The efficient synthesis of carbon nano-onions using chemical vapor deposition on an unsupported Ni-Fe alloy catalyst

Well graphitized carbon nano-onions (CNOs) with large yield have been synthesized by the catalytic decomposition of methane over an unsupported Ni-Fe catalyst at 850 degrees C. The unsupported Ni-Fe catalyst was prepared by a reduction-substitution method. In the Ni-Fe alloy particle, alpha-Fe(Ni) phase (kamacite) transforms to gamma-Fe-Ni phase at the high temperature for hydrogen reduction and chemical vapor deposition. The synthesized CNOs contain either a Fe0.64Ni0.36 particle or a hollow core with thick graphitic layers and a polyhedral shape. Based on the characterization, we believe that the catalyst involved in the synthesis of carbon products is Fe-Ni-C austenite rather than the gamma-Fe-Ni phase (Fe0.64Ni0.36). A growth mechanism for the CNOs is proposed. (C) 2010 Elsevier Ltd. All rights reserved.