Catalyst-free activation of CH4 and air into platform chemicals and H2 using parametrized nanosecond pulsed plasma

The CH4 valorization process has attracted enormous research attention in recent years because of its essential role in carbon-based chemical synthesis and renewable energy production. Herein, we report a promising plasma approach for the catalyst-free partial oxidation of CH4 into hydrogen and value-added oxygenates (e.g., alcohol, acetic acid, and aldehydes) using a parameterized dielectric barrier discharge, achieving the maximum H2 selectivity (46.3 %) and total liquid selectivity (76.8 %) under different operating conditions. Experimental results show that the ratios of air and Ar are the main factors to control oxidation depth and the selectivity of liquids. The pulsed parameters determine the average discharge power and electron-induced exaction process, simultaneously affecting the reactant conversion and the gaseous/aqueous product distribution. It is noted that the proper CH4/air/Ar ratio would greatly improve the energy efficiency of H2 (476.5 mmol/kW h) and CH3OH (503.6 mmol/kW h), the H2O2 addition would significantly promote the CH3OH selectivity (39.1%). Compre-hensive electrical and optical diagnostics reveal that the regulation of pulse rising and falling times dominates the transient oxidizing specie generation and energy-transfer process by tuning discharge characteristics, and the possible reaction mechanism is proposed. This work provides new insights into the regulating strategy and contribution of process parameter for optimizing the selective CH4 conversion to renewable energy and chemicals.

Automated summary

This study reports a promising plasma approach for the catalysis-free partial oxidation of CH4 to produce hydrogen and value-added oxygenates. The ratios of air and Ar are found to be the main factors in controlling oxidation depth and liquid selectivity. The pulsed parameters also affect the reactant conversion and product distribution. The proper CH4/air/Ar ratio significantly improves the energy efficiency and H2O2 addition promotes CH3OH selectivity.