The Effect Of Oxygenous Surface Functional Groups And Heteroatom Doping Of Carbon Nanotubes On Catalytic Oxidation Of Cumene

Carbon nanotubes(CNTs) can be used as catalysts in various catalytic reactions due to their unique physical and chemical properties of outstanding electron conductivity, high surface area, strong corrosion-resistance, good thermal stability and easy modified, and to be a promising candidate for metal catalysts widely applied in catalysis. Researches indicated that surface properties of carbon materials have a great influence on their catalytic activities. In this thesis, CNTs were chosen as a research object. We designed and synthesized nanocarbon catalysts with different concentrations of surface functional groups, defects and heteroatoms and studied the mechanism of these catalysts in the free-radical oxidation of cumene liquid phase reactions, which is an important petrochemical process. The main contents and results are as follows:(1) Carbon nanotubes modified with oxygen-containing functional groups were prepared by gas-phase oxidation and concentrated nitric acid oxidation. The catalysts have been systematically characterized by a variety of characterization methods, meanwhile the catalytic performance of these catalysts for cumene selective oxidation were evaluated. This study indicates that the oxidized CNTs are not conducive to cumene catalytic reaction, the catalytic activity decrease with the increasing of oxidation degree. Oxygen-containing functional groups on the surface of CNTs can be removed gradually by thermal treatment at different temperatures in inert gas, and the surface defects get partial repair at the same time. The catalytic activity of the annealed O-CNTs recover successfully or even higher than the original CNTs. Further studies indicate that the defect has no obvious impact on the activity of cumene oxidation, and the surface oxygen functional groups on CNTs are the main reason for the decreased catalytic activity.(2) In order to investigate the mechanism of oxidative carbon nanotubes in cumene selective oxidation, we added oxidative CNTs treated by nitric acid into the commercial CNTs which has a good activity in cumene reaction. We found that the conversion of cumene reduced from 24.06% to 3.5% at the same conditions. This phenomenon also existed in other metal catalyst system, we used Cu O powder as catalyst, and the cumene conversion decreased from 27% to 6.71% when adding the oxidative CNTs. These results show that the mechanism of oxygenous surface functional groups of CNTs is that the oxidative CNTs can be acted as free radical quenchers, capturing the free radical intermediate of reaction and inhibiting the free radical chain transfer, thereby reducing the catalytic activity of free radical reaction in liquid phase.(3) The P and N doped carbon nanotubes were prepared by different methods including chemical vapor deposition(CVD), thermolysis and hydrothermal synthesis. The catalysts have been systematically characterized and the catalytic performance of these catalysts were investigated in cumene selective oxidation. These results show that N-doped CNTs prepared by any kind of methods have better cumene activity than non-doped CNTs, while P-doped CNTs are unfavorable to cumene oxidation and the catalytic activity decreased with the increasing of phosphorus contents. Besides, P and N co-doped CNTs have a lower catalytic activities than N-doped CNTs. It is probably that the phosphorus atomic radius is bigger than the carbon atoms and the integrity structure of CNTs is undermined, resulting in a decrease of conductivity, electron mobility and electron transfer capability, thus causing the decrease of catalytic activity.