Influence of ceria on the NOx storage/reduction behavior of lean NOx trap catalysts

Yaying Ji, Jae Soon Choi, Todd J. Toops, Mark Crocker, Mojghan Naseri

Research output: Contribution to journalArticlepeer-review

72 Scopus citations

Abstract

The effect of La2O3-stabilized ceria incorporation on the functioning of fully formulated lean NOx trap catalysts was investigated. Monolithic catalysts were prepared, corresponding to loadings of 0, 50 and 100 g CeO2/L, together with a catalyst containing 100 g/L of ceria-zirconia (Ce0.7Zr0.3O2). Loadings of the other main components (Pt, Rh and BaO) were held constant. Catalyst evaluation was performed on a bench flow reactor under simulated diesel exhaust conditions, employing NOx storage/reduction cycles. NOx storage efficiency in the temperature range 150-350 °C was observed to increase with ceria loading, resulting in higher NOx conversion levels. At 150 °C, high rich phase NOx slip was observed for all of the catalysts, resulting from an imbalance in the rates of nitrate decomposition and NOx reduction. Optimal NOx conversion was obtained in the range 250-350 °C for all the catalysts, while at 450 °C high rich phase NOx slip from the most highly loaded ceria-containing catalyst resulted in lower NOx conversion than for the ceria-free formulation. N2O was the major NOx reduction product at 150 °C over all of the catalysts, although low NOx conversion levels limited the N2O yield. At higher temperatures N2 was the main product of NOx reduction, although NH3 formation was also observed. Selectivity to NH3 decreased with increasing ceria loading, indicating that NH3 is consumed by reaction with stored oxygen in the rear of the catalyst.

Original languageEnglish
Pages (from-to)146-155
Number of pages10
JournalCatalysis Today
Volume136
Issue number1-2
DOIs
StatePublished - Jul 15 2008

Bibliographical note

Funding Information:
The authors thank Eduardo Santillan-Jimenez for TEM measurements, and Dr. Shazam Williams (DCL International Inc.) for helpful discussions. 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.

Keywords

  • Ceria
  • LNT
  • NO
  • Reduction
  • Storage

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry

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