Structural effects on the oxidation of soot particles by O2: Experimental and theoretical study

Handle URI:
http://hdl.handle.net/10754/562929
Title:
Structural effects on the oxidation of soot particles by O2: Experimental and theoretical study
Authors:
Raj, Abhijeet; Yang, Seung Yeon ( 0000-0003-4512-8713 ) ; Cha, Dong Kyu; Tayouo Djinsu, Russell; Chung, Suk-Ho ( 0000-0001-8782-312X )
Abstract:
Soot particles are composed of polycyclic aromatic hydrocarbons (PAHs), which have either planar or curved structures. The oxidation behaviors of soot particles differ depending on their structures, arrangement of PAHs, and the type of surface functional groups. The oxidation rate of curved PAHs in soot is thought to be higher than that of planar ones. To understand the role that PAH structure plays in soot reactivity towards O2, experimental studies are conducted on two types of commercially produced soot, Printex-U and Fullerene soot, using high resolution transmission electron microscopy, electron energy loss spectroscopy, thermo-gravimetric analysis and elemental analysis. The relative concentrations of active sites, oxygenated functional groups, aliphatics and aromatics present in soots are evaluated. The activation energies for soot oxidation at different conversion levels are determined. The average activation energies of the two soots are found to differ by 26kJ/mol. To understand the reason for this difference, quantum calculations using density functional (B3LYP) and Hartree-Fock theories are conducted to study the reaction pathways of the oxidation by O2 of planar and curved PAHs using 4-pyrenyl and 1-corannulenyl as their model molecules, respectively. The energetically preferred channels for curved PAH oxidation differ from the planar one. The addition of O2 on a radical site of a six-membered ring to form a peroxyl radical is found to be barrierless for both the model PAHs. For peroxyl decomposition, three pathways are suggested, each of which involve the activation energies of 108, 170 and 121kJ/mol to form stable molecules in the case of planar PAH, and 94, 155 and 125kJ/mol in the case of curved PAH. During the oxidation of a five-membered ring, to form stable molecules, the activation energies of 90kJ/mol for the curved PAH and 169kJ/mol for the planar PAH relative to the energy of the peroxyl radical are required. The low activation barriers of preferred pathways for the oxidation of six and five-membered rings present on curved PAH (as compared to the planar one) explain and support its experimentally observed high reactivity. © 2013 The Combustion Institute..
KAUST Department:
Clean Combustion Research Center; Advanced Nanofabrication, Imaging and Characterization Core Lab; Water Desalination and Reuse Research Center (WDRC); Physical Sciences and Engineering (PSE) Division; Mechanical Engineering Program; Core Labs; Combustion and Laser Diagnostics Laboratory
Publisher:
Elsevier BV
Journal:
Combustion and Flame
Issue Date:
Sep-2013
DOI:
10.1016/j.combustflame.2013.03.010
Type:
Article
ISSN:
00102180
Sponsors:
This work was supported by Saudi Aramco through KAUST CCRC.
Appears in Collections:
Articles; Advanced Nanofabrication, Imaging and Characterization Core Lab; Physical Sciences and Engineering (PSE) Division; Mechanical Engineering Program; Clean Combustion Research Center; Water Desalination and Reuse Research Center (WDRC)

Full metadata record

DC FieldValue Language
dc.contributor.authorRaj, Abhijeeten
dc.contributor.authorYang, Seung Yeonen
dc.contributor.authorCha, Dong Kyuen
dc.contributor.authorTayouo Djinsu, Russellen
dc.contributor.authorChung, Suk-Hoen
dc.date.accessioned2015-08-03T11:15:54Zen
dc.date.available2015-08-03T11:15:54Zen
dc.date.issued2013-09en
dc.identifier.issn00102180en
dc.identifier.doi10.1016/j.combustflame.2013.03.010en
dc.identifier.urihttp://hdl.handle.net/10754/562929en
dc.description.abstractSoot particles are composed of polycyclic aromatic hydrocarbons (PAHs), which have either planar or curved structures. The oxidation behaviors of soot particles differ depending on their structures, arrangement of PAHs, and the type of surface functional groups. The oxidation rate of curved PAHs in soot is thought to be higher than that of planar ones. To understand the role that PAH structure plays in soot reactivity towards O2, experimental studies are conducted on two types of commercially produced soot, Printex-U and Fullerene soot, using high resolution transmission electron microscopy, electron energy loss spectroscopy, thermo-gravimetric analysis and elemental analysis. The relative concentrations of active sites, oxygenated functional groups, aliphatics and aromatics present in soots are evaluated. The activation energies for soot oxidation at different conversion levels are determined. The average activation energies of the two soots are found to differ by 26kJ/mol. To understand the reason for this difference, quantum calculations using density functional (B3LYP) and Hartree-Fock theories are conducted to study the reaction pathways of the oxidation by O2 of planar and curved PAHs using 4-pyrenyl and 1-corannulenyl as their model molecules, respectively. The energetically preferred channels for curved PAH oxidation differ from the planar one. The addition of O2 on a radical site of a six-membered ring to form a peroxyl radical is found to be barrierless for both the model PAHs. For peroxyl decomposition, three pathways are suggested, each of which involve the activation energies of 108, 170 and 121kJ/mol to form stable molecules in the case of planar PAH, and 94, 155 and 125kJ/mol in the case of curved PAH. During the oxidation of a five-membered ring, to form stable molecules, the activation energies of 90kJ/mol for the curved PAH and 169kJ/mol for the planar PAH relative to the energy of the peroxyl radical are required. The low activation barriers of preferred pathways for the oxidation of six and five-membered rings present on curved PAH (as compared to the planar one) explain and support its experimentally observed high reactivity. © 2013 The Combustion Institute..en
dc.description.sponsorshipThis work was supported by Saudi Aramco through KAUST CCRC.en
dc.publisherElsevier BVen
dc.subjectDensity functional theoryen
dc.subjectKinetic mechanismen
dc.subjectOxidationen
dc.subjectPAHen
dc.subjectSooten
dc.titleStructural effects on the oxidation of soot particles by O2: Experimental and theoretical studyen
dc.typeArticleen
dc.contributor.departmentClean Combustion Research Centeren
dc.contributor.departmentAdvanced Nanofabrication, Imaging and Characterization Core Laben
dc.contributor.departmentWater Desalination and Reuse Research Center (WDRC)en
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.contributor.departmentMechanical Engineering Programen
dc.contributor.departmentCore Labsen
dc.contributor.departmentCombustion and Laser Diagnostics Laboratoryen
dc.identifier.journalCombustion and Flameen
dc.contributor.institutionDepartment of Chemical Engineering, The Petroleum Institute, Abu Dhabi, United Arab Emiratesen
kaust.authorRaj, Abhijeeten
kaust.authorYang, Seung Yeonen
kaust.authorCha, Dong Kyuen
kaust.authorChung, Suk-Hoen
kaust.authorTayouo Djinsu, Russellen
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