Syntheses of aluminosilicate mesostructures with high aluminum content

Ordered aluminosilicate mesostructures having a S/O-2/Al2O3 ratio near 5 we re prepared using a surfactant-templated synthesis. The solid structures we re analyzed by scanning electron microscopy (SEM), nitrogen sorption to det ermine pore volume and pore sizes, powder X-ray diffraction (PXRD), thermal desorption of a chemisorbed base to determine strong acid site density, an d magic-angle-spinning (MAS) NMR spectroscopy for the Al-27 and Si-29 nucle i. We were successful in synthesizing a mesoporous aluminosilicate having a SiO2/Al2O3 ratio near 5 when the source of the aluminum ion was Al hydroxi de and the surfactant was cetyltrimethylammonium cation (C(16)TMA(+)). The uncalcined samples showed only tetrahedral aluminum as confirmed by Al-27 M AS NMR. When the pH of the synthesis gel was 10.5, the mesostructure develo ped. pore volume of 0.59 cm(3)/g with an average pore diameter of 2.2 nm. T he pore volume was less at pH values other then 10.5 (e.g., for pH 12.6 and 8.1, the pore volumes were 0.50 and 0.43 cm(3)/g, respectively). The alumi nosilicate mesostructure showed Bronsted and Lewis sites as confirmed by th e IR vibrational spectroscopy of chemisorbed pyridine. The mesostructure Br onsted acid site density was 0.36 mu mol H+/m(2)-solid, based on Bronsted a cid site titration by isopropylamine temperature-programmed desorption. It was similar to that observed for an amorphous alumina-silica having a SiO2/ Al2O3 ratio near 6. However, the mesostructure Bronsted site density per un it mass was much lower than that measured for an acidic Y-faujasite with a SiO2/Al2O3 ratio of 2.75.