Zeolite is a type of microporous silicate or aluminosilicate crystal, which forms a system of uniformly sized internal channels and cavities (usually 0.3–2 nm) through the connection of silicate tetrahedrons or aluminate tetrahedrons via oxygen bridges.
By virtue of physical adsorption (van der Waals force), it can adsorb molecules smaller than its pore diameter into the interior of the cavities. It is capable of separating molecules with different polarity, saturation, molecular size and boiling point, namely it has the function of molecular sieving, hence it is also called molecular sieve.