Fischer–Tropsch synthesis over model iron catalysts supported on carbon spheres: The effect of iron precursor, support pretreatment, catalyst preparation method and promoters Original Research Article

Carbon spheres (d = 900 ± 50 nm) were prepared by a chemical vapor deposition method. Iron catalysts supported on the functionalized carbon spheres (CSs) were prepared by impregnation and deposition precipitation methods using different iron precursors (iron nitrate and iron acetate). The Fischer–Tropsch synthesis (FTS) performances for these supported model catalysts have been investigated as a function of preparation method, iron precursor, different methods of functionalization and the addition of promoters (Mn, K, Cu). Our results reveal that: (i) the functionalized CSs, that were treated in nitric acid at a higher reaction temperature showed a higher degree of functionalization. (ii) The iron catalysts synthesized from the CSs functionalized at the 90 °C temperatures showed higher catalytic activity. (iii) The iron catalyst prepared from iron acetate showed a higher metal time yield than the catalyst prepared from iron nitrate. (iv) An iron catalyst supported on carbon spheres functionalized using nitric acid or KMnO4 showed comparable catalytic activity and higher long chain hydrocarbon selectivity. (v) The iron catalyst prepared by deposition precipitation gave a higher metal time yield than the catalyst prepared by impregnation. In all cases the results can be associated with the Fe dispersion. For the iron catalyst supported on carbon spheres promoted with K (0.05–1%), the K was found to inhibit the reduction of the iron catalysts. The addition of K decreased the catalytic activity but increased the olefin selectivity, leading to a higher long chain hydrocarbon selectivity. Promotion with copper improved the reduction of the iron catalyst and suppressed the gasification of the carbon sphere support. The addition of Cu decreased the CH4 selectivity and had no significant effect on the catalytic activity. All data point for Fe/CS catalysts showed conventional behavior but with a reduced metal-support interaction compared to oxide supports.