Ni-Doped MoS2 Nanoparticles Prepared via CoreâShell Nanoclusters

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Ni-doped MoS2 nanoparticles prepared via core-shell nanoclusters and catalytic activity for upgrading heavy oil Gwangsik Jeong, Chan Hun Kim, Young Gul Hur, Geun-Ho Han, Seong Ho Lee, and Kwan-Young Lee Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02092 • Publication Date (Web): 17 Aug 2018 Downloaded from http://pubs.acs.org on August 21, 2018

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Energy & Fuels

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Manuscript for Energy&Fuels

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Ni-doped MoS2 nanoparticles prepared via core-shell nanoclusters and

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catalytic activity for upgrading heavy oil

6 7 8

Gwangsik Jeong a, Chan Hun Kim a, Young Gul Hur a, Geun-Ho Han a, Seong Ho Lee

9

Kwan-Young Lee a *

a*

,

10 11 12

a

Department of Chemical and Biological Engineering, Korea University, 145 Anam-ro, Seoul 02841, Republic of Korea

13 14 15 16 17 18 19 20 21 22

* Co-corresponding authors: Tel: +82-2-3290-3299; Fax: +82-2-926-6102;

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E-mail: [email protected] (Prof. Kwan-Young Lee);

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Tel: +82-2-3290-3727; Fax: +82-2-926-6102

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E-mail: [email protected] (Dr. Seong Ho Lee)

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ACS Paragon Plus Environment

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Abstract General hydrotreatment catalyst is alumina supported molybdenum sulfide catalyst which is usually

3

promoted by cobalt and nickel. However, supported catalysts are easily deactivated because of high

4

portion of asphaltenes which cause pore-plugging and mass transfer limitation. For this reason, recent

5

studies are focused on unsupported nano-catalysts especially for slurry reactor application.

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To synthesize nanomaterials, generally, there are top-down methods such as sputtering, and bottom-

7

up methods using chemical precursors to synthesize nanomaterials. Since the synthesis of

8

nanomaterials with complex chemical formulas is limited in the top-down method, the bottom-up

9

method through liquid phase reaction is mostly used. However, in the case of nanomaterials produced

10

in liquid phase, calcination process is sequentially needed in order to obtain desired crystallinity and

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to remove impurities. Even if it succeeds in synthesizing uniform and nano-sized materials in liquid

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phase process, it is difficult to finally obtain nanomaterials due to particle growth by sintering

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between nanomaterials in the calcination process.

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This study presents new synthetic approach of Ni-doped MoS2 nanoparticles via core-shell

15

nanoclusters, enabling to control the crystallization and the size of the target nanomaterials even after

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high temperature calcination process. Ni-doped MoS2 (Ni/Mo weight ratio = 0.45) nanoparticle

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exhibited the highest catalytic performance. The slab structures and surface oxidation states of the

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nanoparticles were investigated according to the amount of doped Ni through the analysis of TEM and

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XPS characteristics, and also related to the catalytic performances of heavy oil upgrading.

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Keywords: MoS2, NiMoS, nanoparticle, slab, core-shell, heavy oil, vacuum residue

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1. Introduction

2 3

Demand for conventional oil increased gradually from 66.1 mb/d in 1990 to 90.1 mb/d in

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2013. This growth tendency is explained by the development of non-OECD countries which has 35%

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and 46% of world oil demand in 1990 and 2013, respectively. Specially, transport sector oil demand

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was 30.5 mb/d and 48.7 mb/d which means increasing demand of well refined liquid oil like naphtha,

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middle distillates, and gas oil 1. To solve upcoming supply problem of oil, unconventional oil can be

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one of the solution. World reservoir of unconventional oil (bitumen, oil sand, kerogen, and tight oil) is

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47% larger than conventional crude oil 2. However, even when the problem is solved by replacing

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with unconventional oil, there is still problems with the unconventional oil itself. Unconventional oil

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has very high portion of impurities such as sulfur and metal (Ni, V, Fe etc.) which deactivate catalysts.

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And, it consists of hydrocarbons with low hydrogen/carbon ratios, which means extra hydrogen

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needed for better quality. Generally, the process of refining unconventional oil impurities is carried

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out in hydrogen atmosphere using catalysts at high temperature. The hydrotreatment (HDT) process is

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usually classified to hydrodesulfurization (HDS), hydrodeoxygenation (HDO), hydrodenitrogenation

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(HDN), and hydrodemetallization (HDM)

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removing undesired impurities and hydrogenating carbon radicals by catalysts.

18

3-6

. These HDT processes have the same purpose of

On the other hand, since the general HDT catalyst includes a porous support material, the 7, 8

19

catalyst performance in the HDT process is inevitably influenced by the quality of the feedstock

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Large amount of heteroatoms in asphaltenes are easily poisoning active sites of catalysts and low H/C

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ratio causes coke deposition on the surface of active metal or blocking pores of support 9. For this

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reason, commercial supported catalysts easily lose their durability in the hydrocracking process of

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heavy oil. To alleviate this problem, recently unsupported catalysts have been proposed as alternatives

24

10, 11

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very challengeable to manufacture the nanoparticles without immobilizing the active components on

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the support. For example, the sulfidation process for HDT catalysts is usually carried out at

.

. However, considering the high calcination temperature of the catalyst production process, it is

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temperatures above 400°C. This temperature causes the nanoparticles to agglomerate (sintering) and

2

not maintain the size of the nanomaterial. Some studies have been reported on the preparation of

3

nanoparticles using a non-ionic surfactant to inhibit aggregation between metal precursors

4

However, it is not possible to produce uniform nanoclusters (< 10nm), and there is concern about

5

carbon impurities due to decomposition of organic matter after high temperature process.

12-14

.

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In this study, the core-shell type NiMoOx@SiO2 nanocluster with about 10nm size is

7

prepared and applied to the sulfidation process to prevent sintering of the core components. Since the

8

shell material, SiO2, has high thermal stability and porosity so that the gases such as H2S pass through

9

the shell, NiMoSx@SiO2 nanocluster is synthesized after the sulfidation of NiMoOx@SiO2. And then,

10

the SiO2 shell is removed by the alkali solution under atmospheric temperature, and finally NiMoSx

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nanoparticle is remained. Even there are some studies of core-shell type material to prevent sintering

12

during catalyst preparation

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catalysts for upgrading heavy oil. The effect of Ni content on the catalyst performance is also studied

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because the structure and activity of the catalyst are different according to the synthesis method even

15

in the same composition. Some studies investigated the effect of Ni amount in the NiMoS catalyst on

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their model reaction

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the support, in-depth studies of the Ni doping amount is not sufficient and the range of doped

18

quantities is also limited. Therefore, various structural, chemical properties and catalytic activities are

19

investigated according to the amount of Ni doping in this study.

19-23

15-18

, there is no application to MoS2, NiMoSx and similar unsupported

. However, for unsupported NiMoS materials that have no interaction with

20 21

2. Experimental

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2.1 Catalyst preparation The synthesis process was following three-steps: (1) synthesizing core-shell MoOx@SiO2, (2)

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sulfidizing core-shell MoOx@SiO2 to make MoSx@SiO2, and (3) stripping out silica shell to get MoS2

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nanoparticle. -4-


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Core-shell MoOx@SiO2 was synthesized by following details: MoCl5 (Sigma Aldrich, 95%;

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1 g), Igepal CO-520 (Aldrich, average Mn 441; 30 g), and cylclohexane (Sigma Aldrich, 99.5%; 300

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ml) were mixed in a 500 ml media bottle. The bright green color mixture was sonicated for 30

4

minutes and stirred for 12 hours at room temperature. To form silica shell, 2.5 ml DI water, 3 ml

5

ammonia solution (Sigma Aldrich, 28-34 wt.%), and 6 ml tetraethylorthosilicate (Aldrich, reagent

6

grade 98% ) were sequentially added to the mixture. The reddish mixture was aged for 16 hours at

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room temperature. After aging, ethanol was added to coagulate the mixture. The MoOxCly@SiO2 solid

8

was filtered off with ethanol and dried at 60oC for overnight. Centrifugation was then carried out at

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8000 rpm for up to 5 minutes. To remove remain surfactant and chloride, dried MoOxCly@SiO2 was

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calcined at 673K for 4 hours.

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MoS2@SiO2 was prepared by following order: MoOx@SiO2 was sulfidized in tubular furnace

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at 673K for 4 h under 5% H2S/H2 gas (60 ml/min). After sulfidation process, tubular furnace was

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purged with nitrogen gas (100 ml/min) while cooling to room temperature.

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MoS2 nanoparticle was obtained by following method: The silica stripping process was

15

performed by using potassium hydroxide. The MoS2@SiO2 powder was mixed with 120 ml KOH

16

solution (1M) and the mixed solution was stirred for at least 12 hours. The stripped MoS2 nanoparticle

17

was separated by centrifugation at 15000 rpm for 5 minutes and rinsed with acetone. Centrifugation

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and rinsing was repeated several times. Finally, the precipitant was dried at 333K for overnight.

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Unsupported NiMoS nanoparticle was synthesized by adding one step to the above-

20

mentioned synthesis process. Nickel (II) chloride hydrate (Aldrich, 99.95%) was mixed with MoCl5,

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Igepal CO-520, and cylclohexane at the beginning of the synthesis process. Unreacted species of

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nickel ions were removed while filtering. The amount of Ni added during the synthesis was 0.25, 1,

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2.5 (Ni/Mo) molar ratio to molybdenum, but ICP analysis showed that the contents of Ni and Mo in

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the final product were slightly different from those expected. The catalyst abbreviation is shown in

25

Table 1 in order to reflect the ICP results and to represent the weight ratio instead of the molar ratio

26

between metals. -5-


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Table 1 Catalyst abbreviation Catalysts

Abbreviated expressions

MoS2 commercial

bulk MoS2

MoS2 nanoparticle

MoS2

0.25 NiMoS nanoparticle

NiMoS(0.19)

1 NiMoS nanoparticle

NiMoS(0.45)

2.5 NiMoS nanoparticle

NiMoS(1.2)

3 4 5 6 7

2.2 Catalytic activity tests The reaction condition and reactants were similar to previous study on our group

24-26

.

8

Vacuum residue (VR) was obtained from SK Innovation, Korea Oil Company, and the properties are

9

shown in Table 2. As commercially available bulk catalysts, MoS2 (powder, 2 µm, ≥99%, Sigma

10

Aldrich) was used. Hydrocracking was carried out in a batch reactor with 30 g of VR and 0.03 g of

11

catalysts (1000 ppm). The reactor was charged with the reactants and purged three times with H2 gas

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at 10 atmospheres to remove residual air. Then the reactor was pressurized to 70 bar with hydrogen at

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300 K, followed by heating to 673 K at a ramp rate of 12.5 K/min. The reaction was carried out at 673

14

K for 4 h. When the reaction was completed, products were collected by using dichloromethane (98%,

15

Sigma Aldrich) as solvent. The collected products were filtered to separate liquid products and solid

16

products (coke + spent catalyst).

17

After the liquid products were completely recovered, dichloromethane was removed via a

18

rotary evaporator at 343 K. Full removal of dichloromethane was confirmed by SIMDIS data. After

19

evaporation, the final products were analyzed via Simulated-Distillation (SIMDIS). SIMDIS analysis

20

was performed by a PerkinElmer gas chromatograph Clarus 700 series using the ASTM D2887

21

method.

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Table 2 The properties of Vacuum Residue Oil Properties

Value

API gravity (°)

2.3

>798K fraction (wt.%)

89.6

C5-Asphaltene (wt.%)

23.1

Elemental analysis (wt.%) C

83.6

H

10.8

N

0.7

S

4.8

C/H ratio

7.7

Ni (ppm)

42.1

V (ppm)

99.3

3 4 5

The conversion and yields were calculated by lower formulas. Liquids product yield % = Solids product yield % =

Liquids product weight g × 100 Total reactant VR weight 30 g

Solids product weight g − Catalyst weight g × 100 Total reactant VRweight 30 g

Gas product yield % = 100 % − $ Liquids & solids product yield % Asphaltene conversion % =

Asphaltent in reactant − Asphaltene in product ∗ 100 Asphaltene in reactant

Commercial liquids yield % =

*+,ℎ.ℎ+ /012ℎ. 2 + 415560 517.166+.07 /012ℎ. 2 + 8+7 916 /012ℎ. 2 :9.+6 ;0+? /012ℎ. 30 2

∗ 100 6 7 8

2.3 Catalyst characterization The specific surface area was carried out using a BELSORP-max instrument (BEL Japan -7-


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1

Inc.) with nitrogen at 77 K and calculated by BET method. Before analysis, the sample was preheated

2

under vacuum condition for 12 h at 150°C.

3

X-ray diffraction (XRD) patterns were gained by a Dmax2500/PC diffractometer (Rigaku).

4

The analysis was operated at 40 kV and 200 mA with Cu Kα1 irradiation (λ = 1.5406 Å) from 5° to 90°

5

by 4°/min.

6

TEM image and EDS elemental mapping were obtained by FEI Titan TEM at 300 kV.

7

Elemental composition analysis was performed by inductively coupled plasma atomic

8

emission spectroscopy (ICP-OES, Thermo Scientific, iCAP 6300) to quantify Ni, Mo, V contents of

9

catalysts. CHNS analyzer (FLASH 2000, Thermo Scientific) was used to measure S contents of

10 11 12

catalysts. The X-ray photoelectron spectroscopy analysis was performed on ESCALAB 250. The Xray source was Mg Kα with C1s reference peak at 284.6 eV.

13 14 15

3. Results and Discussion

16 17

3.1 Characterization of catalysts

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TEM images of the nanoparticles for each synthesis step are shown in Fig. 1 and Fig. 2. As

19

can be seen in Fig. 1 (a), molybdenum oxide is well coated with SiO2 to form a core-shell

20

MoOx@SiO2 structure and the core materials MoOx have uniform nanoclusters of less than 10 nm.

21

After the sulfidation process, the molybdenum oxide turns into MoS2 and the typical slabs of MoS2 in

22

silica shell is shown in Fig. 1 (b). This result means that silica pores are enough for H2S gas to

23

penetrate even though there is no special treatment for the silica shell.

24

Fig. 2 shows TEM images of the silica-stripped MoS2 nanoparticles. From image (a) to (d),

25

the Ni/Mo weight ratio of the catalyst increases from zero to 1.2. Unusually, the shape of MoS2

26

nanoclusters below 10 nm as seen in Fig. 1 (b) is invisible, as if these particles clumped together. It is -8-


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presumed that aggregation and crystal growth occurred between the nanoclusters in the silica strip

2

process and the drying process. Especially, the drying process is performed at 333K and is considered

3

to be an environment where the particle growth of nanoclusters can occur. Average slab size and

4

surface area are presented in Table 3. Fig. 2 (a) - (d) shows that the slab length and stack thickness

5

increase and it was confirmed by average values in Table 3. Additionally, the BET surface area is

6

decreasing with Ni content increasing. Therefore, it is considered that the crystallization more

7

progressed as the nanoclusters contained more Ni content.

8 9

Fig. 1 TEM images of (a) MoOx@SiO2 and (b) MoS2@SiO2

10

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Fig. 2 TEM images of MoS2 and NiMoS samples (a) MoS2, (b) NiMoS(0.19), (c) NiMoS(0.45), and

3

(d) NiMoS(1.2)

4 5

6 7 8 9

Table 3 The BET surface area and slab size by TEM Catalyst

nano MoS2

NiMoS(0.19)

NiMoS(0.45)

NiMoS(1.2)

Surface Area (m2/g)

113.5

126.6

107.3

12.5

Slab Lengtha (nm)

3.5

4.6

5.2

9.77

Stack Thicknessa(nm)

3.1

3.9

4.5

6.2

a: the values of slab length and stack thickness were detected at 10 local points in each TEM image and averaged.

XRD analysis results are correlated with TEM images of MoS2 and NiMoS series. Fig. 3 shows that all samples basically have similar peak patterns with MoS2 material

27

. Unlike MoS2,

10

NiMoS series are considered to form multi-layer structure because of the high intensity at (002) peak,

11

which represents that the particles are stacking in the c direction 28. These results are consistent well - 10 -


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with the results of TEM analysis. For sample with Ni/Mo ratio 1.2, there are nickel sulfide peaks.

2

Therefore, it is considered that some nickel components did not stick together with MoS2 structure in

3

case of the sample with rich Ni content.

4 5

Fig. 3 XRD patterns of NiMoS samples: (a) MoS2, (b) NiMoS(0.19), (c) NiMoS(0.45), and (d)

6

NiMoS(1.2)

7 8

The distribution of each element (Ni, Mo, S) in NiMoS structure is shown in Fig. 4. NiMoS

9

(0.19) and (0.45) EDS images show that Ni, Mo, and S component exist at same points. Not like other

10

NiMoS samples, NiMoS(1.2) EDS image shows that the high intensity location in Ni component is

11

different from that of high intensity location in S. This results can be correlated with XRD results in

12

Fig. 3.

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Fig. 4 TEM-EDS elemental mapping images (a) NiMoS(0.19), (b) NiMoS(0.45), and (c) NiMoS(1.2)

3 4

The chemical states on the surface of NiMoS was evaluated by XPS analysis. Fig. 5 shows

5

the decomposition of Mo 3d spectra. Molybdenum can exist as sulfide (MoIV), oxide (MoVI), and

6

oxysulfide (MoV) phases. First higher peak at 229.0 @ 0.1 eV (Mo3d5/2) can be assigned to sulfide

7

phase (MoS2). Second peak observed at 232.2 @ 0.1 eV (Mo3d5/2) belongs to oxide phase of

8

molybdenum (MoOx). According to the literature, the presence of decomposed peak at 230.2 @ 0.1

9

eV (Mo3d5/2) is indicating oxysulfide phase (MoOxSy)

29

. Peak points at 226 @ 0.1 eV and 227.6

10

@ 0.2 eV are known as S 2s that refers to S2- and S22- sources. Binding energies and atomic

11

percentages of MoIV, MoV, and MoVI are summarized in Table 4. NiMoS(0.45) has the highest atomic

12

percentage of MoS2 phase (MoIV), while it has the lowest atomic percentage of oxysulfide phase - 12 -


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(MoV). The results indicate that nickel contents in catalyst material obviously influence on the

2

forming of Mo-S phase.

3

Table 4 Mo 3d XPS parameters of the different contributions for NiMoS series MoIV

MoV

MoVI

Catalyst B.E.(eV)

at.%

B.E.(eV)

at.%

B.E.(eV)

at.%

NiMoS (0.19)

228.9

42.8

229.9

6.1

231.9

51.1

NiMoS (0.45)

228.9

43.2

229.9

5.0

231.9

51.8

NiMoS (1.2)

228.9

37.7

229.9

6.3

231.9

56.0

4 5

Fig. 5 Deconvolution of the Mo 3d XPS spectra (a) NiMoS(0.19), (b) NiMoS(0.45), and (c)

6

NiMoS(1.2)

7 8

Two main peaks of decomposed S 2p XPS spectra are illustrated in Fig. 6. First peak at

9

161.6 @ 0.1 eV (S 2p) is assigned to S2- state, which implies the presence of MoS2, NiS, and NiMoS

10

phases. The other peak at 162.7 @ 0.1 eV (S 2p) refers to S22- state which denotes oxysulfide phase

11

30-33

. Table 5 summarizes binding energies and atomic percentages of S2- and S22-. Both chemical - 13 -


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states appear to be related to the Ni/Mo ratios in the catalyst materials. The tendency of atomic

2

percentage is similar with molybdenum XPS results, and NiMoS(0.45) has the highest atomic

3

percentage of sulfide phase (S2-) and the lowest atomic percentage of oxysulfide phase (S22-).

4

Table 5 S 2p XPS parameters of the different contributions for NiMoS series S2Catalyst

S22-

S (wt.%) B.E.(eV)

at.%

B.E.(eV)

at.%

NiMoS (0.19)

33.72

161.6

59.6

162.7

40.4

NiMoS (0.45)

34.96

161.6

62.0

162.7

38.0

NiMoS (1.2)

24.11

161.6

61.0

162.8

39.5

5 6

Fig. 6 Deconvolution of the S 2p XPS spectra (a) NiMoS(0.19), (b) NiMoS(0.45), and (c)

7

NiMoS(1.2)

8 9

Fig. 7 shows Ni 2p XPS spectra. The main deconvoluted peaks contribute to NiMoS phase

10

and Ni(II) phase (nickel oxide). The peaks at 853.9 @ 0.1 eV and 855.8 @ 0.2 eV (Ni 2p3/2) refer

11

to NiMoS phase and Ni(II) phase, respectively. Table 6 summarizes binding energies and atomic - 14 -


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percentages of NiMoS and Ni(II) phases. The atomic percentage of NiMoS phase over NiMoS(0.45),

2

which was calculated between only nickel sources, is lower than NiMoS(0.19). However, in case of

3

the atomic percentage, which was calculated among total nickel, molybdenum and sulfur sources, it

4

can be shown that total atomic percentage of NiMoS phase over NiMoS(0.45) is 0.3% higher than

5

NiMoS(0.19). Typically, NiMoS material system has three phases which are NiMoS, nickel sulfide,

6

and nickel oxide (Ni(II))

7

852.8 @ 0.2 eV (Ni 2p3/2). However, Fig. 7 has no specific signal at that point. It could be inferred

8

that most of nickel is involved in NiMoS structure or small amount of additional nickel species

9

exists as oxide phase instead of sulfide. In case of NiMoS(1.2), nickel sulfide peaks are shown in

10

XRD result of NiMoS(1.2), but there are no deconvoluted peaks of nickel sulfide or NiMoS phase on

11

XPS spectra. Considering EDS images and average slab sizes, it is supposed that excess nickel

12

species exist as nickel oxides covering NiMoS particles. On the other hand, the XRD result (Fig. 3)

13

of NiMoS(1.2) shows the peaks of the nickel sulfide instead of nickel oxide but the XPS result is

14

opposite. Therefore, it would be reasonable to assume that a considerable amount of NiS2 covering

15

NiMoS and outer surface of NiS2 oxidize to form NiO2. In summary, most of XPS results show that

16

unsupported nano NiMoS is quite vulnerable in atmosphere condition. Extra Ni species are

17

considered to agglomerate with each other and grow around NiMoS or nickel sulfide.

34-36

. According to the literature, nickel sulfide peak could be noticed at

18 19

Table 6 Ni 2p3/2 XPS parameters of the different contributions for NiMoS series NiMoS

Ni(II)

Catalyst B.E.(eV)

at.%

at.% tot

B.E.(eV)

at.%

at.% tot

NiMoS (0.19)

853.9

51.2

0.8

855.8

48.8

0.8

NiMoS (0.45)

853.9

34.4

1.1

855.8

65.6

2.1

NiMoS (1.2)

-

-

856.0

100

6.5

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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

1

.

2

Fig. 7 Deconvolution of the Ni 2p3/2 XPS spectra (a) NiMoS(0.19), (b) NiMoS(0.45), and (c)

3

NiMoS(1.2)

4 5

3.2 Activity test of unsupported nano NiMoS catalysts

6

In Table 7, the performances of nano NiMoS catalysts were compared to those of non-

7

promoted MoS2 catalysts and also compared to that without catalyst. The portions of gas, liquid, and

8

solid are also summarized. Detail mass fractions of liquid products were sorted by boiling point of

9

each product as naphtha (< 450K), middle distillate (450-616K), gas oil (616-798K), and residue (>

10

798K). The quality of oil products was determined depending on the yield of liquid products and solid

11

(coke) products. Also, as shown in Fig. 8, the quality of liquid products can be determined by the

12

yield of commercial liquid products which is summation of naphtha, middle distillate, and gas oil.

13

In more detail, without using catalysts, the effectiveness of converting vacuum residue is the

14

worst. In that case, gas and solid mass fractions are 17.3 and 18.6 weight %, which were the highest

15

ratios respectively among all hydrocracking results. The performance of a non-promoted MoS2 is

16

better than without catalysts. Comparing the products by nano and bulk MoS2 catalysts, there is no - 16 -


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significant difference in the phase (gas, liquid, and solid) distribution (Table 7) and the yield of

2

commercial liquid products (Fig. 8). However, it is founded that the amounts of Naphtha and middle

3

distillate are remarkably higher in nano MoS2 catalysts. On the other hand, the solid products over all

4

NiMoS catalysts are remarkably reduced. Especially, NiMoS(0.45) catalyst shows the best product

5

quality as 80.5 and 47.5 weight %, which are the highest total liquid product and commercial liquid

6

product ratios. Comparing the performances of both NiMoS(0.45) and bulk MoS2 catalysts, the yields

7

of solid and residual oil are much lower in the NiMoS(0.45) catalyst, but the yields of middle distillate

8

and Naphtha as liquid products are much higher in the NiMoS(0.45) catalyst. Therefore, it can be

9

suggested that nano-sized NiMoS(0.45) catalyst can effectively convert heavy oil to commercial

10 11

liquid products while inhibiting coke formation. In the NiMoS material system, the catalytic active site is known as the edge of typical slab 37-40

12

structure and the activity depends on the chemical states on the slab edge

13

NiMoS(0.45) catalyst could be predicted by characterization results. It is considered that NiMoS(0.45)

14

catalyst has the highly dispersed slab structure formed by the nanocluster synthesis, and the optimum

15

chemical state on the slab edge could be controlled by the addition of appropriate Ni amount.

. The high activity of

16 17

Table 7 Yield of each product after hydrocracking reactions w/o nano Catalysts bulk MoS2 catalyst MoS2

NiMoS (0.19)

NiMoS (0.45)

NiMoS (1.2)

Gas products (wt.%)

17.3a

14.6

14.9

14.5

14.1

14.7

Liquid products (wt.%)

64.1

74.4

74.1

75.5

80.5

77.4

Solid products (wt.%)

18.6

11.0

11.0

10.0

5.4

7.9

Distribution of liquid products (wt.%, on the basis of liquid product weight) 798K (Residue)

3.6

3.7

8.0

8.0

11.0

9.0

22.1

22.9

25.0

24.0

28.0

25.0

38.9

39.3

35.0

34.3

33.0

32.0

35.4

34.1

32.0

33.7

28.0

34.0

- 17 -


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

1

Reaction conditions: initial H2 pressure, 70 bar; temperature, 673K; reaction time, 4 h.

2

a

3

more.

: All the values in the figure are the average of the results of the experiments repeated three times or

4

5 6

Fig. 8 The performance of catalysts for the hydrocracking of VR (a) and yield of commercial liquid

7

products (naphtha + middle distillates + gas oil – 10.4 wt.%) (b). All the values in the figure are the

8

average of the results of the experiments repeated three times or more.

9 10 11

4. Conclusions

12 13

Novel synthetic method using core-shell nanocluster was used to synthesize nano-scaled

14

NiMoS catalysts. The characterization and catalytic evaluation of the material demonstrated that the

15

new method is suitable for the synthesis of unsupported NiMoS nanoparticle. By limiting the thermal

16

growth of the particles with silica shell, uniform nanoclusters of NiMoS were achieved and the

17

nanoclusters could be applied to control the typical slab structure (slab length, stack thickness and

18

dispersion), as known to be catalytic active site. In conclusion, unsupported NiMoS(0.45) catalyst has - 18 -


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Energy & Fuels

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highly dispersed slabs and the highest concentration of MoS2, NiMoS, and S2- phases on slab edge

2

among the evaluated catalysts, and therefore showed the highest performance for upgrading heavy oil.

3 4 5 6 7

Acknowledgments This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (NRF-2015R1A2A1A13001856).

8 9

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21. Mérida-Robles, J.; Rodrıguez-Castellón, E.; Jiménez-López, A., Characterization of Ni, Mo and Ni–Mo catalysts supported on alumina-pillared α-zirconium phosphate and reactivity for the thiophene HDS reaction. J. Mol. Catal. A: Chem. 1999, 145 (1-2), 169-181. 22. Purón, H.; Pinilla, J. L.; Montoya de la Fuente, J.; Millán, M., Effect of metal loading in NiMo/Al2O3 catalysts on Maya vacuum residue hydrocracking. Energy Fuels 2017, 31 (5), 48434850. 23. Lai, W.; Xu, Y.; Ren, Y.; Yang, L.; Zheng, J.; Yi, X.; Fang, W., Insight into the effect of non-stoichiometric sulfur on a NiMoS hydrodesulfurization catalyst. Catal. Sci. Technol. 2016, 6 (2), 497-506. 24. Eom, H.-J.; Lee, D.-W.; Kim, S.; Chung, S.-H.; Hur, Y. G.; Lee, K.-Y., Hydrocracking of extra-heavy oil using Cs-exchanged phosphotungstic acid (CsxH 3− xPW 12 O 40, x= 1–3) catalysts. Fuel 2014, 126, 263-270. 25. Hur, Y. G.; Kim, M.-S.; Lee, D.-W.; Kim, S.; Eom, H.-J.; Jeong, G.; No, M.-H.; Nho, N. S.; Lee, K.-Y., Hydrocracking of vacuum residue into lighter fuel oils using nanosheet-structured WS 2 catalyst. Fuel 2014, 137, 237-244. 26. Hur, Y. G.; Lee, D.-W.; Lee, K.-Y., Hydrocracking of vacuum residue using NiWS (x) dispersed catalysts. Fuel 2016, 185, 794-803. 27. Lai, W.; Chen, Z.; Zhu, J.; Yang, L.; Zheng, J.; Yi, X.; Fang, W., A NiMoS flower-like structure with self-assembled nanosheets as high-performance hydrodesulfurization catalysts. Nanoscale 2016, 8 (6), 3823-3833. 28. Seo, J. w.; Jun, Y. w.; Park, S. w.; Nah, H.; Moon, T.; Park, B.; Kim, J. G.; Kim, Y. J.; Cheon, J., Two‐Dimensional Nanosheet Crystals. Angew. Chem. Int. Edit. 2007, 46 (46), 8828-8831. 29. Gandubert, A.; Legens, C.; Guillaume, D.; Rebours, S.; Payen, E., X-ray photoelectron spectroscopy surface quantification of sulfided CoMoP catalysts–relation between activity and promoted sites–Part I: influence of the Co/Mo Ratio. Oil Gas Sci. Technol. 2007, 62 (1), 79-89. 30. Garreau, F.; Toulhoat, H.; Kasztelan, S.; Paulus, R., Low-temperature synthesis of mixed NiMo sulfides: structural, textural and catalytic properties. Polyhedron 1986, 5 (1-2), 211-217. 31. Houssenbay, S.; Kasztelan, S.; Toulhoat, H.; Bonnelle, J.; Grimblot, J., Nature of the different nickel species in sulfided bulk and alumina-supported nickel-molybdenum hydrotreating catalysts. J. Phys. Chem. 1989, 93 (20), 7176-7180. 32. Karroua, M.; Matralis, H.; Grange, P.; Delmon, B., UNSUPPORTED NiMo CATALYSTS. INFLUENCE OF THE SULFINDING TEMPERATURE AND EVOLUTION OF THE UNSUPPORTED NiMoS PHASE DURING REACTION. B. Soc. Chim. Belg. 1995, 104 (1), 11-18. 33. Ninh, T.; Massin, L.; Laurenti, D.; Vrinat, M., A new approach in the evaluation of the support effect for NiMo hydrodesulfurization catalysts. Appl. Catal. A: Gen. 2011, 407 (1), 29-39. 34. Wang, X.; Saleh, R. Y.; Ozkan, U. S., Effect of S-compounds and CO on hydrogenation of aldehydes over reduced and sulfided Ni–Mo/Al 2 O 3 catalysts. Appl. Catal. A: Gen. 2005, 286 (1), 111-119. 35. Escobar, J.; Barrera, M. C.; Toledo, J. A.; Cortés-Jácome, M. A.; Angeles-Chávez, C.; Núñez, S.; Santes, V.; Gómez, E.; Díaz, L.; Romero, E., Effect of ethyleneglycol addition on the properties of P-doped NiMo/Al 2 O 3 HDS catalysts: Part I. Materials preparation and characterization. Appl. Catal. B: Environ. 2009, 88 (3), 564-575. 36. Marchand, K.; Legens, C.; Guillaume, D.; Raybaud, P., A Rational Comparison of the Optimal Promoter Edge Decoration of HDT NiMoS vs CoMoS Catalysts. Oil Gas Sci. Technol. 2009, 64 (6), 719-730. 37. Baubet, B.; Devers, E.; Hugon, A.; Leclerc, E.; Afanasiev, P., The influence of MoS2 slab 2D morphology and edge state on the properties of alumina-supported molybdenum sulfide catalysts. Appl. Catal. A: Gen. 2014, 487, 72-81. 38. Raybaud, P.; Hafner, J.; Kresse, G.; Kasztelan, S.; Toulhoat, H., Structure, energetics, and electronic properties of the surface of a promoted MoS2 catalyst: an ab initio local density functional study. J. Catal. 2000, 190 (1), 128-143. - 21 -


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Energy & Fuels

1

Table Captions

2

Table 2. Catalyst abbreviation

3

Table 2. The properties of Vacuum Residue Oil

4

Table 3. The BET surface area and slab size by TEM

5

Table 4. Mo 3d XPS parameters of the different contributions for NiMoS series

6

Table 5. S 2p XPS parameters of the different contributions for NiMoS series

7

Table 6. Ni 2p3/2 XPS parameters of the different contributions for NiMoS series

8

Table 7. Yield of each product after hydrocracking reactions

9 10 11 12

Figure Captions

13

Figure 1. TEM images of (a) MoOx@SiO2 and (b) MoS2@SiO2

14

Figure 2. TEM images of MoS2 and NiMoS samples (a) MoS2, (b) NiMoS(0.19), (c) NiMoS(0.45),

15

and (d) NiMoS(1.2)

16

Figure 3. XRD patterns of NiMoS samples: (a) MoS2, (b) NiMoS(0.19), (c) NiMoS(0.45), and (d)

17

NiMoS(1.2)

18

Figure 4. TEM-EDS elemental mapping images (a) NiMoS(0.19), (b) NiMoS(0.45), and (c)

19

NiMoS(1.2)

20

Figure 5. Deconvolution of the Mo 3d XPS spectra (a) NiMoS(0.19), (b) NiMoS(0.45), and (c)

21

NiMoS(1.2)

22

Figure 6. Deconvolution of the S 2p XPS spectra (a) NiMoS(0.19), (b) NiMoS(0.45), and (c)

23

NiMoS(1.2)

24

Figure 7. Deconvolution of the Ni 2p3/2 XPS spectra (a) NiMoS(0.19), (b) NiMoS(0.45), and (c)

25

NiMoS(1.2)

26

Figure 8. The performance of catalysts for the hydrocracking of VR (a) and yield of commercial

27

liquid products (naptha + middle distillates + gas oil – 10.4 wt.%) (b)

28

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Ni-Doped MoS2 Nanoparticles Prepared via CoreâShell Nanoclusters

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