Hydrothermal Synthesis Approach to Zeolites

Some synthetic regularities and features of the hydrothermal synthesis of zeolites could be illustrated by the synthesis of zeolites in presence of sodium ions from Na20-Al203-Si02-H20 hydrothermal system which will be discussed in the following sections. 

Na20 Si02(aq) + NaAl(OH)4(aq) + NaOH(aq)- hydrated aluminosilicate 

The reaction represented by Equation (3.1) looks like a very simple synthetic reaction at first glance. In fact, it is a very complicated process. General synthetic regularities of zeolites will be discussed in the following sections by using the crystallization of sodium-type zeolites as an example. 

Basic reactants used in the synthesis of zeolites include silicon source, aluminum source, metal ions, base, mineralizer, and water. Some additives such as organic template or inorganic salts could be critical for the successful crystallization of a specific zeolite. Among them, silicon source and aluminum source are the two most important reactants. Frequently used silicon source and aluminum source reactants are listed below  

Sodium aluminate NaA102 Boehmite (pseudo-boehmite) AlOOH, A1203 70%, H20 30% aluminum hydroxide (Gibbsite), Al(OH)3 aluminum isopropoxide A1(0- C3H7)3 aluminum nitrate A1(N03)3 9 H20 metallic aluminum. 

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