The structure of ZSM-5 molecular sieve

The structure of ZSM-5 molecular sieve

The chemical composition of ZSM-5 zeolite can be expressed by the molar ratio of oxides as: 0.9±0.2M2/nO:Al2O3:5--100SiO2:ZH2O, where M is a cation (alkali metal sodium ion and organic amine ion); n Is the valence of the cation; Z is from 0 to 40.

ZSM-5 zeolite has a high silicon-to-aluminum ratio, and molecular sieves with different silicon-to-aluminum ratios can be synthesized according to needs and can be varied in a wide range from 10 to 3000.

ZSM-5 zeolite contains ten-membered rings, and the basic structural unit is composed of eight five-membered rings. Its crystal structure belongs to the orthorhombic system, space group Pnma, lattice constant a=20.1Å, b=19.9Å, c=13.4Å. It has a special structure without cages like A-type, X-type and Y-type zeolite, and its pores are its cavities. The skeleton is composed of two intersecting channel systems. The straight cylindrical channel is elliptical, with a major axis of 5.7~5.8 Å and a minor axis of 5.1~5.2 Å; the other is a "Z"-shaped transverse channel with a cross-section close to a circle with a hole diameter. It is 5.4±0.2Å. Belongs to medium pore zeolite. The bend angle of the "Z"-shaped channel is 110 degrees. Sodium ions are located on the symmetry plane of the 10-membered ring channel. Its anion skeleton density is about 1.79 g/cm3. Therefore, the crystal structure of ZSM-5 zeolite is very stable.

Relative crystallinity: Na type> 85% H type> 95%

Aperture: 5A

Skeleton density: 1.81 (determined by isooctane)

Thermal stability: 1200℃ molecular sieve can maintain the structure

Hydrothermal stability: 700℃ steam treatment, molecular sieve can maintain the structure