Metal Fluorides: All-In-One Supports for Ruthenium-Catalyzed Ammonia Synthesis

Ammonia, an emerging energy carrier, demands advanced catalysts for synthesis under mild conditions to integrate with green hydrogen. We herein establish a family of metal fluoride supports (MFn, M = Li, Na, K, Mg, Ca, or Ba) as a tunable "all-in-one" platform for ruthenium (Ru) catalysts. These Ru/MFn systems unify the critical merits of various existing catalysts, such as support-mediated activation of reactants and air stability. Varying the host cation can direct the catalytic pathway. Consequently, Ru/NaF exhibits excellent turnover frequency, while Ru/BaF2 delivers an NH3 synthesis rate of 58.0 mmolNH3 gcat-1 h-1 at 400 °C and 0.9 MPa─surpassing all reported Ru-based catalysts with ≤4 wt % Ru and without external promoters. Advanced characterization reveals that the fluorine vacancy formation energies of the alkali and alkaline-earth lattices, together with the vacancy-reactant interactions, dictate the divergent catalytic mechanisms mediated by different active sites. This work expands the chemistry of metal fluorides, launching a new paradigm for potentially viable NH3-synthesis under mild conditions.