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The effect gas composition during thermal aging on the dispersion and NO oxidation activity over Pt/Al2O3 catalysts

Paper ID Volume ID Publish Year Pages File Format Full-Text
46034 46428 2013 11 PDF Available
Title
The effect gas composition during thermal aging on the dispersion and NO oxidation activity over Pt/Al2O3 catalysts
Abstract

The aging of a model 1 wt.% Pt/Al2O3 catalyst was performed stepwise under different reactive atmosphere to study the evolution of metal dispersion and NO oxidation activity. After each aging step the dispersion was evaluated by CO chemisorptions and the activity of the catalyst for NO oxidation was measured using 500 ppm NO and 8% O2 diluted in Ar. After a degreening step at 500 °C, aging was performed at 600, 700, 800 and 900 °C. Five wash-coated cordierite monoliths were aged in Ar, 10% O2, 1% H2, 30 ppm SO2 and 30 ppm SO2 + 10% O2, respectively. The general trend showed a linear decrease in dispersion when increasing the aging temperature for the lower aging temperatures and for the highest ones the dispersion levels off. When the platinum dispersion decreased the NO oxidation activity increased, due to that the reaction is structure sensitive. H2 seemed to hinder sintering at low aging temperature. Interestingly, after aging in 10% oxygen at 600 °C the NO oxidation activity was significantly higher compared to the Ar aged sample, although the dispersions were similar. Aging in oxygen at higher temperatures resulted in a decrease of dispersion and a slightly decreasing NO oxidation activity. Moreover lower dispersion limit was reached with oxygen aging. Aging in SO2 provoked a severe dispersion drop at low aging temperature meanwhile the activity increased only moderately. However, activity kept increasing with further treatments at higher temperature. The combination of O2 and SO2 enabled to decrease rapidly the dispersion and to greatly enhance the catalytic NO oxidation activity after the first aging step at only 600 °C. The best overall conversion was obtained for the catalyst treated with this mixture after aging at 800 °C. A 22-h aging at 250 °C in a mixture containing 500 ppm NO, 10% O2 and 30 ppm SO2 led to a significant decrease of Pt dispersion, which shows the ability of SO2 to promote platinum sintering already 250 °C. The low temperature sintering was confirmed with STEM measurements. Several larger particles were observed, but also many small particles remained. Thus the SO2 + O2 induced low temperature sintering results in a large variation of particle sizes. This treatment resulted in an increase of the maximum NO conversion (after reduction of the sample) from 45% to 76%. The different aging experiments show that it is beneficial to add SO2 during aging and the reason is the increased particle size, but also a clear chemical effect was observed.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Sintering is influenced by aging atmosphere. ► Larger Pt particles have higher activity for NO oxidation. ► Similar dispersion results in different activity, depending on aging atmosphere. ► SO2 promotes platinum sintering, even at 250 °C. ► Similar activities can be obtained after different treatments involving SO2.

Keywords
NO oxidation; NO2; Pt/Al2O3; DOC; Diesel oxidation catalyst; Aging; Deactivation; SO2; Flow reactor; TEM
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The effect gas composition during thermal aging on the dispersion and NO oxidation activity over Pt/Al2O3 catalysts
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 129, 17 January 2013, Pages 517–527
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