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Methane Dehydroaromatization by Mo/HZSM-5: Mono- or Bifunctional Catalysis?

Nikolay KosinovSchuit Institute of Catalysis, Laboratory of Inorganic Materials Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The NetherlandsFerdy J. A. G. CoumansSchuit Institute of Catalysis, Laboratory of Inorganic Materials Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The NetherlandsEvgeny A. UslaminSchuit Institute of Catalysis, Laboratory of Inorganic Materials Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The NetherlandsAlexandra S. G. WijpkemaSchuit Institute of Catalysis, Laboratory of Inorganic Materials Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The NetherlandsBrahim MezariSchuit Institute of Catalysis, Laboratory of Inorganic Materials Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The NetherlandsEmiel J. M. HensenSchuit Institute of Catalysis, Laboratory of Inorganic Materials Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

2016en

ABI

Annotatsiya

The active site requirements for methane dehydroaromatization by Mo/HZSM-5 were investigated by employing as catalysts physical mixtures of Mo-bearing supports (HZSM-5, SiO2, γ-Al2O3, and activated carbon) and HZSM-5. Separation of the two catalyst components after activation or reaction was possible by using two different sieve fractions. Our comparison demonstrates that migration of volatile Mo oxides into the micropores of HZSM-5 is at the origin of the observed catalytic synergy in methane dehydroaromatization for physical mixtures. The propensity of Mo migration depends on the activation method and the Mo–support interaction. Migration is most pronounced for Mo/SiO2. Prolonged exposure of HZSM-5 zeolite to Mo oxide vapors results in partial destruction of the zeolite framework. Mo carbide dispersed on nonzeolitic supports afforded predominantly coke with only very small amounts of benzene. The main function of the zeolite is to provide a shape-selective environment for the conversion of methane to benzene. A comparison of Mo/HZSM-5 and Mo/Silicalite-1 demonstrates that aromatization of methane is an intrinsic ability of molybdenum carbides dispersed in the 10-membered-ring micropores of MFI zeolite. Thus, one important role of the Brønsted acid sites is to promote the dispersion of the Mo oxide precursor and, accordingly, the active Mo carbide phase in the micropores of HZSM-5.

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DOI: 10.1021/acscatal.6b02497

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