Optical Emission Spectroscopy of N₂/CH₄ Plasmas for Plasma Catalytic Methane Coupling

Non-thermal plasmas (NTPs) can produce reactive chemical environments including electrons, ions, radicals, and vibrationally excited molecules. The integration of a catalyst with reactive NTPs can drive thermodynamically unfavorable chemical transformation at low temperatures and pressures. In particular, we are interested in the direct coupling of light hydrocarbons (e.g. methane) and nitrogen to produce value-added liquid chemicals (e.g. pyrrole and pyridine) in a plasma-assisted catalytic process. To design effective catalysts and plasma-catalytic systems requires comprehensive understanding of the plasma-phase chemistry alone, including thorough characterization of plasma-phase properties. While there have been many studies on nitrogen (N₂) and methane (CH₄) plasmas, there is limited understanding on how operating parameters (i.e. feed N₂/CH₄ gas ratio, plasma power) affect the plasma properties. In this work, we vary different plasma parameters and optically characterize the plasma using optical emission spectroscopy (OES) to determine relevant thermodynamic information such as the electron temperature and electron density to better understand their effects, if any, on product formation during methane coupling.