(216h) The Effects of Catalyst Aging on Sulfur Degradation over Fully Formulated Lean NOx Trap Catalysts

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 NO_x 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.