VANADIUM-CONTAINING CRYSTALLINE MESOPOROUS MOLECULAR-SIEVES - LEACHING OF VANADIUM IN LIQUID-PHASE REACTIONS

Vanadium (V) containing mesoporous molecular sieves, V-HMS have been s ynthesized at room temperature in the presence of dodecylamine as temp late and vanadyl(IV) sulfate hydrate or vanadium(V) triisopropoxide as vanadium source. The presence of V in the silicate matrix was investi gated by UV-visible spectroscopy, V-51 MAS NMR and catalytic measureme nts. Samples were also characterized using chemical analysis, XRD, SEM , FTIR and adsorption properties. It was found that the vanadium cente rs in V-HMS molecular sieves consist of three-legged (SiO)(3)V=O speci es, similar to those in amorphous V/SiO2. V-HMS materials catalyze the oxidation of organic substrates such as phenol, 2,6-di-tert-butyl phe nol, naphthalene and cyclododecanol in the presence of either dilute h ydrogen peroxide or tert-butyl hydroperoxide as the oxidant. Leaching of active vanadium species from the silicate matrix during reaction wa s investigated. The stability of vanadium during liquid phase reaction s was found to depend on the nature of the substrate, the solvent and the oxidant.