Mechanocatalysis: Simple and Rapid Mechanochemical Synthesis of Ammonia in Hydrogen, Nitrogen, and Water System

Mechanical force-induced N-2 fixation is an emerging strategy for single-step ammonia synthesis under room temperature and atmospheric pressure. Here, we demonstrate a simple and rapid approach to synthesize NH3 in the N-2+H-2+H2O system and illustrate the reaction mechanism by theoretical calculations. The NH3 generation rate can reach 2.847 mg L-1 h(-1) with an NH4+ selectivity of 99.45 wt.%. The presence of H-2 can inhibit oxidation reactions to form NO3- by-products and promote proton generation from H2O dissociation. The calculated formation energy of H-adatom and OH-adatom from H2O cleavage is -2.86 eV in N-2+H-2+H2O system, much lower than that in N-2+H2O system, verifying much easier dissociation of H2O molecules and significantly facilitated proton generation to enlarge the NH4+ yield. This work provides a simple approach to improve mechanochemical N-2 fixation performance and highlights a proton generation enhancement mechanism.

Automated summary

Mechanical force-induced N-2 fixation is a promising strategy for ammonia synthesis at room temperature and atmospheric pressure. This study demonstrates a simple and rapid approach to synthesize NH3 in the N-2+H-2+H2O system and elucidates the reaction mechanism through theoretical calculations. The NH3 generation rate reaches 2.847 mg L-1 h(-1) with a high NH4+ selectivity of 99.45 wt.%. The presence of H-2 inhibits oxidation reactions and promotes proton generation, resulting in increased NH4+ yield. This work provides a simple method to enhance mechanochemical N-2 fixation and highlights the mechanism of proton generation.