Coprecipitated Ni-alumina and Ni-Cu-alumina catalysts of methane decomposition and carbon deposition .3. Morphology and surface structure of the carbon filaments

Filamentous carbons produced by the coprecipitated Ni-alumina and Ni-Cu-alumina catalysts of methane decomposition were studied with high resolution transmission electron microscopy and scanning tunneling microscopy. Graphite layers were found to orient at an angle to the filament axis in carbon prepared by Ni catalysts, and perpendicular to the axis in those deposited on Ni-Cu catalysts. In both cases the surface was very rough and was likely represented by the misoriented edges of graphite crystallites. However, these graphite edges were generally bent so that at the filament surface of the carbon, deposited on Ni catalyst, the basal planes tend to be parallel to the filament axis. In prepared by Ni-Cu one the neighbor and/or next-neighbor layers were linked, therefore, producing the closed-layers structures. This surface reconstruction likely lowers the surface energy of the deposited carbons during catalytic reaction.