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.