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

摘要

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 °C. The unsupported Ni-Fe catalyst was prepared by a reduction-substitution method. In the Ni-Fe alloy particle, α-Fe(Ni) phase (kamacite) transforms to γ-Fe-Ni phase at the high temperature for hydrogen reduction and chemical vapor deposition. The synthesized CNOs contain either a Fe_(0.64)Ni_(0.36) 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 γ-Fe-Ni phase (Fe_(0.64)Ni_(0.36)). A growth mechanism for the CNOs is proposed.