Answer: Molecular sieves can be divided into carbon molecular sieve, zeolite molecular sieve and silicon molecular sieve according to their material. Among them, zeolite molecular sieve is the most common type. According to the different silicon-aluminum ratio (Si/Al), it can be divided into type A (Si/Al is 1.5-2.0), type X (Si/Al is 2.1-3.0), type Y (Si/Al is 3.1-6.0), etc. In addition, depending on the type of ion exchange, it can also be divided into potassium molecular sieve, sodium molecular sieve, calcium molecular sieve, etc.