CN22– Vacancies Enhance Ammonia Synthesis over Air-Durable Alkaline Earth Metal Cyanamide-Supported Cobalt Catalysts

Transition metals play a crucial role as catalysts in artificial ammonia synthesis. Ruthenium (Ru) stands out as the most active metal, but its industrial application is constrained due to its natural scarcity and hydrogen poisoning at low temperatures. Cobalt (Co) has been extensively studied as a more cost-efficient and non-noble metal catalyst. However, the goal of a high-performance, air-durable Co catalyst has not been reached to date. The crucial obstacle in this study lies in the inherent weak Co–N interaction and the use of atmospherically sensitive support materials to activate Co. Here, SrCN2 is demonstrated as a promising support material for Co ammonia synthesis catalysts. The optimized catalyst, Co(10 wt %)/SrCN2/Al2O3, exhibits high activity (4.43 mmol g–1 h–1 at 300 °C and 0.90 MPa) with a low apparent activation energy (52.7 kJ mol–1; 300–380 °C; at 0.90 MPa). It has also been proven that SrCN2 has good air durability due to its chemical inertness to ambient atmosphere. Under ammonia synthesis conditions, CN22– vacancies are readily formed on the surface of SrCN2, leaving electrons at the vacancy sites and thereby generating a low-work-function surface (WF = 2.0 eV). Such a surface enables effective electron donation to the loaded Co particles, enhancing N2 activation and promoting ammonia synthesis.