Carbon Nanofibers: Catalytic Synthesis and Applications

Carbon nanofibers (diameter range, 3-100 nm; length range, 1.1-1000 µm) have been known for a long time as a nuisance that often merges during catalythic conversion of carbon-containing gases. The recent outburst of interest in these graphitic materials originates from their potential for unique applications as well as their chemical similarity to fullerenes and carbon nanotubes. In this review, we focus on the growth of nanofibers using matallic particles as a catalyst to precipitate the graphitic carbon. First we summarize some of the earlier literature that has contributed greatly to understand the nucleation and growth of carbon nanofibers and nanotubes. Thereafter, we describe in detail recent progress to control the fiber surface structure, texture, and growth into mechanically strong agglomerates. It is argued that carbon nanofibers are unique high-surface-area materials (~200 m2/g) that can expose exclusively either basal graphite planes or edge planes. Subsequently, we will present the recently explored applications of carbon nanofibers: polymer additives, gas storage materials, and catalyst supports. The latter application is described in detail. It is shown that the graphite surface structure and the lyophilicity play a crucial role during metal emplacement and catalystic use in liquid-phase catalysis. A case in piont is fiber-supported Pd catalysts for nitrobenzene hydrogeneration. Finally, we summarize issues with respect to the large-scale production of carbon nanofibers, including production cost estimates and research items to be dealt with in future work.