Having a high catalytic activity for hydrocarbon combustion, Pd-containing catalysts are commonly used in automotive-engine aftertreatment systems for emissions abatement. Since extended times on stream as well as high temperature, water, and trace sulfur exposure are associated with this application, these catalysts typically experience activity loss due to sintering and sulfur poisoning. Bimetallic Pd/Pt catalyst utilization has increased due to their improved activity and potential resistance to sintering. However, research shows that these bimetallic benefits were not observed in the presence of sulfur. Here, sulfur interactions with bimetallic Pd/Pt/Al2O3 catalysts were characterized. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed desorption (TPD) studies show that SO2 sorption characteristics depend on both precious metal crystallite particle size and Pd:Pt mole ratio. In general, the amount of SO2 adsorbed and later desorbed during TPD decreased with increasing particle size or Pt content in the bimetallic Pd/Pt catalysts. Catalysts with a small particle size or high Pd content tended to have greater activity for oxidizing sulfur species at low temperatures and as a result formed more aluminum sulfate species. These sulfate species were stable and only decomposed at high temperatures. Large particle size or low Pd content catalysts tended to form more low-temperature decomposing and desorbing species, such as molecular SO2 and aluminum surface sulfite. To assess how sulfur exposure impacts catalytic activity, DRIFTS and CH4 combustion studies were conducted with fresh and SO2-treated Pt/Pd mono- and bimetallic catalysts. CO and SO2 DRIFTS studies were used to identify sites impacted by SO2 exposure and evaluate how the Pd:Pt mole ratio influences sulfur surface species formation. In an effort to recover CH4 oxidation performance of SO2-treated catalysts, temperature-programmed regeneration experiments were conducted in various gas environments. The findings show that for bimetallic catalysts with higher Pt content, the temperature-programmed regeneration methods had a greater negative impact on the catalytic activity than the sulfur exposure. Overall, this work provides evidence that sulfur interactions with bimetallic Pd/Pt catalysts vary with precious metal molar composition and over the life of the catalyst.

Sulfur interactions with bimetallic Pd/Pt catalysts

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.