Zeolite Synthesis and its Properties

Zeolites are formed by hydrothermal synthesis,1 typically under mild conditions. The nature of the zeolite obtained is determined by the synthesis conditions, i.e., reactant concentrations, pH, time, temperature, and the nature and concentration of added promoters. The zeolite framework which crystallizes from a given batch is determined mainly by its composition and its temperature. Most of the early work in the synthesis of zeolites involved crystallization of the aluminosilicate gel from solutions containing alkali hydroxide as the base. The cations are distributed within the same intercrystalline pore systems as the zeolitic water. As a result of the open structure, the cations, like the zeolite water, can be mobile. However, unlike the water, the cations are not free to leave the crystals unless they are replaced by their electrochemical equivalent of other cations because neutralization of the anionic charge of the aluminosilicate framework must be maintained.