Mechanochemical ammonia synthesis enhanced by silicon nitride as a defect-inducing physical promoter.

Abstract

By enabling ammonia synthesis under near ambient conditions, mechanochemistry provides a paradigm shift, a new decentralized production method that avoids the high temperature (above 400 °C) and high pressure (above 200 bar) requirements of the centralized Haber-Bosch process. Leveraging the principles of mechanochemistry and its dynamic reaction environment, we hypothesize that inducing high-density defects on iron (Fe) catalyst can amplify catalytic activity by increasing initial state and adsorption capacity. In this study, we introduce a novel mechanochemical ammonia synthesis method utilizing silicon nitride (Si₃N₄) as a defect-inducing physical promoter. The physical properties of Si₃N₄ make it an ideal candidate to more efficiently generate active surfaces on Fe catalyst via mechanochemical actions. The Fe catalyst with Si₃N₄ (3.0 at%) promoter achieves an ammonia concentration 5.6-fold higher than unpromoted Fe, while maintaining substantial stability. This research not only establishes a promising pathway for low-energy ammonia production but also provides insights into dynamic defect engineering strategies for catalytic systems.