Boosting mechanochemical N₂-to-amine conversion through nanosizing iron nitride mediators

The direct conversion of N₂ into organonitrogen compounds under mild conditions remains a grand challenge due to the inertness of N₂. Mechanochemical looping using iron nitride (Fe_xN) as the nitrogen carrier has emerged as an alternative strategy for N₂-to-amine conversion, yet the overall efficiency remains limited by the weak N₂ dissociation capability, low N uptake of bulk Fe and relatively slow kinetics. In this study, we employed nanostructured Fe powder as the feedstock to synthesize the Fe_xN mediator through ball milling under a N₂ atmosphere. Downsizing the Fe particle size led to a considerable enhancement in N₂ fixation and the N content of the Fe_xN mediator increased from 27.1 to 46.7 μmol g^-1. The Fe_xN species were subsequently employed for the octanol amination, achieving a tri-octylamine yield of 43.5 μmol g^-1 under 250 °C and 10 bar H₂ conditions without detectable ammonia formation. The high density of defect sites in nanostructured Fe not only enables efficient N₂ fixation, but also facilitates the subsequent activated N release. The crystallite refinement of nanostructured Fe during cycling generates abundant grain boundaries, facilitating N species turnover and enabling continuous N₂-to-amine operation via mechanochemical looping.