Preparation And Characterization Of Carbon Nanotubes

In this work, Ni/SiO2 catalyst was prepared with impregnation method. Multi-walled carbon nanotubes were produced using carbon monoxide as carbon source via Chemical Vapor Deposition method. Methane was also used as carbon source as a comparison. The effect of catalyst preparation and the reaction condition on the formed carbon nanotubes was studied.It is suggested that the Ni loading is important for the configuration of carbon nanotubes. Within the Ni loading of 5%~35%, carbon yield increased with the increase of Ni loading. The yield decreased after Ni loading was over 35%. But the configuration of carbon nanotubes became worse when the Ni loading increased. Configuration of carbon was better when calcination temperature of catalyst was 500℃. The carbon yield remained almost the same when the impregnation time changed from 2h to 30h. Without hydrogen in the feed gas, the diameter of carbon nanotubes was in a narrow range of 15~20nm. After hydrogen was introduced into the system, the configurations and the amount of carbon were improved and the optimum concentration of H2 was 25.8%. With the increase of reaction time, the yield of carbon increased. The reaction rate remained stable at the first 2h and became very slow after 4h. TEM image proved that the average length of carbon nanotubes became longer when the reaction time increased while the curvature and the diameter of the carbon nanotubes exhibited little difference.Ni/SiO2 was also used as a catalyst for the reaction of CH4 decomposition. When CH4 was the only feed gas, some of the carbon produced was carbon fibers with diameter of 70~80nm and length of 10μm, and the other was extremely short carbon nanotubes with diameter of 20~40nm. After hydrogen was introduced into the system, the length of carbon nanotubes became 1~2μm and the diameter was within 30~50nm. The optimum reaction temperature was 600℃.