Vanadium-Incorporated MCM-48 Materials:  Optimization of the Synthesis Procedure and an in Situ Spectroscopic Study of the Vanadium Species

Abstract

Highly crystalline and porous vanadium-incorporated MCM-48 materials were prepared 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 typical cubic MCM-48 structure. The synthesis conditions were optimized to yield reproducible V−MCM-48 materials of high quality. The resulting materials are thoroughly characterized by UV−vis diffuse reflectance, electron spin resonance, 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 chemical and spectroscopic tools were employed to distinguish the incorporated V sites (which are present inside the silica walls) and species that are situated 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.

Periodic Mesoporous Silicas and Organosilicas: An Overview Towards Catalysis

“…However, for V-C 16 -and V-C 14 -PMO samples the 260 nm band becomes broadened without any red shift and the absence of peak above 300 nm shows that tetrahedral symmetry may be the local structure for the comparatively short chain surfactants. 51 V MAS NMR of V-PMO samples produced a less intense, broad signal at *500 ppm, showing that vanadium exists in disordered tetrahedral environment on the support surface, in well accordance with the presence of an intense band at 1,039 cm -1 (from FT-Raman analysis) attributed to the stretching vibrations of short V=O bonds of isolated tetrahedral vanadium species [41]. Table 1 lists the catalytic results of styrene epoxidation reaction using H 2 O 2 oxidant over the V-PMO samples.…”

MCF Material as an Attractive Support for Vanadium Oxide Applied as a Catalyst for Propene Epoxidation with N2O

“…5A, B). UV-Vis spectra of 3V/ MCF and 5V/MCF samples recorded under dehydrated conditions showed the strongest band at about 250 nm, which according to earlier literature is attributed to charge transfer transitions of isolated V 5+ species in tetrahedral coordination [29,30]. The weaker bands with maxima located at about 300 and 350 nm point to the presence of a small amount of polymerized vanadium occurring in a square-piramidal coordination.…”

One-pot Hydrothermal Synthesis of Mesoporous V-SBA-16 with a Function of the pH of the Initial Gel and its Improved Catalytic Performance for Benzene Hydroxylation

“…Recently, various vanadium containing mesoporous molecular sieves such as V-MCM-41 [22,23], V-MCM-48 [24] and V-SBA-15 [25,26] have been prepared by hydrothermal methods through different synthesis routes. Park and co-workers [27] have firstly reported the synthesis of well ordered V-SBA-16 with isolated framework V species and examined the effects of reaction conditions including pH, stirring temperature, aging and Si/V ratio.…”