Extremely Low CO/H2 Ratio Activation of a Precipitated Iron Catalyst for Enhanced Fischer-Tropsch Performance

Fischer-Tropsch synthesis (FTS) is a non-petroleum and effective routeto produce fuels and key chemicals from syngas. Precipitated iron catalyst, as anindustrial catalyst for FTS has attracted much attention. The catalytic performance ofiron catalysts strongly depends upon the activation progress, which is of significance toindustrial application. Herein, we regulated the CO/H2ratio of pretreatment gas andinvestigated its influence on a precipitated iron catalyst. The textural structure, phasecompositions, and carbon deposit of the catalysts were analyzed systematically by X-raydiffraction, transmission electron microscopy, Mo??ssbauer effect spectroscopy, Raman,X-ray photoelectron spectroscopy, and temperature-programmed reaction. It was foundthat activation with an extremely low CO/H2ratio (3:100) achieves a balance of COdissociation, permeation, and diffusion and facilitates the formation of chi-Fe5C2speciescoated with a thin carbon layer. Such a catalyst exhibits high CO conversion of 68%, selectivity to C5+hydrocarbons of 93.6%, andexcellent stability under typical medium-temperature Fischer-Tropsch conditions (270 degrees C and 2.0 MPa). In contrast, pure H2reduction is favorable to form epsilon '-Fe2.2C. With the increase of the CO/H2ratio, the carbon deposition becomes more severe. Bycalculation of the intrinsic activity (TOF) of different iron carbides (epsilon '-Fe2.2C and chi-Fe5C2), we established the influence of theactivation atmosphere on the FTS catalytic performance.