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Reactivity of NH3 over (Fe)/H-ZSM-5 zeolite: Studies of temperature-programmed and steady-state reactions

Paper ID Volume ID Publish Year Pages File Format Full-Text
55714 47063 2011 10 PDF Available
Title
Reactivity of NH3 over (Fe)/H-ZSM-5 zeolite: Studies of temperature-programmed and steady-state reactions
Abstract

The NH3 reactivity was investigated over H-ZSM-5 and iron oxide deposited H-ZSM-5 by temperature-programmed surface interaction (TPSI) of adsorbed NH3 (NH3(ad)) with NO, O2, and “NO + O2”, and by steady-state dynamic reactions consisting of “NH3 + NO”, “NH3 + O2”, and “NH3 + NO + O2” systems. It was found that O2 primarily interacts with NH3(ad) on Brønsted acid sites. NO mainly interacts with NH3(ad) on Lewis acid sites, whereas its interaction with NH3(ad) on Brønsted acid sites results in N2O formation. TPSI provides direct evidence of the “fast” reaction of NO/NO2 with NH3(ad) on Brønsted acid sites in “NO + O2” environment, where O2 concentration plays a critical role. Iron oxide enhances all interactions, particularly those with NH3(ad) on Brønsted acid sites, as witnessed by both TPSI and steady-state reactions. But, iron oxide does not change the activation energy barrier for NH3 conversion, indicating that both acid sites and iron oxide are essential for NH3 SCR of NOx. As a result, a dual mechanism over Lewis and Brønsted acid sites was proposed.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (188 K)Download as PowerPoint slideHighlights► Temperature-programmed surface interaction (TPSI) was used to study the interactions of adsorbed NH3 with NO, O2, and “NO + O2”. ► NH3 adsorbed on Lewis and Brønsted acid sites interacts primarily with NO and O2, respectively. Dispersed iron oxide accelerates all interaction rates, but does not change the activation energy barrier for steady-state NH3 conversion. ► TPSI provides direct evidence of the “fast” reaction of NO/NO2 with NH3(ad) on Brønsted acid sites in “NO + O2” environment, where O2 concentration plays a critical role.

Keywords
Ammonia; Selective catalytic reduction; NO; NO2; ZSM-5; Acidity; Iron oxide; Adsorption; Release; Temperature programmed surface interaction (TPSI)
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Reactivity of NH3 over (Fe)/H-ZSM-5 zeolite: Studies of temperature-programmed and steady-state reactions
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Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Today - Volume 175, Issue 1, 25 October 2011, Pages 2–11
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