Study On The Performance Of Fischer-tropsch Synthesis Of The TiN Supported Co Catalyst

Fischer-Tropsch synthesis（FTS）is an important process used in the production of liquid fuels and fine chemicals from syngas（CO and H₂）.Iron and cobalt are considered as optimal catalysts.Cobalt catalysts are widely studied due to their high CO conversion activity,high selectivity for long-chain linear hydrocarbons,and long-term durability.Cobalt catalysts are often dispersed on a carrier to improve the dispersion,increase the activity,and enhance the stability,or improve the selectivity of the products.In this study,TiN was used as the carrier to load the cobalt nanoparticles.The effects of the cobalt species loading,particle size,reduction temperature on the structure and performance of the cobalt catalysts are investigated.The results can further clarify the relationship between the structure of the catalysts and the performance of the Fischer-Tropsch synthesis,and provide a reference for the preparation of excellent catalysts.The results of the studies are listed as follow:1.Co₃O₄ nanoparticles with a particle size of 10 nm was prepared using the hydrothermal method.X%Co/TiN catalysts with different cobalt loading（X=5,10,15,20）were prepared by mechanical mixing method.we characterized the properties and structures of the catalysts using TEM,XPS,H₂-TPR and XRD,and studied the performance in a fixed-bed.The results shows that the most of the Co₃O₄ nanoparticles were completely mixed with the TiN carrier,and evenly dispersed on the carrier.The particle size did not significantly change in the process of mechanical mixing.For the20%Co/TiN catalyst with higher loadings,the distance between the Co₃O₄nanoparticles is reduced,the agglomeration occurs in some areas.The performance showed that the stability of the 20%Co/TiN catalyst was the worst,the cobalt particles may have grown up to larger particles during the reaction.The CO conversion continues to decrease.With the increasing of the cobalt loading,the initial CO conversion increased from 5.1%to 29.7%,the TOF and CTY values also gradually increased.For all catalyst,the product selectivity did not change significantly.2.The 10%Co/TiN catalyst was reduced with H₂ at different temperatures（300℃,350℃,400℃）.XRD analysis result shows that the crystal phase of cobalt in the catalyst belongs to HCP type.With the reduction temperature increasing,the Co⁰/(Co³⁺+Co²⁺+Co⁰)gradually increased,but the total content of cobalt species on the catalyst surface decreased（Co/Ti decreased）.The performance shows that when the catalyst is reduced at 350℃,the activity is the highest.When reduced at 400℃,the activity is lowest.The cause is probably that the reduction temperature is higher,there is a strong interaction between the carrier and the cobalt.The carrier（mainly Ti species）may have migrated to the surface of the active metal,part of active site was covered with the Ti species.3.The Co₃O₄ nanoparticles with different particle size were prepared by changing the conditions of the hydrothermal reaction.The catalysts with the same cobalt loading,different size（6 nm,10 nm,13 nm,16 nm）were prepared using TiN as the carrier by the mechanical mixing method.The results shows that the Co₃O₄ nanoparticles are uniformly dispersed on the surface of the carrier.With increasing the particle size of the Co₃O₄ nanoparticles in the catalyst,the interaction between the cobalt metal and the carrier decreases,the reducibility of the catalyst increases.The performance result shows that the CO conversion,TOF and CTY increase with increasing the particle size.