Structure-function Relationship For Metal/Carbon Hybrid Materials In Catalyzing Ethylbenzene Dehydrogenation Reactions

Developing novel and highly efficient catalysts and related reaction systems become one of the most popular research topic in the field of material science,chemistry and chemical engineering,facing the urgent demand of the green and sustainable chemical industry.Nanocarbon shows exceptional catalytic performance and great potential to efficiently utilize or replace traditional metal-based catalysts in many heterogeneous catalytic reactions as catalytic active components or supports.Related research mainly focuses on the synthetic technology of nanocarbon or nanocarbon supported metal-based catalysts and the evaluation of their apparent catalytic activity.However,the in-depth understandings on the function of the catalyst are still insufficient.In particular,the qualification and quantification of the active sites,the catalytic reaction pathways,the catalytic reaction mechanism and the origin of the high catalytic activity etc.have not been really clarified.The in-depth studies aiming at above issues could establish the basic theory of structure-activity relationship,shedding light on the rational design of the highly efficient nanocarbon or nanocarbon supported metal-based catalysts and related reaction systems.The present thesis mainly focuses on the alkane(ethylbenzene)dehydrogenation reaction under the catalysis of nanocarbon or nanocarbon supported metal-based catalysts,and the main contents can be summarized as following:(1)A novel hollow nanosphere carbon-based catalyst(HNSs)was synthesized via the polymerization of dopamine and subsequent carbonization method and was applied in the oxidative dehydrogenation(ODH)reaction of ethylbenzene(EB).The ketonic carbonyl/quinone groups on this nanocarbon were identified as active sites for EB ODH reaction,and the number of ketonic carbonyl/quinone groups and the intrinsic catalytic activity could be determined via the in situ titration strategy.C-H bond activation was the rate determining step for the reaction system.The key promotion effect might come from the strong chemical adsorption/activation ability of carbon-based catalyst due to the introduction of high content of quaternary nitrogen species.(2)A Pd/hollow nanocarbon spheres(Pd@HNSs)bifunctional catalyst was prepared,by which a special dual-path dehydrogenation(DPDH)route for efficiently convert EB to styrene(ST)was realized.Pd single-atoms and quinone groups served as actives sites for EB direct dehydrogenation(DH)and ODH reactions,respectively.The dual-path dehydrogenation route was not the simple sum but the synergy between DH and ODH reaction,leading to relatively high styrene formation rate.Oxidative dehydrogenation reactions on quinone groups yielded small amount of H2O that could lower the energy barrier for H2 formation and desorption via proton transfer process as well as facilitated the DH process.(3)A series of Ni-P/oxidized carbon nanotube(oCNT)catalysts were prepared via a simple impregnation and reduction process using commercial oCNT as support,by which an efficient EB DH reaction system with high activity and stability was realized even without the protection of superheated steam.The Ni2POx component on Ni-P/oCNT-x might be the active phase for the reaction,as well as the relatively strong redox ability and relatively weak ethylbenzene adsorption ability might be the primary reason for highly efficient EB DH reaction.(4)A novel electrochemical route for cycloaddition of CO2 and styrene oxide to value-added styrene carbonate was proposed using non-metallic nanocarbon material(HNSs)as the catalyst electrode,and the detailed catalytic activity and reaction mechanism of this reaction system was investigated.The efficiency of HNSs catalyzed cycloaddition reaction reached the best level even comparing with conventional metal catalysts.Correlating the catalytic performance results with related structure analysis information,the synergistic cooperation between nitrogen and oxygen functionalities was the key for the admirable catalytic performance of HNSs.The doped graphitic N in HNSs provided additional electrons into the delocalized π-system,which could facilitate the electron transfer in the electrochemical reaction process.The pyridine N group might be the active sites for CO2 activation,and the-COOH groups facilitated the activation and ring opening of styrene oxide.