Mechanistic aspects of plasma-enhanced catalytic methane decomposition by time-resolved <i>operando</i> diffuse reflectance infrared Fourier transform spectroscopy
Shiqiang Zhang, Yueming Li, A Knoll, G. S. Oehrlein
Abstract
Abstract To study mechanistic aspects of plasma-enhanced catalysis, methane is decomposed by a supported Ni catalyst assisted by an Ar/O 2 atmospheric pressure plasma jet (APPJ). The time-resolved surface response of the Ni catalyst is investigated by operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) using various experimental settings. Catalyst temperatures of room temperature and 500 °C and nozzle-catalyst surface distances of 3, 5 and 8 mm were examined, and the amount of O 2 of the Ar/O 2 gas mixture flowing through the APPJ was either 0 or 0.5%. A synergistic effect of surface bonded C–O was observed during the exposure of the Ni catalyst to the APPJ for low oxygen operating conditions (pure Ar jet). Surface bonded C–O formed only when there was plasma present and the C–O signal was enhanced for higher catalyst temperature. When the supported Ni catalyst was subjected to the plasma-generated particle fluxes using highly oxidizing conditions, the presence of surface bonded C–O was suppressed. The plasma-catalytic CO and CO 2 production in the gas phase measured downstream mirrored the surface behavior of C–O bonds when the plasma source operating condition was changed from a low oxygen portion to a high oxygen portion at high catalyst temperature (500 °C). CH n ( n = 1, 2, 3) species on the catalyst surface were also studied by DRIFTS, and CH n destruction was found to correlate with C–O formation. In particular, the time-resolved CH n response showed a possible conversion process of CH n to C–O when the Ni catalyst was exposed to the plasma source. This finding may indicate a plasma-mediated regeneration of the catalyst by plasma-catalyst surface interactions.