Growth of graphite nanofibers from the decomposition of CO/H2 over silica-supported iron-nickel particles

Extremely fine, tubular,graphite nanofibers of varying geometries and degrees of crystallinity were produced by the decomposition of CO and hydrogen over various compositions of nickel-iron particles supported on silica. High-resolution transmission electron microscopy coupled with temperature programmed oxidation studies revealed that, as the iron content of the catalyst was increased, the bimetallic particles precipitated a chainlike graphitic fibrous structure in a stepwise mechanism. The high-iron-content system Fe-Ni (8:2) yielded a small amount of these chainlike graphite fibers that were extremely resilient to oxidation, suggesting a highly crystalline structure. When the catalyst particles consisted of a nickel-iron mixture, Fe-Ni (5.5), there was a decrease in the degree of crystallinity of the fibers (78% graphite) and a corresponding increase in the amount of amorphous carbon precipitated (22% amorphous) within the structure. The high-nickel catalyst Fe-Ni (2:8) generated the largest amount of the tubular nanofiber product. It was significant that there was an increase in the amorphous carbon content (58%) precipitated as opposed to graphitic carbon (42%) in the structures. In some cases, amorphous carbon was deposited inside the graphite core of the nanofibers. The influence of the catalyst composition and nature of the metal-support interaction are key factors in the continuing development of graphite nanofibers possessing desired structures for potential uses in a variety of applications.