<i>Operando</i> PEPICO unveils the catalytic fast pyrolysis mechanism of the three methoxyphenol isomers

Pan, Zeyou; Bodi, Andras; Bokhoven, Jeroen A. van; Hemberger, Patrick

doi:10.1039/d2cp02741k

Cited by 10 publications

(7 citation statements)

References 49 publications

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“…Although ketene could not be detected yet directly in the FTS chemistry, it bears direct relationships to other detected carbonylated species: (i) as also highlighted before in Section ; acetate is nothing but a physisorbed ketene with an energy gain of >50 kJ/mol and a minimal energy barrier of ≤17 kJ/mol, , as well as both (ii) acetone (via Schmidlin synthesis) and (iii) diacetyl at high temperature could be formed to/from ketene (Figure a). Considering the recently accelerating research activities on ketene chemistry, we strongly recommend utilizing the sophisticated PEPICO technology in the distant future, as popularized by Hemberger and his team, ,− to provide more mechanistic information in this regard. The feasibility of oxygenate intermediates in FTS chemistry has also been supplemented by well-designed control experiments based on cofeeding methanol after simulating the FTS reaction conditions.…”

Section: Hydrogenation Of Co/co2 Over Metal-zeolite Bifunctional Cata...mentioning

confidence: 99%

Evaluating the Role of Descriptor- and Spectator-Type Reaction Intermediates During the Early Phases of Zeolite Catalysis

Gong

Chowdhury

2022

ACS Catal.

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The philosophy of "Ikigai"�a reason for being�could be extended to rationalize the role of organic reaction intermediates in zeolite catalysis. Each reaction intermediate's ikigai is specific under the confined microenvironment of the zeolite: either controlling the product selectivity (i.e., "descriptor"-type reaction intermediates) or promoting the catalyst deactivation (i.e., "spectator"-type reaction intermediates). Based on the process conditions and zeolite topologies, the ikigai of reaction intermediates could be altered, where the "descriptor" character could turn into a "spectator" depending on the working environment. Although the spectroscopy-/mechanism-driven development of catalytic technologies has been accelerated in the past decade and can now identify "elusive" zeolite-trapped reaction intermediates, it still does not always necessarily imply their "positive" impact during catalysis. Therefore, future research activities should be dedicated to recognizing the true ikigai of identified reaction intermediates: i.e., differentiating their spectator role from the catalytically relevant descriptor. Considering its potential industrial application, we will present our account and philosophy on the current status and future impact of mechanism-driven development of zeolite-mediated catalytic technologies in this Perspective.

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Section: Hydrogenation Of Co/co2 Over Metal-zeolite Bifunctional Cata...mentioning

confidence: 99%

Evaluating the Role of Descriptor- and Spectator-Type Reaction Intermediates During the Early Phases of Zeolite Catalysis

Gong

Chowdhury

2022

ACS Catal.

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“…The possibility of low-barrier hydrogen transfer between adjacent functional groups greatly alters the dissociation channel in both charged states. While the vicinity of the interacting functional groups is central in unimolecular processes, the stability of the H-transfer intermediates plays a more important role in catalytic processes, where the catalyst can participate as the proton donor and acceptor, thereby facilitating H-transfer across larger distances, as seen recently, for example, in catalytic pyrolysis experiments of the three methoxyphenol isomers …”

Section: Resultsmentioning

confidence: 99%

“…While the vicinity of the interacting functional groups is central in unimolecular processes, the stability of the H-transfer intermediates plays a more important role in catalytic processes, where the catalyst can participate as the proton donor and acceptor, thereby facilitating H-transfer across larger distances, as seen recently, for example, in catalytic pyrolysis experiments of the three methoxyphenol isomers. 50 The Journal of Physical Chemistry A pubs.acs.org/JPCA Article…”

Section: Comparison Of the Neutral And Cationmentioning

confidence: 99%

Isomer-Dependent Threshold Photoelectron Spectroscopy and Dissociative Photoionization Mechanism of Anisaldehyde

Bjelić

Hemberger

et al. 2023

J. Phys. Chem. A

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We studied the threshold photoionization and dissociative ionization of para-, meta-, and ortho-anisaldehyde by photoelectron photoion coincidence spectroscopy in the 8.20–19.00 eV photon energy range. Vertical ionization energies by equation of motion–ionization potential–coupled cluster singles and doubles (EOM–IP–CCSD) calculations reproduce the photoelectron spectral features in all three isomers. The dissociative photoionization (DPI) pathways of para- and meta-anisaldehyde are similar and differ markedly from those of ortho-anisaldehyde. In the para and meta isomers, the lowest-energy DPI channel corresponds to hydrogen atom loss to form the C8H7O2 + fragment at m/z 135, which undergoes sequential dissociation processes at higher energies, such as carbon monoxide loss to C7H7O+ (m/z 107) and further, sequential CH3, CH2O, and CH2CO losses to produce C6H4O+ (m/z 92), C6H5 + (m/z 77), and C5H5 + (m/z 65), respectively. Carbon monoxide loss from the parent ions, yielding C7H8O+ (m/z 108), is a subordinate dissociation channel parallel to H atom loss. At higher energies, it also gives rise to sequential formaldehyde (CH2O) loss to produce C6H6 + (m/z 78). In the ortho-anisaldehyde cation, the vicinity of the aldehyde and methoxy groups opens up low-energy hydrogen-transfer processes, which allow for seven fragmentation channels to compete effectively with the H- and CO-loss channels. Thus, the fragmentation mechanism changes considerably, thanks to the steric interaction of the substituents. Functional group interactions, in particular H transfer pathways, must therefore be considered when predicting the isomer-specific unimolecular decomposition mechanism of cationic and neutral species, as well as mass spectra for isomers.

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“…Toluene is a prevalent product in the catalytic fast pyrolysis (CFP) of lignin constituents. The elusive fulvenone ketene (c-C 5 H 4 CO) cannot be detected by gas chromatography-mass spectrometry (GC/MS) analysis, but it has the same nominal mass, m / z 92. ,, The ms-TPES spectrum in Figure a shows contributions of toluene (features above 8.8 eV) in the catalytic pyrolysis of all three methoxyphenol (MP) isomers over H-ZSM5. Fulvenone, on the other hand, shows distinct vibrational features at 8.25 eV and appears only in the CFP of 2-MP (guaiacol, red curve) .…”

Section: Applicationsmentioning

confidence: 99%

Section: Applicationsmentioning

confidence: 99%

Photoion Mass-Selected Threshold Photoelectron Spectroscopy to Detect Reactive Intermediates in Catalysis: From Instrumentation and Examples to Peculiarities and a Database

Hemberger,

Pan,

et al. 2023

J. Phys. Chem. C

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Photoion mass-selected threshold photoelectron spectroscopy (ms-TPES) is a synchrotron-based, universal, sensitive, and multiplexed detection tool applied in the areas of catalysis, combustion, and gas-phase reactions. Isomer-selective vibrational fingerprints in the ms-TPES of stable and reactive intermediates allow for unequivocal assignment of spectral carriers. Case studies are presented on heterogeneous catalysis, revealing the role of ketenes in the methanol-to-olefins process, the catalytic pyrolysis mechanism of lignin model compounds, and the radical chemistry upon C−H activation in oxyhalogenation. These studies demonstrate the potential of ms-TPES as an analytical technique for elucidating complex reaction mechanisms. We examine the robustness of ms-TPES assignments and address sampling effects, especially the temperature dependence of ms-TPES due to rovibrational broadening. Data acquisition approaches and the Stark shift from the extraction field are also considered to arrive at general recommendations. Finally, the PhotoElectron PhotoIon Spectral Compendium (https://pepisco.psi.ch), a spectral database hosted at Paul Scherrer Institute to support assignment, is introduced.

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Operando PEPICO unveils the catalytic fast pyrolysis mechanism of the three methoxyphenol isomers

Abstract: 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.

Cited by 10 publications

References 49 publications

Evaluating the Role of Descriptor- and Spectator-Type Reaction Intermediates During the Early Phases of Zeolite Catalysis

Evaluating the Role of Descriptor- and Spectator-Type Reaction Intermediates During the Early Phases of Zeolite Catalysis

Isomer-Dependent Threshold Photoelectron Spectroscopy and Dissociative Photoionization Mechanism of Anisaldehyde

Photoion Mass-Selected Threshold Photoelectron Spectroscopy to Detect Reactive Intermediates in Catalysis: From Instrumentation and Examples to Peculiarities and a Database

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