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 (FexN) 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 FexN 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 FexN mediator increased from 27.1 to 46.7 μmol g-1. The FexN 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.