Abstract: Ethylene was used as a probe to detect the N₂-binding site in nitrogenase.It was found that ethylene couldn't compete with N₂ in the nitrogenase system.So the N₂-binding site in nitrogenase might probably be the mode of 6Fe[μ₆(η²,ε₄)]and the mode of 3Fe +1Mo[μ₄(η³,ε₁)] in the cage of the protein-bonded FeMo-co, but not be the mode of dinuclear coordination occurred on the 2Fe-sites at the gap of FeMo-co.In ammonia synthesis with iron catalysts,the N₂-binding site might probably be the mode of 6Fe [μ₆(η³,ε₃)].

Key words: Ethylene probe, N₂-binding site, Nitrogenase, Ammonia synthesis, Iron catalysts