A Novel Catalyst Prepared By MOFs Precursor For Cycloaddition Of Epoxides With CO₂

In recent years,human health has been seriously affected by global warming and haze pollution.It is recognized that the emission reduction of greenhouse gas?CO₂?is urgent.In addition,CO₂ represents a green,stable,inexpensive and abundant C1source.Therefore,the resource utilization of CO₂ to generate the corresponding value-added chemical products not only meets the requirements of"green chemistry",but also can realize sustainable development of economy and ecological environment.The cycloaddition of CO₂ and epoxides to yield cyclic carbonate is a hot topic in the field of CO₂ transformation.Therefore,it is important for the cycloaddition of CO₂and epoxides to develop a novel catalyst with high efficiency,inexpensive and excellent cycle performance and stability.In this paper,two green and efficient catalysts were synthesized by different kinds of MOFs as precursor.The crystal phase,surface morphology and structure of MOFs derivatives were characterized by XRD,FT-IR,SEM,BET,XPS and TG-MS.Both of them were applied to the chemical fixation of CO₂ into cyclic carbonates,and the catalytic properties and catalytic mechanism of the catalysts were studied.The main research contents are as follows:?1?A novel MOFs?Zn-Asp?was synthesized by using natural amino acid L-aspartic acid?L-Asp?as ligand.Using Zn-Asp as the precursor,a kind of environment-friendly catalyst was obtained by heat treatment method.It is shown that after heat treatment,the skeleton of Zn-Asp has been carbonized and the metal nodes have been oxidized,generated amorphous N-doped porous carbon-ZnO hybrid materials,which produces multiple alkaline sites?pyridinic N?.The resultant catalyst exhibits excellent activity,selectivity and recyclability in the CO ₂ cycloaddtion reactions with epoxides.In the absence of solvents,the co-catalyst and catalyst synergistic catalysis the cycloaddition,the yield of cyclic carbonate is 91.97%under the mild conditions?80 ^oC,1 MPa,2 h?.Moreover,the catalyst can be facilely separated and reused for five successive cycles without significant loss of activity and structural rigidity.?2?The new catalyst of[Zn₂?iso?₂?bpy?₂]_n-300 with more active sites and higher CO₂ adsorption capacity was prepared the MOFs?[Zn₂?iso?₂?bpy?₂]_n?by regulating the heat treatment temperature.The structure of the[Zn₂?iso?₂?bpy?₂]_n-300 was not destroyed after heat treatment,but the specific surface area and the ability of adsorption CO₂ increased and more unsaturated metal active sites were exposed.Therefore,[Zn₂?iso?₂?bpy?₂]_n-300 demonstrated excellent catalytic performance for CO₂ fixation into cyclic carbonates under relatively mild reaction conditions?80 ^oC,2MPa,2 h?with close to 95.58%yield to cyclic carbonate.The catalyst exhibited satisfactory stability and conld be reused five times without any loss of activity.