Splitting of Hydrogen Atoms into Proton–Electron Pairs at BaO–Ru Interfaces for Promoting Ammonia Synthesis under Mild Conditions

Ru catalysts promoted with alkali and alkaline earth have shown superior ammonia (NH 3 ) synthesis activities under mild conditions. Although these promoters play a vital role in enhancing catalytic activity, their function has not been clearly understood. Here, we synthesize a series of Ba-Ru/MgO catalysts with an optimal Ru particle size (∼2.3 nm) and tailored BaO–Ru interfacial structures. We discover that the promoting effect is created through the separate storage of H + /e – pairs at the BaO–Ru interface. Chemisorbed H atoms on Ru dissociate into H + /e – pairs at the BaO–Ru interface, where strongly basic, nonreducible BaO selectively captures H + while leaving e – on Ru. The resulting electron accumulation in Ru facilitates N 2 activation via enhanced π-backdonation and inhibits hydrogen poisoning during NH 3 synthesis. Consequently, the formation of intimate BaO–Ru interface without an excessive loss of accessible Ru sites enables the synthesis of highly active catalysts for NH 3 synthesis.