Influence of molybdenum on the chemical vapour deposition production of carbon nanotubes

Large numbers of multi-wall carbon nanotubes have been produced using a Co-Mo sol-gel catalyst with a high Mo/Co ratio. Carbon yields up to 4000% and carbon nanotubes with low levels of impurities have been obtained, pointing out the promoter character of Mo in the reaction. Therefore, the influence of Mo species has been studied in detail. The analysis of the different catalysts and samples shows that two magnesium molybdate phases can be present in the catalysts: MgMoO4 and MgMo2O7. However, the MgMoO4 one plays a dominant role in the production of the tubes by helping the dispersion of the active Co nanoparticles and promoting the aromatization of the carbon source. Such active metal nanoparticles come from the decomposition of the CoO phase existing in the catalyst.