Reaction mechanism for the free-edge oxidation of soot by O2

A. Raj, G.R. da Silva, S.H. Chung
Combust. Flame, 159, pp. 3423-3436, (2012)

Reaction mechanism for the free-edge oxidation of soot by O2

Keywords

PAH, Soot, Oxidation, Kinetic mechanism, Density functional theory, Transition state theory

Abstract

​The reaction pathways for the oxidation by O2 of polycyclic aromatic hydrocarbons present in soot particles are investigated using density functional theory at B3LYP/6-311++G(d,p) level of theory. For this, pyrene radical (4-pyrenyl) is chosen as the model molecule, as most soot models present in the literature employ the reactions involving the conversion of 4-pyrenyl to 4-phenanthryl by O2 and OH to account for soot oxidation. Several routes for the formation of CO and CO2 are proposed. The addition of O2 on a radical site to form a peroxyl radical is found to be barrierless and exothermic with reaction energy of 188 kJ/mol. For the oxidation reaction to proceed further, three pathways are suggested, each of which involve the activation energies of 104, 167 and 115 kJ/mol relative to the peroxyl radical. The effect of the presence of H atom on a carbon atom neighboring the radical site on the energetics of carbon oxidation is assessed. Those intermediate species formed during oxidation with seven-membered rings or with a phenolic group are found to be highly stable. The rate constants evaluated using transition state theory in the temperature range of 300–3000 K for the reactions involved in the mechanism are provided.

Code

DOI: 10.1016/j.combustflame.2012.06.004

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