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 °C. After addition of the cationic surfactant cetyltrimethylammonium bromide these so called “seeding gels” were crystallised at 120 or 150 °C. From gels aged at 60 °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.