Methane, Propene and Toluene Oxidation by Plasma-Pd/γ-Al₂O₃ Hybrid Reactor: Investigation of a Synergetic Effect

The combination of a sub-microsecond pulsed dielectric barrier discharge with Pd/γ-Al₂O₃ catalyst was investigated for the oxidation of low concentration of methane, propene, and toluene in air at atmospheric pressure. The systematic comparison of the plasma-catalysis with the thermal-catalysis and the plasma-alone have been made for temperature window of 20–400 °C and energy deposition in the range 23–148 J L⁻¹. To emphasis the reactivity of plasma produced species on the activation of the catalyst, two reactor configurations were used [in-plasma catalysis (IPC), and post-plasma catalysis (PPC)]. Fourier transform infrared spectrometer was used to follow the VOCs conversion and to quantify the mineralized products. The plasma-catalyst combination leads to higher VOCs conversion and decreases the catalyst activation temperature in both IPC and PPC configurations. For hybrid system, the light-off temperature is always lower than those observed for catalytic oxidation. In addition, the formation of the by-products such as formaldehyde, formic acid, and ozone was reduced significantly. A significant synergetic effect of hybrid plasma-catalytic system is not really observed in the presence of CH₄ and C₃H₆. However, for C₇H₈ oxidation the synergetic effect was demonstrated at low temperature (<150 °C) for the IPC configuration.