Performance Research About Cobalt-based And Ruthenium-based Catalysts Supported On Multilayer Mesoporous Silica Nanosphere For Fischer-tropsch Synthesis

The Fischer-Tropsch synthesis（FTS）reaction is an effective way to convert synthesis gas（CO+H₂）derived from non-petroleum based raw materials into green hydrocarbon fuel and value-added chemicals（diesel,gasoline,kerosene,wax,etc.）,and catalyst is the core of FTS technology.Among them,cobalt based and ruthenium based catalysts are considered to be the best candidates for Fischer-Tropsch synthesis due to their high activity and selectivity about long chain alkane.However,traditional catalyst supports have the drawbacks of easy aggregation of active components,difficulty in reducing metals,and limited heat and mass transfer.Therefore,the preparation of efficient catalyst support is crucial.Ordered mesoporous materials have the characteristics of large specific surface area,regular pore structure,adjustable pore size,etc.,and have become the commonly used catalyst support.In addition to the above characteristics,double-layer silica mesoporous nanospheres also have three-dimensional interconnected pore structure,which is conducive to the transfer and diffusion of reactants,products and heat in the pore.In this paper,the catalytic performance of cobalt and ruthenium based catalysts with different support structures for FTS was studied.The effects of mesoporous layers,active components and their distribution in the catalyst channels on the structure and catalytic performance of the catalysts were systematically investigated.The specific research contents are as follows:1.Synthesis of solid SiO₂ sphere by sol-gel method,single-layer and double-layer SiO₂ mesoporous sphere by oil-water two-phase stratification,combined with equal volume impregnation method to prepare Co/SiO₂ catalysts with different support structures.The effect of support structure on the catalytic performance of the catalysts was systematically investigated.The results show that the unique two channel structure of the double-layer mesoporous SiO₂ sphere can effectively promote the dispersion and reduction of CO species,and contribute to the formation of Co nanoparticles with relatively appropriate size（6 nm）,which is helpful to expose more active sites to promote the transformation of CO.In addition,the Co/SiO₂-c catalyst exhibits the best catalytic performance.2.Ru/SiO₂ catalyst was prepared by loading low content metal Ru on solid SiO₂sphere,single-layer and double-layer SiO₂ mesoporous sphere by equal volume impregnation,aiming to study the effects of metal Ru and the support structure on the catalytic performance of the catalysts.It is found that the introduction of monolayer mesoporous SiO₂ sphere promotes the reduction of RuO₂ to Ru⁰,which results in the formation of more active sites to participate in the transformation of CO and improves the CO conversion.Combined with the selectivity test,the Ru/SiO₂-b catalyst also has the highest C₅₊hydrocarbon selectivity.In addition,compared with the Co/SiO₂ catalyst,the introduction of metal Ru significantly improves the C₅₊hydrocarbon selectivity of the catalysts.3.The distribution of metal Co in mesoporous channel is adjusted by changing the loading period of Co species.It is found that when the metal Co is supported on the inner channel of the double-layer SiO₂ mesoporous sphere,although the CO conversion of the catalyst decreases due to the partial blockage of the mesoporous channel,the C₅₊selectivity of the catalyst is higher derived from the distribution of Co particles in the inner mesoporous channel,which is beneficial to prolong the residence time of intermediate product and further improve C₅₊selectivity.