Carbon nanotubes （CNTs） were prepared using different carrier gases, with ferrocene as the catalyst precusor and acetylene as the carbon source. The effects of ammonia and nitrogen as carrier gases on the structure and morphology of CNTs were investigated. Transmission electron microscope （TEM）, high-resolution electron microscope （HRTEM）, scanning electron microscope （SEM） and X-ray diffraction （XRD） were employed to characterize the products and the catalyst. Experiment results show that the CNTs grown in N2 gas exhibited cylindrical and tubular structure, while a bamboo-like structure was observed for the CNTs grown in NH3 gas. Moreover, vertically aligned CNTs were obtained on an A12O3 disk when NH3 was used as the carrier gas. The carrier gas also exerted influence on the shape of the catalyst. Based on the theory of active centers of catalysis and combined with the particle shape of the catalyst, a growth model for the vertically aligned CNTs on the substrate is given.
The effect of reaction modes,i.e.fluidized bed and fixed bed operations,on catalyst life for hydrogen production from methane decomposition was investigated over a 75Ni15Cu10Al catalyst and a 2Co1Al catalyst.Pure methane was used as the feed.The results showed that the apparent reaction rate in the fluidized bed was much higher than that in the fixed bed,indicating that in the fixed bed the reaction was transport-controlled.The carbon formed was characterized with TEM technique,and the results showed that the size of metal particles increased with rising reaction temperature,and at the same reaction temperature the size of metal particles on the catalyst in the fixed bed was larger than that on the catalyst in the fluidized bed,signifying that fluidized bed reactor is beneficial to preventing the sintering of active metals.
