Dry reforming of CH 4 process can convert greenhouse gases into high-value-added fuels and chemicals with its broad application prospects in environmental protection and renewable energy. Non-thermal plasma is considered an effective alternative method because it can activate CH 4 and CO 2 under low temperature and atmospheric pressure. This paper is aimed to optimize the plasma-assisted dry reforming of CH 4 process in a unipolar microsecond pulsed coaxial dielectric barrier discharge by investigating the effects of reactor structures. The results show that the conversions of reactants and the yields of syngas were significantly affected by the reactor structures. Specifically, a multi-stage or foil external electrode and negative polar discharge could promote CH 4 and CO 2 conversions, gas product yields, and energy conversion efficiencies. For different electrodes, the maximal conversions of CH 4 and CO 2 were 20.4% and 14.1%, with an energy conversion efficiency of 4.4% under our experimental conditions. Higher conversions, yields, and energy conversion efficiencies were obtained with lower power input when applying heat insulation measures. CH 4 conversion was promoted to 27.9% with a moderate energy conversion efficiency of 3.8%, but the conversion of CO 2 was only 12% when packing materials into the reactor. The results can provide specific guidance for designing plasma or plasma-catalytic dry reforming reactor.

Sustainable, renewable-energy-powered, and low-carbon-emission alternatives for the energy-intensive and extreme-process-conditions-demanding industrial Haber–Bosch ammonia synthesis are urgently needed to meet global net-zero emission targets. Plasma catalysis enables renewable-electricity-driven ammonia synthesis under mild conditions. To reveal unknown energy-efficient pathways for ammonia synthesis, here, we specify energy loss pathways and maximize the energy efficiency of the ammonia synthesis in atmospheric-pressure and low-temperature pulsed plasmas. The ammonia yield, energy efficiency, and process temperature are obtained under variable process parameters (i.e., the pulse voltage, pulse width, and gap distance) in a nanosecond pulse dielectric barrier discharge reactor. The ways to reduce energy losses for “power-to-chemical (= ammonia)” production including N2 vibrational excitation and relaxation are revealed by combining plasma optical emission spectroscopy with chemical reaction kinetics modeling. Multiparameter process optimization based on the Bayesian neural network model allows us to select the pulse waveforms, voltages, and discharge gaps to achieve high ammonia yields with a high energy efficiency and a low emission footprint.