High-silica hierarchical ZSM-5 prepared by conventional alkali treatment: A highly stable MTP catalyst

High-silica hierarchical ZSM-5 zeolite is an attractive catalyst for the methanol to propylene (MTP) process because of its enhanced diffusion properties. However, its practical application is restricted by the disadvantages of the present preparation methods, such as high cost and complicated operation. Here we prepare a high-silica hierarchical ZSM-5 by the conventional alkali treatment method without using any expensive raw material and special operation. The limitation of the conventional alkali treatment method coming from the framework Si/Al ratio of parent zeolite is circumvented by introducing plentiful intergrowth boundaries into zeolite particle. More interestingly, these intergrowth boundaries are constructed only via controlling the content of NaOH in the synthesis gel. This approach retains all of the advantages of the conventional alkali treatment method and can be easily extended to industry scale. The resulting high-silica hierarchical ZSM-5 exhibits an abundant interconnected intracrystalline mesoporous structure with slight loss of microporosity. In the MTP reaction, the unique hierarchical pore structure causes a significant alteration in the rate and the location of coke deposition. As a result, the prepared high-silica hierarchical ZSM-5 catalyst shows an extremely long catalytic lifetime, which is 20.6 times that of the microporous counterpart.