Elucidation of the behavior of oxygen remaining in water molecules after hydrogen atom abstraction in the plasma/liquid (P/L) interfacial reaction: improvement in the selectivity of ammonia synthesis and parallel production of hydrogen gas

Abstract

The plasma/liquid interfacial (P/L) reaction is a non-catalytic reaction conducted at an ambient temperature and pressure. The reaction employs activated (dissociated or excited) nitrogen and abstracted hydrogen from water molecules to form ammonia. Herein we demonstrated that dissociated nitrogen (atomic nitrogen; N_atom) promoted ammonia selectivity more efficiently than excited nitrogen molecules in P/L reactions. We investigated the behavior of water-derived oxygen after abstracting a hydrogen atom from a water molecule. We constructed a connecting reactor that directly connects the P/L reaction locus with a titania bead-filled packed-bed dielectric barrier discharge (PbDBD) device that exhibits high N_atom generation efficiency. In this reactor, the P/L reaction produced aqueous ammonia with high selectivity and minimal aqueous nitrate ions, which are the typical by-products of the reaction. We also observed that oxygen and hydrogen atoms from water were released into the gas phase to form NO and hydrogen gases. The removal of oxygen as NO gas from the P/L reaction locus significantly improved the ammonia synthesis selectivity of the P/L reaction. Additionally, the ability to generate hydrogen gas during ammonia synthesis in the P/L reaction enables the simultaneous production of ammonia and hydrogen gas.