Plasma assisted hydrogen peroxide synthesis

Hydrogen Peroxide (H2O2) is an important chemical for many industrial processes. However, the current industrial production of H2O2 by Anthraquinone Auto-oxidation is considered as non-environmentally friendly, which stirs the interest of looking for more sustainable synthesis methods.
Plasmas are an alternative platform for a decentralized H2O2 production that have instant on/off times, and in principle, can activate molecules such as oxygen and water without the assistance of a catalyst. Plasma configurations as dielectric barrier discharges (DBDs) and gliding arc (GA) discharges are the most studied for synthesis of H2O2. Figure 1a) presents a comparison of energy yield and production rate of H2O2 between different configurations using H2O, O2 or H2 mixtures as reactants. 81 g/kWh of energy yield was achieved using water spray in a Gliding Arc configuration; authors also observed that the energy yields increased with the flow rate of the water sprayed into the plasma zone.1 In turn, Liu and co-workers concluded that plasma-water interface phenomena controlled the H2O2 synthesis at atmospheric pressure. These phenomena include sputtering, electric field induced ion emission, and evaporation.2
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Microwave plasmas are less commonly explored for H2O2 production, even if they are interesting since they can handle higher gas flow rates, do not require electrodes and have shown potential for efficient use of energy in comparison with other plasma methods. Nevertheless, the direct combination of H2 and O2 at high temperatures usually present in microwave plasmas (up to 3000K) are a concern for safety reasons and thermal stability of hydrogen peroxide. In this sense, in line with a decentralized production concept, we aim to use directly water in combination with oxygen to produce H2O2. The interface phenomena between water and plasma are the main subject of study (Figure 1b), along with the mixing regime, spray conditions and flow pulses which have shown to affect both, the efficiency and yield of the reaction. Thus, we aim to balancing the increased contact of plasmas and water together with the reaction control inside the aqueous phase.