Pyrolysis and oxidation of benzene and cyclopentadiene by NO: a ReaxFF molecular dynamics study.

Benzene (CH) and 1,3-cyclopentadiene (c-CH) are critical intermediate species in the combustion of fossil fuel and the formation of polycyclic aromatic hydrocarbons (PAHs). This study investigates the underlying mechanisms of pyrolysis and oxidation of CH and c-CH in the presence of O, NO and NO, respectively, under combustion conditions ReaxFF molecular dynamics simulations. The size growth in the pyrolysis system is accompanied by an amorphous nature as well as an increase in the C/H ratio. In the oxidation sytems, NO is the most effective in the oxidation of both CH and c-CH, followed by NO and O. In the presence of NO, O and N radicals generated in the high-temperature decomposition reactions of NO and NO are actively involved in the addition and H-abstraction reactions of CH and c-CH. Remarkably, the decomposition of NO dramatically increases the number of O radicals in the system, which significantly accelerates the ring-opening of CH and c-CH by O-addition and forms linear-CHO and CHO species, respectively. Afterwards, the formation of -CH- by H-transfer plays an essential role in the decomposition of linear-CHO and -CHO. Reaction pathways of O and N radicals with CH and c-CH are reported in detail. The O and N-addition of CH facilitate the decomposition to resonance-stabilized cyclopentadienyl radicals after the restructuring of the C-C bond.