Paper PS1-WeM12
Examining Plasma-Surface Interactions During Plasma Catalytic Removal of Atmospheric Pollutants

Wednesday, October 22, 2008, 11:40 am, Room 304

Nitric oxide (NO) and sulfur dioxide (SO₂) are atmospheric pollutants that are produced from engine exhaust. Improvement in catalytic treatment of exhaust gases is therefore necessary to reduce these emissions. We are using plasma-catalytic processes to aid in the removal of pollutants from exhaust gases. An understanding of the fundamental chemical gas-phase and gas-surface processes is required to address this issue. With our imaging of radicals interacting with surfaces (IRIS) technique, we can simultaneously examine the gas-phase, perform surface analyses, and probe the gas-surface interface. IRIS combines laser-induced fluorescence and molecular beam techniques, thus we can probe a variety of important atmospheric species such as NO, SO₂, OH, CH, and CN. We have used IRIS to address the fundamental issue of NO and SO₂ removal by measuring relative gas-phase densities and by examining the steady-state surface reactivity of plasma-generated species on catalytic surfaces. For example, gas phase densities for NO demonstrate a significant decrease in NO at higher applied rf powers and when additives such as H₂O and CH₄ are added to the system. Water has also been added to the gas mixtures containing NO and SO₂ to monitor the effect of OH production in these processes. Comparison of surface interaction data shows that NO scatters substantially whereas OH has a higher surface reaction probability. Substrates used include silicon wafers and a variety of catalytic surfaces such as Pt and Au. Additional optical emission spectroscopy and mass spectrometry data will also be presented on all of these systems. Preliminary IRIS data on CH and CN will also be included for comparison to NO, OH, and SO₂.