Activation Energies for Chain Growth Propagation and Termination in Fischer–Tropsch Synthesis on Iron Catalyst as a Function of Catalyst Particle Size

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