Roles of C3H6 in NH3 generation and NOx reduction over a Cu-chabazite SCR catalyst under lean/rich cycling conditions

Mi Young Kim, Jae Soon Choi, Mark Crocker

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18 Scopus citations


We studied the spatiotemporal profiles of NOx reduction with NH3, C3H6, or NH3 + C 3H6 over a commercial Cu-chabazite SCR catalyst (washcoated honeycomb monolith) to better understand the effects of C 3H6 on NOx reduction under fast lean/rich cycling conditions relevant to coupled LNT-SCR catalysts. NOx reduction by NH3 was very effective with total NH3 consumption within the first quarter of the catalyst at all temperatures. By contrast, NOx reduction by C3H6 was more gradual along the catalyst length and sensitive to temperature with maximum performance obtained at 300-400 °C. Temperature-programmed desorption performed after cycling experiments with C3H6 evidenced the presence of NH3 and/or NH3-precursor intermediates on the surface. These surface species were formed as a result of reactions between NOx and C3H6 during the rich as well as lean phases, but started to be used for NOx reduction only when all the stored hydrocarbons were depleted. When fed together, the contributions of C3H6 and NH3 to the cycle-averaged NO x conversion were essentially additive. However, temporally resolving N2 formation using isotopically-labeled NO and a mass spectrometer revealed that C3H6 actually inhibited reactions between NOx and feed NH3 until well into the subsequent lean phase, i.e., until the stored hydrocarbons were depleted. This study highlights the importance of controlling lean/rich cycling time partitioning to alleviate the impact of the inhibiting effect of C3H6 on NH 3 chemistry and achieve the maximum NOx reduction possible over the SCR catalyst in coupled LNT-SCR systems.

Original languageEnglish
Pages (from-to)90-98
Number of pages9
JournalCatalysis Today
StatePublished - Aug 1 2014

Bibliographical note

Funding Information:
This project was funded by the U.S. Department of Energy (DOE) under award No. ( DE-EE0000205 . The authors thank BASF for providing the catalyst used in this study, and Drs. William P. Partridge and Todd J. Toops at Oak Ridge National Laboratory for useful discussions.


  • Coupled LNT-SCR
  • LNT
  • SCR
  • Selective catalytic reduction

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry


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