Molecular sieve is an artificial or naturally occurring hydrated aluminosilicate (zeolite) with the ability to sieve molecules. Its chemical formula is (M′2M)O·Al2O3·xSiO2·yH2O, where M′ and M are monovalent and divalent cations, such as K+, Na+, Ca2+, and Ba2+. It features many uniformly sized channels and orderly arranged cavities in its structure, separating molecules of different sizes and shapes based on their pore sizes. Different molecular sieve with varying ratios of SiO2 to Al2O3 yields sieves with different pore sizes.

Its models include: 3A (Potassium A-Type), 4A (Sodium A-Type), 5A (Calcium A-Type), 10Z (Calcium Z-Type), 13Z (Sodium Z-Type), Y (Sodium Y-Type), and Sodium Silk Zeolite-Type, etc. It boasts high adsorption capacity, strong selectivity, and high heat resistance. It is widely used in organic and petrochemical industries, and is an excellent adsorbent for coal gas dehydration. Its importance in waste gas purification is also growing.