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Possibility of VOx/SiO2 complexes speciation: comparative multi-wavelength Raman and DR UV-vis study
Authors: Bulánek Roman | Čičmanec Pavel | Setnička Michal
Year: 2013
Type of publication: článek v odborném periodiku
Name of source: Physics Procedia
Publisher name: Elsevier Science BV
Place: Amsterdam
Page from-to: 195-205
Titles:
Language Name Abstract Keywords
cze Možnost rozlišení VOx/SiO2 komplexů: srovnávací studie multivlnové Ramanovy a DR UV-vis spektroskopie Ramanova spektroskopie se často používá k charakterizaci vanadadiových částic na povrchu. Ramanova spektra VOx na silice jsou však více komplexní a jejich analýza je složitá. Proto interpretace některých vibračních pásů je stále problematická a je nutné hledat jiné cesty, jak charakterizovat vanadiové částice. vanad; katalyzátor; UV-VIS spektroskopie; Ramanova spektroskopie
eng Possibility of VOx/SiO2 complexes speciation: comparative multi-wavelength Raman and DR UV-vis study Raman spectroscopy is one of the very often used spectroscopic methods for characterization of vanadium surface species. However, Raman spectra of VOx-silica systems are more complex and interpretation is more difficult in comparison with other supports (like Al2O3, ZrO2, TiO2 or Nb2O5) because there is strong vibrational coupling between the vanadia species and the silica support. Therefore, assignment and interpretation of some vibrational bands is still subject of controversy. This fact results in incongruity of suggested molecular structure and population of individual vanadium surface complexes. In this contribution, we present systematic comparative study of diffuse reflectance UV-vis spectra and Raman spectra excited by 325 and 514.5 nm lasers obtained on set of dehydrated vanadium modifed hexagonal mesoporous silica (VOx-HMS) samples with vanadium loading from 2 up to 12 wt. %. We prove that changes in population of oligomeric and monomeric VOx species in individual samples are not manifested by significant changes in the character of Raman signals. On the other hand it is evident that with increasing of vanadium loadings the UV-vis spectra show systematic changes. Raman spectroscopy is useful characterization technique for detection presence of very small amount of V2O5 microcrystallites, especially if suitable wavelength of laser is used for remarkable resonant enhancement of Raman intensity of its bands (e.g. 514.5 nm). vanadium; catalyst; difuse-reflectance UV-vis spectroscopy; Raman spectroscopy; speciation

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