(610f) Characteristics of Pt-BaO/CeO2 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 [1]. 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.

Cerium oxide is widely used as an important component of the generally used 3-way catalysts due to its excellent oxygen storage/release properties, as well as its role in maintaining precious metal dispersion. It has also been used as a support or a promoter in LNT catalysts [2]. The main known advantage of using ceria in LNT catalysts is stemming from its role in the generation of hydrogen through water-gas shift and/or hydrocarbon steam reforming reaction, which provides a more efficient route of desulfation.

In the presentation, we will report on superior intrinsic NOx uptake of Pt-BaO/CeO2 sample over Pt-BaO/Al2O3 in the entire temperature range studied. It was also found that this ceria-supported sample showed better sulfur resistance than the latter after exposing it to the same amount of SO2. Moreover, the former exhibited a remarkably high resistance against Pt sintering during high temperature reductive desulfation. In addition, the desulfation of pre-sulfated Pt-BaO/CeO2 lean NOx trap catalysts was investigated by H2 TPRX (temperature programmed reaction), in-situ TR-XRD (time-resolved X-ray diffraction) and in-situ S K-edge XANES (X-ray absorption near edge spectroscopy) techniques. Compared with the Pt-BaO/Al2O3, the reductive treatment in H2 for CeO2 supported sample up to 1073 K hardly removes any sulfur species.

[1] W.S. Epling, L.E. Campbell, A. Yezerets, N.W. Currier, J.E. Parks II, Cat. Rev.-Sci. Eng. 2004, 46, 163.

[2] Casapu, M.; Grunwaldt, J. D.; Maciejewski, M.; Wittrock, M.; Gobel, U.; Baiker, A. Applied Catalysis B-Environmental 2006, 63, 232.