| 초록 |
Ordered mesoporous materials with excellent hydrothermal stability have been prepared by sequential synthesis of MCM-41 mesoporous frame and ZSM-5 microporous frameworks using a mixture of amphiphilic block copolymer, poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (EO20PO70EO20, numbers in subscripts denote the molar ratios of each component) and cetyltrimethylammonium bromide, C16H33(CH3)3NBr (CTAB) as a structure directing agent. By addition of EO20PO70EO20 in CTAB micellar solutions, the electrostatic molecular interactions between EO20PO70EO20 and CTAB enhance the molecular packing density especially in the hydrophobic core, leading to a hard-gel type micellar formation. With the tightly-coiled molecular conformation, the organic-inorganic templates may not be ruptured even during the solid phase conversion of the MFI-type zeolite precursors into the ZSM-5 crystals at high temperatures and pH 12. The successful incorporation of non-ionic EO20PO70EO20 in the cationic CTAB solution depends on the molar ratio of two components with given molecular weights which changes the molecular packing density of the mixed micelles which determines the hydrothermal stability of the organic-inorganic templates during thermal crystallization of ZSM-5 precursors.
|
