SYNTHESIS AND CHARACTERIZATION OF VANADOSILICATE MESOPOROUS MOLECULAR-SIEVES MCM-41

A range of mesoporous vanadosilicate molecular sieves with the MCM-41 structure and the atomic ratio Si/V = 10-160 have been synthesized usi ng vanadyl sulfate as the source of vanadium. The products were charac terized by XRD and V-51 and Si-29 MAS NMR spectroscopy. The increase o f the unit-cell parameter (monitored by XRD) and the decrease of the Q (3)/Q(4) ratio (determined from the Si-29 spectra) with increasing van adium content indicate the incorporation of vanadium into the MCM-41 s tructure. In as-synthesized [Si,V]-MCM-41, vanadium is in an octahedra l environment and is located mainly on the surface of the channels, Th e amount of octahedral vanadium decreases and tetrahedral V is increas ingly created as the calcination temperature increases.