A systematic study was undertaken to investigate the effects of the addition of nickel on the bulk phase composition and reduction/carburization behaviors of a Fe-Ni bimetallic catalyst. The catalyst samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Mossbauer spectroscopy, X-ray photoelectron spectroscopy (XPS) and H-2 (or CO) temperature-programmed reduction (TPR). The Fischer-Tropsch synthesis (FTS) performance of the catalysts was measured at 1.5 MPa, 250 degrees C and syngas with H-2/CO ratio of 2.0. The characterization results indicated that the fresh nickel-promoted catalysts are mainly composed of alpha-Fe2O3 and NiFe2O4. The addition of nickel improves the dispersion of iron oxides and decreases the crystallite size of metal oxides. The presence of nickel increases the rates of reduction and carburization in H-2 and CO, respectively, while suppresses the formation of the iron carbides in the syngas reduction. The incorporation of nickel improves the selectivity to methane and suppresses the formation of heavy hydrocarbons (C5+). The catalyst with high nickel content has a high selectivity to methane and low selectivity to heavy hydrocarbons (C5+). (C) 2013 Elsevier B.V. All rights reserved.