Probing the role of a non-thermal plasma (NTP) in the hybrid NTP-catalytic oxidation of CH4

Three recurring hypothesis are often used to explain the effect of non-thermal plasma (NTP) on NTP-catalytic hybrid reactions, namely, modification or heating of the catalyst or the ability of plasma produced species to open up new reaction pathways. By directly monitoring the catalyst by X-ray absorption fine structure (XAFS) coupled with end of pipe mass spectrometry the NTP assisted CH4 oxidation over Pd/Al2O3 was investigated. This in situ study has shown that the catalyst did not undergo any significant structural changes under NTP conditions. However, the NTP did lead to the Pd nanoparticle temperature increasing but this temperature rise was insufficient to activate the thermal CH4 oxidation reaction. The contribution of a lower activation barrier alternative reaction pathway involving the formation of CH3(g) via electron impact reactions is proposed.