We show a significant effect of the preparation method of the Ni/CaO catalysts on the properties and growth mechanism of the multi-walled carbon nanotubes (MWCNTs). MWCNTs were synthesized by the catalytic chemical vapor deposition (CCVD) method using ethylene as a carbon source. The purity, the distribution of the inner and outer diameters, the morphology of MWCNTs and the structure of the catalyst were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and the nitrogen adsorption-desorption method. Our studies reveal that the interaction between the CaO support and Ni nanoparticles is mainly weak resulting in the “tip-growth” mechanism. However, the structure and diameter distribution of the carbon nanotubes depend on the method of preparation of the Ni/CaO catalysts. Differences in the structure and in the diameters of the MWCNTs are caused by the chemical transformation of the support during the catalyst preparation and by the formation of the nickel nanoparticles of different size distributions and shapes.
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