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Type: Artigo de periódico
Title: Local order structure and surface acidity properties of a Nb2O5/SiO2 mixed oxide prepared by the sol-gel processing method
Author: Francisco, MSP
Landers, R
Gushikem, Y
Abstract: The sol-gel processing method was used as an alternative route to obtain Nb2O5 phase homogenously dispersed in the SiO2 matrix, improving the thermal stability of the Bronsted acid sites, Nb-OH and Nb-OH-Si groups. The local niobium structure and the influence of the amount of niobia, on the surface of the Nb2O5/SiO2 system were studied by XAS and XPS, respectively. For the samples calcined at 423 and 873 K, the 3d(5/2) BE values are at ca. 208.2 eV, indicating an ionic character for Nb(V) species in the SiO2 matrix, probably associated to Si-O-Nb linkages. The features of Nb K-edge XANES spectra of samples show the absence of Nb=O species. The Nb K-edge EXAFS oscillations exhibit a shoulder at ca. 5.6 Angstrom(-1), which probably arises from Nb-O-Si. This fact corroborates the EXAFS simulation data of the second coordination shell, whose best fitting is achieved with three distances, two Nb-Nb lengths and one Nb-Si. (C) 2004 Elsevier Inc. All rights reserved.
Subject: niobia supported in silica
sol-gel processing method
acid sites
Country: EUA
Editor: Academic Press Inc Elsevier Science
Rights: fechado
Identifier DOI: 10.1016/j.jssc.2004.03.035
Date Issue: 2004
Appears in Collections:Artigos e Materiais de Revistas Científicas - Unicamp

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