Selective synthesis of carbon nanofibers with various structures through the catalytic pyrolysis of ethylene

Carbon nanofibers (CNFs) with various structures were selectively synthesized through the catalytic pyrolysis of ethylene using non-supported and SiO_2-supported metals (such as iron, nickel, iron/nickel alloy). Tubular, solid herringbone and hollow herringbone structures were obtained by using SiO_2-supported Fe, Ni and Fe-Ni catalyst, respectively. Uniform CNFs with small diameter and high yield were synthesized using SiO_2-supported catalyst because of the strong metal-support interaction, which results in high reactive activity at relatively a low temperature. The different structures of the resultant CNFs were ascribed to the dispersion of the metal catalyst and the different growth mechanisms. Normally Fe catalyst displays poor activity for the synthesis of CNFs by CVD of ethylene even at high temperature up to 650℃. However, tubular CNFs were prepared at a very low temperature of 500℃ by using SiO_2-supported iron catalyst in our experiments.