Formation of Carbon Nanofibers and Carbon Nanotubes through Methane Decomposition over Supported Cobalt Catalysts

Catalytic performance of Co catalysts supported on different supports (MgO, Al2O3, SiO2, and TiO2) for the formation of carbon nanofibers through methane decomposition was investigated. Catalytic activity and the life of supported Co catalysts for methane decomposition at 773 K strongly depended on the type of catalytic supports; i.e., the catalytic performances of Co/Al2O3 and Co/MgO were superior to those of Co/TiO2 and Co/SiO2. All the Co catalysts produced carbon nanofibers with relatively uniform diameters (10−30 nm) through the reaction at 773 K irrespective of the kind of catalytic supports, although an average crystallite size of Co metal was different for these catalysts. These results implied that Co metal particles with diameters from 10 to 30 nm grew carbon nanofibers from methane preferentially, while ones larger than 30 nm were inactive for the reaction. The structures of carbons formed by methane decomposition over Co/Al2O3 depended on the reaction temperatures. Multiwalled carbon nanotubes...