Structural evolution of carbon in an Fe@C catalyst during the Fischer-Tropsch synthesis reaction

A pseudo-in situ research method was applied to provide insight into the structural evolution of carbon in an Fe@C catalyst at different stages of the Fischer-Tropsch reaction. Five typical stages of the catalyst were selected for in-depth structural investigation; these were: the fresh catalyst, reduced catalyst, and catalyst in the stable conversion period, in an increased-conversion period and at the inactivation stage. The results indicated that the integral structure of Fe@C constantly changed in the Fischer-Tropsch reaction. Iron carbide transformed from the Fe phase that was easily oxidized under high temperature Fischer-Tropsch conditions, and the carbon framework was completely destroyed in the reaction process, leading to a drastic decrease in the specific surface area of the material. This destruction could have two opposing effects: on the one hand, the loss of carbon could re-expose the active sites that have been covered by carbon at a reaction temperature of 320 degrees C and favor the reaction; on the other hand, the deposition of carbon could block the active sites and lead to inactivation when the reaction temperature is over 340 degrees C.