Preparation Of Carbon Nanotubes Supported Metal Catalysts And Their Performance In Chloronitrobenzene Hydrogenation Reactions

The hydrogenation of chloronitrobenzene to chloraniline is one of the most important organism unit reactions.It is of great industrial value.Therefore,much attention has been paid to the design and synthesis of catalysts with excellent catalytic properties for chloronitrobenzene hydrogenation reactions.In this thesis,the preparation of carbon nanotubes supported metal catalysts and their catalytic performances in the hydrogenation of CNBs have been investigated.Carbon nanotubes supported Pt and PtM(M=Ni,Co,Fe,Cu) catalysts exhibit good o-CNB hydrogenation properties.It is found that the activation temperature is one of the key factors that affect both the nanopartiele size and the catalytic performance of Pt/CNTs.The Pt particles size increases with temperature.Pt/CNTs catalyst activated at 400℃shows the highest catalytic activity in o-CNB hydrogenation reaction.For PtNi/CNTs bimetallic catalysts,the effect of impregnation sequence is found to influence the hydrogenation acitivty remarkably.The catalytic acitivity of Pt-Ni/CNTs catalysts prepared with a fixed Pt loading using the co-impregnation method decreases with Ni loading.However,for the Pt/Ni/CNTs catalysts with Ni loading ranging from 0.05～0.45%,prepared by impregnation of Ni precursor and reduction,followed by the impregnation of Pt precursor and reduction,the catalytic activity is higher than Pt/CNTs catalyst.The catalytic activity is the highest when Ni loading is 0.15%.Pt/Fe/CNTs,Pt/Co/CNTs and Pt/Cu/CNTs catalysts also have excellent activities for o-CNB hydrogenation.Moreover,Pt/CNTs and Pt/M/CNTs catalysts are found to have good selecticity toward o-CAN.Pd/SnO₂/CNTs catalysts with different Sn/Pd molar ratios have been synthesized and tested in the hydrogenation of CNBs.The results show that very good o-CAN selectivity can be obtained over Pd/SnO₂/CNTs catalysts,whereas the catalytic activity depends on the Sn/Pd ratio.Pd/SnO₂/CNTs with Sn/Pd is 11 has the highest activity,with 96%o-CNB conversion at 1 atm and 60℃,which is comparable to that of Pd/CNTs catalyst prepared via the impregnation method.However,the o-CAN selectivity over Pd/SnO₂/CNTs is much higher with 95%o-CAN selectivity when o-CNB is completely consumed,while the o-CAN selectivity is only 22%over Pd/CNTs catalyst.The coordination of SnO₂ is responsible for the relative high o-CAN selectivity.Ni/CNTs are also ideal catalysts for o-CNB hydrogenation reactions.Both the preparation methods and conditions influence the activity of the as-obtained Ni/CNTs catalysts greatly. Based on the comparison results of different methods,it is found that the Ni/CNTs catalyst prepared using deposition-precipitation(DP) in polyol shows the highest catalytic activity. The precipitation temperature and types of solvent are crucial factors that affect the properties of Ni/CNTs catalyst.For Ni/CNTs prepared using DP in ethylene glycol(EG),the Ni content are similar at different precipitation temperatures,however,the Ni particle sizes as well as the catalytic properties vary a lot.The Ni nanoparticle sizes are smaller for Ni/CNTs prepared via DP in EG at the precipitation temperature of 120℃and 160℃,5.1 and 5.7 nm respectively. Ni/CNTs catalysts obtained at 80℃exhibits the highest activity,the conversion of o-CNB can reach 91%with 97%o-CAN selectivity at 2 MPa,140℃in 30 min.Glycerol has also been used as a solvent to prepare Ni/CNTs catalyst,and the results show that both the Ni content and the catalytic activity increase with the precipitation temperatures.Ni/CNTs catalysts show better activity than Ni/AC,which is probably due to the different metal-support interaction and the unique electronic properties of CNTs.Moreover,the mesepore structure of CNTs also favors the mass transfer of the reactants.Ag/CNTs catalysts have been prepared via deposition precipitation method,and the feasibility of the as-synthesized Ag/CNTs catalysts for o-CNB hydrogenation has been investigated.The results show that the hydrodechlorination can be depressed to some degree over Ag/CNTs catalyst,implying that Ag/CNTs is of potential as selective catalyst for the hydrogenation of CNBs.