Morphology oriented ZrO2 supported vanadium oxide for NH3-SCR process: importance of structural and textural properties.

Author(s) Liu, S.; Wang, H.; Wei, Y.; Zhang, R.; Royer, S.
Journal ACS Appl Mater Interfaces
Date Published 2019 May 24

ZrO2 supports, with diverse morphologies (hollow sphere, star, rod, mesoporous) were produced using hydrothermal and evaporation-induced self-assembly (EISA) methods. Zirconia supported vanadium oxide catalysts were prepared by wet impregnation, and used for the low-temperature selective catalytic reduction (SCR) of NO with ammonia. Characterization of catalysts includes N2 physisorption, elementary analysis, X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, temperature programmed reduction by H2, Temperature programmed desorption of NH3. Significant differences in terms of activity are measured. V/MZ (3 wt.% V2O5 supported on mesoporous ZrO2) presents excellent N2 yields (>90%, in the 200-400 ºC interval), with a wide operating temperature window (NO conversion > 95%, in the 225-425 ºC interval), and less interesting performances were obtained when vanadium oxide is supported over stars, hollow spheres, rods. Surface characterization showed a content of tetravalent vanadium ion, when supported, decreasing in the order mesoporous > hollowsphere > star > rod. This order is in perfect agreement which order of performance of catalyst in the NH3-SCR reaction. The impact of tetravalent ion presence on the surface is confirmed by DRIFTS analysis, Brønsted acid sites generated on surface, V4+-OH, species being involved in the reaction. The more important production of nitrite species over tetragonal supported vanadium oxide catalyst could be another reason for the excellent NH3-SCR performance displayed by the V/MZ catalyst. When supported over monoclinic zirconia, like vanadium oxide over star-type morphology, the adsorbed NH3 species (NH4+ and coordinated NH3) reacted with NOx adsorption species (nitrate) to form ammonium nitrate. Ammonium nitrate can be decomposed to N2 and N2O (or NO2). Thus, NO conversion curves and N2 yield curves over tetragonal zirconia (MZ) at lower temperature were ahead of over V/SZ because of the higher V4+ surface content and more active B acid sites associated with an easy formation of nitrito intermediate.

DOI 10.1021/acsami.9b03429
ISSN 1944-8252
Citation ACS Appl Mater Interfaces. 2019.

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