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Effects of potassium loading and thermal aging on K/Pt/Al2O3 high-temperature lean NOx trap catalysts

Paper ID Volume ID Publish Year Pages File Format Full-Text
54719 47023 2014 9 PDF Available
Title
Effects of potassium loading and thermal aging on K/Pt/Al2O3 high-temperature lean NOx trap catalysts
Abstract

•In-situ XRD results indicate that KNO3 is extremely mobile on the Al2O3 surface.•Low K levels yields less stable surface KNO3 while excess blocks surface Pt sites.•KNO3 experiences very complex phase transformations upon heating.•Thermal aging yields large metallic Pt particles and finely dispersed oxidized Pt.•Oxidized Pt usefully interacts with K species allowing facile re-dispersion.

The effects of K loading and thermal aging on the structural properties and high temperature performance of Pt/K/Al2O3 lean NOx trap (LNT) catalysts were investigated using in situ X-ray diffraction (XRD), temperature-programmed decomposition/desorption of NOx (NOx-TPD), transmission electron microscopy (TEM), NO oxidation, and NOx storage tests. In situ XRD results demonstrate that KNO3 becomes extremely mobile on the Al2O3 surface, and experiences complex transformations between orthorhombic and rhombohedral structures, accompanied by sintering, melting and thermal decomposition upon heating. NOx storage results show an optimum K loading around 10% for the best performance at high temperatures. At lower K loadings where the majority of KNO3 stays as a surface layer, the strong interaction between KNO3 and Al2O3 promotes KNO3 decomposition and deteriorates high-temperature performance. At K loadings higher than 10%, the performance drop is not caused by NOx diffusion limitations as for the case of barium-based LNTs, but rather from the blocking of Pt sites by K species, which adversely affects NO oxidation. Thermal aging at 800 °C severely deactivates the Pt/K/Al2O3 catalysts due to Pt sintering. However, in the presence of potassium, some Pt remains in a dispersed and oxidized form. These Pt species interact strongly with K and, therefore, do not sinter. After a reduction treatment, these Pt species remain finely dispersed, contributing to a partial recovery of NOx storage performance.

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Keywords
Potassium; NOx storage and reduction; NO oxidation; Thermal aging; Pt catalyst; Sintering
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Effects of potassium loading and thermal aging on K/Pt/Al2O3 high-temperature lean NOx trap catalysts
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Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Today - Volume 231, 1 August 2014, Pages 164–172
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us