This study investigates the surface chemistry of Fe and Ru catalysts during the Haber–Bosch process using operando X-ray photoelectron spectroscopy (XPS). The research reveals that, despite high temperatures and pressures, surface-sensitive techniques like XPS can be applied to study the reaction mechanism. The study shows that the rate-limiting step on Ru is always N₂ dissociation, while on Fe, it switches from N₂ dissociation to hydrogenation of surface species as temperature decreases. The Fe(210) surface forms nitrides more rapidly than Fe(110), and the Ru(10 1̄ 3) surface remains almost adsorbate-free. The study also shows that the presence of hydrogen reduces nitride formation on Fe surfaces, indicating the importance of hydrogenation in the reaction mechanism. The results highlight the role of surface steps in nitrogen activation and the differences in reactivity between Fe and Ru. The findings provide insights into the reaction mechanism and could help improve the efficiency of the Haber–Bosch process. The study also discusses the challenges of performing operando studies under high-pressure conditions and the importance of understanding the surface chemistry of catalysts for optimizing industrial processes.This study investigates the surface chemistry of Fe and Ru catalysts during the Haber–Bosch process using operando X-ray photoelectron spectroscopy (XPS). The research reveals that, despite high temperatures and pressures, surface-sensitive techniques like XPS can be applied to study the reaction mechanism. The study shows that the rate-limiting step on Ru is always N₂ dissociation, while on Fe, it switches from N₂ dissociation to hydrogenation of surface species as temperature decreases. The Fe(210) surface forms nitrides more rapidly than Fe(110), and the Ru(10 1̄ 3) surface remains almost adsorbate-free. The study also shows that the presence of hydrogen reduces nitride formation on Fe surfaces, indicating the importance of hydrogenation in the reaction mechanism. The results highlight the role of surface steps in nitrogen activation and the differences in reactivity between Fe and Ru. The findings provide insights into the reaction mechanism and could help improve the efficiency of the Haber–Bosch process. The study also discusses the challenges of performing operando studies under high-pressure conditions and the importance of understanding the surface chemistry of catalysts for optimizing industrial processes.