Sulfur desorption characteristics as a function of Pd:Pt mole ratio for low-temperature methane combustion bimetallic Pd/Pt catalysts

Monique Shauntá  Wilburn, University of Virginia; University of Houston

Sulfur desorption characteristics as a function of Pd:Pt mole ratio for low-temperature CH4 combustion bimetallic Pd/Pt catalysts

Monique Shauntá Wilburn and William S. Epling

Department of Chemical and Biomolecular Engineering

University of Houston; Chemical Engineering Department

University of Virginia

Typical natural gas engine exhaust will contain uncombusted CH4 that will need to be oxidized. Due to their high catalytic activity for the complete oxidation of methane, Pd-based catalysts are the typical choice for such oxidation systems. These catalysts can be exposed to trace amounts of sulfur compounds present in the engine exhaust. Due to Pd’s sensitivity to sulfur[1], any exposure to sulfur can lead to degradation in activity. The focus of this study was to identify how sulfur interacts with Pd-based oxidation catalysts, as well as bimetallic Pd/Pt systems because Pt has been shown to have some resistance to sulfur poisoning[1].

Temperature programmed desorption and oxidation (TPD and TPO) were used to probe these interactions, as was DRIFTS to characterize surface species. The reactor experimental results show that the temperature at which sulfur species are desorbed from sulfur-treated, mono and bimetallic Pd and Pt/Al2O3 catalysts is strongly dependent on the Pd-to-Pt mole ratio of the catalyst. During surface characterization studies, it was found that catalysts with a higher Pd content tended to have greater activity for oxidizing sulfur species at low temperatures and as a result formed more thermally stable sulfur species such as sulfites and sulfates. In general, the amount of SO2 adsorbed and later desorbed during TPD as well as the activity for oxidizing sulfur species at low temperatures decreased with increasing Pt content in the bimetallic Pd/Pt catalysts. This work provides evidence that the sulfur sorption characteristics, as well as the potential for sulfur decay, for mono- and bimetallic Pd/Pt catalysts are heavily influenced by the Pd:Pt mole ratio.

[1]: M.S. Wilburn, W.S. Epling / Applied Catalysis B: Environmental 206 2017 p. 589-598