Enhancement of CO2 splitting in a coaxial dielectric barrier discharge by pressure increase, packed bed and catalyst addition

An experimental investigation of the dissociation of CO2 in a symmetric pin-to-pin dielectric barrier discharge (DBD) is presented. The reactor geometry allows for an accurate control of the number of filaments (microdischarges) and is used to study the impact of one single filament on the CO2 dissociation. We show the number of filaments per half cycle follows a power-law with as a function of the injected power and does not depend on pressure, flow or other process parameters. It is shown that for pressures between 200 and 700 mbar approximately 0.5 W per filament is required and the charge transferred per filament remains constant at 0.5 nC. Furthermore, the dependence of CO2 conversion on only specific energy input is shown to be valid down to a single filament. Additionally, by using quantum cascade laser (QCL) absorption spectroscopy the absolute number of CO molecules produced per filament is measured and is found to be in the range from 5.1011 to 2.1012. The conversion degree of CO2 into CO is estimated to be lower than 0.1% within a single filament and increases with specific energy input. In the presence of a couple of filaments, the maximum energy efficiency obtained is 25%.A comparison of the conversion degrees in pin-to-pin DBD and plane-to-plane DBD configuration shows that these two reactor geometries follow the same power law. This means the geometry is not the most important parameter in CO2 dissociation in DBDs, but the specific energy input and thus the number of filaments ignited per unit of time. This result means that the dependence of conversion degree on the specific energy input can be extended to a single filament. This observation leads to the conclusion that the specific energy input appears to be valid as a universal scaling parameter down to very low values.

Section: Effect Of the Pressurementioning

confidence: 80%

The role of the number of filaments in the dissociation of CO₂ in dielectric barrier discharges

Douat

Ponduri

Boumans

et al. 2023

“…In Ref . [10], an increase of CO 2 splitting and energy yield has been demonstrated using glass supports with CeO 2 coating. The sensitivity of synthesis induced differences in the morphology of millimeter-sized SiO2@TiO2 packing spheres on a PB-DBD CO 2 conversion rate has been shown in Ref.…”

Section: Introductionmentioning

confidence: 93%

“…The ease of connection of DBD reactors in series or in parallel operation is yet another advantage of such very well-studied plasma sources in ambient conditions, towards increased conversion efficiency [8]. In addition, DBDs can be easily arranged in a co-axial configuration and packed with catalysts towards packed bed DBD (PB-DBD) reactors [9,10], leveraging plasma-catalyst synergies. Focusing on the latter, plasma catalysis remains an emerging field with large unexplored potential.…”

Section: Introductionmentioning

confidence: 99%

Full-wave and plasma simulations of microstrip excited, high-frequency, atmospheric pressure argon microdischarges

Kourtzanidis

2023

Two-dimensional fully coupled EM wave-plasma simulations are used to study the formation, early transient and quasi-steady state of the argon plasma excited by a two-dimensional discontinuous microstrip line. The electromagnetic waves that normally propagate in the microstrip transmission line, radiate and scatter at the position of the gap and the electric field is enhanced primarily at the corner of the gap. The microdischarge is preferentially formed at this position of the EM field hotspot and in low frequencies propagates on the dielectric surface, much like a microwave surface streamer. In longer times, diffusion dominates and the whole gap is filled with plasma of maximum density in the order of $10^{20}$ $m^{-3}$ while it occupies a volume larger than the gap. Mean electron temperatures range from 2.8 to 3.9 eV, while the plasma reaches a quasi-static regime in approximately 2 $\mu$ s having reconfigured the transmission and radiation patterns of the slitted microstrip line. The tunability of the microstrip due to plasma formation provides means for sustaining the discharge in a stable regime. For the same input EM power, the electron temperature increases with increasing excitation frequency while electron densities found to decrease. For the same wave frequency, a decrease of the electron densities with increasing gap is also found in addition to a restriction of the discharge expansion. Finally, thicker dielectrics result to higher electron densities and electron temperatures as well as absorbed power from the plasma. These findings are attributed to the dependence of absorbed EM power and skin depth on the EM wave angular frequency, the critical for shielding electron density as well as the restructuring of the S-parameters due to the changes in operational parameters.

“…Still, under atmospheric conditions, DBDs offer the simplest, more robust and highly modular design compared to other plasma sources while they can reach conversion rates higher than 30% [7,8]. In addition, DBDs can be easily arranged in a co-axial configuration and packed with catalysts towards packed bed DBD (PB-DBD) reactors [9,10], leveraging plasma-catalyst synergies. Coupling plasma reactors with catalysts present significant synergetic effects in multiple scales, that can further boost conversion efficiency [11,12].…”

Section: Introductionmentioning

confidence: 99%

“…Coupling plasma reactors with catalysts present significant synergetic effects in multiple scales, that can further boost conversion efficiency [11,12]. Concerning PB-DBDs, the influence on CO 2 conversion of packing and catalyst materials, gap and sphere size combination as well as overall reactor setup and flow rates has been extensively studied [10,[13][14][15][16][17]. The above studies are surely a non-exhaustive list of the expanding literature on plasma assisted CO 2 conversion in PB-DBDs, but demonstrate the increasing interest of the technology as well as the complexities of plasma-catalyst synergies.…”

Section: Introductionmentioning

confidence: 99%

Full cycle, self-consistent, two-dimensional analysis of a packed bed DBD reactor for plasma-assisted CO2 splitting: spatiotemporal inhomogeneous, glow to streamer to surface discharge transitions

Kourtzanidis

2023

We investigate the full-cycle operation of a coaxial Packed Bed Dielectric Barrier Discharge (PB-DBD) reactor operating in pure CO2. The reactor is packed with high permittivity dielectric rods and is analyzed with a two-dimensional (2D) self-consistent plasma model. We show that the PB-DBD operation is governed by both glow and volume/surface streamer discharges, forming alternatively and non-uniformly inside the gas volume. The presence and surface charging of the dielectric rods and dielectric layer is crucial for the initiation, propagation, annihillation and afterglow of these microdischarges. Our calculations show maximum electron and CO2 + densities in the order 1020 m-3 , an average discharge power of 353.42 W/m in the first cycle, microdischarge peak currents in the order of 50-400 A/m, total half-cycle plasma charge of around 6 μC/m. Dominant negative ions are found to be CO3 -. CO molecules and O atoms are mainly formed during the MDs development and the streamer-surface ionization waves. Molecular oxygen (O2) is preferentially formed during the glow, current-decaying and afterglow phase of each microdischarge. The spatially average reduced electric field inside the reactor lies in the 20-100 Td range. Each MD, presents distinct non-uniform and non-repeatable glow and volume/streamer discharges owed to the non-uniform surface charging processes which dictate the complex spatial distribution of produced neutral (and ion) species. These detailed results shed light on crucial, largely non-uniform plasma spatiotemporal characteristics that can help design efficient PB-DBD reactors for CO2 splitting and beyond, while emphasizing the important insights obtained by 2D simulations which can not be captured with 0D-global or 1D models.