Nonthermal Plasma-Stimulated C-N Coupling from CH 4 and N 2 Depends on the Presence of Surface CH x and Plasma-Phase CN Species.

Formation of C-N containing compounds from plasma-catalytic coupling of CH 4 and N 2 over various transition metals (Ni, Pd, Cu, Ag, and Au) is investigated using a multimodal spectroscopic approach, combining polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS) and optical emission spectroscopy (OES). Through sequential experiments utilizing CH 4 and N 2 nonthermal plasmas, we minimize plasma-phase reactions and identify key intermediates for C-N coupling on metal surfaces. Results show that simultaneous CH 4 and N 2 exposure with plasma stimulation produces surface C-N species. However, N 2 -CH 4 sequential exposure does not lead to C-N species formation, while CH 4 -N 2 sequential exposure reveals the presence of CH x surface species and CN radical species as key precursors to C-N species formation. From further analysis using X-ray photoelectron spectroscopy and liquid chromatography-mass spectrometry, the influence of exposure conditions on the degree of nitrogen incorporation and the nature of C-N species formed were revealed. The work highlights the importance of surface chemistry and exposure conditions in surface C-N coupling with plasma stimulation.