V(2)O(5)/TiO(2) catalytic xerogels raman and EPR studies
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Data
2002-08-01
Autores
Rodella, C. B.
Franco, RWA
Magon, C. J.
Donoso, J. P.
Nunes, LAO
Saeki, Margarida Juri [UNESP]
Aegerter, M. A.
Sargentelli, V
Florentino, A. O.
Título da Revista
ISSN da Revista
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Editor
Springer
Resumo
Raman spectroscopy and Electron Paramagnetic Resonance (EPR) studies were performed on a series of V(2)O(5)/TiO(2) catalysts prepared by a modified sol-gel method in order to identify the vanadium species. Two species of surface vanadium were identified by Raman measurements, monomeric vanadyls and polymeric vanadates. Monomeric vanadyls are characterized by a narrow Raman band at 1030 cm(-1) and polymeric vanadates by two broad bands in the region from 900 to 960 cm(-1) and 770 to 850 cm(-1). The Raman spectra do not exhibit characteristic peaks of crystalline V(2)O(5). These results are in agreement with those of X-ray Diffractometry (XRD) and Fourier Transform Infrared (FT-IR) previously reported (C.B. Rodella et al., J. Sol-Gel Sci. Techn., submitted). At least three families of V(4+) ions were identified by EPR investigations. The analysis of the EPR spectra suggests that isolated V(4+) ions are located in sites with octahedral symmetry substituting for Ti(4+) ions in the rutile structure. Magnetically interacting V(4+) ions are also present as pairs or clusters giving rise to a broad and structureless EPR line. At higher concentration of V(2)O(5), a partial oxidation of V(4+) to V(5+) is apparent from the EPR results.
Descrição
Palavras-chave
catalyst, vanadium and titanium oxides, sol-gel, characterization
Como citar
Journal of Sol-gel Science and Technology. Dordrecht: Springer, v. 25, n. 1, p. 83-88, 2002.