Effect of Calcination Temperature on the Reduction Kinetics of Iron-Based Fischer-Tropsch Catalyst

A typical iron-based Fischer-Tropsch catalyst was prepared by the combination of precipitation and spray drying. The catalyst was then calcined at different temperatures. The textural properties and the crystal structure of the calcined catalyst samples were characterized by N-2 adsorption and Mossbauer effect spectroscopy, respectively. The thermogravimetric analysis was employed to follow the reduction process of the catalysts. The experimental data were then regressed using gas-solid reaction models. The results indicated that the reduction process of the catalysts calcined at 300-600 degrees C could be described by the same models. The reduction of alpha-Fe2O3 to Fe3O4 was regressed by the 1-dimentional formation and growth of nuclei model, and the reduction of Fe3O4 to alpha-Fe was controlled by the 2-dimentional formation and growth of nuclei model. The reduction of the catalyst calcined at 700 degrees C was influenced by both the formation and growth of nuclei model and the shrinking core model. With the increase of the calcination temperature, the reduction capability of the catalysts decreased and the apparent activation energy increased, being due to the increase of the crystal size and the decrease of the lattice defects in the catalysts.