473866 The Effects of Catalyst Aging on Sulfur Degradation over Fully Formulated Lean NOx Trap Catalysts

Monday, November 14, 2016: 5:00 PM
Franciscan A (Hilton San Francisco Union Square)
Travis Wentworth, Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden, Louise Olsson, Chemical Engineering, Chalmers University of Technology, Göteborg, Sweden and Marie Stenfeldt, Volvo Cars, Gothenburg, Sweden

Lean NOx trap catalysts are subjected to both hydrothermal aging and sulfur deactivation in real world environments.  Studies have shown that hydrothermal aging can increase noble metal particle size and subsequently reduce the ability of the catalyst to oxidize NO.  This results in reduced NOx storage, and ultimately reduced NOx conversion.  Furthermore, literature has observed that the degree of sulfur deactivation varies with changes in catalysts parameters such as barium loading1, this is an indicator that changing catalyst morphology via another mechanism such as hydrothermal aging could also change the degree to which the catalyst is sulfated.  Because, both catalyst aging and deactivation due to sulfur occur in real world environments it is important to understand the effects of these two mechanism in conjunction.

In the following study a model Pt/Ba/CeZr/Al2O3 catalyst was subjected to hydrothermal aging.  The hydrothermally aged catalysts were subjected to 1 hour sulfation in a lean gas environment.  It was found that while hydrothermal aging initially resulted in variations in, NOx uptake, total NOx conversion, as well as ammonia and N2O production, after sulfation, the cycling trends changed, most dramatically during the rich phase.  Figure 1 shows that prior to sulfation ammonia production upon rich gas introduction is greatest for the catalyst aged at 700°C and the least for the catalyst aged at 600°C.  After sulfation, ammonia production for the 600°C and 700°C aged catalysts are increased substantially, while the 800°C catalyst shows only a small increase in ammonia production and as a result has the lowest total ammonia production.  The effects of hydrothermal aging and sulfation have also been characterized by BET, CO-Chemisorption, XRD and TEM and used to identify the dominant factors that have resulted in the observed deviations upon lean/rich cycling.

Figure 1 shows the variation in ammonia production after Lean/rich cycling at 300°C after presulfation (left) and post sulfation (right)

Acknowledgements

This project has received funding from the European Union’s Horizon 2020 research and

innovation programme under grant agreement No 636380.

1.    Kim, D. H.; Szanyi, J.; Kwak, J. H.; Szailer, T.; Hanson, J.; Wang, C. M.; Peden, C. H. F., Effect of Barium Loading on the Desulfation of Pt-BaO/Al2O3 Studied by H2 TPRX, TEM, Sulfur K-edge XANES, and in Situ TR-XRD. The Journal of Physical Chemistry B 2006, 110 (21), 10441-10448.

 


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