Single-Atom Fe Catalysts with Improved Metal Loading for Efficient Ammonia Synthesis under Mild Conditions

Ammonia synthesis is a cornerstone in the chemical industry. Given the traditional Haber-Bosch (H-B) process requires very high temperature and pressure, it is imperative to develop catalysts capable of facilitating ammonia synthesis under mild conditions. In this work, a post-metal replacement strategy is developed to improve the Fe loading in single-atom Fe-implanted N-doped carbon catalysts. Starting from the Zn-Fe-N-C material with single-atom Zn and Fe sites coexisting in N-doped porous carbon pyrolyzed from porphyrinic metal-organic frameworks (MOFs), the replacement of single-atom Zn with Fe sites is performed, which significantly increases the Fe loading from 1.33 wt% to 2.39 wt%. This effectively suppresses the migration and agglomeration of Fe, yielding Fe-N-C with high metal loading (FeHL-N-C). Notably, the FeHL-N-C catalyst exhibits a catalytic rate of 558 μmol·gcat-1·h-1 at 300 °C for ammonia synthesis at atmospheric pressure, far surpassing the performance of the traditional dominant fused iron and even Ru-based precious metal catalysts.