Seed-Assisted Synthesis of ZSM-5 Aggregates Assembled from Regularly Stacked Nanosheets and Their Performance in <i>n</i>-Hexane Aromatization
Zhanggui Hou, Xiaotong Mi, Xiaoguo Li, Hongtao Liu
Abstract
HZSM-5 crystals with short straight channels possess the advantages of easier diffusion and less coke formation in petrochemical processes. In this work, aggregated ZSM-5 zeolite assembled by regularly stacked nanosheet-like crystals with a b-axis thickness of 60 nm was synthesized using specially designed silicate-1 as seed. Silicate-1 (S-2) was synthesized using relatively lower cost silica sol as a silica source, tetrapropylammonium bromide (TPABr) as a structure-directing agent (SDA), and ethylamine as an assistant compared with traditional silicate-1 (S-1: tetraethyl orthosilicate (TEOS) as a silica source and tetrapropylammonium hydroxide (TPAOH) as an SDA). When S-2 seeds were added into the synthesis system, the seeds could limit the crystal growth along the b-axis direction under the assistance of ethylamine. Meanwhile, the adjacent ZSM-5 nanosheet crystals would spontaneously stack together. The catalyst Zn/S-2-1 exhibited relatively higher n-hexane conversion and selectivity of benzene, toluene, ethylbenzene, and xylene (BTEX) as well as catalytic stability in contrast to the catalyst synthesized using S-1 as seed when being used in the n-hexane aromatization reaction. This work opened up a new prospective for ZSM-5 aggregates assembled from the nanosheet catalyst design in the application of hydrocarbon aromatization.