Intermetallic catalyst for carbon nanotubes (CNTs) growth by thermal chemical vapor deposition method

The methane conversion and carbon yield of the chemical vapor deposition (CVD) reaction suggests that the optimum reaction conditions of the formation of multi-wall carbon nanotubes (MWCNTs) can be obtained by using a 50 mg of nano-MgNi alloy under pyrolysis of the pure CH4 gas with the flow rate about 100-120 cm(3)/min at 650 degrees C for 30 min. Raman results indicate the CNTs are in multi-wall structure, since no single-wall characteristic features appearing in the 200-400 cm(-1) region. This is consistent with those of the XRD and TGA findings. Under selected condition, the carbon yield and the CNTs purity can reach up to 1231% and 92% in the presence of hydrogen. It is presumable that the presence of hydrogen in the pyrolysis of CH4 prevents the deactivation of catalysts and enhances the graphitization degree of CNTs. In addition, the presence of Mg metal in the alloy can prevent the aggregation of the Ni metal and forms the active Mg2Ni phase to enhance the CH4 Pyrolysis to form CNTs. After the purification procedures with both air oxidation at 550 degrees C and HCl treatments, the final purified yield and purity of CNT reach to 73.2% and (98.04 +/- 0.2)% respectively. (C) 2006 Elsevier Ltd. All rights reserved.