Catalytic and Nitriding Competition of Nitrogen Atom on Graphene and Its Finite Rate Surface Chemistry Model

Gas-surface interactions during hypersonic atmospheric reentry remain incompletely understood, particularly with respect to the catalytic recombination and nitridation of nitrogen atoms on carbon-based thermal protection materials. In this study, reactive molecular dynamics (RMD) simulations were employed to investigate the temperature-dependent transition of dominant reaction pathways on graphene surfaces over the range of 900-4000 K. Below 1400 K, catalytic recombination dominates, and nitrogen atoms mainly contribute to heat transfer through Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) pathways. At intermediate temperatures (1400-2500 K), catalytic recombination and nitridation proceed concurrently, accompanied by progressive graphene decomposition. Above 2500 K, nitridation becomes dominant and results in substantial CN formation. A finite-rate surface chemistry model developed from the RMD data yields activation energies of 27.34 kJ/mol for E-R II and 48.24 kJ/mol for L-H recombination. By identifying plausible catalytic pathways for nitrogen atoms and clarifying the competition between catalysis and nitridation, this work extends the classical C-N reaction models of Park and Zeldovich-Anderson and provides a basis for correcting their tendency to overpredict nitridation rates while underpredicting catalytic reaction rates.