Preparation Of Carbon Based Catalytic Materials And Their Catalytic Performance For Olefin Hydroformyaltion

Due to the stable physical and chemical properties,large specific surface area and easy recovery of noble metals from spent catalysts,carbon materials are commonly used as supports for noble metals catalysts preparation.Owing to its unquie structure and properties,graphene become the hot research area in materials science quickly,which is regarded as a potential catalyst support for heterogeneous catalysis?In this work,we used different methods to prepare carbon supported rhodium catalyst.Our purpose is to develop carbon-based catalysts with high catalytic activity and product selectivity for 1-olefin hydroformylation and to study the role of carbon materials in catalysis.Activated carbon suppored rhodium?Rh/AC?catalyst was treated by HNO₃ at varied temperatures to implant oxygen-containing functional groups.These catalysts were investigated to clarify the influence of catalyst's oxygen-containing functional groups on hydroformylation of 1-hexene for the first time.The treated catalysts exhibited enhanced n/i ratio of heptanal.Especially the 5%Rh/AC-80 catalyst treated by HNO₃ at 80 ^oC owned the highest n/i ratio as 2.3,indicating that more functional groups were promotional to enlarge the n/i ratio of heptanal.These oxygen-containing functional groups could alter the surface property of catalysts,thus affect the adsorption action and reaction between the active sites and reactants,which was beneficial to improve the selectivity of n-heptanal in hydroformylation.Moreover,more functional groups on the catalyst could suppress hydrogenation of hexene and decrease the selectivity of hexane.These findings suggested the surface property of catalysts had a close relationship with selectivity of products in heterogeneous hydroformylation,which might bring a new insight into the future research of heterogeneous hydrofromylation.Reduced graphene oxide supported Rh nanoparticles?Rh/RGO?catalyst was prepared via one-pot liquid phase reduction by glycol-water solution.The graphene based catalyst was firstly applied in 1-hexene hydroformylation reactions,which extends the application of graphene in heterogeneous catalysis.The catalytic performances of Rh/RGO catalyst with different reaction temperature and time were investigated.Low reaction temperature and time could effectively promote 1-hexene hydroformylation to form n-heptanal.The heptanal yield obtained by this Rh/RGO catalyst reached up to 90%,and the n/i ratio was kept at 1.1 even for 10 h under the low reaction temperature.Three kinds of carbon materials?activated carbon,carbon nanotubes and reduced graphene oxide?supported Rh catalysts were prepared by the same method to investigate the effect of catalyst support on the catalytic performance.The structure and property of catalyst support can affect the preparation and catalytic performance of the catalyst.The Rh/RGO catalyst showed the highest catalytic activity of 38.4%and n/i ratio of 4.0 respectively,much better than those of Rh/AC and Rh/CNTs catalysts.The excellent catalytic performance of Rh/RGO catalyst should be attributed to its unique 2D nano-sheet structure that determined its largest Rh exposed surface area,highest nanoparticle dispersion and smallest nanoparticle size among three catalysts,as well as the unhindered diffusion of reactants and products in the liquid-phase 1-hexene hydroformylation,along with the lower H₂/CO ratio near Rh sites.Organic ligand PPh₃ was used as reducing agent to reduce GO and as functional group to obtain PPh₃ functionalized Rh/RGO heterogeneous catalyst simultaneously.The as-made PPh₃-Rh/RGO catalyst is an efficient catalyst for heterogeneous hydroformylation of 1-olefins and exhibits excellent catalytic performance,not only the high yield of aldehyde?99.2%?,but also high selectivity of linear product?n/i=2.1?.This work demonstrates the first example of organic ligand using as multifunctional reducing agent for the reduction of GO and develops an efficient and simple method for the synthesis of ligand modified metal complex catalyst supported on RGO as heterogeneous catalyst,which makes the immobilization of homogeneous ligand catalysts onto the solid support easily.Moreover,the great varieties of organic ligands can be chosen pertinently to extend the synthetic strategy for preparing RGO supported catalysts for various reactions.Therefore,the result provides a new viewpoint for extending the selection of reducing agent to synthesize graphene-based materials for special applications.