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Pan Z, Bodi A, van Bokhoven JA, Hemberger P. Operando PEPICO unveils the catalytic fast pyrolysis mechanism of the three methoxyphenol isomers. Phys Chem Chem Phys 2022; 24:21786-21793. [PMID: 36082786 PMCID: PMC9491049 DOI: 10.1039/d2cp02741k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The development of lignin valorization processes such as catalytic fast pyrolysis (CFP) to produce fine chemicals and fuels leads to a more sustainable future. The implementation of CFP is enabled by understanding the chemistry of lignin constituents, which, however, requires thorough mechanistic investigations by detecting reactive species. In this contribution, we investigate the CFP of the three methoxyphenol (MP) isomers over H-ZSM-5 utilizing vacuum ultraviolet synchrotron radiation and operando photoelectron photoion coincidence (PEPICO) spectroscopy. All isomers demethylate at first to yield benzenediols, from which dehydroxylation reactions proceed to produce phenol and benzene. Additional pathways to form benzene proceed over cyclopentadiene, methylcyclopentadiene, and fulvene intermediates. The detection of trace amounts of methanol in the product stream suggests a demethoxylation reaction to yield phenol. Guaiacol (2- or ortho-MP) exhibits slightly higher reactivity compared to 3-MP and 4-MP, due to the formation of the fulvenone ketene, which opens additional routes to benzene and phenol. When compared to benzenediol catalytic pyrolysis, the additional methyl group in MP leads to high conversion at lower reactor temperatures, which is mostly owed to the lower H3C–O vs. H–O bond energy and the possibility to demethoxylate to produce phenol. Demethylation, demethoxylation and fulvenone ketene formation determine the reactivity of methoxyphenols over H-ZSM-5 to yield phenols, benzene and toluene. Intermediates are isomer-selectively detected utilizing threshold photoelectron spectroscopy.![]()
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Affiliation(s)
- Zeyou Pan
- Paul Scherrer Institute, 5232 Villigen, Switzerland. .,Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
| | - Andras Bodi
- Paul Scherrer Institute, 5232 Villigen, Switzerland.
| | - Jeroen A van Bokhoven
- Paul Scherrer Institute, 5232 Villigen, Switzerland. .,Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
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2
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Zinck N, Bodi A, Mayer PM. VUV photoprocessing of oxygen-containing polycyclic aromatic hydrocarbons: iPEPICO study of the unimolecular dissociation of ionized benzofuran. CAN J CHEM 2022. [DOI: 10.1139/cjc-2022-0062] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Oxygen-containing polycyclic aromatic hydrocarbons (OPAHs) are potential contributors to the 11.3 m band in interstellar observations. To further explore their role in the interstellar medium, we have investigated their fate after photoprocessing by VUV radiation; in particular, we studied the dissociative photoionization of the simplest OPAH, benzofuran, with imaging photoelectron photoion coincidence spectroscopy, iPEPICO. Ionized benzofuran dissociates by loss of CO, followed by a sequential H atom loss. The parallel HCO-loss channel, leading to the same bicyclic C7H5+ fragment ion, is not competitive at low excess energies above the ionization threshold. However, the collision-induced dissociation tandem mass spectrometry results suggest that CO and HCO may be formed in parallel at higher energies. An RRKM fragmentation model reproduced the iPEPICO data well assuming the initial 1,2-H shift transition state to be rate determining to CO loss. The breakdown diagram and the measured dissociation rates agreed well at the CBS-QB3-calculated activation energy of 2.99 eV, which could be relaxed to 3.25 eV, and only a slight adjustment of the ab initio activation entropy. The model barrier to sequential H-loss is larger than the computed H-loss threshold and the breakdown diagram rises less steeply than predicted, which indicates suprastatistical kinetic energy release after the tight H-transfer transition state of the first step. HCO cleavage is possible after a ring-opening transition state, which is looser than and isoenergetic with the CO-loss transition state. However, a subsequent ring formation transition state at 3.85 eV is moderately tight, which suppresses HCO loss at low excess energies.
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Affiliation(s)
- Nicholas Zinck
- University of Ottawa, 6363, Chemistry and Biomolecular Sciences, Ottawa, Ontario, Canada
| | - Andras Bodi
- Paul Scherrer Institut PSI, 28498, Laboratory for Synchrotron Radiation and Femtochemistry, Villigen, Aargau, Switzerland
| | - Paul M Mayer
- University of Ottawa, 6363, Chemistry and Biomolecular Sciences, Ottawa, Ontario, Canada,
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McCabe M, Hemberger P, Reusch E, Bodi A, Bouwman J. Off the Beaten Path: Almost Clean Formation of Indene from the ortho-Benzyne + Allyl Reaction. J Phys Chem Lett 2020; 11:2859-2863. [PMID: 32202794 PMCID: PMC7168585 DOI: 10.1021/acs.jpclett.0c00374] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Accepted: 03/23/2020] [Indexed: 06/07/2023]
Abstract
Polycyclic aromatic hydrocarbons (PAHs) play an important role in chemistry both in the terrestrial setting and in the interstellar medium. Various, albeit often inefficient, chemical mechanisms have been proposed to explain PAH formation, but few yield polycyclic hydrocarbons cleanly. Alternative and quite promising pathways have been suggested to address these shortcomings with key starting reactants including resonance stabilized radicals (RSRs) and o-benzyne. Here we report on a combined experimental and theoretical study of the reaction allyl + o-benzyne. Indene was found to be the primary product and statistical modeling predicts only 0.1% phenylallene and 0.1% 3-phenyl-1-propyne as side products. The quantitative and likely barrierless formation of indene yields important insights into the role resonance stabilized radicals play in the formation of polycyclic hydrocarbons.
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Affiliation(s)
- Morgan
N. McCabe
- Laboratory
for Astrophysics, Leiden Observatory, Leiden
University, P.O. Box 9513, 2300 RA Leiden, The Netherlands
| | - Patrick Hemberger
- Laboratory
for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Engelbert Reusch
- Institute
of Physical and Theoretical Chemistry, University
of Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Andras Bodi
- Laboratory
for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Jordy Bouwman
- Laboratory
for Astrophysics, Leiden Observatory, Leiden
University, P.O. Box 9513, 2300 RA Leiden, The Netherlands
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Mercier X, Faccinetto A, Batut S, Vanhove G, Božanić DK, Hróðmarsson HR, Garcia GA, Nahon L. Selective identification of cyclopentaring-fused PAHs and side-substituted PAHs in a low pressure premixed sooting flame by photoelectron photoion coincidence spectroscopy. Phys Chem Chem Phys 2020; 22:15926-15944. [DOI: 10.1039/d0cp02740e] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Selective on-line identification of polycyclic aromatic hydrocarbons (PAHs) formed in a low-pressure methane sooting flame, carried out using the double imaging Photoelectron Photoion Coincidence Spectroscopy method (i2PEPICO).
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Affiliation(s)
- X. Mercier
- Université Lille
- CNRS
- UMR 8522 – PC2A – Physicochimie des Processus de Combustion et de l’Atmosphère
- F-59000 Lille
- France
| | - A. Faccinetto
- Université Lille
- CNRS
- UMR 8522 – PC2A – Physicochimie des Processus de Combustion et de l’Atmosphère
- F-59000 Lille
- France
| | - S. Batut
- Université Lille
- CNRS
- UMR 8522 – PC2A – Physicochimie des Processus de Combustion et de l’Atmosphère
- F-59000 Lille
- France
| | - G. Vanhove
- Université Lille
- CNRS
- UMR 8522 – PC2A – Physicochimie des Processus de Combustion et de l’Atmosphère
- F-59000 Lille
- France
| | - D. K. Božanić
- Synchrotron SOLEIL
- L ‘Orme des Merisiers
- 91192 Gif sur Yvette
- France
| | | | - G. A. Garcia
- Synchrotron SOLEIL
- L ‘Orme des Merisiers
- 91192 Gif sur Yvette
- France
| | - L. Nahon
- Synchrotron SOLEIL
- L ‘Orme des Merisiers
- 91192 Gif sur Yvette
- France
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5
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Zhao L, Prendergast MB, Kaiser RI, Xu B, Lu W, Ablikim U, Ahmed M, Oleinikov AD, Azyazov VN, Mebel AM, Howlader AH, Wnuk SF. Reactivity of the Indenyl Radical (C 9 H 7 ) with Acetylene (C 2 H 2 ) and Vinylacetylene (C 4 H 4 ). Chemphyschem 2019; 20:1437-1447. [PMID: 30938059 DOI: 10.1002/cphc.201900052] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Revised: 02/28/2019] [Indexed: 11/09/2022]
Abstract
The reactions of the indenyl radicals with acetylene (C2 H2 ) and vinylacetylene (C4 H4 ) is studied in a hot chemical reactor coupled to synchrotron based vacuum ultraviolet ionization mass spectrometry. These experimental results are combined with theory to reveal that the resonantly stabilized and thermodynamically most stable 1-indenyl radical (C9 H7 . ) is always formed in the pyrolysis of 1-, 2-, 6-, and 7-bromoindenes at 1500 K. The 1-indenyl radical reacts with acetylene yielding 1-ethynylindene plus atomic hydrogen, rather than adding a second acetylene molecule and leading to ring closure and formation of fluorene as observed in other reaction mechanisms such as the hydrogen abstraction acetylene addition or hydrogen abstraction vinylacetylene addition pathways. While this reaction mechanism is analogous to the bimolecular reaction between the phenyl radical (C6 H5 . ) and acetylene forming phenylacetylene (C6 H5 CCH), the 1-indenyl+acetylene→1-ethynylindene+hydrogen reaction is highly endoergic (114 kJ mol-1 ) and slow, contrary to the exoergic (-38 kJ mol-1 ) and faster phenyl+acetylene→phenylacetylene+hydrogen reaction. In a similar manner, no ring closure leading to fluorene formation was observed in the reaction of 1-indenyl radical with vinylacetylene. These experimental results are explained through rate constant calculations based on theoretically derived potential energy surfaces.
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Affiliation(s)
- Long Zhao
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii, 96822, USA
| | - Matthew B Prendergast
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii, 96822, USA
| | - Ralf I Kaiser
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii, 96822, USA
| | - Bo Xu
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Wenchao Lu
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Utuq Ablikim
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Musahid Ahmed
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | | | | | - Alexander M Mebel
- Samara National Research University, Samara, 443086, Russia.,Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA
| | - A Hasan Howlader
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA
| | - Stanislaw F Wnuk
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA
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West B, Rodriguez Castillo S, Sit A, Mohamad S, Lowe B, Joblin C, Bodi A, Mayer PM. Unimolecular reaction energies for polycyclic aromatic hydrocarbon ions. Phys Chem Chem Phys 2018; 20:7195-7205. [PMID: 29480289 PMCID: PMC6031295 DOI: 10.1039/c7cp07369k] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Imaging photoelectron photoion coincidence spectroscopy was employed to explore the unimolecular dissociation of the ionized polycyclic aromatic hydrocarbons (PAHs) acenaphthylene, fluorene, cyclopenta[d,e,f]phenanthrene, pyrene, perylene, fluoranthene, dibenzo[a,e]pyrene, dibenzo[a,l]pyrene, coronene and corannulene. The primary reaction is always hydrogen atom loss, with the smaller species also exhibiting loss of C2H2 to varying extents. Combined with previous work on smaller PAH ions, trends in the reaction energies (E0) for loss of H from sp2-C and sp3-C centres, along with hydrocarbon molecule loss were found as a function of the number of carbon atoms in the ionized PAHs ranging in size from naphthalene to coronene. In the case of molecules which possessed at least one sp3-C centre, the activation energy for the loss of an H atom from this site was 2.34 eV, with the exception of cyclopenta[d,e,f]phenanthrene (CPP) ions, for which the E0 was 3.44 ± 0.86 eV due to steric constraints. The hydrogen loss from PAH cations and from their H-loss fragments exhibits two trends, depending on the number of unpaired electrons. For the loss of the first hydrogen atom, the energy is consistently ca. 4.40 eV, while the threshold to lose the second hydrogen atom is much lower at ca. 3.16 eV. The only exception was for the dibenzo[a,l]pyrene cation, which has a unique structure due to steric constraints, resulting in a low H loss reaction energy of 2.85 eV. If C2H2 is lost directly from the precursor cation, the energy required for this dissociation is 4.16 eV. No other fragmentation channels were observed over a large enough sample set for trends to be extrapolated, though data on CH3 and C4H2 loss obtained in previous studies is included for completeness. The dissociation reactions were also studied by collision induced dissociation after ionization by atmospheric pressure chemical ionization. When modeled with a simple temperature-based theory for the post-collision internal energy distribution, there was reasonable agreement between the two sets of data.
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Affiliation(s)
- Brandi West
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa K1N 6N5, Canada.
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