Hydrogen production by the steam reforming and partial oxidation of methane under the dielectric barrier discharge

The steam reforming and partial oxidation of methane to produce hydrogen under dielectric barrier discharge were conducted in the CH₄-O₂-N₂-H₂O reaction system; the effects of H₂O/CH₄ molar ratio, O₂/N₂ molar ratio, total gas flow, discharge voltage and discharge frequency on the hydrogen production were investigated and the reaction mechanism was analyzed on the basis of the in-situ diagnostic emission spectroscopy. The results indicate that the conversion of methane and the yield of hydrogen increase with the increase of H₂O/CH₄ molar ratio, O₂/N₂ molar ratio, and discharge voltage, but decrease with the increase of the total gas flow rate and show an volcano-shape trend with the increase of discharge frequency (peaked at 9.8 kHz). Under the conditions with an H₂O/CH₄ molar ratio of 1.82, O₂/N₂ molar ratio of 2.1, total flow rate of 136 mL/min, discharge voltage of 18.6 kV and discharge frequency of 9.8 kHz, in particular, the conversion of methane and the yield of hydrogen reach 47.45% and 21.33%, respectively. During the reaction, methane and water vapor may dissociate by the action of high energy electrons to generate CH_x ·, H·, OH·, O· and other free radicals and hydrogen is then produced through the collision between the free radicals. H· may come from the electronic dissociation of CH₄ as well as the dissociation of OH· formed primarily from the water vapor dissociation. The partial oxidation of methane is mainly manifested by the oxidation of CH₂· with O·, where O· is produced by the electronic dissociation of O₂ as well as the further dissociation of OH·.