Aromatization of Methane over Supported and Unsupported Mo-Based Catalysts

Author： Solymosi F. Cserenyi J. Szoke A. Bansagi T. Oszko A.

ISSN： 0021-9517

Source： Journal of Catalysis, Vol.165, Iss.2, 1997-02, pp. : 150-161

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Abstract

The interaction of methane with unsupported and supported molybdenum compounds (Mo, MoO 2 , MoO 3 , Mo 2 C, and MoC (1- x ) ) has been investigated at 973 K. ZSM-5 was used as a support. Reaction products were analyzed using gas chromatography. Changes in the composition of catalyst samples were followed by X-ray photoelectron spectroscopy. Molybdenum metal and oxides interacted strongly with methane at 973 K to give H 2 (Mo) and H 2 O and CO 2 (oxides), but only a trace amount of ethane. When these compounds were contacted with ZSM-5, the reaction pathway of methane initially was the same. Afterward, however, a dramatic change occurred in the product distribution: the formation of ethane, ethylene, and benzene came into prominence. This was particularly the case when these compounds were highly dispersed on ZSM-5. The selectivity to benzene was 80-85%. XPS analysis of Mo-containing catalysts demonstrated the formation of Mo carbides during the catalytic reaction. Unsupported Mo carbides behaved like metallic Mo; the dominant process was the decomposition of methane to hydrogen and carbon. The deposition of Mo 2 C on ZSM-5 in a well-dispersed state, however, produced a very active and selective catalyst for the conversion of methane into benzene. The results suggest that Mo 2 C is the active surface species in the Mo-containing catalysts, which converts methane into ethylene, the primary compound for the production of benzene on the zeolite surface.