Single- and multi-wall carbon nanotubes have been synthesized by the gas-phase catalytic reaction of colloidal solutions of metal nanoparticles using a vertical flow reactor. The reverse micelle solution of the Co-Mo nanoparticles with the mean diameter of 11 nm dissolved in toluene was injected directly into the reactor maintained at 1200degreesC. The nanoparticles and the solvent act as the catalyst and carbon source, respectively. When the concentration of the thiophene additive is low (1wt.%), the formation of SWNT bundles preferentially occurred. The SWNT bundles were present together with the relatively small metal nanoparticles with the diameter of 0.5-5.5 nm. It is likely that the original nanoparticles with the diameter of 11 nm break into smaller ones, 1-2 nm diameters, which is suitable for the SWNT growth. The synactic effect of Co and Mo was also observed. (C) 2004 Elsevier B.V. All rights reserved.