Catalytic Synthesis of Carbon Nanotubes

Abstract

Catalytic synthesis of carbon nanotubes has been investigated over supported transition metal catalysts. The samples were characterized by trans-mission electron microscopy. For catalyst preparation, different methods such as ion-exchange, impregnation, etc. were applied. Activity of the catalyst samples prepared in different ways depended on the nature of the catalyst support (silica of different pore diameter, zeolites of various structure) and on the pH of the solution during the synthesis of catalyst samples. Supported cobalt and iron were found to be active in the catalytic decomposition of acetylene and other carbon-containing compounds. While the activity of iron samples is always higher, the quality of the nanotubes (degree of graphitization) is superior in cobalt samples. The quality and the quantity of carbon nanotubes produced in the catalytic reaction have been stud-ied also as a function of reaction time and reaction temperature. Increasing reaction time can result in a greater amount of amorphous carbon due to the deactivation of catalytically active sites in time. The optimum reaction temperature depends on the initial reactant applied in the decomposition. Increasing temperature is favorable for the formation of a wellgraphitized structure, on the other hand, above a certain temperature homogeneous decomposition of the reactant molecules can take place. In summarizing these results some aspects of the mechanism of nanotube formation can be explained.