Single-Atom Fe Catalysts With Improved Metal Loading for Efficient Ammonia Synthesis Under Mild Conditions

Abstract

Ammonia synthesis is a cornerstone in the chemical industry. Given that 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 to 2.39 wt%. This effectively suppresses the migration and agglomeration of Fe, yielding Fe–N–C with high metal loading (Fe_HL–N–C). Notably, the Fe_HL–N–C catalyst exhibits a catalytic rate of 558 µmol·g_cat⁻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.