Nickel–molybdenum sulfide naphthalene hydrogenation catalysts synthesized by the in situ decomposition of oil-soluble precursors

Article abstract of DOI:10.1134/S096554411707009X

Nickel–molybdenum sulfide catalysts for the hydrogenation of aromatic hydrocarbons have been prepared by the in situ decomposition of oil-soluble precursors Mo(CO)₆ and Ni(С₇H₁₅СOO)₂ in a hydrocarbon feedstock and characterized by HRTEM and XPS. The resulting Ni–Mo sulfide material exhibits high catalytic activity in the naphthalene hydrogenation reaction. An optimum Mo/Ni ratio of 1/2 has been selected.

Full text of DOI:10.1134/S096554411707009X

ISSN 0965-5441, Petroleum Chemistry, 2017, Vol. 57, No. 7, pp. 595–599. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © I.A. Sizova, A.L. Maksimov, 2017, published in Nanogeterogennyi Kataliz, 2017, Vol. 2, No. 1, pp. 50–54.
Nickel–Molybdenum Sulfide Naphthalene Hydrogenation Catalysts
Synthesized by the In Situ Decomposition of Oil-Soluble Precursors
a,
a, b
I. A. Sizova * and A. L. Maksimov
a
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, Russia
b
Faculty of Chemistry, Moscow State University, Moscow, Russia
*
e-mail: isizova@mail.ru
Received December 20, 2016
Abstract⎯ Nickel–molybdenum sulfide catalysts for the hydrogenation of aromatic hydrocarbons have been
prepared by the in situ decomposition of oil-soluble precursors Mo(CO) and Ni(С H СOO) in a hydrocar-
6
7
15
2
bon feedstock and characterized by HRTEM and XPS. The resulting Ni–Mo sulfide material exhibits high cat-
alytic activity in the naphthalene hydrogenation reaction. An optimum Mo/Ni ratio of 1/2 has been selected.
Keywords: molybdenum hexacarbonyl, unsupported catalysts, nickel–molybdenum sulfide catalyst, hydro-
genation of aromatic hydrocarbons
DOI: 10.1134/S096554411707009X
The study of using nanocatalysts in oil refining hexanoate [5] and molybdenum acetylacetonate [6]
began with the development of nanocatalysts for the have been studied to a slightly lesser extent.
hydroconversion and hydrocracking of heavy crude
oil. It was shown that a number of unsupported ultra-
fine materials exhibit a higher activity and/or selectiv-
ity in hydrotreating reactions than conventional
Cobalt and/or nickel are used as promoters for
molybdenum catalysts to increase their catalytic activ-
ity. The promoting metal (Co or Ni) provides a signifi-
cant increase in the catalytic activity of this composite
compared with the activity of the nonpromoted catalyst
Ni/Co–Mo/W catalysts supported on γ-Al O [1].
2
3
To date, various methods for synthesizing catalyti- [7, 8]. Co–Mo sulfide catalysts are commonly used in
cally active ultra- and nanosized particles have been hydrodesulfurization reactions [9–11]; the substitution
developed and are being used. Nanocatalyst synthesis of Ni for Co leads to an increase in the hydrogenation
methods are conventionally divided into two groups: activity of the catalysts [12]. However, there are few
ex situ (providing synthesis of an active catalyst outside studies addressing the activity of Ni–Mo catalysts in the
the reaction zone) and in situ (providing the formation hydrogenation of aromatic hydrocarbons.
of a catalyst directly in the hydroprocessing reactor).
In this study, a method for the in situ synthesis of
The catalyst synthesis techniques pertaining to
Ni–Mo sulfide catalysts by the decomposition of oil-
nanoparticle formation bottom-up technologies pro-
soluble precursors—molybdenum hexacarbonyl and
viding formation of a nanocatalyst in situ in the reaction
nickel(II) 2-ethylhexanoate—is proposed; the catalyst
zone have gained widespread use. With respect to the
activity in the hydrogenation of aromatic hydrocar-
feed materials used for the in situ synthesis of a nano-
bons is studied using the example of naphthalene
catalyst, precursors are divided into two main groups,
hydrogenation.
namely, oil-soluble and water-soluble precursors.
Oil-soluble precursors are readily dispersed in a
hydrocarbon feedstock and generate nanoparticles
exhibiting a high catalytic activity. The general scheme
of synthesis of sulfide catalysts using oil-soluble precur-
sors dispersed in a hydrocarbon phase includes the
thermal decomposition of a precursor in a hydrocarbon
medium with a sulfiding agent [2, 3]. Most of the stud-
ies address heavy feedstock hydroconversion catalysts
EXPERIMENTAL
Catalyst Synthesis Procedures
The nickel–molybdenum sulfide catalyst was syn-
thesized in situ in the hydrocarbon feedstock. The pre-
cursors were the following oil-soluble salts: molybde-
num hexacarbonyl Mo(CO) (99.99%, Aldrich) and
6
synthesized using Mo-based oil-soluble precursors. nickel(II) 2-ethylhexanoate Ni(С H15СOO) (78% (in
7 2
The most thoroughly studied oil-soluble precursor for 2-ethylhexanoic acid), Aldrich). Catalytically active
sulfide catalysts based on molybdenum sulfide is particles were formed directly during the hydrogena-
molybdenum naphthenate [4, 5]; molybdenum 2-ethyl- tion reaction under the process conditions. Elemental
595

5
96
SIZOVA, MAKSIMOV
1
9
00
bon C 1s line at a binding energy of 284.9 eV. Decon-
volution of the spectra was conducted by the nonlinear
least-squares method using the Gaussian–Lorentzian
function.
0
0
0
0
0
0
0
0
8
7
6
5
4
3
2
Catalytic Testing Procedure
Catalytic tests on the naphthalene hydrogenation
were conducted in a steel autoclave in a hydrogen
atmosphere under high pressure and vigorous stirring
of the reaction mixture. A 10% solution of naphtha-
lene in benzene was used in the tests. Molybdenum
hexacarbonyl and nickel(II) 2-ethylhexanoate were
predissolved in the hydrocarbon feedstock; 2 mL of
the resulting solution was placed in the glass cartridge
of the autoclave. After that, the autoclave was filled
with hydrogen to a pressure of 5.0–7.0 MPa and held
at a temperature of 350°C for 2–10 h; the hydro-
gen/substrate molar ratio was 60 mol/mol. The
molybdenum content in the feedstock was calculated
by the formula
1
0
0
200 400 600 800 1000 1200 1400
Mo content, mg/kg
Fig. 1. Dependence of naphthalene conversion on the Mo
content in the feedstock. Reaction conditions: 5.0 MPa, 5 h.
sulfur in an amount of 2.5 wt % was added to the feed-
stock as a sulfiding agent for the formation of nickel–
molybdenum sulfide particles.
m
(
Mo
(
)
m
CO 6
)
M
(
Mo
)
6
⎛mg⎞
⎝ kg ⎠
[
Mo
]
=
× 10 ⎜
, (3)
⎟
M
(
Mo CO 6
(
)
)
(
feedstock
)
Catalyst Investigation Procedures
where m(Mo(CO) ) is the weight of molybdenum hex-
6
acarbonyl dissolved in the hydrocarbon feedstock, g;
After the hydrogenation reaction, the resulting
nickel–molybdenum catalysts were characterized by
high-resolution transmission electron microscopy
М(Mo) is the molar mass of molybdenum, 96 g/mol;
М(Mo(CO) ) is the molar mass of molybdenum hex-
6
(
(
HRTEM) and X-ray photoelectron spectroscopy acarbonyl, 264 g/mol; and m(feedstock) is the weight
XPS). The structure and morphology of the samples of the hydrocarbon feedstock, g.
were examined on a JEOL JEM-2100 analytical elec-
tron microscope. A statistical estimation of the dimen-
sional characteristics of more than 300 particles of the
active component in various TEM images for each of
the catalysts was conducted to determine the distribu-
tion of the sulfide particles with respect to their length
and number of layers in the multilayer agglomerates.
Product Analysis
The hydrogenation products of the model systems
were analyzed on a Kristallyuks 4000M chromato-
graph equipped with a flame ionization detector and a
SPB-1 capillary column coated with the polydimeth-
The average length of the active phase L was calcu- ylsiloxane liquid stationary phase (dimensions, 30 m ×
lated by the formula
0.25 mm; carrier gas, helium; split ratio, 1 : 90). Chro-
matograms were calculated using the NetChromWin
software program. Naphthalene conversion was calcu-
lated as the degree of conversion to decalins and
∑
li
L =
,
(1)
n
where l is the length of the ith crystallite and n is the tetralin. Selectivity was calculated as the ratio of the
i
weight of a given product to the total weight of the
resulting products.
number of crystallites.
The average number of active component layers
was calculated by the formula
RESULTS AND DISCUSSION
Catalytic Properties
∑
niNi
n
N =
,
(2)
where n is the number of particles with N layers.
i
i
The dependence of naphthalene conversion on the
The XPS studies of the catalyst samples were con- molybdenum content in the feedstock without the
ducted using a Physical Electronics PHI-5500 ESCA addition of nickel is shown in Fig. 1. An increase in the
XPS instrument. Photoemission was excited using molybdenum content in the feedstock from 240 to
3
00-W nonmonochromatized AlK radiation (hν = 1350 mg/kg leads to an increase in the naphthalene
α
1
486.6 eV). The powders were pressed in an indium conversion from 33 to 98%. The main product of the
plate. The diameter of the analyzed area was 1.1 mm. reaction is tetralin; decalins are hardly formed in the
Photoelectron peaks were calibrated against the car- system. At a molybdenum content in the feedstock of
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No. 7
2017

NICKEL–MOLYBDENUM SULFIDE NAPHTHALENE HYDROGENATION CATALYSTS
00 100
597
1
9
0
0
0
0
0
0
0
0
90
80
70
60
50
40
30
8
7
6
5
4
3
2
1
0
0
20
10
0
2.5
5.0
7.5
10.0
Reaction time, h
without Ni 3/1
2/1
1/1
1/2
1/3
Mo/Ni, mol/mol
Fig. 2. Dependence of naphthalene conversion on the
reaction time. Reaction conditions: 5.0 MPa, 350 mg/kg.
Fig. 3. Dependence of naphthalene conversion on the
Mo/Ni molar ratio. Reaction conditions: 5.0 MPa,
3
50 mg/kg, 5 h.
1
350 ppm, the amount of produced decalins (cis- and
trans-stereoisomers) is no more than 3%.
An increase in the reaction time from 2.5 to 10 h products (Table 1). Thus, an increase in the initial
leads to an increase in the naphthalene conversion hydrogen pressure by 2.0 MPa leads to an increase in
from 14 to 90% (Fig. 2). The main product of the reac- the decalin content to 30%; the ratio of decalins also
tion is also tetralin. Even in the case of a 10-h reaction, changes and achieves a value of 2/1, while the naph-
the decalin content does not exceed 3% (ratio between thalene conversion is up to 99%.
cis- and trans-decalins of 1.2/1).
According to the literature [13], the promoting
Catalyst Characteristics
effect of Ni and Co atoms is directly dependent on the
amount of the promoter added to molybdenum or
The sulfide material synthesized at a Mo/Ni
tungsten sulfides. Different authors indicate different molar ratio of 1/2 was characterized by HRTEM and
optimum atomic ratios between the promoter and the XPS. Analysis of the TEM images showed the forma-
parent metal. An increase in the promoter atom con- tion of spherical agglomerates of Ni–Mo particles
tent above an optimum value leads to a decrease in the with an average diameter of 220–270 nm (Fig. 4a).
catalytic activity of the sample in hydrotreating reac- The resulting particles consist of promoted MoS
2
tions owing to the formation of an individual bulk NiS
phase that blocks the promoted active sites on the cat-
alyst surface [7, 14]. In this context, it was of interest
to study the effect of the Mo/Ni ratio on the catalytic
activity of the resulting materials.
nanosheets (Fig. 4b), as evidenced by an interplanar
spacing of 0.65 nm, which is characteristic of the (002)
basal plane of molybdenum disulfide crystallite [15].
The average length of the active component is
9
.7 nm; the average number of layers in the multi-
layer agglomerate is 5.5.
The addition even of a small amount of nickel
Mo/Ni = 3/1) leads to an increase in the naphthalene
conversion from 45 to 87% (Fig. 3). The main product
of the reaction is tetralin; however, the decalin content
achieves 11.0% (ratio between cis- and trans-decalins
of 1.5/1). The optimum Mo/Ni ratio is 1/2; in this
case, the naphthalene conversion achieves 97%. The
decalin selectivity is 13.5%; the ratio between cis- and Table 1. Dependence of naphthalene conversion and reac-
trans-decalins changes and achieves a value of 1.8/1. A tion product selectivity on hydrogen pressure
further increase in the nickel content in the system
leads to a decrease in the catalytic activity of the result-
ing material owing to formation of the individual
phase of nickel sulfide.
An increase in the initial hydrogen pressure leads to
an increase in the naphthalene conversion and a sig-
nificant increase in the decalin fraction in the reaction
(
Table 2 lists the XPS data on the binding energies
and weight ratios of the phases. The molybdenum
present on the catalyst surface can be in the form of
molybdenum disulfide MoS , in the oxide phase
2
Selectivity, %
Pressure,
MPa
Conversion, %
decalins
tetralin
5
6
.0
.0
13.5
21.0
30.0
86.5
79.0
70.0
96
97.5
99
7.0
PETROLEUM CHEMISTRY Vol. 57 No. 7 2017

5
98
SIZOVA, MAKSIMOV
200 nm
10 nm
(a)
(b)
Fig. 4. Micrographs of the in situ synthesized Ni–Mo catalyst: (a) a general view of the particles and (b) the microstructure of the
active NiMoS phase.
MoO , and in the intermediate state, i.e., in the form sulfiding of the final material. Molybdenum in the
x
form of molybdenum oxide was not detected.
of molybdenum oxysulfide MoO S [8, 16–18]. The
x
y
deconvolution of the Mo 3d level showed that more
The nickel present on the catalyst surface can be in
than 95% of the molybdenum is in the form of molyb- the form of nickel sulfides NiS (Ni S , Ni S , NiS), in
x 2 3 9 8
denum disulfide; this feature indicates a high degree of the form of oxide NiO
, and part of complex sulfide
x
Table 2. XPS data for the Mo 3d, Ni 2p, and S 2p levels
Element
Binding energy, eV
229.0
Weight fraction, %
5.2
State
Mo 3d
Ni 2p
S 2p
3d5/2
9
MoS2
3
3
3
3
3
d3/2
d5/2
d3/2
d5/2
d3/2
232.2
229.9
4.8
MoOxSy
MoOx
NiSx
233.3
232.2
0
235.3
2p3/2
852.8
10.0
2p1/2
2p3/2
2p1/2
2p3/2
2p1/2
869.5
853.6
65.5
24.5
86.9
NiMoS
871.7
855.7
NiOx
873.7
2p3/2
161.8
S2–
2p1/2
2p3/2
2p1/2
2p3/2
2p1/2
163.0
163.2
2
2
−
4
.5
.6
S
164.2
168.7
(SO4)2–
No. 7
8
169.4
PETROLEUM CHEMISTRY
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NICKEL–MOLYBDENUM SULFIDE NAPHTHALENE HYDROGENATION CATALYSTS
599
NiMoS [8, 19–21]. The deconvolution of the
Ni 2p level showed that more than 75% of nickel is in
the sulfide environment, where 65% of the nickel is
part of the NiMoS phase and as little as 10% is in the
form of nickel sulfides; this finding indicates a high
degree of promotion with nickel in the molybdenum
disulfide crystallites.
6. N. Panariti, A. Del Bianco, G. Del Pieroa, M. Mar-
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(
7. H. Topsoe, B. S. Clausen, and F. E. Massoth, Hydro-
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8
. T. K. T. Ninh, L. Massin, D. Laurenti, and M. Vrinat,
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2
–
9. W. Lai, Z. Chen, J. Zhu, L. Yang, J. Zheng, X. Yi, and
W. Fang, Nanoscale 8, 3823 (2016). doi 10.1039/
C5NR08841K
the form of both sulfur S (MoS , NiS, NiMoS
2
2
−
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2
x y
of a peak in the region of 167–169 eV [22] suggests that 10. H. Yin, T. Zhou, and X. Liu, J. Porous Mater. 22, 1291
(2015).
the amount of sulfur in the sulfate state is small (no
more than 9%).
11. H. Liu, C. Yin, B. Liu, X. Li, Y. Li, Y. Chai, and C. Liu,
Energy Fuels 28, 2429 (2014).
Thus, Ni–Mo sulfide catalysts have been synthe-
sized by the in situ decomposition of oil-soluble precur-
sors molybdenum hexacarbonyl and nickel(II) 2-ethyl-
hexanoate. The resulting catalysts exhibit high activity
in the hydrogenation of aromatic hydrocarbons, in par-
ticular, naphthalene. At a reaction time of 5 h, a reac-
tion temperature of 350°C, and an initial hydrogen
pressure of 7.0 MPa, the naphthalene conversion
achieves 99%, while the decalin selectivity is 30%.
1
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ACKNOWLEDGMENTS
E. Payen, Surf. Interface Anal. 38, 206 (2006).
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7. Transition Metal Sulphides: Chemistry and Catalysis, Ed.
by T. Weber, R. Prins, and R. A. van Santen (Springer
Science & Business Media, Dordrecht, 2013).
This work was supported by the Russian Science
Foundation, agreement no. 15-13-00123.
1
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Translated by M. Timoshinina
PETROLEUM CHEMISTRY Vol. 57 No. 7 2017