Abstract
Traditional ionic liquids (ILs) catalysts suffer from the difficulty of product purification and can only be used in homogeneous catalytic systems. In this work, by reacting ILs with co-catalyst (ZnBr2), we successfully converted three polyether imidazole ionic liquids (PIILs), i.e., HO-[Poly-epichlorohydrin-methimidazole]Cl (HO-[PECH-MIM]Cl), HOOC-[Poly-epichlorohydrin-methimidazole]Cl (HOOC-[PECH-MIM]Cl), and H2N-[Poly-epichlorohydrin-methimidazole]Cl (H2N-[PECH-MIM]Cl), to three composite PIIL materials, which were further immobilized on ZSM-5 zeolite by chemical bonding to result in three immobilized catalysts, namely ZSM-5-HO-[PECH-MIM]Cl/[ZnBr2], ZSM-5-HOOC-[PECH-MIM]Cl/[ZnBr2], and ZSM-5-H2N-[PECH-MIM]Cl/[ZnBr2]. Their structures, thermal stabilities, and morphologies were fully characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The amount of composite PIIL immobilized on ZSM-5 was determined by elemental analysis. Catalytic performance of the immobilized catalysts was evaluated through the catalytic synthesis of propylene carbonate (PC) from CO2 and propylene oxide (PO). Influences of reaction temperature, time, and pressure on catalytic performance were investigated through the orthogonal test, and the effect of catalyst circulation was also studied. Under an optimal reaction condition (130 °C, 2.5 MPa, 0.75 h), the composite catalyst, ZSM-5-HOOC- [PECH-MIM]Cl/[ZnBr2], exhibited the best catalytic activity with a conversion rate of 98.3% and selectivity of 97.4%. Significantly, the immobilized catalyst could still maintain high heterogeneous catalytic activity even after being reused for eight cycles.
Highlights
Carbon dioxide (CO2 ) is a rich carbon resource in nature
-1 pattern (a), the peak at cm corresponds to the Si–Ocatalysts characteristic of out Fourier-transform infrared spectroscopy (FT-IR) studies on zeolite ZSM-5 and its immobilized were peak carried
The results showed that the grafted rate of composite polyether imidazole ionic liquids (PIILs) catalyst decreased over 1 to 3 cycles, and there was negligible change after three cycles
Summary
Experts and scholars around the world have been working on the catalytic conversion and utilization of CO2 [1,2,3,4,5]. Research results have shown that the chemically speaking CO2 is extremely inactive, careful selection of proper catalysts could make CO2 become a low-cost and widely used resource. The development of efficient catalysts is the key to achieve chemical fixation and conversion of CO2 under mild conditions. Studies on the conversion of CO2 to cyclic carbonate using ILs as catalysts have been widely reported [11,12,13], demonstrating that the catalytic performance of ILs as a single component in catalysts is unfavorable, and the addition of Lewis acids or other co-catalysts in the catalysts is necessary to achieve better catalytic activity
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