Bifunctional Carbon-Nitrogen Materials Supported Cu/Fe Catalyzed CO₂ Cycloaddition Reaction

Facing the environmental problems caused by the increasing concentration of CO₂in the atmosphere,catalytic CO₂ conversion has become an important research topic in recent years.The cycloaddition reaction route of CO₂ and epoxide can achieve 100%atomic utilization,and the product cyclic carbonate has high commercial value,which has attracted extensive attention of scientific researchers.Homogeneous catalysts such as ionic liquids,metal complexes,organic salts,etc.can achieve sufficient contact with the substrate,so they have good catalytic activity.But after the reaction,the product is difficult to separate,the catalyst cannot be recycled.Heterogeneous catalysts such as porous organic polymers（POPs）and metal-organic frameworks（MOFs）have excellent performance in CO₂ cycloaddition reactions due to the presence of open metal coordination sites.But the synthesis steps are usually cumbersome and the cost is high.Therefore,the development of efficient,low-cost,green and recyclable heterogeneous catalysts is of great research significance.In this work,bifunctional Lewis acid-base energy catalysts were prepared by the strategy of coordination polymer pyrolysis,which have excellent performance in catalyzing CO₂ cycloaddition reaction.（1）Transition metals（such as Co,Cu,Al,Zn,etc.）have low toxicity,make little damage to the environment,and have incompletely filled 3d empty orbitals,which are widely used as Lewis acid sites for activated epoxides.Therefore,copper nitrate was selected as the metal source,and the polymer precursor was synthesized in one pot with formaldehyde and dicyandiamide.Changed the carbonization temperature to obtain different catalyst materials named Cu/N-C-T,where T represents the carbonization temperature.Characterization analysis and performance test results showed that the Cu/N-C-400 catalyst has the highest N element content,the best Lewis acid-base performance,and the highest product yield of the catalytic reaction.At 100°C,CO₂balloon and catalyst dosage of 10 mg,the reaction was carried out for 24h.The product yield can reach 92%,selectivity is greater than 99%,the TON value is as high as 3123,and the catalyst can be recycled for many times.（2）Iron metal stands out among transition metals due to its high natural abundance,low toxicity,and low cost.Different iron nanoparticles supported nitrogen-doped carbon-based catalyst materials were prepared by the same method with the iron nitrate.The results showed that the prepared iron-based catalyst had more abundant Lewis acid-base sites.At 600°C calcination temperature,the catalyst is magnetic,which is easier to recover and reuse.The catalyst material Fe/N-C-500 with the best activity was reacted at 100°C,CO₂ balloon and catalyst dosage of 10 mg for 24 h,the product yield could reach 95%,the TON value could reach 3005,and the catalyst had good cycle stability.The preparation method of the nitrogen-doped carbon-based material is simple,the cost is low,the synthetic route is green,and it is harmless to the environment.The catalyst can efficiently realize the catalytic CO₂ cycloaddition reaction,which provides an idea for sustainable development and industrial application.