Knowledge of the structure and characteristics of molecular sieve

Molecular sieve is a silicate or a crystalline aluminosilicate, and formed of silicon oxide or aluminum oxide tetrahedra linked by oxygen bridges tetrahedron. Molecular size (typically 0.3 ~ 2.0 nm) of the pore and cavity system, so as to have characteristics of solid molecules. However, with the synthesis and application of molecular sieve-depth study, researchers found that the aluminophosphate molecular sieves and sieve skeleton elements (silicon or aluminum or phosphorus) may be composed of B, Ga, Fe, Cr, Ge, Ti, V , Mn, Co, Zn, Be and Cu, substituted, its pore size and the cavity may reach 2 nm or more, the zeolite framework elements can be divided according to type aluminosilicate zeolite, Activated alumina adsorbent molecular sieves and molecular sieve framework heteroatoms ; divided by pore size, pore size of less than 2 nm, 2 ~ 50 nm and the molecular sieve is larger than 50 nm are referred to as micropores, mesopores and large pore molecular sieves. Because of the larger aperture size becomes larger carrier molecules react well, but the pore walls of mesoporous materials are amorphous, resulting in the hydrothermal stability and thermal stability still can not meet the required conditions for petrochemical applications demanding .