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

Abstract

Abstract 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 Fe 1 Cu 0.5 /MgO catalyst exhibits remarkable catalytic performance, achieving an impressive H 2 production rate of 139.1 mmol H 2 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 NH 3 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.