Studies On The Design And Preparation Of Nanometer Palladium Alloys-based Catalysts And Their Application In The Suzuki Coupling Reactions

The Suzuki coupling reaction,also known as the Suzuki-Miyaura coupling reaction,is a kind of cross coupling reaction between unsaturated organic boron reagents and aryl halides.Due to its advantages such as mild reaction conditions,high conversion and selectivity and low toxicity of reactants,it is widely used in the synthesis of pharmaceutical intermediates,natural products,biologically active molecules,complex ligand,functional materials synthesis,etc.The core in the research of Suzuki coupling reaction system is the development of new catalysts.However,the conventionally used homogeneous palladium catalysts with organic ligands are frequently encountered with many disadvantages,such as expensive and toxic materials,tedious separation processes and poor catalyst stability and recyclability.Therefore,with the development of nanomaterials research,heterogeneous nanocatalysts are expected to provide solutions to the above problems.In this dissertation,several types of novel palladium alloys?palladium-nickel,palladium-gold and palladium/MIL-100?Fe??were designed and prepared for the Suzuki coupling reactions.Most of them demonstrated high activity,easy separability,good stability and recyclability for the title reaction due to synergistic effect of metals.This research not only provides new catalytic systems for the Suzuki coupling reaction,but also lays some foundations for the development of nanocatalysts.The main results of this dissertation can be summarized as follows:1.Preparation of the Pd-Ni/TiO₂ nanocatalyst and its application in the Suzuki coupling reactionsThe Pd-Ni/TiO₂ catalysts,which were used in the Suzuki coupling reaction,were synthesized by a one-step reduction method via immobilization of Pd-Ni nanoparticles on TiO₂.ICP-OES,XRD,TEM and XPS characterization were used to confirm their composition and structure.The results showed that the synergistic effect of palladium and nickel could effectively improve catalytic activity,as well as that the catalyst also showed excellent stability,recyclability and wide substrate scopes in the Suzuki coupling reaction.2.Preparation of the Pd-Au/TiO₂ nanocatalyst and its application in the Suzuki coupling reaction under visible lightPd-Au/TiO₂ was synthesized by a one-step reduction method,the composition,structure and photoresponsivity of which were confirmed by XRD,TEM,XPS,UV-vis DRS and PL characterization.In this work,we report for the first time that Pd-Au/TiO₂ could catalyze the Suzuki coupling reaction efficiently under visible light.The experiment results showed that the catalyst was used in mild conditions with excellent stability,recyclability and broad substrate scope in the Suzuki coupling reaction.The catalytic mechanism was investigated by means of electron-hole quenching experiments and XPS studies,which proved that the synergistic effect of all the Pd-Au/TiO₂ components is vital for the substrates activation under visible light.Au could increase the electron density of Pd through its LSPR phenomenon,which facilitated the oxidative addition of halogenated aromatics.Simultaneously,the photogenerated holes of TiO₂ enriched,diffused,and activated arylboronic acid to promote the transmetallation step,giving the target biphenyls by reductive elimination.3.Preparation of the Pd/MIL-100?Fe?nanocatalyst and its application in the Suzuki coupling reaction under visible lightIt is known that MIL-100?Fe?has excellent visible light responsivity and photocatalytic activity,as well as good water and chemical stability,which is potentially served as an excellent catalyst carrier.In this dissertation,Pd/MIL-100?Fe?was synthesized and used to catalyze the Suzuki coupling reaction under visible light,of which the composition,structure and photoresponsivity were confirmed by XRD,TEM,XPS,UV-vis DRS and PL characterization.The experiment results showed that Pd/MIL-100?Fe?could be used in mild conditions,and MIL-100?Fe?could effectively utilize visible light to increase the activity of the catalyst.Simultaneously,its stability and recyclability were studied by experimentation and TEM,XPS characterization.