Growth of graphite nanofibers from the iron-copper catalyzed decomposition of CO/H2 mixtures

We have investigated the formation of graphite nanofibers from the catalytic decomposition of CO/H-2 mixtures over a series of powdered Fe-Cu catalysts at temperatures ranging from 500 to 700 degreesC. The physical and structural characteristics of the nanofibers have been established from examination of the materials by a variety of techniques including transmission electron microscopy, temperature-programmed oxidation, nitrogen surface area measurements, and X-ray diffraction. It was found that the addition of Cu to Fe did not exert a significant influence on the amount of solid carbon product formed in the reaction. On the other hand, examination of the nanofibers by high-resolution TEM revealed that the materials generated from Fe-rich Cu bimetallics were notably more graphitic in nature than those grown from pure Fe. As the reaction temperature was increased from 600 to 700 degreesC, the structure of the graphite nanofibers underwent a dramatic change from a "platelet" to "tubular" configuration. It is suggested that this transformation is directly associated with the alpha-Fe to gamma-Fe phase change over this temperature range.