Advances in Ammonia Synthesis: An Externally Field-Coupled Catalytic Strategy Under Mild Gas-Solid Phase Conditions

Ammonia (NH₃), the world's second most produced chemical, is indispensable to modern society, with widespread applications in agriculture, chemical manufacturing, refrigeration, and energy storage. However, the conventional Haber-Bosch process for NH₃ synthesis is characterized by lengthy process flows, harsh operating conditions, and significant carbon emissions, rendering it increasingly misaligned with global carbon peaking and neutrality objectives. Consequently, there is an urgent need to develop new NH₃ synthesis technologies that are both energy-efficient and environmentally benign. This review specifically examines three promising gas-solid phase NH₃ synthesis routes driven by external fields: photocatalysis, plasma catalysis, and the emerging technique of alternating magnetic field (AMF) catalysis. We summarize recent progress in this area, discuss catalyst design strategies tailored to each approach, and identify persistent challenges at the level of catalytic materials, reaction mechanisms, and reactor engineering. Finally, we outline future research directions, emphasizing the importance of multi-scale collaborative design to advance toward the ultimate goal of green and low-carbon NH₃ production.