Surfactant-assisted hydrothermally synthesized MoS2 samples with controllable morphologies and structures for anthracene hydrogenation

Article abstract of DOI:10.1016/S1872-2067(17)62779-7

MoS₂ samples with controllable morphologies and structures were synthesized using surfactant-assisted hydrothermal processes. The effects of surfactants (PEG, PVP, P123, SDS, AOT, and CTAB) on the morphologies and structures of MoS₂ samples were investigated. The results revealed that spherical, bulk-like, and flower-like MoS₂ particles assembled by NH₄⁺-intercalated MoS₂ nano-sheets were synthesized. The morphologies of the MoS₂ samples and their structures (including the slab length and the number of stacked layers) of MoS₂ nano-sheets in these samples could be controlled by adjusting the surfactants. Mono-dispersed spherical MoS₂ particles could be synthesized with PEG via the creation of MoS₂ nano-sheets with slab lengths shorter than 15 nm and fewer than six stacked layers. Possible formation mechanisms of these MoS₂ samples created via surfactant-assisted hydrothermal processes are proposed. Further, the catalytic activities of MoS₂ samples for anthracene hydrogenation were evaluated in a slurry-bed reactor. The catalyst synthesized with the surfactant PEG exhibited the highest catalytic hydrogenation activity. Compared with the other catalysts, it had a smaller particle size, mono-dispersed spherical morphology, shorter slab length, and fewer stacked layers; these were all beneficial to exposing its active edges. This work provides an efficient approach to synthesize transition metal sulfides with controllable morphologies and structures.

Full text of DOI:10.1016/S1872-2067(17)62779-7

Chinese Journal of Catalysis 38 (2017) 597–606
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Surfactant‐assisted hydrothermally synthesized MoS2 samples with
controllable morphologies and structures for anthracene
hydrogenation
Min Lia,b,c, Donge Wangb, Jiahe Lib,c, Zhendong Panb, Huaijun Mab, Yuxia Jiangb,c, Zhijian Tianb,d,*,
Anhui Lua
a State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, Liaoning, China
b Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China
c University of Chinese Academy of Sciences, Beijing 100049, China
d State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, ChiZhendong nese Academy of Sciences, Dalian 116023, Liaoning, China
A R T I C L E I N F O
A B S T R A C T
Article history:
MoS2 samples with controllable morphologies and structures were synthesized using surfactant‐
assisted hydrothermal processes. The effects of surfactants (PEG, PVP, P123, SDS, AOT, and CTAB)
on the morphologies and structures of MoS2 samples were investigated. The results revealed that
Received 30 November 2016
Accepted 30 December 2016
Published 5 March 2017
+
spherical, bulk‐like, and flower‐like MoS2 particles assembled by NH4 ‐intercalated MoS2
nano‐sheets were synthesized. The morphologies of the MoS2 samples and their structures (includ‐
ing the slab length and the number of stacked layers) of MoS2 nano‐sheets in these samples could be
controlled by adjusting the surfactants. Mono‐dispersed spherical MoS2 particles could be synthe‐
sized with PEG via the creation of MoS2 nano‐sheets with slab lengths shorter than 15 nm and fewer
than six stacked layers. Possible formation mechanisms of these MoS2 samples created via surfac‐
tant‐assisted hydrothermal processes are proposed. Further, the catalytic activities of MoS2 samples
for anthracene hydrogenation were evaluated in a slurry‐bed reactor. The catalyst synthesized with
the surfactant PEG exhibited the highest catalytic hydrogenation activity. Compared with the other
catalysts, it had a smaller particle size, mono‐dispersed spherical morphology, shorter slab length,
and fewer stacked layers; these were all beneficial to exposing its active edges. This work provides
an efficient approach to synthesize transition metal sulfides with controllable morphologies and
structures.
Keywords:
Molybdenum sulfide
Surfactant‐assisted
Controllable morphology
Mono‐dispersed
Active edges
Anthracene hydrogenation
© 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
tween two trigonal atomic layers of S atoms [5]. The Mo and S
atoms are linked by strong covalent bonds, while the S‐Mo‐S
Molybdenum sulfide (MoS2), a typical lamellar transition
metal sulfide, has been widely used in catalysis, electrochemis‐
try, lubrication, and intercalation chemistry [1‒4]. MoS2 has a
S‐Mo‐S layered structure, where a Mo atom is sandwiched be‐
layers interact with each other via van der Waals forces [2,6]. In
MoS2 crystals, there are two types of exposed surfaces: the
(00l) planes along the S‐Mo‐S edges (c axis), which are referred
to as the basal planes, and the (100) planes along the edges of
* Corresponding author. Tel/Fax: +86‐411‐84379151; E‐mail: tianz@dicp.ac.cn
This work was supported by the National Natural Science Foundation of China (21303186) and the Strategic Priority Research Program of the Chi‐
nese Academy of Sciences (XDA07020300).
DOI: 10.1016/S1872‐2067(17)62779‐7 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 38, No. 3, March 2017

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Min Li et al. / Chinese Journal of Catalysis 38 (2017) 597–606
S‐Mo, which are referred to as edges. Density functional theory
calculations and atom‐resolved scanning tunneling microscopy
(STM) have revealed that the edges of MoS2 nano‐sheets are
active sites for the hydro‐treating processes of crude petroleum
products and for electrochemical hydrogen evolution reaction
(HER) [3,7,8]. It has been reported that the number of active
sites is closely related to the morphological and structural
characteristics of the MoS2 catalysts [1,9,10].
tants, namely polyethylene glycol (PEG), polyvinylpyrrolidone
(PVP), polyoxyethylene‐polypropylene oxygen‐polyoxyeth‐
ylene (P123), sodium dodecyl sulfonate (SDS), sodium
di‐2‐ethylhexylsulfosuccinate (AOT), and cetyl trimethyl am‐
monium bromide (CTAB). The effects of these surfactants on
the morphologies and structures of MoS2 samples were sys‐
tematically investigated, and the growth mechanisms of the
MoS2 samples with their various morphologies and structures
are proposed in this paper. Further, the catalytic activities of
these samples were investigated in a slurry‐bed reactor via the
hydrogenation of anthracene. Anthracene (AN) was used as a
model compound for polyaromatic hydrocarbons in heavy oil
fractions such as bitumen, which are the most difficult constit‐
uents in heavy oils to hydrogenate. Of these samples, one was a
mono‐dispersed spherical MoS2 sample synthesized with the
PEG surfactant; the sample was assembled from MoS2
nano‐sheets with short slabs and which contained only a few
stacked layers; it exhibited the highest catalytic activity for
anthracene hydrogenation of all the samples tested here.
Recently, various approaches have been used to prepare
MoS2 nano‐sheets with controllable morphologies and struc‐
tures. Guo et al. [11] synthesized graphene‐like MoS2
nano‐sheets with tunable stacking layers via the thermal de‐
composition of a single source (Mo(Et2NCS2)4) under an Ar
atmosphere. Gao et al. [12] synthesized interlayer‐expanded
MoS2 nano‐sheets with edge‐terminated structures using a
microwave‐assisted strategy and investigated their catalytic
activities for HER. The results revealed that the excellent HER
performances of these MoS2 nano‐sheets could be ascribed to
the exposure of the active edges, which was promoted by hav‐
ing edge‐terminated structures and an expanded interlayer
distance. Varrla et al. [13] synthesized MoS2 nano‐sheets with
different slab lengths and different numbers of stacked layers
using shear exfoliation. They found that the slab length and the
number of stacked layers of the MoS2 nano‐sheets could be
changed by adjusting the surfactant solutions, and that MoS2
nano‐sheets with short slab lengths and reduced numbers of
stacked layers promoted the exposure of the active edges. Uz‐
canga et al.[14] synthesized hollow spherical MoS2 aggregates
assembled from MoS2 nano‐sheets using an aqueous
sono‐chemical route. They found that the high catalytic activi‐
ties of hollow spherical MoS2 catalysts for thiophene hy‐
drodesulfurization could be ascribed to the material having a
high content of exposed active edge sites and that the spherical
skeletons facilitate the exposure of the active edges of the MoS2
nano‐sheets. Wang et al. [10] synthesized three‐dimensional
(3D) hierarchical MoS2 nano‐spheres and large aggregated
MoS2 nano‐particles via a hydrothermal method using surfac‐
tants as soft templates. Surfactant‐assisted hydrothermal
preparation has been widely used to control the morphology
and structure of metal oxides and sulfides such as SnS and CeO2
[15‒18]. However, there are still very few studies on surfac‐
tant‐assisted hydrothermal preparation of MoS2 samples with
controllable morphologies and structures.
2. Experimental
2.1. Synthesis of MoS2 samples
A certain amount of surfactant (PEG, PVP, P123, SDS, AOT,
or CTAB) was dissolved into 60 mL of distilled water under
constant stirring at room temperature for 0.5 h. 1.4 mmol am‐
monium molybdate and 22.9 mmol thioacetamide were dis‐
solved into the above mentioned solution under stirring to
form a homogenous solution. Then, 2 mL hydrazine hydrate
was added into the resulting solution. After stirring for 0.5 h,
the solution was transferred into a 100 mL Teflon‐lined stain‐
less steel autoclave and maintained at 200 °C for 24 h. The pre‐
cipitate was centrifuged and washed with water and then eth‐
anol three times, and then dried at 60 °C for 12 h in a vacuum
drying oven. The samples prepared with PEG, P123, SDS, PVP,
AOT, and CTAB are referred to as MoS2‐PEG, MoS2‐P123,
MoS2‐SDS, MoS2‐PVP, MoS2‐AOT, and MoS2‐CTAB, respectively.
MoS2‐PEG was annealed at 400 °C for 4 h in H2 and is referred
to as MoS2‐PEG‐C.
2.2. Characterization of the MoS2 samples
As crude oil becomes heavier and more inferior, the conver‐
sion of heavy oils into liquid fuels has increased greatly in sig‐
nificance. Hydrogenation of heavy oils can increase their H/C
ratio and decrease their viscosity, which aids the realization of
clean and efficient upgrading of heavy oils. Slurry bed technol‐
ogy is an advanced technique for hydrotreating heavy oils into
liquid fuels. However, the challenge for heavy oil hydrogenation
lies in developing MoS2 catalysts with high catalytic activities.
Therefore, to develop high activity catalysts, it is essential to
synthesize MoS2 catalysts with controllable morphologies and
structures.
X‐ray diffraction (XRD) measurements were performed on a
PANalytical X’Pert Pro diffractometer with Cu radiation (λ =
0.15418 nm). Fourier transform infrared spectroscopy (FTIR)
measurements were conducted using a Nicolet iS50 instru‐
ment. The thermogravimetry‐differential scanning calorimetry
(TG‐DSC) measurements were performed with a Netzsch
STA449F3 TG‐DSC analyzer under a protective nitrogen at‐
mosphere. The Brunauer‐Emmett‐Teller (BET) surface area
was measured using a Micromeritics ASAP 2040 apparatus via
N2 physisorption at ‒196 °C. Static contact angle measurements
of the MoS2 samples under ambient conditions using deionized
water were performed with a DSA100 optical contact angle
measuring device. Scanning electron microscopy (SEM) images
were taken on a Quanta 200 FEG at a voltage of 20 kV. Trans‐
In this work, surfactant‐assisted hydrothermal processes
were applied to synthesize MoS2 samples with controllable
morphologies and structures. Here, we employed six surfac‐

Min Li et al. / Chinese Journal of Catalysis 38 (2017) 597–606
599
mission electron microscopy (TEM) measurements were car‐
ried out with a JEM 2100 EX field emission electron microscope
at a voltage of 200 kV.




MoS2-CTAB
2.3. Catalytic activities of the MoS2 samples
The catalytic activities of the MoS2 samples synthesized with
the different surfactants for AN hydrogenation were evaluated
in a slurry‐bed reactor (a Parr batch micro‐reactor). The mi‐
cro‐reactor was loaded with 30 g of tridecane as the solvent,
3.0 g of anthracene as the model compound, and 0.15 g of MoS2
sample as the catalyst. The system was purged three times and
pressurized with H2 to 80 bar. Then the reactor was heated to
400 °C and maintained for 4 h. The stirring speed was 300
r/min. Liquid products were filtered with microporous mem‐
branes to remove the catalysts and analyzed using an Agilent
7890A gas chromatograph (GC) fitted with a flame ionization
detector (FID). The GC used nitrogen as the carrier gas and was
equipped with a HP‐5 column (60 m × 320 μm  0.25 μm). The
liquid products were identified using an Agilent 7890B‐5977A
GC‐mass spectrometer (GC‐MS). The GC‐MS was equipped with
a HP‐5 column (30 m  250 μm  0.25 μm).
The selectivity of the hydrogenated products (anthracene
derivatives) is defined as the molar ratio of one single AN de‐
rivative to the total amount of hydrogenated products ob‐
tained. Hydrogenated products including anthracene perhy‐
dride (14HN), octahydroanthracene (8HN), tetrahydroanthra‐
cene (4HN), and dihydroanthracene (2HN) were detected. No
cracking products were detected. Conversion of AN (Conv.) is
defined as: Conv. = ([AN]0 – [AN])/[AN]0 × 100%, where [AN]0
is the concentration of AN before the hydrogenation reaction,
and [AN] is the AN concentration after the hydrogenation reac‐
tion.
MoS2-AOT
MoS2-PVP
MoS2-SDS
MoS2-P123
MoS2-PEG
10
20
30
40
2/
50
60
70
Fig. 1. XRD patterns of MoS2 samples synthesized with different surfac‐
tants.
peaks, referred to as peak I and II. The locations of the two
peaks in each sample and their corresponding interlayer spac‐
ings are listed in Table 1. For each sample, a near diploid rela‐
tion of the two interlayer spacings indicate that the expanded
interlayer spacing of MoS2 may result from the intercalation of
hetero molecules. Similar results have also been reported in the
case of oxygen‐incorporated, alkali metal ions‐intercalated, and
+
NH4 ‐intercalated MoS2 samples [19–24]. Compared with
standard 2H‐MoS2, the interlayer spacings of our samples were
0.33–0.40 nm larger, which is comparable to the increase in
interlayer spacing observed in MoS2 nano‐sheets in our previ‐
ous report, in ammoniated layered molybdenum, and in other
transition mental chalcogenides [22–24]. In those studies, the
enlarged interlayer spacings in the 0.31–0.37 nm range were
+
ascribed to the intercalation of NH4 ions whose diameter is
To visualize the activities of the MoS2 catalysts in anthra‐
cene hydrogenation, it was proposed to study the hydrogena‐
tion ratio (HR). The hydrogenation ratio is defined as the ratio
of moles of hydrogen incorporated into the hydrogenated
products per mol of AN divided by 7. The hydrogenation ratio
of 14HN is 100%, and that of unreacted AN is 0%. The overall
hydrogenation ratio is calculated according to: HR% = ([2HN] ×
1 + [4HN] × 2 + [8HN] × 4 + [14HN] × 7)/7 × Conv.
–0.35 nm. Thus, it can be deduced that the enlarged interlayer
spacing of 0.33–0.40 nm may be caused by the intercalation of
NH4+ ions [22]. The slight differences in the enlarged interlayer
spacings may be caused by different amounts of intercalated
NH4 . Hence, MoS2 samples synthesized with different surfac‐
tants all have intercalated NH4+ in their structures.
The compositions of the MoS2 samples synthesized with
different surfactants were characterized using CHNS and
TG‐DSC measurements. The results of the CHNS analysis are
listed in Table 2. Each sample contained S and a small amount
of N, H, and C. This suggests that the samples contained MoS2,
+
3. Results and discussion
3.1. Structures and compositions of the MoS2 samples
synthesized with different surfactants
+
NH4 , surfactant molecules, and H2O. The presence of the ele‐
ment C should originate from the surfactant molecules, and the
The XRD patterns of the MoS2 samples synthesized with dif‐
ferent surfactants are shown in Fig. 1. In the high angle range
(30°–75°), each sample exhibits diffraction peaks at 33.8° and
57.7°, corresponding to the (100) and (110) peaks of standard
2H‐MoS2 (JCPDS Card No. 37‐1492). However, the (100) peak is
obviously asymmetric, which is similar to results reported by
Gao et al. [12] for edge‐terminated MoS2. They ascribed the
asymmetric (100) peak to the existence of stacking faults in the
MoS2 layers resulting from a‐b plane gliding. In the low angle
range (5°–20°), each sample exhibits two broad, but weak
Table 1
The locations of peak I and peak II for each sample and the corre‐
sponding interlayer distances.
Sample
2θI (°)
9.29
9.01
8.69
8.74
9.40
9.01
dI (nm)
0.95
0.98
1.02
1.01
0.94
0.98
2θII (°)
16.40
17.02
17.02
15.52
16.40
17.72
dII (nm)
0.54
0.52
0.52
0.57
MoS2‐PEG
MoS2‐P123
MoS2‐SDS
MoS2‐PVP
MoS2‐AOT
MoS2‐CTAB
0.54
0.49

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Min Li et al. / Chinese Journal of Catalysis 38 (2017) 597–606
Table 2
CNHS analysis of MoS2 samples synthesized with different surfactants.
Composition (wt%)
Sample
Hetero species
(NH4)y
0.24
C
N
H
S
(surfactant)x
(C2H4O)0.19
(H2O)z
3.27
8.17
6.17
3.18
5.75
6.26
MoS2‐PEG
MoS2‐PVP
MoS2‐AOT
MoS2‐P123
MoS2‐SDS
MoS2‐CTAB
1.87
2.87
1.61
3.57
1.67
1.13
1.34
1.81
1.04
1.67
1.03
1.47
4.34
8.93
6.94
4.95
6.85
7.15
25.72
27.50
30.41
27.69
32.05
29.78
(C6H9NO)0.08
(C8H15O)0.03
(C18H36O5)0.03
(C12H25SO4)0.02
(C19H42N)0.01
0.30
0.16
0.28
0.15
0.23
+
+
presence of N may mainly arise from NH4 ions, which may
originate from ammonium hepta‐molybdate and the hydrolysis
of hydrazine hydrate. The approximate chemical formulae of
these samples were calculated and are listed in Table 2. The
results show that there are 0.19 mol of PEG monomers and
0.24 mol of NH4+ ions per mole of MoS2 in MoS2‐PEG. For other
samples, there are only 0.01–0.08 mol of surfactant monomers
for one mole of MoS2.
ascribed to the differences in the interactions between the NH4
ions, the surfactants, and the MoS2.
Fig. 3 shows the FTIR spectra of adsorbed surfactant mole‐
cules. It can be observed that the spectrum of each sample
weakly shows the broad bonds of C–O–S (940 cm−1 and 901
cm−1) and C–S (604 cm−1) [20,25]. In the spectra of MoS2‐AOT,
MoS2‐PVP, and MoS2‐CATB the C–N (1120 cm−1) bonds and
–NH groups (1620 cm−1) may origin from the hydrophilic
groups of AOT, PVP, and CTAB [26,27]. In these samples, the
surfactants bridge the MoS2 mainly through C–O–S and C–S
bonds. Hence, MoS2 samples synthesized with different surfac‐
TG‐DSC measurements of these samples were performed in
N2, as shown in Fig. 2. The MoS2 samples synthesized with dif‐
ferent surfactants exhibited similar thermal degradation pro‐
cesses. The weight loss in the 40–180 °C range can be ascribed
to the removal of adsorbed H2O. The weight losses at this stage
for different samples were in the range of 0.77%–2.31%. The
weight loss in the 180–800 °C range was ascribed to the re‐
moval of NH4+ ions and surfactant molecules. In that stage, the
weight losses were 33.59%, 17.42%, 14.64%, 13.87%, 8.27%,
and 7.11% for MoS2‐PEG, MoS2‐PVP, MoS2‐P123, MoS2‐AOT,
MoS2‐SDS, and MoS2‐CTAB, respectively. In the DSC curves,
only a broad exothermal peak in the 180–800 °C range was
observed for each sample, which may be ascribed to the re‐
moval of NH4+ ions and surfactant molecules. The broad peaks
centered at 280–350 °C may result from peak overlapping ow‐
ing to the removal of NH4+ ions and surfactant molecules. It has
been reported that for nano‐MoS2 materials with different em‐
bedded guest species, the differences in the interactions be‐
tween the MoS2 and guest species resulted in a shift of the en‐
dothermal peak corresponding to the oxidation of MoS2 [20].
Thus, the different shifts of the endothermal peak correspond‐
+
tants mainly contain MoS2, NH4 , surfactant molecules, and H2O.
C-N
C-O-S
-NH
MoS2-CTAB
-CH2
S-PVP
MoS2-PEG
MoS2-P123
MoS2-SDS
MoS2-AOT
C-S
2000
1600
1200
Wavenumber (cm1)
800
400
Fig. 3. FTIR spectra of MoS2 samples synthesized with different surfac‐
+
ing to the removal of NH4 ions and surfactant molecules was
tants.
(b)
(a)
100
MoS2-CTAB
90
MoS2-SDS
MoS2-AOT
MoS2-PVP
MoS2-P123
MoS2-SDS
MoS2-CTAB
MoS2-AOT
80
70
60
MoS2-P123
MoS2-PVP
S-PEG
MoS2-PEG
0
100 200 300 400 500 600 700 800
Temperature (oC)
100 200 300 400 500 600 700 800
Temperature (oC)
Fig. 2. TG (a) and DSC (b) curves of MoS2 samples synthesized with different surfactants.

Min Li et al. / Chinese Journal of Catalysis 38 (2017) 597–606
601
3.2. The morphologies of MoS2 samples synthesized with
different surfactants
(b)
(a)
The morphologies of the MoS2 samples synthesized with
different surfactants were characterized by SEM and high res‐
olution TEM (HRTEM). From Fig. 4 it can be deduced that both
MoS2‐PEG and MoS2‐PVP are spherical particles. The mono‐
dispersed spherical particles in MoS2‐PEG have a diameter of
about 250 nm (Fig. 4(a)). However, the aggregated spherical
particles in MoS2‐PVP have a diameter of 200–450 nm (Fig.
4(b)). Both MoS2‐P123 and MoS2‐AOT are composed of
bulk‐like particles that show obvious signs of aggregation.
These particles are 1–3 µm in size in MoS2‐P123 (Fig. 4(d)) and
1–2.2 µm in size in MoS2‐AOT (Fig. 4(c)). Highly aggregated
MoS2‐SDS and MoS2‐CTAB display flower‐like particles with
diameters of 0.8–1.5 µm (Fig. 4(c)) and 1–3 µm (Fig. 4(f)), re‐
spectively. Therefore, MoS2‐PEG has a good morphology con‐
sisting of mono‐dispersed spheres and relatively small‐sized
particles.
(c)
(e)
(d)
(f)
The morphologies and structures of the MoS2 samples were
further characterized by HRTEM, as shown in Fig. 5. In Fig.
5(a)–(c) the loosely arranged and disordered MoS2 nano‐sheets
with slab lengths shorter than 15 nm and 4–6 stacked layers
can be observed in MoS2‐PEG, MoS2‐PVP, and MoS2‐AOT. In Fig.
5(d)–(f) it can be observed that the compacted and ordered
MoS2 nano‐sheets in MoS2‐P123, MoS2‐AOT, and MoS2‐P123
exhibit slabs longer than 20 nm with more than 8 stacked lay‐
ers. From the HRTEM images of all the MoS2 samples, the de‐
tected interlayer distances of the MoS2 nano‐sheets are in the
range of 0.94–1.02 nm or 0.49–0.57 nm; these distances coin‐
cide with the calculated values from the XRD patterns. The
MoS2 samples synthesized with the different surfactants show
obvious differences in their morphologies and structures in‐
cluding the interlayer distances, slab lengths, and the number
of stacked layer. Among these samples, MoS2‐PEG, which has
Fig. 5. HRTEM images of MoS2 samples synthesized with different sur‐
factants. (a) MoS2‐PEG; (b) MoS2‐PVP; (c) MoS2‐AOT; (d) MoS2‐P123; (e)
MoS2‐SDS; (f) MoS2‐CTAB.
the smallest diameter of 250 nm, exhibits a mono‐dispersed
spherical morphology, and the MoS2 nano‐sheets in MoS2‐PEG
exhibit enlarged interlayer distances, shorter slabs, and fewer
stacked layers.
3.3. The formation of MoS2 samples in hydrothermal processes
Spherical, bulk‐like and flower‐like MoS2 samples assem‐
bled from MoS2 nano‐sheets were synthesized using surfac‐
tant‐assisted hydrothermal processes. The possible growth
mechanisms of MoS2 samples in surfactant‐assisted hydro‐
(b)
(a)
(c)
(f)
(e)
(d)
500 nm
Fig. 4. SEM images of MoS2 samples synthesized with different surfactants. (a) MoS2‐PEG; (b) MoS2‐PVP; (c) MoS2‐AOT; (d) MoS2‐P123; (e) MoS2‐SDS;
(f) MoS2‐CTAB.

602
Min Li et al. / Chinese Journal of Catalysis 38 (2017) 597–606
Ⅳ
Ⅲ
Ⅰ
Ⅱ
PEG/PVP
S‐PEG/S‐PVP
6-
Mo7O24
N2H4H2O
Crystallization
v
CS(NH2)2
P123
AOT
S‐AOT/S‐P123
+
NH4
4-
MoS4
CTAB
MoS2
SDS
S‐SDS/S‐CTAB
nano-sheets
Fig. 6. The formation mechanisms of MoS2 samples in surfactant‐assisted hydrothermal synthesis.
thermal processes follow a soft‐template mechanism, as shown
in Fig. 6. First, surfactant molecules self‐assemble into micelles
from which the hydrophilic groups are projected outward and
in which the hydrophobic alkyl backbones face toward the in‐
terior; these micelles act as soft templates, as shown in step (Ι).
It has been reported that the self‐assembly behaviors of sur‐
factant micelles depend on balancing the hydrophobic attrac‐
tion between their hydrophobic tails and the electrostatic re‐
pulsion or steric repulsions between their hydrophilic head
groups; these issues play a key role in the formation of ther‐
modynamically stable morphologies (shapes and sizes) for
surfactant micelles [28]. In this work, the surfactants PEG, PVP,
SDS, and CTAB all self‐assemble into spherical micelles because
of the strong hydrophobic attraction between the straight alkyl
tails. In addition, the diameter of the SDS and CTAB micelles are
larger than those of PEG and PVP micelles owing to the greater
steric repulsion between their hydrophilic groups. However,
P123 and AOT surfactants give rise to lamellar micelles. P123,
as a common triblock copolymer, has a central hydrophobic
chain and two hydrophilic chains and is facile to assemble into
“lamellar” micelles because it is weakly hydrophobic [29]. It is
easy for AOT to form lamellar micelles owing to the steric hin‐
drance of its wedge‐like structures [30]. Second, molybdate
ions (Mo7O246−) are easily adsorbed on the outer surfaces of
these micelles via electrostatic interactions, as shown in step
(II). For PEG, PVP, and P123 micelles are easily protonated
because PEG, PVP, and P123 are non‐ionic surfactants. The
adsorption of Mo7O246− on protonated PEG, PVP, and P123 mi‐
celles is facile owing to electrostatic interactions. With regard
to AOT and SDS micelles, AOT and SDS are ionic surfactants and
so their micelles carry negative charges: the negatively charged
SC(NH2)2 + 2H2O = CO2↑ + 2NH3↑ + H2S↑
(1)
(NH4)6Mo7O24 + 28H2S + 8NH3 = 7(NH4)2MoS4 + 24H2O (2)
2−
MoS4 + 2N2H4 = MoS2 + (NH4)2S↑ + N2 + S2− (3)
Third, MoS42− is reduced by N2H4 into MoS2 as shown in Eq.
(3). MoS2 nano‐sheets are generally obtained because of the
material's inherent 2D crystalline structure, as shown in step
(III). Then, as the hydrothermal crystallization proceeds, the
growth and assembly of the MoS2 nano‐sheets takes place, as
shown in step (IV). The growth of the MoS2 nano‐sheets is in‐
hibited by the surfactant molecules. The slab length and the
number of stacked layers are closely correlated with the steric
hindrance of the surfactant molecules, which is determined by
the interactions and the electrostatic interaction distance be‐
tween the MoS2 nano‐sheets and the surfactant molecules. This
is in agreement with research reported by Wang et al. [31],
which details the formation of MoS2/graphene composites with
the assistance of cationic surfactants. According to their report,
MoS2 nano‐sheets with short slab lengths and few stacked lay‐
ers were obtained when using CTAB because of the strong in‐
teractions and short interaction distances between MoS2 and
CTAB. Here, when it comes to MoS2‐PEG and MoS2‐PVP, MoS2
nano‐sheets with short slabs (15 nm) and few stacked layers
(4–6 layers) were obtained owing to the strong interactions
and short electrostatic interaction distances between the MoS2
nano‐sheets and PEG or PVP. For MoS2‐SDS and MoS2‐CATB,
MoS2 nano‐sheets with long slabs (> 20 nm) and many more
stacking layers (> 8 layers) were obtained because of the weak
interactions and long electrostatic interaction distances be‐
tween the MoS2 nano‐sheets and SDS or CTAB. Meanwhile, the
assembly of these MoS2 nano‐sheets was templated on these
micelles, thus resulting in the formation of MoS2 samples with
different morphologies. In addition, the nano‐sheets of the
+
micelles thus attract the NH4 ions in the precursor solution.
6−
+
With the assistance of the NH4+ ions, the adsorption of Mo7O24
samples exhibited a structure with NH4 intercalated in MoS2.
+
groups on AOT and SDS micelles can overcome the charge in‐
The intercalation of NH4 ions from the precursors into the
6−
compatibility between Mo7O24 and the negatively charged
structures of the MoS2 nano‐sheets was promoted by the rela‐
tively high temperature and pressure used during the hydro‐
thermal process, leading to the formation of MoS2 nano‐sheets
with obvious lattice expansions, which agrees with the results
reported by Xie et al. [19]. Hence, MoS2 samples with different
morphologies and structures can be achieved by adjusting the
surfactants.
AOT and SDS molecules. As CTAB is a cationic surfactant, CTAB
micelles carry positive charges. Hence, the adsorption of
6−
Mo7O24 on CTAB micelles is easy because of favorable elec‐
6−
trostatic interactions. Then, Mo7O24 is sulfurized in situ into
MoS42− by H2S, which is produced by the hydrolysis of (NH2)2CS
according to Eqs. (1) and (2).

Min Li et al. / Chinese Journal of Catalysis 38 (2017) 597–606
603
To further confirm the growth mechanism, a calcination at
400 °C in H2 for 4 h was performed to remove the templates
from the obtained MoS2 samples. MoS2‐PEG was used as a rep‐
resentative example. MoS2‐PEG after the calcination is referred
to as MoS2‐PEG‐C. The four peaks in the XRD patterns of
MoS2‐PEG‐C (Fig. 7(a)) at around 14.0°, 33.4°, 39.7°, and 59.2°
can be ascribed to the (002), (100), (103), and (110) peaks of
hexagonal 2H‐MoS2, respectively. The TG curve of MoS2‐PEG‐C
shows hardly any weight loss in the 20–800 °C range, revealing
the absence of NH4+ and surfactant molecules. In the material's
DSC curve, a broad exothermic peak centered around 400 °C is
visible, which corresponds to the crystallization of 2H‐MoS2
[32]. We propose that during the calcination process the struc‐
tural transformation from NH4+ intercalated MoS2 into crystal‐
lized 2H‐MoS2 took place, with the removal of NH4+ and surfac‐
tant molecules. The SEM image (Fig. 7(c)) of MoS2‐PEG‐C shows
that the particles have a good spherical morphology with a
diameter of 100–200 nm and that they show no obvious signs
of aggregation. The HRTEM image (Fig. 7(d)) of MoS2‐PEG‐C
shows MoS2 nano‐sheets with slab lengths much longer than 20
nm and up to 10 stacked layers. An interlayer spacing of 0.62
nm was detected in MoS2‐PEG‐C, which is in agreement with
the value calculated from its XRD pattern. The comparison be‐
tween MoS2‐PEG and MoS2‐PEG‐C with regard to the morphol‐
ogy revealed that after calcination, the good spherical shape of
the MoS2 particles was retained; however, the diameter of the
2HN
AN
(cis+trans)-8HN
4HN
14HN
sym-8HN
Scheme 1. The pathway for anthracene hydrogenation using the MoS2
samples as catalysts.
+
removal of NH4 . The results confirm the role of the surfactant
molecules as a template during the growth process of MoS2
samples with different morphologies and structures.
3.4. The catalytic performances of MoS2 samples in anthracene
hydrogenation
The catalytic performance of MoS2 samples with different
morphologies and structures was evaluated, using the anthra‐
cene hydrogenation in a slurry‐bed batch micro‐reactor. In
accordance with the GC‐MS results, the pathway for the an‐
thracene hydrogenation using the MoS2 samples as catalysts is
shown in Scheme 1. The stepwise reaction pathway of the an‐
thracene hydrogenation is the same as in our previous research
using MoS2 nano‐sheets as catalysts and the same as that re‐
ported by Pinilla et al. [22,33,34]. The hydrogenation of AN to
the primary product 2HN is fast, and proceeds to a nearly com‐
plete conversion. The hydrogenation of 2HN proceeds via the
intermediate product 4HN, and subsequently produces 8HN
(cis and trans, symmetric). Then, 8HN was hydrogenated into
14HN. The high catalytic activity may result from the high se‐
lectivity of the highly hydrogenated products (8HN and 14HN).
The selectivity of the hydrogenation products is shown in
Fig. 8(a). It can be observed that the highly hydrogenated
product 14HN could only be detected when MoS2‐PEG was
used as a catalyst. The selectivity of the highly hydrogenated
product 8HN for MoS2 catalysts decreased in the following or‐
der: MoS2‐PEG > MoS2‐PVP > MoS2‐P123 > MoS2‐AOT >
MoS2‐SDS > MoS2‐CATB. The highest 8HN selectivity achieved
was with MoS2‐PEG (52.8%), and the lowest 8HN selectivity
was achieved with the MoS2‐CATB catalyst and was 19.5%.
However, the selectivity to 4HN and 2HN decreased in reverse
order. MoS2‐PEG exhibited the lowest selectivity toward 4HN
and 2HN, while the MoS2‐CATB catalyst exhibited the highest
selectivity to 4HN and 2HN. The AN conversion and hydro‐
genation ratio of AN have been used to evaluate the catalytic
activities of MoS2 catalysts [33,34]. The AN conversions and
hydrogenation ratios of AN for our samples are shown in Fig.
8(b). The AN conversions for different MoS2 catalysts were all
above 92.0%. Further, the hydrogenation ratio decreased in the
following order: MoS2‐PEG > MoS2‐PVP > MoS2‐P123 >
MoS2‐AOT > MoS2‐SDS > MoS2‐CATB. The highest hydrogena‐
tion ratio of 44.04% was achieved with MoS2‐PEG, and the
lowest hydrogenation ratio of 29.55% was achieved with
MoS2‐CATB. MoS2‐PEG had a higher selectivity to the highly
hydrogenated products 8HN and 14HN and a lower selectivity
+
MoS2‐PEG‐C spheres decreased. The removal of the NH4 and
the surfactant molecules did not influence the spherical shape
of the MoS2 particles, but resulted in them shrinking. Mean‐
while, the slab length and number of stacked layers of the MoS2
nano‐sheets increased; however, the interlayer spacing of the
MoS2 nano‐sheets decreased, which may also result from the
(b)
(a)
2
100
1
(002)
95
90
85
80
(100)
(103)
0
(110)
-1
-2
0
200
400
600
10 20 30 40 50 60 70
Temperature (oC)
2(o )
(c)
(d)
Fig. 7. XRD pattern (a), TG/DSC profiles (b), SEM (c) and HRTEM imag‐
es (d) of MoS2‐PEG‐C.

604
Min Li et al. / Chinese Journal of Catalysis 38 (2017) 597–606
70
60
50
40
30
20
10
0
100
(b)
(a)
2HN
4HN
8HN
14HN
45
40
35
30
80
60
40
20
0
MoS2-PEG MoS2-PVP MoS2-AOT MoS2-P123 MoS2-SDS MoS2-CTAB
MoS2-PEG MoS2-PVP MoS2-AOT MoS2-P123 MoS2-SDS MoS2-CTAB
Fig. 8. (a) The selectivity of AN derivatives; (b) the conversion of AN and hydrogenation ratio of anthracene for the MoS2 catalysts prepared with
different surfactants. Reaction conditions: anthracene 3.0 g, tridecane 30.0 g, catalyst 0.15 g, 400 °C, 4 h, an initial pressure 80 bar.
to 2HN and 4HN, and exhibited the highest catalytic activity.
The increase in the hydrogenation ratio of our samples resulted
in a concurrent increase of the 8HN selectivity and decreases of
the selectivity to 4HN and 2HN. It can be deduced that the high
selectivity to the highly hydrogenated products 8HN and 14HN
is at the expense of the selectivity to 4HN and 2HN, which re‐
sults in the pathway of anthracene hydrogenation that is pre‐
sented in Scheme 1.
catalytic activities [35]. Thus, the surface areas may not dictate
the catalytic hydrogenation activity. Moreover, MoS2‐SDS,
which has longer slab lengths and more stacked layers, exposed
few active sites. Increased aggregation of these particles was
observed (Fig. 5(e)). Aggregation inhibits the exposure of active
MoS2 edges and decreases the dispersion of the catalyst.
Therefore, MoS2‐SDS, which has a large surface area but only a
few exposed active MoS2 edges, exhibited a low catalytic hy‐
drogenation activity. It can be deduced that the catalytic activi‐
ties of these MoS2 catalysts are mainly correlated with their
morphological and structural features.
Both the experimental results and theoretical calculations
reveal that MoS2 nano‐sheets with short slab lengths and few
stacked layers exhibit a large number of exposed active edges
[12,36,37]. As the slab lengths and number of stacked layers in
the MoS2 nano‐sheets increases in the MoS2 catalysts, the
number of exposed active edges decreases. In addition, mono‐
dispersed spherical MoS2 particles with smaller particle sizes
could be highly dispersed in a slurry‐bed reactor, which facili‐
tated the exposure of the active edges. However, aggregated
particles showed poor dispersion, which impeded the exposure
of partially active edges. Furthermore, a mono‐dispersed
spherical morphology of the MoS2 catalysts is helpful to further
expose the active edges and improve the dispersion of the cat‐
alyst in the slurry‐bed reactor. The excellent hydrogenation
activity of MoS2‐PEG may be ascribed to its highly exposed ac‐
tive edges. Therefore, it can be concluded that the catalytic ac‐
tivities of MoS2 catalysts for anthracene hydrogenation mainly
depend on the number of exposed active edges.
Summarizing the above results, it was found that the highest
activity for AN hydrogenation was obtained with the MoS2‐PEG
catalyst, which was composed of mono‐dispersed spherical
particles with smaller particle sizes. Furthermore, the MoS2
nano‐sheets in the MoS2‐PEG catalyst had shorter slab lengths
and fewer stacked layers (Table 3). Conversely, the lowest cat‐
alytic activity was obtained with the MoS2‐CATB catalyst, which
was composed of aggregated micro‐scaled flower‐like particles
with MoS2 nano‐sheets with longer slab lengths and more
stacked layers (Table 3). With the increase of the particle size,
aggregation, slab length, and number of stacked layers in the
MoS2 catalysts, the catalytic activity decreased. In addition, the
physical properties of the MoS2 catalysts, such as their surface
areas (ABET) and water contact angles were determined and are
listed in Table 3. The results reveal that ABET and the contact
angles had no direct relationship with the catalytic hydrogena‐
tion activities of these catalysts. It is noteworthy, however, that
MoS2‐SDBS possesses the largest surface area. For MoS2 mate‐
rials, the surface area may depend on the basal plane (001),
which may be much larger than the edge plane (100). The basal
plane possesses excellent lubricating properties and photo‐
Table 3
Surface areas, water contact angles, and the shape and diameter of the MoS2 samples synthesized with different surfactants along with the number of
stacked layers and slab lengths of the MoS2 nano‐sheets, as well as the hydrogenation ratio of AN when the MoS2 samples were used as catalysts.
Sample
Shape
Diameter (μm) Stacking layers Slab length (nm) ABET (m2/g) Contact angle (°) Hydrogenation ratio (%)
MoS2‐PEG mono‐dispersed spherical
0.25
0.20–0.45
1.0–3.0
1.0–2.2
0.8–1.5
1.0–3.0
4–6
4–6
4–6
>8
>8
>8
<15
<15
<15
>20
>20
>20
17.13
39.29
27.36
18.51
126.98
11.71
77.46
60.40
43.75
33.82
57.20
59.14
44.04
41.51
40.19
39.37
32.13
29.55
MoS2‐PVP
MoS2‐P123
MoS2‐AOT
MoS2‐SDS
MoS2‐CTAB
spherical
bulk‐like
bulk‐like
flower‐like
flower‐like

Min Li et al. / Chinese Journal of Catalysis 38 (2017) 597–606
605
458–472.
4. Conclusions
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We have successfully and controllably synthesized spheri‐
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MoS2 nano‐sheets with different structures (such as with dif‐
ferent slab lengths and different number of stacked layers)
using a facile surfactant‐assisted hydrothermal approach. We
found that the morphologies and structures of the MoS2 sam‐
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we proposed a possible formation mechanism. The catalytic
activities of MoS2 catalysts for anthracene hydrogenation re‐
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which was ascribed to the high exposure of its active edges,
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Graphical Abstract
Chin. J. Catal., 2017, 38: 597–606 doi: 10.1016/S1872‐2067(17)62779‐7
Surfactant‐assisted hydrothermally synthesized MoS2 samples with
controllable morphologies and structures for anthracene
hydrogenation
100
80
60
40
20
0
Min Li, Donge Wang, Jiahe Li, Zhendong Pan, Huaijun Ma, Yuxia Jiang,
Wei Qu, Lin Wang, Zhijian Tian *, Anhui Lu
Dalian University of Technology;
Dalian Institute of Chemical Physics, Chinese Academy of Sciences;
University of Chinese Academy of Sciences
MoS2 particles with controllable morphologies and structures were syn‐
thesized with various surfactants. Mono‐dispersed spherical MoS2 cata‐
lysts exhibited higher catalytic activities for anthracene hydrogenation,
which can be ascribed to its highly exposed active edges.
nanospheres
bulk-like
flower-like

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