Micro/Mesoporous Composites Based on Colloidal Zeolite Grown in Mesoporous Matrix

Abstract

Composite materials containing micro- and mesopores are prepared under instantaneous hydrothermal treatment of initial solutions generally used for zeolite Beta and precursor solutions for mesoporous Al-MCM-41 material. The resulting composites are compared with pure, highly crystalline colloidal microporous Beta zeolite and hexagonally ordered mesostructured samples. The porosity and morphological features of the composite materials are influenced by the conditions of hydrothermal synthesis of the initial colloidal solutions used for the preparation of Beta seeds, as well as by the conditions of the synchronized crystallization of the final composites. The embedding of Beta seeds in the mesoporous silica matrix is possible via immediate heating of mesoporous precursor solutions with Beta seeds primarily formed. The composite materials contain either microcrystalline Beta nanodomains with sizes of about 5-10 nm surrounded by mesoporous material or defined Beta nanocrystals (20-40 nm), and at the same time connected with mesostructured material. The presence of highly crosslinked silicate framework walls and tetrahedrally coordinated aluminum in the composite material are confirmed by solid-state 29Si and 27Al MAS NMR spectroscopy. The concentration of Brønsted acid sites in the micro/mesoporous composites is increased substantially in comparison with pure mesoporous Al-MCM-41 material proven by FTIR acetonitrile-d3 adsorption study.