The Haber–Bosch process, which converts N₂ and H₂ into NH₃ over Fe and Ru catalysts, is a critical industrial process for fertilizer production. The active component of the catalyst and the rate-limiting steps have been subjects of debate. This study uses X-ray photoelectron spectroscopy (XPS) to investigate the surface chemistry of Fe and Ru catalysts during NH₃ production at high pressures and temperatures. The results show that while both catalysts remain metallic, Ru surfaces are almost adsorbate-free, whereas Fe catalysts retain a small amount of adsorbed N and develop high amine coverages on stepped surfaces at lower temperatures. These findings indicate that N₂ dissociation is the rate-limiting step on Ru, while hydrogenation of adsorbed N atoms is the rate-limiting step on Fe. The study also demonstrates the effectiveness of operando XPS in revealing surface-sensitive information during catalytic reactions, providing insights into the mechanism of the Haber–Bosch process.The Haber–Bosch process, which converts N₂ and H₂ into NH₃ over Fe and Ru catalysts, is a critical industrial process for fertilizer production. The active component of the catalyst and the rate-limiting steps have been subjects of debate. This study uses X-ray photoelectron spectroscopy (XPS) to investigate the surface chemistry of Fe and Ru catalysts during NH₃ production at high pressures and temperatures. The results show that while both catalysts remain metallic, Ru surfaces are almost adsorbate-free, whereas Fe catalysts retain a small amount of adsorbed N and develop high amine coverages on stepped surfaces at lower temperatures. These findings indicate that N₂ dissociation is the rate-limiting step on Ru, while hydrogenation of adsorbed N atoms is the rate-limiting step on Fe. The study also demonstrates the effectiveness of operando XPS in revealing surface-sensitive information during catalytic reactions, providing insights into the mechanism of the Haber–Bosch process.