Preparation of Fe₃O₄@PI and its catalytic performances in Fischer-Tropsch synthesis

Polyimide (PI) modified Fe₃O₄@PI and Fe₃O₄-PI catalyst samples were prepared by hydrothermal-coating and ball milling methods, respectively. The effect of PI modification on the product distribution of the Fe-based catalysts for Fischer-Tropsch synthesis was investigated. The catalysts were characterized by XRD, SEM, TEM, H₂-TPR, CO-TPD, FT-IR, XPS, TG and contact angle measurements. The results showed that Fe₃O₄, Fe₃O₄@PI and Fe₃O₄-PI were spherical with uniform particle size, and the Fe₃O₄@PI particle size was smaller. PI modification promoted the reduction and the hydrophilicity of Fe₃O₄. For Fe₃O₄@PI sample, PI was uniformly coated on Fe₃O₄ surface, which led to good thermal stability. Compared with Fe₃O₄ and Fe₃O₄-PI samples, CO adsorption was promoted on Fe₃O₄@PI. Compared with Fe₃O₄, the catalytic activity of Fe₃O₄@PI and Fe₃O₄-PI decreased, and the secondary hydrogenation ability was inhibited, resulting in increase of olefin selectivity. For Fe₃O₄@PI, the olefin selectivity was enhanced significantly with olefin to alkane ratio in C_2-4 fraction increased from 0.50 to 2.15. PI modification with suitable content favored the formation of C₅₊ hydrocarbons.