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.