Novel Dimine Palladium,Nickel And Ni/Pd Bimetallic Catalyst Self-assembly Films Immobilized On Graphene Oxode For Heterogeneous Catalysis

In this paper,self-assembly films of diimine-coordinated palladium complexes,nickel complexes and nickel/palladium catalyst were prepared and immobilized on graphene oxide nanosheet to form hybrid catalytic materials(F-GO-Pd 、F-GO-Ni、 F-GO-Ni/Pd1、F-GO-Ni/Pd2、F-GO-Ni/Pd3).These catalysts were characterized by XRD,FTIR,Raman,XPS,SEM,and TEM.The catalytic properties of different catalysts and the role of graphene oxide in catalysis were studied by Suzuki coupling reaction as template reaction.The catalytic mechanism,deactivation mechanism of the catalyst cycle and the synergistic mechanism of the bimetallic catalyst were investigated by means of kinetic study,thermal filtration,catalyst poisoning and other experiments,as well as on-line infrared(Rea IR)and X-ray photoelectron spectroscopy(XPS).The main research contents and conclusions are as follows:1.A novel diimine ligand was successfully synthesized and grafted to the graphene oxide nanosheet by self-assembly process(Figure 1).The modified graphene oxide coordinated with palladium to form functionalized hybrid material(F-GO-Pd).The F-GO-Pd catalyst was characterized by XRD,FTIR,Raman,XPS,SEM,and TEM.2.The heterogeneous catalytic performance of F-GO-Pd catalyst was studied by using Suzuki coupling reaction as reaction template.F-GO-Pd showed high catalytic activity with a very low amount of catalyst(0.01 mol%)and a high turnover frequency(TOF)(>20000 h-1)under mild condition.In particular,high yields also could be obtained at room temperature with prolonged time.F-GO-Pd also showed good stability and recyclability at seven times with a superior catalytic activity.3.The heterogeneous catalytic mechanism was investigated with kinetic studies,hot filtration tests,catalyst poisoning tests,and in situ FTIR spectroscopy with a React IR and the deactivation mechanism of the catalysts was proposed through analysis of its chemical stability by TEM,SEM,Raman,and XRD,which indicated that a heterogeneous catalytic process occurred at the interface(Figure 2)and the changes of the catalytic activity during the recycling were related to the micro-environment of the catalyst surface.4.Graphene oxide-supported Ni,Ni/Pd bimetallic complexes with high ratio of Ni to Pd atomic ratios(2136:1,333:1 and 97:1)(F-GO-Ni/Pd1 、 F-GO-Ni/Pd2、F-GO-Ni/Pd3)were prepared(Figure 3)and characterized by XRD,FTIR,UV-Vis DRS,XPS,SEM.5.The catalytic performance of graphene oxide-supported dimine nickel and bimetallic catalysts was studied.Suzuki reaction catalyzed by F-GO-Ni yielded moderate yields.The yield of Suzuki reaction catalyzed by F-GO-Ni/Pd2 was superior to other nickel/palladium bimetallic catalysts.In order to reduce the amount of palladium,F-GO-Ni/Pd1 was chosen to screen the optimumic reaction conditions,with which equivlent yield and a high TOF(21492 h-1)were obtained.Meanwhile,F-GO-Ni/Pd1 catalyst exhibited good substrate applicability and even for the chloride substrate moderate catalytic activity could be maintained.6.The heterogeneous catalytic mechanism of F-GO-Ni/Pd1 was explored by kinetic study,thermal filtration test and catalyst poisoning experiment.The synergetic mechanism of nickel and palladium was premlinary investigated with XPS.The results showed that the Suzuki reaction catalyzed by F-GO-Ni/Pd1 was a heterogeneous reaction at the interface.The doping of palladium in bimetallic complex led to the changes in the chemical environment of the catalyst,which made electrons of the graphene oxide transferred to the bimetallic catalytic center and improve catalytic activity.