(147e) Various Roles of Water In the Regeneration Processes Over the Pt-BaO/Al2O3 Lean NOx Trap Catalysts
The LNT (lean NOx trap) is generally considered as one of the promising solutions for the exhaust control of gasoline lean burn and diesel engine in order to meet future stringent emission regulations. In the LNT technology, an active (alkali and/or alkaline earth) oxide material takes up NOx under lean engine operation conditions and stores them as nitrates . In a brief rich cycle these nitrates are released form the active oxide catalyst component, and reduced to N2 on the precious metal component of the catalyst. SO2, which is inevitably included in the diesel engine emissions, acts as a poisoning element by transforming the barium species into the more stable barium sulfates, which eventually leads to the decrease in the NOx storage. Therefore, the regeneration step by applying reductants (e.g. H2) at high temperature enough to convert barium sulphate into BaO/BaCO3 is required to desulfate the catalyst. The high temperature treatment, however, induced the deactivation of the catalyst, such as Pt sintering and BaAl2O4 formation.
The roles of water, which always exists in the emitted gases, in the LNT catalyst include the positive and negative aspects during regeneration process. While it is known that the addition of H2O to H2 promotes desulfation, it is also found that the significant and irreversible Pt sintering arising from the presence of water is unavoidable. In this presentation, we describe the various roles of water on the regeneration process of the LNT catalyst. Then we introduce a new method that minimizes irreversible Pt sintering during the regeneration of sulfated Pt/BaO/Al2O3 lean NOx trap (LNT) catalysts.
 W.S. Epling, L.E. Campbell, A. Yezerets, N.W. Currier, J.E. Parks II, Cat. Rev.-Sci. Eng. 2004 46, 163.