Nonhydrolytic Sol-Gel Reactions for the Synthesis of Oxide Materials
|Original title:||Nonhydrolytic Sol-Gel Reactions for the Synthesis of Oxide Materials|
Nonhydrolytic sol-gel processes are promising new routes for the preparation of new oxide, silicate and phosphate materials. These reactions are based on aprotic polycondensations with the elimination of small organic molecules (ethers, esters, alkylhalides, etc.) in the absence of hydroxyl groups. One of our goals was the synthesis of new precursors - aluminum chloride-alkoxides - and their nonhydrolytic transformation to alumina by alkylhalide elimination. The second area of interest was improving the synthesis of phosphosilicate gels. We prepared phosphosilicate gels by the elimination of acetic acid esters in heteropolycondensation reactions between silicon(IV) acetate and tris(trimethylsilyl) ester of phosphoric acid. The nonhydrolytic ester elimination provides clear amorphous hybrid phosphonosilicate gels at room temperature. Finally, a novel non-hydrolytic syntheses of a SiO2-TiO2 mixed oxide system by the polycondensation of silicon(IV) acetate with titanium(IV) dimethylamide, diethylamide,and isopropoxide was studied. The materials were tested in the epoxidation of cyclohexene by cumyl hydroperoxide and showed a high selectivity but a mediocre activity. Catalytic properties were significantly improved by combining non-hydrolytic and hydrolytic methods yielding mesoporous and homogeneously mixed silica-titania dioxide.