A series of size dependent kinetic models based on thermodynamic method are developed for indirect CO2 hydrogenation to higher hydrocarbons by an iron catalysts via the Fischer–Tropsch synthesis. The size dependent parameters in these kinetic models are evaluated over a series of iron catalysts with different average particle sizes. The results showed that the reaction between surface CO and hydrogen species is the key reaction step in producing of the higher hydrocarbons. The heats of CO2 and H2 adsorption are calculated about 45.5 and 52.1 kJ mol-1, respectively, and the apparent activation energy for CO2 hydrogenation is 146 kJ mol-1. The results showed that the best kinetic model is developed based on two hypotheses; the change in Gibbs free energy of adsorption due to the nanosize effect is negative and surface occupation is low. In addition, the calculated sizeindependent CO2 hydrogenation reaction for large particles is about 0.0086 [mol/ (gcat h)].

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