DIRECT CONVERSION OF METHANE TO HIGHER HYDROCARBONS VIA AN OXYGEN-FREE, LOW-TEMPERATURE ROUTE

The direct conversion of methane to higher hydrocarbons over a silica- supported Ru catalyst has been investigated via an oxygen free, two-st ep route. The reaction consists of decomposition of methane over a 3% silica-supported Ru catalyst at temperatures (T-CH4) between 400 and 8 00 K to produce surface carbonaceous species followed by rehydrogenati on of these species to higher hydrocarbons at T-H2 of 368 K. It was fo und that the Ru/SiO2 catalyst exhibits a trend similar to that for sin gle-crystal Ru catalysts. However, the temperature at which a maximum in ethane selectivity occurs shifts toward a higher temperature. It wa s also found that the ethane yield can be optimized by changing the su rface carbon coverage. Under optimum conditions a net ethane yield of about 13-15% has been realized. For this two-step reaction sequence, o nly a few reaction cycles could be operated without intermediate high temperature rehydrogenation and without significant loss in ethane yie ld. This is attributed to large amounts of inactive carbon that could not be hydrogenated at 368 K. Higher methane partial pressures were fo und to be desirable for this reaction. The activity of the catalyst co uld also be maintained at total pressures up to 10 atm.