Facile synthesis of hierarchical macro/microporous ZSM-5 zeolite with high catalytic stability in methanol to olefins

Abstract

Hierarchical macro/microporous ZSM-5 zeolite (defined as ZSM-5(MM)) was successfully synthesized by using silica spheres as silica source. The effects of template, sodium ions, hydroxyl ions, aluminum and water contents as well as crystallization temperature on the morphology and pore structure of ZSM-5 were investigated in detail. The formation mechanism was studied by XRD, SEM, N 2 sorption, ICP-AES, XPS, 27 Al MAS NMR and 29 Si MAS NMR, confirming that the silica spheres during synthesis process were served as not only silica nutrients to accelerate the generation of crystal nucleus, but also morphology guiding agents that induce the formation of macro/microporous structure followed by quasi solid hydrogel transformation mechanism. The prepared ZSM-5(MM) zeolite exhibited much longer catalytic lifetime and higher light olefins selectivity in the methanol to olefins (MTO) than those of the conventional microporous sample. This is because the hierarchical macro/microporous structure can effectively improve the diffusion of feedstocks and products, suppressing the rapid coke deposition. Meanwhile, the contribution of alkene cycle in MTO is enhanced and it produces more propene and butene. ● A facile strategy has been developed to synthesize hierarchical macro/microporous ZSM-5 zeolite ● The silica spheres not only serve as silica source, but also play a morphology-oriented role ● The formation of hierarchical structure is related to the dissolution rate of silica spheres. ● Macro/microporous ZSM-5 exhibited longer catalytic lifetime and higher olefin selectivity in MTO