A Density Functional Study of Amine Catalysts for CO2 Fixation into Cyclic Carbonates

Abstract

The catalytic efficiency of three different kinds of amine groups for a prototype reaction of propylene oxide and carbon dioxide was investigated using density functional and energetic span model calculation. Our study demonstrated that tertiary amine groups perform best as catalyst at 100 °C and 10 bars because the corresponding catalytic cycle is free of any proton to be transferred around different molecular fragments. With primary or secondary amine catalysts, however, one or two protons at the nitrogen atom of amine can be transferred to the oxide oxygen, leading to intermediate structures stabilized by intramolecular hydrogen bonding at a deep valley in catalytic cycle. It is concluded that, when compared with the cases of primary or secondary amine groups, the effectiveness of tertiary amine group in catalysis originates from least hindrance to final products in catalytic cycle due to the absence of protons transferred.