The Preparation Of Quantitative Functionalized CNTs And Application In Catalytic Hydrogenation

Carbon nanotubes (CNTs) have special pore size, huge aspect ratio and extraordinary electrical property in nanoscale, and advantages over the conventional supports as used in the heterogeneous catalysis. However, the inert surface made CNTs difficult to solve, to disperse metal, which is unfavorable for its applications. It is, hence, necessary to develop the technique for the quantitative functionalize CNTs. In this thesis, we studied this issue and prepared CNTs with different functional groups with different amounts on its surface. Then we used them for the support of the Pt catalyst in the hydrogenation of nitrobenzene. Effects including the structure of functionalized CNTs, the amount of functional groups, and the different preparation methods, on the catalyst performance were carefully investigated, which was summarized as follows.Using inorganic acids as the oxidative media, the effects of temperature, acid type, the concentration of acids, and the time on the defect degree of CNTs and on the amount of functional groups were characterized by Raman,IR,TEM and acid-base titration. Controllable functionalized method was obtained to modify the CNTs surface, but to remain its excellent physical property unchanged. It is proposed here the weak oxidation firstly creates OH and C=O group and then strong oxidation creates the COOH in large amounts.Effects of the amount and type of functional groups on the structure of CNTs were characterized by TEM,SEM,Raman,XPS,XPS,Nitrogen adsorption and the acid-base titration. Functionalized CNTs and pristine CNTs have characteristic meso-and large pores, which were the stack pores between different tubes. The created functional group jam the micropores (0.7-0.8nm) between CNT layers and those (2-5nm) at the open end of CNTs. Such effect became drastically with the increase of the amount of functional groups and made an optimal value existed for the total surface area varied with the amount of functional groups. In addition, defect degree and hydrophilic ability of CNTs increases with the amount of functional groups.And a simple quantitative characterization method was built by the combination of XPS and the acid-base titration.Pt catalyst supported on such CNTs with clear surface property and structure showed better activity and selectivity for the hydrogenation of nitrobenzene to aniline, as compared to that supported on conventional activate carbon. The large pores of the granulated CNTs agglomerate favor the easy mass transfer and increase the catalytic performance significantly. The effect of functional groups lies in increasing the dispersion of Pt and the interaction of Pt and CNTs. The amount of functional groups can be tailored by changing the calcination temperature, which evidenced that excess functional groups not only enhanced the mass transfer of reactants to CNTs surface in solution, but also created more defects on CNTs surface to enhance the hydrogen spillover effect, which both increased the activity of the catalyst. The comparison of different preparation methods of Pt catalyst, including the impregnation, ion-exchange, the reduction by NaBH4 or ethylene glycol, suggested the electron charge of Pt precursor influenced the dispersion effect of Pt on the CNTs surface significantly. Proper control can greatly increase the dispersion degree, which allows the low loading of Pt and low cost for the preparation. Such method is easily repeatable for scale up.