Introduction to the definition of zeolite molecular sieve

Molecular sieve is a class of adsorbent or film-like substance with uniform micropores, mainly composed of silicon, aluminum, oxygen and some other metal cations, whose pore size is comparable to the general molecular size, according to its effective pore size to sieve various fluid molecules. 

Zeolite molecular sieves are those natural and synthetic crystalline silica-aluminates with molecular sieving effect. Zeolite molecular sieve has become an independent discipline due to its unique structure and performance, the application of zeolite molecular sieve has been throughout the petrochemical, environmental protection, biological engineering, food industry, pharmaceutical and chemical fields. With the development of various industries in the national economy, the application of zeolite molecular sieve is increasingly promising.

Zeolite molecular sieve is an inorganic crystalline material with regular pore structure, strong acidity and high hydrothermal stability, which is widely used in the fields of catalysis, adsorption and ion exchange, and plays an irreplaceable role. The synthetic research on zeolite molecular sieve can be traced back to the 1940s, when Barrer et al. first synthesized zeolite molecular sieve by studying the phase transition of natural minerals in hot salt solution, which has opened the curtain of synthetic zeolite molecular sieve.

The first discovered natural zeolites, there are about 50 kinds of zeolites, and their early use is rarely developed. Its application is mainly limited to the drying, purification and separation of gases. The synthesis of A- and X-type zeolites, especially Y-type zeolites, and their application in catalytic cracking in the 1950s was regarded as the beginning of the industrial and commercialization of zeolite materials. 

In the half century from then to now, the research on zeolite molecular sieves has gone through three main development stages, namely, the synthesis of ZSM-5 in the 1970s, the synthesis of AIPO4-n series molecular sieves in the 1980s and the synthesis of M4lS mesoporous type molecular sieves in the 1990s. Nowadays, there are more than 120 kinds of zeolite molecular sieves, the pore size has been expanded from microporous to mesoporous, and the chemical composition of the skeleton has been expanded from alumino-silicate to silico-aluminate and phosphor-aluminate with various heteroatoms, which has become an indispensable catalytic and adsorption material in petroleum processing and fine chemical industry.

Zeolite molecular sieve is the hydrate of crystalline aluminosilicate metal salt, its chemical formula is: Mx/m[(AlO2)x-(SiO2)y]-zH2O. m represents cation, m indicates its valence number, z indicates hydration number, x and y are integers. After the activation of zeolite molecular sieve, the water molecules are removed and the remaining atoms form a cage-like structure with pore size of 3~10Å. 

There are many cavities of certain size in the molecular sieve crystal, and many holes of the same diameter (also called "windows") are connected between the cavities. Because the molecular sieve can be smaller than its pore size molecules adsorbed to the inside of the cavity, and than the pore size of the molecules rejected outside the cavity, to play the role of sieving molecules, so the name molecular sieve. Zeolite molecular sieve can exist in nature, artificially synthesized in large quantities from the 1970s.