Characterisation of as-synthesised MOx-MCM-41 (M = Mo, W) mesophases using Raman spectrometry and 29Si MAS NMR

Abstract MCM-41 mesostructured silicas containing molybdenum and tungsten have been prepared in an acidic medium at room temperature. Two procedures were considered: the so-called oxo–peroxo route with low-nuclearity peroxo metal precursors (route A) and the oxo–polyoxo pathway, involving or generating polyoxometalates (route B). The native materials have been characterised by chemical analysis, powder X-ray diffraction, Raman spectrometry and 29 Si MAS NMR. The results show that, in route A, the use of peroxo compounds leads to a distribution of the low-nuclearity metal species throughout the silica-surfactant assembly whereas Keggin type polyoxometalates are generated in route B. The different dispersions of the MO x species (M=Mo, W) on and into the silica matrix and, hence, the formation of MO 3 (route B), previously observed for calcined materials, can be explained on the basis of different specific interactions in these organic–inorganic mesophases.