Date(s) - 11/04/2019
9:35 am - 10:25 am
New Engineering Building – Room 201
William S. Epling, Ph.D.
Professor, Department Chair
University of Virginia
“The Reversible Nature of Sulfur Poisoning of Automotive Emissions Catalysts”
Sulfur dioxide is a common poison in automotive catalysis, and thus the catalyst design must take into account changes with time, or controls developed for catalyst regeneration to mitigate sulfur impacts. The sulfur compounds originate from oil and fuel, are combusted in the engine, which mainly leads to SO2as the sulfur species. But complicating the effects, SO2can be oxidized to SO3over an oxidation catalyst, and in the presence of water this leads to formation of H2SO4. SO2and SO3impacts the various automotive catalysts via different mechanisms, with SO3typically leading to more severe deactivation, at least partly due to its affinity to form H2SO4. In this talk, sulfur poisoning of diesel oxidation catalysts (DOCs) will be highlighted, and will include some discussion of metal-exchanged small pore zeolite selective catalytic reduction (SCR) catalysts.
For the oxidation catalyst, we investigated the impact of different sulfur species on model Pt/Pd/Al2O3oxidation catalysts. SO2oxidation kinetics and adsorption/desorption over these were determined as a function of Pt/Pd ratio and particle size. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results show that the higher Pd content or smaller particles lead to higher extents of surface and bulk sulfate formation relative to higher Pt content or larger particle sizes. Kinetic studies show Pt to be the better SO2oxidation catalyst, with the formation of the sulfates correlated to the differences in activity.
The poisoning effects of the different sulfur species on the SCR reaction over Cu-SAPO-34 and Cu-SSZ13 catalysts were also investigated. Surface species formed during exposure of the catalysts to sulfur, NOxand NH3were characterized with in-situ DRIFTS. Temperature programmed desorption (TPD) was also used to characterize the samples after exposure to sulfur. Results clearly demonstrate that ammonium sulfate forms and tends to be the key low-temperature degradation mode. SO2oxidation and ammonium sulfate formation kinetics were derived and a model predicting both will be presented.
Bill Epling is a Professor in, and Chair of, the Department of Chemical Engineering at the University of Virginia. He joined UVa as Chair in August 2016. Bill Epling received his PhD from the University of Florida in 1997 and his BS from Virginia Tech in 1992, both in Chemical Engineering. Prior to joining academia, he followed a relatively unique path that has given him a broad perspective in the field of environmental catalysis, including catalyst design, manufacture, characterization and application. This was accomplished working across a spectrum of locations; a national lab (Pacific Northwest National Lab), in academia (University of Waterloo, University of Houston and University of Virginia), a catalyst manufacturing company (EmeraChem) and an engine manufacturer (Cummins Inc). His research has most recently focused on diesel and natural gas engine emissions reduction and utilization of natural gas in the production of value-added chemicals.