Mechanochemical Synthesis of Ammonia Employing H2O as the Proton Source Under Room Temperature and Atmospheric Pressure

Realizing nitrogen fixation under mild conditions is of great significance to modern industry, agriculture, and society. Several approaches have been attempted to replace the conventional Haber–Bosch process to avoid high temperature and pressure reaction conditions, including photocatalysis, electrochemical catalysis, biomimetic catalysis, and so forth. This work demonstrates a conceptually novel, more cost-effective, and environment-friendly approach to nitrogen fixation by mechanical ball milling of nitrogen gas in water under room temperature and atmospheric pressure. Without extra catalysts, the stainless steel texture of the container and grinding balls has a crucial catalytic effect on direct nitrogen fixation. The presence of the ammonium ion (NH4+) in the solution is verified by both Nessler's reagent method and ion chromatography. The process is demonstrated to be a zero-order reaction as CNH4+=2.432t(mg·L−1) (t: hour), and the optimized NH4+ selectivity reaches as high as 99.2%. Water is employed as a proton source instead of hydrogen, preventing the environmental pollution that originated from hydrogen production. Moreover, the characterizations of the resulted powders and theoretical calculations illustrate the superiority of H2O as the proton source, which lowers the energy requirement of the rate-determining step. This work provides a feasible aqueous-phase mechanochemical nitrogen fixation by ball milling N2 and H2O under mild conditions.