Application of spaciMS to the study of ammonia formation in lean NO x trap catalysts

Vencon Easterling, Yaying Ji, Mark Crocker, Mark Dearth, Robert W. McCabe

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


SpaciMS was employed to understand the factors influencing the selectivity of NO x reduction in two fully formulated LNT catalysts, both degreened and thermally aged. Both catalysts contained Pt, Rh, BaO and Al 2O 3, while one of them also contained La-stabilized CeO 2. The amount of reductant required to fully regenerate each catalyst was first determined experimentally based on the OSC of the catalyst and the NO x storage capacity (NSC). In this way a correction was made for the change in catalyst OSC and NSC after aging, thereby eliminating these as factors which could affect catalyst selectivity to NH 3. For both catalysts, aging resulted in an elongation of the NO x storage-reduction (NSR) zone due to a decrease in the concentration of NO x storage sites per unit catalyst length. In addition to decreased lean phase NO x storage efficiency, stretching of the NSR zone affected catalyst regeneration. Three main effects were identified, the first being an increase of the NO x "puff" that appeared during the onset of the rich front as it traversed the catalyst. Spatially, NO x release tracked the NSR zone, with the result that the NO x concentration peaked closer to the rear of the aged catalysts. Hence the probability that NO x could re-adsorb downstream of the reduction front and subsequently undergo reduction by NH 3 (formed in the reduction front) was diminished, resulting in higher rich phase NO x slip. Second, the stretching of the NSR zone resulted in increased selectivity to NH 3 due to the fact that less catalyst (corresponding to the OSC-only zone downstream of the NSR zone) was available to consume NH 3 by either the NH 3-NO x SCR reaction or the NH 3-O 2 reaction. Third, the loss of OSC and NO x storage sites, along with the decreased rate of NO x diffusion to Pt/Rh sites (as a result of Pt/Rh-Ba phase segregation), led to an increase in the rate of propagation of the reductant front after aging. This in turn resulted in increased H 2:NO x ratios at the Pt/Rh sites and consequently increased selectivity to NH 3.

Original languageEnglish
Pages (from-to)339-350
Number of pages12
JournalApplied Catalysis B: Environmental
StatePublished - Jul 23 2012

Bibliographical note

Funding Information:
This project was funded by the U.S. Department of Energy (DOE) under award No. DE-EE0000205 . The authors also wish to thank Ford Motor Co. for additional funding, provided under the auspices of the Ford University Research Program.


  • Aging
  • Ammonia
  • Lean NO trap
  • NO adsorber catalyst
  • Reduction
  • SpaciMS
  • Storage

ASJC Scopus subject areas

  • Catalysis
  • General Environmental Science
  • Process Chemistry and Technology


Dive into the research topics of 'Application of spaciMS to the study of ammonia formation in lean NO x trap catalysts'. Together they form a unique fingerprint.

Cite this