Fischer-Tropsch Synthesis Over ZrO₂-SiO₂ Supported Cobalt Catalysts

The synthesis of liquid fuels based on Fischer-Tropsch(FT) synthesis from coal-, nautral gas- or biomass-derived syngas have received much attention from the viewpoint of decreasing the dependency on petroleum.The design and synthesis of FT synthesis catalysts with high activity and high selectivity are of significant in the efficient utilization of non-petroleum resources such as coal,natural gas and biomass. This dissertation contributes to the studies on the FT synthesis catalyzed by supported cobalt heterogeneous catalysts.The cobalt catalysts loaded on ZrO₂-SiO₂ composite oxide support have mainly been studied,and the enhancing effect of ZrO₂ has been investigated.The structrures of catalyst have been characterized to gain insights into structure-performance relationships.We found that as compared to single ZrO₂ and SiO₂,ZrO₂-SiO₂ composite-supported Co catalysts exhibited higher C₅⁺ selectivities and lower CH₄ selectivities.The optimization of catalyst composition by changing the cobalt loading, method for preparation of composite oxides and the weight ratio of ZrO₂ to SiO₂, reveals that the 5 wt%Co/ZrO₂-SiO₂(ZrO₂/SiO₂ = 1) shows the best performance for C₅⁺ formation.Under 523 K,2.0 MPa,gas flow 20 ml/min,and CO/H₂ = 2/1,the 5 wt%Co/ZrO₂-SiO₂(ZrO₂/SiO₂=1) provided 45.9%CO conversion and 91.6%C₅⁺ selectivity,and methane selectivity was 4.2%.Characterizations using N2-physical adsorption,XRD,TEM,CO-chemical absorption and H₂-TPR suggested that ZrO₂ enhance the reducibility of the cobalt species and increased the dispersion of cobalt.We propose that the dispersion, appropriate particle size and reducibility of cobalt species are key factors in FT synthesis.