Synthesis of three-dimensional macro-porous networks of carbon nanotubes by chemical vapor deposition of methane on Co/Mo/Mg catalyst

Three-dimensional (3D) macro-porous structures composed by carbon nanotubes (CNTs) are synthesized by chemical vapor deposition (CVD) of methane at 1173 K and atmospheric pressure on Co/Mo/Mg catalyst. 3D-structures are due to formation of interconnected CNT bundles. Strong metal/support interaction, breaking of the metal particles and large difference between surface- and bulk-diffusion are at base of the "double-base" growth mechanism, proposed to account for their formation. The variation of CH4 partial pressure (0.32-1.00 atm) reflects on changes in the products' morphology and carbon yield. These changes result to be determined by the competition between effects (release of H2 and spreading and diffusion of the carbon atoms over and into the catalyst) promoted by the CH4 dissociation. At lower CH4 partial pressure the rate of dissolution of the C atoms is faster than that of the Co/Mo dispersion and bundled CNTs prevailingly form; at higher CH4 partial pressure the situation inverts and unbundled component of the 3D-structures increases.