Hydroconversion of Thiophene Derivatives over Dispersed Ni–Mo Sulfide Catalysts

Article abstract of DOI:10.1134/S0965544118140141

Abstract: The activity of unsupported Ni–Mo sulfide catalysts is studied in the hydroconversion of benzothiophene and dibenzothiophenes in the temperature range of 340–380°С and at an increased H₂ pressure and in the СО/H₂О system. The structure of dispersed catalysts formed by the in situ high-temperature decomposition of oil-soluble precursors (molybdenum hexacarbonyl, nickel naphthenate) is investigated by TEM. Effects of СО/H₂О molar ratio, water mass content in the system, and CO pressure on the activity of the catalysts and yields of the products are explored. It is shown that, in the СО/H₂О system, the highest conversion of benzothiophene and dibenzothiophene is attained at a temperature of 380°С, a СО pressure of 5?MPa, and a СО/H₂О molar ratio of 2. The introduction of alkyl substituents into a dibenzothiophene molecule causes a reduction in the rate of reaction that predominantly occurs via the hydrogenation of aromatic rings. The catalyst activities in hydrogenation under H₂ pressure and in the СО/H₂О system are comparable.

Full text of DOI:10.1134/S0965544118140141

ISSN 0965-5441, Petroleum Chemistry, 2018, Vol. 58, No. 14, pp. 1227–1232. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © A.V. Vutolkina, D.F. Makhmutov, A.V. Zanina, A.L. Maximov, D.S. Kopitsin, A.P. Glotov, S.V. Egazar’yants, E.A. Karakhanov, 2018, published in
Nanogeterogennyi Kataliz, 2018, Vol. 3, No. 2, pp. 130–135.
Hydroconversion of Thiophene Derivatives
over Dispersed Ni–Mo Sulfide Catalysts
A. V. Vutolkinaa, *, D. F. Makhmutova, A. V. Zaninaa, A. L. Maximova, b, D. S. Kopitsinc,
A. P. Glotova, c, S. V. Egazar’yantsa, and E. A. Karakhanova
aFaculty of Chemistry, Moscow State University, Moscow, 119991 Russia
bTopchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 119991 Russia
cGubkin Russian State University of Oil and Gas (National Research University), Moscow, 119991 Russia
*e-mail: annavutolkina@mail.ru
Received August 10, 2018
Abstract⎯The activity of unsupported Ni–Mo sulfide catalysts is studied in the hydroconversion of ben-
zothiophene and dibenzothiophenes in the temperature range of 340–380°С and at an increased H2 pressure
and in the СО/H2О system. The structure of dispersed catalysts formed by the in situ high-temperature
decomposition of oil-soluble precursors (molybdenum hexacarbonyl, nickel naphthenate) is investigated by
TEM. Effects of СО/H2О molar ratio, water mass content in the system, and CO pressure on the activity of
the catalysts and yields of the products are explored. It is shown that, in the СО/H2О system, the highest con-
version of benzothiophene and dibenzothiophene is attained at a temperature of 380°С, a СО pressure of
5 MPa, and a СО/H2О molar ratio of 2. The introduction of alkyl substituents into a dibenzothiophene mol-
ecule causes a reduction in the rate of reaction that predominantly occurs via the hydrogenation of aromatic
rings. The catalyst activities in hydrogenation under H2 pressure and in the СО/H2О system are comparable.
Keywords: hydrodesulfurization, nickel–molybdenum sulfide catalysts, dispersed catalysts, water-gas shift
reaction
DOI: 10.1134/S0965544118140141
In recent years, considerable attention has been shift reaction. This study concerns the behavior of the
paid to the study of activity of unsupported dispersed title catalyst systems in the hydroconversion of aro-
catalysts distributed in the hydrocarbon feedstock. matic sulfurous compounds.
These catalysts are characterized by a high content of
the active phase and, as a consequence, possess high
activity in hydrogenation reactions [1–3]. Moreover,
EXPERIMENTAL
in the case of supported catalyst systems, steric hin-
drances may arise during the diffusion of substrate
molecules in support pores. The use of fine unsup-
ported catalysts makes it possible to avoid the impact
of the mentioned processes hindering access of a sub-
strate to the active component [4].
High-temperature decomposition (at a tempera-
ture above 300°С) of oil/water-soluble metal precur-
sors in a hydrocarbon medium in the presence of a sul-
fiding agent (elemental sulfur) is the most widespread
method of synthesizing these catalysts. This method
enables the obtainment of stable dispersed particles
with a high content of the active phase [4–6].
As was shown in [7], dispersed Ni–Mo sulfide cat-
alysts formed directly in the reaction medium from
oil-soluble precursors exhibit high activity in the
hydrogenation of aromatic substrates conducted at an
increased CO pressure in the presence of water provid- generated in the reaction medium. To provide forma-
ing the in situ generation of hydrogen via the water-gas tion of the active phase of the catalyst (molybdenum
Substrates were benzothiophene (BT, 98% Alfa
Aesar), dibenzothiophene (DBT, 98% Alfa Aesar),
4-methyldibenzothiophene (4-МеDBT, 96% Sigma
Aldrich),
4,6-dimethyldibenzothiophene
(4,6-
diMeDBT, 97% Sigma Aldrich), and 4,6-dieth-
yldibenzothiophene (4,6-diEtDBT, 97% Sigma
Aldrich). Catalytic tests were run in a 50-mL batch
reactor under vigorous stirring of the reaction mixture.
The temperature was maintained constant using an
electric resistance furnace equipped with a thermo-
couple and a temperature controller. The reaction was
mediated by the unsupported bimetallic Ni–Mo sul-
fide catalyst formed in situ during the decomposition
of oil-soluble precursors, namely, molybdenum hex-
acarbonyl Mo(CO)6 (98% Sigma Aldrich) and
nickel(II) naphthenate Ni(С10H7СOO)2. (6–12 wt %
Ni, Sigma Aldrich). Catalytically active species were
1227

1228
VUTOLKINA et al.
Mо : substrate
Table 1. Ratios and amounts of initial reagents
Substrate
ω (Mо), wt %
ω(S), wt %
Mo : Ni (wt)
3 : 1
ω (substrate), wt %
(mol/mol)
Benzothiophene
0.15
1 : 65
10
Dibenzothiophene
4-Methyldibenzothiophene
4,6-Dimethyldibenzothiophene
4,6-Diethyldibenzothiophene
2.5
0.45
1 : 33
5
sulfide), 2.5 wt % elemental sulfur was additionally oil-soluble precursors were run in the temperature
introduced in the reaction mixture. The hydrogena- range of 360–380°С under an increased pressure of
tion of aromatic substrates was conducted under an СО. The activity of the catalyst system based on the
increased pressure of СО in toluene (Table 1).
Ni–Mo sulfide catalyst in the hydrodesulfurization
reaction was estimated using benzothiophene and
dibenzothiophene and alkyl-substituted dibenzothio-
phenes (4-methyl, 4,6-dimethyl, 4,6-diethyldiben-
zothiophene) as substrates.
In the event of hydrogenation with molecular
hydrogen, the pressure in the reaction system was
5 MPa. Tests in the system water-carbon monoxide
were run in the CO pressure range of 2–5 MPa at the
ratio СО/Н2О = 1–5 and the weight content of water
in the initial system of 20 wt %.
The qualitative composition of liquid products in
the hydroconversion of sulfurous compounds was
determined by gas chromatography-mass spectrome-
try on a Thermo Scientific Trace GC Ultra DSQ II
instrument equipped with a HP-5MS capillary col-
umn (30 m × 0.25 mm × 0.25 μm) under temperature
programming in the range of 45–250°С. Mass scan-
ning was performed in the range of 40–550 amu.
The reaction products were analyzed on a Kristal-
lyuks 4000M gas-liquid chromatograph equipped with
a flame-ionization detector and a PetrocolTM
(Supelco) capillary column (0.25 mm × 30 m) under
programmed heating.
After the reaction, the catalyst formed in situ was
isolated from the reaction mixture by centrifugation,
washed with toluene, and dried under an inert atmo-
sphere. The structure and morphology of the synthe-
sized catalysts were investigated on a JEOL JEM-2100
analytical electron microscope at an electron tube
voltage of 100 kV.
The mass concentration of water in the system and
the pressure of carbon monoxide provide a certain
СО/Н2О ratio in the reaction medium and may affect
both the generation of the catalyst active phase and the
concentration of active hydrogen in the system. The
maximum activity of the catalysts in the hydrogena-
tion of DBT is achieved at СО/Н2О = 2. At the stoi-
chiometric ratio between water and carbon monoxide
in the reaction mixture, the DBT conversion
decreases by more than three times (Fig. 1a). Proba-
bly, the pressure of hydrogen in the system is insuffi-
ciently high in order to provide both the formation of
hydrogen sulfide required for catalyst transition to the
sulfide form and the occurrence of hydrogenation pro-
cesses. When the content of СО in the system is high
(СО/Н2О > 2), the conversion of dibenzothiophene
does not exceed 25%. This may be explained by the
fact that СО molecules occupy catalyst active sites and
thus hinder the sorption of substrate molecules on its
surface.
The pressure of CO provided that the established
ratio is preserved also influences the process. For
example, at a СО pressure of 5 MPa and a temperature
of 380°С, the conversion of dibenzothiophene
attained over 6 h is 54% and the main products are
diphenyl and cyclohexylbenzene. Selectivity for these
products is as high as 90%. Reduction in pressure to 2
or 3 MPa leads to a marked decline in conversion to 10
and 8%, respectively (Fig. 1b).
X-ray photoelectron spectroscopy studies were
conducted on a Kratos Axis Ultra DLD electronic
instrument equipped with a photoelectron analyzer
with an OPX-150 retarding field. Photoemission was
excited using X-ray radiation of the aluminum anode
(AlKα = 1486.6 eV) at a tube voltage of 12 kV and an
emission current of 20 mA. Photoelectron peaks were
calibrated against the line of carbon C1s with a binding
energy of 285 eV.
The activity of catalyst systems is determined by the
nature of an organosulfur substrate, specifically, by
steric hindrances arising during its sorption on catalyst
active sites. Ni–Mo sulfide catalysts are more active in
the hydroconversion of benzothiophene. For exam-
RESULTS AND DISCUSSION
Catalytic tests on the hydrogenation of sulfurous ple, if the reaction is conducted at a temperature of
compounds mediated by unsupported Ni–Mo sulfide 360°С under hydrogen pressure, its almost quantita-
catalysts formed in situ during the decomposition of tive conversion is achieved, whereas for dibenzothio-
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HYDROCONVERSION OF THIOPHENE DERIVATIVES
1229
70
60
50
40
30
20
10
0
70
60
50
40
30
20
10
0
(а)
(b)
2
3
4
5
5
4
3
2
1
CO/H2O, mol/mol
p(CO), MPa
Fig. 1. Dibenzothiophene conversion vs. (a) СО/Н О molar ratio and (b) СО pressure (СО/Н О = 2). T = 380°С, t = 6 h.
2
2
phene conversion does not exceed 20%. In the system aromatic rings followed by the hydrogenolysis of C–S
СО/Н2О, the identical dependence is observed; how-
ever, the conversion of model substrates is somewhat
lower and it grows with increasing temperature
(Fig. 2).
Because catalytically active species are generated
directly in the reaction medium, the catalyst activity is
considerably influenced by the temperature and time
of reaction.
With increasing time of reaction, the conversion of
organosulfur substrates grows appreciably. Probably,
this may be explained by the fact that, at the initial
stage of reaction, sulfide species are formed which are
characterized by a smaller number of edge and angular
sites, a lower proportion of the active phase, and a
smaller degree of promotion [2, 3]. For example, in
the case of benzothiophene when the reaction is car-
bonds or through the direct desulfurization. For ben-
zothiophene, ethylbenzene is the main reaction prod-
uct in both cases; further hydrogenation of ethylben-
zene gives rise to ethylcyclohexane. In the case of
dibenzothiophene, the implementation of the reaction
by the direct desulfurization route leads to the forma-
tion of diphenyl. A high selectivity for tetrahydrod-
ibenzothiophene and cyclohexylbenzene suggests that
the hydrogenation route prevails.
The hydroconversion of benzothiophene over the
Ni–Mo sulfide catalyst leads to the generation of eth-
ylbenzene; the selectivity for this product is above 90%
for hydroconversion reactions both under hydrogen
pressure and in the system СО/Н2О. The content of
ethylcyclohexane does not exceed 6–12%. Only when
ried out under hydrogen pressure at a temperature of the temperature is increased to 380°С after 8 h of reac-
360–380°С, the catalyst active phase is formed during
1–2 h, as evidenced by the quantitative substrate con-
Benzothiophene, Н2
Dibenzothiophene, Н2
version attained after this time is elapsed (Fig. 3a). At
a lower temperature (340°С), on the order of 3–4 h are
required to generate catalytically active species. In the
system СО/Н2О at a temperature of 380°С, the cata-
lyst active phase is formed over 2–3 h and the quanti-
tative conversion of benzothiophene is reached in 6 h.
Benzothiophene, CO/Н2O
Dibenzothiophene, CO/Н2O
100
80
60
40
20
The conversion of dibenzothiophene in the tem-
perature range of 340–380°С at a CO pressure of
5 MPa over 4 h is no greater than 24%. In the case of
hydrogenation under hydrogen pressure, the substrate
conversion grows to 41%. When the reaction is carried
out for 6 h, the conversion of dibenzothiophene
increases appreciably for the two systems (Fig. 3b). In
the case of dibenzothiophene, low conversions are
probably related to steric hindrances in the sorption of
substrate molecules on the catalyst surface. This also
adversely affects the water-gas shift reaction.
0
360
Temperature, °C
380
340
Fig. 2. Temperature dependences of conversion for model
substrates under H pressure and in the CO/H O system.
2
2
The hydroconversion of benzothiophene and
dibenzothiophene may occur via the hydrogenation of
Reaction conditions: t = 4 h, p(H ) = 5 MPa/p(СО) =
2
5 MPa, and СО/Н О = 2.
2
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1230
VUTOLKINA et al.
(а)
(b)
380°С, H2
360°С, H2
340°С, H2
100
90
80
70
60
50
40
30
20
10
100
80
60
40
20
380°С, CO/H2O
360°С, CO/H2O
340°С, CO/H2O
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
8
Time, h
Time, h
Fig. 3. Conversion vs. the time and temperature of reaction conducted under hydrogen pressure and in the СО/Н О system:
2
(a) benzothiophene, and (b) dibenzothiophene. Reaction conditions: р(Н ) = 5 MPa, p(СО) = 5 MPa, СО/Н О = 2.
2
2
tion under hydrogen pressure does its proportion in ibenzothiophene is identified in the reaction mixture.
reaction products grow to 22%.
The content of products formed by direct hydrogeno-
lysis is no greater than 13%.
For processes involving dibenzothiophene, diphe-
nyl and cyclohexylbenzene are the main products.
When the reaction is carried out for 4 h (Т = 380°С),
the ratio of these products is 1 : 1. As the time of reac-
tion is increased to 8 h, the proportion of cyclohexyl-
benzene grows noticeably; the selectivity for this prod-
uct attains 70%. In addition, the reaction products
contain the traces of dicyclohexyl. When the process is
conducted under the pressure of molecular hydrogen,
its content is 16%, whereas for the system СО/Н2О it
is no greater than 6%.
The introduction of alkyl substituents into a
dibenzothiophene molecule entails a decline in the
rate of conversion of model compounds. For exam-
ple, when the reaction is carried out under hydrogen
pressure at a temperature of 380°С for 8 h, the con-
version of 4-methyl- and 4,6-dimethyldibenzothio-
phenes is 40 and 49%, respectively (Table 2). For
the system СО/Н2О under these conditions, the
substrate conversion is somewhat smaller—38 and
42%. The main reaction products are 1-cyclohexyl-
3-methylbenzene and 3-methylcyclohexylbenzene;
their content is 16%. The proportion of 4- and
6-methylhexahydrodibenzothiophenes is 17%,
while 4-methyltetrahydrodibenzothiophene is con-
tained as traces (no more than 5%). This finding
indicates that the reaction occurs via both the direct
hydrogenolysis of C–S bonds and the hydrogena-
tion of the thiophene ring followed by ring opening.
In hydrogenation under hydrogen pressure at a
temperature of 380°С, the conversion of 4,6-dieth-
yldibenzothiophene is as high as 97%. For the system
СО/Н2О, this value is 91% (Table 2). The reaction
proceeds by the direct hydrogenolysis of С–S
bonds, as indicated by a high selectivity of the process
for 1-ethyl-3-(3-ethylcyclohexyl)benzene and 3,3'-
diethyl-1,1'-dicyclohexane. It is important that the
content of 3,3'-diethyl-1,1'-diphenyl does not exceed
5%. The products of thiophene ring hydrogenation are
present as traces, and their total amount is less
than 4%.
The data on the dispersity, surface morphology,
and structure of the catalyst active component formed
during dibenzothiophene hydroconversion at a tem-
perature of 380°С in the system CO/H2O (p(CO) =
5 MPa, CO/H2O molar ratio = 2.0) were obtained
by TEM.
According to the TEM data, the active component
in the synthesized sulfide catalysts is multilayered bent
stacks of molybdenum sulfide (Figs. 4a, 4b). Presence
of the layered phase of molybdenum sulfide is also
confirmed by the fact that the interplanar distance is
0.44 nm, indicating the basal (002) plane of the МоS2
crystallite.
The average length of particles for the active Ni–
Mo sulfide component is 7–9 nm. In addition, multi-
layered agglomerates with a length above 10 nm are
formed; their proportion is on the order of 23%
(Fig. 4c). The average number of active component
layers is 4–5.
In the case of 4,6-dimethyldibenzothiophene the
main reaction products are 4,6-dimethyltetrahydrod-
ibenzothiophene and 4,6-hexahydrodimethyldiben-
zothiophene. This fact provides evidence that the
reaction occurs via the hydrogenation of the aromatic
ring because the direct removal of sulfur is sterically
According to the deconvolution of the Mo3d level,
molybdenum is present in the form of sulfide MoSх
(91%) and oxide МоО3, (no greater than 1.7%). The
hindered. In addition, 4,6-dimethyldodecahydrod- XPS spectrum also shows bands at 231.6 eV assigned to
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HYDROCONVERSION OF THIOPHENE DERIVATIVES
1231
Table 2. Experimental data on substituted dibenzothiophenes in systems Н2 and СО/Н2О
4,6-
4-Methyldibenzothiophene
selectivity, %
4,6-Dimethyldibenzothiophene
Diethyldibenzothiophene
Hydrogen source
selectivity, %
conversion,
selectivity, %
conversion,
conversion,
%
%
%
1
2
3
4
1а
2a
3а
4а
1b 2b 3b
Molecular H2
40
38
43
42
18
21
18
18
20
13
49
42
15
33
33
21
22
14
8
97
91
30 55
44 33
3
5
System СО/Н2О
12
Reaction conditions: 380°С, 8 h, р(Н2) = 5 MPa, p(СО) = 5 MPa, and СО/Н2О = 2.
1–4 are 4-МеDBT hydroconversion products, 1a−4a are 4,6-diMeDBT hydroconversion products, and 1b−3b are 4,6-
diEtDBT hydroconversion products.
1
2
3
4
1a
2a
3a
4a
1b
2b
3b
S
S
S
H C
C H
C H
CH
CH
CH
3
2
5
5
5
2
5
5
5
3
3
3
H
C
3
S
S
C H
2
C H
2
H C
3
H C
3
C H
C H
2
2
H C
3
H C
3
H C
3
H
C
3
CH
3
30
25
(a)
(b)
(c)
20
15
10
5
0
20 nm
20 nm
Particle length, Å
Fig. 4. (a, b) TEM microimages of Ni–Mo sulfide catalysts and (c) length distribution of sulfide particles. (b).
PETROLEUM CHEMISTRY Vol. 58 No. 14 2018

1232
VUTOLKINA et al.
Table 3. XPS data for Mo3d, Ni2p, and S2p levels
Element
Mo3d5/2
Surface concentration, at %
4.55
Binding energy, eV
Content, %
91.0
State
228.5
231.6
232.9
160.3
MoSx
MoSxOy
MoOx
7.3
1.7
S2–
S2p3/2
16.58
4.08
49.0
161.8
163.9
167.3
S22−
27.2
(SO4)2–
NiSx
23.8
Ni2p3/2
852.0
854.6
857.8
31.0
51.0
18.0
NiMoS
NiOx
the mixed phase of molybdenum oxysulfide MoSxOy
(Table 3) [8–10].
ACKNOWLEDGMENTS
This work was supported by the Russian Founda-
tion for Basic Research, project no. 18-38-00593.
In the spectrum of the Ni2p level, bands at 852.0,
857.8, and 854.6 eV corresponding to nickel sulfide
and oxide and mixed NiMoS phase are observed [8,
11]. The proportion of the oxide forms is on the order
of 20% (Table 3).
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2018