The ability to grow the zeolite structure in a continuous manner is an important advantage over discontinuous synthesis processes. The size of the indigenous clusters can be controlled by the acidity of the starting reagents and the prevention of the nucleation, as well as by the control of the synthesis time and temperature. The structure-directing agent and the reagents can be chosen to produce zeolites with a variety of characteristic properties.
The most critical decisions in zeolite synthesis are the choices of both the structure-directing agent and the reagents (solvents). The choice of both the structure-directing agent and the reagents in the formation of the structure is an important step in determining zeolite structure. Subsequent growth of the skeleton can be assigned to the specific reagent-some of the reagents will have different effects on the overall structure growth. The key step in synthesis is the production of the skeleton. Generally, both the SiO2 and Al2O3 are present in excess during synthesis. With the exceptions of quaternary structures, the application-specific zeolite synthesis is based on the starting reagents. In addition, the silica-alumina ratio can be varied depending on the specific micropore requirements of the desireds. For example, the framework Al2O3/SiO2 ratio can be altered to meet a variety of specific requirements. Application-specific improvements can be made to the basic composition of molecular sieving zeolites.
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