Catalysts Preparation And Influence Of Reaction Conditions On Carbon Nanotubes

As a new carbon material, carbon nanotubes (CNTs) have many super properties, such as mechanical, electromagnetic, optical and their thermal stability. Due to these properties, they have potential applications in many fields, like nano-material, nano-biology, nano-chemistry. If the CNTs can be used in many areas, it is very important to know the growth rules and the influence factors of CNTs, and the control technologies of CNTs on shape, distribution, diameter and so on.In this work, the catalytic chemical vapor deposition (CCVD) method was used to synthesize the CNTs, the metal species and preparing conditions of catalysts, the carbon sources and reaction conditions of CNTs were studied. The experiment results suggested that when the CH4 as the carbon source, the shape and yield of the CNTs were better; and the CO as the carbon source, the yield and the core-hollow of the CNTs were better too; however the C2H2 as the carbon source, quantity of carbon fibers and ladderlike carbon strips were produced, the content of CNTs was very low. The orthogonal experiment result suggested that when the V_CH4:V_N2:V_H2=4:0:1,reaction temperature was 600℃,and reaction time was 60 min, the yield of CNTs reached the maximum. When the V_CH4:V_N2:V_H2=4:1:1,reaction temperature was 600℃,and reaction time was 60 min, both the shape and the yield of CNTs were better. The importance order of influence factors is: reaction temperature>gas ratio>reaction time.The products were characterized by X-ray Diffraction (XRD), Transmission Electron Microscope (TEM), Raman, BET and Thermogravimetric (TG). It was suggested that among the different supports, the specific surface areas of SiO₂ was maximum, it was the appropriate supports in this work. The catalytic activities order of metals was: Niï¹¥Coï¹¥Fe. When the CH4 as carbon source, Ni loading was 40%, the yield of CNTs reached the maximum; low loading was benefit to good shape of CNTs; the specific surface area was decreasing with the metal loading content increasing; when the calcination temperatures were increasing, the specific surface areas were decreasing too; the specific surface areas were increasing as the particle size of supports decreasing; the diameters of CNTs were related to the particle size of catalysts.