GROWTH OF CARBON NANOTUBES BY CATALYTIC DECOMPOSITION OF CH4 OR CO ONA NI-MGO CATALYST

By using a Ni-MgO catalyst, carbon nanotubes with small and even diame ter could be prepared from catalytic decomposition of CH4 or CO. These carbon nanotubes prepared by this method are more or less twisted, wi th the outer diameter at 15-20 nm, and the tube length up to 10 mu m. The results of XRD measurements and pulse reaction testing indicated t hat the NiO and MgO components in this catalyst precursor formed, due to their highly mutual solubility, a NixMg1-xO solid solution. The hig h dispersion of Ni-species in this solid solution and the effect of va lence-stabilization by the MgO crystal field would be in favor of inhi biting deep reduction of Ni2+ to Ni-0 and aggregation of the Ni-0 to f orm large metal particles at the surface of catalyst, making the carbo n nanotubes grown on this catalyst relatively small and even in size o f diameter. The experimental results also indicated that, in the growi ng process of carbon nanotubes, the rate-determining step was dependen t upon the conditions of preparation (i.e. feedgas used, reaction temp erature, flow-rate of the feedgas, etc.). The growth mechanism of the carbon nanotubes on the Ni-MgO catalyst is discussed together with the experimental results. (C) 1997 Elsevier Science Ltd.