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.

The dissociation of CH4 and CO,, as well as the reaction between CH4 and CO,, has been investigated over supported Rh in a fixed-bed continuous-flow reactor. The decomposition of methane on rhodium occurred above 423 K, when transient evolution of hydrogen and ethane were observed. The deposition of different kinds of carbon species was established, which led to the termination of the decomposition. The reactivity of surface carbon towards hydrogen exhibited a great variance, and sensitively depended on the conditions of its formation. The dissociation of CO, was detected by infrared spectroscopy only above 523 K, and it was promoted by the presence of CH4. The reaction between CO, and CH4 proceeded rapidly above 673 K to give CO and H, with different ratios. No decay in the activity of Rh catalysts was experienced, and only very little, if any, carbon deposition was observed. The effects of different supports on all of the above processes have been examined.

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The reforming of methane with carbon dioxide has been investigated at 673-773 K on supported palladium catalysts in a fixed-bed continuous-flow reactor. In addition, the dissociation of carbon dioxide and methane, and the reactivity of the surface carbon formed have also been examined. The dissociation of carbon dioxide, detected by infrared spectroscopy, occurred at the lowest temperature, 373 K, on Pd/TiO> It was greatly promoted by the presence of methane. The decomposition of methane at the temperature of the CH4 + CO2 reaction (ca. 773 K) proceeded initially at a high rate yielding hydrogen and small amounts of ethane and ethene. The deposition of surface carbon was also observed, which was hydrogenated only above 720 K. The reaction between carbon dioxide and methane occurred rapidly above 673 K to give carbon monoxide and hydrogen with a ratio of 1.3-1.7. Very little carbon was deposited during the reaction of a stoichiometric gas mixture. Kinetic parameters of the reaction were determined and a possible reaction mechanism is proposed.