Growth of single and double walled carbon nanotubes over Co/V/MgO catalysts

Highlights: → Co/V/MgO has remarkable catalytic activity on the growth of SWCNTs and DWCNTs. → The diameter of CNTs can be controlled by adjusting molar ratio of Co-V to MgO. → The formation of C7V8 is critical to the synthesis of thin CNTs. -- Abstract: High quality single walled carbon nanotubes (SWCNTs) and double walled carbon nanotubes (DWCNTs) were synthesized on Co/V/MgO catalysts by catalytic decomposition of CH4 in H2. Raman spectroscopy data revealed that the diameters of as-prepared SWCNTs are 1.28 and 0.73 nm. The diameter value of DWCNTs from Raman analysis also showed a narrow diameter distribution. Using field emission transmission electron microscopy (TEM), it was found that the diameter of carbon nanotubes can be controlled mainly by adjusting the molar ratio of Co-V versus the MgO support. The structure properties of catalysts were examined by X-ray diffraction (XRD). The formation of C7V8 may play an important role in preserving carbon in the catalyst particle and favoring the dissociation balance of CH4.