Mechanisms and kinetics for the reduction of a precipitated iron-based Fischer-Tropsch catalyst in H-2 have been investigated using in situ Mossbauer effect spectroscopy (MES) and thermogravimetric (TG) method in the temperature range of 250-350 degrees C. In situ MES results indicate that the reduction of paramagnetic (PM) alpha-Fe2O3 (70%) and superparamagnetic (spm) Fe3+ (30%) in the fresh catalyst proceed via different steps. PM alpha-Fe2O3 is firstly reduced to magnetite and then to metallic iron, while the reduction of spm Fe3+ proceeds in three consecutive steps: it is first reduced to magnetite with a significantly rapid rate, then to non-stoichiometric wustite, and finally to metallic iron. The reduction of PM alpha-Fe2O3 to Fe3O4 can be described by a two-dimensional Avrami-Erofe' ev phase change model (formation and growth of nuclei). However, the corresponding overall reduction, which includes the reduction of PM alpha-Fe2O3 and spm Fe3+ to Fe3O4, can be described by a three-dimensional phase-boundary-control led reaction model based on the overall extraction ratio of oxygen. The difference between the two models selected for the PM alpha-Fe2O3 reduction and the corresponding overall reduction is attributed to the rapid reduction of spm Fe3+ to Fe3O4. For the reduction of PM magnetite to alpha-Fe and its corresponding overall reduction (including the reduction of PM and spin Fe3O4 to alpha-Fe), it is found that both of them follow the Avrami-Erofe' ev phase change model (two-dimensional or three-dimensional). The value of apparent activation energy for the overall reduction has been calculated and compared with the literature data. (C) 2009 Elsevier B.V. All rights reserved.