Two-step, oxygen-free route to higher hydrocarbons from methane over ruthenium catalysts

Methane coupling on single-crystal ruthenium catalysts has been studied utilizing combined elevated-pressure kinetic measurements/surface science studies. The reaction consists of the activation of methane on Ru(0001) and Ru(112̄0) surfaces to produce carbonaceous deposits at temperatures (TCH4) between 350 and 700 K and rehydrogenation of these species to ethane and propane at TH2≂ 370 K. It is found that under reaction conditions employed, the maximum yield in ethane/propane production occurs at TCH4≂ 500 K on both the surfaces. High-resolution electron energy-loss spectroscopy (HREELS) has been used to identify various forms of hydrocarbonaceous intermediates following methane decomposition. The HREELS data reveal that methane decomposes on both the surfaces to produce methylidyne (CH) and vinylidene (CCH2) intermediates. A correlation between the hydrocarbon intermediates identified by HREELS and the gas phase products observed in the elevated pressure experiments has been found. The results show that the surface vinylidene species is likely to be the key intermediate responsible for the C2 production.