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Facile synthesis of catalytically active porous titanosilicates for liquid-phase epoxidation of allyl alcohol with hydrogen peroxide

Titanosilicate composite catalysts were synthesized from inorganic and elementorganic titania precursors and nanostructurized silicas as substrate by chemical liquid-phase deposition approach or from soluble titania and silica precursors by sol-gel process. The nature of TiO2 precursors and silica substrate affect by a level of intercomponent interactions (because of a formation of Si-O-Ti bonds was identified) and structurization of surface active layer of the catalysts. Phase structure and porosity of the composites could be regulated by changing a composition and synthesis conditions. Applying the different synthetic approaches the catalysts with meso- or microporous structures were prepared. From UV-DRS analysis it was found that TiO2 surface layer of the composites consists of as catalytically active tetracoordinated titanium sites (λabs ~ 200 nm) as well as low active pentacoordinated (λabs ~ 225 nm) and hexacoordinated titanium atoms (λabs ~ 245 nm). A relative ratio of the titanium sites could be controlled by selecting a nature of silica substrates. Efficiency of titanosilicate catalysts obtained was demonstrated in a reaction of liquid-phase oxidation of allyl alcohol by aqueous hydrogen peroxide. The yield of glycidol in the process reaches 25 %. Among other products the hydroxyl-and carboxyl-containing compounds are detected.