Enhancing Ammonia Synthesis over Ru-Based Catalysts via Engineering of Rare-Earth Oxide Supports

Rare-earth oxide-supported Ru metal catalysts are promising for NH₃ synthesis owing to a strong metal-support interaction. Modifying rare-earth oxides with a second metal offers an effective approach to tuning support properties, while systematic support engineering to enhance NH₃ synthesis performance remains scarce. In this work, a series of Ru/Ce1-aLaaOx catalysts with varying Ce-to-La molar ratios were synthesized and evaluated for NH₃ synthesis. The NH₃ synthesis rate of Ru/Ce1-aLaaOx exhibits a volcano relationship with an increase in the La content. The optimal Ru/Ce0.7La0.3Ox catalyst exhibits a remarkable NH₃ synthesis rate of 34.13 mmolNH3 gcat⁻¹ h⁻¹ with over 500 h long-term stability at 400 °C and 1 MPa, which is 1.65-fold that of Ru/CeO₂. Various characterizations reveal that La doping is beneficial to increase the charge density of Ru sites via facilitation of oxygen vacancy formation, which consequently ensures fast N₂ cleavage. In addition, the La doping can avoid hydrogen poisoning more effectively through enhanced hydrogen spillover, which together with promoted N₂ activation are responsible for high-performance NH₃ synthesis over Ru/Ce0.7La0.3Ox catalyst under mild conditions.