Study On Cobalt-based Catalyst For Preparation Of Light Olefins Via Fischer-tropsch Synthesis

In the large-scale chemical production in the 21st century,the status of light olefins is extraordinary.As the world’s oil reserves are shrinking,the conversion of syngas（the mixture of CO and H2）from non-oil resources to produce light olefins has attracted more and more attention from the Academia and the Industry.Compared with other processes,the process of production of olefins by Fischer-Tropsch synthesis has shorter process flow,lower energy consumption and lower price of feed gas.The olefins and other products produced by this process are safe and environmentally friendly,and conform to the concept of green and sustainable development.In the reaction of this process,the catalyst undoubtedly plays a decisive role.Among all Fischer-Tropsch catalysts,the cobalt-based catalyst has long service life,stable activity and easy to adjust the product distribution,which is the hotspot of current scientific research.In this paper,Co₃O₄ catalyst with known preparation methods was used,and sodium metal promoter was loaded on its surface by excessive impregnation method,in order to achieve high selectivity of light olefins on the premise of ensuring stable activity.XRD,H2-TPR,XPS and other methods were used to study the grain size,element distribution,reducibility and other properties of the C03O4 catalyst to prove the rationality of the experimental data.The preparation and reaction conditions of Co₃O₄ catalyst should be determined in the first place.It was found that the catalyst could maintain high activity when the calcination condition was set at 300℃ for 4 h,and the reaction pressure was set at 1 MPa.After the preparation conditions and the reaction conditions were determined,sodium was loaded on Co₃O₄ catalyst and observed its FTS performance.Sodium citrate and sodium hydroxide were selected as the sodium sources,respectively.When the loading amount reached 2 wt%Na,the selectivity of light olefins and the olefin-to-alkene ratio of C2～C4 hydrocarbons of the two kinds of Co₃O₄ modified by sodium promoter reached the highest value（trisodium citrate:33.28%,3.81;sodium hydroxide:34.05%,3.72）,and they both kept great activity during the reaction.The content of light olefins and the olefin-to-alkene ratio of C2～C4 hydrocarbons in products increased significantly after loading sodium metal promoter.Subsequently,the FTS performance differences of the two kinds of Co₃O₄ modified by sodium promoter was demonstrated by XRD,H2-TPR,XPS and CO2-TPD（The differences between the selectivity of light olefins and the olefin-to-alkene ratio of C2～C4 hydrocarbons were mainly compared.）,which further demonstrated the rationality of the experimental data.