Synthesis and Characterization of Ti—MCM-41-Type Mesoporous Molecular Sieves with High Titanium Contents

Abstract

By employing a sodium silicate + titanium tetrabutoxide + trimethylmyristylammonium bromide system, it has been possible to obtain mesoporous titanosilicate Ti–MCM-41-type molecular sieves containing systematically varying titanium contents. The samples obtained possessed a high BET specific surface area and exhibited the perfect hexagonal mesoporous structure characteristic for MCM-41 materials even when the titanium fraction present was as great as 20 mol%. It has been shown that most of the titanium can be expelled from the structure when the materials are treated with sulphuric acid solution. However, such treatment does not destroy their inherent hexagonal structure, thereby suggesting that the titanium is preferentially localized in the mesopore surface layer. The structure/sorption properties of the materials were investigated by X-ray diffraction methods and by the adsorption of n-hexane and water vapour. A possible mechanism for the formation of such MCM-41-type molecular sieves is proposed which suggests that the use of organometallic ethers M(OR) n , accompanied by ether solubilization with organic micellar templates, leads to the preferential localization of M in the mesopore surface.