CVD production of double-wall and triple-wall carbon nanotubes

Carbon nanotubes with a drastically reduced number of graphitic layers were synthesized in high yield by chemical vapor deposition of methane over a sol–gel Mo–Co catalyst supported on magnesium oxide particles. We show that both the catalyst composition and the methane flow rate strongly influence the porosity of the catalyst support, the catalyst dispersion, the degree of aromatization of the hydrocarbon feedstock as well as the degree of carbon deposition, and thus can be used efficiently to control the number of graphitic layers of the grown carbon nanotubes. A low content of molybdenum in the catalyst combined with a low methane flow rate especially leads to the formation of thin-wall carbon nanotube materials which are predominantly composed of double- and triple-wall carbon nanotubes. These types of carbon nanotubes are of special interest as reinforcement components in the field of advanced composite materials.