The effect of H2O/SiO2 ratio in precursor solution on the crystal size and morphology of zeolite ZSM-5

A series of zeolites ZSM-5 has been synthesized in hydrothermal conditions under various ratios of H2O/SiO2 ranging from 10 to 300. Materials have been characterized by X-ray diffraction, scanning and transmission electron microscopy, nitrogen adsorption measurements, X-ray fluorescence spectrometry, inductively coupled plasma optical emission spectrometry and temperature-programmed desorption of ammonia. The effect of H2O/SiO2 ratio in precursor solution on ZSM-5 product yield, crystallinity, crystal size, crystal size distribution, morphology, texture and acidity has been studied. The increase of H2O/SiO2 ratio in precursor solution from 10 to 300 results in decreasing the average crystal size from 1250 to 180 nm, the higher H2O/SiO2 ratio, the wider crystal size distribution. Aggregate-like mesoporous/hollow ellipsoid crystals and smooth pill-shaped crystals have been produced from precursor solutions with H2O/SiO2 = 25-100 and H2O/SiO2 = 10; 300, respectively. The average size of domains forming aggregate-like crystals is 40-50 nm. The specific acidity of ZSM-5 samples, synthesized from precursor solutions with different H2O/SiO2 molar ratios and the same Si/AI, has a trend to decrease along with the average crystal size increase. (C) 2017 Elsevier Inc. All rights reserved.