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Impacts of niobia loading on active sites and surface acidity in NbOx/CeO2–ZrO2 NH3–SCR catalysts

Paper ID Volume ID Publish Year Pages File Format Full-Text
45468 46412 2015 15 PDF Available
Title
Impacts of niobia loading on active sites and surface acidity in NbOx/CeO2–ZrO2 NH3–SCR catalysts
Abstract

•NbOx/Ce0.75Zr0.25O2 catalyst achieves a high SCR activity and high selectivity.•The surface acidity can be tuned by the amount and state of NbOx species.•The amount and reactivity of active sites are enhanced by Ce–Nb electron interaction.•“L–H” and “E–R” mechanisms are presented at low and high temperatures, respectively.

A series of NbOx/Ce0.75Zr0.25O2 catalysts for the selective catalytic reduction of NO with ammonia (NH3–SCR) were synthesized using a wetness impregnation method. The effect of niobia loading was studied in relation to the active sites and surface acidity. NH3/NO oxidation, X-ray diffraction, Infrared spectroscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, O2/NH3 temperature-programmed desorption, and diffuse reflectance infrared Fourier transformed spectroscopy experiments were performed to correlate the catalyst structure and surface properties to catalytic performance after Nb2O5 modification. The catalyst with 15 wt.% Nb2O5 loading showed high NH3–SCR activity and nearly 100% N2 selectivity within a broad operation temperature window (190–460 °C) at a high space velocity (300,000 h−1). On this catalyst, Nbn+ was mainly distributed in the form of typical monomeric and polymeric NbOx species, and was partially incorporated into the Ce0.75Zr0.25O2 lattice at the Nbn+OCen+ (Zrn+) interface. The electron redistribution effect arising from the occupation of cerium sites by Nbn+ ions promoted the formation of Ce3+ ions, oxygen vacancies and active oxygen species. This interaction was closely associated with the distribution of NbOx species which varied with niobia loading. NbOx themselves were acid sites and by attracting electrons they enhanced Lewis acid sites on CZ surface, which promoted the adsorption of NH3 and inhibited the unselective oxidation of NH3 to NOx. The increased amounts of active oxygen species over NbCZ catalysts promoted the adsorptive oxidation of NH3 to NH2 and NO to NO3− at low temperatures, and thus facilitated the reaction of ads-NH3 and ads-NO3−/NO2− species. This effect as well as the increased amount of acid sites led to good NH3–SCR performance of Nb15CZ in a wide temperature range.

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Keywords
Niobia; CeO2–ZrO2; Electronic interaction; Surface acidity; NH3–SCR
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Impacts of niobia loading on active sites and surface acidity in NbOx/CeO2–ZrO2 NH3–SCR catalysts
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 179, December 2015, Pages 380–394
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