Low-temperature and alkali-free dual template synthesis of micro-mesoporous aluminosilicates based on precursors of zeolite ZSM-5

Abstract

The aim of this study was to determine the influence of the conditions of low-temperature sequential dual template synthesis of micro-mesoporous aluminosilicates based on precursors of ZSM-5 on their phase composition, structure, sorption properties, and acidity. The methods of X-ray powder diffraction and volumetric adsorption (N2, 77 K) analysis, dynamic light scattering (for characterization of sol-precursors), IR-spectroscopy, energy-dispersive X-ray spectroscopy, scanning and transmission electron microscopy, solid-state 29Si MAS NMR and 29Si{1H} cross-polarization MAS NMR spectroscopy, temperature-programmed desorption of ammonia, ad(de)sorption of pyridine and 2,6-di-tert-butylpyridine with IR-spectral control were used for characterization of the obtained micro-mesoporous aluminosilicates. It was shown that the convergence of compositions of the reaction mixtures and conditions of formation of zeolites and mesoporous molecular sieves, in particular, the use of alkali-free reaction medium and relatively low temperature of hydrothermal treatment (100 °C) allowed to obtain the X-ray amorphous and partially zeolitized micro-mesoporous aluminosilicates. Such aluminosilicates have appropriate structural and sorption properties and the acidity inherent to ZSM-5 and MCM-41, including the Bronsted and Lewis acid sites which are accessible for bulk molecules of organic substances. The possibility of purposeful regulation of characteristics of micro-mesoporous aluminosilicates depending on the conditions of their preparation was confirmed. Herewith the investigated aluminosilicates possess the sorption and acidic properties which are different from the mechanical mixture of two phases.