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

ABSTRACT

Ru catalysts promoted with alkali and alkaline earth have shown superior ammonia (NH3) 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 N2 activation via enhanced π-backdonation and inhibits hydrogen poisoning during NH3 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 NH3 synthesis.