X-ray Photoelectron Spectroscopy Analysis of Hydrotreated Athabasca

Subscriber access provided by UNIVERSITY OF CONNECTICUT

Article

X-ray Photoelectron Spectroscopy (XPS) Analysis of Hydrotreated Athabasca Asphaltenes Hector J Guzman, Fernanda Isquierdo, Lante Antonio Carbognani Ortega, Gerardo Vitale, Carlos E. Scott, and Pedro Rafael Pereira-Almao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01863 • Publication Date (Web): 29 Aug 2017 Downloaded from http://pubs.acs.org on August 30, 2017

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 free 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 accessible to all readers and 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.

Energy & Fuels 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 27

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

Energy & Fuels

X-ray Photoelectron Spectroscopy (XPS) Analysis of Hydrotreated Athabasca Asphaltenes

Héctor J. Guzmán, Fernanda Isquierdo, Lante Carbognani, Gerardo Vitale, Carlos E. Scott, Pedro Pereira-Almao Schulich School of Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada.

Abstract C7 asphaltenes from Athabasca crude oil were hydrotreated using a commercial NiW/Al2O3 catalyst and analyzed using X-ray Photoelectron Spectroscopy (XPS). Results showed that the catalyst performed better in the removal of sulfur rather than nitrogen and that sulfur concentration is higher at the surface in comparison to the bulk structure. Moreover, the sample after reaction had a higher oxygen content in comparison to the untreated asphaltene indicating poor hydrodeoxygenation (HDO) performance of the catalyst in addition to a higher reactivity towards atmospheric oxygen at the surface of the asphaltene. The latter is proposed to arise once the layer of resin covering the asphaltene is partially converted during the hydrotreating process.

1.- Introduction Asphaltenes are defined as the fraction of crude oil that is insoluble in n-paraffins, typically n-C5 and n-C7, but soluble in aromatic solvents such as toluene and benzene. It has been reported that extraction of crude oils and bitumen is extremely dependent on reservoir conditions and the natural occurring viscosity of the material, which has been correlated to the type of molecules present in the crude oil matrix, mainly resins and asphaltenes. Some researchers have pointed out that the distribution of such compounds in the bituminous layer on the sand grains present in the sub-rock also offers an influence in the quality of the extraction process1. Nevertheless, understanding the dynamic equilibria played by these two fractions will offer the advantage of assessing the role that such molecules have in the stability and properties of crude oil and bitumen2, providing the foundation to improve the quality of extraction and the upgrading parameters in order to achieve the desired properties in the oil and its different fractionation products. One key factor that plays a major role is the identification of the molecules present in the asphaltene and resin fractions and how they interact with each other. There are many studies in the open literature dealing with sampling and identification of many different compounds present in those fractions and the changes that they undergo when submitted to different treatments and solvent extraction procedures. Thus far, many families of compounds have been identified by diverse techniques involving solvent extraction procedures, fractionation and reactions and their subsequent identification by many analytical techniques: GC-MS3–7, Size Exclusion

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

Chromatography8, NMR9 or by direct measurement using spectroscopy techniques, such as IR10,11, XANES12–14, Near-UV/Visible Absorption Spectroscopy15, TOF-SIMS16,17, Auger Electron Spectroscopy18 and XPS19–25; although with a limited scope and some of them with errors26. Many of these techniques have been discussed in more detail by Merdrignac et al27. In each case, such studies have answered many questions about the chemical nature of asphaltenes but still fall short from what it is required to provide breakthrough knowledge in terms of processing and converting such fraction, if possible, into more desirable products. Hydrotreating of asphaltenes is one of the many paths currently researched to improve the quality of such fraction and convert it into a more economically attractive product. Under this scope, XPS offers the advantage of identifying the functional groups present at the surface of the solid and the possibility of quantifying the changes carried out by the catalyst in such macromolecules. Most of the XPS studies cited so far have only dealt with the characterization of asphaltenes in a superficial fashion, but an in-depth study of asphaltenes and resins fractions at different take off angles is lacking. Such approach has proven to shed light into the dynamics of the catalysis conversion and in the overlooked fact that precipitation of asphaltenes is highly dependent of manipulation conditions; parameters which are not taken into account by traditional precipitation methods and obviously, influence the properties and behavior of the material.

2.- Experimental methodology Materials Toluene of HPLC grade from Sigma-Aldrich was used as received. Air, Ar, H2, He, and N2 of UHP grade were purchased from Praxair Canada. A commercial NiW/Al2O3 catalyst was used for the tests and the asphaltenes samples were precipitated from a commercial pitch provided by Nexen-CNOOC Ltd. Details about sample and catalyst preparation and sample separation after reaction are reported by Isquierdo28,29.

2.1.-Precipitation of Asphaltenes The precipitation of the n-C7 asphaltenes samples used in this study were obtained using the procedure reported elsewhere28,30. The samples were analyzed as received without any pretreatment. The samples were named as follow: Asphaltenes before reaction (C7 ATH BR); Asphaltenes After reaction (C7 ATH AR); Asphaltenes after reaction + Resins (C7 ATH AR + Resins) and C7 resins (Resin).

2.2.- Hydrotreatment The precipitated asphaltenes were treated with a commercial NiW/Al2O3 catalyst in a batch reactor (Parr). The treatment was performed at 380 ºC with 800 psi of H2 for a total reaction time of 6 h28,29.

2.3- X-Ray Photoelectron Spectroscopy (XPS) analysis The XPS experiments were performed in a PHI VersaProbe 5000 (Physical Electronics, USA) under a vacuum of 10-9 Pa (10-10 Torr). The spectra were taken using a monochromatic Al source


Page 2 of 27

Page 3 of 27

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

Energy & Fuels

(1486.6 eV) at 50 W, with a beam diameter of 200.0 µm and 15 KV. For the high-resolution spectra, a pass energy of 23.5 eV and an energy step of 0.1 eV were employed while for the survey spectra, a pass energy of 187.85 eV with an energy step of 1 eV were used instead. The samples were loaded in a custom-made sample holder, pressed on In foil, and spectra taken with a double neutralization, i.e., a low energy electron beam and low energy Ar+ beam. The binding energies are reported relative to C1s at (284.8 +/- 0.2) eV and peak fitting was performed using the Multipak 9.2.0.5 software (Physical Electronics, USA). For the destructive depth profiling experiments, the sputtering protocol involved 10 min of Argon bombardment at 45°, 2 kV, 1.5 µA 2 × 2 mm (~10.5 nm/min). Calibration was performed with a wafer SiO2/Si having a SiO2 layer of 100 nm.

2.4- Angle resolved (AR) analysis Due to the reactive nature of asphaltenes molecules, angle resolved XPS was chosen as a method of analysis in order to study the surface layer of such compounds in a non-destructive manner31. In this case, when acquiring data from different angles the procedure is called an angled resolved profiling and it is used to determine the composition of the different layers comprising the solid as function of depth32. It is estimated that the sampling depth of the XPS technique is about 10 nm; but when using angle resolved analysis such depth can increase up to 30 nm. Normally, with a destructive depth profiling (sputtering), this number can increase up to a 1000 nm. The setup of the PHI Versa-probe XPS instrument used is shown in Fig. 1. When acquiring signal at different angles, the angle of the sample holder (surface normal) with respect to the analyzer is increased while the X-ray source is kept in a fixed position33 as illustrated in Fig. 2. This angle is called the take-off angle of the photoelectrons. The photoelectrons thus are originated from an increased localized zone as take-off angle increments.


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

• Electrons • X-rays • Photoelectrons

Page 4 of 27

Ellipsoidal Monochromator

LaB6 Scanning Electron Source

Scanning Input Lens

Al Anode

SCA = Spherical capacitor analyzer 5-Axis Stage

Fig. 1: Setup for the angle resolved analysis in a PHI VersaProbe 5000 (courtesy of Physical Electronics USA, modified).

Fig. 2: Depth profiled at different take-off angles (courtesy of Physical Electronics USA, modified). Spectra were fitted using a Shirley background. Gaussian/Lorentzian contributions were allowed to vary independently to compensate for broadening of the FWHM (Full Width to Half Maximum) due to changes in the chemical environment of the asphaltenes. Energy resolution was measured using the 3d5/2 Ag peak. A FWHM value of 0.75 was obtained with an asymmetric background (pass energy of 23.5 eV). In the case of the S region, the peak fitting conditions used were the following:


Page 5 of 27

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

Energy & Fuels

• • •

Difference in binding energy between the S2p3/2 and S2p1/2 signals ≈ 1.18 eV. Area ratio for the S2p3/2/S2p1/2 signals = 0.5 Ratio of the full width to half maximum S2p1/2/S2p3/2 signals ≈ 0.9 - 1.2 (depending on the specie).

3.- Analysis of Asphaltenes using X-ray Photoelectron Spectroscopy

The changes that occurred at the surface of the asphaltene can be appreciated in Fig. 3 along with other two samples for comparison purposes. At first look, the enormous change in the C1s and S2p signals indicates that the converted asphaltenes showed more oxidized species that its untreated counterpart. It has been speculated in the literature that such changes can occur once the treated asphaltene is exposed to air30. According to the results obtained this seems to have occurred. On the other hand, several authors have reported the increase of oxygen and nitrogen content when asphaltenes are hydrotreated with NiMo catalysts. Song et al.34 explained that such behavior might be the consequence of the type of molecules (heavier or lighter) containing the oxygen groups. Heavier molecules will tend to be adsorbed better as the pore size of the catalyst is increased in detriment of lighter molecules, hence showing a competitive conversion. Similar results were obtained with NiW catalysts35. The increase in oxygen content in these cases would be a matter of a concentration effect. The authors never addressed the changes at the surface of the asphaltenes (oxidation).


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

S2p

C1s

Page 6 of 27

O1s

N1s

45º

Resins

C=O +

N

S

C-C

R

C-O-C C-O-H

1

S

-

πe

C-OH

O + N

COO

C7 ATH AR

O O S 1 R R

-

C7 ATH AR + Resins

C-O-C

O2

O R

S

R

C7 ATH BR

N H

1

COO

N

C=O, O=C-N

292

288

284 172

168

164

404

400

396

537

534

531

Binding Energy (eV) Fig. 3: XPS signals for the different asphaltene samples analyzed.

It is well established that resins play a fundamental role in the suspension of asphaltenes in crude oils forming a steric layer that provides stabilization36,37. There are indications that during the extraction process, this resin layer co-precipitates along with the asphaltene molecules. Assuming the former scenario, a portion of that resin layer will be located at the surface of the asphaltene and it will be converted first when submitted to hydrotreatment. In order to corroborate such claims, a sample was prepared mixing isolated C7 resin with the asphaltene obtained after reaction. This sample has a concentration of 25 % wt. of resins (discussed in a previous work30). From Fig. 3, the resemblance of the spectra for the Asphaltenes before reaction, asphaltene + resins and the pure isolated resins samples are significantly high. These results suggest that any treatment performed to precipitated asphaltenes will invariably need to


Page 7 of 27

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

Energy & Fuels

convert the resin layer before reaching the asphaltene “core”. The binding energies for the most common functionalities reported in asphaltenes are summarized in Fig. 4.

Aliphatic (C-C, C-H) ~284.8 eV

HO

Alcohol (C-OH) ~287 eV ~533 eV

O Carboxylic acids (COOH)/ Ester (COOR) ~289 eV ~535 eV

O

OH

Polycondensate aromatics (C-C, C-H) ~284.8 eV1

H 2N

Amine (C-NH) ~285.7 eV

NH

O O

NH2

Ether (C-O-C) ~286 eV ~532.5 eV

O

Ketones (C=O) ~288 eV ~531.5 eV

Amide (O=C-N) ~287.7 eV

Sulfite/sulfate ~167.0 eV

Sulfone ~165.5 eV

Sulfonic acid ~168.0 eV

O

O

Sulfoxide ~165.0 eV

O O S

O

S

S O

O

Pyridinic ~398.5 eV

Pyrrolic ~400.0 V

O OH

H N

O

N Graphitic or Quaternary N ~401.0 eV

S

N

S

+

N

S

Thiophenic ~164.0 eV

S

N Aliphatic ~163.0 eV

O

+ -

Pyridine N-oxide ~402.0 eV

Fig. 4: Representative functionalities found in asphaltenes (not an actual representation of an asphaltene molecule)


Energy & Fuels

From the atomic percentages (Fig. 5), it can be concluded that during hydrotreatment the sulfur species were the ones that were converted the most, which goes in agreement with the proposed mechanism of asphaltene conversion proposed by Asaoka et al.38, indicating that the sulfur linkages are the weakest ones and more reactive towards cracking. This behavior might also explain the increase in the oxidation state for the sulfur species. Despite the fact the hydrotreatment was carried out under reducing atmosphere it seems that those sulfur functionalities are extremely sensible to oxygen once exposed to air3. It would be interesting to address how the remaining species in the molecules rearranged themselves to stabilize the converted asphaltene. On the other hand, the atomic concentration of carbon remained stable, indicating that, probably, only cracking of the alkyl chains occurred39, with lesser contributions from reactions, such as gasification40; although around 1 % of coke formation was detected29. Additionally, nitrogen compounds were barely affected, most likely, because they are part of the polyaromatic structures rather than of the alkyl chains; for instance, to be able to convert them, high severity conditions should be employed41. Despite the fact that NiW catalysts have powerful hydrogenating capabilities, it is well known that to be able to perform HDN the aromaticity of the molecule has to be broken first42 . The usual metals found in asphaltenes: Fe, V, etc., were not detected with this set of samples; only the resin fraction showed the presence of Si with a 0.3 % (Fig. 5).

C1s 91.75

% Atomic

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 27

O1s 91.49

91.45

93.56

4.36

3.75

S2p

2 1.39

3.1 2.16

1.91

5.35 3.42

N1s 1.28

2.32 0.69

Si2p C7 ATH BR C7 ATH AR C7 ATH AR + Resins Resins

0.3

Fig. 5: Atomic percentages for the different analyzed samples.


Page 9 of 27

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

Energy & Fuels

Comparing the concentration of elements at the surface with respect to the bulk (Table 1), it can be noticed that the nitrogen concentrations are extremely similar; although it is not the case for the sulfur content, especially for the asphaltenes, where the differences amount to about 1.5 %. More sulfur is concentrated at the surface of the molecules and most probably is due to the presence of the sulfur linkages that stabilize the different aromatic sheets as discussed by several authors38,43. A similar trend is observed with nitrogen, although with a lesser extent and thus might be a consequence of an enhanced exposure of such functionalities at the periphery of the asphaltene core once the sulfur linkages were removed. Table 1: Weight percentages for the surface and the bulk of the studied samples Sample C7 ATH BR C7 ATH AR Resins

C 86.04 85.79 87.73

Wt. % (surface) O S 4.68 7.76 5.45 5.41 4.27 5.81

N 1.52 2.19 0.75

Wt. % (elemental analysis) S N 6.1 1.13 4.03 1.43 5.13 0.77

Fig. 6 shows the C1s signal for the analyzed samples; the peak at 284.8 eV is normally assigned to adventitious carbon and it is used as a reference for the energy scale. In this case, due to the nature of the asphaltenes, it is assigned to the C-C bonds present in such samples, although it is indistinguishable if this carbon is in aromatic or aliphatic form. In addition, the binding energy values detected at about 285.4 eV have been reported for C-S bonds44; which, according to Asaoka et al38, are the main constituents of aliphatic chains. This is supported by the fact that a change from 65 to 26 % occurred in the signal after catalytic treatment. This also indicates that the binding energy for the C-S bonds in these species are lower to what is normally reported; falling under the area of the 284.8 peak. According to Isquierdo28,29, one the main characteristics of the catalytic treatment with NiW based catalysts is the removal of aliphatic chains from the asphaltenes and the subsequent increase in aromaticity, as reported by NMR measurements. Other authors have reported the same behavior45. This observation is corroborated by the increase of the signal assigned to π ein aromatic rings (~ 290 eV)44,46,47 (Fig. S1). The other interesting feature is the higher concentration of the C-C signal for the resin in comparison to the rest of the samples, which may correspond mainly to aliphatic carbon rather than aromatic as reported by Speight et al36. Hydrotreating of pure resin samples will be interesting to address. Carbonates also have a contribution at about 290 eV, and for petroleum derivatives such a specie occurs mainly as calcite (CaCO3). Nonetheless, the survey spectra (Fig. S14) for these samples did not show the presence of calcium or other metals (only the resin sample showed the presence of Si); therefore, its contribution can be ruled out. The rest of the signals were assigned as follows: ~285 eV for ether or C-N bonds48; ~287 eV for C-O bonds (alcohols)49,50; ~288 eV for ketones51 or amide52 groups and ~289 eV for carboxylic acids or esters48.


0


0.22

1.12

π e-

Binding energy (eV)

Fig. 6: C1s signals for the different analyzed samples. 1.82

1.19

1.69

1.51

Binding energy (eV)

O

π−π∗

O R 293

290.6 291.5 290.8 290.2

289.1 290 289.5 289.2

1.3 1.51 1.69 1.19

1.82

1.12

1.4 1.6 1.29 1.03

0.31 1.13 0.82 0.22

0.53 1.93 1.42 0.24

1.41 1.49 1.46

1.23 1.51 1.72

C7 ATH BR C7 ATH AR C7 ATH AR + Resins Resin

293

290.2

1.13

OH O

290.8

1.3

287.5 2.09 288.3 3.49 3 288.4

9.44

41.21

C-O-C

0.82

0.31

290.6

1.03

286.9

11.2

286.5 287

C1s

291.5

0.24

289.2

C=O, O=C-N

1.29

1.6

1.4

Reported range of B.E

1.42

1.93

1.08 1.51 1.35 1.45

C-NH

289.5

0.53

12.34 16.23 16.14 15.03

285.8 285.9 285.7 285.9

78.07

1.35 1.4 1.39 1.44

C-S

290

1.46

1.49

60.63

65.28

C-C, C-H

289.1

3

3

288.4

3.49

6 1.41

40 26.38

80

288.3

2.09

0 284.8

120

287.5

% Atomic

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 % Atomic

Energy & Fuels Page 10 of 27

FWHM

C-OH

Page 11 of 27

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

Energy & Fuels

Assessing aromaticity using XPS spectra can be challenging at times. The literature is split regarding the best approach for analysis. Principally, there are two ways of determining the aromatic content: the first approach consist in analyzing the C1s shake up satellite feature that normally arises between 290 and 293 eV44. The second one consists in analyzing the Auger transition C KLL (C KVV) usually in its derivative form53,54, and determining a parameter called the D value, which is the distance between the maximum and the minimum in the derivative spectrum. Both methods offer its advantages but also suffer of shortcomings. Strictly speaking, the value that can be determined using either method is most specifically the sp2 character of the sample, not the aromaticity. C=C bonds, either in an alkyl chain or in a cyclic molecule will give rise to the same features. Some points to be considered while using these methods are the following: 1. The shake up satellite feature is not very sensitive to the effect of heteroatoms contained in the molecules55; although Rozada et al.56 reported that the intensity of the signal can increase after removal of oxygen atoms by thermal treatment. Other authors have reported the same57. It seems that such effect is more relevant to the ordering of the material than to the chemical environment surrounding the carbon atoms, because Kelemen et al.55 analyzed a wide variety of asphaltenes without any significant difference; while in the work of Rozada, the samples studied were graphene oxides which tend to resemble Highly Oriented Pyrolytic Graphite (HOPG) after annealing, inclusive decreasing the FWHM values of the C1s signals56 and the symmetry of the peak55. The same effect has been observed for the Auger peak; it is highly sensitive to oxygen content53. As a consequence, the D value will be usually grossly underestimated when this heteroatom is present. 2. In the Auger peak, changes observed in the A part (Fig.7) are usually associated with the appearance of new C-H bonds whereas, for the B part, the changes are associated with the formation of new π bonds. In principle, this is the general trend; nonetheless, the appearance of π-π* features in the B part and the broadening of the A part when, for example, HOPG is submitted to Ar+ sputtering has been recorded53. It seems that the cause of this behavior arises from the degree of disorder created in the sample and not from changes in the sp2 character; thus, in the case of amorphous materials the Auger method becomes highly unreliable. 3. Both methods are accurate within the limits of the calibration curve performed. For graphitic/graphenic materials the calibration curves match the expected evolution/chemical environment of the samples, inclusive, to the point of being highly accurate in comparison with other methodologies of assessing sp2/sp3 ratios, such as NMR or FTIR. It is yet to be determined if any of these methods will work with asphaltenes or with another type of molecules, probably polymers, with a high degree of heteroatoms contents. Fig. 7 shows the Auger transition recorded for the samples in this work, unfortunately, high resolution spectra of the region could not be acquired and the region obtained from the survey spectra was used instead. Despite the fact of the poor resolution, different features in the


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 27

spectra can be observed. Comparing the A part of the spectra, it can be noticed that the resin sample shows a higher intensity in such region, which goes in agreement with the reported chemical structure of resins, where they exhibit a higher degree of aliphatic chains in comparison to that of asphaltenes; and that such region is similar to all the samples excepting the hydrotreated asphaltenes where such contribution seem to have decreased. In this case, the D values calculated for the analyzed samples are 14-15 eV; which, according to the reported values, would give a sp character close to that of diamond54, which is erroneous. As mentioned earlier, the reason for these discrepancies, chemically speaking, have to do mainly, with the presence of oxygen in the samples and other heteroatoms, although the influence of sulfur or nitrogen in the C KLL spectrum has not yet been addressed. C7 ATH AR + resins

Resin C7

14

15

A

D

B

C7 ATH AR

14

C7 ATH BR

15

1300 1280 1260 1240 1220 1200 1180 1160

1300 1280 1260 1240 1220 1200 1180 1160

Binding energy (eV) Fig. 7: Auger C KLL transition and first derivative signals for the different analyzed samples (appended numbers = calculated D values).

Fig. 8 shows the distribution of sulfur species for the analyzed samples. As reported in the literature6,27,58, the dominant species in asphaltenes and resin fractions are thiophenic sulfur (~ 164 eV) followed by sulfides (~163 eV). In this study, hydrotreating the asphaltene caused a significant reduction in the superficial aliphatic chains (0.5 % to 0 %) along with thiophenic


Page 13 of 27

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

Energy & Fuels

sulfur. Interestingly enough, as mentioned earlier, more oxidized species appeared for the converted asphaltene. The signal at around 165.4 eV can be assigned to sulfones while the one between 166.5 and 167.7 eV can be assigned to a variety of functionalities: thiosulfates (RS-SO2-OR’), ester sulfates (RO-SO2-OR’) or organic sulfites (RO-SO-OR’)59–61; some of them forming part of the pure resin as well. In addition, sulfoxides (~165 eV)23 and sulfonic acids (~168 eV)23 were already present in the asphaltene to begin with. From these results, it can be inferred that once the aliphatic sulfur links (thioethers38) are cleaved, the sulfur remains as the final group in the newly form structure seeking to react with the H2 in the media and form thiol groups (~163 eV). In a similar behavior, if the thiophenic ring is opened, a similar functionality will be created, although since the aromatic rings were not converted, most likely, the thiophenic sulfur reacted to form thiophene sulfones, once exposed to air, as the results suggest. The presence of these type of molecules have been reported elsewhere58. Overall, the hydrogenation of the molecules during the course of the reaction should have occurred but once the asphaltene was exposed to air, these functionalities reacted further to stabilize the structure. The evolution of asphaltenes when exposed to air has been reported, resulting in oxygen uptake, as well as sulfur, when exposed to elemental sulfur or sulfur containing minerals36. Oxidation occurs naturally, although it seems that in the converted asphaltene the rate of oxidation is faster than in the natural occurring structure, probably because of the partial removal of the resin layer and/or by further reaction of metastable aromatic free radicals generated during thermal cracking.


Energy & Fuels


S2p3/2

FWHM R O

O

S

R

1

O

O

S

S

R

S

R

1

O

O O S 1 R R

Thiophenic

Sulfoxide

Sulfone

S

S O

1

R

S

OH

O O R

1.01 1.16 1.63

1.37 0.96 1.28

1.31 1.15 0.94

1.16 1.2 0.88 1.24

1.12

0.93 1.28

5

4

R

O

R

Aliphatic

O

S O O

1

Sulfonic acid 1.53 1.73

R

O

168.3

168 0.13 169.3 0.07

166.5

0.36 167.7 0.09 167.5 0.05

0.9 0.21 0.3 165.4 165

165.9

164.5

0.8 0.2 0.53 165.4 165

163.9

0.63 0.81 163.9 164

163.1

0

0.5

1

0.24 0.44

2

1.53

1.67

3

163.3

% Atomic (S2p3/2 + S2p1/2)

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 27

Binding energy (eV)

Fig. 8: S2p signals for the different analyzed samples. It has been reported, for example, that in Athabasca asphaltenes between 40 and 70 % of the oxygen containing molecules are in the form of phenolic hydroxyl groups3. In this case, Fig. 9 shows that the most important contribution is located at about 533 eV, which is the value normally attributed to these functionalities49,50, while ether groups appear at about 532 eV44,62. Organic sulfites and sulfonic groups have been also reported at binding energies of about 533 eV60. On the other hand, the contribution at about 531 eV corresponds to carbonyl groups, although sulfoxides and sulfone groups have been reported at the same values44,60,62. Carboxylic acids, ester groups and sulfates have similar binding energies at about 535 eV63. Interestingly enough, a small signal appeared at 536.9 eV for the sample after treatment. Hao et al.64 have discussed that such signal might correspond to absorbed molecular oxygen or water; which according to the results discussed thus far seems to be a plausible scenario.


Page 15 of 27


O1s

FWHM

O R

S

OH

O

O R

S=O

O

1

O

2

2.02

0.25

0.16

1.8

2.1 2.1 535.8

0.53

1.63

536.9

2.1 2.1 2.03

C-OH

534.8 535

2.18 1.08 532.5

532.3

OH

2.15 1.97 2.92

1.68 2.18 531.3

1.07 0.6 531.8

R

533.1 533.3 533.7 533.8 0.16

1.83 1.82

C-O-C

C=O

4

0

O

Occluded O2

2 2

8

O R S O

O=S=O

% Atomic

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

Energy & Fuels

Binding energy (ev)

Fig. 9: O1s signals for the different analyzed samples.

According to the open literature, alkyl carbazoles are the most important nitrogen containing species present in asphaltenes65. The pyrrole ring of the structure is the most intense signal detected by XPS66 and it normally appears at a binding energy of 400 eV67. The second most intense contribution is attributed to species containing a pyridinic ring at binding energies of 398 eV68. It is worth mentioning the effect of hydrogen in the chemical shift; although hydrogen cannot be directly detected by XPS its influence can be observed since it increases the ionic character of any given bond50; for instance, it would be expected that the pyrrole nitrogen would have a higher binding energy than the pyridine nitrogen, although this is not the case. For the pyrrole system, the lone pair of electrons of the nitrogen atom are located in an unhybridized p orbital, which overlaps with the pi system of the carbon ring participating, for instance, in the resonance. In contrast, the lone pair of electrons for the pyridine nitrogen are localized in a p orbital perpendicular to the pi system; therefore, delocalization of electrons does not occur; hence the effect in the binding energies. The binding energy at 401 eV can be assigned to graphitic nitrogen69–71, a quaternary nitrogen72– or protonated analog, while the value at 402.372,76 can be assigned to a N-oxide compound69,77– 79 . Hydrotreating of the asphaltene seems to have targeted the basic nitrogen molecules

75


Energy & Fuels

(pyridine) instead of the non-basic type (pyrrole) as usually found for other systems41,80; which is a direct consequence of the preferred mode of adsorption of the basic nitrogen molecule (through the lone pair of electrons) versus the non-basic nitrogen molecules (through the aromatic ring) over the catalyst surface. C7 ATH BR C7 ATH AR C7 ATH AR + Resins Resin

N1s

FWHM

-

O + N N H

N

Pyrrolic

Quaternary

Pyridine N-oxide 1.69

1.8

1.49

2 1.66

1.5

1

0.73 400.9

402.3

0.13

0.09

401.7

0.33 401.4

0.45 399.8

400.1

400

400.5

0.15 398.5

0.27

0.18 398.6

0.0

0.32

0.5

0.74

1.0

0.88

1.09

1.3

1.35

1.3

1.43

1.5

+

1.16

Pyridinic

2.0

R

1.69

N

% Atomic

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 27

Binding energy (eV)

Fig. 10: N1s signals for the different analyzed samples.

Interestingly enough, many of the nitrogen containing groups reported in this work for asphaltenes have been found in compounds such as graphene oxides and humic acids, with which they share many similarities81–85. Isquierdo28,29 reported that the treated asphaltenes exhibited a higher degree of stacking in comparison to the untreated sample, according to XRD results. Such behavior was triggered once the alkyl chains were removed during the hydrotreating process and also when the resin layer present at the surface of the molecules was converted. Once this occurred, the stabilization provided by the resins was no longer present making the asphaltenes more reactive towards oxygen, thus justifying the highly-oxidized nature of the sample after reaction.


Page 17 of 27

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

Energy & Fuels

3.2- Athabasca C7 after reaction + resins (angle resolved analysis) Fig. 11 shows the spectra acquired at two different take off angles, 45 and 90º, with the former “closer” to the surface. It can be noticed that most of the oxidized sulfur species are present at the surface as seen in Fig. 3, although, when probing deeper into the sample, this behavior reverted; less of the oxidized sulfur species were detected, while, for example, a signal of an Noxide compound appeared. Nevertheless, the amount of oxygen was higher at 90º, while the rest of the heteroatoms showed a decreased atomic percentage, although this can be explained by a concentration effect rather than a diffusion of oxygen into the bulk of the structure. Even after probing the sample at 90º the signals obtained did not resemble entirely the spectra for the sample after reaction, meaning that the layer of resins is thicker that a few nanometers or that the resins got intermixed with the asphaltene to such an extent where a clear boundary between the two fractions does not exist.

S2p

C1s

O1s

N1s

45º C-C, C-H

C-O-C

S

C-O

N H

C=O, O=C-N

N

S

COO

90º

-

-

COO

292

288

πe

R

O

O

O S

N

R

1

+

+

N R

1

C-OH

284

172

168

164

160

404

400

396

536

C=O

532

528

Binding Energy (eV)

Fig. 11: Angle resolved regions for the Athabasca C7 asphaltene after reaction + resins.

3.3- Athabasca C7 after reaction + resins (depth profile analysis)

Fig. 12 shows the depth profiles for each one of the signals analyzed. As expected, the O1s changed the most (from 5.78 to 1.2 %) indicating preferential sputtering of that atom as usually found for metal oxides86,87; while the concentration of nitrogen decreased slightly (from 0.96 to


Energy & Fuels

0.6 %). Lastly, the concentration of sulfur remained practically the same, whereas the carbon changed very little (Fig. S8). This indicates that reduction by Ar sputtering mostly occurs to C-O bonds rather than to the S-O or N-O species. The variation determined for the atomic percentage of the carbon signal 4.91 % would be in this case the sum of the concentrations of oxygen (4.58 %) and nitrogen (0.33 %) sputtered.

C1s

O1s

5

292

290

288

286

284

282

25

524

Binding Energy (eV)

528

532

536

540

544

Binding Energy (eV)

S2p

N1s

25

168

164

Binding Energy (eV)

160

10

Tim e( mi n)

15 20

5

mi n)

5 10

172

mi n)

15 20

Tim e(

25

10

Tim e(

15 20

5

mi n)

10

15

Tim e(

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 27

20 25

412

408

404

400

396

392

Binding Energy (eV)

Fig. 12: Depth profile regions for the Athabasca C7 asphaltene after reaction + resins.

Judging by the spectra acquired before sputtering (Fig. 13), the changing nature of the sample becomes apparent. Either the resin and the asphaltene kept reacting after the initial analysis or the sample is highly inhomogeneous.


Page 19 of 27

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

Energy & Fuels

S2p

C1s C-C, C-H

O1s

N1s

After sputtering

C-O-C

S

C-O C=O, C-N

N H

S

O

-

Before sputtering

+

N

-

πe

292

R

COO

N

O

O S

R

1

C-OH

288

284

172

168

164

160

402

400

398

536

534

532

530

Binding Energy (eV)

Fig. 13: Depth profile regions for the Athabasca C7 asphaltene after reaction + resins (before and after sputtering).

The effect of Ar sputtering has been widely reported in the open literature, principally, for metal oxides, were the main effect is the preferential removal of oxygen atoms with the subsequent reduction of the metal oxide. Preferential sputtering of S has been observed in transition metal sulfides as well88–91. According to Malherbe87 and Mitchell et al.86, such effect is influenced by two parameters: surface binding energies and mass difference effects. There are several reports of the damaging influence of argon sputtering in organic molecules, either by monoatomic Ar sputtering or by Ar Gas Cluster ion beam (GCIB) sputtering; the latter to a lesser extent92,93. Nevertheless, studies with asphaltenes molecules are still lacking. Expanding the behavior observed for metal oxides and some organic molecules94,95, the degradation of some of the oxygen functionalities is expected (C-O, S-O, C=O, etc); although as suggested by the results, removal of oxygen seem to only have occurred with the C-O functionalities. The reason for this may lie in the fact that such functionalities are not part of a fused or aromatic ring as in the case of the S-O or N-O bonds. Functionalities that are not part of cyclic molecules will be the easiest to reduce, the rest, will require extra energy to break the cyclic molecule apart first and form more stable compounds afterward.


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 27

4.-Conclusions XPS analysis has shown the distribution of species in asphaltenes samples and how they change when submitted to hydrotreating conditions. The surface of asphaltenes seem to be inhomogeneous and greatly populated by a variety of functionalities with an increased concentration of sulfur according to surface analysis; although not vastly different to the concentration of heteroatoms normally found in the bulk. Scission of these sulfur species seem to be the easiest reaction that occurs during hydrotreating. On the other hand, results suggest that a layer of resin is still adsorbed at the surface of the asphaltenes even when using a careful precipitation protocol36. Such layer greatly impacts the stability of the asphaltene, making it more reactive toward air oxidation once removed. Understanding such interaction resinasphaltene at the surface of the molecules, and the type of functionalities oxidized at various levels of the asphaltenes (from surface to bulk) are key to design better catalysts to convert these families of compounds at lower severities.

5.-Acknowledgements The authors want to acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC), Nexen-CNOOC Ltd, and Alberta Innovates-Energy and Environment Solutions (AIEES) for the for the financial support provided through the NSERC/NEXEN/AIEES Industrial Research Chair in Catalysis for Bitumen Upgrading. Also, the contribution of facilities from the Canada Foundation for Innovation, the Institute for Sustainable Energy, Environment and Economy, the Schulich School of Engineering and the Faculty of Science at the University of Calgary are greatly appreciated.

6.-References 1.

He, L., Li, X., Wu, G., Lin, F. & Sui, H. Distribution of Saturates, Aromatics, Resins, and Asphaltenes Fractions in the Bituminous Layer of Athabasca Oil Sands. Energy & Fuels 27, 4677–4683 (2013).

2.

He, L., Lin, F., Li, X., Sui, H. & Xu, Z. Interfacial sciences in unconventional petroleum production: from fundamentals to applications. Chem. Soc. Rev. 44, 5446–5494 (2015).

3.

Frankman, Z., Ignasiak, T. M., Lown, E. M. & Strausz, O. P. Oxygen Compounds in Athabasca Asphaltene. Enery & Fuels 4, 263–270 (1990).

4.

Sagachenko, T. A., Sergun, V. P., Cheshkova, T. V, Kovalenko, E. Y. & Min, R. S. Chemical nature of the oil and tarry-asphaltene components of natural bitumen from the Ashal’chinsk deposit in Tatarstan. Solid Fuel Chem. 49, 349–355 (2015).

5.

Sergun, V. P., Kovalenko, E. Y., Sagachenko, T. A. & Min, R. S. Low-molecular-mass asphaltene compounds from USA heavy oil. Pet. Chem. 54, 83–87 (2014).

6.

Peng, P., Morales-Izquierdo, A., Hogg, A. & Strausz, O. P. Molecular structure of


Page 21 of 27

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

Energy & Fuels

athabasca asphaltene: Sulfide, ether, and ester linkages. Energy & Fuels 11, 1171–1187 (1997). 7.

Strausz, O. P., Mojelsky, T. W., Lown, E. M., Kowalewski, I. & Behar, F. Structural features of Boscan and Duri asphaltenes. Energy and Fuels 13, 228–247 (1999).

8.

Carbognani, L. & Espidel, J. Preparative Subfractionation of Petroleum Resins and Asphaltenes. II. Characterization of Size Exclusion Chromatography Isolated Fractions. Pet. Sci. Technol. 21, 1705–1720 (2003).

9.

Rafenomanantsoa, A., Nicole, D., Rubini, P. & Lauer, J. C. Structural Analysis by NMR and FIMS of the Tar-Sand Bitumen of Bemolanga (Malagasy). Energy & Fuels 8, 618– 628 (1994).

10.

Coelho, R. R., Hovell, I. & Rajagopal, K. Elucidation of the functional sulphur chemical structure in asphaltenes using first principles and deconvolution of mid-infrared vibrational spectra. Fuel Process. Technol. 97, 85–92 (2012).

11.

Zhao, S., Xu, Z., Xu, C., Chung, K. H. & Wang, R. Systematic characterization of petroleum residua based on SFEF. Fuel 84, 635–645 (2005).

12.

George, G. N. & Gorbaty, M. L. Sulfur K-Edge X-ray Absorption Spectroscopy of petroleum asphaltenes and model compounds. J. Am. Chem. Soc. 111, 3182–3186 (1989).

13.

Sarret, G., Connan, J., Kasrai, M., Eybert-Bérard, L. & Bancroft, G. M. Characterization of sulfur in asphaltenes by sulfur K- and L-edge XANES spectroscopy. J. Synchrotron Radiat. 6, 670–2 (1999).

14.

Waldo, G. S., Carlson, R. M. K., Moldowan, J. M., Peters, K. E. & Penner-Hahn, J. E. Sulfur speciation in heavy petroleums: Information from X-ray absorption near-edge structure. Geochim. Cosmochim. Acta 55, 801–814 (1991).

15.

Duncan, J. A. Asphaltenes: characterization, properties, and applications. (Nova Science Publishers, 2010).

16.

Abdallah, W. A. & Taylor, S. D. Study of Asphaltenes Adsorption on Metallic Surface Using XPS and TOF-SIMS. J. Phys. Chem. C 112, 18963–18972 (2008).

17.

Wang, S., Liu, Q., Tan, X., Xu, C. & Gray, M. R. Study of Asphaltene Adsorption on Kaolinite by X-ray Photoelectron Spectroscopy and Time-of-Flight Secondary Ion Mass Spectroscopy. Energy & Fuels 27, 2465–2473 (2013).

18.

Larachi, F., Dehkissia, S., Adnot, A. & Chornet, E. X-ray photoelectron spectroscopy, photoelectron energy loss spectroscopy, X-ray excited Auger electron spectroscopy, and time-of-flight-secondary ion mass spectroscopy studies of asphaltenes from Doba-Chad heavy crude hydrovisbreaking. Energy and Fuels 18, 1744–1756 (2004).

19.

Siskin, M., Kelemen, S. R., Eppig, C. P., Brown, L. D. & Afeworki, M. Asphaltene Molecular Structure and Chemical Influences on the Morphology of Coke Produced in Delayed Coking. 21, 2447–2454 (2006).


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 22 of 27

20.

Rudrake, A., Karan, K. & Horton, J. H. A combined QCM and XPS investigation of asphaltene adsorption on metal surfaces. J. Colloid Interface Sci. 332, 22–31 (2009).

21.

Woods, J. et al. Canadian Crudes: A Comparative Study of SARA Fractions from a Modified HPLC Separation Technique. Oil Gas Sci. Technol. - Rev. l’IFP 63, 151–163 (2008).

22.

Rueda-Velásquez, R. I., Freund, H., Qian, K., Olmstead, W. N. & Gray, M. R. Characterization of Asphaltene Building Blocks by Cracking under Favorable Hydrogenation Conditions. Energy & Fuels 27, 1817–1829 (2013).

23.

Kelemen, S. R., George, G. N. & Gorbaty, M. L. Direct determination and quantification of sulphur forms in heavy petroleum and coals 1. The X-ray photoelectron spectroscopy (XPS) approach. Fuel 69, 939–944 (1990).

24.

Ostlund, J. A., Nyden, M., Fogler, H. S. & Holmberg, K. Functional groups in fractionated asphaltenes and the adsorption of amphiphilic molecules. Colloids Surfaces A Physicochem. Eng. Asp. 234, 95–102 (2004).

25.

Abdallah, W. A. & Taylor, S. D. Surface characterization of adsorbed asphaltene on a stainless steel surface. Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms 258, 213–217 (2007).

26.

Sun, Z. H. et al. Characterization of asphaltene isolated from low-temperature coal tar. Fuel Process. Technol. 138, 413–418 (2014).

27.

Merdrignac, I. & Espinat, D. Physicochemical Characterization of Petroleum Fractions: the State of the Art. Oil Gas Sci. Technol. - Rev. l’IFP 62, 7–32 (2007).

28.

Isquierdo, F. Mild Hydroprocessing with Dispersed Catalyst of Highly Asphaltenic Pitch. (University of Calgary, 2015). doi:10.1017/CBO9781107415324.004

29.

Isquierdo, F., Pereira-almao, P., Vitale, G. & Scott, C. E. Asphaltenes Hydroprocessing. Prepr. Pap.-Am. Chem. Soc., Div. Energy Fuels 59, 599–600 (2014).

30.

Ortega, L. C. et al. Effect of Precipitating Conditions on Asphaltene Properties and Aggregation. Energy & Fuels 29, 3664–3674 (2015).

31.

Cumpson, P. J. Angle-resolved XPS depth-profiling strategies. Appl. Surf. Sci. 144–145, 16–20 (1999).

32.

Ratner, B. D. & Castner, D. G. Electron Spectroscopy for Chemical Analysis. Surface Analysis – The Principal Techniques (John Wiley & Sons, Ltd. New York, USA, 2009).

33.

Niemantsverdriet, J. W. Spectroscopy in Catalvsis. An introduction. (Wiley-VCH Vcrlag GmbH, 2000).

34.

Song, C. et al. Effect of pore structure of nickel-molybdenum/alumina catalysts in hydrocracking of coal-derived and oil sand derived asphaltenes. Ind. Eng. Chem. Res. 30, 1726–1734 (1991).


Page 23 of 27

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

Energy & Fuels

35.

Leckel, D. Hydrodeoxygenation of Heavy Oils Derived From Low-Temperature Coal Gasification over NiW Catalysts—Effect of Pore Structure. Energy & Fuels 22, 231–236 (2008).

36.

Speight, J. G. Petroleum Asphaltenes Part 1: Asphaltenes, Resins and the Structure of Petroleum. Oil Gas Sci. Technol. – Rev. IFP 59, 467–477 (2004).

37.

León, O. et al. Adsorption of native resins on asphaltene particles: A correlation between adsorption and activity. Langmuir 18, 5106–5112 (2002).

38.

Asaoka, S. & Nakata, S. Asphaltene cracking in catalytic hydrotreating of heavy oils. 2. Study of changes in asphaltene structure during catalytic hydroprocessing. Ind. Eng. Chem. Process Des. Dev. 22, 242–248 (1983).

39.

Muhammad, A. B. Thermal evolution of aliphatic and aromatic moieties of asphaltenes from coals of different rank: possible implication to the molecular architecture of asphaltenes. Chinese J. Geochemistry 34, 422–430 (2015).

40.

Hassan, A. et al. Catalytic steam gasification of n-C5 asphaltenes by kaolin-based catalysts in a fixed-bed reactor. Appl. Catal. A Gen. 507, 149–161 (2015).

41.

Bej, S. K., Dalai, A. K. & Adjaye, J. Comparison of hydrodenitrogenation of basic and nonbasic nitrogen compounds present in oil sands derived heavy gas oil. Energy and Fuels 15, 377–383 (2001).

42.

Furimsky, E., Ranganathan, R. & Parsons, B. I. Catalytic hydrodenitrogenation of basic and non-basic nitrogen compounds in Athabasca bitumen distillates. Fuel 57, 427–430 (1978).

43.

Murgich, J., Abanero, J. A. & Strausz, O. P. Molecular recognition in aggregates formed by asphaltene and resin molecules from the Athabasca oil sand. Energy and Fuels 13, 278–286 (1999).

44.

Louette, P., Bodino, F. & Pireaux, J.-J. Poly(p-phenylene ether sulfone) (PES) XPS Reference Core Level and Energy Loss Spectra. Surf. Sci. Spectra 12, 38 (2005).

45.

Ancheyta, J., Centeno, G., Trejo, F. & Marroquín, G. Changes in asphaltene properties during hydrotreating of heavy crudes. Energy and Fuels 17, 1233–1238 (2003).

46.

Hontoria-Lucas, C., López-Peinado, A. J., López-González, J. d. D., Rojas-Cervantes, M. L. & Martín-Aranda, R. M. Study of oxygen-containing groups in a series of graphite oxides: Physical and chemical characterization. Carbon. 33, 1585–1592 (1995).

47.

Louette, P., Bodino, F. & Pireaux, J. Poly(styrene) XPS Reference Core Level and Energy Loss Spectra. Surf. Sci. 12, 96–99 (2006).

48.

Beamson, G. & Briggs, D. High Resolution XPS of Organic Polymers: The Scienta ESCA 300 Database. J. Chem. Educ. 70, A25 (1993).

49.

Louette, P., Bodino, F. & Pireaux, J.-J. Poly(vinyl alcohol) (PVA) XPS Reference Core


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 24 of 27

Level and Energy Loss Spectra. Surf. Sci. Spectra 12, 38 (2005). 50.

Kerber, S. J. The nature of hydrogen in x-ray photoelectron spectroscopy: General patterns from hydroxides to hydrogen bonding. J. Vac. Sci. Technol. A Vacuum, Surfaces, Film. 14, 1314 (1996).

51.

Louette, P., Bodino, F. & Pireaux, J.-J. Poly(acroleine) XPS Reference Core Level and Energy Loss Spectra. Surf. Sci. Spectra 12, 38 (2005).

52.

Louette, P., Bodino, F. & Pireaux, J.-J. Poly(n-vinylpyrolidone) (PNVP) XPS Reference Core Level and Energy Loss Spectra. Surf. Sci. Spectra 12, 38 (2005).

53.

Calliari, L. AES and core level photoemission in the study of a-C and a-C:H. Diam. Relat. Mater. 14, 1232–1240 (2005).

54.

Kaciulis, S. Spectroscopy of carbon: From diamond to nitride films. Surf. Interface Anal. 44, 1155–1161 (2012).

55.

Kelemen, S. R., Rose, K. D. & Kwiatek, P. J. Carbon aromaticity based on XPS II to II∗ signal intensity. Appl. Surf. Sci. 64, 167–174 (1993).

56.

Rozada, R., Paredes, J. I., Villar-Rodil, S., Martínez-Alonso, A. & Tascón, J. M. D. Towards full repair of defects in reduced graphene oxide films by two-step graphitization. Nano Res. 6, 216–233 (2013).

57.

Rabek, J. F. Polymer Photodegradation: Mechanisms and experimental methods. (Springer Science & Business Media, 1994).

58.

Zhang, L. et al. Speciation and quantification of sulfur compounds in petroleum asphaltenes by derivative XANES spectra. J. Fuel Chem. Technol. 41, 1328–1335 (2013).

59.

Littlejohn, D. & Chang, S.-G. An XPS study of nitrogen-sulfur compounds. J. Electron Spectros. Relat. Phenomena 71, 47–50 (1995).

60.

Lindberg, B. J. et al. Molecular Spectroscopy by Means of ESCA II. Sulfur compounds. Correlation of electron binding energy with structure. Phys. Scr. 1, 286–298 (1970).

61.

Grzybek, T., Pietrzak, R. & Wachowska, H. The Comparison of Oxygen and Sulfur Species Formed by Coal Oxidation with O2/Na2CO3 or Peroxyacetic Acid Solution. XPS Studies. Energy & Fuels 18, 804–809 (2004).

62.

Louette, P., Bodino, F. & Pireaux, J.-J. Poly(sulfone resin) XPS Reference Core Level and Energy Loss Spectra. Surf. Sci. Spectra 12, 38 (2005).

63.

Louette, P., Bodino, F. & Pireaux, J.-J. Poly(vinyl sulfate) Potassium Salt XPS Reference Core Level and Energy Loss Spectra. Surf. Sci. Spectra 12, 38 (2005).

64.

Hao, S., Wen, J., Yu, X. & Chu, W. Effect of the surface oxygen groups on methane adsorption on coals. Appl. Surf. Sci. 264, 433–442 (2013).

65.

Jokuty, P. & Gray, M. Resistant nitrogen compounds in hydrotreated gas oil from


Page 25 of 27

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

Energy & Fuels

Athabasca bitumen. Energy & fuels 5, 791–795 (1991). 66.

Mitra-Kirtley, S. et al. Determination of the nitrogen chemical structures in petroleum asphaltenes using XANES spectroscopy. J. Am. Chem. Soc. 115, 252–258 (1993).

67.

Louette, P., Bodino, F. & Pireaux, J.-J. Poly(pyrrole) (PPY) XPS Reference Core Level and Energy Loss Spectra. Surf. Sci. Spectra 12, 38 (2005).

68.

Cohen, M. R. & Merrill, R. P. Adsorption of Pyridine on Ni(111): A High-Resolution Electron Energy Loss Spectroscopy, Angular-Resolved UV Photoemission, and X-ray Photoelectron Spectroscopy Study. Langmuir 6, 1282–1288 (1990).

69.

Biddinger, E. J., Deak, D. Von & Ozkan, U. S. Nitrogen-containing carbon nanostructures as oxygen-reduction catalysts. Top. Catal. 52, 1566–1574 (2009).

70.

Wang, W. W., Dang, J. S., Zhao, X. & Nagase, S. Formation Mechanisms of Graphitic-N: Oxygen Reduction and Nitrogen Doping of Graphene Oxides. J. Phys. Chem. C 120, 5673–5681 (2016).

71.

Gammon, W. J., Kraft, O., Reilly, A. C. & Holloway, B. C. E xperimental comparison of N (1s) X-ray photoelectron spectroscopy binding energies of hard and elastic amorphous carbon nitride films with reference organic compounds. Carbon. 41, 1917–1923 (2003).

72.

Chambrion, P., Suzuki, T., Zhang, Z.-G., Kyotani, T. & Tomita, A. XPS of NitrogenContaining Functional Groups Formed during the C-NO Reaction. Energy Fuels 11, 681– 685 (1997).

73.

Atanasoska, L., Naoi, K. & Smyrl, W. H. XPS studies on conducting polymers: polypyrrole films doped with perchlorate and polymeric anions. Chem. Mater. 4, 988–994 (1992).

74.

Rao, C. V., Cabrera, C. R. & Ishikawa, Y. In search of the active site in nitrogen-doped carbon nanotube electrodes for the oxygen reduction reaction. J. Phys. Chem. Lett. 1, 2622–2627 (2010).

75.

Kelemen, S. R., Gorbaty, M. L. & Kwiatek, P. J. Quantification of Nitrogen Forms in Argonne Premium Coals. Energy Fuels 8, 896–906 (1994).

76.

Bag, S., Roy, K., Gopinath, C. S. & Raj, C. R. Facile Single-Step Synthesis of NitrogenDoped Reduced Graphene Oxide-Mn3O4 Hybrid Functional Material for the Electrocatalytic Reduction of Oxygen. ACS Appl. Mater. Interfaces 6, 2692–2699 (2014).

77.

Pels, J. R., Kapteijn, F., Moulijn, J. A., Zhu, Q. & Thomas, K. M. Evolution of nitrogen functionalities in carbonaceous materials during pyrolysis. Carbon. 33, 1641–1653 (1995).

78.

Stańczyk, K., Dziembaj, R., Piwowarska, Z. & Witkowski, S. Transformation of nitrogen structures in carbonization of model compounds determined by XPS. Carbon. 33, 1383– 1392 (1995).


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 26 of 27

79.

Kumar, B. et al. Renewable and metal-free carbon nanofibre catalysts for carbon dioxide reduction. Nat. Commun. 4, 1–8 (2013).

80.

Bianchini, C., Meli, A. & Vizza, F. Modelling the Hydrodenitrogenation of Aromatic NHeterocycles in the Homogeneous Phase. Eur. J. Inorg. Chem. 43–68 (2001).

81.

Konkena, B. & Vasudevan, S. Understanding Aqueous Dispersibility of Graphene Oxide and Reduced Graphene Oxide through pKa Measurements. J. Phys. Chem. Lett. 3, 867– 872 (2012).

82.

Vega, S. S., Urbina, R. H., Covarrubias, M. V. & Galeana, C. L. The zeta potential of solid asphaltene in aqueous solutions and in 50:50 water + ethylene glycol (v/v) mixtures containing ionic surfactants. J. Pet. Sci. Eng. 69, 174–180 (2009).

83.

Anielak, A. M. & Grzegorczuk-Nowacka, M. Significance of zeta potential in the adsorption of fulvic acid on aluminum oxide and activated carbon. Polish J. Environ. Stud. 20, 1381–1386 (2011).

84.

Klučáková, M. & Kalina, M. Composition, particle size, charge, and colloidal stability of pH-fractionated humic acids. J. Soils Sediments 15, 1900–1908 (2015).

85.

Alvarez-Puebla, R. A. & Garrido, J. J. Effect of pH on the aggregation of a gray humic acid in colloidal and solid states. Chemosphere 59, 659–667 (2005).

86.

Mitchell, D. F., Sproule, G. I. & Graham, M. J. Sputter Reduction of Oxides by Ion Bombardment during Auger Depth Profile Analysis. Surf. Interface Anal. 15, 487–497 (1990).

87.

Malherbe, J. B., Hofmann, S. & Sanz, J. M. Preferential sputtering of oxides: a comparison of model predictions with experimental data. Appl. Surf. Sci. 27, 355–365 (1986).

88.

Sundberg, J. et al. Understanding the effects of sputter damage in W–S thin films by HAXPES. Appl. Surf. Sci. 305, 203–213 (2014).

89.

Fox, D. S. et al. Nanopatterning and Electrical Tuning of MoS2 Layers with a Subnanometer Helium Ion Beam. Nano Lett. 15, 5307–5313 (2015).

90.

Griffis, D. P. & Linton, R. W. Quantitative comparison of direct and derivative AES with XPS of metal sulfides. Surf. Interface Anal. 4, 197–203 (1982).

91.

Baker, M. A., Gilmore, R., Lenardi, C. & Gissler, W. XPS investigation of preferential sputtering of S from MoS2 and determination of MoSx stoichiometry from Mo and S peak positions. Appl. Surf. Sci. 150, 255–262 (1999).

92.

Bernasik, A. et al. Chemical stability of polymers under argon gas cluster ion beam and xray irradiation. J. Vac. Sci. Technol. B, Nanotechnol. Microelectron. Mater. Process. Meas. Phenom. 34, 30604 (2016).

93.

Haberko, J. et al. XPS depth profiling of organic photodetectors with the gas cluster ion


Page 27 of 27

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

Energy & Fuels

beam. J. Vac. Sci. Technol. B, Nanotechnol. Microelectron. Mater. Process. Meas. Phenom. 34, 03H119 (2016). 94.

Yun, D.-J. et al. Study on the molecular distribution of organic composite films by combining photoemission spectroscopy with argon gas cluster ion beam sputtering. J. Mater. Chem. C 3, 276–282 (2015).

95.

Yun, D. J. et al. Damage-Free Photoemission Study of Conducting Carbon Composite Electrode Using Ar Gas Cluster Ion Beam Sputtering Process. J. Electrochem. Soc. 159, H626–H632 (2012).


X-ray Photoelectron Spectroscopy Analysis of Hydrotreated Athabasca

Recommend Documents