On the synthesis and characterization of ZSM-5/MCM-48 aluminosilicate composite materials

Abstract

Composite micro/mesoporous ZSM-5/MCM-48 materials have been prepared using a simple two step crystallisation process. The synthesis process involved the assembly of precursor zeolite species, containing ZSM-5 units at various stages of crystallisation, into a mesostructured material. By varying the time allowed for the crystallisation of the precursor zeolite species (between 2 and 8 hours) it was possible to modify the composition of the composite materials (i.e., zeolite/MCM-48 ratio). Furthermore, it was possible to obtain relatively pure forms of both end members (ZSM-5 and MCM-48) from the precursor zeolite species after appropriate aging. The resulting composite materials were characterized by powder XRD, nitrogen sorption, IR spectroscopy, TGA, SEM and TEM and found to exhibit varying levels of zeolitisation. The ZSM-5 present in the composite materials was made up of nanosized zeolite crystallites. The textural properties of the composite materials were, in some cases, comparable to conventional mesoporous materials. The acidity and hydrothermal stability of the composite materials was found to be dependent on the extent of zeolitisation, i.e., ZSM-5/MCM-48 ratio.