Energetically favored formation of MCM-48 from cationic-neutral surfactant mixtures

Abstract

The cubic mesoporous silica molecular sieves MCM-48 have been obtained as an energetically favorable mesophase via a synthesis route using the surfactant mixtures between alkyltrimethylammonium bromides and polyoxyethylene alkyl ethers, with sodium silicate as the silica source. The MCM-48 mesophase was stable under the synthesis conditions for longer than a month, preventing a subsequent transformation to lamellar phases. Metal sources and salts could be added to the synthesis mixture during this period to incorporate metallic elements within the siliceous framework and to increase hydrothermal stability. The product yield amounted to 4.2 mol of SiO2 per surfactant, which was 5 times that of the previously reported synthesis procedure using hexadecyltrimethylammonium bromide and tetraethyl orthosilicate. The present synthesis results demonstrate that the use of mixed surfactants is emerging as a new useful strategy for the synthesis of mesoporous molecular sieves.