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The formation of carbon monoxide, oxygen and ozone in a barrier corona discharge (BCD) operating in pure carbon dioxide (CO2) and binary mixtures of CO2 and argon is studied. The asymmetric electrode configuration of the BCDs allows plasma operation at pressures exceeding 1 atm, up to 6 bar, at moderate high-voltage amplitudes below 15 kV. Charge–voltage plots and an equivalent circuit model are employed to characterize the electrical parameters at different pressures and gas compositions. Depending on these conditions and the voltage amplitude, full or partial coverage of the electrodes with plasma is obtained. The existence of an optimum pressure for power dissipation for each given operation voltage amplitude and gas composition can be confirmed and explained by the equivalent circuit model. Increasing the CO2 concentration in the working gas increases the mean reduced electric field strength E/N while pressure reduces it in the BCD. The CO2 conversion shows a maximum efficiency of about 4% at 1.5 bar for the gas mixture Ar/CO2 = 1:1 and a voltage amplitude of about 10 kV. The calculation of thermodynamic equilibrium parameters reveals that a relatively small increase in pressure can affect both, the equilibrium parameters and the reaction rates. As a result, the specific required energy for the reaction ( Δ H / SEI ) shows an optimum, but only 8% of the electrical input energy is spent for CO2 dissociation at these optimum conditions. [ABSTRACT FROM AUTHOR]

This short review provides a general perspective on ozone formation and includes a brief history of the great German inventor Werner von Siemens, who invented the prototype ozonizer. The main structure of Siemens ozonizer still serves as the de facto model in large-scale applications. This review places particular focus on the thermodynamic aspect of ozone formation in dielectric barrier discharge (DBD), which is fundamental but puzzling to newcomers in plasma chemistry. As is often mentioned in the chemistry of nonthemal plasmas, non-equilibrium reactions initiated by highenergy electrons allow for the dissociation of oxygen molecules at ambient temperature, even though it is a highly endothermic process. Once atomic oxygen is formed, it spontaneously combines with oxygen molecules to form ozone with a heat release. This elaborate coupling of the non-equilibrium with equilibrium processes, as well as exothermic and endothermic processes, makes the DBD reactor an efficient and effective method for O3 formation against the thermodynamic limits. Understanding the interplay of these elementary processes in the DBD reactor is essential in comprehending how ozone is generated, and it sheds light on further development. This review aims to provide valuable insights into the thermodynamic mechanisms behind ozone formation and some noticeable applications of ozone, assisting newcomers in plasma chemistry to grasp the underlying principles of this crucial process. [ABSTRACT FROM AUTHOR]

This contribution attempts to establish an easy-to-apply non-thermal plasma reactor for efficient toluene removal. Derived from the already established knowledge of the so called Dielectric Barrier Discharge (DBD) Stack Reactor a new model reactor was used in this work. The DBD Stack Reactor is a multi-elements reactor but in this work only one stack element was used to investigate the efficiency and efficacy of toluene removal. In case of reliable results the scalability process for industrial application is already well known. Therefore, laboratory experiments were conducted in dry and wet synthetic air with an admixture of 50 ppm toluene. Along with the toluene removal process the electrical behaviour of the discharge configuration was investigated. It was found that the electrical capacitance of the dielectric barrier changes with variations of the operating voltage. This could be due to the changes in the area of the dielectric barrier which is covered with plasma. Additionally, it was found that the power input into the plasma, at a fixed operating voltage, is proportional to the frequency, which is in agreement with the literature. Regarding the decomposition process, the total removal of toluene was achieved at specific input energy densities of 55 J L-1 under dry conditions and 110 J L-1 under wet conditions. The toluene removal was accompanied by the production of nitric acid (dry conditions) and formic acid (wet conditions). The latter suggested a combination of the plasma reactor with a water scrubber as an approach for total removal of pollutant molecules. [ABSTRACT FROM AUTHOR]

Oxidation mechanisms in air nonthermal plasma (NTP) at room temperature and atmospheric pressure were investigated in a corona reactor energized by +dc, -dc, or +pulsed high voltage.. The two bromomethanes CF2Br2 and CH2Br2 were chosen as model organic pollutants because of their very different reactivities with OH radicals. Thus, they served as useful mechanistic probes: they respond differently to the presence of humidity in the air and give different products. By FT-IR analysis of the postdischarge gas the following products were detected and quantified: CO2 and CO in the case of CH2Br2, CO2 and F2C-O in the case of CF2Br2. F2C-O is a long-lived oxidation intermediate due to its low reactivity with atmospheric radicals. It is however removed from the NTP processed gas by passage through a water scrubber resulting in hydrolysis to CO2 and HF. Other noncarbon containing products of the discharge were also monitored by FT-IR analysis, including HNO3 and N2O. Ozone, an important product of air NTP, was never detected in experiments with CF2Br2 and CH2Br2 because of the highly efficient ozone depleting cycles catalyzed by BrOx species formed from the bromomethanes. It is concluded that, regardless of the type of corona applied, CF2Br2 reacts in air NTP via a common intermediate, the CF2Br radical. The possible reactions leading to this radical are discussed, including, for -dc activation, charge exchange with O2-, a species detected by APCI mass spectrometry. [ABSTRACT FROM AUTHOR]

This paper reports isotopic evidence on nonthermal plasma-induced fixation of gas-phase oxygen on the surface of several catalysts such as TiO, Ag/TiO, Ag/γ-AlO and Ag/MS-13X at atmospheric-pressure. On-line mass spectrometric analysis and stoichiometric comparison of reactants and products revealed that the fixed surface oxygen can be activated by nonthermal plasma. The fixed O by nonthermal plasma survived for a certain period of time (about 30 min), and involved in the formation of isotope-exchanged oxygen (OO) and isotope containing CO (CO and CO). Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Oxidation mechanisms in air nonthermal plasma (NTP) at room temperature and atmospheric pressure were investigated in a corona reactor energized by +dc, -dc, or +pulsed high voltage.. The two bromomethanes CF(2)Br(2) and CH(2)Br(2) were chosen as model organic pollutants because of their very different reactivities with OH radicals. Thus, they served as useful mechanistic probes: they respond differently to the presence of humidity in the air and give different products. By FT-IR analysis of the postdischarge gas the following products were detected and quantified: CO(2) and CO in the case of CH(2)Br(2), CO(2) and F(2)C ═ O in the case of CF(2)Br(2). F(2)C ═ O is a long-lived oxidation intermediate due to its low reactivity with atmospheric radicals. It is however removed from the NTP processed gas by passage through a water scrubber resulting in hydrolysis to CO(2) and HF. Other noncarbon containing products of the discharge were also monitored by FT-IR analysis, including HNO(3) and N(2)O. Ozone, an important product of air NTP, was never detected in experiments with CF(2)Br(2) and CH(2)Br(2) because of the highly efficient ozone depleting cycles catalyzed by BrOx species formed from the bromomethanes. It is concluded that, regardless of the type of corona applied, CF(2)Br(2) reacts in air NTP via a common intermediate, the CF(2)Br radical. The possible reactions leading to this radical are discussed, including, for -dc activation, charge exchange with O(2)(-), a species detected by APCI mass spectrometry.