Promotional Effect of Mn On NH₃ Synthesis Over Inverse Iron Catalyst

The Haber-Bosch process has been established for over a century, and it still remains central to global ammonia production. To this day, industrial NH₃ synthesis still relies on fuzed iron catalysts developed in the early 20th century, which underscores the ongoing challenge in the development of alternative catalysts with superior activity under mild conditions. Here, we report a Mn-incorporated iron (FeMn) catalyst prepared via a facile sol-gel method. The resultant FeMn catalyst exhibits an approximately twofold higher NH₃ formation rate than that for the conventional commercial iron catalyst under mild conditions. Kinetic analysis revealed that Mn incorporation results in ammonia synthesis with a lower apparent activation energy, which suggests enhanced N₂ activation. Further structural and surface analyses indicate that Mn enrichment at the catalyst surface favors N₂ activation, which likely facilitates N≡N bond cleavage and contributes to the observed activity enhancement. This work highlights a simple yet effective strategy to boost the performance of Fe-based catalysts for ammonia synthesis under mild conditions.