Abstract Submitted to the    NANOTUBE'04 Conference:

The influence of the proportions of Cobalt and Molybdenum within (Mg, Co, Mo)O catalysts has been studied in details for the CCVD synthesis of carbon nanotubes (CNTs) in a H₂-CH₄ atmosphere. The MgO matrix and most of the residual (Co, Mo) catalyst are easily dissolved by a HCl soaking, leading to CNTs samples with a high elemental purity (up to 98.6 at. % of carbon). The variation of the ratio between cobalt and molybdenum was found to modify both the yield in CNTs and their basic characteristics (number of walls, diameter distribution, quality and purity). Increasing the molybdenum proportion until x < 0.67 leads to an increase in the yield in CNTs. However, this also leads to an increase in the number of walls of the CNTs, together with a growing proportion of CNTs with a large amount of structural defects (bamboo-like structures), as well as the presence of some deposits of poorly-organised carbon. Fine tuning the key synthesis param eters such as the ratio between cobalt and molybdenum and the total amount of these elements in the starting oxide, the reduction temperature and the atmosphere composition, should allow a better control on the number of walls.