Methyl Radicals in Oxidative Coupling of Methane Directly Confirmed by Synchrotron VUV Photoionization Mass Spectroscopy

Luo, Liuxuan; Tang, Xiaofeng; Wang, Wendong; Wang, Yu; Sun, Shaobo; Qi, Fei; Huang, Weixin

doi:10.1038/srep01625

Cited by 89 publications

(90 citation statements)

References 41 publications

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“…We set out to identify the missing reactive intermediates using a temporal analysis of products-type (TAP)26 pyrolysis reactor coupled with our imaging PEPICO spectrometer (py-iPEPICO) at the VUV beamline of the Swiss Light Source. This combination is unique since it brings together a catalytic reactor, which works in the low-density regime (<1 mbar) allowing for the detection of desorbed reactive intermediates using PEPICO, which also provides superior isomer selectivity and fragment free soft ionization2728. Reactive intermediates desorbed from the catalyst surface are quenched rapidly at atmospheric pressure, which means the experiment must take place at low pressures and in the presence of an inert buffer gas.…”

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confidence: 99%

Understanding the mechanism of catalytic fast pyrolysis by unveiling reactive intermediates in heterogeneous catalysis

et al. 2017

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Catalytic fast pyrolysis is a promising way to convert lignin into fine chemicals and fuels, but current approaches lack selectivity and yield unsatisfactory conversion. Understanding the pyrolysis reaction mechanism at the molecular level may help to make this sustainable process more economic. Reactive intermediates are responsible for product branching and hold the key to unveiling these mechanisms, but are notoriously difficult to detect isomer-selectively. Here, we investigate the catalytic pyrolysis of guaiacol, a lignin model compound, using photoelectron photoion coincidence spectroscopy with synchrotron radiation, which allows for isomer-selective detection of reactive intermediates. In combination with ambient pressure pyrolysis, we identify fulvenone as the central reactive intermediate, generated by catalytic demethylation to catechol and subsequent dehydration. The fulvenone ketene is responsible for the phenol formation. This technique may open unique opportunities for isomer-resolved probing in catalysis, and holds the potential for achieving a mechanistic understanding of complex, real-life catalytic processes.

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confidence: 99%

Understanding the mechanism of catalytic fast pyrolysis by unveiling reactive intermediates in heterogeneous catalysis

et al. 2017

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“…At present, it is difficult to obtain direct evidence for these mechanisms. However, no matter which route is responsible for CH 4 activation, it is well accepted that free CH 3 radicals are first formed during OCM …”

Section: Discussionmentioning

confidence: 94%

Catalytic coupling of CH₄ with CHF₃ for the synthesis of VDF over LaOF catalyst

et al. 2018

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The oxidative coupling of methane (OCM) with CHF3 facilitates the synthesis of vinylidene fluoride (VDF). The aim is to utilize CHF3, which is otherwise considered a waste with a very high global warming potential. This study focuses on the effect of a LaOF catalyst on OCM occurring in the presence of CHF3, which engenders a promoting effect of O2 on CH4 activation. It examines the structural and phase changes of the lanthanum catalyst during the reaction and then speculates on the reaction mechanism. In combining OCM with CHF3, both the conversion of CH4 and the formation rate of VDF are almost tripled at 700°C. However, at higher temperatures, gas‐phase reactions play a dominating role in the conversion of CH4 and LaOF catalyst plays a very minor role in the reaction system at elevated temperatures. Irrespective of the reaction temperature, VDF is produced via the gas‐phase coupling of CH3 radicals with CF2. During pretreatment or during the reaction itself, La2O3 is fluorinated by CHF3 and HF, yielding the formation of surface LaOF and LaF3 species. LaF3 is a relatively inactive catalyst for CH4 conversion, whereas, in comparison LaOF appears to play a very important role in the activation of CH4 at low temperatures. The activation mechanism of CH4 at relatively low temperatures is similar with that postulated to occur during the OCM. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.

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“…Experimental studies show that the C 2 formation rates depend strongly on methyl-radical concentrations [123,131,149,150] . There is general agreement that the methyl radicals recombine in the gas-phase to form C 2 H 6 .…”

Section: Reaction Kineticsmentioning

confidence: 99%

Process intensification in the catalytic conversion of natural gas to fuels and chemicals

Kee

Karakaya

Zhu

2017

Proceedings of the Combustion Institute

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This paper explores alternative technologies for the conversion of natural gas to higher-value products. Because of methane's chemical stability, all practical processes require elevated temperature (e.g., T > 700 °C) and catalysts to activate the methane. Some approaches are mature and widely practiced at the commercial scale (e.g., steam reforming and Fischer-Tropsch synthesis). Others are emerging, based on laboratory-scale experimentation (e.g., oxidative coupling of methane). In all cases, the present paper is concerned with aspects of process intensification, seeking chemical methods and reactor implementations that can improve overall performance. Performance metrics include reactor size, energy efficiency, conversion rates, and product selectivity. Process intensification approaches include integrated microchannel reactors and heat exchangers as well as a range of permselective membranes.

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Methyl Radicals in Oxidative Coupling of Methane Directly Confirmed by Synchrotron VUV Photoionization Mass Spectroscopy

Cited by 89 publications

References 41 publications

Understanding the mechanism of catalytic fast pyrolysis by unveiling reactive intermediates in heterogeneous catalysis

Understanding the mechanism of catalytic fast pyrolysis by unveiling reactive intermediates in heterogeneous catalysis

Catalytic coupling of CH₄ with CHF₃ for the synthesis of VDF over LaOF catalyst

Process intensification in the catalytic conversion of natural gas to fuels and chemicals

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Methyl Radicals in Oxidative Coupling of Methane Directly Confirmed by Synchrotron VUV Photoionization Mass Spectroscopy

Cited by 89 publications

References 41 publications

Understanding the mechanism of catalytic fast pyrolysis by unveiling reactive intermediates in heterogeneous catalysis

Understanding the mechanism of catalytic fast pyrolysis by unveiling reactive intermediates in heterogeneous catalysis

Catalytic coupling of CH4 with CHF3 for the synthesis of VDF over LaOF catalyst

Process intensification in the catalytic conversion of natural gas to fuels and chemicals

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Catalytic coupling of CH₄ with CHF₃ for the synthesis of VDF over LaOF catalyst