Three-Dimensional Amine-terminated Ionic Liquid Functionalized Graphene Loaded Pd Based Composite Aerogels As Highly Efficient And Recyclable Catalysts For The Suzuki Cross-coupling Reactions

With the advancement of economy,science and technology,people are demanding more and more products in the fields of energy and chemical industry,fine chemical industry and medical food,which also promotes the development of the chemical industry.Suzuki cross-coupling reaction is one of the most important organic reactions in chemical industry.It is the basis of the synthesis of functional materials,natural products,drugs and living organisms.So far,transition metal palladium catalyst is the most widely used catalyst for Suzuki cross-coupling reaction.Traditional homogeneous palladium catalysts need to add toxic and expensive phosphine ligands to stabilize the catalyst,which is environmental unfriendly.�Phosphine-free�heterogeneous palladium catalysts have attracted much attention due to their large specific surface area,simple synthesis method,environmental protection and high recycling efficiency.Three-dimensional?3D?graphene architectures have honeycomb-like porous structure and large specific surface area,which can provide multiple conductive transfer paths for catalytic reaction.Therefore,they can be excellent supports for palladium nanoparticles?Pd NPs?.However,during the process of assembling,the high specific surface area inherited from graphene nanosheets is sacrificed due to the irreversible agglomerate of graphene nanosheets.The amine-terminated ionic liquid?NH₂-IL?can covalent functionalization withgraphene to reduce the restacking of graphene sheets and enlarge the specific surface area.What'more,the negatively charged Pd precursors(PdCl₄^2-)are adsorbed on positively charged imidazolium ring moiety of NH₂-IL to engender Pd NPs with small particle sizes uniformly distributed on the graphene sheets,which can maximize the active surface area of catalysts and enhance their catalytic activity.Based on the above analysis,we developed a facile and green reduction-inducing self-assembly approach to successfully fabricate the 3D IL-rGO/Pd and 3D IL-rGO/Pd_xCu_y composite aerogels as the catalysts for the Suzuki cross-coupling reactions.The main research contents were as follows:1?The preparation,charaterization and catalytic activity of 3D IL-rGO/Pd composite catalystsNH₂-IL[1-?3-aminopropyl?-3-methylimidazolium bromide]was functionalized onto graphene oxide through the nucleophilic ring-opening reaction.Then,we successfully fabricated the 3D IL-rGO/Pd composite catalyst by reduction-inducing self-assembly approach with Na₂PdCl₄ as the source of palladium.The Suzuki cross-coupling reaction of iodobenzene with phenylboronic acid was chose as the model reaction to evaluate the catalytic activity of the 3D IL-rGO/Pd composite catalysts.Firstly,the effects of solvents and bases on the catalytic performance were investigated and the optimum reaction conditions were selected.Secondly,the effects of ionic liquid dosage,metal loading and catalyst dosage on the catalytic performance were investigated,and the optimal catalyst was screened out.Next,Substrates were expanded and the recycling performance of the catalyst was investigated.The catalytic studies showed that the 3D IL-rGO/Pd composite aerogels had excellent catalytic activity on Suzuki cross-coupling reactions under mild conditions,and the catalytic efficiency shows no obvious loss even after ten repeated cycles.The morphology and composition of the obtained 3D IL-rGO/Pd composite aerogels were studied by means of Raman spectroscopy,XRD,TEM,ICP-AES,SEM,FTIR,XPS and BET.The results showed that the cations of NH₂-IL introduced to the surface of graphene sheets can avoid the restacking of graphene sheets and enlarge the specific surface area,which provide efficient transport pathways for improving the catalytic performance.The negatively charged Pd precursors(PdCl₄^2-)are adsorbed on positively charged imidazolium ring moiety of NH₂-IL to engender Pd NPs with small particle sizes uniformly distributed on the graphene sheets,which can maximize the active surface area of catalysts and enhance their catalytic activity.2?The preparation,charaterization and catalytic activity of 3D IL-rGO/Pd_xCu_y composite catalystsIn order to reduce the consumption of precious metal Pd and save costs,a series of bimetallic composite catalysts?3D IL-rGO/Pd_xCu_y?with different mass ratios of Pd-Cu were prepared by introducing non-precious metal Cu with low price and abundant reserves,using ionic liquid?NH₂-IL?functionalized graphene oxide as support and Na₂PdCl₄ and CuCl₂�2H₂O as metal sources.We still chose the Suzuki cross-coupling reaction of iodobenzene with phenylboronic acid as the model reaction to explore the optimal mass ratio of Pd and Cu,under the condition that the catalytic activity of Pd-based catalysts was not decreased.The results showed that when the loading of Pd and Cu were 2.5 wt%,the same catalytic activity could be obtained as that of 5 wt%Pd.In addition,bimetallic catalysts with the best mass ratio of Pd-Cu also had universality in a series of Suzuki cross-coupling reactions,and their activity did not decrease after 10 cycles.XRD,TEM,HRTEM,HAADF-STEM,EDS mapping,ICP-AES and XPS were used to characterize the 3D IL-rGO/Pd-Cu bimetallic catalysts.The results showed that the active metal Cu can form alloys with metal Pd.They had a specific synergistic effect,which improved the stability and catalytic activity of palladium in the reaction process.