Ru Single Atom and Nanoparticle Tandem Catalyst Unlocking High-Efficiency Ammonia Synthesis under Mild Conditions

The development of highly efficient catalysts that enable Haber-Bosch ammonia (NH₃) synthesis under mild conditions remains critically challenging since the competitive activation of coadsorbates, particularly excessive N₂ or H₂ binding at active sites, is a trade-off and detrimental to NH₃ synthesis. Herein, we design a novel Ru tandem catalyst that combines Ru single atom (Ru₁) with nanoparticle sites (Ru_NP) on CeO₂ nanoislands, leveraging cascade hydrogen catalysis between functionally distinct Ru sites to realize highly efficient NH₃ synthesis under mild conditions. Our studies reveal that Ru_NP sites suffer from hydrogen poisoning, whereas Ru₁ sites exclusively adsorb N₂. The hydrogen spillover from Ru_NP to Ru₁ sites reduces hydrogen coverage on Ru_NP sites to effectively decrease the N₂ dissociation barrier and also greatly facilitates N₂ hydrogenation at Ru₁ sites for NH₃ synthesis, thus overcoming the trade-off in the dynamic N₂/H₂ activation equilibrium. As a result, the Ru single atom and nanoparticle tandem catalyst achieves a remarkable NH₃ synthesis rate of 59.0 mmol g_cat^-1 h^-1 with 600 h long-term operational stability at 400 °C and 1 MPa, possessing an exceptionally high specific rate among reported Ru-based catalysts. This catalyst structure design paves a new path for NH₃ synthesis under mild conditions.