Co/carbon-nanotube monometalic system: the effects of oxidation by nitric acid

Multi-walled carbon nanotubes, produced from catalytic decomposition of C2H2, were pre-oxidized by boiling nitric acid before being used as support media in a Co/carbon-nanotube monometallic catalyst system. The microstructures of nanotubes and the cobalt particles were examined by using high-resolution transmission electron microscopy and X-ray diffractometry. Various structural modifications on the nanotubes, such as thinned tubes, tubes with holes, and stepped surface with open edges of graphitic sheets were observed. In comparison with cobalt particles on unoxidized nanotubes, the cobalt nanoparticles deposited on the oxidized nanotubes have much smaller size and higher dispersion, resulting in significantly better catalytic performance (18.4% higher in initial conversion) in dehydrogenation of cyclohexanol to cyclohexanone.