The structure of ZSM-5 zeolite molecular sieve

ZSM-5 molecular sieve



ZSM-5 molecular sieve is a new structure of zeolite molecular sieve with high silicon three-dimensional cross-connection. ZSM-5 molecular sieves are lipophilic and hydrophobic, and have high thermal and hydrothermal stability. Most of the pores are about 0.55nm and belong to mesoporous molecular sieves. Because of its unique pore structure, it not only provides space restriction for shape-selective catalysis, but also provides abundant access channels for reactants and products. It is also used for the preparation of industrial catalysts with high selectivity, high activity, and strong resistance to carbon deposition and deactivation. Provides the basis for the crystal structure. As a result, it has become one of the most important catalytic materials in shape-selective reactions in the petroleum industry. ZSM-5 molecular sieve has also been widely used in the fields of fine chemicals and environmental protection. The application fields of ZSM-5 molecular sieve products with different silicon-to-aluminum ratios are also different.





ZSM-5 molecular sieve structure



ZSM-5 molecular sieve belongs to the orthorhombic crystal system, the space group is Pnm a, the unit cell parameters are a=2.017nm, b=1.996nm, c=1.343nm. The unit cell composition of ZSM-5 can be expressed as NanAlnSi96-nO192·16H2O. In the formula, n is the number of Al atoms in the unit cell, which can be changed from 0 to 27, that is, the amount ratio of silicon to aluminum can be changed in a larger range, but the total number of silicon to aluminum atoms is 96.
The crystal structure of ZSM-5 molecular sieve is composed of silicon (aluminum) oxygen tetrahedron. The silicon (aluminum) oxygen tetrahedron forms a five-membered silicon (aluminum) ring through the common vertex oxygen bridge, and 8 such five-membered rings form the basic structural unit of the ZSM-5 molecular sieve. The pore structure of ZSM-5 molecular sieve is composed of straight cylindrical pores with an elliptical cross section (pore size 0.54×0.56nm) and approximately circular Z-shaped pores (pore size 0.52×0.58nm) cross-section, as shown in the figure 1 as shown. The size of the intersection of the two channels is 0.9nm, which may be the concentration of the catalytic activity of ZSM-5 and its strong acid. ZSM-5 molecular sieve has a regular pore structure, large specific surface area, high hydrothermal stability, good ion exchange performance and rich and adjustable surface properties.