Drastically Increase in Atomic Nitrogen Production Depending on the Dielectric Constant of Beads Filled in the...

Nitrogen activation, especially dissociation (production of atomic nitrogen), is a key step for efficient nitrogen fixation, such as nitrogen reduction to produce ammonia. Nitrogen reduction reactions using water as a direct hydrogen source have been studied by many researchers as a green ammonia process. We studied the reaction mechanism and found that the nitrogen reduction could be significantly improved via efficient production of atomic nitrogen through electric discharge. In the present study, we focused on packed-bed dielectric barrier discharge (PbDBD) using dielectric beads as the packing material. The experimental results showed that more atomic nitrogen was produced in the nitrogen activation by the discharge in which the discharge space was filled with the dielectric beads than in the nitrogen activation by the discharge without using the dielectric beads. Then, it was clarified that the amount of atomic nitrogen increased as the dielectric constant of the beads to be filled increased, and the amount of atomic nitrogen produced increased up to 13.48 times. Based on the results, we attempted ammonia synthesis using water as a direct hydrogen source with the efficiently generated atomic nitrogen. When the atomic nitrogen gas generated by the PbDBD was sprayed onto the surface of the water phase and subsequently reacted as a plasma/liquid interfacial reaction, the nitrogen fixation rate increased by 7.26-fold compared to that when using the discharge without dielectric beads, and the ammonia production selectivity increased to 83.7%.