STUDIES ON MESOPOROUS MATERIALS .1. SYNTHESIS AND CHARACTERIZATION OF MCM-41

The mesoporous molecular sieves MCM-41 are synthesized and characterized by X-ray powder diffraction, nitrogen adsorption/desorption, cyclohexane and water adsorption, transmission electron micrographs (TEM), thermogravimetric analysis (TGA), ammonia temperature-programmed desorption (TPD), FTIR, FT-Raman, Si-29, Al-27 and C-13 magic angle spinning (MAS) NMR spectroscopy. Raman spectra from these materials exhibit a common band at approximately 610 cm-1 assignable to cyclic trisiloxanes (3-membered rings), indicating in combination with TEM, IR and NMR results that the inorganic portion of MCM-41 resembles amorphous silicas or aluminosilicates rather than crystalline molecular sieves in terms of the local structure and bonding. Pure-silica MCM-41 can be heated to at least 850-degrees-C in dry air or 800-degrees-C in air with 8 Torr water vapor before structural collapse begins. Using sodium aluminate as the aluminum reagent, aluminosilicate MCM-41 can be prepared with a Si/Al ratio as low as 29 without observing the presence of octahedral aluminum. Such is not the case when using Catapal alumina. Adsorption of cyclohexane and water reveals that pure-silica and aluminosilicate (Si/Al = 39) MCM-41 are both hydrophobic. Based on ammonia TPD results, aluminosilicate MCM-41 has acidity similar to that of amorphous aluminosilicates.