Unveiling the generation of mesoporous MFI zeolites with one-dimensional fins in the assistance from small quaternary ammonium cation and its application in propane aromatization

Abstract

In this work, a kind of ZSM-5 zeolite with one-dimensional fins growing along the [010] direction has been successfully synthesized utilizing both tetrapropylammonium hydroxide (TPAOH) and tetramethylammonium hydroxide (TMAOH) as co-templates. With the aid of molecular dynamic simulations and a series of experimental evidences, the formation mechanism of the one-dimensional feature is determined to arise from the synergic effects between TPA⁺ and TMA⁺. Two TPA⁺ and three TMA⁺ would co-exist in a unit MFI cell at a certain crystallization period depending on the composition of zeolite and precursor, and this configuration ensures a minimum stabilization energy required for the growth along [010] direction. Investigations manifest these needle-like fins with diameters of ca. 60 nm could function as pseudo nano crystals and introduce additional pores ranging from 10 to 90 nm, which effectively promotes the diffusion capability and substantially improves the catalytic performance in propane aromatization.