Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 143, Issue 31, Pages 12212-12219Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.1c05030
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Funding
- National Research Foundation (NRF), Prime Minister's Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) program
- EPSRC [EP/R029369/1]
- ARCHER
- Johnson Matthey
- Alexander von Humboldt Foundation
- ERC Consolidator Grant AMSEL [682144]
- European FET-OPEN project SPRING [863098]
- EPSRC [EP/R029369/1] Funding Source: UKRI
- European Research Council (ERC) [682144] Funding Source: European Research Council (ERC)
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Evidence of a reactive pi-diradical aromatic soot precursor imaged using non-contact atomic force microscopy has been shown, which can undergo barrierless chain reactions to form thermally stable aromatic rim-linked hydrocarbons under flame conditions. Quantum molecular dynamics simulations demonstrate physical condensation of aromatics that survive for tens of picoseconds, providing a rapid, thermally stable chain reaction toward soot nanoparticle formation.
Soot emitted from incomplete combustion of hydrocarbon fuels contributes to global warming and causes human disease. The mechanism by which soot nanoparticles form within hydrocarbon flames is still an unsolved problem in combustion science. Mechanisms proposed to date involving purely chemical growth are limited by slow reaction rates, whereas mechanisms relying on solely physical interactions between molecules are limited by weak intermolecular interactions that are unstable at flame temperatures. Here, we show evidence for a reactive pi-diradical aromatic soot precursor imaged using non-contact atomic force microscopy. Localization of p-electrons on non-hexagonal rings was found to allow for Kekule aromatic soot precursors to possess a triplet diradical ground state. Barrierless chain reactions are shown between these reactive sites, which provide thermally stable aromatic rim-linked hydrocarbons under flame conditions. Quantum molecular dynamics simulations demonstrate physical condensation of aromatics that survive for tens of picoseconds. Bound internal rotors then enable the reactive sites to find each other and become chemically cross-linked before dissociation. These species provide a rapid, thermally stable chain reaction toward soot nanoparticle formation and could provide molecular targets for limiting the emission of these toxic combustion products.
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