V2O5/TiO2 Catalytic Xerogels Raman and EPR Studies

• Published in: Journal of sol-gel science and technology 2002-08, Vol.25 (1), p.83-88
• Main Authors: Rodella, Cristiane B, Roberto WA Franco, Magon, Claudio J, Donoso, Jose P, Luis AO Nunes, Saeki, Margarida J, Aegerter, Michel A, Sargentelli, Vagner, Florentino, Ariovaldo O
• Format: Article
• Language: English
• Subjects: Catalysis; Electron paramagnetic resonance; Fourier transforms; Oxidation; Raman spectra; Raman spectroscopy; Sol-gel processes; Spectrum analysis; Titanium dioxide; Vanadates; Vanadium pentoxide; Vanadium pentoxide-Titanium dioxide; Xerogels
• ISSN: 0928-0707; 1573-4846
• DOI: 10.1023/A:1016049212766

Raman spectroscopy and Electron Paramagnetic Resonance (EPR) studies were performed on a series of V2O5/TiO2 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 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.