RuCo Nanoalloy Catalysts Obtained From In-Situ Reconstruction of High-Entropy Oxides for Green Ammonia Synthesis

Optimizing promoters is crucial for designing efficient catalysts for ammonia (NH₃) synthesis under mild conditions. However, this endeavor is often hampered by a fundamental trade-off: weak metal-promoter interactions (MPI) lead to promoter segregation, while excessively strong ones block active sites, both diminishing the efficiency of promotion. In this work, we report a high-entropy oxide (HEO) nanoparticle catalyst integrated with active metals (Ru/Co) and promoters (La/Ce/Sm) for efficient NH₃ synthesis via an in situ reconstruction strategy. Our investigation reveals that the HEO undergoes in situ reconstruction to form RuCo nanoalloys anchored on rare-earth oxide nanoislands, which simultaneously realizes the exposure of active sites and strong metal-promoter interaction. This entropy reduction process facilitates the formation of surface oxygen vacancy sites with low work function electrons, facilitating electron transfer to the metal alloys to drive N₂ dissociation. Furthermore, alloying Ru with Co metal lowers the d-band center to promote NH₃ desorption. Consequently, the optimized RuCo-HEO catalyst delivers a remarkable NH₃ synthesis rate of 58.2 mmol g^{- 1} h^{- 1} (2.41% concentration) at 400°C and 1 MPa, approaching the thermodynamic equilibrium value (2.44%). This work provides an in situ reconstruction strategy to engineer active sites exposure and promoter effect for efficient green NH₃ synthesis.