Metalloenzymes catalyze difficult chemical reactions under mild conditions. Mimicking their functions is a challenging task and it has been investigated using homogeneous systems containing metal complexes. The nitrogenase that converts N₂ to NH₃ under mild conditions is one of such enzymes. Efforts to realize the biological function have continued for more than four decades, which has resulted in several reports of reduction of N₂, ligated to metal complexes in solutions, to NH₃ by protonation under mild conditions. Here, we show that seemingly distinct supported small tungsten clusters in a dry environment reduce N₂ under mild conditions like the nitrogenase. N₂ is reduced to NH₃ via N₂H₄ by addition of neutral H atoms, which agrees with the mechanism recently proposed for the N₂ reduction on the active site of nitrogenase. The process on the supported clusters gives a model of the biological N₂ reduction.

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