Study On The Preparation Of Cu-ZnO-MnO_x Catalysts And Its Performance In Catalytic CO~2 Hydrogenation To Methanol

The exploitation of fossil fuels has led to a dramatic increase in atmospheric CO2 concentrations year on year.CO2 is an abundant,readily available and renewable carbon resource that can be converted into high value-added products in many viable ways,of which CO2 hydrogenation to methanol is of great interest because it has a high economic value and is an important industrial chemical feedstock.Cu-based cataly sts have been extensively investigated because they are inexpensive and easily modified and show great potential for industrial applications,however,they still have the disadvantages of poor stability and low selectivity.Based on the fact that manganese oxide(MnOx)is an inexpensive and abundant metal oxide with good tunability and physicochemical properties.In this paper,Cu-ZnOMnOx three-component catalysts for CO2 hydrogenation to methanol were prepared and investigated in terms of catalyst composition,catalyst characterization and catalytic activity evaluation,and reaction working conditions,as follows:1.Cu-ZnO,Cu-MnOx two-component and Cu-ZnO-MnOx three-component catalysts were prepared by a parallel-flow co-precipitation method,and the effect of catalyst composition on the catalytic activity of CO2 hydrogenation to methanol was investigated.The results showed that the activity of the Cu-ZnO-MnOx three-component catalyst was significantly enhanced compared to that of the two-component catalyst,and the combination of Cu,Zn and Mn metal oxides resulted in enhanced interactions,the maximum oxygen vacancy concentration of the catalyst and a significant increase in the medium to strong basic sites on the catalyst surface,and the methanol time-space yield was 198 gMeOH/(kgcat·h)at a reaction temperature of 220℃,an increase of 88.5%and 58.4%compared to the CZ and CM catalysts,respectively.2.The effect of MnOx loading on the physicochemical and catalytic properties of Cu-ZnO-MnOx catalysts in the hydrogenation of CO2 to methanol reaction is systematically investigated.The results show that the doping of appropriate amount of MnOx enhances the synergistic effect of Cu and ZnO,increases the concentration of oxygen vacancies and the strong basic sites in the surface of the catalyst,thus promoting the adsorption and conversion of CO2.Therefore,the doping of appropriate amount of MnOx was beneficial to improve the activity of CO2 hydrogenation for methanol synthesis,and when the Cu/Zn/Mn molar ratio was 6:3:1,the CO2 conversion reached 10.68%,the methanol selectivity was 52.19%and the methanol time-space yield was up to 233.23 gMeOH/(kgcat·h).3.The effects of process conditions such as catalyst roasting temperature,reaction pressure and reaction air velocity on the catalytic activity of Cu-ZnO-MnOx catalysts were investigated.It was found that the optimum process conditions for the CO2 hydrogenation to methanol reaction with the CZM-10 catalyst were:calcination temperature of 450℃,reaction pressure of 5 MPa and reaction air velocity of 12000 mL/g-h.Under these conditions,the catalyst performance was optimal with a CO2 conversion of 11.2%,a methanol selectivity of 54.6%and a methanol time-space yield of 256.7 gMeOH/(kgcat·h).The stability of the CZM-10 catalyst was also tested and found to exhibit good stability performance over a continuous 200 h reaction time.