Green chemical pathway of N2 fixation: perspectives from plasma modeling

Abstract

Given its significant environmental and economic impact, substantial research has been dedicated to improving the Haber–Bosch process. Leveraging the advantages of renewable energy sources and sustainable feedstocks, plasma catalysis is emerging as a promising green technology for small-scale, onsite nitrogen (N₂) fixation. However, current plasma-catalysis applications for nitrogen fixation face several challenges. These include high energy consumption for hydrogen (H2) production prior to ammonia synthesis, low energy efficiency, and a limited understanding of the underlying mechanisms. In this study, we compare two green chemical pathways for plasma catalysis in NH3 and NOx production and their effective storage in water from a plasma chemistry modeling perspective. Our model incorporates both electron and vibrational kinetics, along with updated surface reactions based on Density Functional Theory (DFT) calculations. These calculations consider catalytic ruthenium (Ru) on MgO supports and non-catalytic SiO2 as a reference for ammonia synthesis and titanium dioxide (TiO2) for NOx synthesis. We will evaluate and discuss key intermediates and pathways for producing high-density NH3 and NOx, and suggest opportunities for further improvement.