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[EN] Biomass gasification is a promising and sustainable process to produce renewable and CO2-neutral syngas (H2 and CO). However, the contamination of syngas with tar is one of the major challenges to limit the deployment of biomass gasification on a commercial scale. Here, we propose a hybrid plasma-catalytic system for steam reforming of tar compounds over honeycombbased catalysts in a gliding arc discharge (GAD) reactor. The reaction performances were evaluated using the blank substrate and coated catalytic materials (gamma-Al2O3 and Ni/gamma-Al2O3). Compared with the plasma alone process, introducing the honeycomb materials in GAD prolonged the residence time of reactant molecules for collision with plasma reactive species to promote their conversions. The presence of Ni/gamma-Al2O3 gave the best performance with the high conversion of toluene (86.3%) and naphthalene (75.5%) and yield of H2 (35.0%) and CO (49.1%), while greatly inhibiting the formation of byproducts. The corresponding highest overall energy efficiency of 50.9 g/kWh was achieved, which was 35.4% higher than that in the plasma alone process. Characterization of the used catalyst and long-term running indicated that the honeycomb material coated with Ni/gamma-Al2O3 had strong carbon resistance and excellent stability. The superior catalytic performance of Ni/gamma-Al2O3 can be mainly ascribed to the large specific surface area and the in situ reduction of nickel oxide species in the reaction process, which promoted the interaction between plasma reactive species and catalysts and generated the plasma-catalysis synergy.

[EN] Biomass gasification is a promising and sustainable process to produce renewable and CO2-neutral syngas (H2 and CO). However, the contamination of syngas with tar is one of the major challenges to limit the deployment of biomass gasification on a commercial scale. Here, we propose a hybrid plasma-catalytic system for steam reforming of tar compounds over honeycombbased catalysts in a gliding arc discharge (GAD) reactor. The reaction performances were evaluated using the blank substrate and coated catalytic materials (gamma-Al2O3 and Ni/gamma-Al2O3). Compared with the plasma alone process, introducing the honeycomb materials in GAD prolonged the residence time of reactant molecules for collision with plasma reactive species to promote their conversions. The presence of Ni/gamma-Al2O3 gave the best performance with the high conversion of toluene (86.3%) and naphthalene (75.5%) and yield of H2 (35.0%) and CO (49.1%), while greatly inhibiting the formation of byproducts. The corresponding highest overall energy efficiency of 50.9 g/kWh was achieved, which was 35.4% higher than that in the plasma alone process. Characterization of the used catalyst and long-term running indicated that the honeycomb material coated with Ni/gamma-Al2O3 had strong carbon resistance and excellent stability. The superior catalytic performance of Ni/gamma-Al2O3 can be mainly ascribed to the large specific surface area and the in situ reduction of nickel oxide species in the reaction process, which promoted the interaction between plasma reactive species and catalysts and generated the plasma-catalysis synergy.

A new atmospheric pressure non-equilibrium plasma source named the 'Propeller Arc' (PA) is developed using the concept of rotating electrodes. The PA device consists of a rotating cathode, driven by a motor, with one or more fixed anodes. Plasma is ignited at or near the narrowest gap as the rotating cathode passes by the anode and then it is extended up to a length of ∼66 mm or longer depending on the supplied power. This allows for efficient ignition, followed by a quick increase in plasma volume. The PA is similar to the widely used gliding arc (GA); however, unlike the GA, PA does not require imposed gas flow, and the PA discharge frequency can be easily controlled by the motor angular velocity. In this paper, the basic characteristics of PA are investigated using two different operation modes: pulse modulation and DC power. Discharge properties including electrical characteristics, time-resolved optical emission images, plasma electrical properties such as resistance and average electric field (discharge voltage divided by gap distance) and plasma power consumption are reported. Use of multiple anodes to increase the plasma volume is also demonstrated. As the PA has a compact design and is relatively easy to stabilize and control without the need for applied gas flow, it has potential to be adapted for many different applications such as nitrogen fixation, fuel and carbon dioxide conversion, waste, odor and hydrogen sulfide treatment, etc.

A new atmospheric pressure non-equilibrium plasma source named the 'Propeller Arc' (PA) is developed using the concept of rotating electrodes. The PA device consists of a rotating cathode, driven by a motor, with one or more fixed anodes. Plasma is ignited at or near the narrowest gap as the rotating cathode passes by the anode and then it is extended up to a length of ∼66 mm or longer depending on the supplied power. This allows for efficient ignition, followed by a quick increase in plasma volume. The PA is similar to the widely used gliding arc (GA); however, unlike the GA, PA does not require imposed gas flow, and the PA discharge frequency can be easily controlled by the motor angular velocity. In this paper, the basic characteristics of PA are investigated using two different operation modes: pulse modulation and DC power. Discharge properties including electrical characteristics, time-resolved optical emission images, plasma electrical properties such as resistance and average electric field (discharge voltage divided by gap distance) and plasma power consumption are reported. Use of multiple anodes to increase the plasma volume is also demonstrated. As the PA has a compact design and is relatively easy to stabilize and control without the need for applied gas flow, it has potential to be adapted for many different applications such as nitrogen fixation, fuel and carbon dioxide conversion, waste, odor and hydrogen sulfide treatment, etc.

Ozone vapor, O3, is here visualized in a gliding arc discharge using photofragmentation laser-induced fluorescence. Ozone is imaged by first photodissociating the O3 molecule into an O radical and a vibrationally hot O2 fragment by a pump photon. Thereafter, the vibrationally excited O2 molecule absorbs a second (probe) photon that further transits the O2-molecule to an excited electronic state, and hence, fluorescence from the deexcitation process in the molecule can be detected. Both the photodissociation and excitation processes are achieved within one 248 nm KrF excimer laser pulse that is formed into a laser sheet and the fluorescence is imaged using an intensified CCD camera. The laser-induced signal in the vicinity of the plasma column formed by the gliding arc is confirmed to stem from O3 rather than plasma produced vibrationally hot O2. While both these products can be produced in plasmas a second laser pulse at 266 nm was utilized to separate the pump- from the probe-processes. Such arrangement allowed lifetime studies of vibrationally hot O2, which under these conditions were several orders of magnitude shorter than the lifetime of plasma-produced ozone.

The details of plasma channel motion are investigated by frame-by-frame image analysis of high speed recording of a gliding arc. The gliding arc is operated in several noble gases at various flow rates, voltages and artificial gravity levels. Several peculiarities in evolution of individual glides are observed, described and discussed, such as accelerating motion of plasma channel or shortcutting events of various kinds. Statistics of averaged parameters are significantly different for buoyancy and gas drag dominated regimes, which is put into relation with differing flow patterns for hypergravity and high gas flow.

The details of plasma channel motion are investigated by frame-by-frame image analysis of high speed recording of a gliding arc. The gliding arc is operated in several noble gases at various flow rates, voltages and artificial gravity levels. Several peculiarities in evolution of individual glides are observed, described and discussed, such as accelerating motion of plasma channel or shortcutting events of various kinds. Statistics of averaged parameters are significantly different for buoyancy and gas drag dominated regimes, which is put into relation with differing flow patterns for hypergravity and high gas flow.

The details of plasma channel motion are investigated by frame-by-frame image analysis of high speed recording of a gliding arc. The gliding arc is operated in several noble gases at various flow rates, voltages and artificial gravity levels. Several peculiarities in evolution of individual glides are observed, described and discussed, such as accelerating motion of plasma channel or shortcutting events of various kinds. Statistics of averaged parameters are significantly different for buoyancy and gas drag dominated regimes, which is put into relation with differing flow patterns for hypergravity and high gas flow.

Rapid transition from glow discharge to thermal arc has been a common problem in generating stable high-power non-thermal plasmas especially at ambient conditions. A sustained diffusive gliding arc discharge was generated in a large volume in atmospheric pressure air, driven by an alternating current (AC) power source. The plasma column extended beyond the water-cooled stainless steel electrodes and was stabilized by matching the flow speed of the turbulent air jet with the rated output power. Comprehensive investigations were performed using high-speed movies measured over the plasma column, synchronized with simultaneously recorded current and voltage waveforms. Dynamic details of the novel non-equilibrium discharge are revealed, which is characterized by a sinusoidal current waveform with amplitude stabilized at around 200 mA intermediate between thermal arc and glow discharge, shedding light to the governing mechanism of the sustained spark-suppressed AC gliding arc discharge.