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 (RuNP) 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 RuNP sites suffer from hydrogen poisoning, whereas Ru1 sites exclusively adsorb N2. The hydrogen spillover from RuNP to Ru1 sites reduces hydrogen coverage on RuNP 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 gcat-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.