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Deactivation of vanadia-based commercial SCR catalysts by polyphosphoric acids

Paper ID Volume ID Publish Year Pages File Format Full-Text
48029 46488 2008 13 PDF Available
Title
Deactivation of vanadia-based commercial SCR catalysts by polyphosphoric acids
Abstract

Commercial vanadia-based SCR monoliths have been exposed to flue gases in a pilot-scale setup into which phosphoric acid has been added and the deactivation has been followed during the exposure time. Separate measurements by SMPS showed that the phosphoric acid formed polyphosphoric acid aerosols, which were characterized by particle number concentrations in the order of 1 × 1014 #/m3 at 350 °C and diameters <0.1 μm. Three full-length monoliths have been exposed to flue gases doped with 10, 100 and 1000 ppmv H3PO4 for 819, 38 and 24 h, respectively. At the end of the exposure the relative activities were equal to 65, 42 and 0%, respectively. After exposure, samples of the spent monoliths have been characterized by ICP-OES, Hg-porosimetry, SEM–EDX and in situ EPR. The results showed that the polyphosphoric acids chemically deactivate the vanadia-based catalysts by decreasing the redox properties of the catalyst surface and by titrating the number of V(V) active species. When plate-shaped commercial catalysts have been wet impregnated with different aqueous solutions of H3PO4 obtaining P/V ratios in the range 1.5–5, the relative activity for the doped catalysts in the whole P/V range was 0.85–0.90 at 350 °C. These results show that the presence of phosphor compounds in the flue gas may be much more harmful than indicated by simple wet chemical impregnation by phosphoric acid. The reason has been found in the nature of the polyphosphoric acid aerosol formed in the combustion process, which cannot be reproduced by the wet impregnation process.

Keywords
SCR catalyst deactivation; Polyphosphoric acid; Vanadia; EPR; SMPS
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Deactivation of vanadia-based commercial SCR catalysts by polyphosphoric acids
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 83, Issues 1–2, 1 September 2008, Pages 110–122
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
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