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Indexed by:期刊论文

Date of Publication:2017-08-09

Journal:ACS APPLIED MATERIALS & INTERFACES

Included Journals:SCIE、EI、PubMed、Scopus

Volume:9

Issue:31

Page Number:26096-26106

ISSN No.:1944-8244

Key Words:Al-zoned ZSM-5; enclosed hollow structure; distorted tetrahedral Al; dealumination-realumination process; reinserted Al; interconnected mesopore structure; MTP

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, N-2 adsorption, and mercury porosimetry.In addition, NH3-TPD, OH-IR, Al-27 MAS NMR, and H-1 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.