Preparation And Characterization Of Functional Mixed Oxides And Their Applications In Oxidative Coupling Reaction Of Alcohols And Amines

N-containing organic compounds,especially imines and their derivatives are very important chemical intermediate materials that have been widely applied to biology,agriculture,and pharmaceuticals.It not only widely exists in compounds and natural products with physiological and pharmaceutical activities,but also constitutes an indispensable substance for some organisms and life activities.At present,the direct oxidative coupling of alcohols and amines is regard as one of the most promising methods for imines synthesis.Because alcohols are cheap and readily available,the only by-product of the reaction is water,which is in line with the concept of green chemical development.However,how to activate the C-H bond of alcohols and stabilize the C(28)N double bond of imines under green and mild reaction conditions is still a challenge.In recent years,functional mixed oxides have been widely studied and applied in many chemical fields due to their superior redox,acid-base amphoteric,chemical stability,shape plasticity,recyclability and other advantages.They are the largest category of catalysts in heterogeneous catalysis.Therefore,it is of great scientific research value and significance to develop new and cheap functional composite oxides and use them as catalysts to realize the direct oxidative coupling of amines and alcohols in liquid phase for imines synthesis under mild reaction conditions.In this dissertation,Pd-CeNi_XO_Y?HS-CeO₂(HS:High Surface Area)and Au/Zn_XAl₂O₃catalyts have been developed for efficient imines synthesie from oxidative coupling of alcohols and amines under green and mild reaction conditions.The preparation and characterization methods of the catalysts and the effects of reaction parameters have been investigated.Finally,the structure-activity relationship and reaction mechanism have been dicussed and establied based on catalysts characterizations and catalytic performances.In this dissertation,Pd-CeNi_XO_Y catalysts were prepared by one pot precipitation method.HS-CeO₂ catalysts were prepared by template induced homogeneous precipitation method.Zn_XAl₂O₃ supports were prepared by co-precipitation method.Au/Zn_XAl₂O₃ catalysts were prepared by immobilization of the PVA-stabilized colloidal Au nanoparticles onto Zn_XAl₂O₃ supports.The NaBH₄ was used to reduce Au micelle precursor solution.In Pd-CeNi_XO_Y catalysts,Pd species and Ni/Ce molar ratio play an important role in the activation of alcohol molecules in the presence of active amine molecules.Among a series of catalysts,Pd-CeNi_0.3O_Y showed the best catalytic performance.In O₂(1bar)the atmosphere and without any alkali promoter,Pd-CeNi_0.3O_Y could efficiently oxidate coupling of various alcohols and amines to form corresponding imines.CeNi_0.3O_Y catalyst at 100?C for 26 hours can obtain(29)99%yield of imine.While Pd-CeNi_0.3O_Y catalyst only at 60?C for 16 hours can obtain(29)99%yield of imine.A very small amount(0.18 mol%)of highly dispersed metallic palladium subatomic nanoclusters significantly accelerates the imines formation rate under mild conditions by accelerating the selective oxidation of benzyl alcohol to benzaldehyde which has been confirmed as the reaction rate-determining step.XRD,XPS,ICP-MS,N₂ isotherms,UV-Raman,H₂-TPR,TEM and EPMA characterization methods were used to characterize the physical and chemical properties of the catalyst.The results show that changing the Ni/Ce molar ratio can regulate the interaction between Ni²⁺and CeO₂ surface interface,enhance the reversible redox process between Ce³⁺and Ni²⁺species,thereby inducing the production of more coordinated unsaturated Ce³⁺ions and oxygen vacancy catalytic active sites.Pd-CeNi_0.3O_Y showed the highest concentration of Ce³⁺species and surface oxygen vacancy,and showed the highest catalytic activity under the synergistic effect of Pd promoter.The strong interaction between Ce³⁺-Ni²⁺redox pairs resists the agglomeration of CeO₂ nanoparticles(5nm)and the depletion of active oxygen vacancy during the reaction process,so that the performance of the catalyst remains stable after repeated continuous cycle experiments.The catalytic performance of HS-CeO₂ catalyst was mainly affect by surfactant,calcination temperature,substrate molar ratio,reaction temperature and reaction time.When used CTAB as template and calcined at 400?C,CeO₂ showed the largest specific surface area and the highest catalytic activity.When aniline/benzyl alcohol molar ratio was 1.5,100%conversion of benzyl alcohol and>99%yield of imine were achievcd at 80?C under air in 2 hours.The catalytic activity,reaction mechanism and route of the catalyst were investigated by thermodynamic and kinetic experiments.XRD,XPS,N₂ isotherms,H₂-TPR,O₂-TPD and UV-Raman characterization methods were used to characterize the physical and chemical properties of the catalyst.The results shown that compared with CeO₂ with low specific surface area(LS-CeO₂),HS-CeO₂ catalyst showed higher species content of surface active oxygen species,higher concentration of surface coordination unsaturated Ce³⁺and stronger redox property.These properties are conducive to the oxidation of benzyl alcohol to benzaldehyde,which has been proved the rate-determining step of the whole reaction,so as to promote the whole reaction.In addition,HS-CeO₂ catalyst showed no obvious deactivation during four recycling uses and showed good stability.The catalytic performamce of the Au/Zn _XAl₂O₃ catalyst was mainly influenced by Zn/Al molar ratio and calcination temperature.In this dissertation,a series of trace(1-4mol%)ZnO-doped?-Al₂O₃ supports were prepared by co-precipitation method,and traces(0.4 wt%)of Au nanoparticles were loaded on the surface.Among the series of catalysts,the Au/Zn_0.02Al₂O₃ catalyst calcined at 400?C shows the highest catalytic activity.It could efficiently oxidate coupling of various primary alcohols and primary amines under the air atmosphere at 30-60?C and(29)99%selectivity of corresponding imines could be achieved.In the oxidative coupling model reaction between benzyl alcohol and aniline,The Au/Zn_0.02Al₂O₃ catalyst exhibited the highest TOF(39.1 h^-1)at60?C based on a>99%yield to benzylideneaniline among all the ever-reported Au-based catalysts.It was demonstrated that the uniform and small(2.9 nm)Au nanoparticles in metallic state were active sites and responsible for activating and converting an alcohol to an aldehyde,i.e.,the rate-determining step.XRD,XPS,ICP-MS,N₂ isotherms,TEM and CO₂/NH₃-TPD characterization methods were used to characterize the physical and chemical properties of the catalyst.The results show that changing the Zn/Al molar ratio can regulate the interaction between ZnO and Al₂O₃ surface interface,thereby inducing the production of more surfacea ctive oxygen species and regulating the acidic-basic property of support.Among the series of catalysts,the Au/Zn_0.02Al₂O₃ catalyst calcined at 400?C showed the highest concentration of surface oxygen species,the largest specific surface area,and suitable acid-base sites,thus showing the highest catalytic activity.The strong interaction between the highly dispersed nano-Au particles and the suppoet resists the agglomeration and oxidation of the Au⁰ species during the reaction,which is the main reason why the activity of the catalyst remains stable after multiple continuous cycle experiments.