Microkinetic modeling of lean NOx trap chemistry under reducing conditions

Richard S. Larson, Josh A. Pihl, V. Kalyana Chakravarthy, Todd J. Toops, C. Stuart Daw

Research output: Contribution to journalArticlepeer-review

35 Scopus citations

Abstract

An elementary surface reaction mechanism describing the chemistry on the precious metal sites of a lean NOx trap is developed. Kinetic parameters for all of the reactions are found by fitting reactor simulations to an extensive experimental database. Each experiment involves the steady flow of a reactant mixture through a monolith core sample under conditions designed to minimize NOx storage; in each case, the temperature is slowly ramped over a wide range in order to provide a large amount of data. A reaction mechanism involving 28 elementary steps is able to reproduce the results for 21 separate experimental runs quite well. The thermodynamic consistency of the mechanism is assured through the imposition of constraints on a well-defined subset of the rate parameters. It is found that the mechanism can occasionally lead to multiple steady-state behavior due to the existence of parallel reduction pathways. DRIFTS experiments corroborate some of the key mechanistic steps.

Original languageEnglish
Pages (from-to)104-120
Number of pages17
JournalCatalysis Today
Volume136
Issue number1-2
DOIs
StatePublished - Jul 15 2008

Funding

The authors thank Dr. Andrew Lutz of Sandia for developing the Chemkin-based transient plug flow reactor code, Dr. Joshua Griffin of Sandia for assistance in applying APPSPACK to the optimization problem solved here, and Dr. Louis Powell of the Oak Ridge Y-12 National Security Complex for use of the MIDAC FTIR spectrometer. The efforts at Oak Ridge were sponsored by the US Department of Energy (DOE) under contract number DE-AC05-00OR22725 with the Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC. The contribution of Josh A. Pihl was supported in part by an appointment to the ORNL Postgraduate Research Associates Program, administered jointly by the Oak Ridge Institute for Science and Education and ORNL. Research at both Oak Ridge and Sandia was sponsored specifically by Gurpreet Singh and Ken Howden of the US DOE's Office of FreedomCAR and Vehicle Technologies. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US DOE's National Nuclear Security Administration under contract number DE-AC04-94AL85000.

Keywords

  • Ammonia formation
  • Lean NOx trap (LNT)
  • NOx storage reduction (NSR)
  • Regeneration

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