Nitrogen is an essential element to plants, animals, human beings and all the other living things on earth. Nitrogen fixation, which converts inert atmospheric nitrogen into ammonia or other valuable substances, is a very important part of the nitrogen cycle. The Haber-Bosch process plays the dominant role in the chemical nitrogen fixation as it produces a large amount of ammonia to meet the demand from the agriculture and chemical industries. However, due to the high energy consumption and related environmental concerns, increasing attention is being given to alternative (greener) nitrogen fixation processes. Among different approaches, plasma-assisted nitrogen fixation is one of the most promising methods since it has many advantages over others. These include operating at mild operation conditions, a green environmental profile and suitability for decentralized production. This review covers the research progress in the field of plasma-assisted nitrogen fixation achieved in the past five years. Both the production of NO_x and the synthesis of ammonia are included, and discussion on plasma reactors, operation parameters and plasma-catalysts are given. In addition, outlooks and suggestions for future research are also given.

We present an innovative approach for reacting carbon dioxide and water to give syngas by combining heterogeneous catalysis and non-thermal plasma techniques. This approach utilizes an abundant water and nickel catalyst, and mitigates the thermodynamic penalty by using a Dielectric Barrier Discharge (DBD) plasma reactor. Argon dilution was used in the experiment to reduce the exothermic recombination of hydrogen and oxygen, which is considered as the major hurdle for H₂O conversion. As a result, the syngas ratio was dramatically improved from 0.07 to 0.86. In addition, the conversions of CO₂ and H₂O were improved by packing Ni/γ–Al₂O₃ catalysts into the DBD reactor. The yields of H₂ and CO were up to 13.8% and 5.6% respectively. The conditions for plasma catalysis and the catalyst characterization are presented and discussed.

Plasma-assisted nitrogen fixation has been considered a potential green alternative for conventional Haber–Bosch process and has recently received a lot of attention. Ammonia synthesis in nonthermal plasma reactors at atmospheric pressure has been investigated in this research with a 5% Ru/ α -Al ₂ O ₃ catalyst. The operating parameters including feed molar ratio, flow rate, applied voltage, discharge power and argon dilution were investigated to provide information for optimization of NH ₃ concentration and energy consumption. Difference between the blank reactor and the catalyst-packed reactor were presented with a discussion on their own optimal parameters. The optimal feed gas ratio (N ₂ :H ₂ ) for blank reactor and the catalyst-packed reactor are 1:3 and 2:1 correspondingly. Higher flow rate resulted in a lower NH ₃ concentration and energy consumption in both blank reactor and the catalyst-packed reactor. Ammonia concentration of 1.49% was achieved in a catalytic DBD reactor with 120 ml min ⁻¹ , 2:1 N ₂ /H ₂ feed gas ratio and 38.4 W discharge power, corresponding to the energy consumption of 32.39 MJ mol ⁻¹ . The discharge power and the reactor temperature is important to the synthesis of ammonia in catalytic DBD reactor and the effect of heat build-up in the reactor on NH ₃ concentration was observed. Argon addition improved the conversion of nitrogen and hydrogen at a cost of energy consumption and production rate in both blank and catalyst-packed reactor, but it is more beneficial for increasing the conversion of reactants in the case of catalytic DBD reactor.

A two-dimensional gliding arc reactor for NO_x synthesis was investigated in this study using AC pulsed mode operation. Tests with a duty cycle of 40 or 60% achieved the lowest energy consumption of 6.95 MJ/mol, which is an improvement of 15% from the case of continuous operation. Based on the results achieved, a new method for analyzing the spatial profile of the reactor was presented. The reactor was divided into five zones along the arc propagation, and results indicated that the first zone and last zone of the gliding arc reactor had higher energy consumption (9.59 and 8.63 MJ/mol, respectively), while lower consumption was observed in the middle parts of the reactor with a minimum of 5.00 MJ/mol. Spatial-resolved optical emission spectra, the deduced electron density, and temperature indicated the nonuniformity in plasma properties, which corresponds to the NO_x production performance across the reactor. This research provides information and discussion that can be used for understanding and optimization of gliding arc reactors toward efficient nitrogen fixation.

In the present study, a plasma-electrochemical method was demonstrated for the synthesis of europium doped ceria nanoparticles. Ce(NO₃)₃ · 6H₂O and Eu(NO₃)₃ · 5H₂O were used as the starting materials and being dissolved in the distilled water as the electrolyte solution. The plasma-liquid interaction process was in-situ investigated by an optical emission spectroscopy, and the obtained products were characterized by complementary analytical methods. Results showed that crystalline cubic CeO₂:Eu³⁺ nanoparticles were successfully obtained, with a particle size in the range from 30 to 60 nm. The crystal structure didn’t change during the calcination at a temperature from 400°C to 1000°C, with the average crystallite size being estimated to be 52 nm at 1000°C. Eu³⁺ ions were shown to be effectively and uniformly doped into the CeO₂ lattices. As a result, the obtained nanophosphors emit apparent red color under the UV irradiation, which can be easily observed by naked eye. The photoluminescence spectrum further proves the downshift behavior of the obtained products, where characteristic ⁵D₀ → ⁷F_1,2,3 transitions of Eu³⁺ ions had been detected. Due to the simple, flexible and environmental friendly process, this plasma-electrochemical method should have great potential for the synthesis of a series of nanophosphors, especially for bio-application purpose.