Cycloaddition Of Carbon Dioxide To Epoxide Catalyzed By Supported Graphitic Carbon Nitride

Fossil fuel provides 85% energy consumption for human. A large amount of CO2 produced from the burning of fossil fuel, which is responsible for the ecological and environmental problems, such as greenhouse. CO2 is a renewable source of carbon and can be used to produce a variety of important chemical materials. Cycloaddition of CO2 to epoxide is an important way for its utilization. In order to develop efficient catalysts for the cycloaddition of CO2 to epoxide, dicyandiamide was loaded on the mesochannels of SBA-15 by impregnation. SBA-15 supported graphitic carbon nitride (g-C3N4) catalyst was obtained after calculation at 550℃。The catalyst was employed to catalyze cycloaddition of CO2 to epoxide. A good result was obtained. The thesis was composed in two parts:(1) Peparation of catalyst; (2) Catalytic performance evaluationThe first part:peparation of catalyst.Dicyandiamide was loaded on the mesochannels of SBA-15 by impregnation using SBA-15 as the carrier and dicyandiamide as the precursor. SBA-15 supported g-CsN4 (g-C3N4/SBA-15) was obtained after calculation at 550℃。The catalyst was characterized by transmission electron microscopy, X-ray diffraction, N2 adsorption and X-ray photoelectron spectroscopy. The results showed that the mesoporous structure of SBA-15 has not changed significantly in the as-prepared g-C3N4/SBA-15. The BET surface area of the catalyst is 492 m2/g. The g-C3N4 nanophases dispersed in the channels of SBA-15. SiO2 in SBA-15 reacted with g-C3N4. The C-O was formed, which could enhance the electronic structure of the catalyst.The second part:Catalytic performance evaluation.The calalyst was employed for the catalytic synthesis of cyclic carbonate from cycloaddition of carbon dioxide to epoxide. The effects of the composition of the catalysts and the reaction conditions on catalytic performance were investigated. The results showed that g-C3N4/SBA-15 can catalyze the cycloaddition of carbon dioxide to epoxide effectively. The pore structure and the surface chemical properties affect the catalytic performance significantly. The pore structure is affected by the amount of the supported g-C3N4, which may affect the catalytic performance. Lewis acid co-catalyst is an important factor for the catalytic performance. The reaction can not be carried out without the co-catalyst. The reaction is speed up with the increasing in ZnBr2. The catalytic performance is affected by the Lewis acid affacts obviously. The highest calalytic activity is achieved by ZnI2.The reaction rate is affected by the temperature and pressure. The reaction rate is increased with the increasing temperature. Compared to temperature, the pressure affects the reaction rate little. The reaction can be carried out under the low pressure of 0.5 MPa. The stability of the supported g-C3N4 catalyst is good. The catalytic activity has not decreased significantly after five times using. The catalyst can be used for the cycloaddition of carbon dioxide to a variety of epoxides. The g-C3N4/SBA-15 catalyst has the advantages of simple preparation method, cheap raw materials and excellent catalytic performance.The third part:Cycloaddition catalyzed by acidified g-C3N4.G-C3N4 was treated with hydrochloric acid. After acidification, the size of g-C3N4 was reduced and the hydrophilicity was improved. The acidified g-C3N4 was used to catalyze the cycloaddition of carbon dioxide to epoxide. The results showed that, after acidification, the catalytic activity of g-C3N4 improved significantly. The preparation conditions and the reaction conditions had a significant effect on the catalytic perfermance. The catalytic activity was increased with the increasing acidification time. Without co-catalysis, acidified g-C3N4 can catalyze the cycloaddition reactions with low activity. After ZnBr2 was added as the co-catalyst, the catalytic activity increased rapidly. Reaction temperature has a greate impact on the cycloaddition rate. The reaction rate is accelerated with the increasing in temperature. The reaction pressure also affects the catalytic perfermance. The cycloaddition reaction is difficult to carry out under atmospheric pressure. After increasing the pressure to 0.5 MPa, the catalytic activity increased rapidly.