Measurement of OH (X2Σ) in immediate vicinity of dielectric surface under pulsed dielectric barrier discharge at atmospheric pressure using two geometries of laser-induced fluorescence

Abstract

The behavior of the ground state OH radical was studied in humid air using pulsed surface dielectric barrier discharge. The validity of OH measurement in immediate vicinity of the dielectric surface was discussed using two geometries of laser-induced fluorescence (LIF) measurement, and surface distribution and temporal profiles of OH were examined. A comparison of parallel- and perpendicular-LIF techniques for OH measurement revealed that OH was mostly produced in a region several tens of μm above the dielectric surface. The surface distribution profile of OH agreed well with that of N2(C), and in both cases, the total production generated by a discharge pulse was proportional to the discharge energy. The OH local density in surface streamer channels was estimated to be 1.3 × 1015 cm−3 according to the decay rate of OH, which was similar to that in corona discharge. Additionally, the local density of OH remained constant regardless of discharge energies. These results indicate that the yield of OH increased with the discharge energy owing to expansion of the surface streamer region, increase in streamer radius or thickness or the number of branches, whereas the local density of OH in the streamer channel remained constant regardless of discharge energy.

Non‐Thermal Plasma Activation of Gold‐Based Catalysts for Low‐Temperature Water–Gas Shift Catalysis

“…[26,27,43] This may also be the case under plasma conditions which shows deactivation with time on stream;t he fact that after three cycles this band has decreased considerably,yet the catalyst is still active would suggest that this species is,i ndeed, being converted into al ess active form (Au d+ ). Under the plasma conditions,i ti sp ostulated that reactive oxygen species (ROS) [1,[44][45][46] formed through the activation of the water leads to oxidation of the gold. This reactive oxygen species, which may be OH, for example,g enerated in the gas phase plasma will also increase the hydrolysis of the gold-support interface and lead to the loss of the interfacial gold species, represented by the band at 2095 cm À1 .P reviously reported density functional theory (DFT) calculations have demonstrated that the decoration of the surface with hydroxy groups significantly weakens the metal-support interaction and ad ewetting of the gold nanoparticle.T his loss of the interfacial gold which is exacerbated by the sintering of the gold particles,l eads to ad eactivation of the catalyst.…”

“…[47] Water has been observed to be activated in the gas phase under plasma conditions to form, for instance,OHand H 2 O + species. [1,[44][45][46]48] Theformer is thought to be ak ey intermediate from the water dissociation on the surface of gold and the subsequent reaction to form COOH before releasing CO 2 .Prior formation of the OH before adsorption would reduce the effective barriers,u sing the method reported by Wang et al, [49] from 2.87 to 0.73 eV on Au(111) and from 2.44 to 0.99 eV on Au(100). Further-more,t he activation barriers for the dissociation of H 2 O x as af unction of the charge x over gold was calculated and was found to be negative for cationic water (Figure S17), suggesting that H 2 O + is not stable and will dissociate into OH and H spontaneously.T herefore,t he plasma activated low temperature WGS is likely to be due to the facile activation of H 2 O reducing the overall activation barrier.…”

Non‐Thermal Plasma Activation of Gold‐Based Catalysts for Low‐Temperature Water–Gas Shift Catalysis

“…This may also be the case under plasma conditions which shows deactivation with time on stream; the fact that after three cycles this band has decreased considerably, yet the catalyst is still active would suggest that this species is, indeed, being converted into a less active form (Au δ+ ). Under the plasma conditions, it is postulated that reactive oxygen species (ROS) formed through the activation of the water leads to oxidation of the gold. This reactive oxygen species, which may be OH, for example, generated in the gas phase plasma will also increase the hydrolysis of the gold‐support interface and lead to the loss of the interfacial gold species, represented by the band at 2095 cm −1 .…”

Laser induced fluorescence in atmospheric pressure discharges

“…It being a very reactive oxidizing specie, it is important in plasma medicine and plasma assisted combustion issues. Many papers have been recently published on OH quantitative detection by LIF: in a pulsed corona discharge [10,11,12,13,14], in a DBD [15], in a pulsed DBD [16,17,18], in a plasma-jet [19,20,21,22,23,24,25], in a pulsed discharge over a liquid surface [13], in a pin-to-pin single filament discharge [26,27,28], in nanosecond discharges for plasma assisted combustion [29,30]. Transitions used for OH LIF detection are those of the OH (X 2 Π − A 2 Σ + ) 3064Å system.…”