Mapping the Catalytic Cycle of Ru‐Catalyzed Ammonia Oxidation

Abstract This study presents a mechanism of ammonia oxidation catalyzed by [ Ru II (NH 3 )][PF 6 ] 2 ( Ru =Ru(tpy)(dmabpy)) complexes. All intermediates, including the elusive [ Ru III (NH 2 )] 2+ and [ Ru IV (NH)] 2+ , were detected, with several intermediates characterized spectroscopically. The catalytic cycle follows multiple reaction pathways branching at the key intermediates [ Ru III (NH 2 )] 2+ and [ Ru II (N 2 H 4 )] 2+ . The competition between the pathways is influenced by ammonia concentration and the local proton concentration generated during electrooxidation at the anode. In the N−N bond‐forming steps, dimerization of [ Ru III (NH 2 )] 2+ and nucleophilic attack of [ Ru IV (NH)] 2+ by ammonia compete, while in the subsequent [ Ru II (N 2 H 4 )] 2+ oxidation, direct oxidation competes with proton‐catalyzed disproportionation. These findings provide molecular‐level insights into the catalytic cycle and offer guidance for developing more efficient ruthenium‐based ammonia oxidation catalysts.