Two-Step, Oxygen-Free Route to Higher Hydrocarbons from Methane Over Ruthenium Catalysts

The direct conversion of methane to higher hydrocarbons over a Ru/SiO2 catalyst as well as Cu-Ru/SiO2 catalysts has been investigated via a two-step, oxygen-free route. The reaction consists of decomposition of methane over supported Ru catalysts at temperatures (TCH4) between 400 to 800K to produce surface carbonaceous species followed by rehydrogenation of these species to higher hydrocarbons at TH2 of 368K. A 3% Ru/SiO2 catalyst exhibited high initial ethane yields, but accumulation of “inactive” carbon led to a complete deactivation of this catalyst in few reaction cycles. For a Cu-Ru/SiO2 catalyst (Cu/Ru=0.1), about 95% carbon deposited could be hydrogenated at 368K thus improving the net ethane yield. However, when tested for multiple reaction cycles, the Cu-Ru/SiO2 catalyst (Cu/Ru=0.1) exhibited a rather slow deactivation, which was mainly attributed to gradual accumulation of inactive carbon on the surface of the catalyst. These results are consistent with the known tendency for Cu to deposit on low coordination Ru sites and with previous suggestions that carbon is predominantly formed on such sites.

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