Understanding Effects of Operating Parameters on Plasma Catalytic Nitrogen-Methane Coupling Using Optical Emission Spectroscopy

Abstract

Non-thermal plasmas (NTPs) produce highly reactive chemical environments made up of electrons, ions, radicals, and vibrationally excited molecules. These reactive species, when combined with catalysts, can help drive thermodynamically unfavorable chemical reactions at low temperatures and atmospheric pressure. We are particularly 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. In order to effectively create these plasma catalytic systems, it is imperative that there is a fundamental understanding of the plasma-phase chemistry alone. While there have been many studies on nitrogen (N 2 ) and methane (CH 4 ) plasmas, there is limited understanding on how changing operating parameters (i.e. feed ratio of N 2 /CH 4 , plasma power, operating temperature) affect the plasma properties. In this work, we characterize the plasma using optical emission spectroscopy (OES) and analyze the products formed to understand the effects, if any, of varying plasma parameters on product formation. This is done by determining relevant thermodynamic information such as electron density, vibrational and rotational temperatures, as well as comparing the presence of key plasma species (C-N, C-H) to relevant products formed during nitrogen-methane coupling in plasma-alone and plasma catalytic reactions. Preliminary results show electron density increases with increasing methane content, corresponding to higher methane conversion due to increased electron activity in the plasma.