The influence of the catalyst particle size in determining Fischer-Tropsch synthesis (FTS) performance for nano-structured iron catalysts was investigated. The catalysts prepared by microemulsion method and to achieve a series of catalysts with different iron particle size, water-to-surfactant molar ratio (W/S) in microemulsion system varied from 4 to 12. The results express the fact that by decreasing in the active phase of the iron catalyst, the termination rates of the chain growth compared to the propagation rates are increased. In addition, the activation energy for chain propagation is lower than chain termination and this difference (Et-Ep) for the hydrocarbon product distributions which is characterized with α1 is lower than the hydrocarbon product distribution which is characterized with α2. The results indicate the H2 concentration on catalyst surface decreased by increasing the catalyst particle size. Thus, the dependence of α (α1 and/or α2) on H2 partial pressures increased by decreasing of catalyst particle size and the dependence of α2 on H2 partial pressures is weaker than α1.

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