Jm. Miller et Lj. Lakshmi, V-51 and H-1 solid-state MAS NMR studies of vanadia catalysts supported onAl2O3-TiO2 sol-gel mixed oxide, J MOL CAT A, 144(3), 1999, pp. 451-459
A series of vanadia catalysts supported on sol-gel derived mixed oxide Al2O
3-TiO2 were synthesized with a V2O5 content varying from 1 to 25 wt.%. The
catalysts were characterized by employing V-51, Al-27, H-1 MAS NMR, diffuse
reflectance FT-IR and BET surface area measurements. In the calcined catal
ysts V-51 NMR studies indicated the peaks corresponding isolated and distor
ted tetrahedral vanadia species at low V2O5 contents and octahedral vanadia
species at high vanadia loadings. Upon outgassing the catalysts, a decreas
e in the intensity of the peak corresponding to distorted tetrahedral speci
es was observed with a consequent increase in the intensity of the peak cor
responding to isolated tetrahedral vanadate species due to the removal of w
ater molecules or hydroxyl groups from the coordination sphere of vanadium.
The H-1 MAS NMR studies showed the presence of terminal and bridged hydrox
yl groups of alumina and titania in the Al2O3-TiO2 mixed oxide support. The
overtone bands corresponding to V = O were seen only at higher vanadia con
tents in the DRIFT spectra of the catalysts. (C) 1999 Elsevier Science B.V.
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