Diffusion effects in formation process of the mesoporous molecular sieve MCM-41

The regular mesoporous molecular sieve MCM-41 has been investigated at different stages during its formation, using high resolution transmission electron microscopy and powder X-ray diffraction. The results not only support the liquid-crystal templating mechanism previously postulated, but allow the extension of its scope to describe details of MCM-41 formation. It has been observed that formation of the hexagonal liquid crystal phase on the one hand and of silica aggregates on the other, occurs simultaneously at the inception of gel formation and throughout the crystallisation. This process is most probably affected by diffusion of both the surfactant molecules and the oligomeric silicate ions. With this postulate it becomes possible to explain several experimental observations (both old and new) and to develop a multi-step synthesis method to grow large particles of MCM-41 using small calcined crystals of MCM-41 as seeds.