Fabrication And Catalytic Performance Of Graphene Oxide Anchored Aryl-diimine Pd(?)/Co(?) Bimetallic Monolayer For Suzuki Coupling Reaction

In this paper,graphene oxide anchored aryl-diimine Pd?II?/Co?II?bimetallic self-assembled monolayer catalysts?GO@DiI-Pdx/Co1-x?were designed and synthesized by self-assembly method.The structure and the catalytic performance of the catalyst were investigated in Suzuki coupling reaction.Combined with kinetics and thermal filtration experiments,catalyst poisoned experiments,cycle experiments,in situ Fourier transform infrared spectroscopy?React-IR?and X-ray photoelectron spectroscopy?XPS?,the catalytic performance and synergistic catalytic mechanism of bimetallic catalysts were discussed.The specific research contents and results are as follows:1.Aryl-diimine ligand was synthesized by terephthalaldehyde and3-aminopropyl-triethoxysilane,and grafted onto graphene oxide by self-assembly method.Graphene oxide-supported aromatic diimine palladium?GO@DiI-Pd?,cobalt?GO@DiI-Co?and different ratio of palladium-cobalt bimetallic catalyst?GO@DiI-Pd0.5/Co0.5,GO@DiI-Pd0.1/Co0.9,GO@DiI-Pd0.01/Co0.99,GO@DiI-Pd0.005/Co0.995?were synthesized.The morphology and structure of the catalyst were characterized by Scanning Electron Microscopy?SEM?,transmission electron microscopy?TEM?,Scanning Electron Microscopy-Energy Dispersive Spectrometer?SEM-EDS?,FT-IR,X-ray powder diffraction?XRD?,Raman spectroscopy?Raman?and XPS.2.Several prepared catalysts were applied to Suzuki template reaction to investigate the catalytic performance.We found that GO@DiI-Co had no catalytic active for the template reaction,while 1 mg of GO@DiI-Pd could achieve quantitative conversion of 0.2 mmol of reaction substrates,but the metal loading was large and the TOF value was low(246 h^-1).In contrast,when the ratio of palladium in the catalyst was reduced,GO@DiI-Pd0.5Co0.5,GO@DiI-Pd0.1Co0.9 could achieved quite catalytic effect with GO@DiI-Pd.To our suppress that the TOF value of GO@DiI-Pd_0.01/Co_0.99(6441 h^-1)was higher than GO@DiI-Pd by 26 times.Moreover,the catalyst can be recycled five times in water and still maintained a yield of about 90%.3.In order to study the reasons of catalyst passivation deactivation,the catalysts in the catalytic process were characterized by Inductively Coupled Plasma-Atomic Emission Spectrometer?ICP-AES?,SEM,TEM,Raman and XRD.The results showed that the catalyst was slight aggregated during the catalytic process,which changed the microenvironment on the surface of the catalyst,and the active center was lost during the catalytic process,which may be the reasons for catalytic performance decrease of catalysts.The catalytic reaction mechanism of GO@DiI-Pd0.01/Co0.99 was studied by kinetic and thermal filtration experiments,catalyst poisoned experiments and React-IR,which gave the results that GO@DiI-Pd0.01/Co0.99 catalyzed the Suzuki coupling reaction as a heterogeneous catalyst at the interface.We speculated the possible mechanism by XPS and theoretical calculation that cobalt translated electrons to palladium through carrier and ligand to form a more negatively charged metal active center.The product intermediate was formed by an oxidative addition reaction,and the target product was obtained by restore elimination.