Iron–Cobalt-Based Materials: An Efficient Bimetallic Catalyst for Ammonia Synthesis at Low Temperatures

Ammonia is one of the most commonly produced chemicals in the industry. As a result, ∼1–2% of the world’s electrical energy is used, and it produces ∼1.5–2% of global CO₂ emissions. Therefore, developing efficient catalysts at milder conditions is highly desirable. Here, efficient iron/cobalt catalysts for ammonia synthesis are prepared with different Fe/Co ratios from phthalocyanine precursors, resulting in Fe–Co bimetallic nanoparticles embedded in a porous carbon–nitrogen matrix. The incorporation of Co to the Fe catalyst up to 20% wt of Co leads to ∼40% enhancement in the activity compared to the monometallic Fe-based catalyst. Interestingly, catalysts exhibit excellent activity even at low temperatures (350 °C). <i>E</i>_a for the most efficient 6K–FePc₈₀CoPc₂₀ catalyst is found to be 29 kJ·mol^–1, suggesting facile activation of N₂ at low temperatures. An in-depth kinetic study revealed that introducing Co in the Fe catalysts drastically tuned the surface of the catalyst by weakening the various NH_<i>x</i> retarding species. Density functional theory calculations confirm the thermodynamic feasibility for introducing 25% of Co at surface Fe sites. This indicates that the presence of Co on the surface draws negative charges from neighboring Fe sites, making the exposed Fe sites neutral and more favorable for N₂ activation on the bimetallic K₂O/Co–Fe catalyst and displaying a more thermodynamically feasible energy profile as compared to the pristine K₂O/Fe catalyst.