The synthesis and application of the mesoporous molecular sieves MCM-41 - A review

We report a "delayed neutralization" process for the preparation of highly- ordered aluminosilicate MCM-41 molecular sieves with high thermal and hydro thermal stability, and sharp pore size distribution. However, the structura l order and pore size are dependent on the carbon chain length. In the mixt ure surfactant systems, the pore size of the MCM-41 materials could be fine -tuned. The pore size can be extended from 2.5 to 4.5 nm by adding a suitab le amount of hydrocarbons. The tubular morphology of the MCM-41 material of 0.3 to 10 micrometers diameter, where the wall consists of coaxial cylindr ical pores of nanometers MCM-41, can be obtained by careful control of the surfactant-water content and the rate of condensation of silica. An optimum condition for automatic synthesis of the hierarchical TWT structure has be en accomplished. The addition of I-alkanols as cosurfactant would not only improve the order of the MCM-41 hexagonal structure but also promote the fo rmation of micrometer-sized hierarchical materials, for example: tubules-wi thin-tubule and uniform-sized hollow spheres of diameter 5.0 +/- 1.0 mu m. However, the inside of the micron spheres has intricate structures possessi ng various topological genus ranks. The MCM-41 is a good supporter for Moly bdenum oxide catalysts. The rate of deactivation in the catalytic reaction of ethyl benzene dehydrogenation to styrene increases in the order: M-tau < M-p < SiO2. The physically mixed samples have higher catalytic activity th an impregnated ones.