A ReaxFF molecular dynamics study of polycyclic aromatic hydrocarbon oxidation assisted by nitrogen oxides

Fossil fuel-derived soot poses a persistent problem. A joint reduction is conducted via the reaction between NO x and soot. The underlying reaction mechanisms of large polycyclic aromatic hydrocarbons (PAHs), as well as the interactions between O-2, NO and NO2, have been extensively investigated by ReaxFF molecular dynamics simulations for the first time. The pyrolysis and oxidation of coronene are conducted at 2500 K and 50 atm. Coronene in the pyrolysis system first experiences dehydrogenation reactions and subsequently undergoes recombination reactions, leading to the formation of large PAHs. Among the three oxidizers, NO2 is the strongest in coronene oxidation, followed by NO and O-2. Meanwhile, the O radical is identified as the key species for PAH oxidation. In the presence of O-2, the formation of O radicals requires the assistance of H radicals that are formed by the dehydrogenation of PAHs, which retards the oxidation process. In the presence of NO, O radicals can be directly formed via reactions of NO -> N+O and N + NO reversible arrow N-2 + O. NO2 first undergoes a decomposition reaction: NO2 -> NO + O, followed by NO decomposition. O-addition and N-addition, as well as subsequent fragmentation reactions including the generation of COx and (H)CN are important routes in PAH oxidation. Furthermore, compared to NO, NO2 provides more O radicals that significantly accelerate PAH oxidation. This study provides fundamental insight into PAH oxidation that may help to design strategies to inhibit soot and NOx emissions at the source. (c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

In this study, the reaction mechanisms of large polycyclic aromatic hydrocarbons (PAHs) and the interactions between O-2, NO, and NO2 were investigated using ReaxFF molecular dynamics simulations. It was found that the O radical is the key species for PAH oxidation and that NO2 is a stronger oxidizer compared to NO and O-2, significantly accelerating PAH oxidation. This research provides fundamental insights for designing strategies to inhibit soot and NOx emissions at the source.