Study On Preparation Of Carbon Nanotubes And Their Applications As Catalyst Support

Proved by a great deal of theoretical and experimental studies, carbon nanotubes (CNTs) have become one of the most promising materials in the fields of catalyst support. Compared with traditional supports, CNTs have unique"template function"in tailing the size of metal particles, for example, Ni/CNTs catalysts can control the nano-diameter of active metal particles effectively and improve the performance of catalysts greatly. Study on preparation methods of metal/CNTs is the key to the industrization of CNTs support. Comparisons are made between multi-walled carbon nanotubes (MWNTs) and traditional supports; Elementary application of CNTs on catalyst support is also studied in this thesis.First, Fe, Co and Ni were loaded on different catalytic supports (α-Al2O3,SiO2,MWNTs, et al) to prepare catalysts. The activity of catalyst was evaluated through catalytic chemical vapor deposition (CCVD) of methane to produce MWNTs. The results indicate that the activity of supported transition metals decreases in the order of: Ni>Co>Fe and the suitable metal loading is 10%. The properities of supports also affect the dispersibility of the metal on them which results in the change of morphology of the MWNTs produced.Then the effect of different promoters on Ni catalysts was tested. The results showed that after La is added, the Ni /MWNTs catalyst becomes more active and the morphology of MWNTs produced is also improved which attributed to the increase of dispersibility of Ni metal on the support.Finally carbon nanotubes were pretreated with HNO3 oxidation method, and new catalyst preparation method was used with combination of long-time circumfluence and ultrasonic treatment of MWNTs and metal salt. The results proved that MWNTs, acting as"template reagent of nano-particles", almost disappear or transfer to another carbon phase after calcination, and that phase change may partly wrap and separate NiO nano-particles, prevent their agglomeration during the reduction process and greatly improve dispersibility of Ni particles(active site of the reaction), which increase activity of the catalyst.