Doped Graphite Carbon Nitride?g-C₃N₄?Supported Rhodium Nanoparticles For Hydroformylation Of Styrene

Hydroformylation refers to the reaction of olefins under the catalysis of transition metals and synthesis gas?a mixture of CO and H₂?under the condition of high pressure heating to form an aldehyde with one carbon more than the original olefins.It is the earliest metal catalyst to realize industrialization and the most widely used catalytic reaction.At present,the research of this reaction mainly focuses on the development and modification of catalytic systems.According to the environment in which the catalyst is applied,it can be divided into homogeneous and heterogeneous catalytic systems.Industrially,olefin hydroformylation is mainly based on Rh-based homogeneous catalytic systems,mainly because of the advantages of high catalytic activity,good product selectivity,and mild catalytic conditions.However,most of Rh-based homogeneous catalysts are soluble in hydroformylation products and organic solvents used in the reaction,which makes the separation of products and catalysts difficult,especially the separation of Rh-based catalysts and high-boiling products.Therefore,how to efficiently separate Rh-based homogeneous catalysts and increase their cycle life has become an urgent problem to be improved in olefin hydroformylation.Among them,the Rh nanoparticle catalyst supported by a carrier with a large specific surface is of particular interest.Immobilizing the Rh nanoparticles on the carrier can not only effectively control the size of the nanoparticles,prevent their agglomeration from becoming larger,effectively increase the contact area of the Rh nanoparticles with the reaction substrate in the catalytic reaction,and improve the catalytic activity.The solid-liquid separation can realize the separation of the catalyst and the product.Among the many carriers,g-C₃N₄ is an excellent catalyst carrier with high surface area,good chemical stability and thermal stability,special electronic structure and low preparation cost.It is widely used in multi-phase Catalyzing.Based on the existing work of the laboratory research group,the following research work is carried out:?1?G-C₃N₄ was prepared by thermal polymerization method using urea as raw material,and rhodium nanoparticle catalysts?Rh/B-g-C₃N₄?supported by carbon nitride?B-g-C₃N₄?with different boron content were successfully synthesized and applied to hydroformylation of styrene.The catalysts were characterized by XRD,FT-IR,SEM,TEM,XPS and so on.Under the optimal reaction conditions,the conversion rate of styrene hydroformylation can reach99%,and the TOF value can reach 12000 h^-1;Rh/3%B-g-C₃N₄ can obtain the corresponding aldehyde in the hydroformylation of various olefins and show very good catalytic activity.Inaddition,the recycling of Rh/3%B-g-C₃N₄ was tested seven times,and the activity and selectivity did not decrease significantly under the optimal reaction conditions.These findings indicate that boron doping is an effective strategy to improve the catalytic performance of heterogeneous hydroformylation;?2?G-C₃N₄ was prepared by the same method,and calcined at high temperature under the protection of nitrogen to prepare different metals?0.25,0.50,0.75,1.00,1.25,1.50 wt.%?.Doped with different contents?Co,Zn,Al,Ti,Fe,Mn,Cu?g-C₃N₄,the rhodium-supported nanoparticle catalyst was successfully prepared by the impregnation chemical reduction method,and applied to hydroformylation of styrene.The catalyst was characterized by XRD and FT-IR.Under the optimal reaction conditions,the TOF values of catalytic styrene catalyzed by Rh/1.0%Co-g-C₃N₄,Rh/1.0%Al-g-C₃N₄ and Rh/1.0%Zn-g-C₃N₄ reached18200h^-1?18000 h^-1?17600 h^-1,respectively.Seven cycles of testing were performed,and therespective conversion rates remained above 90%.This shows that metal doping is an effectivemeasure to improve the catalytic performance of heterogeneous hydroformylation...