Correlation of the amount of carbonaceous species with catalytic performance on iron-based Fischer–Tropsch catalysts

The different types of iron precursors (iron nitrate, citrate and acetate) and supports like Al2O3 and SiO2 significantly alter catalytic performances by largely changing physicochemical properties, reducibility of iron oxides and different extent of carbon deposition during Fischer-Tropsch synthesis (FTS). The Al2O3-supported iron-based catalysts generally showed the favorable physicochemical properties such as a high reducibility and carburization compared to that of SiO2-supported ones. The observed facile reducibility of iron oxides on the moderate amount of acidic sites on Al2O3-based FTS catalyst, especially on the catalyst prepared from iron nitrate precursor, is found to show a high catalytic activity with a high olefin yield in the range of C2–C4 hydrocarbons, which is superior to that of SiO2-based catalysts. The significant correlation of catalytic performances with the extent of carbon deposition analyzed by X-ray photoelectron spectroscopy (XPS) on the used FTS catalysts was established. The intensity ratio of C1s such as deposited carbon species at biding energy of 288.2 eV to adsorbed carbon at that of 284.4 eV is well correlated with catalytic performance. An observed high intensity ratio of C1s peaks is responsible for a high CO conversion and C2–C4 selectivity due to the sufficient formation of active iron carbide species on Al2O3-based FTS catalyst.