Synthesis of Single Walled Carbon Nanotubes Using Cobalt Grafted on MCM-41 Catalysts

In this work single walled carbon nanotubes (SWNT) have been synthesized by high pressure CO disproportionation using cobalt grafted on MCM-41 by means of grafting method employing cobalt (II) acetylacetonate. The reduction temperature of the metal species of these catalysts and their physical properties characterized by XRD, nitrogen physisoption and temperature reduction programmed are compared to those of the catalyst prepared by in-situ incorporation. The carbon nanotubes synthesized are characterized by Raman spectroscopy, transmission electron microscopy (TEM) and thermogravimetrical analysis (TGA). The results show a good and uniform dispersion of cobalt metallic particles on the MCM-41 even with higher loadings of metal than 3 wt%. The onset of reduction temperatures for the metal species as well as the pore size distribution of mesoporous catalysts decreased linearly with the increasing of metal concentration. The ratio between the G and D intensity bands for the carbon nanotubes remains constant with the metal concentrations used, however, the carbon yield increased linearly with the metal loading, without evidence of amorphous carbon corroborated by TEM and TGA. The results also showed that a better yield for the SWNT synthesis is obtained in the catalyst prepared by grafting in comparison to the catalysts prepared by in-situ incorporation, which is an important alternative in the production of SWNTs on a bigger scale.