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B, et al. (2018) Polycyclic aromatic hydrocarbons in pyrolysis of gasoline surrogates ( nheptane/ iso -octane/toluene). Proceedings of the Combustion Institute.

Detailed mechanisms of PAH growth involving methylene (CH2) were studied using accurate ab initio density functional theory B3LYP/6-311+G(d,p) calculations, as well as approximate QCISD(T,full)/6-311++G(3df,2pd) calculations. The PAH growth can be divided into five essential reaction steps, namely, addition C2H2 → intramolecular hydrogen migration → addition CH2 → cyclization → H-elimination. The aliphatic species of indene and 1H-phenalene are found in the pathways of PAH growth, which is in accord with the experimental results that reveal the formation of aliphatic species in flames. It was found that the simultaneous removal of two H atoms in one reaction step is feasible in PAH evolution, and this can reasonably interpret the absence of a H atom in the post-flame region. The corresponding rate coefficients at 1 atm were evaluated by using TST and RRKM theory by solving the master equations in the temperature range of 500-2500 K. The calculated branching ratios suggest that the pathways involving CH2 are competitive in PAH growth.

Thermal decompositions of polycyclic aromatic hydrocarbon (PAH) oxyradicals on various surface sites including five-membered ring, free-edge, zigzag, and armchair have been systematically investigated by using ab initio density functional theory B3LYP/6-311+G(d,p) basis set. The calculation based on Hückel theory indicates that PAHs (3H-cydopenta[a]anthracene oxyradical) with oxyradicals on a five-membered ring site have high chemical reactivity. The rate coefficients of PAH oxyradical decomposition were evaluated by using Rice-Ramsperger-Kassel-Marcus theory and solving the master equations in the temperature range of 1500-2500 K and the pressure range of 0.1-10 atm. The kinetic calculations revealed that the rate coefficients of PAH oxyradical decomposition are temperature-, pressure-, and surface site-dependent, and the oxyradical on a five-membered ring is easier to decompose than that on a six-membered ring. Four-membered rings were found in decomposition of the five-membered ring, and a new reaction channel of PAH evolution involving four-membered rings is recommended.