Templates for the synthesis of zeolites

Though zeolites have been successfully synthesized for several decades, the roles of templates for zeolite synthesis are still not fully understood yet. Currently, many types of templates have been employed such as inorganic alkali metal ions, organic quaternary ammonium cations, organic amines, organic quaternary phosphonium cations, metal complexes and zeolite seeds, and the roles are mainly summarized into three aspects: structure-directing, space-filling and charge-balancing. In order to synthesize zeolites efficiently, the proposed principles to guide zeolite synthesis are the stabilization of energy between templates and zeolite framework, charge density mismatching (CDM) and structure matching between zeolite frameworks and templates. The purpose of this review is to briefly summarize the progresses in recent years, clearly showing the roles of the templates for zeolite synthesis.