M. Mathieu et al., Vanadium-incorporated MCM-48 materials: Optimization of the synthesis procedure and an in situ spectroscopic study of the vanadium species, J PHYS CH B, 105(17), 2001, pp. 3393-3399
Highly crystalline and porous vanadium-incorporated MCM-48 materials were p
repared using gemini surfactants as structure-directing agents and vanadyl
sulfate pentahydrate as the source of the heteroelements. Materials with Si
/V ratios varying from 20 to 100 were synthesized without loss of the typic
al cubic MCM-48 structure. The synthesis conditions were optimized to yield
reproducible V-MCM-48 materials of high quality. The resulting materials a
re thoroughly characterized by W-vis diffuse reflectance, electron spin res
onance, Raman, and Fourier transform infrared spectroscopies. It was proven
that the V ions in the MCM-48 are present as isolated surface species and
as incorporated species in the silica matrix. For the first time, both chem
ical and spectroscopic tools were employed to distinguish the incorporated
V sites (which are present inside the silica walls) and species that are si
tuated externally on the surface. A fairly low amount (1 wt %) of V species
is really incorporated, but these species are extremely stable, and do not
leach, whereas the surface species are easily lost in aqueous media.