Growth of Tailored Oxide Nanostructures for Use as Catalyst Support Media

Graphite nanofibers are a family of materials consisting of graphene sheets arranged at various angles with respect to the growth axis. Graphite nanofibers possessing a structure in which the individual sheets constituting the material are aligned in a direction perpendicular to the growth axis have been used as templates for the deposition of selected metal oxides. The abundant number of exposed edges in the substrate act as collection centers onto which the chemical vapor deposited oxides nucleate and grow in an epitaxial manner. When the mixed oxide/graphite nanofiber structure is treated in CO<INF>2</INF> at 1100 °C, it is possible to selectively remove the carbon skeleton so that one is left with a highly crystalline metal oxide faceted nanotube. Electron diffraction and X-ray diffraction studies demonstrate that these oxides adopt preferred orientations that are quite different from those encountered with the corresponding oxide powders, which are generally amorphous in nature. These novel oxide structures provide a well-ordered surface on which to disperse small metal particles for subsequent use as catalysts. Preliminary results indicate that when iron is supported on the graphite nanofiber-modified alumina surface, the catalytic behavior of the system is significantly different from that observed when the metal is dispersed directly onto the nanofibers or the oxide powder. This effect is discussed in terms of the possibility that the metal particles adopt a preferred crystallographic orientation on the oxide nanotube surface, which favor interaction with certain gas-phase molecules.