Low silica MCM-41 composites and mesoporous solids (vol 11, pg 1342, 1999)

Aluminosilicate MCM-41 mesophase solids have been prepared under alkaline conditions with high degrees of mesoscopic order and silicon-to-aluminum molar ratios approaching unity. One- and two-dimensional solid-state NMR techniques, in conjunction with elemental analyses, infrared spectroscopy, and powder X-ray diffraction (XRD), establish that high concentrations of aluminum have been incorporated into the aluminosilicate MCM-41 frameworks, with retention of mesoscopic order. Hexagonal low silica MCM-41 has been prepared with a bulk molar Si/Al ratio as low as 1.3, while retaining a minimum of three indexable p6mm reflections in the XRD pattern prior to calcination. Following calcination to remove the structure-directing surfactant molecules, the hexagonal MCM-41 structures are preserved. The decreased thermal stabilities and dealumination of the materials with higher aluminum contents have been studied using 2D 27Al{1H} heteronuclear correlation NMR and 27Al MAS intensity calibration techniques to examine surface structures and quantify Al species present before and after calcination. © 1999 American Chemical Society.