HYBRID TIO2-SIO2 ORGANIC INORGANIC GELS - PREPARATION, CHARACTERIZATION, AND TEMPERATURE-PROGRAMMED PYROLYSIS AND OXIDATION STUDIES/

Permethylated cyclooligosiloxane rings, tetraethylortosilicate (TEOS), and Ti(iPr)(2)Cl-2 were used to prepare hybrid TiO2-SiO2 xerogels. A number of solvents were ineffective for leaching the organic silicon f rom the samples at 336 K after several hours. The nitrogen desorption isotherms of these materials reveal that microporous structures with b road pore size distributions are generated upon gelation. Characteriza tion of the samples by means of Si-29 CP/MAS NMR shows incorporation o f the ''organic silicon'' into the amorphous structure and also sugges ts a great extent of homogeneity in the proton distribution around all tetrahedral silicate centers. The thermal stability of these hybrid T iO2-SiO2 materials was studied under flowing nitrogen and air by means of temperature-programmed (TP) techniques, and in situ diffuse reflec tance infrared spectroscopy (DRIFTS). The stability of the Si-C bond i n the absence of oxygen is hardly influenced by the presence of Ti. Al l Ti-containing samples undergo high-temperature pyrolytic decompositi on of the Si-C bond, even when oxygen was present. In the presence of oxygen, the Ti function catalyzes the complete oxidation of the remain ing alkoxide groups, rather than Si-C bond oxidation. The thermal stab ility of the latter and the decomposition of alkoxide groups into olef ins are confirmed by both TP methods and DRIFTS.