Molecular Simulation Of Ionic Liquid-catalyzed CO₂ Synthesis Of Cyclic Carbonates

As people pay more and more attention to environmental protection,carbon dioxide as the main greenhouse gas content in the air has become the focus of scientific research workers.One of the crucial ways to solve the problem of high carbon dioxide abundance in the air is the fixation of carbon dioxide,fixation carbon dioxide with chemical has a good application prospect because it can realise the resource utilisation of carbon dioxide.In various ways of fixation carbon dioxide with chemical,the coupling of carbon dioxide and epoxide to produce cyclic carbonate is one of the most successful methods because of its high atom utilisation rate,which can replace the traditional synthesis route of high pollution phosgene.The development of green and efficient reaction catalyst is the key to carbon dioxide conversion.The catalysts currently reported for the synthesis of cyclic carbonate from carbon dioxide can be divided into homogeneous and heterogeneous catalysts,and ionic liquids have attracted much attention due to their green,high efficiency and excellent catalytic performance.In this paper,the reaction mechanism of the coupling of carbon dioxide and ethylene oxide to produce ethylene carbonate catalysed by a series of ionic liquids is calculated by quantum chemistry method,and the interaction and mechanism of hydrogen bond and van der Waals force in the reaction system were investigated.Firstly,The coupling reaction mechanism of carbon dioxide(CO₂)and ethylene oxide(EO)catalysed by ionic liquids with different cations,such as imidazole,pyridine,quaternary ammonium salt and quaternary phosphorus salt,was studied by quantum chemistry theory.The carbonylation of carbon dioxide catalysed by ionic liquids with different anions was also calculated in detail.On this basis,the catalytic activities of different ionic liquids were systematically studied and compared.Then,the interaction of the catalytic reaction system was analysed by using a variety of wave function analysis software.The individual interaction of hydrogen bond and electrostatic force in the system is analysed,and it is found that the hydrogen bond between carbon dioxide and epoxide plays a vital role in carbonylation;The interaction energy of the system is decomposed,it is found that the electrostatic action energy is the primary energy term,while for the hydroxyl functionalised ionic liquids with high catalytic activity,the value of the induced action energy term is relatively high,indicating that they have strong covalency;The change of orbit and charge of the system is analysed,and it is found that the main factor leading to ring-opening is the nucleophilic attack of anion,the second factor is the hydrogen bond between cation and ethylene oxide,and the number of charge transfer of hydrogen bond is obviously more than the traditional hydrogen bond.Finally,the mechanism of carbon dioxide carbonylation catalysed by the ionic liquid in the presence of water was simulated,and the interaction of the reaction system was analysed.For the mechanism of water action,two mechanisms,like proton transfer and hydrogen bond,are proposed.Through the calculation of the reaction barrier,it is found that the primary mechanism of water action is the former.The catalytic activity of different imidazole ionic liquids in the presence of water was compared.It was found that the addition of water did not change the original order of catalytic activity,and the catalytic performance of imidazole bromide ionic liquid was greatly affected by water.