Abstract
We report observations of the nature and spatial distribution of sulfur species on a sulfated Ba-based commercial lean NOx trap (LNT) catalyst. The monolithic catalyst was sulfated in a bench flow reactor during 60/5-s NOx-storage/reduction cycling to achieve a total sulfur loading of 3.4 g L-1 of catalyst. Washcoat composition, structure and sulfur distribution were analyzed with electron probe microanalysis, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction. The most significant washcoat elements of catalytic relevance were Pt, Pd, Rh, Ba, Ce, Zr, Mg, Al, and these were present mainly in four distinct domains: (i) Mg/Al mixed oxide with Pt, Ce; (ii) Al oxide with Rh, Pd; (iii) Ce/Zr mixed oxide with Pt, Pd, Ba (high Ba content); (iv) Ce/Zr mixed oxide with Pt, Pd, Ba (low Ba content). Sulfur was present in the form of sulfates that decreased in concentration along the LNT axis from front to back. Barium showed the highest sulfur affinity leading to a plug-like axial progression of its sulfation. The sulfation of Al, Mg/Al, and Ce/Zr oxides was less vigorous with a more axially dispersed and less penetrating front.
Original language | English |
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Pages (from-to) | 354-361 |
Number of pages | 8 |
Journal | Catalysis Today |
Volume | 151 |
Issue number | 3-4 |
DOIs | |
State | Published - Jun 19 2010 |
Funding
This research was sponsored by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program, with Ken Howden and Gurpreet Singh as the Program Managers. We thank Dr. Owen Bailey at Umicore for assistance in obtaining the commercial LNT catalyst used in this study. The authors are also grateful to colleagues at ORNL for useful discussions and experimental help, in particular Dr. Harry Meyer for the XPS and Mr. Nathan Ottinger for the powder-sample TPR measurements. Notice: This submission was sponsored by a contractor of the United States Government under contract DE-AC05-00OR22725 with the United States Department of Energy. The United States Government retains, and the publisher, by accepting this submission for publication, acknowledges that the United States Government retains, a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this submission, or allow others to do so, for United States Government purposes.
Funders | Funder number |
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U.S. Department of Energy | |
Office of Energy Efficiency and Renewable Energy |
Keywords
- Barium
- Lean NO trap
- NO storage/reduction
- Oxygen storage capacity
- Spatial distribution
- Sulfation