Preparation And Catalytic Performance Of Co-Based Catalysts Supported On Mesoporous Materials For Fischer-Tropsch Synthesis

With the rising serious energy crisis and environment issues,Fischer-Tropsch synthesis（FTS）,which can convert syngas from coal,biomass,and CO₂electroreduction to clean fuels,has catched more and more attention.The study on catalyst structure,especially the support structure,is of great significance for a high FTS performance.In this thesis,carbon materials and mesoporous silicon materials supported cobalt-based catalysts have been systematically studied,including the influence of support microenvironment around active Co⁰ sites,the comparison of carbon support and silicon support,the metal-support interactions,and the construction of bifunctional catalysts.This thesis is tried to discover and clarify the influence of metal-support interactions and the structure-activity relationship of FTS catalysts,in order to develop high-performance FTS catalysts.Firstly,the core-shell structured Co@C catalyst was synthesized by one-pot carbonization method to reveal the influence of carbon shell microenvironment.The precise control of the graphitization degree of the carbon shell was achieved by adjusting the carbonization temperature and gas.The increase in the graphitization degree could decrease H₂ concentration around active Co⁰ sites and promote the carbon chain growth to inhibit more CH₄.With the highest graphitization degree,Co@C-750performed high C₅₊selectivity of 73%and low CH₄ selectivity of 10%.The highly ordered mesoporous material SBA-15 and CMK-3 were used as the supports to synthesized Co-based FTS catalysts.The study confirmed that different support surface properties and different pore structures could directly affect the catalytic behavior.Co/SBA-15 catalyst possessed the best FTS performance with CO conversion of 74.6%.Heteroatom doping was used to modify the mesoporous silica.Titanium was incorporated into the framework of SBA-15 to synthesize OMSTx support.With the titanium content increase,the interaction between the cobalt and the support was obviously enhanced.Therefore,the CO adsorbility on active Co⁰ sites was increased,which promoted the C₅₊selectivity to 77.7%.Co₂Si O₄ was incorporated into the framework of SBA-15 by doping Co²⁺.The dispersion of supported cobalt particles was enhanced on OMSCx supports.During the FTS reaction,the presence of Co₂Si O₄ in the support could cut off the contact between supported cobalt and silica to avoid more Co₂Si O₄ formation.And the anchoring effect of Co₂Si O₄also promoted the FTS stability of Co/OMSCx catalysts.With the modification of Co₂Si O₄,the CO and CH₄adsorbility on Co/OMSC40 were strengthened,which effectively enhanced carbon chain growth and led to high C₅₊selectivity（78.5%）at high CO conversion（70.1%）.Bifunctional catalysts with different proximity between active Co⁰ sites and acidic sites were constructed by coupling Co/SBA-15 and HZSM-5.The effect of different reaction temperatures was also investigated.Co/SZ-B catalysts with proper active sites proximity exhibited better CO conversion and gasoline selectivity.The distribution of gasoline in C₅₊of Co/SZ-B could reach 89.5%.It’s demonstrated that the high gasoline selectivity on Co/SZ-B at high temperature was the result of synergistic hydrocracking effect of active Co⁰ sites and acidic sites.