Rational Design And Synthesis Of Polymers Catalysts With Ketonic Carbonyl Groups For Dehydrogenation/Hydrogenation Reaction

The application of nanocarbon materials in catalysis has been developed unprecedentedly in recent years due to its unique physical and chemical properties.Nanocarbon have shown promising activity in many catalytic processes,especially in redox reactions(Dehydrogenation and Hydrogenation).Although fruitful results have been achieved in synthesis of new nanocarbon materials and exploration of new carbon catalytic systems,there is only limited growth of mechanistic interpreation of carbon-catalyzed reactions.Although temperature programmed desorption(TPD),X-ray photoelectron spectroscopy(XPS)and chemical titration techniques have provided us valuable insight into nanocarbon,it is still scarcely possible to investigate the carbon-catalyzed process at molecular level using these characterization methods due to the complexity and uncertainty of the nanocarbon surface.In this thesis,we designed and synthesized a kind of polymer model catalyst with defined structure and single kind of functional group,and applied them to the mechanism investigation of ethylbenzene oxidative dehydrogenation(ODH)and nitrobenzene dehydrogenation reduction.Combining operando spectroscopy results,chemical titration,isotope labelling method and catalytic kinetics results,we propose the reaction pathway for the above carbon-catalyzed reactions.In addition,we also develop a novel nanocarbon/polymer nano composites,which exhibits good activity in alkane ODH and nitroaromatic reduction reactions.The main research contents and results are listed as follows:(1)A series of conjugated polymers(YPB-x)with designated defined structure were synthesized using 3,6-dibromo phenanthrenequinone and 1,3,5-tribromobenzene as monomer via Yamamoto coupling.Chemical titration results show that ketonic carbonyl groups are catalytic active center of the nanocarbon-catalyzed EB ODH reactions.In addition,direct spectroscopic evidence on the evolution of configurations of the active sites during ODH reactions was provided based on in situ DRIFT analysis.Combining operando spectroscopy results,isotope labelling and catalytic kinetics results,we propose a reaction mechanism that relying on the transformation between carbonyl group and hydroxyl groups.The reaction mechanism can be divided into hydrogen-abstraction process and re-oxidation process,while the former is rate-determining step.(2)YPB-x series was further used as model catalysts to investigate the kinetics and mechanism of carbon catalyzed nitroaromatic reduction reactions.The influence of temperature,reductant usage,nitrobenzene concentration on the catalytic activity were carefully investigated.Kinetics results show that ketonic carbonyl groups are the active sites for nitroaromatic reduction reactions.The reaction show pseudo-first order behavior when reductant hydrazine hydrate is excessive.A catalytic reaction mechanism is proposed based on the FT-IR experiments and kinetics analysis,which includes forming active reduzate[H](activation of hydrazine hydrate on carbonyl groups)and reduction of nitrobenzene by[H].Among the reaction pathways,the reduction of nitrobenzene to nitrosobenzene is rate-determining step.In addition,the intrinsic activity of YPB-x catalysts(TOFYPB-6=23.6 h-1)was calculated through comparison of activity among several classic carbon catalysts.(3)A novel kind of CNT/YPB nanocomposites was successfully synthesized through ?-?interactions between carbon nanotube(CNT-1300)and monomers of polymer.The synthesis was accomplished via in situ polymerization on CNT-1300.CNT/YPB exhibits the advantages of considerable ketonic carbonyl groups concentration of YPB and good thermal stability of CNT,respectively.The activity of CNT/YPB in EB ODH and nitrobenzene reduction reaction is increased with the content of YPB on composites.However,the intrinsic activity of CNT/YPB remains nearly constant for all synthesized composites(the TOF of CNT/YPB-1 and CNT/YPB-2 for ODH reactions are 1.02×10-5 s-1 and 1.11×10-5 s-1).Although polymer content is much less than that of pure YPB-x,CNT/YPB-2 shows negligible lower apparent activity comparing with YPB-6,which indicates that CNT/YPB nano composites can make full use of YPB polymer and reduce the catalyst cost.(4)Using another high graphitization carbon nanotube(HHT)as substrate,we further synthesized HHT/YPB nanocomposites using in situ polymerization method.The structure and physico-chemical property of HHT/YPB is similar to CNT/YPB nano composites,and the activity of HHT/YPB is also increased with the content of YPB.This results confirm that the proposed method for the fabrication of nanocarbon/YPB composites is a universal strategy for different types of carbon nanotubes.However,the activity of HHT/YPB in EB ODH and nitroaromatic reduction reactions is obviously different from that of CNT/YPB,suggesting that the property of substrate could prominently influence the activity of the nanocarbon/YPB composites.