The structure of the molecular sieve is very empty, with a pore volume of 40% to 50% of the total volume, with a large specific surface area, generally up to 500 to 1,000 square meters/gram, and the inner surface is also very large, accounting for about 99% of the total surface area. Its most basic structural units are silicon oxygen tetrahedrons (SiO 4) and aluminum oxygen tetrahedrons (AlO 4). The adjacent tetrahedrons connect to form multi-compartmented oxygen rings in different ways through shared oxygen atoms, thus forming a three-dimensional polyhedron (cage) of various configurations. These cages are connected in different ways to form molecular sieves of various microscopic framework structures.