To control the fine structure of Co species on calcined Co/SiO
2 catalyst, especially to depress the formation of Co silicate-like species after the calcination, the present study has investigated effects of some preparation conditions (pH of the impregnating solution, and heating rate during calcination) on the fine structure of Co species on the calcined catalysts prepared with trans-1,2-diamino-cyclohexane-N,N,N',N'-tetraacetic acid (CyDTA) or nitrilotriacetic acid (NTA), and their Fischer-Tropsch synthesis (FTS) activities. Characterization results by Co K-edge EXAFS and TPR showed that the fine structure of Co species on calcined Co/SiO
2 and NTA-Co/SiO
2 is not affected by these preparation conditions, and Co
3O
4-like species is mainly formed after the calcination. On the contrary, the fine structure of Co species on calcined CyDTA-Co/SiO
2 depended on these preparation conditions. An irreducible α-Co
2SiO
4-like species is formed after the calcinations when CyDTA-Co/SiO
2 catalyst was prepared from the impregnating solution with higher pH (>9.1), and/or was calcined at the rate above 1.0 K min
-1, whereas Co
3O
4-like species was formed when prepared from the impregnating solution with lower pH (<3.1), and/or calcined at lower heating rate (0.1 K min
-1). TG-DTA measurements during the calcination of CyDTA-Co/SiO
2 showed that the pH of the impregnating solution and heating rate during calcinations affect the decomposition temperature of the CyDTA-Co complex formed in the impregnating solution. The reducibility of Co species became 6-8 times greater when the complex was decomposed at lower temperatures. Therefore, it is suggested that the fine structure of Co species after the calcination is affected by the decomposition temperature (stability) of CyDTA-Co complex during the calcination. The FTS activity of CyDTA-Co/SiO
2 was ca. two times greater than that of Co/SiO
2 catalyst, when the catalyst was prepared from the impregnating solution with lower pH, and then calcined at a lower heating rate.
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