The Preparation Of Co- Or Zn-MOFs And Catalysts For The Coupling Reaction Of CO₂ And Epoxides

Taking advantage of CO2 as an environmental friendly raw material for the preparation of commercially valuable compounds has attractive prospects. When CO2 participates in reaction, high energy barrier is needed due to the low reactivity of CO2. Yet, highly active substrates may be more likely to overcome the energy barrier, and catalyst is further needed to reduce the reaction barrier. The epoxides are highly active starting materials, thus the most widely research of CO2 fixation and transformation is the coupling of CO2 and epoxides for the synthesis of cyclic carbonates.In this paper, two novel lewis acid-base integrated MOFs catalysts were fabricated and catalyzed the coupling reaction of CO2 and epoxide. The first part focus on the synthesis of bifunctional Co species based metal-organic framework(denoted as Co-MOF) by solvothermal method. Four-coordinated Co site and free NH2 groups are contained in Co-MOF. And its structure was thoroughly characterized by X-ray crystallography, PXRD, TGA, FTIR and N2 adsorption/desorption characterizations. Then Co-MOF was used to catalyzed the coupling reaction of CO2 and epoxides. Moreover, the influences of various reaction parameters on catalytic activity were investigated, including reaction temperature, CO2 pressure, co-catalyst dosage, reaction time. The yield of propylene carbonate reached 98% at the optimized reaction conditions(100 oC, 2 MPa, 6 h). Also the catalyst was efficiently versatile to the coupling of CO2 with other epoxides. Additionally, the catalyst possessed good recycling performance, after repeated uses for three times, there was no significant loss of catalytic activity. In addition, the possible mechanism of the CO2 coupling reaction catalyzed by Co-MOF was tentatively proposed based on the experimental results.The second part developed bifunctional Zn species based metal-organic framework(denoted as Zn-MOF), which contained four-coordinated and six-coordinated Zn site and free NH2 groups by solvothermal method. Satisfactorily, the bifunctional zinc species based metal-organic framework was a highly active, selective and stable heterogeneous catalyst for the coupling reaction of CO2 with epoxides under mild and solvent-free conditions. Additionally, the influences of reaction parameters such as reaction temperature, CO2 pressure, catalyst loadings and reaction time on catalytic activity were investigated thoroughly. The yield of propylene carbonate reached 92 % at 90 oC, 1 MPa, 6 h. And the catalyst exhibited excellent catalytic performance towards CO2 cycloaddition to various epoxides under mild and solvent-free conditions. The reported catalyst also exhibited good recyclibility for six times recycles. At last, based on the experimental results and the characterization of the catalyst, the self-catalyzed mechanism as well as synergistic mechanism with tetrabutylammonium bromide(Bu4NBr) for CO2 conversion was proposed.