Catalytic Conversion of Nonequilibrium Hydrogen and Nitrogen Species from Low-Pressure Inductively Coupled Plasma to Ammonia

Gas conversion between hydrogen (H2), nitrogen (N2), and ammonia (NH3) is a scientific topic of interest in both methods for low-temperature synthesis of ammonia and energy-efficient production of hydrogen for powering fuel cells. The efficiency of catalysts for ammonia synthesis at room temperature was evaluated. A mixture of hydrogen and nitrogen with a ratio in a broad range between 1.5:1 and 80:1 was passed through a plasma sustained by inductively coupled radio frequency discharge in the H mode at a power of 700 W and pressures between 40 and 100 Pa. Several catalysts were placed in the flowing afterglow where the H and N densities were of the order of 1021 m−3, and the conversion efficiency (η) was evaluated. The efficiency increased almost linearly with increasing enthalpy of nitride formation. The best results were observed for copper, for which the conversion was almost twice the value in the same system without the catalyst. The efficiency of NH3 production by the conversion of N atoms into NH3 molecules versus the gas mixture exhibited a broad maximum and was as large as η ≈ 29% in the mixture of hydrogen and nitrogen between 3:1 and 10:1.