A Study On Catalysts For Reaction Of Carbon Dioxide

As a greenhouse gas,carbon dioxide is recognized to be highly naturally abundant,inexpensive,recyclable,and nontoxic carbon source of various organic reactions.The chemical fixation of carbon dioxide into valuable chemicals such as propylene carbonate is generally regarded as an excellent solution both from an environmental protection and resource utilization standpoint.So the development of environmentally friendly processes based on carbon dioxide,one of the key greenhouse effect gases,has attracted considerable attention in recent years.Propylene carbonate?PC?is not only a low toxicity and high boiling point solvent,but also an important organic product that has been used widely in the fields of organic synthesis,gas separation,electrochemistry.Great efforts are still being made to develop novel and efficient catalyst system to catalyze cycloaddition reaction of carbon dioxide under mild reaction conditions,while most of them suffered from some shortcomings,such as low catalytic activity,high pressure and high temperature conditions,and difficult separation of catalysts from products.In this study,two high-efficiency homogeneous catalyst systems were designed and fabricated for the synthesis of cyclic carbonates from CO2 and propylene oxide.Rare earth porphyrin complexes were synthesized and characterized via UV-Vis,IR and elemental analyses,then investigated their catalytic activity for the synthesis of cyclic carbonates from carbon dioxide and propylene oxide.?1?Different reaction conditions?temperature,pressure and reaction time?were also investigated.The range analysis optimal reaction conditions as follows: reaction temperature is 80°C,reaction time is 60 min,and reaction perature is 1.5 Mpa.?2?We have a research on the performance of different metalloporphyrins and different ligands combined with different co-catalyst such as TBAB and DMAP in the cycloaddition reaction of PO and carbon dioxide.The following conclusions have been reached:?1?The catalytic activity is inversely proportional to their ionic radii: with the smallest radius and the highest charge density among the three metals,Lu3+ showed the best yield.This is consistent with that the Lu3+ is harder and stronger Lewis acid than Pr3+,Er3+ and Yb3+,which allows a stronger metal-ligand interactions.?2?TBAB is the best co-catalyst.?3?Electron withdrawing groups will help improve the Lewis acidity of the central metal ion,so that the axial chlorine-substituted metal complexes can promote the activation of propylene oxide and improve the yield of the product.When chloro tetraphenyl porphyrin complex as a catalyst,the yields of propylene carbonate increased significantly,which rises to 97%.?3?Catalytic reaction tests were investigated by altering the reaction substrate.Increasing the reaction substrate epichlorohydrin and styrene oxide to TPPYb / TBAB catalytic system,respectively cycloaddition reaction with carbon dioxide,can be effectively converted into the corresponding organic carbonates,the yield in 80 %the above.The results show that the catalytic system has good versatility.Extended metal-atom chain?EMAC?complexes were fristly investigated their catalytic activity for the synthesis of cyclic carbonates from carbon dioxide and propylene oxide.Eight EMAC complexes [Ni₆??₆-dpznda?₄?Cl?₂]?PF6?₂?1?,[Ni₆??₆-dpznda?₄?NCS?₂]?PF6?₂?2?,Ni₅??₅-dpznda?₄Cl₂?3?,Ni₅??₅-dpznda?₄?NCS?₂?4?,Co₅??₅-dpznda?₄Cl₂?5?,Co₅??₅-dpznda?₄?NCS?₂?6?,Cr₅??₅-dpznda?₄Cl₂?7?,Cr₅??₅-dpznda?₄?NCS?₂?8?with H2 dpznda have been successfully synthesized and structurally characterized via IR,MS and elemental analyses.The complexes consist of a linear metal chain and four supporting ligands which are helically wrapped around the metal core.Then we studied the catalytic function for the synthesis of PC.It was found that EMAC complexes have strong capability of catalyzing the reaction of propylene carbonates from propylene oxide and CO2 without solvent with very high TOF,which could up to 23964 h^-1.