Paramagnetic centers in particulate formed from the oxidative pyrolysis of 1-methylnaphthalene in the presence of Fe(III)2O3 nanoparticles

Herring, Paul; Khachatryan, Lavrent; Lomnicki, Slawo; Dellinger, Barry

doi:10.1016/j.combustflame.2013.06.025

Cited by 14 publications

(9 citation statements)

References 53 publications

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“…The detected EPR spectra present a simple singlet line (Figure a, inset spectra) with low g-values (from 2.0031 to 2.0034) and a relatively narrow spectrum with Δ H p‑p in the range of 4.9–5.8 G (Figure b) characteristic most probably to carbon centered radicals. Similar radicals (identified as soot radicals) were reported in our earlier publication . Formation of soot is typical during lignin low temperature and longtime pyrolysis and is reported as coke formation .…”

Section: Results and Discussionsupporting

confidence: 87%

“…Similar radicals (identified as soot radicals) were reported in our earlier publication. 53 Formation of soot is typical during lignin low temperature and longtime pyrolysis and is reported as coke formation. 54 In fact, the secondary processes (condensation/polymerization) occur in the gas phase 16 as well as on the surface of residue from lignin pyrolysis producing coke/soot particles with characteristic EPR spectra, Figure 4a (inset spectra).…”

Section: Resultsmentioning

confidence: 99%

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Peculiarities of Pyrolysis of Hydrolytic Lignin in Dispersed Gas Phase and in Solid State

et al. 2017

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The unique decomposition pathways of hydrolytic lignin (HL) dissolved in an acetone/water mixture (9:1) and dispersed by a droplet evaporation technique under nitrogen gas flow has been investigated in a conventional reactor at atmospheric condition, a temperature region of 400–550 °C, and a residence time of 0.12 s. The results validate the fact that dispersion of the lignin into the gas phase by decreasing the sample size (as well as “minimizing the char area to avoid catalytic contact” of molecular products/radicals with the surface) may open new perspectives in understanding the chemistry of the depolymerization of lignin. Using Laser Desorption Ionization-Time of Flight-Mass Spectrometry (LDI-TOF-MS) the intrinsic ion m/z = 550, as the major MS peak from fresh HL dissolved in an acetone/water mixture before pyrolysis, was detected. Surprisingly, the expected phenolic compounds after pyrolysis were in trace amounts at less than 15% conversion of lignin. Instead, oligomeric intermediate substances with low (<550 Da) and high molecular weight (>550 Da) containing lignin-substructures (trapped on quartz wool located at the end of the reactor at ∼300 °C) were detected as major products using LDI-TOF-MS. The hypothesis about a largely disputed key question on lignin pyrolysis as to whether the phenolic compounds or oligomers (dimers, trimers, etc.) are the primary products is discussed. Additionally, a focus on the free-radical mechanism of depolymerization of solid lignin by formation of free intermediate radicals from initial lignin macromolecules as well as from inherent, low molecular weight oligomer molecules is developed based on the Low Temperature Matrix Isolation (LTMI) EPR technique.

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Section: Results and Discussionsupporting

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Peculiarities of Pyrolysis of Hydrolytic Lignin in Dispersed Gas Phase and in Solid State

et al. 2017

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“…The spectra of the coking sample with added Fe 3+ contained a signal with a very wide half-width, which is different from the signal in the spectrum of coked glucose alone; however, this effect is not clear. Previous studies have shown that the formation of EPFRs from the oxidative pyrolysis of 1-methylnaphthalene can be promoted by the addition of Fe 2 O 3 nanoparticles in a reaction system that contains Fe 2 O 3 nanoparticles and gas organic molecules in a flow reaction tube and an oxygen atmosphere; 51,52 this study, the pyrolysis of the mixture of glucose and Fe 2 (SO 4 ) 3 solutions occurred in an oxygen-free atmosphere. Soluble metal ions had an inhibitory effect on EPFR formation.…”

Section: Environmental Science and Technologymentioning

confidence: 68%

Dominant Fraction of EPFRs from Nonsolvent-Extractable Organic Matter in Fine Particulates over Xi’an, China

Chen

Sun

Wang

et al. 2018

Environ. Sci. Technol.

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To understand the nature and possible sources of environmentally persistent free radicals (EPFRs) in atmospheric aerosols, the present study used a solvent extraction method to fractionate aerosol components with different polarities and solvent resistance in fine particulate matter (PM) from Xi'an, China. The characteristics of EPFRs, that is., their concentration, type and lifetime, were obtained based on their electron paramagnetic resonance spectra. The results showed that the EPFRs in the PM samples were carbon-centered with a nearby heteroatom ( g = 2.0031) and had a long half-life of more than 3 years. Nearly all of the extractable EPFRs were detected in the water-insoluble organic fraction and showed characteristics indicating that may contain oxygen-centered radical ( g = 2.0038). Most of the total EPFRs in the PM were derived from solvent-resistant organic matter (88%), which likely consisted of graphene oxide analogues. The results suggest that previous studies may have missed the major proportion of EPFRs in atmospheric particulates if they only focused on solvent-extractable or metallic oxide-formed EPFRs. Our results showed that the EPFR concentration was significantly and positively correlated with the elemental carbon and NO concentrations, suggesting that traffic emissions may be an important source of EPFRs in PM over Xi'an.

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“…Both line types were narrower than the line widths of radicals obtained for carbon black (23e66 G) [75]. The ESR signal of pyrolyzed lignocellulosic materials is often only a broad featureless singlet without the hyperfine splitting which is caused by the presence of multiple radical species or strong matrix interaction occurred between the products [76]. In addition, the heterogeneity of biomass samples and that the radicals are not exclusively centered on single atoms could lead to broad featureless singlets, as reported by Herring et al [76].…”

Section: Discussionmentioning

confidence: 78%

“…The ESR signal of pyrolyzed lignocellulosic materials is often only a broad featureless singlet without the hyperfine splitting which is caused by the presence of multiple radical species or strong matrix interaction occurred between the products [76]. In addition, the heterogeneity of biomass samples and that the radicals are not exclusively centered on single atoms could lead to broad featureless singlets, as reported by Herring et al [76]. Investigations of Ross et al [77] showed that the differences in line widths were caused by the formation of the disorganized carbon with unpaired electrons (narrow signal) and organized carbon with the conductive electrons (broad signal).…”

Section: Discussionmentioning

confidence: 99%

Characterization of free radicals by electron spin resonance spectroscopy in biochars from pyrolysis at high heating rates and at high temperatures

Trubetskaya

Jensen

et al. 2016

Biomass and Bioenergy

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a b s t r a c tThe concentration and type of free radicals from the decay (termination stage) of pyrolysis at slow and fast heating rates and at high temperatures (above 1000 C) in biomass char have been studied. A roomtemperature electron spin resonance spectroscopy study was conducted on original wood, herbaceous biomass, holocelluloses, lignin and their chars, prepared at high temperatures in a wire mesh reactor, an entrained flow reactor, and a tubular reactor. The radical concentrations in the chars from the decay stage range up between 7$10 16 and 1.5$10 18 spins g À1. The results indicated that the biomass major constituents (cellulose, hemicellulose, lignin) had a minor effect on remaining radical concentrations compared to potassium and silica contents. The higher radical concentrations in the wheat straw chars from the decay stage of pyrolysis in the entrained flow reactor compared to the wood chars were related to the decreased mobility of potassium in the char matrix, leading to the less efficient catalytic effects of potassium on the bond-breaking and radical re-attachments. The high Si levels in the rice husk caused an increase in the char radical concentration compared to the wheat straw because the free radicals were trapped in a char consisting of a molten amorphous silica at heating rates of 10 3 e10 4 K s À1. The experimental electron spin resonance spectroscopy spectra were analyzed by fitting to simulated data in order to identify radical types, based on g-values and line widths. The results show that at high temperatures, mostly aliphatic radicals (g ¼ 2.0026e2.0028) and PAH radicals (g ¼ 2.0027e2.0031) were formed.

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Paramagnetic centers in particulate formed from the oxidative pyrolysis of 1-methylnaphthalene in the presence of Fe(III)2O3 nanoparticles

Cited by 14 publications

References 53 publications

Peculiarities of Pyrolysis of Hydrolytic Lignin in Dispersed Gas Phase and in Solid State

Peculiarities of Pyrolysis of Hydrolytic Lignin in Dispersed Gas Phase and in Solid State

Dominant Fraction of EPFRs from Nonsolvent-Extractable Organic Matter in Fine Particulates over Xi’an, China

Characterization of free radicals by electron spin resonance spectroscopy in biochars from pyrolysis at high heating rates and at high temperatures

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