Effect of Si/Al ratio of ZSM-5 support on structure and activity of Mo species in methane dehydroaromatization

Mustafizur Rahman, Antonia Infantes-Molina, Adam S. Hoffman, Simon R. Bare, Kayla L. Emerson, Sheima J. Khatib

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1 Scopus citations

Abstract

The effect of the Si/Al ratio of the ZSM-5 support on the structure and activity of Mo/HZSM-5 catalysts in methane dehydroaromatization (MDA) was studied. ZSM-5 (with Si/Al = 15, 25, and 40) supported Mo oxide catalysts (MoOx/ZSM-5) with 3 and 10 wt% Mo loading were prepared by incipient wetness impregnation followed by calcination in air at 500 °C. The as-prepared catalysts were activated by temperature programmed reduction in hydrogen in order to maximize Mo dispersion. To understand the structure-activity relationship, the fresh and spent samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 adsorption isotherms, Scanning Transmission Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (STEM-EDS), X-ray absorption spectroscopy (EXAFS and XANES), thermogravimetric analysis (TGA), and Raman spectroscopy. The results show that the Si/Al ratio does not influence the the local structure around the Mo centers. It does however affect the number of available Brønsted acid sites in the support and the amount of Mo species entering the zeolite channels. A lower Si/Al ratio and higher Mo loading resulted in a higher Mo occupation within the zeolite channels. The higher channel occupation directly correlated with higher benzene selectivity and yield, as well as a lower catalyst deactivation rate.

Original languageEnglish
Article number118290
JournalFuel
Volume278
DOIs
StatePublished - Oct 15 2020

Keywords

  • Brønsted acid sites
  • Methane dehydroaromatization
  • MoC
  • MoO
  • Supported molybdenum carbide

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