Experimental and theoretical studies on CO2 and propylene oxide (PO) copolymerization catalyzed by ZnEt2–glycerine–Y(CCl3COO)3 ternary catalyst

• The copolymerization of CO2 with propylene oxide studied by experiment and DFT.
• Supported ZnEt2–glycerine–Y(CCl3COO)3 ternary catalyst with SiO2 and Al2O3/SiO2.
• Supported catalyst exhibited the highest activity with 3 wt% Al2O3/SiO2 as support.
• The activity of the supported catalysts was related to the acidity of the support.
• Appropriate electron density of zinc center of the ternary catalyst was crucial.

Alternating copolymerization of CO2 and propylene oxide (PO) catalyzed by ZnEt2–glycerine–Y(CCl3COO)3 ternary catalyst was investigated through combined experimental and theoretical approaches. The ternary catalyst showed an increased activity by introducing a support of SiO2. The catalytic activity was further improved when Al2O3 modified SiO2 was used as support. For the supported ternary catalyst using Al2O3 modified SiO2, the catalyst activity increased with increasing of the amount of Al2O3, and the highest activity with 69% of enhancement in catalytic activity compared with the non-supported ternary catalyst was achieved at 3 wt% Al2O3 followed by a further decrease of activity. NH3–TPD measurement confirmed that the surface acidity of the Al2O3 modified SiO2 increased with increasing the amount of Al2O3, which indicated that a proper increment of surface acidity of the SiO2 support was favorable for the improvement of the catalytic activity for the supported ternary catalyst. Moreover, the mechanism for the alternating copolymerization of CO2 and PO over ZnEt2–glycerine binary catalyst and ternary catalyst system has been studied by DFT. The insertion of PO into Zn-carbonate bond was rate-determining and the corresponding activation barrier decreased with increasing of the natural bond order (NBO) charge of the zinc species. The combined experimental and theoretical results suggested that electron deficiency of zinc centers of the ternary catalyst was crucial for the alternating copolymerization of CO2 and PO.

The ZnEt2−glycerine−Y(CCl3COO)3 ternary catalyst has been supported on SiO2 and Al2O3/SiO2 to improve catalytic activity. Meantime, copolymerization mechanisms of CO2 and propylene oxide (PO) over five models of ZnEt2--glycerine binary catalyst and ternary catalyst system with different NBO charge on zinc centers are investigated using the DFT method.Figure optionsDownload as PowerPoint slide