Selective synthesis of thin carbon nanofibers: I. Over nickel-iron alloys supported on carbon black

Selective and efficient synthesis of thin carbon nanofibers (CNF) of fish bone-like texture with diameter below 40 nm was shown at low temperatures (673-873 K) from an ethylene and hydrogen (4:1) mixture, using Ni-Fe alloys supported on carbon blacks of relatively small surface area. A particular alloy of a Ni-Fe (8:2 w/w) was highly dispersed to produce thinner fibers at 753 K than Ni alone or Ni-Fe catalysts of other compositions on carbon black, although the fiber yield was similar when the Ni content was more than 60%. It must be noted that unsupported alloy showed activity when the Ni content was higher than 75% at the same temperature. Catalyst particles were observed by using TEM and XRD to confirm the roles of carbon black and alloy composition on dispersion of the catalyst, even if the catalyst particle was degraded into a finer one at the growth of CNF. Carbon black of smaller surface area carries the catalyst particles on its surface to be active for CNF synthesis. (C) 2004 Elsevier Ltd. All rights reserved.