The purpose of this study is to investigate the influence of activation gas type (CO, syngas and H-2), activation temperature and pressure on FTS activity and selectivity. A series of Fischer-Tropsch synthesis (FTS) reactions in a continuously stirred tank reactor (CSTR) for 400-1000 h were carried using a Fe/K/Si = 100/1.25/5.1 (atomic ratio) catalyst. The highest CO conversion was obtained for a CO activated catalyst while hydrogen activation yielded the lowest, regardless of the activation temperature. A higher activation temperature yielded a higher peak CO conversion during the induction period. FTS activity for syngas pretreatment showed a dependency on the activation pressure. In addition to the FTS activity, CO activation showed the best overall hydrocarbon productivity. The lowest hydrocarbon production rate was obtained with the H activated catalyst. Carbon monoxide activation also yielded the lowest methane selectivity and activation temperature did not affect the CH4 selectivity in the range of 230-270 degreesC. Activation temperature had little effect on the formation of olefin (C-2-C-20) and the olefin fraction decreased in the order of H-2>syngas>CO activation. The induction period was present following each of the three pretreatments: CO, H-2, or syngas with the same H-2/CO ratio as used during the synthesis period. (C) 2003 Elsevier Science B.V. All rights reserved.