Synthesis of mesoporous ZSM-5 by crystallisation of aged gels in the presence of cetyltrimethylammonium cations

ZSM-5 synthesis gels were aged during 18-72 h at temperatures between 30 and 90 degrees C. After addition of the cationic surfactant cetyltrimethylammonium bromide these so called "seeding gels" were crystallised at 120 or 150 degrees C. From gels aged at 60 degrees C, ZSM-5 crystals possessing uniform mesopores with diameters around 2.5 nm were obtained. SEM micrographs of these samples revealed, independently of the ZSM-5 crystallinity, a morphology typically for mesoporous MCM-41. Furthermore, the formation of a hexagonal mesopore array analogous to MCM-41, was indicated by X-ray diffraction (XRD). However, the symmetry of the mesopore array decreased with the ZSM-5 crystallinity of the samples, indicating the dislocation of the surfactant micelles during the transformation of the primary formed MCM-41 particles into ZSM-5. Otherwise, the crystallinity of the obtained ZSM-5 was influenced by the crystallisation temperature, by the time used in the seed ageing and by the Si/Al ratio of the gel. (c) 2008 Elsevier B.V. All rights reserved.