Highly porous organic-inorganic hybrid silica and its titanium silicate analogs as efficient liquid-phase oxidation catalysts

Vinyltrimethoxysilane was polymerized under non-aqueous conditions through radical initiation. The resulting polymer was used as precursor in the presence of self-assembly of cationic surfactant cetyltrimethylammonium bromide (CTAB) to obtain the mesoporous organic-inorganic hybrid polyvinylsiloxane (HPVS-1). An identical synthesis procedure was followed together with the addition of different amounts of titanium(IV) source in the synthesis gels to obtain its titanium silicate analogs (Ti-HPVS-1). XRD, TEM and N-2 sorption measurements suggested highly porous wormhole-like disordered framework structures with high BET surface areas for these materials. Solid-state Si-29 MAS NMR, UV-vis and FT IR spectroscopic tools and ICP-OES elemental analysis were used to characterize these materials. Spectroscopic results suggested the incorporation of isolated tetrahedral Ti(IV) sites in the organically modified hybrid silica frameworks. Ti-HPVS-1 showed excellent catalytic activity and high selectivity in the liquid-phase oxidation of R-(-)-carvone to the corresponding epoxide, using dilute aqueous H2O2 as oxidant. (c) 2008 Elsevier B.V. All rights reserved.