Abstract: A non-thermal atmospheric pressure plasma by dielectric barrier discharge was used to study the direct oxidation of methane to hydrogen peroxide. The effects of the structure of plasma reactors, as well as the ratio of CH4 to O2, were investigated. It is observed that, at room temperature and atmospheric pressure, methane and oxygen can be directly converted into hydrogen peroxide with high yield. When a double dielectric barrier discharge (DDBD) plasma reactor is fed with a CH4/O2 mixture containing 50 vol% at a total flow rate of 50ml min-1 (CH4+O2), it generates H2O2 with 29.2% yield and the H2O2 formation efficiency is estimated to be 221.6 g per m3 CH4/O2 mixture. The high H2O2 yield obtained by CH4/O2 plasma method may be attributed to the nonequilibrium property of non-thermal plasma that the electron energy inside the conductive filament corresponds to a few eV, while the gas temperature stays close the temperature of the background gas. As a result, the energetic electrons in the plasma region collide with molecules and atoms of the CH4/O2 mixture and generate excited species, atoms, as well as other molecular fragments that initiate the ensuing chemical reactions and produce H2O2, while the thermal decomposition of H2O2 is neglectable because of low gas temperature.

Key words: Hydrogen peroxide, Dielectric barrier discharge, Plasma, Methane