Work

Circular Low‐Carbon Ammonia Synthesis Enabled by Microwave‐Induced CH Bond Activation Reactions

Year: 2026

Type: article

Abstract: This article presents an ammonia synthesis strategy that utilizes H 2 produced in‐situ as a byproduct of the methane coupling reaction. This approach eliminates the need for CO 2 ‐intensive hydrogen production via steam methane reforming while lowering the operating temperature required for CH bond activation through microwave‐assisted (MW) catalysis. The process demonstrates strong potential for decarbonizing process heat via MW‐driven electrification. A two‐stage MW–thermal hybrid system is employed for the simultaneous activation of methane and nitrogen. In the first stage, methane undergoes nonoxidative coupling (NOCM) over a 1Cs–3Mo/CeO 2 catalyst under MW irradiation, enabling stable CH activation and selective formation of C 2 hydrocarbons with an apparent activation energy of 136 kJ·mol −1 . Ethylene is the dominant product below 750°C. The hydrogen‐rich effluent from the NOCM reactor is routed directly to a downstream Ru‐based catalytic reactor for ammonia synthesis, thereby eliminating the need for externally supplied hydrogen. Among the catalysts evaluated, 2Cs–4Ru/MgO exhibits the highest NH 3 formation rate (0.60 mmol·g −1 ·h −1 ). The influence of cofed ethylene on NH 3 productivity relative to conventional H 2 /N 2 feed is examined to assess competitive adsorption between olefins and ammonia. Catalyst characterization using chemisorption, NH 3 ‐TPD, and operando Raman spectroscopy provides insights into surface chemistry relevant to NH 3 formation. Operando Raman results indicate that the reduction of Ce 4+ to Ce 3+ generates oxygen vacancies that modify the electronic environment of adjacent Ru species, enhancing electron donation and strengthening back‐donation into the antibonding π* orbitals of adsorbed N 2 . For the nitrogen circular economy, MW‐driven ammonia decomposition is demonstrated using monolithic catalyst. Overall, the MW–thermal hybrid platform offers a promising pathway toward decentralized and sustainable chemical manufacturing. Integration with renewable electricity and biomethane resources could further reduce the carbon footprint and enhance the overall sustainability of the system.

Source: ChemSusChem

DOI: 10.1002/cssc.202502404