Preparation of highly active unsupported Ni–Si–Mo catalyst for the deep hydrogenation of aromatics

Article abstract of DOI:10.1016/j.jallcom.2020.155076

A mesoporous nickel-silicon-molybdenum composite oxide with the phase of ammonium nickel (or silicon) molybdate was synthesized by chemical precipitation and unsupported nickel-silicon-molybdenum sulfide catalysts with various Ni/Si ratios were obtained by sulfidation of the oxide precursors. The oxide precursors and unsupported sulfide catalysts were characterized by XRD, N₂ adsorption-desorption, SEM, TPR, and HRTEM. The unsupported nickel-silicon-molybdenum sulfide catalysts were tested in the hydrogenation of naphthalene. It was found that the introduction of Si could increase the specific surface area and improve the pore structure of precursors, and reduce the reduction temperature of Mo species. The results of naphthalene hydrogenation showed that the introduction of Si could significantly improve the hydrogenation activity of the catalysts, especially the Ni9.5Si0.5Mo10 catalyst exhibited the highest aromatic hydrogenation activity at low temperature. Interestingly, it is found that the tetralin selectivity is 100% in the low temperature range (220–260 °C) over Si10Mo10 catalyst, which might be attractive in the production of tetralin and other industrial application.

Full text of DOI:10.1016/j.jallcom.2020.155076

Journal Pre-proof
Preparation of highly active unsupported Ni–Si–Mo catalyst for the deep
hydrogenation of aromatics
Changlong Yin, Tongtong Wu, Chengwu Dong, Fan Li, Dong Liu, Chenguang Liu
PII:
S0925-8388(20)31439-0
DOI:
https://doi.org/10.1016/j.jallcom.2020.155076
JALCOM 155076
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 24 November 2019
Revised Date: 16 March 2020
Accepted Date: 5 April 2020
Please cite this article as: C. Yin, T. Wu, C. Dong, F. Li, D. Liu, C. Liu, Preparation of highly active
unsupported Ni–Si–Mo catalyst for the deep hydrogenation of aromatics, Journal of Alloys and
Compounds (2020), doi: https://doi.org/10.1016/j.jallcom.2020.155076.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition
of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of
record. This version will undergo additional copyediting, typesetting and review before it is published
in its final form, but we are providing this version to give early visibility of the article. Please note that,
during the production process, errors may be discovered which could affect the content, and all legal
disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier B.V.

Credit Author Statement
Authors' individual contributions
Changlong Yin: Conceptualization, Data curation, Investigation, Methodology,
Writing-Original Draft.
Tongtong Wu: Data curation, Formal analysis, Validation, Visualization,
Writing-original draft.
Chengwu Dong: Formal analysis, Validation, Visualization.
Fan Li: Formal analysis, Validation, Visualization.
Dong Liu: Writing-Review & Editing.
Chenguang Liu: Writing-Review & Editing.

Preparation of highly active unsupported Ni-Si-Mo catalyst for the
deep hydrogenation of aromatics
Changlong Yin*, Tongtong Wu, Chengwu Dong, Fan Li, Dong Liu, Chenguang Liu
(State Key Laboratory of Heavy Oil Processing and Key Laboratory of Catalysis of CNPC, China University of
Petroleum, Qingdao 266580, P. R. China)
Corresponding Author: yincl@upc.edu.cn (Changlong Yin); TEL: +86-532-86984629
ABSTRACT A mesoporous nickel-silicon-molybdenum composite oxide with the
phase of ammonium nickel (or silicon) molybdate was synthesized by chemical
precipitation and unsupported nickel-silicon-molybdenum sulfide catalysts with
various Ni/Si ratios were obtained by sulfidation of the oxide precursors. The oxide
precursors and unsupported sulfide catalysts were characterized by XRD, N2
adsorption-desorption,
SEM,
TPR,
and
HRTEM.
The
unsupported
nickel-silicon-molybdenum sulfide catalysts were tested in the hydrogenation of
naphthalene. It was found that the introduction of Si could increase the specific
surface area and improve the pore structure of precursors, and reduce the reduction
temperature of Mo species. The results of naphthalene hydrogenation showed that the
introduction of Si could significantly improve the hydrogenation activity of the
catalysts, especially the Ni9.5Si0.5Mo10 catalyst exhibited the highest aromatic
hydrogenation activity at low temperature. Interestingly, it is found that the tetralin
selectivity is 100 % in the low temperature range (220-260 °C) over Si10Mo10
catalyst, which might be attractive in the production of tetralin and other industrial
application.

Keywords
nickel-silicon-molybdenum
composite
oxide;
unsupported
nickel-silicon-molybdenum sulfide catalysts; naphthalene; hydrogenation activity
1. Introduction
High content of aromatics in distillates such as diesel, gasoline and jet fuel will reduce
the quality of fuel [1] and produce harmful exhaust gases such as PM2.5 and NOx that
pollute the environment [2-4]. Meanwhile, these aromatics and the resulting emissions
are potentially dangerous and carcinogenic [5]. Therefore, increasingly stringent
environmental regulations and fuel codes require the reduction of aromatics in fuels
[6]. It can be seen that deep dearomatization has become an important issue in the
production of clean fuels, and it is imperative to develop the production technology of
ultra-clean fuel for efficient dearomatization.
Traditional industrial hydrotreating processes can simultaneously remove S and N by
hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions. The current
hydrotreating process is also applicable to hydrodearomatization (HDA). FCC diesel
contains a large number of aromatics, most of which contain bicyclic aromatics of
more than 50%. However, aromatics are the root cause of poor combustion
performance and high density of FCC diesel oil [7-9]. FCC diesel has a high content
of monocyclic aromatics through the conventional hydrofining method, which is
mainly due to the relative ease of partial hydrogenation and saturation reactions of the
polycyclic aromatics. However, the hydrogenation of monocyclic aromatics can be
completely saturated by catalysts with high hydrogenation activity. High temperature
is needed to catalyze the hydrogenation of aromatics if we use the traditional

supported metal sulfide system, but kinetically, the high temperature is not conducive
to the hydrogenation of aromatics. The unsupported catalyst has no support, which
greatly increases the content of active components and makes the catalyst have higher
catalytic activity. Moreover, the unsupported catalyst has a strong catalytic
hydrogenation activity also depends on its high resistance to S, N poisoning [10, 11].
However, the unsupported catalyst has problems such as small specific surface area
and small pore size, which is not suitable for catalyzing the hydrogenation reaction of
macromolecular polycyclic aromatics. Therefore, further research is needed on how to
obtain a highly active unsupported catalyst with a high specific surface area and good
pore structure.
Pang et al [12] prepared Mo2C/AC transition metal carbide catalyst with different load
by microwave radiation method using activated carbon (AC) as the carrier. The
catalyst 20 wt.%-Mo2C/AC can make the selectivity of tetralin up to 100 % and the
conversion rate of naphthalene up to 95 %. The activated carbon carrier is very
important for the catalyst to obtain high activity and good stability. Liang et al [13]
successfully synthesized CoSi/SiO2 catalyst in a fluidized bed using Co(SiCl3)(Co)4 as
the precursor by the MOCVD method, which has high aromatic hydrogenation
activity and selectivity of 100% for the hydrogenation of naphthalene into tetralin. In
the relatively short contact time between naphthalene and catalyst (3.76 min), the
reaction of further hydrogenation of tetralin to decalin did not occur, which indicates
that the hydrogenation of tetralin is the rate control step of catalytic hydrogenation of
naphthalene. Under the same reaction conditions, the naphthalene hydrogenation

reaction catalyzed by the contrast catalyst Co/SiO2 did not get any product, which
means that the activity of CoSi/SiO2 catalyst is higher than that of Co/SiO2 catalyst.
The results show that the introduction of Si into transition metals can produce novel
catalysts of aromatic hydrogenation, which are expected to be used in petroleum
processing. Thermodynamic calculation shows that the transition metal silicides can
tolerate higher H2S concentration than the corresponding carbides and nitrides [14],
which means that the introduction of Si in the transition metal catalyst is more stable
and sulfur-tolerant in the reaction of sulfur-containing compounds.
Therefore, unsupported NiSiMo catalysts with different Ni/Si molar ratios were
synthesized by chemical precipitation method. The effects of the addition of Si on the
physicochemical properties of unsupported NiMo catalysts and the hydrogenation
performance of aromatics were investigated. Since the proportion of bicyclic
aromatics in FCC diesel is the highest, the hydrogenation saturation of bicyclic
aromatics is mainly studied. In scientific research, naphthalene is generally used as a
model compound to study the hydrogenation of bicyclic aromatics [15-17]. Therefore,
the hydrogenation activity evaluation of the unsupported catalyst prepared in this
paper was carried out by using naphthalene as a model compound.
2. Experimental
2.1. Preparation of unsupported NiSiMo catalyst
A solution of 0.1 mol ammonium molybdate, a certain amount of nickel nitrate and
tetraethyl silicate was dissolved in a 500 mL three-necked, round-bottomed flask. The
solution was heated to 90 °C. Then ammonia water was added in drops until the

solution pH was about 12. The green precipitate (the precursor of Si10Mo10 was
white precipitate) was produced by heating at a constant temperature for 12 h. The
precipitate was isolated by vacuum filtration and dried for 12 h at 100 °C to obtain the
powder catalyst precursor. According to the different molar ratios of Ni/Si, the
prepared catalysts were named NixSiyMo10, where x and y were the molar ratios of
Ni and Si added in the preparation, and the molar ratio of (Ni+Si)/Mo was always
maintained at 1:1.
2.2. Characterization of the catalyst
2.2.1 X-ray diffraction (XRD)
The crystal phase of the catalysts was measured by X-ray diffraction (XRD) on an
X’Pert Pro MPD instrument with Cu Kα. The scanning angle was 5-75o, the scanning
speed was 5o min-1, and the step speed was 0.0001°. The detector was a scintillation
counter with a tube pressure of 45 kV and a current of 40 mA. Before the
measurement, the sample was ground into powder and pressed into a smooth sheet.
2.2.2 Low temperature N2 adsorption-desorption (BET)
The pore structure properties of the samples were determined by using the ASAP
2010 automatic adsorption apparatus (Micromeritics, USA). The samples were
processed at 300 °C in vacuum before the measurement, and the N2
adsorption-desorption temperature was -196 °C. The specific surface area was
obtained by the BET method, the pore volume was calculated by the BJH method, and
the average pore size was calculated by the desorption curve. All samples were
calcined at 300 °C for 4 h for pretreatment before measuring the pore structure

properties.
2.2.3 Scanning electron microscopy (SEM)
The morphology analysis of the samples was carried out by S-4800 cold field
emission scanning electron microscope (Hitachi Company, Japan). The X650
scanning electron microscope was vacuumized for 25-30 min, and the sample was put
into the sample chamber after the vacuum degree of the instrument reached above
1×10-4 Pa, the operating voltage was 5.0 kV and the working distance was 8.2 mm,
and then the surface structure of the sample was observed.
2.2.4 High-resolution transmission electron microscope (HRTEM)
The morphology of the sulfided catalysts was observed by a JEM-2100UHR
high-resolution transmission electron microscope (JEOL Company, Japan) operated at
200 kV. The sulfided catalysts were stored and ground in ethanol to avoid oxidation
due to exposure to air. After grinding, the sample was thoroughly dispersed in ethanol
by ultrasound for 30 min, and then a small amount of upper suspension was taken for
observation.
2.2.5 Temperature programmed reduction (TPR)
The reduction performance of the samples was performed on a CHEMBET-3000 TPR
Analyzer. The sample loading quantity was 0.05 g, and the size of the sample was
20-40 mesh. The reduced gas was H2/Ar with a volume fraction of 10 % and a gas
flow rate of 80 mL min-1. During the heating process, the hydrogen consumption of
the sample was recorded with a thermal conductivity detector (TCD). The rate of
heating was 10 min-1 and the temperature was raised to 900 °C.

2.3. Catalyst activity evaluation
The aromatic hydrogenation performance of unsupported catalysts was evaluated by a
10 mL fixed bed high pressure hydrogenation micro-reactor. 5 mL of 20-40 mesh
catalyst particles were packed into the middle of the reaction tube, and the upper and
lower ends of the reaction tube were filled with quartz sand of the same particle size.
Before the evaluation of the aromatic hydrogenation activity of the unsupported
catalyst was started, the oxide precursor was in situ presulfided using a 3.0 wt%
CS2/petroleum ether solution at 330 °C for 8 h at a H2 pressure of 3 MPa, and a liquid
hourly space velocity (LHSV) of 2 h-1. The aromatic hydrogenation activity of the
catalyst was evaluated using an 8.0 wt% naphthalene/petroleum ether solution as the
feed oil. The reaction conditions were: reaction temperatures of 220°, 240, 260, 280,
300 and 320 °C, a reaction pressure 3 MPa, a liquid hourly space velocity of 2 h-1, a
H2/oil ratio of 400:1. The product distribution of naphthalene hydrogenation was
analyzed by a GC-7820 gas chromatograph.
3. Results and discussion
3.1. Characterization of oxidic NiSiMo precursor
Figure 1 shows the XRD characterization results of the NiSiMo precursors with
different Ni/Si molar ratios. The characteristic diffraction peaks of ammonium nickel
molybdate crystals are found in the samples Ni10Mo10, Ni9.5Si0.5Mo10,
Ni8Si2Mo10 and Ni5Si5Mo10 ((NH4)HNi2(OH)2(MoO4)2, JCPDS card No.50-1414)
[18]. However, the diffraction peaks are not found in the sample Si10Mo10, which is
almost in an amorphous or microcrystalline state. The introduction of Si will change

the crystal structure of ammonium nickel molybdate of the original NiMo precursor.
With the increase of the amount of Si introduced, the characteristic diffraction peak
intensity of the ammonium nickel molybdate crystal phase gradually weakens until it
disappears into an amorphous or microcrystalline structure. Besides, the diffraction
peaks of Si species are not detected in the XRD patterns, which may be caused by the
high dispersion of Si species in the precursors.
(Figure 1.)
The N2 adsorption-desorption isotherms and pore size distributions of the NiSiMo
precursors are shown in Figure 2. It can be seen from Figure 2(a) that the
low-temperature N2 adsorption-desorption curves of the NiSiMo precursors with
different Ni/Si molar ratios are all Type IV [19], indicating that the NiSiMo precursors
are mesoporous materials. From the pore size distributions of the NiSiMo precursors
(Figure 2b), it can be found that the pore size distribution of the Si10Mo10 precursor
is wider than that of other NiSiMo precursors. The pore size of the Si10Mo10
precursor is distributed from less than 2 nm to 70 nm. The pore size distributions of
the Ni10Mo10, Ni9.5Si0.5Mo10, Ni8Si2Mo10 and Ni5Si5Mo10 precursors are
narrow, and the most probable pore sizes are 3.74, 3.58, 3.91 and 3.90 nm
respectively.
(Figure 2.)
The pore properties of the NiSiMo precursors are summarized in Table 1. The pore
structure is an important factor affecting the catalytic activity. The higher specific
surface area is beneficial to the uniform distribution of hydrogenation active sites on

the surface of the catalyst, which is favorable for the continuous hydrogenation
reactions. Clearly, as the amount of Si introduced increases, the specific surface area
of the NiSiMo precursors also increases. Compared with the Ni10Mo10 precursor, the
pore size of the Ni8Si2Mo10 precursor decreases, and the pore sizes of the
Ni9Si0.5Mo10, Ni5Si5Mo10, and Si10Mo10 precursors increase.
(Table 1.)
Shown in Figure 3 are the SEM images of the NiSiMo precursors. The Ni10Mo10
precursor contains many irregular bulk structures of 200-1000 nm, on which some
spherical particles of about 30 nm adhere. The Ni9.5Si0.5Mo10 precursor also has a
bulk structure similar to the Ni10Mo10 precursor, but the size of about 300-800 nm is
smaller than the Ni10Mo10 precursor, and more small particles of less than 50 nm are
attached to the bulk structure. In addition to bulk crystals, the Ni8Si2Mo10 precursor
also have flower-like structures, which are formed by the self-assembly of
nano-spherical structures. The Ni5Si5Mo10 precursor is similar to the Ni8Si2Mo10
precursor, it can be clearly seen that the large bulk structure formed by the
accumulation of nanoparticles, and the nano-spherical structures adhere to the bulk
crystals. The morphological structure of the Si10Mo10 precursor is mainly
transformed into small particles with a relatively uniform dispersion of about 20 nm.
It can be seen that with the increase of the amount of Si introduced, the bulk structure
of the precursor gradually disappears, and the nano-spherical structure adheres to the
large bulk crystals, and then gradually transforms into the nano-spherical particles.
The results further validate the XRD characterization results, as the amount of Si

increases, the peak intensity of the ammonium nickel molybdate gradually weakens
until it transforms into an amorphous or microcrystalline structure similar to that of
the Si10Mo10 precursor.
(Figure 3.)
The TPR profiles of the NiSiMo precursors are presented in Figure 4. It is generally
considered that the Ni10Mo10 precursor shows only a large and broad reduction peak
in the range of 400-690 °C, and the other NiSiMo precursors have two reduction
peaks. According to the literature reports, the reduction peak in the range of 400 °C to
690 °C should be attributed to the reduction of Mo species with octahedral
coordination, that is, the reduction of Mo6+ to Mo4+ [20]. The reduction peak at 750 °C
to 900 °C can be ascribed to the reduction of Mo species with tetrahedral coordination,
that is, the reduction of Mo4+ to the metal Mo0 [21, 22]. The reduction temperature is
above 800 °C, which is due to the difficult reduction of the Mo species with
tetrahedral coordination [23, 24]. As can be seen from the figures that the introduction
of Si can reduce the reduction temperature of Mo species, and the reduction
temperature of the Mo species decreases as the amount of Si increases. It has been
proved that the introduction of Ni species could make the reduction of Mo species
easier [25]. The reduction peaks of Ni species easily overlap with those of Mo species,
making it difficult to distribute the reduction temperature of Ni species [20]. However,
there are some differences in the intensities of reduction peaks. The intensities of
reduction peaks of the Ni10Mo10, Ni9.5Si0.5Mo10, Ni8Si2Mo10, and Ni5Si5Mo10

precursors are significantly greater than those of the Si10Mo10 precursor, which may
be due to the overlap of the Ni and Mo signals in the precursors.
(Figure 4.)
3.2 Characterization of sulfided NiSiMo catalysts
The XRD patterns of the sulfided unsupported NiSiMo catalysts are displayed in
Figure 5, from which we can find that the characteristic diffraction peaks of the MoS2
and Ni3S2 crystal phases are detected in the sulfided NiSiMo catalysts [26, 27]. As the
amount of Si increases in the catalysts, the peak intensities of the MoS2 and Ni3S2
crystal phases decrease. The average crystal sizes of Ni3S2 and MoS2 in the sulfided
catalysts calculated by the Scherrer equation are shown in Table 2. It can be
concluded from the results that the average crystal size of Ni3S2 phase and MoS2
phase gradually decreases with the increase of the amount of Si introduced, which is
consistent with the XRD characterization results. Although the nickel content on the
catalysts is different, the molybdenum content on the five catalysts is basically the
same, which indicates that the introduction of Si contributes to the dispersion of active
metal components in the catalysts, thereby making the NiSiMo catalysts have good
potential for aromatic hydrogenation.
(Figure 5 and Table 2)
The N2 adsorption-desorption isotherms and pore size distributions of the sulfided
NiSiMo catalysts are depicted in Figure 6. It can be observed that the adsorption and
desorption curves of the sulfided NiSiMo catalysts are all Type IV, which is a typical
characteristic of mesoporous materials. The pore size distributions of the sulfided

Ni9.5Si0.5Mo10 and Ni8Si2Mo10 catalysts are narrow, and the pore size distributions
of the sulfided Ni10Mo10 and Ni5Si5Mo10 catalysts are relatively wide. Obviously,
the sulfided Si10Mo10 catalyst has a very wide pore size distribution.
(Figure 6.)
Table 3 shows the pore properties of the sulfided NiSiMo catalysts. Compared with
Table 1, it can be found that except for the Ni5Si5Mo10 precursor, the specific surface
area of other NiSiMo precursors increases after sulfurization. The pore volume of
Ni10Mo10 precursor increases after sulfurization, and the pore volume of other
sulfided NiSiMo catalysts is basically unchanged. Meanwhile, the pore size of the
Ni10Mo10 and Ni5Si5Mo10 precursors increases, and the pore size of other NiSiMo
precursors decreases after sulfurization.
(Table 3.)
The microstructure of the active components in the sulfided catalysts was investigated
by HRTEM. The results are shown in Figure 7. As seen by the images, the black
stripes with a spacing of about 0.6 nm are found in the HRTEM images of all catalysts,
which can be attributed to the structure of the MoS2 crystal [28, 29]. The
hydrogenation activity of the sulfided NiMo catalyst is also related to the slab length
and the stacking layer number of MoS2 [30]. The shorter slab length and the more
stacking layer number can produce higher hydrogenation activity [31-33]. The Ni3S2
fringes with a spacing of about 0.29 nm are also detected for the Ni10Mo10 and
Ni9.5Si0.5Mo10 catalysts [34]. The length of the MoS2 nanoparticle layer in the
sulfided Ni10Mo10 catalyst is longer than those of the other sulfided catalysts, and

the stacking numbers of the MoS2 layers of the Si10Mo10 catalyst are lower than
those of the other NiSiMo catalysts, which are consistent with the XRD results of the
sulfided NiSiMo catalysts. The MoS2 observed in the sulfided Ni9.5Si0.5Mo10
catalysts is more striped, indicating that the Ni9.5Si0.5Mo10 catalyst will have higher
hydrogenation activity. On the whole, the dispersion of MoS2 increases with the
increase of silicon content in the catalysts.
(Figure 7.)
3.3. Evaluation of aromatic hydrogenation activity of unsupported NiSiMo catalysts
3.3.1. Activity evaluation of the NiSiMo catalysts
The conversion rate of naphthalene hydrogenation reaction on the unsupported
NiSiMo catalysts is shown in Figure 8(a). The selectivity of decalin on the
unsupported NiSiMo catalysts is shown in Figure 8(b). In the range of 220-320 °C,
the conversion of naphthalene hydrogenation reaction increases first and then
decreases slowly, and the NiSiMo catalysts can reach a high conversion rate (>
99.8 %). The hydrogenation conversion rate of naphthalene on the NiSiMo catalysts
exceeded 98.61 % in the temperature range of 220-260 °C, which was significantly
higher than that of the Ni10Mo10 catalyst. This indicates that the introduction of Si
can significantly improve the naphthalene hydrogenation activity of the unsupported
NiMo catalyst, especially the low temperature aromatic hydrogenation performance of
the catalyst (220-260 °C). In addition, Figure 8(b) shows that the selectivity of decalin
increases with the increase of reaction temperature, indicating that the temperature is
beneficial to obtain more decalin on the sulfided NiSiMo catalyst. On the other hand,

the selectivity of decalin decreases in the order of Ni10Mo10 > Ni9.5Si0.5Mo10 >
Ni8Si2Mo10 > Ni5Si5Mo10, indicating that the selectivity of decalin gradually
decreases with the increase of the amount of Si introduced, and the introduction of Si
is not beneficial for the conversion of naphthalene into decalin. Catalysts with
different content of Si have different aromatic hydrogenation activities. The
Ni9.5Si0.5Mo10 catalyst has the highest aromatic hydrogenation activity, the
conversion of naphthalene hydrogenation is 100 % and the selectivity of decalin is
68.81 % at 260 °C, which is slightly lower than that of the Ni10Mo10 catalyst
(69.61 %). The high aromatic hydrogenation activity of the Ni9.5Si0.5Mo10 catalyst
is closely related to the physicochemical characteristics of the sulfided catalysts. The
XRD results of the sulfided catalysts showed that compared with other NiSiMo
catalysts, the sulfided Ni9.5Si0.5Mo10 catalyst had higher crystallinity MoS2 and
Ni3S2 crystal phases. HRTEM showed that there were more clutter-stacked MoS2
nanoparticles in the sulfided Ni9.5Si0.5Mo10 catalyst. These properties can make the
Ni9.5Si0.5Mo10 catalyst has higher aromatic hydrogenation activity.
(Figure 8.)
3.3.2. Activity evaluation of the Si10Mo10 catalyst
The conversion of naphthalene hydrogenation reaction, the selectivity of decalin and
the selectivity of tetralin of the Si10Mo10 catalyst are shown in Figure 9. The
conversion of naphthalene hydrogenation of the Si10Mo10 catalyst increases
remarkably with the increase of reaction temperature, the conversion rate is only 4.71 %
at 220 °C and 72.3 % at 320 °C, but it is still significantly lower than other NiSiMo

catalysts. In addition, the Si10Mo10 catalyst is not conducive to the deep
hydrogenation of naphthalene, and its decalin selectivity is almost 0. However, it has
a very high selectivity of tetralin, and the tetralin selectivity is 100 % in the low
temperature range (220-260 °C). In summary, the Si10Mo10 catalyst can be used as a
selective hydrogenation of naphthalene to produce tetralin. At 320 °C, the naphthalene
conversion rate of the Si10Mo10 catalyst is 71.97 %, and the selectivity of tetralin is
98.95 %.
(Figure 9.)
4. Conclusion
A series of NiSiMo precursors with different Ni/Si molar ratios were synthesized by
chemical precipitation method. The results showed that the introduction of Si in the
unsupported catalysts could increase the specific surface area of the catalysts, and
decrease the average grain size of MoS2 and Ni3S2. The results of naphthalene
hydrogenation evaluation showed that the introduction of Si could significantly
improve the naphthalene hydrogenation activity of the unsupported catalyst,
especially the low temperature aromatic hydrogenation performance of the catalyst
(220-260 °C). The Ni9.5Si0.5Mo10 catalyst exhibited the highest aromatic
hydrogenation activity, and the Si10Mo10 catalyst was not conducive to deep
hydrogenation of naphthalene, but it had a very high selectivity of tetralin (about
100 %).
Acknowledgements

This work was financially supported by the National Natural Science Fund of China
(Grant No. 21676301), the National key R & D program of China
(2017YFB0602500). Financial support from the program of China Scholarships
Council (No.201806455007) and Petro China Corporation Limited was also greatly
appreciated.
References
[1] T. Tang, C. Yin, L.Wang, Good sulfur tolerance of a mesoporous Beta zeolite
supported palladium catalyst in the deep hydrogenation of aromatics, Journal of
Catalysis 257 (2008) 125-133.
[2] M.A. Vicerich, M. Oportus, V.M. Benitez, Influence of Na content on the
catalytic properties of Pt-Ir/Al2O3 catalysts for selective ring opening of decalin,
Applied Catalysis A: General 480 (2014) 42-49.
[3] G.N. Yun, Y.K. Lee, Dispersion effects of Ni2P catalysts on hydrotreating of light
cycle oil, Applied Catalysis B Environmental 150 (2014) 647-655.
[4] A.C.A. Monteiro-Gezork, A. Effendi, J.M. Winterbottom, Hydrogenation of
naphthalene on NiMo- and Ni/Al2O3 catalysts: Pre-treatment and deactivation,
Catalysis Today 128 (2007) 63-73.
[5] A.Rubio-Clemente, R.A Torres-Palma, G.A. Peñuela, Removal of polycyclic
aromatic hydrocarbons in aqueous environment by chemical treatments: A review,
Science of the Total Environment 478 (2014) 201-225.
[6] A. Zhao, X. Zhang, X. Chen, Cobalt Silicide Nanoparticles in Mesoporous Silica

as Efficient Naphthalene Hydrogenation Catalysts by Chemical Vapor Deposition,
Journal of Physical Chemistry C 114 (2010) 3962-3967.
[7] L. Wang, B. Shen, F. Fang, Upgrading of light cycle oil via coupled
hydrogenation and ring-opening over NiW/Al2O3 -USY catalysts, Catalysis
Today 158 (2010) 343-347.
[8] Y. Choi, J. Lee, J. Shin, Selective hydroconversion of naphthalenes into light
alkyl-aromatic hydrocarbons, Journal of Solid State Electrochemistry 492 (2015)
140-150.
[9] C. Peng, X.C. Fang, R.H. Zeng, Commercial analysis of catalytic
hydroprocessing technologies in producing diesel and gasoline by light cycle oil,
Catalysis Today 276 (2016) 11-18.
[10] F.L. Plantenga, R. Cerfontain, S. Eijsbouts, “Nebula”: A hydroprocessing catalyst
with breakthrough activity, Studies in Surface Science & Catalysis 145 (2003)
407-410.
[11] S. Eijsbouts, S.W. Mayo, K. Fujita, Unsupported transition metal sulfide catalysts:
From fundamentals to industrial application, Applied Catalysis A: General 322
(2007) 58-66.
[12] M. Pang, C. Liu, W. Xia, Activated carbon supported molybdenum carbides as
cheap and highly efficient catalyst in the selective hydrogenation of naphthalene
to tetralin, Green Chemistry 14 (2012) 1272-1276.
[13] C. Liang, A. Zhao, X. Zhang, CoSi particles on silica support as a highly active
and selective catalyst for naphthalene hydrogenation, Chemical Communications
15 (2009) 2047-2049.

[14] R. Prins, Catalytic hydrodenitrogenation, Advances in Catalysis 46 (2001)
399-464.
[15] A.C.A. Monteiro-Gezork, R. Natividad, J.M. Winterbottom, Hydrogenation of
naphthalene on NiMo- Ni- and Ru/Al2O3 catalysts: LangmuirHinshel-wood
kinetic modelling, Catalysis Today 130 (2008) 471-485.
[16] M. Du, Z. Qin, H. Ge, Enhancement of Pd-Pt/Al2O3 catalyst performance in
naphthalene hydrogenation by mixing different molecular sieves in the support,
Fuel Processing Technology 91(2010) 1655-1661.
[17] S. Ren, P. Zhang, H. Shui, Promotion of Ni/SBA-15 catalyst for hydrogenation of
naphthalene by pretreatment with ammonia/water vapour, Catalysis
Communications 12 (2010) 132-136.
[18] D. Levin, S.L. Soled, J.Y. Ying, ChemInform Abstract: Crystal Structure of an
ammonium Nickel Molybdate prepared by Chemical Precipitation, ChemInform
35 (14) (1996) 4191-4197.
[19] S.L. Amaya, G.Alonso-Núñez, T.A.Zepeda, Effect of the divalent metal and the
activation temperature of NiMoW and CoMoW on the dibenzothiophene
hydrodesulfurization reaction, Applied Catalysis B: Environmental 148-149
(2014) 221-230.
[20] C. F. Linares, M. Fernández, Study of the Individual Reactions of
Hydrodesulphurization of Dibenzothiophene and Hydrogenation of
2-Methylnaphthalene on ZnNiMo/γ-Alumina Catalysts, Catalysis Letters 126
(3-4) (2008) 341-345.

[21] J. Zhang, Z. Xin, X. Meng, Effect of MoO3 on the heat resistant performances of
nickel based MCM-41 methanation catalysts, Fuel 116 (2014) 25-33.
[22] C. F. Linares, J. López, A. Scaffidi, Preparation of ZnNiMo/γ-alumina catalysts
from recycled Ni for hydrotreating reactions, Applied Catalysis A General 292
(2005) 113-117.
[23] S. Garg, K. Soni, T. A. Prabhu, Effect of ordered mesoporous Zr SBA-15 support
on catalytic functionalities of hydrotreating catalysts 2. Variation of molybdenum
and promoter loadings, Catalysis Today 261 (2016) 128-136.
[24] H. Liu, Y. Li, C. Yin, Preparation of highly active unsupported nickel–zinc–
molybdenum catalysts for the hydrodesulfurization of dibenzothiophene,
Applied Catalysis B Environmental 174-175 (2015) 264-276.
[25] H. Liu, Y. Li, C. Yin, One-pot synthesis of ordered mesoporous NiMo-Al2O3
catalysts for dibenzothiophene hydrodesulfurization, Applied Catalysis B:
Environmental 198 (2016) 493-507.
[26] C. Yin, Y. Wang, S. Xue, Influence of sulfidation conditions on morphology and
hydrotreating performance of unsupported Ni-Mo-W catalysts, Fuel 175 (2016)
13-19.
[27] H. Liu, C. Yin, B. Liu, Effect of Calcination Temperature of Unsupported NiMo
Catalysts on the Hydrodesulfurization of Dibenzothiophene, Energy & Fuels 28
(2014) 2429-2436.
[28] Y. Gochi, C. Ornelas, F. Paraguay, S. Fuentes, L. Alvarez, J.L. Rico, G.
AlonsoNúñez, Effect of sulfidation on Mo-W-Ni trimetallic catalysts in the HDS
of DBT, Catalysis Today 107 (2005) 531-536.

[29] C. Yin, L. Zhao, Z. Bai, H. Liu, Y. Liu, C. Liu, A novel porous ammonium nickel
molybdate as the catalyst precursor towards deep hydrodesulfurization of gas oil,
Fuel 107 (2013) 873-878
[30] X. Liu, X. Li, Z. Yan, Facile route to prepare bimodal mesoporous γ-Al2O3 as
support for highly active CoMo-based hydrodesulfurization catalyst, Applied
Catalysis B: Environmental 1211-22 (2012) 50-56.
[31] R.Y. Zhao, L.Y. Zeng, J. Liang, C.G. Liu, Interaction between Ni promoter and
Al2O3 support and its effect on the performance of NiMo/γ-Al2O3 catalyst in
hydrodesulphurization, Journal of Fuel Chemistry and Technology 44 (2016)
564-569.
[32] L. Vradman, M.V. Landau, Structure-Function Relations in Supported Ni-W
Sulfide Hydrogenation Catalysts, Catalysis Letters 77 (2001) 47-54.
[33] E.J.M. Hensen, P.J. Kooyman, Y.V.D. Meer, A.M.V.D. Kraan, V.H.J.D. Beer,
J.A.R.V. Veen, R.A.V. Santen, The Relation between Morphology and
Hydrotreating Activity for Supported MoS2 Particles, Journal of Catalysis 199
(2001) 224-235.
[34] G. Ali, B.A. Korgel, Nickel sulfide and copper sulfide nanocrystal synthesis and
polymorphism, Langmuir 21 (2005) 9451-9456.

Table 1. Pore properties of the NiSiMo precursors
Table 2. Average crystal sizes of Ni3S2 and MoS2 in the sulfided NiSiMo catalysts
Table 3. Pore properties of the sulfided NiSiMo catalysts

Table 1. Pore properties of the NiSiMo precursors
a
b
c
SBET (m2/g)
VP (cm3/g)
DP (nm)
NiMo precursor
Ni10Mo10
31
30
0.06
0.11
0.04
0.03
0.62
6.26
8.94
5.74
7.37
18.96
Ni9.5Si0.5Mo10
Ni8Si2Mo10
Ni5Si5Mo10
Si10Mo10
69
71
122
a SBET: BET surface area.
b VP: Pore volume was calculated by the BJH method.
c Dp: Average pore diameter was calculated by the BJH method from the desorption
branch of the isotherms.

Table 2. Average crystal sizes of Ni3S2 and MoS2 in the sulfided NiSiMo catalysts
Catalyst
Ni10Mo10
40.6
Ni9.5Si0.5Mo10
37.8
Ni8Si2Mo10
30.7
Ni5Si5Mo10 Si10Mo10
Ni3S2/nm
18.2
15.6
-
MoS2/nm
32.5
30.1
24.3
5.8

Table 3. Pore properties of the sulfided NiSiMo catalysts
NiMo precursor
Ni10Mo10
SBET (m2/g)
60
VP (cm3/g)
0.15
DP (nm)
8.72
Ni9.5Si0.5Mo10
Ni8Si2Mo10
Ni5Si5Mo10
Si10Mo10
77
87
0.10
0.05
0.02
0.61
5.96
4.84
10
11.86
18.75
126

Fig. 1. XRD patterns of the NiSiMo precursors
Fig. 2. N2 adsorption-desorption isotherms (a) and pore size distributions (b) of the NiSiMo
precursors
Fig. 3. SEM images of the NiSiMo precursors
Fig. 4. TPR profiles of the NiSiMo precursors
Fig. 5. XRD patterns of the sulfided NiSiMo catalysts
Fig. 6. N2 adsorption-desorption isotherms (a) and pore size distributions (b) of the sulfided
NiSiMo catalysts
Fig. 7. HRTEM images of the sulfided NiSiMo catalysts
Fig. 8. The conversion rate of naphthalene hydrogenation (a) and the selectivity of decalin (b) on
the unsupported NiSiMo catalysts
Fig. 9. Hydrogenation of naphthalene on the Si10Mo10 catalyst

Ν
(NH4)HNi2(OH)2(MoO4)2
Η
(
6
2
Ν
4
Ni10Mo10
Ni9.5Si0.5Mo10
Ni8Si2Mo10
Ni5Si5Mo10
Si10Mo10
10
20
30
40
2 Theta (°)
50
60
70
Fig. 1. XRD patterns of the NiSiMo precursors

0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
3.58 nm
Ni10Mo10
Ni9.5Si0.5Mo10
Ni8Si2Mo10
Ni5Si5Mo10
Si10Mo10
Ni10Mo10
Ni9.5Si0.5Mo10
Ni8Si2Mo10
Ni5Si5Mo10
Si10Mo10
(a)
(b)
3.74 nm
0.0
0.2
0.4
Relative pressure
0.6
P/P
0.8
1.0
2
3
4
5
6 7 8 910
Pore diameter(nm)
20
30 40 50 607080
（
）
0
Fig. 2. N2 adsorption-desorption isotherms (a) and pore size distributions (b) of the NiSiMo
precursors

Fig. 3. SEM images of the NiSiMo precursors