Effect of pretreatment conditions on Fe-ZSM-5 properties and performance for Fischer–Tropsch synthesis†

Iron supported on ZSM-5 is a widely studied catalyst for Fischer–Tropsch synthesis (FTS). Iron is activated with H₂, CO, or a mixture of CO and H₂ prior to FTS, resulting in phase transformations that make it challenging to understand structure–property relationships. In this work, we demonstrate that increasing the pretreatment temperature of Fe–Na-ZSM-5 reduces CO conversion irrespective of the reductant, but the product selectivity, iron particle size, composition, CO adsorption properties, and zeolite structure is dependent on both the pretreatment temperature and reductant. Pretreatment of Fe–Na-ZSM-5 in H₂ induces sintering of iron particles, increasing C₂–C₄ olefins and C₅₊ hydrocarbons selectivity from 19.0% and 14.0% at 350 °C to 28.2% and 25.4% at 770 °C, respectively. Conversely, CO pretreatment facilitates carbide formation, coke deposition, and CH₄ formation.