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 m2/g, depending on the amount of Al and Ti. Also, they exhibit narrow pore size distributions in the range of 31-35 A according to the addition of Al and Ti. 29Si MAS NMR indicate that all samples mainly contain Q4 types sites. Also, the peak intensity of Q3 sites decreases with increasing amount of aluminum. In 27Al 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.