As a catalyst, molecular sieves have many key functions in chemical reactions, which are mainly due to their unique structure and chemical properties. The following are the main functions of molecular sieves as catalysts:

1. Providing active sites

Structural characteristics of molecular sieves: Molecular sieves are a type of inorganic crystal material with a regular and uniform pore structure. Its interior is full of dense pores and holes, providing channels for molecules to enter and exit and active sites for catalytic reactions.

The role of active sites: The active sites of molecular sieves can adsorb and activate reactant molecules and promote chemical reactions. These active sites are usually located in the pores or on the surface of the molecular sieves, and accelerate the reaction rate by adsorbing and catalyzing reactant molecules.

2. Shape-selective catalysis

The screening effect of pore size: The pore size of molecular sieves is comparable to that of ordinary molecules. Only molecules whose size and shape match the pores of molecular sieves can enter or exit from the pores of molecular sieves, thus becoming reactants or products. This pore size screening effect gives molecular sieves a unique shape-selective catalytic function.

Application of shape-selective catalysis: In the fields of petrochemicals, coal chemical industry, etc., the shape-selective catalytic function of molecular sieves is widely used in catalytic cracking, isomerization, reforming and other reactions. For example, using ZSM-5 molecular sieve as a catalyst, the selectivity of xylene is as high as 99%, which is the basic principle of shape-selective catalysis.

3. Acid catalysis

Formation of proton acid sites: After proton exchange treatment, the molecular sieve has abundant proton acid sites on the surface, becoming a solid acid catalyst.

Acid-catalyzed reaction: The acid catalysis of molecular sieves performs well in many acid-catalyzed reactions, such as isomerization, alkylation and cracking reactions. These reactions are of great significance in the fields of petrochemicals, fine chemicals, etc.