Interconnected Hierarchical ZSM-5 with Tunable Acidity Prepared by a Dealumination-Realumination Process: A Superior MTP Catalyst

Junjie Li, Min Liu, Xinwen Guo, Shutao Xu, Yingxu Wei, Zhongmin Liu, Chunshan Song

Research output: Contribution to journalArticle

30 Scopus citations

Abstract

ZSM-5 that uses TPAOH as a template has an Al-rich exterior and defective Si-rich interior; thus, a simple base leaching selectively removed the Si-rich interior while the Al-rich exterior was protected. This catalyst showed no change in stability comparing with parent ZSM-5 during the MTP reaction that was attributed to the enclosed hollow structure and richly acidic outer shell. A preliminary fluorination, however, both removed defective Si-sites and caused distortion in tetrahedral aluminum that made the outer shell susceptible to alkaline treatment. These distorted tetrahedral Al were mostly leached out by NaOH in 1 min. Furthermore, aluminum in the filtrate was slowly redeposited onto the zeolite, serving as external pore-directing agents to control silicon dissolution from the Si-rich interior. This dealumination-realumination alkaline treatment process led to a higher solid yield and a uniform opened-mesopore structure with mesopores around 13 nm in diameter. This material was characterized by SEM, TEM, N2 adsorption, and mercury porosimetry. In addition, NH3-TPD, OH-IR, 27Al MAS NMR, and 1H MAS NMR results demonstrated that the reinserted Al were unlike the framework Al, contributing less to acidity. The dealumination-realumination process, therefore, was also capable of tuning the acidity of the mesoporous ZSM-5. This mesoporous catalyst exhibited a longer lifetime and a higher propylene selectivity than other catalysts with an enclosed mesopore structure.

Original languageEnglish (US)
Pages (from-to)26096-26106
Number of pages11
JournalACS Applied Materials and Interfaces
Volume9
Issue number31
DOIs
StatePublished - Aug 9 2017

All Science Journal Classification (ASJC) codes

  • Materials Science(all)

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