Titanium-containing porous silica prepared by a modified sol-gel method

Titanium-containing porous silica with a mesostructured unit as secondary pore walls has been synthesized at room temperature by a modified sol-gel method using a structure-directing agent. The transparent gel formed as a precursor resulted in high titanium incorporation in the silicate framework of up to 15 mol % Ti. The increase in Ti in the silicate network was accompanied by a change in the framework porosity from mesoporous to microporous properties. Microporous samples with more than 12 mol % Ti have a high specific surface area of over 900 m(2)/g at 500 degrees C and a uniform micropore diameter of 0.84-0.90 nm, irrespective of the broad pore size distribution for mesoporous products. The X-ray absorption near-edge structure, extended X-ray absorption fine structure, Raman spectra, and UV-vis spectra indicated that most Ti atoms were incorporated as isolated Ti sites into the silicate framework up to 15 mol % Ti, while additional small amounts of a titania phase were formed in the silica matrix at 25 mol % Ti. The products exhibit catalytic activities in the liquid phase in peroxide oxidations of olefins with tert-butyl hydroperoxide and reveal a higher conversion on cyclic than on linear olefins.