Preparation And Characterization Of Iron Catalysts Supported On Carbon Nanocages And Its Catalytic Performance For Fischer-Tropsch Synthesis

With the fast development of China's economy and the rapid growth in energy demand,combined with China's less oil and more coal energy structural features,changes in energy supply and utilization mode is imperative.It is an effective way to use Fischer-Tropsch synthesis technology to convert coal into syngas to produce liquid fuels and other high value-added chemical raw materials.Fischer-Tropsch synthesis catalysts directly affect the product distribution,wherein the catalyst support can greatly influence the catalytic activity,stability and selectivity.The used catalyst supports,including oxides,molecular sieves,activated carbon,carbon nanotubes?CNTs?and carbon nanofibers?CNFs?,have obvious disadvantages.For example,CNFs and CNTs showed a better catalytic performance than traditional activated carbon?AC?,Al₂O₃ and SiO₂,but they do not enough high surface area and their surfaces are relatively inert.Our group recently synthesized carbon nanocages?CNCs?,featured by ultra-high surface area?larger than CNTs by one order of magnitude?,good graphitization and many surface defects.They exhibited excellent performance in supercapacitors and metal-free oxygen reduction?ORR?.CNCs'ultra-high surface area and rich defect sites are conducive to disperse and load iron nanoparticles.This thesis focused on the preparation,characterization and catalytic performance of iron catalysts supported on Carbon Nanocages.The results are summarized as follows:1?CNCs,synthesized with 4MgCO3·Mg?OH?2·5H2O and benzene precursors,has the characteristics of ultra-high surface area,high degree of graphitization and more surface defects.Because of its ultra-high surface area and rich defect sites,without any pre-treatment,Fe/CNCs catalysts can be easily constructed.2?With the iron loading increasing from 10%to 60%,there was a significant increase in the number of particles on the CNCs surface;with the iron content below 20%,the nanoparticles were distributed sparsely on the CNCs surface;with the iron loading of 40%,the particles were close to each other and a few started to aggregation;with the iron load reaches 60%,the particles aggregated seriously.The size of the nanoparticles with the iron content below 40%were relatively the same?about 8±4 nm?;when the iron loading reached 60%,nanoparticles had a significant size increase.Compared to CNTs,the strong catalyst-support interactions and electron transfer between CNCs and Fe,can significantly promote iron oxide reduction.With the increase of iron loading,every peak temperature of iron oxide reduction process was increased,namely reduction becoming more and more difficult.3?The Fischer-Tropsch Synthesis catalytic performance of 10Fe/CNCs and 10Fe/CNTs were compared.With the reaction condition of atmospheric pressure,300? and 2000 mL h^-1 g^-1,the C₂^?-C₄^? selectivity of 10Fe/CNCs was 33%,5%higher than 10Fe/CNTs,and the activity was about three times higher than 10Fe/CNTs.The better performance of 10Fe/CNCs stemmed from its active phase?Fe5C2?with the features of higher content,better dispersion,and smaller particle size,stronger active phase-support interactions and electron transfer from the support to the active phase.With the iron loading increasing to 40%,the CO conversion rate reached the highest 16%,with relatively decrease C₂^?-C₄^?selectivity and C5+ selectivity of 55%.The optimized Fischer-Tropsch synthesis conditions:atmospheric pressure,300? and 4000 mL h^-1 g^-1.These results provide a reference for the design and development of high-performance Fe-based carbon material Fischer-Tropsch synthesis catalyst.