| Autor: |
Rodella, Cristiane, Franco, Roberto, Magon, Claudio, Donoso, Jose, Nunes, Luis, Saeki, Margarida, Aegerter, Michel, Sargentelli, Vagner, Florentino, Ariovaldo |
| Zdroj: |
Journal of Sol-Gel Science and Technology; August 2002, Vol. 25 Issue: 1 p83-88, 6p |
| Abstrakt: |
Raman spectroscopy and Electron Paramagnetic Resonance (EPR) studies were performed on a series of V2O5/TiO2catalysts 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−1and polymeric vanadates by two broad bands in the region from 900 to 960 cm−1and 770 to 850 cm−1. The Raman spectra do not exhibit characteristic peaks of crystalline V2O5. 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 V4+ions were identified by EPR investigations. The analysis of the EPR spectra suggests that isolated V4+ions are located in sites with octahedral symmetry substituting for Ti4+ions in the rutile structure. Magnetically interacting V4+ions are also present as pairs or clusters giving rise to a broad and structureless EPR line. At higher concentration of V2O5, a partial oxidation of V4+to V5+is apparent from the EPR results. |
| Databáze: |
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