Cascade N2 Reduction Process with DBD Plasma Oxidation and Electrocatalytic Reduction for Continuous Ammonia Synthesis

Due to the extremely high bond energy of N≡N (∼941 kJ/mol), the traditional Haber-Bosch process of ammonia synthesis is known as an energy-intensive and high CO2-emission industry. In this paper, a cascade N2 reduction process with dielectric barrier discharge (DBD) plasma oxidation and electrocatalytic reduction as an alternative route is first proposed. N2 is oxidized to be reactive nitrogen species (RNS) by nonthermal plasma, which would then be absorbed by KOH solution and electroreduced to NH4+. It is found that the production of NOx is a function of discharge length, discharge power, and gas flow rate. Afterward, the cobalt catalyst is used in the process of electrocatalytic reduction of ammonia, which shows high selectivity (Faradic efficiency (FE) above 90%) and high yield of ammonia (45.45 mg/h). Finally, the cascade plasma oxidation and electrocatalytic reduction for ammonia synthesis is performed. Also, the performance of the reaction system is evaluated. It is worth mentioning that a stable and sustainable ammonia production efficiency of 16.21 mg/h is achieved, and 22.16% of NOx obtained by air activation is converted into NH4+. This work provides a demonstration for further industrial application of ammonia production with DBD plasma oxidation and electrocatalytic reduction techniques.

Reduced electric field and gas temperature effects on chemical product dynamics in air surface dielectric barrier discharges: from macro-physical parameters to micro-chemical mechanisms

To gain insights into the mechanisms of plasma chemical product interactions, the dynamic changes of the surface dielectric barrier discharge (SDBD) products are experimentally related to the reduced electric field and gas temperature. The higher applied voltage and frequency cause faster product changes from the O₃-containing to the O₃-free state, while raising the electron energy and gas temperature. The electron energy affects the electron collision reactions and the production of various reactive species, steering the chemical reactions towards the predominant production of NO over O₃. The gas temperature affects the generation and quenching rates of the key products. Collectively, this work bridges macro-physical parameters and micro-chemical mechanisms through the electron energy and gas temperature effects, and contributes to better understanding of the physico-chemical processes in low-temperature plasmas.

Dielectric Barrier Discharge Coupling Catalytic Oxidation for Highly Efficient Hg0 Conversion

In this work, we prepared CuCe/Ti catalysts in a dielectric barrier discharge (DBD) reactor and proposed a new method for flue gas mercury oxidation using DBD coupling CuCe/Ti catalyst. Our experiments verified the oxidation efficiency of flue gas Hg⁰ (η_Hg) and clarified the influence of O₂ content, NO concentration, SO₂ concentration, water vapor content, and discharge voltage on η_Hg. The oxidation mechanism of Hg⁰ in the DBD-CuCe/Ti reactor was also illustrated. The Hg⁰ oxidation experiment on the simulated flue gas (70 μg/m³ Hg⁰ + 300 mg/m³ NO + 1000 mg/m³ SO₂ + 6%O₂) with a flow rate of 1 L/min showed that when the amount of catalyst was 1.25 g and the discharge voltage was 9.5 kV, a η_Hg of 93% can be achieved, which indicates that the DBD coupling CuCe/Ti technology is suitable for Hg⁰ conversion and flue gas mercury removal.

Application of Non-Thermal Plasma for NOx Reduction in the Flue Gases

Over the years, ever more stringent requirements on the pollutant emissions, especially NOX, from combustion systems burning natural gas are introduced by the European Union (EU). Among all NOX reduction methods, the flue gas treatment by plasma is widely applied and could be used for both small scale and domestic combustion systems. However, the removal efficiency depends on concentrations of oxygen, water vapor, traces of hydrocarbons, and nitrogen oxides in flue gas. In order to analyze the application of the NOX reduction for small-scale or domestic combustion systems, experiments of NOX reduction by non-thermal plasma from real flue gases originating from premixed methane combustion at different equivalence ratio (ER) values were performed. It was determined that the residual oxygen in flue gas plays an important role for improvement of NO to NO2 oxidation efficiency when O2 concentrations are equal to or higher than 6%. The power consumption for the plasma oxidation constituted approximately 1% of the burner power. In the case of ozone treatment, the addition of O3 to flue gas showed even more promising results as NO formed during combustion was fully oxidized to NO2 at all ER values.

Conversion of dilute nitrous oxide (N2O) in N2 and N2–O2 mixtures by plasma and plasma-catalytic processes

Production and conversion of N₂O occur simultaneously, with production and conversion being dominant at room and high temperature, respectively.