Non‐oxidative methane conversion in diffuse, filamentary, and spark regimes of nanosecond repetitively pulsed discharge with negative polarity

Abstract

Methane conversion for higher hydrocarbons was carried out in the diffuse, filamentary, and spark regimes of nanosecond repetitively pulsed discharge with negative polarity in a pin‐to‐plate reactor. The diffuse discharge was characterized as a regime with low‐plasma energy, and only trace hydrogen and C2H6 were found in this regime. In filamentary regime, the conversion rate reached 2.2–7.6% with energy conversion efficiency (ECE) of 8.8–12.7%. Meanwhile the selectivity of C2H6, C2H4, C2H2, and C3 were 24.3–18.6%, 9.3–7%, 5.6–7.3%, and 0–5%, respectively. As for the spark regime, C2H2 became the main hydrocarbon product with the selectivity of 12.8%, conversion rate of 44.7–74.4% and ECE of 12.3%. Electrical measurements and ICCD photographs showed that the short pulse could prevent the streamer turning into spark discharge, and thus realize smooth transitions among each regime. Optical emission spectroscopy was used to investigate the plasma chemistry in each regime. It found that the highest spectral line, gas temperature, and electron density varied in these regimes. These results suggested that, comparing with electron impact reactions, the thermal chemistry became more and more important as the plasma energy increased.

Sustainable nitrogen fixation with nanosecond pulsed spark discharges: insights into free-radical-chain reactions

“…55 The H α (n = 3 → n = 2, 656.3 nm) is also detected. 39 Typical atomic Fe spectral lines (4p 5 D°→ 4s 5 F) and many Fe + spectral lines can also be found, 56 even though the Fe + spectral lines are feeble. The spectra of the diatomic molecule are detected, including the N 2 second positive system (SPS) N 2 (C 3 Π μ → B 3 Π g , ν′-ν″) and the N 2 + first negative systems (FNS) N 2 + (B 2 Σ μ + → X 2 Σ g + , 0-0, 391.4 nm), 57,58 but the γ bands of NO (A 2 Σ + → X 2 Π, ν′-ν″) are not observed.…”

“…17 In recent years, various plasma discharge modes have been studied for NH 3 synthesis, including transient spark discharge [18][19][20][21][22][23][24][25] and gliding arc discharge [26][27][28] plasmas, which are attractive for their reasonable energy efficiency (the best energy efficiency reported to be ∼32 kW h kg −1 ) and the ability to be used along with the common electrocatalytic processes, 6,15,16 though the energy efficiency is still inferior to the H-B process. 2,18 The transient spark discharge is usually triggered by a nanosecond repetitive pulse (NRP) power source [29][30][31][32][33][34][35][36][37][38][39][40] to effectively restrain the spark-to-arc transition by the short pulse voltage. From an economic point of view, the transient spark discharge device is compact in size, low in cost, and easy to scale up.…”

Plasma‐water‐based nitrogen fixation: Status, mechanisms, and opportunities

“…The introduction of UV light into the system shown in Figure 2b causes the synthesis rate of NO 2 − and NH 4 + to increase about three times and two times, respectively, while the synthesis rate of NO 3 − only increases in about 1.3 times. [ 20,21 ] Temperature control and stirring mechanisms are also possible in this system. Its optimal operating temperature is around 40°C; at this temperature, the nitrogen fixation rate is the highest, the NO x formation rate is the highest, and the by‐products are low.…”

“…times. [20,21] Temperature control and stirring mechanisms are also possible in this system. Its optimal operating temperature is around 40°C; at this temperature, the nitrogen fixation rate is the highest, the NO x formation rate is the highest, and the by-products are low.…”

Numerical investigation on the heterogeneous pulsed dielectric barrier discharge plasma catalysis for CO2 hydrogenation at atmospheric pressure: Effects of Ni and Cu catalysts on the selectivity conversions to CH4 and CH3OH

“…[13,14] Pulsed dielectric barrier discharge (DBD) can produce abundant active species, including energetic electrons, excited-state species, and radicals, at atmospheric pressure and form large-volume homogenous nonequilibrium plasma. [15,16] Combining gas phase plasma reactions and the catalyst surface reactions, the synergistic effect of heterogeneous pulsed DBD plasma catalysis is an emerging alternative to the conventional catalytic route. [17] In our previous research, [18] we have developed a plasma catalytic system coupled pulsed DBD plasma with Ni-Fe bimetallic catalyst and achieved CO 2 conversion of 67.5% and CH 4 selectivity of 99% as well as the energy efficiency of 57 823 μg/kJ.…”