(335a) Elucidating Non-Thermal Plasma-Activated Carbon-Nitrogen Coupling on a Catalytic Surface from Methane and Nitrogen

From inelastic collisions between the energetic electrons and gas molecules, non-thermal plasma (NTP) produces reactive chemical environments (e.g., electrons, ions, radicals, and vibrationally-excited molecules) at temperatures where such species are thermally inaccessible. Integrating reactive NTP with heterogeneous catalysis has recently gained interest to enhance catalytic activities/selectivities and promote a novel chemical transformation that neither plasma nor catalysis could deliver individually. To better control plasma-catalyst coupling, it is important to understand the interaction between the NTP-activated species and a catalytic surface. In this work, we utilized a multi-modal spectroscopy tool combining polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS), optical emission spectroscopy (OES), and mass spectrometry (MS) to investigate the interaction between NTP-activated CH₄/N₂ species and model surfaces (Ni, Pd, Cu, Ag, Au, and SiO₂) for C-N coupling. To minimize the plasma-phase interaction between CH₄ and N₂, we introduce CH₄/N₂ feed gas sequentially: (1) CH₄-N₂ in sequence and (2) N₂-CH₄ in sequence. We show that different sequences lead to CN signatures in OES spectra corresponding to C-N coupled products forming on a catalytic surface. The effects of different surfaces on the nature of surface-adsorbed C-N coupled products are further investigated with ex-situ X-ray photoelectron spectroscopy (XPS) and liquid chromatography-mass spectrometry (LC-MS).