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/Ce_1-aLa_aO_<i>x</i> catalysts with varying Ce-to-La molar ratios were synthesized and evaluated for NH₃ synthesis. The NH₃ synthesis rate of Ru/Ce_1-aLa_aO_<i>x</i> exhibits a volcano relationship with an increase in the La content. The optimal Ru/Ce_0.7La_0.3O<i>_x</i> catalyst exhibits a remarkable NH₃ synthesis rate of 34.13 mmol_NH3 g_cat^-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/Ce_0.7La_0.3O<i>_x</i> catalyst under mild conditions.