Study On Direct Synthesis Of DEC/DMC With CO₂ And Ethanol/Methanol

Carbon dioxide（CO₂）,as a greenhouse gas and major contributor to anthropogenic climate change,is most commonly discussed in negative terms.Recently,the use of CO₂ as an abundant carbon resource has received increased attention.Because it incorporates a waste resource in the production of value-added,sustainable substances,direct conversion of CO₂ to green chemicals diethyl carbonate,dimethyl carbonate is an attractive application.Therefore,the research and development of highly active catalysts for DEC and DMC synthesis reactions is the focus of this research.（1）In this work,spherical CeO₂（CeO₂dp.）,rod-shaped CeO₂（CeO₂ ht.）,ZrO₂ with different crystal phases（t-ZrO₂,m/t-ZrO₂）and their corresponding supported catalysts were prepared（CeO₂/CaCO₃,CeO₂/SrCO₃,CeO₂/BaCO₃）.In the direct synthesis of DEC/DMC from CO₂ and ethanol/methanol,the catalyst activity order is as follows:CeO₂/CaCO₃>t-ZrO₂>CeO₂/SrCO₃>CeO₂/BaCO₃>m/t-ZrO₂>CeO₂dp.>CeO₂ ht.The structure,acidity and basicity of CeO₂/CaCO₃,CeO₂/SrCO₃ and CeO₂/BaCO₃ catalysts were characterized by XRD,SEM,CO₂-TPD and NH₃-TPD and other physical and chemical methods.According to XRD and TEM,it is proposed that the CeO₂（111）is favored in the formation of DEC.t-ZrO₂ exposed more t-ZrO₂（101）and（112）crystal planes,and m/t-ZrO₂ mainly exposed m-ZrO₂（-111）and（111）crystal planes.CeO₂/CaCO₃contains strong acid-base sites,and the highest yield of DEC is 4.97%.（2）Direct synthesis of DMC from methanol and CO₂ were investigated over CeO₂catalysts with different morphologies,CeO₂ supported on carbonate catalysts,ZrO₂ with different crystal phases,and Ce_xZr_1-xO₂.CeO₂/CaCO₃ showed the highest catalytic activity,the highest yield of DMC reached 6.78%.The catalytic activity of Ce_xZr_1-xO₂ catalyst is higher than that of single CeO₂ catalyst,which may be due to the addition of Zr which enhanced the thermal stability and oxygen storage capacity of CeO₂.The crystalline structure and the number of acid-base sites of the catalyst may be different when x takes different values.The ZrO₂ catalyst prepared in this work demonstrated competitive advantages compared with reported ZrO₂ catalysts in literatures.In addition,the reaction pressure,time and temperature are also crucial parameters for improving the yield of DMC.