Deciphering the N─N Coupling Mechanism Over Iron-Copper Alloy Catalysts During Ammonia Decomposition

The production of CO_x-free hydrogen via the ammonia decomposition reaction (ADR) using Fe-based non-precious metal catalysts has attracted much attention. N─H bond cleavage and N─N coupling are two key steps in ADR, however, stronger Fe─N binding leads to lower activity of iron catalysts. Herein, we develop FeCu alloy catalysts with optimized metal-nitrogen binding energy by incorporating Cu, a metal with inherently weaker nitrogen affinity, into Fe-based catalysts. The optimized Fe₁Cu_0.5/MgO catalyst exhibits remarkable catalytic performance, achieving an impressive H₂ production rate of 139.1 mmol H₂ g_cat ^-1 h^-1 at 550 °C under a high gas hourly space velocity (GHSV = 360 000 h^-1). Mechanistic studies reveal that the modulation of the d-band structure due to the alloying effect optimizes the dissociation of NH₃ and the binding ability of N* intermediates in the ADR process. Notably, in situ X-ray absorption spectroscopy (XAS) combined with theoretical calculations confirm that FeCu alloying effectively reduces the N─N recombination energy barrier from 2.25 eV (Fe cluster) to 1.77 eV (FeCu cluster). These findings provide valuable insights for the rational design of highly active Fe-based catalysts for efficient ammonia decomposition and sustainable hydrogen production.