Preparation And Performance Control Of Silicon Carbide Supported Cobalt Catalysts For Fischer-Tropsch Synthesis

Fischer-Tropsch synthesis(FTS)is the process of converting syngas obtained from coal,biomass,shale gas,and natural gas into green fuel and high value-added chemicals.Due to the wide source of raw gas and the product's environmental protection,FTS has attracted more and more attention.FTS is a strongly exothermic reaction,and its catalysts often deactivate due to the formation of hot spots.The new catalyst carrier silicon carbide has the advantages of good thermal conductivity,corrosion resistance,and high mechanical strength,etc,which is superior to common catalyst carriers.Therefore,silicon carbide with high specific surface area has received extensive attention as a catalyst carrier for FTS.The commercial SiC was first selected in this study as the carrier of catalysts for FTS.The effects of preparation methods,SiO2 and La2O3 additives on the performance of Co/SiC catalyst for FTS were systematically investigated.The Co/SiC catalyst with honeycomb pore structure wasprepared.The catalyst prepared by the sol-gel method to properly balance the two contradictory needs,ie,reducing degree and dispersion.The prepared sample showed that lower CH4 selectivity,higher C5+ selectivity and the better stability than other preparation methods.Addition of SiO2 promoter increased the specific surface area of the catalyst,which was beneficial to the dispersion of active components of the catalyst on carrier surface.It also enhanced the interaction between cobalt and support,reducing the aggregation and loss of catalyst.The 15%Co/3.0%SiO2-SiC catalyst showed that the best catalytic stability.Addition of SiO2 increased the selectivity of methane and slightly decreased the selectivity of C5+.It is also found that the addition of SiO2 is beneficial to the formation of kerosene.In the catalysts bearing La2O3,it was found that there exists proper interaction between La2O3 promoter and cobalt species,which was beneficial to the dispersion of cobalt species and the improvement of initial activity.It is helpful for the formation of gasoline.The 15%Co/SiC catalyst promoted with 2.0%La2O3 showed the best catalytic stability for FTS.Compared with powdered catalysts,the 15%Co/SiC catalysts with honeycomb pore structure yields lower CH4 selectivity and higher C5+selectivity.The results indicated that this pore structure is beneficial to gas and liquid transfer in catalysts,and is unfavorable for carbon deposition.Addition of TiO2 to Co/SiC catalysts enhanced the cobalt-support interaction,leading to the high dispersion of cobalt species on support surface and low aggregation or loss of cobalt component.The 15%Co/SiC catalyst promoted with 5.0%TiO2 showed the best catalytic stability for FTS.