| Solid catalysts used in the liquid phase reaction system usually have some problems,such as poor dispersibility in organic solvents,unable to be separated from the reaction system and loss of the loaded metal particle.Considered from core-shell structure,magnetic nanoparticles support and chemical modifications,this thesis us carried out to solve the problems in solid catalysts used in the liquid phase reaction system,and this thesis is mainly divided into the following five parts:(1)An acid-base bifunctionalized magnetic nanoparticles catalyst Fe3O4@SiO2-A/B was successfully synthesized by immobilization of both organic base and acid groups together over silica-coated magnetite nanoparticles.The catalyst has been characterized by transmission electron microscopy(TEM),vibrating sample magnetometer(VSM),X-ray diffraction(XRD),fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectra(XPS)measurements.The bifunctionalized magnetic nanoparticles act as an easily recovered,highly efficient catalyst for the Henry reaction of 4-nitrobenzaldehyde with nitromethane at mild reaction conditions,even exceeding any monofunctionalized catalyst or physical mixture of two monofunctionalized nanoparticles in the catalytic behavior.In addition,a probable mechanism has been proposed to explain the cooperative interactions from the presence of the immobilized base and acid groups in close proximity.Importantly,the catalyst can be simply recoverable from the reaction mixture by magnetic decantation and recycled without significant degradation in reactivity.(2)Fe3O4@PPy composite microspheres have been synthesized using Fe3O4 microspheres as a chemical template under an ultrasonic treatment process.Pt nanoparticles(NPs)were immobilized onto Fe3O4@PPy by using ethylene glycol(EG)and NaBH4 as reducing agent.The information of the morphologies,sizes,and dispersion of Pt NPs of the as-prepared catalysts was verified by TEM,XRD,FTIR and XPS.As expected,the chemical reduction methods remarkably affected the size of Pt NPs(?2.5nm and?5.5nm,respectively)and the prepared catalysts exhibited high catalytic activities as well as awsome stabilities for aerobic oxidation of benzylic alcohols and hydrogenation reduction of nitroaromatics.It was highlighted that size effects for the catalytic properties of the two reactions were found to be quite different.Fe3O4@PPy-Pt(2.5nm)afforded a higher conversion for benzylic alcohols aerobic oxidation,while the selectivities toward benzaldehyde over these two catalysts were similar.However,they showed almost same catalytic performance for hydrogenation reduction of a majority of nitroaromatics.What's more,Fe3O4@PPy-Pt(5.5nm)gave better activities of several nitroaromatics which were relatively difficult to be hydrotreated under the same conditions.In addition,the EG reduced Fe3O4@PPy-Pt catalyst exhibited slightly poorer stability than the NaBH4 reduced Fe3O4@PPy-Pt catalyst in the recycle tests,which might due to the agglomeration of small Pt NPs.(3)Three core-shell structures were prepared with pyrrole,glucose,and tetraethyl orthosilicate(TEOS)respectively,encasing magnetic Fe3O4 microparticles,through three different "green" approaches without any toxic solvents.Pt nanoparticles(NPs)were immobilized onto these supports with NaBH4 as reducing agent.The as-prepared catalysts were characterized thoroughly by TEM,VSM,XRD,FT-IR,ICP,and XPS.As expected,the shells remarkably affected the distribution of Pt NPs and catalytic activity.Pt NPs evenly dispersed evenly on the surface of Fe3O4@PPy and Fe3O4@C,which were much better than Fe3O4@SiO2.Most attractively,the prepared catalysts exhibited better kinetics,higher activity and stability than the Pt/Fe3O4 and Pt/C for selective oxidation of ethanol to acetic acid and glycerol to glyceric acid with molecular oxygen in water.Among them,the catalyst with a shell of polypyrrole(PPy)showed the best catalytic property,affording yields of 88%and 55%,respectively.Moreover,it could be recovered facilely from the reaction mixture and recycled four times without any significant loss in activity.(4)Solvent-dispersible magnetite nanoparticles(Fe3O4)end-functionalized with amino groups were successfully prepared by a facile one-pot template-free method to immobilize Pd? and Pd0 with a metal adsorption and reduction procedure.They were characterized by TEM,XRD,XPS,FT-IR and VSM.Interestingly,Pd? catalyst exhibited better catalytic activity for carbonylative cross-coupling reactions than Pd0 catalyst.According to the catalytic activities of a variety of arylboronic acids and aryl iodides catalyzed by two kinds of Pd catalysts,proposed reaction mechanism of Suzuki carbonylative cross-coupling reactions by Pd catalyst were also inferred.More importantly,agglomeration of Pd0 nanoparticles was obvioUsly observed in the TEM images of the catalysts after reactions.Therefore,agglomeration of Pd0 nanoparticles should be considered as a significant reason for different catalytic activities of the reactions catalyzed by immobilized Pd? and Pd0 catalysts.Furthermore,the Pd?catalyst revealed high efficiency and stability during recycling stages.(5)Halloysite-nanotube-supported Mo salen(HNTs-Mo-SL)catalysts were successfully prepared using a facile chemical surface modification and self-assembly method.The morphologies,sizes,structure,and dispersion of the as-prepared catalysts were investigated by transmission electron microscopy,X-ray diffraction,and Fourier-transform infrared,inductively coupled plasma,and X-ray photoelectron spectroscopy,which confirmed the existence of the Mo salen structure and successful synthesis of the halloysite-nanotube-supported Mo catalyst.The immobilized catalyst was found to be highly reactive in the epoxidation of a wide range of alkenes,including linear,cyclic,and aromatic alkenes.The immobilized catalyst exhibited a higher catalytic activity for alkene epoxidation than homogeneous Mo.In contrast experiments,it was determined that the salen structure played an important role in immobilizing MoO(O2)2(DMF)2 and improving the conversion and efficiency of alkene epoxidation,which could not be obtained using other ligands,such as the N atom as a single ligand.Furthermore,the bonding between Mo and the salen ligands and the possible mechanism of alkene epoxidation catalyzed by the catalyst were determined.The catalyst could be reused several times without significant loss of catalytic activity.Given that halloysite nanotubes are cheap and easy to obtain,this catalyst offers a novel alternative for the rational design of catalysts with desired features. |
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