Phase transition of mesoporous SiO2 impregnated with an organic templating agent by post-synthetic microwave heating

Structural and sorption characteristics of the products from zeolitization of sba-15 in the presence of tetraalkylammonium hydroxides

“…One involves the use of nanoparticles of the initial precursor sol of the Zt as starting material for the subsequent "assembly" and formation of the MMS structure in the presence of an appropriate structure-directing agent (a micellar template) [4][5][6][7]. The other approach presupposes partial zeolitization of the MMS in the so-called "dry gel conversion" process after preliminary impregnation with an aqueous solution of the organic template, which is required for the nucleation and formation of the crystallites of the Zt phase [5,[8][9][10]. …”

“…The materials obtained by such a method and particularly by partial crystallization of the siliceous mesoporous molecular sieves in zeolites with the MFI structure [8,10] are predominantly composite materialsmixtures of the zeolite phase with amorphous mesoporous silica. Even the use of microwave radiation, which as considered in [9] creates milder conditions for uniform nucleation and subsequent growth of the crystals during the conversion of mesoporous silica impregnated with the reaction solution, does not lead to the formation of hybrid micro-mesoporous materials. The slow rate of zeolite formation under the conditions of brief microwave irradiation probably complicates the formation of the zeolite nuclei uniformly over the whole volume of the sample, resulting in localized crystallization of silica.…”