Anomalous crystallization mechanism in the synthesis of nanocrystalline ZSM-5

Nanocrystalline ZSM-5 (crystal size in the range 10-100 nm) has been synthe sized in only 24 h by hydrothermal crystallization of clear supersaturated homogeneous synthesis mixtures. The influence of the aluminum source, aging time, pH, water content and presence of alkaline cations on the properties of the final nanocrystalline zeolite have been studied. Samples with diffe rent degrees of crystallinity have been prepared and characterized by X-ray fluorescence, X-ray diffraction, solid state MAS-NMR, transmission electro n microscopy and nitrogen adsorption (BET) in order to investigate the crys tallization mechanism. The process involves the formation of an initial amo rphous solid prior to the zeolite crystallization, which is gradually trans formed into nanocrystalline ZSM-5 through solid-solid transformations. Addi tionally, the conventional formation of ZSM-5 from crystalline nuclei gener ated in the remaining liquid solution is observed after 48 h. (C) 2000 Else vier Science B.V. All rights reserved.