The molecular sieve MCM-22 contains structural features previously unobserved in this class of materials. Its framework topology, derived from high-resolution electron micrographs and refined with synchrotron x-ray diffraction powder data, contains two independent pore systems, both of which are accessed through rings composed of ten tetrahedral (T) atoms (such as Si, Al, and B). One of these pore systems is defined by two-dimensional, sinusoidal channels. The other consists of large supercages whose inner free diameter, 7.1 angstroms, is defined by 12 T-O species (12-rings) and whose inner height is 18.2 angstroms. These coexisting pore systems may provide opportunities for a wide variety of catalytic applications in the petrochemical and refining industries. Another structural feature is an unusual -T-O-T- chain that passes through the center of a modified dodecasil-1H [4(3)5(6)6(3)] cage.
The influence of surfactanthilica molar ratio (Sur/Si) in the synthesis of the mesoporous molecular sieve materials (M41S) was studied in a simple ternary synthesis system containing tetraethylorthosilicate (TEOS), water, and the cetyltrimethylammonium (CTMA) cation at 100 "C. The resulting silicate materials were characterized by X-ray diffraction, 29Si NMR, and FTIR. As the Sur/Si molar ratio increased from 0.5 to 2, the siliceous products obtained could be classified into four separate groups: MCM-41 (hexagonal), MCM-48 (cubic), thermally unstable M41S, and a molecular species, the cubic octamer [(CTMA)SiO2.5]8. One of the thermally unstable structures has been identified as a lamellar phase. These results are consistent with known micellar phase transformations that occur a t various surfactant concentrations and reinforce the concept that liquid-crystal structures serve as templating agents for the formation of M41S type materials.
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