Chem. J. Chinese Universities ›› 2020, Vol. 41 ›› Issue (12): 2681.doi: 10.7503/cjcu20200474

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Structure, Nature and Activity of Ga Species for Propane Aromatization in Ga/ZSM-5 Revealed by Solid-state NMR Spectroscopy

ZHAO Xingling1,2, QI Guodong1, WANG Qiang1, CHU Yueying1, GAO Wei1,2, LI Shenhui1, XU Jun1,3(), DENG Feng1   

  1. 1.State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics,Wuhan Institute of Physics and Mathematics,Innovation Academy for Precision Measurement Science and Technology,Chinese Academy of Sciences,Wuhan 430071,China
    2.University of Chinese Academy of Sciences,Beijing 100049,China
    3.Wuhan National Laboratory for Optoelectronics,Huazhong University of Science and Technology,Wuhan 430074,China
  • Received:2020-07-20 Online:2020-12-10 Published:2020-12-09
  • Contact: XU Jun E-mail:xujun@wipm.ac.cn

Abstract:

A series of Ga-modified ZSM-5 zeolites were prepared by different methods. The structure and aci-dity of these catalysts were characterized by solid-state NMR(ssNMR). The catalytic reactions for propane aromatization were also investigated. With the help of 71Ga NMR and trimethylphosphine(TMP) probe 1D 31P and 2D 1H-31P HETCOR NMR, it was found that the Ga2O3/ZSM-5 sample prepared by physical mixing only contains Ga2O3 species with weak Lewis acidity, and the samples prepared by impregnation(Ga/ZSM-5-ox) and impregnation followed by reduction-oxidation treatment(Ga/ZSM-5-redox) contain both highly dispersed ga- llium clusters and cationic Ga species. Cationic Ga species was favored on Ga/ZSM-5-IE prepared by ion exchange. Both dispersed gallium clusters and cationic Ga exhibited stronger Lewis acidity. The results of propane aromatization over Ga-modified ZSM-5 showed that the speciation and acidity of Ga have significant effect on the propane conversion. The conversion and selectivity to aromatics followed the order of Ga/ZSM-5-IE > Ga/ZSM-5-redox > Ga/ZSM-5-ox > Ga2O3/ZSM-5 > H-ZSM-5. The synergic active sites composed of Br?nsted acid site(BAS) and Lewis acid sites(cationic Ga and dispersed Ga species) on Ga/ZSM-5 zeolite were identified by 2D 1H-31P HETCOR NMR spectroscopy, which were correlated to the catalytic activity.

Key words: Metal-modified zeolite, Active site, Structural characterization, Propane aromatization, Solid-state NMR

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