A Study On Catalysts For Fixation And Conversion Of Carbon Dioxide

The catalytic transformation of CO2 into biodegradable poly–(propylene carbonate)(PPC)by alternating copolymerization with propylene oxide(PO)has drawn much attention in both academic and industrial fields in view of economic and environmental benefits arising from application of an easily available renewable carbon resource.Although reaction which synthesis of PC with CO2 and propylene now has been commercialized,the catalytic reaction mechanism needs to be further studied.In this study,two high–efficiency homogeneous catalyst systems were designed and fabricated for the synthesis of cyclic carbonates from CO2 and propylene oxide;The multiple catalytic systems,including transition metal salts,heterocyclic amine ligands,TBAB and zinc powder,which had been developed for the coupling of carbon dioxide and epoxides to form cyclic carbonates under mild reaction conditions.The results of catalytic activity with monocyclic amine ligands show that different hybridization form of nitrogen–atoms and locality of the substituted amine have little effect on the catalytic activity.The introduction of the sulfur atom in ligand molecule obviously improved activity due to flexibility of sulfur atom.The results of polycyclic amine ligands indicate that the poor rigidity of ligand molecule have a higher catalytic activity for preparation of cyclic carbonate.The more nitrogen atoms in ligand have,the higher catalytic activity have.Cerium(IV)tetraphenyl porphyrin(TPP)was 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.We found that Cerium(IV)acetylacetonate hydrate catalyst demonstrated a catalytic activity for conversion of CO2 and epoxides into carbonates under mild conditions,the yield of carbonates was 32 %.Compared with [YbTPP(acac)] / TBAB,the catalytic activity of[Ce(TPP)(acac)2] / TBAB have been less effectivitely,decreasing carbonates yield 10%.Higher space steric hindrance of cerium complex caused decrease in catalytic activity.Three compounds,SalenCoTFA,SalenCrTFA,SalenMnTFA were synthesized with Schiff–base ligand and characterized via UV–Vis,IR and elemental analyses,all of complexes were probed their catalytic behavior in the process of copolymerization of CO2 and PO.The polymer molecular structure and molecular weight,weight–distribution were characterized with GPC,FT–IR,1HNMR and 13 CNMR.(1)The results showed SalenCoTFA/PPNTFA was an active catalyst system.The polymer was obtained from PO /CO2 copolymerization with 20 equiv water under catalyst SalenCoTFA / PPNTFA,2h,and 1.5 MPa CO2.Under the optimal conditions,the yield of PPC was 92%,molecular weight distribution of PPC was 1766,TOF = 613 h–1;(2)PPNTFA is the best co–catalyst;(3)Water was not the true chain–transfer reagent during the PO / CO2 coupling reaction.Indeed,the formation of 1,2–propanediol during the catalytic coupling of CO2 / PO in the presence of water is anticipated based on studies of the hydrolytic kinetic resolution(HKR)of epoxides.