Paper PS+SS-ThA10
Efforts towards Plasma-assisted Catalysis: Elucidating Gas-phase Energetics, Kinetics, and Surface Interactions

Thursday, October 24, 2019, 5:20 pm, Room B131

With increasing concern about environmental health and climate change, there is a greater need to investigate fundamental reactivity of pollutant species. Improving the effectiveness of substrates used in vehicular emissions abatement hinges on the ability to discern the contributions of gas-phase species in surface reactions. A fundamental understanding of interactions between plasma species is essential to characterizing complex plasma chemistry phenomena. Inductively-coupled N_XO_Y plasma systems were investigated to determine possible synergisms between precursor chemistry and gas-surface interface reactions with a variety of catalytic substrates (i.e., Pt substrates and zeolites). The impact of adding dilute amounts of water vapor to the gas feed was also systematically explored. Precursor chemistry was probed via gas-phase diagnostics; time-resolved optical emission data elucidated NO (g) and N₂(g) production kinetics from N_XO_Y source gases, whereas steady-state emission and absorbance data provide information regarding energy partitioning between rotational and vibrational degrees of freedom. The presence of micro-structured catalysts within the plasma significantly decreases excited N₂ vibrational temperature, suggesting these materials promote vibrational relaxation within the discharge. Our unique Imaging of Radicals Interacting with Surfaces (IRIS) allows us to probe the gas-surface interface and provides evidence of how plasma species synergistically interact with catalytic substrates. In addition to evaluating the spectroscopic characteristics of the discharge (N_XO_Y), we have assessed material morphology and chemical composition before and after plasma exposure. The porous network of zeolite substrates was maintained after prolonged plasma exposure, although surface etching of oxygen or N-doping occurred at different plasma operating conditions. This holistic experimental approach, combining gas-phase diagnostics, IRIS, and robust materials characterization will be essential to realizing the potential of plasma assisted catalysis for pollution remediation.