Effects of composition of W-Fe-MgO catalyst and reaction conditions on preparation of single-walled carbon nanotubes by catalytic decomposition of methane

The W-Fe-MgO catalyst was prepared by calcination of the mixture of Mg(NO3)(2) (.) 6H(2)O, Fe(NO3)(3) (.) 9H(2)O, ammonium tungstate and citric acid at 823 K and used to prepare single-walled carbon nanotubes (SWCNTs) in a fluidized bed reactor with 25% CH4-H-2 or 25% CH4-Ar gas mixture at 1073similar to1373 K. The effects of reaction temperature, carrier gases and catalyst composition on the carbon production were investigated by Raman spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicated that the optimal temperature of methane catalytic decomposition was 1 373 K using H-2 as carrier gas and 1073 K using Ar as carrier gas. In H-2 atmosphere at 1373 K, the carbon yield increased with the W content in the catalyst and the SWCNTs content in the products was constantly high; the highest carbon yield of SWCNTs could be up to 55% (based on the catalyst mass) on the catalyst with a W:Fe: Mg molar ratio of 3: 10: 100. In Ar atmosphere at 1073 K, a high SWCNTs content product could be obtained on the catalyst with W:Mg = 1:100, but with W:Mg more than 1: 100 the SWCNTs content in the products dropped sharply. According to the results of XRD and XPS analysis, active phases for the SWCNTs growth is suggested.