts with higher Pt content, the associated sintering effects from the temperature-programmed regeneration methods were more significant.

Regeneration of bimetallic Pt/Pd methane oxidation catalysts after sulfur exposure

254th National Meeting (2017)

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