Descriptor-Guided Design of Ruthenium Catalysts for Ammonia Synthesis and Decomposition: From Promoters to Interfaces

Ruthenium (Ru) catalysts exhibit high activity for ammonia (NH 3 ) synthesis and decomposition, governed by promoter chemistry, catalyst structure, and metal–support interactions (MSI). This review presents a descriptor-guided framework linking electronic, geometric, interfacial, and dynamic properties to reaction mechanisms and catalytic performance. Key steps, including nitrogen (N 2 ) dissociation, hydrogenation, nitrogen recombination, and hydrogen (H 2 ) inhibition, are examined alongside support selection, particle-size control, morphology, and interfacial engineering. Alkali, alkaline-earth, and rare-earth promoters are evaluated for their effects on Ru electronic structure, adsorption energetics, and active-site accessibility. Oxygen vacancies (OVs), strong metal–support interactions (SMSI), and electronic metal–support interactions (EMSI) are discussed as regulators of interfacial reactivity. Emphasis is placed on distinguishing mechanistic descriptors from experimental proxies and accounting for their coupling under reaction conditions. Finally, machine learning (ML) approaches are assessed for identifying transferable descriptors and guiding rational Ru catalyst design.