Catalytic Ammonia Formation in a Microreaction Chamber with Electrically Intensified Arc Plasma

• Published in: ChemCatChem 2024-07, Vol.16 (13), p.n/a
• Main Authors: Van Duc Long, Nguyen, Pourali, Nima, Lamichhane, Pradeep, Mohsen Sarafraz, Mohammad, Nghiep Tran, Nam, Rebrov, Evgeny, Kim, Hyun‐Ha, Hessel, Volker
• Format: Article
• Language: English
• Subjects: Ammonia; Ammonia synthesis; Catalysts; Electric fields; Electrodes; Energy efficiency; Flow distribution; Free electrons; Microplasmas; Nitrogen fixation; Non-thermal plasma; Optical emission spectroscopy; Plasma; Plasma catalysis; Process intensification; Reactor design; Symbiosis
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.202400005

Ammonia (NH3) production is of global concern for today's food supply security and as future energy vector. Plasma technology can add to supply‐chain resilience of fertilizer production and improve the environmental profile using renewable energy; allowing distributed NH3 production. With the objective to provide process intensification of small‐capacity reactors for local supply, a novel micropyramid‐disk plasma reactor operated in micro‐arc mode was developed. NH3 was synthesized from N2, nitrogen, and H2, hydrogen over Ru/MCM‐41 catalyst at atmospheric pressure. The microplasma brings plasma and catalyst surface close together and intensifies the electric field. The arc plasma elevates temperature, ‘nonthermal’, releasing high‐energy free electrons, known to be effective in converting low‐reactive molecules. The study demonstrates that microplasma, with reduced electrode‐to‐electrode dimensions and a microstructured reaction environment, enhances the performance of the NH3 synthesis and opens novel process windows. This is detailed on the impact of feed ratio (N2/H2), applied voltage, frequency, electrode gap, and the flow distribution by which the gas is fed in. Optical emission spectroscopy (OES) was used to identify vibrationally and other excited species generated by the microplasma and confirms the catalyst is in symbiosis with the radicals. Ammonia synthesis conducted under arc conditions in a microfabricated multi‐pyramid plasma reactor shows that increasing the strength of the electric field leads to improved reaction performance. Dedicated fluid distribution structures for flow equidistribution and mixing demonstrate relevant impact on ammonia formation. Our study deciphers a symbiosis of the radicals and vibrationally excited species generated by plasma with the catalyst.