Experimental and theoretical evidence for the temperature-determined evolution of PAH functional groups

Elucidating the chemical evolution of various functional groups in polycyclic aromatic hydrocarbons (PAH) and soot aids in understanding soot formation chemistry. In this work, the chemical evolution of various functional groups, including aromatic C -H, aliphatic C -H, C = O, C -OH and C -O -C bonds, was experimentally investigated online, rather than with offline diagnostics . Oxidation was performed in a jet-stirred reactor (JSR), fueled with benzene/C 2 H 2 /air/N 2 and benzene/phenol/C 2 H 2 /N 2 for a temperature range of 600-1400 K. Kinetic modelling, including ab initio quantum chemistry calculations, reaction rate coefficient calculations and JSR simulations, were conducted to interpret the experimental data and the evolutionary chemistry of the various functional groups. Results show that the formation of functional groups on PAH and oxygenated PAH (OPAH) are highly sensitive to temperature. Aliphatic C -H bonds survive mainly in the form of C -CH 2 -C, C -CH 2 -CH 2 -C or C equivalent to CH functional groups above 1200 K, and exist in the CH = CH 2 functional group below 1000 K. For the OPAH, the C -O -C functional group presents stronger thermal stability than C -OH and C = O functional groups. Simulation results indicate that HACA-like pathway (hydrogen abstraction carbon addition), in which C 2 H 2 attacks the O atom, followed by cyclization and H-atom elimination reactions, qualitatively describe the formation of OPAH with the C -O-C functional group at different temperatures. The addition reaction involving PAH radical and C 2 H 4 / C 2 H 3 captures the evolution of PAH with the CH = CH 2 functional group, but fails to explain the formation of C -CH 2 -C and C -CH 2 -CH 2 -C functional groups. (c) 2020 Published by Elsevier Inc. on behalf of The Combustion Institute.

Automated summary

The study investigates the chemical evolution of various functional groups in PAH and soot, revealing their sensitivity to temperature and different reaction pathways at different temperatures. Kinetic modeling and experimental data interpretation suggest a qualitative description of the formation of OPAH with the C-O-C functional group through the HACA-like pathway, while the evolution of PAH with different functional groups is captured through different reactions involving PAH radicals and C2H4/C2H3.