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) 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 activation via enhanced π-backdonation and inhibits hydrogen poisoning during NH 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 synthesis.