Modified Graphite-like Carbon Nitride (g-C₃N₄) Supported Rhodium Nanoparticles Catalysts For Hydroformylation Of Styrene

Hydroformylation refers to the reaction process in which olefins react with synthesis gas(CO and H₂)to produce one more carbon atomic aldehyde at a certain temperature,pressure and catalyst,which has important applications in industry.Nowdays,the catalysts used in industry are rhodium-based complexes.Although the reaction conditions are mild,and the catalytic performances are excellent,most of the rhodium-based homogeneous catalysts are dissolved in the used solvent or obtained products,which makes Rh-based complexes difficult to separate and reuse.In order to solve this problem,heterogeneous catalysts are becoming the research interest in the field of hydroformylation,especially supported catalysts,which can not only prevent the agglomeration of Rh nanoparticles and improve the catalytic activity,but also separate the catalysts efficiently from the products by solid-liquid separation.In the design of heterogeneous supported Rh particle catalysts,the nature of supports affects extremely the catalytic preformance of heterogeneous catalysts.Therefore,developing new supports which can suitablely interact with the supported metal is urgent.Graphite-like carbon nitride(g-C₃N₄)has been widely used in heterogeneous catalytic reactions because of its good thermal and chemical stability,unique electronic properties and high specific surface area.In this paper,nonmetallic elements modified g-C₃N₄ supported metal Rh nanoparticles were prepared and applied in the hydroformylation of olefins.The details are as follows:(1)G-C₃N₄ was prepared from urea by thermal polymerization and the defected g-C₃N₄was synthesized via the treatment of phosphoric acid(P-g-C₃N₄).Simultaneously,a series of P-g-C₃N₄ supported Rh nanoparticle catalysts(Rh/P-g-C₃N₄)have been successfully synthesized by impregnation-chemical reduction method.The as-prepared Rh/P-g-C₃N₄catalysts were characterized by XRD,FT-IR,SEM,TEM,XPS and TG,and applied in the hydroformylation of styrene.In the hydroformylation of styrene,the highest conversion of styrene is 99.3%and the highest TOF of styrene can reach 11145 h^-1.In addition,Rh/P-g-C₃N₄ also showed excellent catalytic preformance for the hydroformylation of various olefins.In the reuse test,the conversion and selectivity were almost the same as the first time for six recycles,indicating that Rh/P-g-C₃N₄ catalyst is an efficient and stable catalyst for the hydroformylation of olefins.(2)A series of boron and sulfur co-modified g-C₃N₄(B-S-g-C₃N₄)were prepared using boric acid and sulfuric acid as the boron and sulfur precursor,respectively.Simultaneously,B-S-g-C₃N₄ supported Rh nanoparticle catalysts(Rh/B-S-g-C₃N₄)were prepared by impregnation-chemical reduction method.Rh/B-S-g-C₃N₄ catalysts were characterized by means of XRD,FT-IR,SEM,TEM,XPS and TG,and applied in the hydroformylation of styrene to explore the catalytic activities of the catalysts.Under the optimal condition,the conversion of styrene is 99.3%and the corresponding TOF is 17838 h^-1.In the recycling test of Rh/B-S-g-C₃N₄,the catalyst can be easily separated by filtration,and reused in the next run.Most important,there is no significant decrease in conversion and selectivity after 8 recycles,indicating that Rh/B-S-g-C₃N₄ catalyst is also an efficient and stable catalyst.