Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE
Fossil Fuels
Chemical Composition of Surface Species in Pyrolysed Brown Coals, and Their Evolution During Steam Gasification Reaction Peter Nikolaevich Kuznetsov, Ludmila I. Kuznetsova, and Yuri L. Mikhlin Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b03909 • Publication Date (Web): 16 Feb 2019 Downloaded from http://pubs.acs.org on February 17, 2019
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 20
Energy & Fuels 1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Chemical Composition of Surface Species in Pyrolysed Brown Coals, and Their Evolution During Steam Gasification Reaction Peter N. Kuznetsov,* Ludmila I. Kuznetsova and Yuri L. Mikhlin Institute of Chemistry and Chemical Technology, Federal Research Center “Krasnoyarsk Scientific Center of Siberian Branch of Russian Academy of Sciences”, 50-24 Akademgorodok, Krasnoyarsk 660036 Russia E-mail:
[email protected];
[email protected]. Phone: +73912494849 ABSTRACT: In this paper, a detailed study focused on the characterization of the surface chemical species on the Kansk-Achinsk brown coal chars with different inherent mineral matter, calcium, in particular, and on the evolution of chemical species upon steam gasification at mild temperature of 700 °C was performed by using surface sensitive XPS and XANES and other techniques. It was found that the naturally occurring calcium surface species represented highly dispersed carbonatelike forms. Before gasification, they represented aragonite-like species. However, on steam gasification, they readily underwent solid-phase polymorphic transition into calcite-like form. The main proportion of the surface carbon atoms (68% to 71 %) on all the chars represented sp2-hybridized carbons in the graphene fragments, while the remaining 29-32 % accounted for as oxidized carbon species of different configurations. Mainly sp2-hybridized carbon atoms were found to be sensitive to activation by calcium catalyst. The conclusion was drawn that these were highly dispersed calcite-like surface species derived from the aragonite-like ones under steam gasification reaction, which could be responsible for catalytic activation of sp2-hybridized carbon atoms and for char gasification reactivity. Keywords: char, gasification, surface composition, calcium, XPS, XANES. 1. INTRODUCTION Gasification is an attractive multipurpose technology that can turn coal into clean power, liquid fuels and into a large variety of valuable chemical products, such as synthesis gas, hydrogen, ammonia, methanol, hydrocarbons, other chemicals and also various carbon materials, sorbents and catalyst supports. This is why gasification processing has grown so fast in many countries and will continue to play an important role in the foreseeable future.1-3 Coal gasification is a highly endothermic process which requires high temperature. The application of the active catalysts is an efficient way to increase the rate of coal gasification, or to decrease the operating temperature within the thermodynamically acceptable level. Among the potential catalysts, the more likely practical ones are Ca containing compounds, they are inexpensive, less volatile, less corrosive and less reactive with the clay minerals as compared to the ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
alkaline gasification catalysts.
4-7
Page 2 of 20 2
Iron is also a commonly used and inexpensive catalyst for coal
gasification.8 Generally postulated mechanism of the catalytic coal gasification suggests an oxidationreduction cycle in which the oxidant molecule is transferred to the specific surface carbon active sites through the catalytically active species.
8-10
However, the structures of the ‘carbon-oxygen
complexes’ proposed and catalytically active species are still under discussion. The catalytically active calcium species can include CaCO3 10, CaO и CaO2 11, and also nonstoichiometric CaxOy which could represent intermediate clusters. Many studies
12-14
were devoted to the investigation of the catalytic effects of the mineral
matter naturally occuring in the coals. In brown coals, calcium is usually an abundant component which can serve as a precursor for the catalytically active species. The acid leaching of brown coal resulted in the extraction of calcium followed by dramatically decreased coal reactivity for gasification.
12,15
Though the intensive experimental researches have been performed, there is an
uncertainty regarding the chemical forms of the calcium-containing species taking part in the gasification and their transformation in the course of reaction. Little is known also about the detailed chemical composition of the ‘carbon-oxygen complexes’ which could be responsible for the gasification reaction and about chemical interaction with the catalyst. It should be noted that determination of the structure of catalytic species and gasification mechanism is difficult because of the high dispersion (often molecular) and relatively low catalyst concentration, and also because of the heterogeneity and complexity of both the organic and inorganic constituents of coal and coal chars. For that matter, the studies by using a set of advanced analytical techniques, including different spectroscopic methods are of particular concern. For example, XPS and XANES have been successfully applied to the investigation of chemical species in the coals and coal chars. 16-18 Recently, the composition and structural properties of pyrolysed brown coals from different deposits of Kansk-Achinsk Basin and their steam gasification reactivities have been studied in our papers. 19,20 It was found that the extent of gasification of a large set of pyrolysed coals at 700-750 oC
was in statistical correlation with the content of the naturally occurring calcium. XPS spectra
revealed calcium in the pyrolyzed brown coals to be represented by highly dispersed carbonate species.20 However, it was not clear whether the correlation was solely due to catalysis or due to some calcium-induced chemical effects, for example, on the surface chemical functionalities which were not studied. In this paper, detailed study focused on the chemical characterization of the surface species on the Kansk-Achinsk brown coal chars with different contents of inherent mineral matter, calcium and iron, in particular, was carried out, and the evolution of surface composition during steam gasification was monitored to reveal key species responsible for char reactivity.
ACS Paragon Plus Environment
Page 3 of 20
Energy & Fuels 3
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
2. EXPERIMENTAL SECTION 2.1. Coal Samples Three brown coal samples with different contents of mineral matter from the Borodino deposit of the Kansk-Achinsk Basin were used in this study. The coals were crushed, and the fraction of 0.5-1.0 mm dried in a vacuum oven at 85 °C was used. Two coal samples were partially demineralized by treatment with 1.0 N HCl solution. An approximately 200 g of coal sample was treated in 2 l of aqueous acid solution in a plastic flask (filled with an inert gas) with stirring at room temperature for 2 h. The solution was decanted, and the treatment with the fresh portion of the acid solution was repeated. The acid-treated coal samples were filtered off, thoroughly washed with deionized water and dried in a vacuum oven at 85 °C. 2.2. Pyrolysis and Gasification Procedures The experiments on the pyrolysis of coals and steam gasification of coal chars were carried our at mild temperature conditions (700 °C) to diminish the volatility of the mineral substances, their sintering and also mass transfer effect on reaction rate. Coal samples were pyrolyzed in a quartz tubular reactor of 20 mm in diameter for 1 h. The reactor charged with 15 g of coal was heated at the controlled rate of 7-8 °C/min under nitrogen flow. The gasification reactor was charged with 5g of char and heated at the rate of 5 °C/min under nitrogen flow. On attaining the reaction temperature, the water was added to nitrogen flow and gasification was carried out at the atmospheric pressure for 45 min. After gasification was over, water feeding was stopped and the reactor with the sample was cooled to room temperature in a stream of dry nitrogen. The gasified char sample unloaded from the reactors was well mixed and immediately placed in a tube with ground-in lid. The pyrolyzed and gasified samples produced were stored in a refrigerator to avoid oxidation with an atmospheric oxygen. Carbon burn-off was evaluated based on the amount of dry ash free carbon matter in the char before and after gasification. 2.3. Analytical Procedures The coals and chars were subjected to proximate and ultimate analysis by conventional procedures. The analyses of C, H, N, S elements were performed on a FLASHTM1112 (Italy) elemental analyzer. Oxygen was calculated by difference. The contents of metals were measured by atomic absorption spectrometry and X-ray fluorescence analysis. The XRD patterns of powdered char samples packed into the aluminium holder were recorded by using a PANalyticalX'Pert PRO diffractometer with PIXcel detector and Сu Kα-radiation at a step-scanning mode (2=0.2 °, 25 s/step). The BET surface area and porous structure were determined from the nitrogen adsorption measurements at 77K using Micromeritics ASAP 2040 analizator. ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 20 4
The chemical characterization of the surface species was performed by using X-ray absorption near edge structure (XANES) spectroscopy and by X-ray photoelectron spectroscopy (XPS). The XPS spectra were obtained using a SPECS instrument (SPECS Surface Nano Analysis GmbH, Germany) equipped with a PHOIBOS 1500 MCD9 electron analyzer, with excitation by a MgKα line (1253.6 eV) of the X-ray tube and with a charge neutralisation gun. Pass energies were 20 eV for survey spectra and 8 eV for high resolution spectra; electron take-off angle was 90°. The data were collected over 0.05 eV increments, and multiple scans were taken to obtain spectra with high-enough signal-to-noise ratios to allow curve resolution techniques to be applied. Elemental concentrations were calculated from the survey spectra as peak areas corrected for atomic sensitivity factors. The photoelectron peaks were curve-resolved using a mixed 70-30 % GaussLorentzian lines shape to assess the relative amounts of the particular chemical species. A Shirleytype background was subtracted prior to fitting. An energy correction was made to account for sample charging by setting the binding energy of the sp2 carbon to 284.6 eV. XANES spectra were recorded in the total electron yield (TEY) mode at room temperature using the Russian-German laboratory equipment at the dipole magnet beam line at the BESSY II synchrotron facility (Helmholtz Zentrum Berlin, Germany); X-ray beam spot on a sample was 0.2 mm 0.5 mm, the angle between the incident beam and the sample was 45°, and the vacuum in the analytical chamber was better than 10-9 mBar. All the experimental procedures (carbonization, gasification, and each analytical measurement) were repeated usually two-three times and the average data were used. 3. RESULTS AND DISCUSSION 3.1. Characterization of the Compositions of Coals and Chars Table 1 shows that the parent brown coal samples had rather similar composition of the organic matter. The contents of the mineral matter (ash) ranged from 4.2 wt. % to 14.8 wt. %. The acid treatment did not affect significantly the composition of organic matter, but decreased the content of the ash up to 0.7%. Table 1. Characterization of Coals
aacid
coal sample
Аd, wt. %
Bor1
wt. % on daf coal C
H
N
S
Odif
7.7
71.3
4.8
0.9
0.2
22.8
Bor2
4.2
71.4
5.3
0.9
0.3
22.1
Bor3
14.8
69.3
5.2
0.7
0.3
23.9
Bor2Aa
0.7
69.3
4.9
0.7
0.3
24.8
Bor3Aa
12.6
70.5
5.0
0.8
0.3
23.4
treated coals ACS Paragon Plus Environment
Page 5 of 20
Energy & Fuels 5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
The coal ash consisted of predominantly silicon and alumina. Calcium was also the majour elements with the concentrations of 10.7 to 38.1 wt. % (Table 2). The concentrations of Mg and Fe ranged from 3.0 wt. % to 10.7 wt. % and from 1.6 wt. % to 10.9 wt. %, respectively. The alkali metals (Na and K) occurred typically with very small concentration (near 0.1 wt. %). Acid leaching resulted in almost complete extraction of Ca, Mg. The extent of Fe extraction ranged 50 % to 90 % depending on the sample. Table 2. Ca, Mg and Fe Contents in Coal Ashes wt. %
coal sample
aacid
Ca
Mg
Fe
Bor1
15.8
3.0
10.4
Bor2
38.1
10.7
10.9
Bor3
10.7
5.6
1.6
Bor2Aa
0.6
0.1
4.3
Bor3Aa
0.1
0.01
0.003
treated coals Coal pyrolysis at 700 °C yielded 54 % to 64 % of chars (Table 3). The contents of carbon,
hydrogen and oxygen in the chars from the parent coals were 91.2-92.3 %, 1.7-1.9 %, 4.3-5.2 wt. %. The contents of the ash ranged 1.4 % to 23.3 %. The acid treated chars had an enhanced carbon content and decreased oxygen and ash contents as compared to the non-treated ones. Table 3. The Yields of Chars from Coal Pyrolysis and Elemental Composition of Char Organic Matter char sample
wt. % on daf char
char yield, wt. %
C
H
N
S
Odif
Bor1C
57
91.2
1.9
1.2
0.5
5.2
Bor2C
64
92,3
1.7
1.3
0.4
4.3
Bor3C
62
91.7
1.9
1.2
0.6
4.6
Bor2AC
54
94.8
1.8
1.3
0.3
1.8
Bor3AC
58
94.7
1.8
1.4
0.4
1.7
XRD patterns showed mainly quartz particles (Q) to be present in all the chars (Fig.1). Some additional weak and broad reflections (Fe) which could be ascribed to some iron oxides (Fe2O3 or/and Fe3O4) were revealed in the chars subjected to gasification. Other XRD reflections were at the level of background and difficult for analysis and identification. XRD patterns showed no calcium particles in all the char samples studied. ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 20 6
Figure 1 XRD patterns of brown coal chars before (Bor1C and Bor1AC) and after steam gasification (Bor1CG). The chars prepared had predominantly microporous structure. According to N2 lowtemperature adsorption, BET surface areas ranged 74 m2/g to 239 m2/g (Table 4). According to previously reported paper 21, the spatial carbon structure consisted mainly of the ordered graphitelike matter and a small amount of the poorly ordered γ-component. The basic structural unit in the graphite-like matter represented the stacks of the planar polyaromatic molecules (3.6-4.0 layes) of 1.6-2.0 nm in diameter. Table 4. Characterization of the Properties of Coal Chars char
Ad,
Ca,
BET surface area,
burn-off,
sample
wt. %
wt. %
m2/g on daf char
wt. % on daf
Bor1C
13.0
2.1
74
27.8
Bor2C
6.9
2.6
162
68.7
Bor3C
23.3
2.5
239
53.8
Bor2AC
1.4
0.008
75
3.2
Bor3AC
19.8
0.03
101
5.9
Hereafter, the chars produced from the pyrolysis of the Born parent coals and from the acid treated BornA coals were denoted as BornС and BornAC, and the chars produced from the gasification of the BornC and BornAC samples were denoted as BornСG and BornACG, respectively. 3.2. Char Gasification Reactivity The data in Table 4 show the burn-off extents of the chars to differ dramatically (from 3.2% to 68.7%). The chars derived from the parent coals exhibited high reactivity depending on the content of calcium (up to 68.7% at 2.6% Ca). On the other hand, the acid treated chars showed very ACS Paragon Plus Environment
Page 7 of 20
Energy & Fuels 7
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
low burn-offs in accordance with our previously reported data chars and with the data of other authors.
12,14
19
for a large set of the brown coal
The evolution of micropores into mesopores and an
increase in the surface area up to 753 m2/g as the burn-off reached 68.7 % were observed, and the acid treated chars remained microporous. 3.3. Characterization of Surface Composition of Chars 3.3.1. Surface Concentrations of the Chemical Elements. The wide-scanning XPS detected major C and O elements on the surface of the brown coal chars, as well as other elements such as Si, Al, Ca, and also Fe, Na, S, N with low contents (1% and less). The atomic concentrations of the main elements normalized to C(1s)+ O(1s)+ N(1s)+ Ca(2p)+ Si(2p)=100 % are shown in Table 5. The carbon and oxygen atomic concentrations on the surface of the non-gasified chars derived from the parent coals ranged 82.2 at. % to 87.7 at. % and 9.9 at. % to 14.3 at. %, depending on the sample, respectively. The oxygen-containing ash minerals contributed likely to increased oxygen concentration on the surface introducing an uncertainty with respect to organic oxygen concentration. The calcium and silicon concentrations in the non-gasified chars ranged 1.0 % to 2.0 % and 0.7 % to 1.5 %, respectively. The concentrations of nitrogen, iron and sulphur were 0.6-0.7 %, near to 0.3 % and 0.2 % in most of the samples. The surface of the chars from the acid-treated coals contained more carbon, less oxygen, much less iron and traces or no calcium as compared to chars derived from the parent coals. Table 5. Characterization of Surface Composition of Chars Before and After Gasification as Detected by XPS Analysis atomic %
Ad,
burn-
sample
wt. %
off, %
C
O
Ca
Si
N
Bor1C
14.0
-
86.1
11.0
1.4
0.8
0.7
Bor2C
6.9
-
87.7
9.9
1.0
0.7
0.7
Bor3C
23.3
-
82.2
14.3
2.0
1.5
0.7
Bor2AC
1.4
-
92.5
6.0
0.1
0.6
0.8
Bor3AC
19.8
-
87.1
8.2
-
2.1
0.9
Bor1CG
18.1
27.8
81.9
14.4
2.1
1.0
0.6
Bor2CG
19.0
68.7
82.5
13.5
2.5
0.9
0.6
Bor3CG
39.7
53.8
77.0
17.8
2.9
3.1
0.8
Bor2ACG
1.5
3.2
91.9
6.2
0.1
0.9
0.9
Bor3ACG
20.8
5.9
90.0
7.8
-
1.5
0.5
char
Steam gasification resulted in decrease in the surface concentration of the carbon and in increase in the concentrations of oxygen, calcium, silicon and iron. Nitrogen concentration decreased a little, however, practically no change in the N/C atomic ratio was observed during char ACS Paragon Plus Environment
Energy & Fuels
gasification up to 68.7 %, i.e. nitrogen species were subjected to steam gasification synchronously with the carbon ones. 3.3.2. Chemical Surface Species. Oxygen-containing species are considered usually to be a key to the understanding of the steam gasification reactions.
9
The O 1s XPS spectra from the chars
showed broad (fwhm of 3.2-4.2 eV) and asymmetric signals between 530 and 535 eV which are characteristic of majority of the oxygen-containing groups in both the organic and inorganic species.
22-24
The spectra were best curve-resolved into three-four sub-peaks depending on the
samples. Displayed in Figure 2 are two examples of the deconvoluted O1s XPS spectra from two chars before gasification. The spectra from the Bor2AC showed two main sub-peaks at the binding energies of 532.3 eV (which could be ascribed to C=O bonds) and 533.6 eV (ether, carbonates) and also two small sub-peaks at near 530.5 eV (carbonic acid) and 535.0 eV (silicate, aluminasilicates). Bor2C sample had different proportions between sub-peaks. Other chars showed also complicated spectral pictures with different proportions between the sub-peaks which were difficult to specify.
O1s Bor2AC
Intensity, arb.unit
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 8 of 20 8
Bor2C
538 536 534 532 530 528
Binding energy, eV Figure 2. O 1s XPS deconvoluted spectra from Bor2AC and Bor2C char samples before gasification. Oxygen K-edge spectra (XANES) were also explored. XANES is more sensitive to the electronic state of the absorbting atom, as compared to XPS, and frequently provides very characteristic fingerprints for different compounds. It is of importance also that we recorded the spectra in the total electron yield mode which is more surface sensitive as compared to fluorescent yield mode. One can see from K-edge TEY XANES spectra in Fig.3 that the spectrum from Bor2CG char shows a distinct characteristic peak at 533.0 eV which can be assigned to carbonates (or perhaps, to organic ethers species). The acid-treated Bor2ACG with least content of inorganics (1.5 %) shows peaks near 529.8 eV and more distinct peak at 531.3 eV which could be assigned to oxides and carboxylic acids. Thus, the O1s XPS and O XANES spectra showed significant diversification in the composition of the surface oxygen-containing species of chars. However, it ACS Paragon Plus Environment
Page 9 of 20
Energy & Fuels 9
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
was impossible to recognize accurately their structures because of the presence of a large variety of the mineral and organic substances.
Figure 3. Oxygen K-edge TEY XANES spectra from partially gasified Bor2CG and Bor2ACG char samples prepared from the parent and acid-treated Bor2 coal. Additional data on the surface oxygen functionalities in the organic matter of the chars were derived from the carbon K-edge XANES and C1s XPS spectra. Considered in the next paragraph are the data obtained. Carbon-containing species. The C 1s emission from the carbon-oxygen substances occurs at higher binding energies from the main C 1s line depending on the type of carbon-oxygen bonds. The shift range for the C1s levels is sufficiently large (5.5-6.0 eV), so that the technique allowed carbon-oxygen functionalities to be differentiated according to their C1s shifts.22 Displayed in Figure 4 are the carbon K-edge XANES spectra from two char samples as examples. The spectra show several more or less resolved peaks, their assignements were made according to the references.
22,24
The main distinct peak at near 285 eV was assigned to sp2-
hybridized carbon atoms in the graphene fragments, while other poorly resolved peaks at the higher binding energies were related to the oxidized carbon species, namely, to hydroxyl/ether/carbonyl species (shoulder around 286.5 eV), to carboxyls (288.3 eV). The energy region between 287-288 eV can correspond also to aliphatic carbons.
22,24
However, according to the literature data25,26,
virtually all the aliphatics in the coals disappeared while heating to 600 oC. This means that aliphatic carbons in the chars studied could present only in insignificant concentration, if any. The significant feature of the spectrum from the Bor2CG char (derived from the parent coal) was a distinct peak at 290.0 eV indicating the presence of the carbonate species, no absorption at this binding energy being observed in the spectrum from the acid-treated chars.
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 10 of 20 10
Figure 4. Carbon K-edge TEY XANES spectra from partially gasified Bor2CG and Bor2ACG char samples prepared from the parent and acid-treated Bor2 coal. Now one can turn to C 1s XPS spectra from different chars before and after gasification. The spectra in Figure 5 show broad peaks (centered at the binding energy of 284.6±0.1 eV) with an asymmetry toward a high binding energy due to oxygen effect. The spectra were best curveresolved using five sub-peaks. The main sub-peak centered at the binding energy of 284.6 eV corresponds to sp2-hybridized carbon in the graphene sheets. The binding energy shifts were classified as follows: sub-peak at 285.6±0.1 eV was assigned to hydroxyls, ethers and epoxides; at 286.7±0.2 eV to C=O in carbonyls, ketones and quinones; at 288.2±0.2 eV to COO in carboxyls and esters, and at 290.3±0.2 eV to COOMe species in carbonates. Summarized in Table 6 are the data on semi-quantitative evaluation of the carbon atom distribution between the particular surface chemical species. One can see that 68-71 % of all the carbon atoms represented sp2-hybridized carbon in the graphene structures, while the remaining 2932 % accounted for as oxidized carbon species of different configurations. The largest proportion of the oxidized carbons (16-18 %) accounted for hydroxyls, epoxides and ethers, and smaller proportion (7-11 %) for ketones/carbonyls and carboxyls. Carbonate species in the chars from the parent coals accounted for 4-5 % of all the carbon atoms, while only about 2 % may occur in the acid treated chars.
ACS Paragon Plus Environment
Page 11 of 20
Energy & Fuels 11
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Figure 5. Variations of the C 1s XPS deconvoluted spectra from different gasified and non-gasified char samples. Gasification of the chars from the parent coals resulted in decrease in the proportion of sp2hybridized carbon atoms and in increase in the proportion of hydroxyl/ether/epoxide species. On the other hand, only moderate and non-regular change in the proportion of carbonyls/ketones and little increase, if any, in the proportion of carboxyls were observed. As a result of carbon burn-off, more carbonate species were observed on the surface. No significant diversification in the distribution of the carbon-oxygen species was observed after gasification of the acid-treated chars. Thus, it follows that before gasification, the distribution of the carbon atoms between different surface species in both the parent and acid treated chars was broadly similar, except for more amount of carbonate species in the chars from the parent coals. During gasification, sp2 -hybridized carbon atoms in the graphene fragments in the presence of surface carbonate species were consumed via oxidation. As a result of oxidation, hydroxyls/ethers/epoxides were generated. However, being intermediates they also could be consumed leading finally to gaseous carbon ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 12 of 20 12
oxides, and an increase in the proportion of the hydroxyls/ethers/epoxides after gasification showed that the rate of generation exceeded that of consumption. As for carbonates, the increase in the proportion after gasification can be explained by carbon burn-off. As a result, the subsurface calcium carbonate species turned out on the carbon surface. Table 6. The Distribution of Carbon Atoms Between Different Functional Groups in the Chars char
burn-
sample
off, %
Bor1C
-
Bor2C
carbon distribution, % at. graphene
hydroxyls,
carbonyls,
carbons
ethers, epoxides
ketones
71
16
68
carboxyls
carbonates
5
4
4
17
6
4
5
Bor3C
-
70
18
4
3
5
Bor2AC
-
71
17
5
5
2
Bor3AC
-
70
17
5
6
2
Bor1CG
27.8
64
18
6
5
7
Bor2CG
68.7
57
21
6
5
11
Bor3CG
53.8
62
19
4
5
10
Bor2ACG
3.2
71
17
6
4
2
Bor3ACG
5.9
69
18
5
5
3
Nitrogen-containing Species. Displayed in Figure 6 are N 1s XPS deconvoluted spectra from the representative chars as examples. The assignement of the peaks was made according to the references.
17,27,28
The spectra from the acid-leached chars were best deconvoluted into two
Gaussian-Lorentzian components with the binding energies at 398.7±0.2 eV and 400.3±0.2 eV. These sub-peaks were assigned, respectively, to pyridinic-N in six-membered aromatic cycles (designated here as N1 species) and to pyrrolic-type of nitrogen (pyrrolic-N in five-membered aromatic cycles) and/or to pyridonic-type form, i.e., to pyridinic-N in six-membered cycles bearing oxygen-containing substituent such as hydroxyl and carboxyl. For the chars from the parent coals, additional components with the binding energies at 401.7±0.2 eV and near 403 eV were required to provide a best fit to the spectra. The peak at 401.7 eV (N3 species) is usually assigned to a quaternary nitrogen covalently bonded with three carbon atoms within the condensed systems or/and to a pyridinic nitrogen with a formal positive charge induced by the nearby hydroxyl or carboxyl groups. The chemical-structural identification of the peak near 403 eV (denoted as N4) is still more ambiguously. Most likely is that it represents an Noxide of pyridinic–N or other form of oxidized nitrogen.
ACS Paragon Plus Environment
Page 13 of 20
Energy & Fuels 13
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Figure 6. N 1s XPS deconvoluted spectra from the non-gasified and partially-gasified chars prepared from the parent and acid leached Bor2 and Bor3 coals. The proportions between the specific nitrogen functionalities varied depending of the sample. One can see from Table 7 that pyridinic N1 and pyrrolic/pyridonic N2 species dominated in all the chars, with major N2 species accounting for 52-65 %. The quaternary N3 species in the non-gasified chars from the parent coals turned out to be the most reactive, and disappeared entirely on steam gasification in favor of an additional amount of N1 species and of new oxidized N4 species. The is intriguing because quaternary N3 species located inside the graphene sheet are considered usually as most stable compared to pyridinic-N and pyrrolic-N.
17,28
Hence, most likely, N3 species on the
non-gasifed chars obtained from the parent brown coals at mild temperature represented alternative quaternery nitrogen species of the pyridinic nature, namely, the edge-located pyridinic-N with a positive charge induced by nearby hydroxyl/carboxyl group. During gasification, the latter could be subjected to dehydroxylation/decarboxylation resulting in the conversion of the positively charged pyridinic-N into the neutral pyridinic-N species and partially into new oxidized-N species. The acid-leached chars only contained N1 and N2 species, the proportion between them being little affected by steam gasification. It should be noted that the conversion of the quaternary nitrogen species into pyridinic-N species upon mild pyrolysis of coals was reported by several authors.
16,27
However, under the
high-severity pyrolysis conditions and during metamorphic maturation, the pyridinic and pyrrolic edge-localized nitrogen atoms tended to localize in the interior of the graphene sheets. 16,28
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 14 of 20 14
Table 7. The Distribution of Nitrogen Atoms Between Different Nitrogen Species char sample
nitrogen proportion, at. % N1
N2
N3
N4
Bor2C
28
52
20
-
Bor2CG
36
53
-
11
Bor3C
32
56
12
-
Bor3CG
39
52
-
9
Bor2AC
35
65
-
-
Bor2ACG
38
62
-
-
Calcium-containing Species. Displayed in Figure 7 are the examples of the Ca 2p XPS spectra from the chars before and after steam gasification. The spectra show doublet peaks of the 2p3/2 and 2p1/2 states with the binding energies of 347.7±0.2 eV and 351.2±0.2 eV attributed to calcium substances, such as oxide, sulphate or carbonate, in particular. 29,30 The coupled evidences from the C K-edge and O K-edge spectra (in Figures. 4 and 3) seem to indicate carbonate nature of the calcium species. However, CaCO3 species can be represented by calcite or aragonite polymorphs which are compositionally identical, but differ with the crystaline structure: in the aragonite, Ca is coordinated with nine oxygen atoms, and in the calcite, it is coordinated with six oxygen atoms.
Figure 7. Ca 2p XPS spectra from the non-gasified Bor2C and partially-gasified Bor2CG and Bor3CG chars. The use of Ca L-edge spectra allowed us to gain more insight into the chemical forms of the calcium species, and to follow their evolution upon char gasification. Shown in Figure 8 are the Ca L-edge spectra from the non-gasified Bor2C char (2.6 wt. % of Ca) and from the respective partially-gasified Bor2CG char (68.7 % of burn-off). Both spectra show two primary peaks at 348.7 ACS Paragon Plus Environment
Page 15 of 20
Energy & Fuels 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
eV and 352.0 eV corresponding to the L2 and L3 absorption edges.
29,30
The peak from the Bor2C
char was more broadened (0.79 eV of fwhm for the primary peak at 352.0 eV) as compared to the respective gasified char (0.66 eV of fwhm). In addition, the spectra show that partially-gasified Bor2CG char has also fairly strong pre-edge peaks at 347.8 eV and 350.9 eV, which, together with two primary peaks, are typical for calcite. In the spectrum from the non-gasified Bor2C char, the pre-edge peak on the low energy side of the L2 absorption edge is hardly visible, but that on the low energy side of the L3 line has only very weak shoulder. Such a spectral feature is characteristic of the aragonite,
29,31
rather than calcite. The broadened aragonite peaks may reflect less developed
structure.
Figure 8. Calcium L-edge TEY XANES spectra from the non-gasified Bor2C and partially gasified Bor2CG char samples. Thus, one can consider calcium species both in the non-gasified chars and in the partially gasified at 700 °C chars as being carbonate forms, but with different chemical structures, both kinds of species being in the states of the nano-sized nuclei, neither of which was identified by XRD (Figure 1). The generation of these highly dispersed calcium carbonate species took place upon mild thermal decomposition of the native calcium carboxylate/phenolate complexes present in the organic matter of brown coals in a molecularly dispersed form. It should be noted here that aragonite itself is relatively unstable and tends to polymorphic transition to calcite at the temperatures of about 400-500 °C. We suggested that the stabilization of the aragonite-like species on the char surface at 700 °C was a result of the intimate chemical bonding with the surface carbon-oxygen functionalities, such as carboxyl, hydroxyl and other functionalities. This chemical bonding could hinder solid-phase transition as may well be the case in the natural bio-mineral systems, where the interaction between the organic macromolecules and the emerging minerals has been shown
31
to govern the formation of the microbially generated
nanoscale oxides, sulfides, carbonates, oxalates, ets. The formation of the dispersed aragonite particles in the organic-rich natural matrix was suggested ACS Paragon Plus Environment
31
to result from the ability of
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 16 of 20 16
macromolecules to promote the formation of numerous nucleation sites and, at the same time, to inhibit growth of the crystallite species by poisoning their surface. Also, we suggest that an additional stabilization of the aragonite species could result from the large alkaline-earth cations, like Sr and Ba, which are typically present in the Kansk-Achinsk coals and could be included into the emerging aragonite species. Exactly these large alkali-earth cations are known
32
to govern the
formation of the aragonite structure, and this is a reason why natural aragonite minerals inevitably comprise of some amounts of these cations. However, under the gasification conditions, the inter-phase chemical bonds were subjected to steam hydrolysis, therefore chemical features inherent to aragonite species were lost resulting in a solid-phase polymorphic transition of the aragonite into more stable calcite. Iron-containing species. The chars derived from the parent coals contained little iron species (surface concentration of near 0.5 %). The Fe L-edge spectra showed several reflexes indicating multiple chemical states of surface iron species (Figure 9). The distinct peak at 708.5 eV can be assigned to some iron oxide species 33, the shoulder at 707 eV could indicate little metallic iron. It should be noted that XRD patterns of the non-gasified chars (Figure 1) showed no iron-containing particles, probably, because of their dispersed states. Steam gasification promoted oxidation and sintering of the iron species, and, as a result, some of them proved to be visible in the XRD patters. The Fe L-edge spectra from the acid-treated chars were broadly similar to those from the parent chars, however, the signals were near-to-noise level.
Figure 9. Iron L-edge TEY XANES spectra from the non-gasified Bor2C and Bor2AC and from partially gasified Bor2CG and Bor2ACG char samples. 4. CONCLUSION In this paper, detailed study focused on chemical characterization of the surface species on the Kansk-Achinsk brown coal chars with different inherent mineral matter, calcium, in particular, and ACS Paragon Plus Environment
Page 17 of 20
Energy & Fuels 17
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
on the evolution of surface species upon steam gasification was performed by using surface sensitive XPS and XANES spectra. The main findings were as follows: (1) The naturally occurring calcium surface species on the brown coal chars at 700 oC both before and after gasification represented dispersed carbonate-like forms. However, before the reaction, they represented aragonite-like species which were chemically stabilized due to bonding with the surface carbon-oxygen functionalities. Under steam gasification conditions, the inter-phase chemical bonds were hydrolysed, and aragonite species underwent solid-phase polymorphic transition into a more stable calcite-like form. Both calcium carbonate polymorphs occurred in the highly dispersed states, neither of which was detected by XRD. (2) The distribution of the carbon atoms between different species on the surface of chars both from the parent mineralized and acid-treated partially demineralized coals was broadly similar before gasification, except for more amounts of the carbonate species on the chars from the parent coals. The main proportion of carbon atoms (68 to 71 %) represented sp2 -hybridized carbons in the graphene fragments, while the remaining 29-32 % accounted for as oxidized carbon species of different configurations. The nitrogen atoms occurred in the carbon cycles at the edges of graphene sheets. (3) Char reactivity for steam gasification differred dramatically depending on the calcium content. Mainly sp2-hybridized surface carbon atoms in the presence of highly dispersed carbonate species exhibited high reactivity, i.e. it is this type of carbon atoms which was sensitive to activation by calcium catalyst. As a result of catalytic oxidation, the hydroxyl/ether/epoxide species were accumulated on the char surface. However, being intermediates they could be further converted leading finally to gaseous carbon oxides. (4) The conclusion was drawn that these were highly dispersed calcite-like surface species arised from the aragonite-like ones under steam gasification reaction which could be responsible for the catalytic activation of sp2-hybridized carbon atoms and for char gasification reactivity. ACKNOWLEDGMENTS. This work was funded by Federal Research Center “Krasnoyarsk Scientific Center of Siberian Branch of Russian Academy of Sciences”, Russia, and supported also by the bilateral program “Russian-German Laboratory at BESSY”, authors thank the staff of RGLab and BESSY. REFERENCES (1) D.J. Harris, D.G. Roberts, Chapter 16 - coal gasification and conversion, in: D. Osborn (Ed.), The Coal Handbook: Towards Cleaner Production, Volume 2 in Woodhead Publishing Series in
Energy,
Woodhead
Publishing
Limited,
https://doi.org/10.1533/9781782421177.3.427 ACS Paragon Plus Environment
Oxford,
2013,
pp.
427–454.
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 18 of 20 18
(2) Dong, L.; Asadullah, M.; Zhang, S.; Wang, X.-S.; Wu, H.; Li, C.-Z. An Advanced Biomass Gasification Technology with Integrated Catalytic Hot Gas Cleaning Part I. Technology and Initial Experimental Results in a Lab-scale Facility. Fuel 2013, 108, 409-416. doi.org/10.1016/j.fuel.2012.11.043. (3) C.E. Snape, Liquid Fuels and Chemical Feedstocks. In Coal in the 21st Century: Energy Needs, Chemicals and Environmental Controls; Hester, R.E., Harrison, R.M. Eds; The Royal Society
of
Chemistry:
London,
UK,
2017,
pp.
173-197.
https://doi.org/10.1039/9781788010115-FP011 (4) Wu, H.; Quyn, D.M.; Li, C.-Z. Volatilisation and Catalytic Effects of Alkali and Alkaline Earth Metallic Species During the Pyrolysis and Gasification of Victorian Brown Coal. Part III. The Importance of the Interactions Between Volatiles and Char at High Temperature. Fuel 2002, 81, 1033-1039. https://doi.org/10.1016/S0016-2361(02)00011-X. (5) Tomita, A.; Ohtsuka, Y. Gasification and Combustion of Brown Coal. In Advances in the Science of Victorian Brown Coal; Li, C.-Z. Ed.; Elsevier: Amsterdam, Netherlands, 2004; Chapter 5, pp 223-285. https://doi.org/10.1016/B978-008044269-3/50006-6. (6) Quyn, D.M.; Wu, H.; Hayashi, J.-I.; Li, C.-Z. Volatilisation and Catalytic Effects of Alkali and Alkaline Earth Metallic Species During the Pyrolysis and Gasification of Victorian Brown Coal. Part IV. Catalytic Effects of NaCl and Ion-exchangeable Na in Coal on Char Reactivity. Fuel 2003, 82, 587-593. https://doi.org/10.1016/S0016-2361(02)00323-X. (7) Gonzalez, J.D.; Mondragon, F.; Espinal, J.F. Effect of Calcium on Gasification of Carbonaceous
Materials
with
CO2:
A
DFT
Study.
Fuel
2013,
114,
199-205.
doi.org/10.1016/j.fuel.2012.04.039. (8) Jimenez-Orozco, C.; Mondragón, F.; Espinal, J.F. Experimental and Computational Analysis of the Formation of Surface Oxygen Functional Groups During Iron Catalyzed Char Gasification
with
CO2.
Combustion
Science
Technology
2018,
190,
687-706.
https://doi.org/10.1080/00102202.2017.1405948. (9) Kapteijn, F.; Meijer, R.; Moulijn, J.A.; Amoros, D.C. On Why Do Different Carbons Show Different Gasification Rates: A Transient Isotopic CO2 Gasification Study. Carbon 1994, 32, 1223-1231. doi.org/10.1016/0008-6223(94)90106-6 (10) Cazorla-Amoros, D.; Linares-Solano, A.; Dekker, F.H.M.; Kapteijn, F. Isotopic Steady-state and Step-response Study on Carbon Gasification Catalyzed by Calcium. Carbon 1995, 33, 1147-1154. https://doi.org/10.1016/0008-6223(95)00068-O. (11) Lizzio, A.A.; Radovic, L.R. Transient Kinetics Study of Catalytic Char Gasification in Carbon
Dioxide.
Ind.
Eng.
Chem.
Res.
https://doi.org/10.1021/ie00056a009.
ACS Paragon Plus Environment
1991,
30,
1735-1740.
Page 19 of 20
Energy & Fuels 19
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
(12) Takarada, T.; Tamai, Y.; Tomita, A. Reactivities of 34 Coals Under Steam Gasification. Fuel 1985, 64, 1438-1442. doi.org/10.1016/0016-2361(85)90347-3. (13) Ma, Z.; Bai, J.; Bai, Z.; Kong, L.; Guo, Z.; Yan, J.; Li, W. Mineral Transformation in Char and its Effect on Coal Char Gasification Reactivity at High Temperatures, Part 2: Char Gasification. Energy Fuels 2014, 28, 1846-1853. https://dx.doi.org/10.1021/ef402382m. (14) Miura, K.; Hashimoto, K.; Silveston, P.L. Factors Affecting the Reactivity of Coal Chars During Gasification, and Indices Representing Reactivity. Fuel 1989, 68, 1461-1467. https://doi.org/10.1016/0016-2361(89)90046-X. (15) Song, Y.; Feng, W.; Li, N.; Li, Y.; Zhi, K.; Teng, Y.; He, R.; Zhou, H.; Liu, Q. Effects of Demineralization on the Structure and Combustion Properties of Shengli Lignite. Fuel 2016, 183, 659-667. https://doi.org/10.1016/j.fuel.2016.06.109. (16) Kelemen, S.R.; Gorbaty, M.L.; Kwiatek, P.J. Quantification of Nitrogen Forms in Argonne Premium Coals. Energy Fuels 1994, 8, 896-906. https://doi.org/10.1021/ef00046a013. (17) Wójtowicz, M.A.; Pels, J.R.; Moulijn, J.A. The Fate of Nitrogen Functionalities in Coal During Pyrolysis and Combustion. Fuel 1995, 74, 507-516. http://doi.org/10.1016/00162361(95)98352-F. (18) Li, N.; Li, Y.; Zhou, H.; Liu, Y.; Song, Y.; Zhi, K.; He, R.; Yang, K.; Liu, Q. Direct Production of High Hydrogen Syngas by Steam Gasification of Shengli Lignite/Chars: Significant Catalytic Effect of Calcium and its Possible Active Intermediate Complexes. Fuel 2017, 203, 817-824. https://doi.org/10.1016/j.fuel.2017.05.010. (19) Kuznetsov, P.N.; Kolesnikova, S.M.; Kuznetsova, L.I. Steam Gasification of Different Brown Coals Catalyzed by the Naturally Occurring Calcium Species. International Journal of Clean Coal and Energy 2013, 2, 1-11. https://doi.org/10.4236/ijcce.2013.21001. (20) Kuznetsov, P.N.; Kuznetsova, L.I.; Mikhlin, Y.L. Chemical Forms and Distribution of Naturally Occurring Calcium in Brown Coal Chars. Fuel 2015, 162, 207-210. https://doi.org/10.1016/j.fuel.2015.09.015. (21) Kuznetsov, P.N.; Kamenskiy, E.S.; Kolesnikova, S.M.; Kuznetsova, L.I. Structural Properties of Carbonization Products Obtained from Brown Coals with Different Mineral Matter
Contents.
Solid
Fuel
Chemistry
2014,
48,
51-57.
https://doi.org/10.3103/S0361521914010054. (22) NIST X-ray Photoelectron Spectroscopy Database, NIST Standard Reference Database Number 20, National Institute of Standards and Technology, Gaithersburg MD, 20899 (2000) (accessed 02 October 2018). http://dx.doi.org/10.18434/T4T88K. (23) Turner, J.A.; Thomas, K.M.; Russell, A.E. The Identification of Oxygen Functional Groups in Carbonaceous Materials by Oxygen K-edge XANES. Carbon 1997, 35, 983-992. https://doi.org/10.1016/S0008-6223(97)00054-7. ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 20 of 20 20
(24) Cody, G.D.; Ade, H.; Alexander, C.M.; Araki, T.; Butterworth, A.; Fleckenstein, H.; Flynn, G.; Gilles, M.K.; Jacobsen, C.; Kilcoyne, A.L.D.; Messenger, K.; Sandford, S.A.; Tyliszczak, T.; Westphal, A.J.; Wirick, S.; Yabuta, H. Quantitative organic and light-element analysis of comet 81P/Wild 2 particles using C-, N-, and O-μ-XaNES. Meteoritic Planetary Science 2008, 43, 353–365. https://doi.org/10.1111/j.1945-5100.2008.tb00627.x. (25) Ibarra, J. V.; Moliner R.; Bonet A. J. FT-i.r. investigation on char formation during the early stages of coal pyrolysis. Fuel 1994, 73, 918-924. https://doi.org/10.1016/0016-2361(94)902879. (26) Solomon P. R.; Carangelo R. M. FT-i.r. analysis of coal: 2. Aliphatic and aromatic hydrogen concentration. Fuel 1988, 67, 949-959. https://doi.org/10.1016/0016-2361(88)90095-6. (27) Pels, J.R.; Kapteijn, F.; Moulijn, J.A.; Zhu, Q.; Thomas, K.M. Evolution of Nitrogen Functionalities in Carbonaceous Materials During Pyrolysis. Carbon 1995, 33, 1641-1653. https://doi.org/10.1016/0008-6223(95)00154-6. (28) Boudou, J.P.; Schimmelmann, A.; Ader, M.; Mastalerz, M.; Sebilo, M.; Gengembre, L. Organic Nitrogen Chemistry During Low-grade Metamorphism. Geochim. Cosmochim. Acta 2008, 72, 1199-1221. https://doi.org/10.1016/j.gca.2007.12.004. (29) Brandes, J.A.; Wirick, S.; Jacobsen, C. Carbon K-edge Spectra of Carbonate Minerals. J. Synchrotron Radiation 2010, 17, 676-682. http://dx.doi.org/10.1107/S0909049510020029. (30) Rez, P.; Blackwell, A. Ca L23 Spectrum in Amorphous and Crystalline Phases of Calcium Carbonat. J. Physical Chemistry B 2011, 115, 11193-11198. http://doi.org/10.1021/jp203057y. (31) Benzerara, K.; Menguy, N.; Lopez-Garcia, P.; Yoon, T.-H.; Kazmierczak, J.; Tyliszczak, T.; Guyot, F.; Brown, G.E. Nanoscale Detection of Organic Signatures in Carbonate Microbiolites. PNAS 2006, 103, 9440-9445. https://doi.org/10.1073/pnas.0603255103. (32) Menadakis, M.; Maroulis, G.; Koutsoukos, P.G.; Incorporation of Mg2+, Sr2+, Ba2+ and Zn2+ Into Aragonite and Comparison with Calcite. J. Math. Chem. 2009, 46, 484-491. https://doi.org/10.1007/s10910-008-9490-4. (33) Grosvenor, A.P.; Kobe, B.A.; Biesinger, M.C. Investigation of Multiplet Splitting of Fe 2p XPS Spectra and Bonding in Iron Compounds. Surf. Interface Anal. 2004, 36, 1564-1574. https://doi.org/10.1002/sia.1984.
ACS Paragon Plus Environment
