High growth of SWNTs and MWNTs from C2H2 decomposition over Co–Mo/MgO catalysts Original Research Article

A series of MgO supported catalysts having Co and Mo metals 5–40 wt.% in a ratio of 1:1 was prepared by impregnation method. Carbon nanotubes (CNTs) were grown over the catalysts by decomposition of C2H2 at 800 °C for 30 min. It was found that 5 and 10 wt.% Co–Mo/MgO catalysts produced single-wall nanotubes (SWNTs), whereas 20, 30 and 40 wt.% Co–Mo/MgO catalysts produced multi-wall nanotubes (MWNTs). The catalyst Mo/MgO was inactive in growing CNTs. In Co–Mo/MgO catalysts, however Mo generated a favorable environment to grow SWNTs. The growth of SWNTs was strongly dependent on the formation of small clusters of cobalt, which may generate from the decomposition of CoMoO4 species during the nanotube growth. MWNTs were produced over comparatively larger cobalt clusters generated from Co3O4 phase during the nanotube growth stage. The yields of SWNTs were about 6% and 27% over 5 and 10 wt.% Co–Mo/MgO catalysts, respectively. MWNTs yield (576%) was observed over 40 wt.% Co–Mo/MgO catalyst. Carbon yield (%) highly varied with acetylene concentration.