Modulating Co-Re Pairs in CoRe Alloy for Efficient NH₃ Synthesis under Mild Conditions

The development of advanced nonprecious-metal catalysts for efficient ammonia (NH₃) synthesis under mild conditions represents significant importance. However, the incompatibility between facile N₂ activation and NH₃ desorption in monometallic catalysts limits their catalytic activity for NH₃ synthesis. Herein, we systematically fabricated CoRe_x alloy (x = 0.25, 0.5, 0.75, 1, 1.5, and 2) catalysts by modulating the Co/Re ratio to achieve efficient NH₃ synthesis. Our studies reveal that the Co/Re ratio in CoRe_x catalysts critically governs the formation of Co-Re paired sites, with the quantity of these pairs demonstrating a strong positive correlation with the NH₃ synthesis rates. Excess Co (CoRe_0.5) or Re (CoRe₂) leads to either insufficient N₂ activation or excessively strong NH₃ adsorption, both detrimental to catalytic efficiency. In contrast, the CoRe₁ alloy featuring abundant Co-Re pairs simultaneously realizes the facile N₂ activation and NH₃ desorption through a synergistic effect of Co-Re orbital hybridization. Consequently, the optimized CoRe₁ delivers a remarkable NH₃ synthesis rate of 12.0 mmol g_cat^-1 h^-1 at 400 °C and 1 MPa, surpassing those of most reported NPM catalysts to date.