Sulfur deactivation and regeneration of mono- and bimetallic Pd-Pt methane oxidation catalysts

- CO/SO2 DRIFTS linked sulfur-covered active sites to CH4 oxidation inhibition.
- Sulfur inhibited CH4 oxidation over a broad range of catalysts containing Pd.
- Sulfate migration reduced the temperature span of CH4 oxidation sulfur inhibition.
- Sulfur regeneration recovered activity for SO2-treated catalysts with >90% Pd.
- SO2-treated catalysts with <90% Pd decayed and sintered during sulfur regeneration.

Complete CH4 oxidation (combustion) studies were conducted with Pt/Pd mono- and bimetallic, γ-Al2O3 supported catalysts before and after exposure to SO2. CO and SO2 adsorption DRIFTS studies were used to identify sites that adsorbed SO2 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 catalysts, i.e. with little to no Pt substitution, tended to form aluminum sulfate species, which could be removed at high temperatures to recover catalytic activity. In contrast, catalysts with higher Pt content were less effective at sulfate formation at low temperatures. In this case, molecular SO2 and aluminum surface sulfite species inhibited 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.

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