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Design of a “high-efficiency” NH3-SCR reactor for stationary applications. A kinetic study of NH3 oxidation and NH3-SCR over V-based catalysts

Paper ID Volume ID Publish Year Pages File Format Full-Text
45448 46412 2015 11 PDF Available
Title
Design of a “high-efficiency” NH3-SCR reactor for stationary applications. A kinetic study of NH3 oxidation and NH3-SCR over V-based catalysts
Abstract

•NH3-SCR tests at NH3/NO > 1 showed that the high temperature decline of NO conversion is not due to the lack of ammonia.•NH3-oxidation is proposed to produce NO.•NH3-oxidation tests are well explained by assuming an indirect reaction scheme wherein NO behaves as a stationary intermediate.

In this work, the kinetics of the NH3/NO/O2 reacting system over V2O5–WO3/TiO2 catalysts was studied under conditions of NH3/NO ratio ≥ 1 and temperature up to 400 °C, where some ammonia oxidation is expected. NH3-SCR and NH3-oxidation tests were performed over powdered catalysts, at varying V-loads.Over a high V-load home-made catalyst, NO conversion passed through a maximum at increasing temperature, as commonly observed in SCR tests at the onset of ammonia oxidation; however, since the experiments were performed under excess ammonia, the high temperature decrease of NO conversion could not be associated with a lack of surface NH3. The experiments were interpreted as the evidence of an unselective NH3-oxidation route, giving rise to some NO production. NH3-oxidation tests, though, showed low selectivity to NO (which is in line with the current literature); however, a quantitative analysis of data showed that the observed product distribution is fully in line with an indirect-consecutive reaction scheme from NH3 to N2, wherein NO is formed by NH3 oxidation and is then rapidly converted to N2 via NH3-SCR.The kinetic investigation was extended to commercial catalysts with low and medium V-loads. NH3-SCR tests showed increasing trends of NO conversion with temperature within the range 250–400 °C, thus they did not show any clear evidence for NH3 oxidation. However, NH3-oxidation tests showed that the reaction was active above 350 °C; notably, over 95% selectivity to N2 was observed. A quantitative analysis of the NH3-oxidation tests, based on the independent estimate of the intrinsic rate of NH3-SCR, showed that the observation of few ppm NO slip is fully in line with the assumption of a two-step kinetic scheme.A reaction path analysis shows that by neglecting the unselective nature of ammonia oxidation on V-catalysts the rate of this reaction is overestimated by a factor of 2.Preliminary evaluations suggest that the impact of NH3-oxidation on the integral performance of monolith reactors (operating at NH3/NO ratios close to 1) is non negligible, so that the correct identification of the reaction stoichiometry is crucial.

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Keywords
V2O5/WO3/TiO2 catalyst; NH3-SCR; NH3 oxidation; Indirect kinetic scheme; Kinetic modeling
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Design of a “high-efficiency” NH3-SCR reactor for stationary applications. A kinetic study of NH3 oxidation and NH3-SCR over V-based catalysts
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 179, December 2015, Pages 185–195
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