This article presents an ammonia synthesis strategy that utilizes H2 produced in-situ as a byproduct of the methane coupling reaction. This approach eliminates the need for CO2-intensive hydrogen production via steam methane reforming while lowering the operating temperature required for CH 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/CeO2 catalyst under MW irradiation, enabling stable CH activation and selective formation of C2 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 NH3 formation rate (0.60 mmol·g-1·h-1). The influence of cofed ethylene on NH3 productivity relative to conventional H2/N2 feed is examined to assess competitive adsorption between olefins and ammonia. Catalyst characterization using chemisorption, NH3-TPD, and operando Raman spectroscopy provides insights into surface chemistry relevant to NH3 formation. Operando Raman results indicate that the reduction of Ce4+ to Ce3+ 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 N2. 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.
Desta et al. (Mon,) studied this question.