Mechanism of CO 2 -formation promotion by Au in plasma-catalytic oxidation of CH 4 over Au/γ-Al 2 O 3 at room temperature

The plasma-catalytic oxidation of methane (CH ) is a potential reaction for controlling CH emissions at low temperatures. However, the mechanism of the CH plasma-catalytic oxidation is still unknown, which inhibits the further optimization of the oxidation process. Herein, a CH oxidation mechanism over an Au/γ-Al O catalyst was proposed based on our experimental findings. CH is first decomposed to CH and H by the discharge, and a fraction of the CH is adsorbed on γ-Al O surface for deep oxidation. The oxygen atoms produced by the discharge react with H O to yield surface reactive OH groups that contribute to the CH oxidation. Oxygen atoms also promote the release of H O from the surfaces of the γ-Al O and Au/γ-Al O and especially promote CO desorption from the surface of the Au/γ-Al O . When γ-Al O was used as the catalyst, the CO selectivity was only 15 vol.%, and the CH conversion decreased after 7 h of plasma-catalytic oxidation. In contrast, when Au/γ-Al O was used, the CO selectivity was 80 vol.%, long-term CH conversion was obtained. Experimental results revealed that Au was beneficial for the decomposition of surface carbonate species into gaseous CO , whereas the carbonate species accumulated on γ-Al O when Au was absent.