Hierarchically porous ITH structural silica-alumina molecular sieve with small crystal grains as well as preparation method and application thereof

The invention provides a hierarchically porous ITH structural silica-alumina molecular sieve with small crystal grains as well as a preparation method and an application thereof. The ITH structural silica-alumina molecular sieve comprises the following elements: silicon, germanium, aluminium, and oxygen, wherein SiO2/Al2O3 (mol ratio)=10-2000, and GeO2/SiO2 (mol ratio)=0.001-2.0; wherein, the small crystal grains show that volume intermediate value of crystal grains is 0.5-10[mu]m, and the hierarchically pores comprise micropores and mesoporous. The hierarchically porous ITH structural silica-alumina molecular sieve with small crystal grains has good hydro-thermal stability; and when the molecular sieve is applied to a reaction for preparation of alkene by a MTO method, the molecular sieve has the advantages of high propylene selectivity, good low carbon selectivity, long service life of catalysts, and the like.