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|Type:||Artigo de periódico|
|Title:||Local Order Structure And Surface Acidity Properties Of A Nb 2o5/sio2 Mixed Oxide Prepared By The Sol-gel Processing Method|
|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 Brønsted 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/SiO 2 system were studied by XAS and XPS, respectively. For the samples calcined at 423 and 873K, the 3d5/2 BE values are at ca. 208.2eV, 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. 5.6Å-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. © 2004 Elsevier Inc. All rights reserved.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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