Influence of Different Catalysts on Ammonia Synthesis Performance in Coaxial DBD Plasma

In the renewable energy-driven “green electricity–green hydrogen–green ammonia” pathway, the development of low-temperature and low-energy-consumption ammonia synthesis technologies is of great significance. In this work, a plasma-catalytic ammonia synthesis system was established using a coaxial dielectric barrier discharge (DBD) reactor. The effects of different catalysts, including Ag, Cu, γ-Al2O3, BaTiO3 and Co/BaTiO3, Ni/BaTiO3 on ammonia synthesis performance were systematically investigated. The reaction process was analyzed using voltage–current waveforms, Lissajous figures, and optical emission spectroscopy (OES). The results show that different catalytic systems have a significant influence on ammonia synthesis performance, with the promotional effect ranked as follows: Ni/BaTiO3 > Co/BaTiO3 > BaTiO3 > Ag > γ-Al2O3 > Cu. Among them, Ni/BaTiO3 exhibited the best performance. Under the conditions of N2:H2 = 1:1 and a gas flow rate of 2.5 L/min, the NH3 synthesis rate reached 259.48 μmol/min, and the maximum energy efficiency reached 1.40 g-NH3/kWh. Catalyst characterization results indicate that the BaTiO3 support maintained a stable crystal structure, while the loaded metal species were highly dispersed and uniformly distributed on the support surface, which is beneficial for the adsorption and conversion of reactive species on the catalyst surface. Discharge characteristic analysis shows that the introduction of BaTiO3 enhanced the local electric field and improved the uniformity of micro-discharges, while the further incorporation of metal active components strengthened the micro-discharge behavior. OES results reveal that the intensities of characteristic emission lines, such as NH, N2+, and Hα, were significantly enhanced in the Ni/BaTiO3 system, facilitating the formation and conversion of NHx intermediates. The superior performance of Ni/BaTiO3 is attributed to the coupling between BaTiO3-induced dielectric enhancement and Ni-promoted surface hydrogenation and NH3 desorption. This work provides mechanistic insight into catalyst-dependent DBD plasma-catalytic ammonia synthesis and offers an experimental basis for the further optimization of plasma-based ammonia production.