The surface interaction of a well-characterized time modulated radio frequency (RF) plasma jet with polystyrene, poly(methyl methacrylate) and poly(vinyl alcohol) as model polymers is investigated. The RF plasma jet shows fast polymer etching but mild chemical modification with a characteristic carbonate ester and NO formation on the etched surface. By varying the plasma treatment conditions including feed gas composition, environment gaseous composition, and treatment distance, we find that short lived species, especially atomic O for Ar/1% O 2 and 1% air plasma and OH for Ar/1% H 2 O plasma, play an essential role for polymer etching. For O 2 containing plasma, we find that atomic O initiates polymer etching and the etching depth mirrors the measured decay of O atoms in the gas phase as the nozzlesurface distance increases. The etching reaction probability of an O atom ranging from 10 −4 to 10 −3 is consistent with low pressure plasma research. We also find that adding O 2 and H 2 O simultaneously into Ar feed gas quenches polymer etching compared to adding them separately which suggests the reduction of O and OH density in Ar/O 2 /H 2 O plasma.

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Catalyst enhancement by atmospheric pressure plasma is a recently emerging field of research that embodies a complex system of reactive species and how they interact with surfaces. In this work we use an atmospheric pressure plasma jet integrated with a nickel on Al2O3/SiO2 support catalyst material to decompose methane gas by partial oxidation reaction. We use Fourier-transform Infrared spectroscopy analysis of the gas phase post reaction to measure the loss of methane and the production of CO, CO2, and H2O and diffuse reflectance Fourier-transform Infrared spectroscopy (DRIFTs) in situ analysis of the catalyst surface as a function of both catalyst temperature and plasma operating parameters. We find reduction of methane by both plasma alone, catalyst alone, and an increase when both plasma and catalyst were simultaneously used. The production of CO appears to be due primarily to the plasma source as it only appears above 2.5 W plasma dissipated power and decreases as catalyst temperature increases. CO2 production is enhanced by having the catalyst at high temperature and H2O production depends on both plasma power and temperature. Using DRIFTs we find that both heating and plasma treatment remove absorbed water on the surface of the catalyst. Plasma treatment alone however leads to the formation of CO and another IR spectral feature at 1590 cm−1, which may be attributed to carboxylate groups, bonded to the catalyst surface. These species exhibit a regime of plasma treatment where they are formed on the surface and where they are significantly removed from the catalyst surface. We see the formation of a new spectral feature at 995 cm−1 and discuss the behavior and possible origins of this feature. This research highlights the potential for plasma regeneration of catalyst materials as well as showing enhancement of the catalytic behavior under low temperature plasma treatment.

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To study mechanistic aspects of plasma-enhanced catalysis, methane is decomposed by a supported Ni catalyst assisted by an Ar/O2 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 O2 of the Ar/O2 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 CO2 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). CHn(n = 1, 2, 3) species on the catalyst surface were also studied by DRIFTS, and CHn destruction was found to correlate with C–O formation. In particular, the time-resolved CHn response showed a possible conversion process of CHn 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.