The kinetic parameters of the Fischer-Tropsch synthesis (FTS) on iron catalyst are analysis by size dependent thermodynamic method. A Langmuir–Hinshelwood kinetic equation considered for evaluation of catalytic activity of lanthanum promoted iron catalyst. A series of unsupported iron catalysts with different particle sizes prepared via microemulsion method. The experimental results showed that catalyst activity pass from a maximum value with increasing the iron particle size. Also, data presented that iron particle size has considerable effects on adsorption parameters and FTS rates. The ratio of surface tension (σ) to nanoparticle radius (r) is important in FTS reaction on iron catalyst. Finally, the analysis of this work data showed by increasing the iron particle from 18 to 45 nm the activation energies of catalysts and heats of adsorption of catalysts as two main parameters of FTS reaction increased from 89 to 114 kJ/mol and from 51 t 71 kJ/mol, respectively.

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