Construction of Reaction System and Regulation of Catalyst Active Sites for Sustainable Ammonia Production

Abstract

Ammonia (NH₃) is widely used for human life and considered a green energy carrier without CO₂ emissions; thus, green and sustainable NH₃ synthesis is of great importance. The traditional Haber-Bosch process requires harsh conditions with serious environmental implications. Therefore, numerous research is focused on the efficient synthesis of NH₃ from abundant N₂/air and water under ambient conditions, utilizing renewable energy sources. Despite the fact that the electrocatalytic N₂ reduction reaction (eNRR) is an ideal method for NH₃ synthesis, the NH₃ yield and Faradaic efficiency (FE) are severally hampered by the inertness of N₂, impeding its industrial application. Various strategies have been proposed to synthesize highly efficient heterogeneous catalysts for N₂ adsorption and dissociation to improve NH₃ yield and FE. Besides, benefiting from the nonthermal plasma N₂ oxidation reaction (pNOR) and electrocatalytic nitrate/nitrite reduction reaction (eNO_xRR), the two-step approach overcomes the limitations of eNRR, attracting significant interest. This strategy facilitates N₂ splitting, which is a crucial step in the synthesis of NH₃. Additionally, eNO_xRR involves complex intermediates, making it essential to investigate catalysts with high selectivity of NH₃. Overall, through the optimization of catalysts and reaction systems, NH₃ can be synthesized with high efficiency. The two-step strategy is the most realistic process for mass NH₃ production, but several challenges still need to be addressed, including improving the overall energy efficiency and scaling up the technology for industrial applications.