Study On Cooper Based Catalytic System For Syntheses Of Methanol And Ethylene Glycol Via Hydrogenation Of Ehtylene Carbonate Derived From Carbon Dioxide

The efficient synthesis of methanol and ethylene glycol via the chemoselective hydrogenation of ethylene carbonate is important for the sustainable utilization of CO2 to produce commodity chemicals and fuels.However,direct hydrogenation of CO2 suffering the unsatisfactory transformation efficiency due to the thermodynamically stability,simultaneously harsh reaction conditions are generally needed to conquer the kinetic inertia of CO2;Hence,indirect synthesis way via the hydrogenation of ethylene carbonate to co-produce methanol and ethylene glycol becomes a promising approach due to the environmentally-friendly syntheses of commodity chemicals and fuels.It should be noted that ethylene carbonate can be easily available from CO2 and epoxides at industrial scale.This paper focuses on the development of copper based catalysts for hydrogenation of ethylene carbonate to methanol and ethylene glycol,because the copper based catalyst exists low activity and the active Cu particles are readily aggregated.Therefore,this thesis mainly focused on developing a highly efficient and stable copper based catalytic system.Concretely,the involvement of second metal(Au)or(3-cyclodextrin in the preparation process to improve the catalytic performance and stability.The catalyst characterization,catalytic performance evaluation,reaction conditions,structure activity relationship analysis,catalyst stability and catalytic mechanism were further systematically studied.The main research contents and conclusions of this paper are summarized as follows:1.A series of Cu-Au/SBA-15 bimetallic catalysts have been successfully prepared by one-step ammonia evaporation for ethylene carbonate hydrogenation.Among the catalysts tested,10Cu-lAu/SBA-15 catalyst with appropriate Au loadings exhibited unprecedented catalytic activity with MHSV of 1628 mgEC·gcat-1·h-1.Compared to monometallic Cu/SBA-15,the involvement of Au in bimetallic 10Cu-1 Au/SBA-15 could remarkably promote the catalytic performance.The enhanced catalytic activity could be primarily attributed to the promotional effect of Au with the form of Cu-Au nanoalloy and the appropriate proportion of Cu+/(Cu0+Cu+).Furthermore,Au evidently improved the catalyst recyclability performance,and the crucial role of the balanced Cu+ and Cu0 species on the catalytic performance was further disclosed.A plausible catalytic mechanism was primarily proposed that Cu0 with the assistance of Au dissociated H2 and Cu+ adsorbed on the carbonyl group of ethylene carbonate.2.Compared with the unmodified 25Cu/SiO2 catalyst,the involvement of β-cyclodextrin in 5β-25Cu/SiO2 could remarkably increase the catalytic activity—excellent activity of 1178 mgEC·gcat-1·h-1 with 98.8%ethylene glycol selectivity,and 71.6%methanol selectivity could be achieved at 453 K.The remarkably improved recyclability was primarily attributed to the remaining proportion of Cu+/(Cu0+Cu+)and suitable amounts of(3-cyclodextrin onto the copper catalyst retarded the aggregation of the Cu species.Furthermore,the DFT calculation results demonstrated that metallic Cu0 dissociated adsorbed H2,while Cu+ activated the carbonyl group of EC and stabilized the intermediates.This study has provided a facile and efficient method to prepare highly dispersed Cu catalysts,and 5β-25Cu/SiO2 catalyst is found to be an effective and stable heterogeneous catalyst for the sustainable synthesis of ethylene glycol and methanol via indirect chemical utilization of CO2.