STUDIES ON MESOPOROUS MATERIALS .2. SYNTHESIS MECHANISM OF MCM-41

The solids obtained during the synthesis of MCM-41 are investigated by X-ray powder diffraction, thermogravimetric analysis and Si-29 NMR spectroscopy. These data, in combination with those obtained from in situ N-14 NMR spectroscopy, are used to elucidate the synthesis mechanism of MCM-41. The results shown here reveal that the liquid crystalline phase, H-1, is not present in the synthesis medium during the formation of MCM-41 and therefore cannot be the structure-directing agent for MCM-41. Rather, the data suggest that randomly ordered rod-like organic micelles interact with silicate species to yield approximately two or three monolayers of silica encapsulation around the external surfaces of the micelles. Subsequently, these composite species spontaneously assemble into the long-range ordered structure (hexagonal packing) characteristic of MCM-41. With further heating, the silicate species in the interstitial spaces of the ordered organic-inorganic composite phase continue to condense. Complete condensation of the silicate species is not possible because SiO- species are necessary for charge compensation of the occluded alkylammonium ions.