Preparation Of Porous Chitosan/Silica Composite Core-shell Microspheres-supported Pd Catalyst And Its Application

The Pd-catalyzed Sonogashira cross-coupling reaction is an important method for the synthesis of carbon-carbon bonds,which is currently the preferred method for the synthesis of substituted alkynes and large conjugated alkynes.The important development of this kind of reaction is focused on the preparation of more efficient supported palladium catalysts,and the noble metal palladium is supported on the functional carrier to facilitate recycling and reduce the consumption of palladium.In this study,an ideal noble metal palladium carrier,chitosan/silica core-shell porous composite microspheres,were developed with a microfluidic platform.The supported palladium catalyst was successfully prepared and applied to a series of Sonogashira cross coupling reactions.The main researches are listed as follows:The first chapter mainly introduced the research background of this thesis,including the development and research status of Sonogashira coupling reactions,application of chitosan-silica composite materials and the special advantages of microfluidics in preparing specific structure.In addition,the research ideas and key scientific issues of this thesis were briefly introduced.In the second and third chapter,Chitosan/silica core-shell porous composite microspheres-supported Pd catalyst was produced.The process could be taken apart into two parts,including microfluidic preparation of droplets and the loading of Pd.First,microfluidic preparation of droplets:Chitosan/silica core-shell porous composite microspheres are carriers with chitosan as core and silica as shell,with porosity of 81.15%.Microdroplets produced in the microchannels are pre-cured in the coagulation bath using the chemical crosslinking of the amino groups of the chitosan with the glutaraldehyde molecules,and the final cured by the silica gelation reaction.The chitosan,is used for pre-curing,and for chemical chelation with the palladium ions at the later stage;the silica,is used for gelation while the shell silica can protect chitosan from excessive cross-linking with glutaraldehyde,providing active sites for palladium adsorption.In addition,silica can enhance the mechanical strength of microspheres,to avoid the loss of palladium during reaction process.Second,The adsorption process of palladium ion into the porous carriers,is fitted to pseudo-second-order kinetic model,which means the chemical chelating is the rate-determining step.The adsorption is in agreement with Langmuir model,which proves that the adsorption is chemical process,and the physical adsorption can be ignored.The maximum adsorption capacity is 130.04 mg/g.The palladium ions adsorbed on the carrier were reduced to palladium by sodium borohydride,and its nanoparticles,with good monodispersity,were concentrated at around 2-3 nm.The lattice was clearly visible at a distance of 0.24 nm,which proves to be the main catalytic lattice,(111).In the fourth chapter,Chitosan/silica core-shell porous composite microspheres supported palladium catalysts were used in a series of Sonogashira cross-coupling reactions.In the example reaction,there only need 5 mg 1 wt.%supported palladium catalyst per 2 mmol of 4-iodoacetophenone,and the reaction yield can reach 98.9%.The actual amount of precious metal palladium is only 50 ?g.After recycling 8 times,the yield is still maintained above 98%,and palladium nanoparticles are still in good monodispersity,with almost no aggregation.The amount of palladium leaching in the solvent was only 0.072 ppm,which was negligible.It is proved that chitosan and the palladium on the functional carriers have strong binding force,which is beneficial to enhance the recycling effect of the noble metal catalyst,while avoiding the residual metal in the product or waste.It can be deduced that the chitosan/silica core-shell porous microspheres prepared in this study can also be used in the field of other precious metal ion adsorption.It is possible to prepare a variety of precious metal supported catalysts,as it is an ideal functional carrier.In the last chapter,we summarized the conclusions and innovation of this dissertation,and previewed the further studies.