Nitrogen-doped Carbon Nanotubes Preparation And Their Catalytic Performance In Nitrobenzene Hydrogenation Reaction

As a kind of important chemical industrial raw material,aromatic amine is widely used in all kinds of industries,and it is usually prepared by catalytic hydrogenation of nitro compounds.In general,catalytic hydrogenation reaction are metal catalysts,due to the cost of precious metal catalyst is higher,more and more researchers tend to use general metal instead of noble metal,but the active component are also easy to loss,catalyst poisoning,easy to clusters and so on,results in the decrease of catalyst activity,therefore exploit a low cost,without the shortcomings of the catalyst is imperative.Non-metal catalysts because of no metal component,so there is no these problems,and carbon nanotubes as a kind of excellent materials are widely used,if we can for its modification,directly used as a hydrogenation catalyst will be of great significance.In this paper,the carbon nanotubes were modified by nitrogen,and the reaction of nitrobenzene hydrogenation was investigated,and the possibility of using it as a hydrogenation catalyst was studied and the activity center was also investigated.In this work,nitrogen doped carbon nanotubes were prepared by in-situ synthesis and post-treatment.In-situ synthesis method is prepared nitrogen doped carbon nanotubes by chemical vapor deposition(CVD),then examines the influence of different carbon and nitrogen source,different temperature on the nitrogen doped carbon nanotubes,found that aniline as carbon and nitrogen source,preparation of the nitrogen doped carbon nanotubes under 850 ? is the best.The post-treatment is use the carbon tubes and melamine to produce nitrogen doped carbon nanotubes at high temperature.By characterization of TEM contrast,diameters are the same about 20 nm,but the in situ synthesis of NCNTs are display bamboo like structure,and the NCNTs prepared by post treatment are not present a bamboo-like structure,and the wall is obviously thicker.In this work,the two NCNTs were used in the catalytic hydrogenation of nitrobenzene which is a probe reaction,fund that the NCNTs prepared by in-situ synthesis did not show the catalytic performance,but the NCNTs prepared by post treatment have shown catalytic activity,through the design experiment to eliminate the influence of residual metal in carbon nanotubes,indicate that is the nitrogen doped lead to carbon nanotubes have hydrogenation catalytic activity.And then through the high temperature remove nitrogen experiment further excludes the separated defects impact,further confirmed a certain type of nitrogen at work,through the XPS characterization of the catalysts found only in the presence of pyrrole nitrogen,nitrogen doped carbon nanotubes is shown catalytic activity,indicate that pyrrole nitrogen may be the active center of catalytic hydrogenation reaction.This work through the various types of nitrogen doped carbon nanotubes simulation theory,found that the adsorption energy of hydrogen adsorption to maximum at the pyrrole nitrogen.And three different types of nitrogen element in the same tubes,structure optimization and calculation,found that the front molecular orbitals are mainly concentrated in the vicinity of pyrrole nitrogen,indicate that at pyrrole nitrogen is more advantageous for hydrogen adsorption and dissociation on carbon nanotubes,which suggests that pyrrole nitrogen is the catalytic hydrogenation reaction reactive activity center.