Tunable dry reforming of methane in a non-catalytic nanosecond-pulsed plasma reactor

Nanosecond-pulsed-discharge (NPD) plasma can effectively promote dry reforming of methane (DRM) to convert feedstock mixtures of methane (CH₄) and carbon dioxide (CO₂), typical of biogas streams, into syngas and C₂ species through sharp energy pulses that can be regulated in amplitude and frequency to optimize energy delivery. Both continuous pulsing and grouped pulses (bursts) drive reactants' conversion by controlling the dissipated power in the discharge. The syngas composition at the outlet can be linearly tuned via the feed gas ratio, as CH₄ coupling reactions and CO₂ dissociation complement the DRM reaction, maintaining the correlation. CH₄ and CO₂ conversions follow a saturation trend with specific energy input (SEI), with maximum values of 83 % and 75 %, respectively. Nonetheless, the energy conversion efficiency (ECE) shows a non-monotonic trend with SEI, likely due to memory effects at high pulse frequencies, which promote gas breakdown at low energy. The latter conditions promote 47 % conversion of discharge energy into chemical energy, whereas higher reactants’ conversions are attained at a lower efficiency (i.e., 27 %). The NPD plasma DRM process produces H₂ with negative CO₂ emissions when powered by wind and solar energy (i.e., −9 kg_CO2 kg_H2⁻¹ and −7 kg_CO2 kg_H2⁻¹, respectively), in contrast to the state-of-the-art steam methane reforming, which emits about 10 kg_CO2 kg_H2⁻¹.