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On the mechanism of the SCR reaction on Fe/HBEA zeolite

Paper ID Volume ID Publish Year Pages File Format Full-Text
47363 46469 2009 9 PDF Available
Title
On the mechanism of the SCR reaction on Fe/HBEA zeolite
Abstract

The mechanism of the so-called standard SCR reaction on an efficient HBEA zeolite catalyst modified with 0.25 wt.% Fe (0.25Fe/HBEA) was elucidated. The studies were systematically performed by using DRIFTS, TPD, XANES and kinetic studies. SCR kinetics were examined between 175 and 275 °C employing a gradient-free loop reactor. DRIFTS and NOx-TPD showed formation of Fe3+-NO species as well as their reaction with NH3. But, only minor adsorption and conversion of NOx on the zeolite substrate occurred. On the contrary, DRIFTS and NH3-TPD showed mainly adsorption of NH3 on the zeolite, whereas XANES and kinetic examinations indicated NH3 adsorption on the Fe3+ sites as well. Moreover, the XANES studies evidenced deNOx on the iron component which is considered to be the major pathway in standard SCR. From our experimental investigations we suggest a dual site mechanism implying the adsorption and reaction of NO and NH3 on neighbouring Fe3+ sites. The uptake of NH3 results in partial reduction of Fe3+ sites which are finally recycled by O2. However, some contribution from a single site mechanism cannot be ruled out completely.Numerical modelling of the NH3-TPD pattern provides kinetic parameters of the adsorption and desorption of NH3 on 0.25Fe/HBEA differentiating the specific adsorption sites of the substrate. As a result, the uptake and release of NH3 on the zeolite is found to be much faster than that of SCR. In connection with a previous SSITKA study, this comparison suggests that NH3 undergoes several adsorption/desorption cycles on the substrate before adsorbing and reacting on the Fe3+ sites.

Keywords
SCR; Mechanism; Fe; BEA zeolite; DRIFTS; XANES; TPD; Kinetics; Numerical modelling
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On the mechanism of the SCR reaction on Fe/HBEA zeolite
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 93, Issues 1–2, 25 November 2009, Pages 185–193
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
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