Plasma-catalytic hybrid reactor: Application to methane removal

• Plasma–catalyst oxidation of methane evidenced at low temperature.
• Plasma-catalytic system more selective for CO2 formation compared to only plasma system.
• Catalytic activity of Pd/Al2O3 significantly enhanced in presence of plasma.
• In-plasma catalysis configuration seems to be more efficient for methane oxidation compared to post-plasma catalysis.

Methane oxidation was investigated in a pulsed dielectric barrier discharge at atmospheric pressure coupled with Pd/Al2O3 catalysts. Comparison between plasma, catalytic, and plasma-catalysis (both in-plasma and post-plasma catalysis) systems were performed in the temperature range of 25–500 °C and specific input energy up to 148 J/L. For plasma-alone experiments, CH4 conversion reached a maximum of 67% and the main products obtained were CO, CO2, O3, and HNO3. The plasma catalytic treatment leads to an increase of the CH4 oxidation even at low temperature. It is evidenced that, compared to plasma alone, both Al2O3 and Pd/Al2O3 catalysts coupled plasma discharge increase the CH4 conversion. Moreover, for all plasma-catalytic systems, the CH4 conversion plots were shifted toward lower temperature as the specific input energy increases. Although the difference is low, the in-plasma catalysis configuration seems to be more efficient compared to post-plasma catalysis. In all cases, CH4 oxidation in presence of Pd/Al2O3 catalyst becomes more selective in CO2 formation than the reaction in plasma alone.

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