Highly efficient K-Fe/C catalysts derived from metal-organic frameworks towards ammonia synthesis

Fe-based catalysts have been discovered as the best elementary metal-based heterogeneous catalysts for the ammonia synthesis in industrial application during the last century. Herein, a novel and scalable strategy is developed to prepare the K-promoted Fe/C catalyst with extremely high Fe loading (> 50 wt.%) through pyrolysis of the Fe-based metal-organic framework (MOF) xerogel. The obtained K-Fe/C catalysts exhibited superior activity and stability towards ammonia synthesis. The weight-specific reaction rate of Fe/C with K₂O as promoter can achieve 12.4 mmol·g⁻¹·h⁻¹ at 350 °C and 30.4 mmol·g⁻¹·h⁻¹ at 400 °C, approximately four and two times higher than that of the commercial fused-iron catalyst (3.4 mmol·g⁻¹·h⁻¹ at 350 °C and 16.7 mmol·g⁻¹·h⁻¹ at 400 °C) under the same condition, respectively. The excellent performance of K-Fe/C can be ascribed to the inherited structure derived from the metal-organic frame precursors and the promotion of potassium, which can modify the binding energy of reactant molecules on the Fe surface, transfer electrons to iron for effective activation of nitrogen, prevent agglomeration of Fe nanoparticle (NPs) and restrain side reaction of carbon matrix to methane. [Figure not available: see fulltext.].