Fischer-Tropsch synthesis in Co/SiO2 catalysts, which were prepared by mixed impregnation of cobalt (II) nitrate and cobalt (II) acetate, was studied under mild reaction conditions (Total pressure=1 MPa, H-2/CO=2, T=513 K). X-ray diffraction indicated that highly dispersed cobalt metal was the main active sites on the catalyst prepared by the same method. It was considered that the metallic crystallines, which were readily reduced from cobalt nitrate, promoted the reduction of Co2+ to metallic a state in cobalt acetate by H-2 spillover mechanism during the catalyst reduction process. The reduced cobalt, from cobalt acetate, was highly dispersed one and remarkably enhanced the catalytic activity. The addition of a small amount of Ru to this type of catalyst remarkably increased the catalytic activity and the reduction degree. Its turn over frequency (TOF) increased but the selectivity of CH4 was unchanged. However, when Pt or Pd were added into catalysts, they exhibited a higher selectivity of CH4. Although Pt and Pd hardly exerted an effect on cobalt reduction degree, they promoted cobalt dispersion and decreased the value of TOR Characterization of these bimetallic catalysts suggested that a different contact between Co and Ru, Pt or Pd existed. Ru was enriched on the metallic cobalt surface but, Pt or Pd dispersed well in the form of Pt-Co or Pd-Co alloy. (C) 2002 Elsevier Science Ltd. All rights reserved.