(698d) DFT Analysis of Speciation and Stability of Surface-Bound Nitrogen Species Under N2 Plasma Exposure

Non-thermal plasma (NTP)-assisted catalysis has attracted growing attention as an alternative method for nitrogen (N₂) activation by combining reactive chemical environments induced by NTP with catalysts to drive chemical transformations at temperatures at which such reactions are thermally inaccessible.^1,2 Despite the substantial attention given to the plasma-catalytic conversion of N₂, the intermediates and mechanisms accessed when a catalytic surface is exposed to plasma-activated N₂ are not well understood. Plasma-enhanced N₂ adsorption on various metal surfaces at ambient temperature had been observed. Previous studies attribute this observation to the presence of atomic N that may cause surface distortion or electronic effect.³ However, the temperature at which species are observed is inconsistent with the assignment to chemisorbed N₂.⁴ Characterization of the species accessible under plasma exposure is key to leveraging plasma catalysis towards desired products. In this work, we use DFT models to compute the structures, vibrational signatures, and potential energy surfaces for the creation or decomposition of potential N-containing adsorbates at various facets of transition metal surfaces. We compare results with observations from polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS) of polycrystalline metals exposed to nitrogen plasma. Results reveal the generation of metastable nitrogen adsorbates inaccessible through thermal routes.