Using model powder catalysts and fully formulated monolithic lean NO x trap (LNT) catalysts, the effect of ceria on LNT desulfation behavior was investigated. TPR experiments performed on the model catalysts showed that each of the oxide phases present (BaO, CeO2, and Al 2O3) is able to store sulfur and that they possess distinct behavior in terms of the temperatures at which desulfation occurs. For a Pt/BaO/Al2O3 catalyst, addition of ceria was found to reduce the degree of sulfur accumulation on the BaO phase, particularly at high sulfur loadings, by contributing to sulfur capture. The importance of maintaining the Pt and Ba phases in close proximity for efficient LNT desulfation was also demonstrated; physically separating the Pt and Ba sites resulted in a shift of the desulfation temperature of the surface BaSO 4 by 20-40 °C towards higher temperature, i.e., towards the position characteristic of bulk BaSO4. From the monolith studies, it was found that relative to a sample containing no ceria, samples containing La-stabilized CeO2 or CeO2-ZrO2 showed a greater resistance to deactivation during sulfation (as reflected by the NO x storage efficiency), and required lower temperatures to restore the NOx storage efficiency to its pre-sulfation value. In addition to the ability of ceria to store sulfur and release it at relatively low temperatures under reducing conditions, these findings can be attributed to the high water-gas shift activity displayed Pt/CeO2, which result in increased intra-catalyst concentrations of H2 under rich conditions. The results also showed that precious metal loadings can significantly impact desulfation efficiency and that both high Rh and Pt loadings are beneficial for catalyst desulfation.
|Number of pages||9|
|State||Published - Jun 19 2010|
Bibliographical noteFunding Information:
This publication was prepared with the support of the U.S. Department of Energy, under Award No. DE-FC26-05NT42631. However, any opinions, findings, conclusions, or recommendations expressed herein are those of the authors and do not necessarily reflect the views of the DOE.
- Lean NO trap
- NO storage catalyst
ASJC Scopus subject areas
- Chemistry (all)