Synergizing Surface Hydride Species and Ru Clusters on Sm2O3 for Efficient Ammonia Synthesis

Metal-oxide-supported Ru catalysts, typically in the form of Ru particles dispersed on oxides, have emerged as the most promising catalysts for the ammonia synthesis reaction. Generally, Ru particles are regarded as catalytically active components and are mainly responsible for the formation of ammonia during ammonia synthesis. Here we show that subnano Ru clusters on Sm2O3 (Ru/Sm2O3) favor the formation of surface hydride (Sm-H) species under reaction conditions, which can trigger the activation of Ru clusters in the ammonia synthesis reaction. The synergy of surface hydride species and Ru clusters boosts the activity relative to Ru clusters alone and affords ammonia yields as high as 90.1-100% of the thermodynamic equilibrium value at 400 degrees C. Mechanistic studies and theoretical calculations reveal that Sm-H species can not only work in synergy with Ru clusters to reduce the energy barrier for nitrogen dissociation, but also directly participate in the formation of ammonia on the Ru clusters. The discovery of the synergy role of surface hydride species can deepen the molecular-level understanding of the ammonia synthesis reaction process, which will eventually help to rationally design efficient oxide-supported metal catalysts in the heterogeneous catalysis process where hydrogen is involved.