Two-dimensional EPR spectroscopic studies on the radicals in argonne premium coals

Tadaaki Ikoma; Osamu Ito; Shozo Tero-Kubota; Kimio Akiyama

doi:10.1021/ef980053q

Two-dimensional EPR spectroscopic studies on the radicals in argonne premium coals

Tadaaki Ikoma, Osamu Ito, Shozo Tero-Kubota, Kimio Akiyama

Division of Organic- and Biomaterials Research

Research output: Contribution to journal › Article › peer-review

12 Citations (Scopus)

Abstract

Two-dimensional electron paramagnetic resonance (2D-EPR) spectra of Illinois No. 6 and Upper Freeport coals have been measured. From 2D-nutation spectroscopy, it is confirmed that the main EPR signal around g = 2 is attributed to free radicals, but not to radical pairs. Both coals showed nuclear modulation effects due to¹H and naturally abundant ¹³C nuclear spins. Spinecho correlation spectroscopy (SECSY) experiments elucidate the distribution of modulation frequencies included in a broad EPR spectrum. The observed dip in the ¹³C matrix spectrum obtained from SECSY is interpreted in terms of the decrease of vitrinite radicals, which are weakly interacting with ¹³C nuclei, in the central region of the EPR spectrum. The analysis of the broad hyperfine spectra due to ¹H and ¹³C nuclei in the hyperfine sublevel correlation spectra suggests the existence of several kinds of radicals in coal. Most of unpaired electrons are considered to be trapped in aromatic rings. The ratio of ¹³C/¹H of hyperfine spectra increases with coal rank, suggesting a new index of coal rank.

Original language	English
Pages (from-to)	996-1000
Number of pages	5
Journal	Energy and Fuels
Volume	12
Issue number	5
DOIs	https://doi.org/10.1021/ef980053q
Publication status	Published - 1998 Jan 1

ASJC Scopus subject areas

Chemical Engineering(all)
Fuel Technology
Energy Engineering and Power Technology

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10.1021/ef980053q

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title = "Two-dimensional EPR spectroscopic studies on the radicals in argonne premium coals",

abstract = "Two-dimensional electron paramagnetic resonance (2D-EPR) spectra of Illinois No. 6 and Upper Freeport coals have been measured. From 2D-nutation spectroscopy, it is confirmed that the main EPR signal around g = 2 is attributed to free radicals, but not to radical pairs. Both coals showed nuclear modulation effects due to1H and naturally abundant 13C nuclear spins. Spinecho correlation spectroscopy (SECSY) experiments elucidate the distribution of modulation frequencies included in a broad EPR spectrum. The observed dip in the 13C matrix spectrum obtained from SECSY is interpreted in terms of the decrease of vitrinite radicals, which are weakly interacting with 13C nuclei, in the central region of the EPR spectrum. The analysis of the broad hyperfine spectra due to 1H and 13C nuclei in the hyperfine sublevel correlation spectra suggests the existence of several kinds of radicals in coal. Most of unpaired electrons are considered to be trapped in aromatic rings. The ratio of 13C/1H of hyperfine spectra increases with coal rank, suggesting a new index of coal rank.",

author = "Tadaaki Ikoma and Osamu Ito and Shozo Tero-Kubota and Kimio Akiyama",

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T1 - Two-dimensional EPR spectroscopic studies on the radicals in argonne premium coals

AU - Ikoma, Tadaaki

AU - Ito, Osamu

AU - Tero-Kubota, Shozo

AU - Akiyama, Kimio

PY - 1998/1/1

Y1 - 1998/1/1

N2 - Two-dimensional electron paramagnetic resonance (2D-EPR) spectra of Illinois No. 6 and Upper Freeport coals have been measured. From 2D-nutation spectroscopy, it is confirmed that the main EPR signal around g = 2 is attributed to free radicals, but not to radical pairs. Both coals showed nuclear modulation effects due to1H and naturally abundant 13C nuclear spins. Spinecho correlation spectroscopy (SECSY) experiments elucidate the distribution of modulation frequencies included in a broad EPR spectrum. The observed dip in the 13C matrix spectrum obtained from SECSY is interpreted in terms of the decrease of vitrinite radicals, which are weakly interacting with 13C nuclei, in the central region of the EPR spectrum. The analysis of the broad hyperfine spectra due to 1H and 13C nuclei in the hyperfine sublevel correlation spectra suggests the existence of several kinds of radicals in coal. Most of unpaired electrons are considered to be trapped in aromatic rings. The ratio of 13C/1H of hyperfine spectra increases with coal rank, suggesting a new index of coal rank.

AB - Two-dimensional electron paramagnetic resonance (2D-EPR) spectra of Illinois No. 6 and Upper Freeport coals have been measured. From 2D-nutation spectroscopy, it is confirmed that the main EPR signal around g = 2 is attributed to free radicals, but not to radical pairs. Both coals showed nuclear modulation effects due to1H and naturally abundant 13C nuclear spins. Spinecho correlation spectroscopy (SECSY) experiments elucidate the distribution of modulation frequencies included in a broad EPR spectrum. The observed dip in the 13C matrix spectrum obtained from SECSY is interpreted in terms of the decrease of vitrinite radicals, which are weakly interacting with 13C nuclei, in the central region of the EPR spectrum. The analysis of the broad hyperfine spectra due to 1H and 13C nuclei in the hyperfine sublevel correlation spectra suggests the existence of several kinds of radicals in coal. Most of unpaired electrons are considered to be trapped in aromatic rings. The ratio of 13C/1H of hyperfine spectra increases with coal rank, suggesting a new index of coal rank.

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Two-dimensional EPR spectroscopic studies on the radicals in argonne premium coals

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