Preparation of silica-based mesoporous materials from fluorosilicon compounds: Gelation of H2SiF6 in ammonia surfactant solution

The silica-based mesoporous molecular sieves were synthesized from fluorosilicon compounds and Al, Ti with the hydrolysis reaction of H2SiF6 in an ammonia-surfactant mixed solution, Well-crystalline mesoporous molecular sieves were obtained after several hours at the atmospheric conditions. The solid products were characterized by X-ray powder diffraction, nitrogen adsorption/desorption, transmission electron microscopy and solid-state NMR spectroscopy. The solid products show high specific surface areas in the range of 627-1040 m(2)/g, depending on the amount of Al and Ti, Also, they exhibit narrow pore size distributions in the range of 31-35 Angstrom according to the addition of Al and Ti. Si-29 MAS NMR indicate that all samples mainly contain Q(4) types sites, Also, the peak intensity of Q(3) sites decreases with increasing amount of aluminum, In Al-27 MAS NMR spectra, all samples give intense lines from 4-coordinate aluminum. These results show that aluminum species are incorporated into the framework of Si-MMS. As the amount of Al increases, the intensity line from 6-coordinate aluminum Increases. This result represents the increase of the fraction of amorphous aluminum species. (C) 1997 Academic Press.