Small angle X-ray scattering from MCM-41 and its synthesis gels

Abstract

We have found optimised conditions for alkaline synthesis of the large pore molecular sieve, MCM-41, by determining small angle X-ray scattering and adsorption isotherms from materials at various stages of the preparation. The presence of highly curved surfaces, sealed structures, and quasicrystalline hexagonal products coexisting with true MCM-41 are all detected by transmission electron microscopy. Calcination must be carried out with care. The product is most crystalline from unstirred preparations which have been heated at 100°C for no longer than three days. Under these conditions, a maximum BET surface area of 1950 m2 g-1 was attained, with evident crystallinity observed by electron diffraction and transmission electron microscopy. In the stirred system, which appears to be in a non-equilibrium state, materials after calcination exhibiting Bragg d-spacings of 35 Å, 37 Å and 38 Å have been identified. Show more