Catalytic synthesis and characterization of carbon nanotubes on unsupported and zeolite-supported transition metal oxides catalysts

Catalytic synthesis of carbon nanotubes using chemical vapor deposition was studied in this work. The influences of supported and unsupported transition metal oxides on the formation of carbon nanotubes were investigated. The morphology of the as - prepared catalysts and the nanotubes formed on the corresponding catalyst was observed by TEM. The thermal stability of nanotubes was measured by DTA - TG. It was found that the formation of carbon nanotubes correlated not only with the kind of transition metal oxides employed but also with the size and dispersion degree of active metal particles. The irregular nanoparticles of active metal oxides were suitable for forming uniform carbon nanotubes. The Co - La catalyst with the diameter of similar to 20 nm was the most active one for the preparation of nanotubes. The particle size of the catalyst was found to be dependent on the diameter of nanotubes formed on both of the unsupported and zeolite - supported metal oxides. The transition metals supported zeolites were good catalysts for the growth of carton nanotubes. The carbon nanotubes formed on zeolite - supported metal catalysts were cleaner than that those formed on unsupported metal oxides catalysts. The high purity of nanotubes that possess well - graphitized structure and good thermal stability can be obtained by further chemical treatment with nitric acid. They can maintain their structure at temperatures over 400 degrees C in air or over 1200 degrees C in a nitrogen atmosphere.