(610g) Types, Spatial Distribution, Stability, and Performance Impact of Sulfur On a Lean NOx Trap Catalyst

Authors: 
Choi, J., Oak Ridge National Laboratory
Ottinger, N. A., Oak Ridge National Laboratory
Toops, T. J., Fuels, Engines and Emissions Research Center, Oak Ridge National Laboratory
Pihl, J. A., Oak Ridge National Laboratory
Lance, M. J., Oak Ridge National Laboratory
Finney, C. E. A., Oak Ridge National Laboratory
Daw, C. S., Oak Ridge National Laboratory


Fundamental understanding of mechanisms associated with sulfation/desulfation of lean NOx trap (LNT) catalysts can enable more durable and energy-efficient aftertreatment systems. Knowledge on the types and spatial distribution of surface sulfur species and how their formation and removal affects the NOx storage/reduction performance is of particular relevance to the development of real LNTs. In the present study, we performed spatially resolved characterization and reactor evaluation of a Ba-based commercial catalyst during stepwise sulfation and desulfation. Different catalyst functions, such as NOx conversion, NH3 selectivity, and oxygen storage capacity, were monitored to assess the impact of different sulfur species. In addition to Ba, several other oxide components present in the washcoat were found to form sulfates with varying stability. Barium showed highest affinity for sulfur leading to plug-like sulfation while ceria-zirconia support led to axially more dispersed sulfation. The axial progression of sulfation of practically relevant NOx storage sites was significantly delayed by sulfur storage on other components acting as ?sulfur trap?. Even though only a portion of sulfur was associated with relevant NOx storage sites, complete removal of sulfur was necessary to fully recover the catalyst performance. In fact, incomplete desulfation could release sulfur from upstream support and form stable sulfates with downstream NOx storage sites. In this presentation, we will propose a conceptual model on how changes in spatial sulfur distribution affect NOx conversion and NH3 selectivity.