Influence of reductant on the regeneration of SO2-poisoned Pt/Ba/Al2O3 NOx storage and reduction catalyst

A 10% Ba/Al2O3 in the presence and absence of 1% Pt was exposed to SO2 at 673 K either in air or in nitrogen, and the ability to recover the NOx storage capacity was compared after exposure to H-2, CO, or C3H6 at 673 K. Exposure to SO2 led to adsorbed sulfite, surface aluminum sulfate, and bulk and surface barium sulfate formation, all of which reduced the NOx storage capacity of the catalyst. The presence of Pt was required for bulk barium sulfate formation. A surface aluminum sulfate was formed from surface sulfite species to a limiting extent at 673 K but this was enhanced by heating in air to higher temperatures and was thermally stable up to 873 K. In the case of the Pt-containing catalyst, hydrogen at 673 K was able to completely reverse the detrimental effect Of SO2 exposure whereas H-2 exposure to SO2-treated Pt-free catalyst was detrimental in terms of recovered NOx storage capacity. The presence of oxygen in the feed stream during the rich regeneration period was significant as this allowed formation of water (and CO2) which plays an important role in the regeneration process. (C) 2004 Elsevier Inc. All rights reserved.