Formation mechanism of polycyclic aromatic hydrocarbons in benzene combustion: Quantum chemical molecular dynamics simulations

Biswajit Saha, Stephan Irle, Keiji Morokuma

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Abstract

High temperature quantum chemical molecular dynamics simulations on the polycyclic aromatic hydrocarbon (PAH) formation during combustion of benzene were performed using the density-functional tight-binding (DFTB) method. Systems with varying H/C of 0.8, 0.6, 0.4, and 0.2 and temperatures of Tn =2500 K and Tn =3000 K were employed for the study of the PAH formation and growth mechanism, and trajectories were analyzed by recording average C:H compositions, common elementary reactions and molecular species, ring count, and other characteristic quantities as functions of time. We found that at H/C=0.8 mostly short polyacetylenic hydrocarbons were formed, and no significant PAH growth was found. At lower H/C ratio, longer polyacetylenic chains started to form and new five- and six-membered rings were created due to chain entanglement. Significant PAH growth forming only pericondensed PAHs was observed at lower H/C ratios of 0.4 and 0.2. In addition, smaller hydrocarbon species, such as C2 H2, C2 H, and C 2, are constantly produced by fragmentation of hydrocarbons (unimolecular reactions) and remain common species, although they are simultaneously consumed by the H-abstraction- C2 H2 -addition growth mechanism. Hydrogen is found to have a clear inhibitive effect on PAH and carbon cluster growth in general, in agreement with recent experimental observations.

Original languageEnglish
Article number224303
JournalJournal of Chemical Physics
Volume132
Issue number22
DOIs
StatePublished - Jun 14 2010
Externally publishedYes

Funding

B.S. acknowledges the Fukui Institute for Fundamental Chemistry for Fukui Institute Fellowship and S.I. acknowledges support from the Program for Improvement of Research Environment for Young Researchers from Special Coordination Funds for Promoting Science and Technology (SCF) commissioned by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. This work was in part supported by a CREST (Core Research for Evolutional Science and Technology) grant in the Area of High Performance Computing for Multiscale and Multiphysics Phenomena from the Japan Science and Technology Agency (JST). Computer resources made available at the Academic Center for Computing and Media Studies (ACCMS) at Kyoto University as well as at the Research Center for Computational Science (RCCS) at the Institute for Molecular Science (IMS) are acknowledged.

FundersFunder number
Fukui Institute for Fundamental Chemistry for Fukui Institute
Special Coordination Funds for Promoting Science and Technology
Saskatoon Community Foundation
Ministry of Education, Culture, Sports, Science and Technology
Japan Science and Technology Agency
Core Research for Evolutional Science and Technology

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