Investigation of hydrogen oxidation in supercritical H₂O/CO₂ mixtures using ReaxFF molecular dynamics simulation

Hydrogen oxidation kinetics in supercritical H₂O/CO₂ mixtures is a fundamental topic in supercritical water oxidation (SCWO) technology. A series of reactive molecular dynamics (ReaxFF-MD) simulations were performed to investigate hydrogen oxidation process in supercritical mixtures. The results showed that HO₂ and H₂O₂ radicals played key roles in the reaction kinetics. High concentration H₂O suppressed the production of OH radical and increased steric hindrance for effective collisions, exerting negative influence on hydrogen oxidation. The presence of CO₂ advanced the oxidation rate of hydrogen mainly through the elementary reaction CO₂ + H → CO + OH. It was found that high O₂ concentration promoted the oxidation of hydrogen and also affected the reaction induction time. The hydrogen reaction mechanisms under supercritical conditions were illustrated, showing different characteristics from those at atmospheric condition. The results will facilitate the development of continuum-scale kinetic models for accurate prediction of hydrogen oxidation behavior in supercritical systems.