Co/carbon-nanotube monometallic system: the effects of oxidation by nitricacid

Multi-walled carbon nanotubes, produced from catalytic decomposition of C2H 2, were pre-oxidized by boiling nitric acid before being used as support me dia in a Co/carbon-nanotube monometallic catalyst system. The microstructur es of nanotubes and the cobalt particles were examined by using high-resolu tion transmission electron microscopy and X-ray diffractometry. Various str uctural modifications on the nanotubes, such as thinned tubes, tubes with h oles, and stepped surface with open edges of graphitic sheets were observed . In comparison with cobalt particles on unoxidized nanotubes, the cobalt n anoparticles 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.