Promoted catalysts for hydrogenation of bicyclic aromatic hydrocarbons obtained in situ from molybdenum and tungsten carbonyls

Article abstract of DOI:10.1134/S0965544118010164

Promoted Мo and W catalysts have been prepared in situ via thermal decomposition of precursors, oil-soluble salts Mo(CO)₆, W(CO)₆, С°C₁₆H₃₀O₄, and NiC₁₆H₃₀O₄. TiO₂, Al₂O₃, and ZrO(NO₃)₂ · 6H₂O have been used as the acidic additives. Also, Mo and W unsupported sulfide catalysts have been prepared in the presence of elemental sulfur as the sulfiding agent. The catalysts have been characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The activity of the catalysts prepared in situ has been evaluated in the hydrogenation reaction of bicyclic aromatic hydrocarbons by the example of model mixtures of 10% solutions of naphthalenes (unsubstituted naphthalene, 1- and 2-methylnaphthalenes, and 1,5- and 2,3-dimethylnaphthalenes) in n-hexadecane. The effect of the precursor/acidic oxide ratio on the activity of the formed catalyst has been found. Hydrogenation of bicyclic aromatic hydrocarbons has been conducted at a hydrogen pressure of 2 and 5 MPa and a temperature of 380 and 400°C for 2 h. Hydrogenation of the unsubstituted aromatic ring has been preferable due to the absence of steric hindrances. The degree of conversion of n-hexadecane under the reaction conditions has been 1.5–7.5% depending on the reaction temperature. It has been found that the activity of the sulfided catalyst in the conversion of 1- and 2-methylnaphthalenes is inferior to the activity of the unsulfided analogue, while partial replacement of TiO₂ by Al₂O₃ results in a decrease in the conversion of the substrates as opposed to the unsulfided catalysts, in which the use of nanocrystalline Al₂O₃ promotes an increase in the conversion.

Full text of DOI:10.1134/S0965544118010164

ISSN 0965-5441, Petroleum Chemistry, 2018, Vol. 58, No. 1, pp. 22–31. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © E.M. Zakharyan, M.I. Onishchenko, A.L. Maksimov, 2018, published in Neftekhimiya, 2018, Vol. 58, No. 1, pp. 26–35.
Promoted Catalysts for Hydrogenation of Bicyclic Aromatic
Hydrocarbons Obtained in situ from Molybdenum
and Tungsten Carbonyls
E. M. Zakharyana, *, M. I. Onishchenkoa, **, and A. L. Maksimova, b
aTopchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 119991 Russia
bFaculty of Chemistry, Moscow State University, Moscow, 119991 Russia
*e-mail: Zakharyan@ips.ac.ru,
**e-mail: onishchenko@ips.ac.ru
Received June 4, 2017
Abstract⎯Promoted Мo and W catalysts have been prepared in situ via thermal decomposition of precursors,
oil-soluble salts Mo(CO)6, W(CO)6, СoC16H30O4, and NiC16H30O4. TiO2, Al2O3, and ZrO(NO3)2 · 6H2O
have been used as the acidic additives. Also, Mo and W unsupported sulfide catalysts have been prepared in
the presence of elemental sulfur as the sulfiding agent. The catalysts have been characterized by transmission
electron microscopy and X-ray photoelectron spectroscopy. The activity of the catalysts prepared in situ has
been evaluated in the hydrogenation reaction of bicyclic aromatic hydrocarbons by the example of model
mixtures of 10% solutions of naphthalenes (unsubstituted naphthalene, 1- and 2-methylnaphthalenes, and
1,5- and 2,3-dimethylnaphthalenes) in n-hexadecane. The effect of the precursor/acidic oxide ratio on the
activity of the formed catalyst has been found. Hydrogenation of bicyclic aromatic hydrocarbons has been
conducted at a hydrogen pressure of 2 and 5 MPa and a temperature of 380 and 400°C for 2 h. Hydrogenation
of the unsubstituted aromatic ring has been preferable due to the absence of steric hindrances. The degree of
conversion of n-hexadecane under the reaction conditions has been 1.5–7.5% depending on the reaction
temperature. It has been found that the activity of the sulfided catalyst in the conversion of 1- and 2-methyl-
naphthalenes is inferior to the activity of the unsulfided analogue, while partial replacement of TiO2 by Al2O3
results in a decrease in the conversion of the substrates as opposed to the unsulfided catalysts, in which the
use of nanocrystalline Al2O3 promotes an increase in the conversion.
Keywords: hydrogenation, hydrocracking, molybdenum hexacarbonyl, tungsten hexacarbonyl, molybdenum
disulfide, nanotitania, nanoalumina, unsupported catalyst, bicyclic aromatic hydrocarbons, naphthalenes
DOI: 10.1134/S0965544118010164
INTRODUCTION
Processes of conversion of polyaromatic hydrocar-
bons (HCs) play a pivotal role in the hydroprocessing
raw materials as well, can serve as an alternative for
such a type of systems [5].
The use of unsupported catalysts in the processes of
of petroleum fractions. Generally, a hydrogenation hydrocracking and hydrogenation of aromatic HCs is
reaction precedes the processes of carbon–carbon characterized by an advantage such as the simplicity of
bond opening and isomerization in the hydrocracking the preparation due to the absence of the need for con-
processes. Hydrogenation of polyaromatic and naph- ducting the stage of application of metals (active
thene-aromatic compounds (hydrodearomatization) hydrogenating components) onto a support as
of middle-distillate fractions, in particular, in the case opposed to supported catalysts (the ex situ method) [6,
of highly aromatic fractions of secondary processes 7]. Such systems can be obtained already during the
(gas oils of catalytic cracking and coking), provides the hydrogenation, hydrocracking, or desulfurization
possibility for the preparation of kerosenes and diesel reaction by the in situ method [8–10]. As the com-
fuels which comply with the limits of the Technical pounds of metals, their salts are generally used, the
Regulations. In industry, bimetallic sulfide catalysts reduction of which to highly dispersed nanocrystalline
on the basis of Group V metals (tungsten and molyb- metal powders in these processes occurs via pyrolysis
denum) supported onto aluminum silicates are gener- because these hydroprocesses proceed at quite high
ally used in these processes [1–3]. Unsupported cata- temperatures (up to 420–450°С) [11]. The advantages
lysts [4], including catalysts dispersed in hydrocarbon of pyrolysis are the low concentration of impurities in
22

PROMOTED CATALYSTS FOR HYDROGENATION
23
the particles being obtained and their narrow size dis- Aldrich), and zirconium oxonitrate ZrO(NO3)2
·
6H2O (99%, Aldrich) were used as the acidic additive
components. Elemental sulfur was used as the sulfid-
ing agent for the preparation of the sulfide forms of the
catalysts.
tribution.
Among unsupported catalysts for the hydroconver-
sion reactions of petroleum fractions [12, 13], catalysts
on the basis of molybdenum and tungsten sulfides
promoted by nickel or cobalt are used most often [14].
The addition of these promoters leads to a substantial
increase in the catalytic activity due to the formation
of additional sulfide (nickel or cobalt sulfide)
Analysis
The structure and morphology of the obtained
and mixed (nickel/cobalt–tungsten sulfide) phases samples of the catalysts were studied using high-reso-
[15, 16].
The use of acidic components such as titanium,
lution transmission electron microscopy (TEM) with
a JEOL JEM 2100 electron microscope at an acceler-
ating voltage of 200 kV.
aluminum, and zirconium oxides, as well as their
combinations, promotes an increase in the activity of
the catalysts in hydroprocesses [17]. Particular interest
of researchers is generated by titanium oxide, for
which three crystallographic structures are character-
istic, namely, rutile, brookite, and anatase, the latter
of which, existing in the metastable state, is the most
active in photocatalysis [18]. Also, there is information
that TiO2 in the form of a mixture of anatase and rutile
possesses higher activity when compared to anatase or
rutile individually [19]. In addition to the photocata-
lytic reactions [20, 21], it is used as the support for sys-
tems in the hydrogenation [22] and oxidation [23]
reactions and as the adsorbent of, e.g., water vapor
[24]. The high catalytic activity of the systems on the
basis of nanosized TiO2 is possibly associated not only
with the small size of particles (up to 100 nm) but also
with the large specific surface area and character of the
interaction of the corresponding sulfide with the sur-
face of the oxide.
During the statistical evaluation of the size charac-
teristics of more than 300 particles of the active com-
ponent in various TEM images for each catalyst, the
distribution of sulfide particles by their length and
number of layers in multilayer agglomerates was
obtained. The average length of the sulfide particles
was calculated by formula (1)
L
li
∑
(1)
L =
,
n
where li is the length of the ith crystallite and n is the
number of crystallites.
The average number of layers in the sulfide parti-
cles was calculated by formula (2)
N
niNi
∑
(2)
N =
,
n
where ni is the number of particles with Ni layers [25].
In connection therewith, it was of interest to form
in situ catalytic systems on the basis of oil-soluble pre-
cursors of molybdenum and tungsten, as well as
sources of promoting additives, nickel and cobalt eth-
ylhexanoates. In addition, a combination of these dis-
persed Мo and W catalysts with the additions of nano-
sized oxides (e.g., TiO2 and Al2O3) as well as their pre-
cursors (zirconium oxonitrate) was proposed. The
activity of the systems obtained was studied in the
hydrogenation reactions of aromatic HCs by the
example of naphthalene, 1- and 2-methylnaphtha-
lenes, and 2,3- and 1,5-dimethylnaphthalenes.
The catalysts were studied by X-ray photoelectron
spectroscopy (XPS) using a VersaProbeII X-ray pho-
toelectron spectrometer (ULVAC-PHI). A mono-
chromatic AlKα radiation (1486.6 eV) with a power of
25 W was used for the excitation of photoelectron
emission. The diameter of the analyzed area was
100 μm. The panoramic spectra were recorded at a
pass energy of the analyzer (Epass) of 117.4 eV and an
increment of 1.0 eV. The high-resolution (HR) spectra
were recorded at Epass of 11.75 eV and an increment of
0.1 eV. The HR spectra of Ti2p were recorded at Epass
of 23.5 eV and an increment of 0.2 eV. The deconvolu-
tion of the spectra was performed via the nonlinear
method of least squares using the Gauss–Lorentz
function.
EXPERIMENTAL
The following oil-soluble compounds were used in
the work: molybdenum hexacarbonyl Mo(CO)6
(99.99%, Aldrich), tungsten hexacarbonyl W(CO)6
(99.99%, Aldrich), nickel(II) 2-ethylhexanoate
Ni(С7H15СOO)2 (a 78% solution in 2-ethylhexanoic
acid, Aldrich), and cobalt(II) 2-ethylhexanoate
Сo(С7H15СOO)2 (a 78% solution in 2-ethylhexanoic
acid, Aldrich). A nanopowder of titanium oxide TiO2
(a mixture of rutile and anatase, a particle size
<100 nm, 99.8%, Aldrich), a nanopowder of alumi-
num oxide Al2O3 (a particle size of 15 nm, 99.8%,
Catalyst Testing and Product Analysis Procedures
Model feedstocks were 10% solutions of substrates
(the bicyclic aromatic HCs unsubstituted naphtha-
lene, 1- and 2-methylnaphthalenes, and 1,5- and 2,3-
dimethylnaphthalenes) in n-hexadecane. A weighed
amount of a substrate, as well as a calculated amount
of the precursor compounds, was introduced into an
insert tube, while adding oxides or their precursors (in
the case of zirconium oxide) where necessary. Then
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24
ZAKHARYAN et al.
the insert was placed into a 20-mL steel autoclave. The num disulfide MoS2 and in the oxide phase MoOx, as
experiments were conducted at 380 and 400°С and a
hydrogen pressure of 2 and 5 MPa under intense stir-
ring. The molar ratios were as follows: substrate/Mo of
18.4 : 1 and 36.8 : 1, substrate/W of 18.4 : 1, sub-
strate/Ti of 2.4 : 1, 4.9 : 1, 7.3 : 1, 9.7 : 1, and 12.5 : 1,
substrate/Al of 4.9 : 1 and 9.7 : 1, substrate/Zr of
70.2 : 1, substrate/Co of 37.2 : 1, and substrate/Ni of
37.2 : 1. The catalysts were sulfided in situ in the
hydrocarbon raw materials by adding elemental sulfur
in the amount of 2.5 wt % relative to the weight of the
raw materials (a solution of a substrate in n-hexadec-
ane). The autoclave was heated to the temperature of
the experiment at a rate of 10 deg/min. Upon the com-
pletion of the experiment, the autoclave was brought
up to room temperature and the catalyst was separated
from the conversion products via centrifugation. No
formation of the gaseous products of the conversion of
the raw materials was observed.
well as in the intermediate state, in the form of molyb-
denum oxysulfide MoOxSy [30, 31]. The results of the
deconvolution of the Mo3d level give the evidence of
the fact that all the molybdenum is in the sulfide form,
which suggests 100% sulfidation of the final material
obtained (Table 1). No molybdenum in the form of
oxide MoOx and oxysulfide MoOxSy was detected
(Table 1). The peak detected at 225.7 eV corresponds
to sulfide sulfur S2–.
Like in the case of the Mo–TiO2 catalyst, titanium
is in the oxide form TiO2 (Еb(Ti2p1/2) = 464.1 eV and
Еb(Ti2p3/2) = 458.8 eV) [27]. It should also be noted
that characteristic satellites were present in the spec-
trum of titanium [31].
Sulfur can be present on the surface of the catalyst
2−
in the form of both sulfur S2– (MoS ) and the
S2
2
phase (MoOxS) [31, 33, 34]. According to the decon-
volution, sulfur is present on the surface of the catalyst
only in the form of sulfide S2– (161.4 eV S2р3/2 and
162.6 eV S2p1/2) (Table 1).
The obtained products of the experiments were
analyzed on a Kristallyuks 4000 М chromatograph
equipped with a flame ionization detector and an
SPB-1 column (30 m × 0.25 mm) with a polydimeth-
ylsiloxane stationary liquid phase. The carrier gas was
helium.
The analysis of the TEM images of the Mo–TiO2
catalyst prepared in situ from the Mo(CO)6 precursor
and TiO2 additive showed that agglomerates of TiO2
and Мo particles were formed; the diameter of the for-
mer varied from 30 to 62 nm (Fig. 1). The lines high-
lighted in white correspond to the (101) plane of ana-
tase TiO2 [35].
The MoS2–TiO2 sulfided catalyst is characterized
by a layered structure (Fig. 2) and consists of MoS2
nanoplates, which is evidenced by the interplanar dis-
tance of 0.64–0.75 nm characteristic for the (002)
basal plane of a molybdenum disulfide crystallite [36].
These particles are combined-into-agglomerates
nanoplates [37] localized on the surface of TiO2 parti-
cles with the (002) lattice of the hexagonal phase [35].
RESULTS AND DISCUSSION
Characterization of the Catalysts
The Mo–TiO2 and sulfided MoS2–TiO2 (Ti/Mo =
3.8 : 1) catalysts formed during the hydrogenation
reaction of a 10% solution of 2-methylnaphthalene in
n-hexadecane at 380°С and 50 atm for 2 h and sepa-
rated from the conversion products via centrifugation
were characterized by XPS and TEM. The concentra-
tion and valence state of the elements on the surface of
the catalysts was determined by XPS.
Molybdenum can exist on the surface of the Mo–
TiO2 catalyst in the oxide phase МoOx (Мo6+ and
Mo4+) [26, 27] and in the form of Mo2C [28] and Mo0
[29]. The deconvolution of the Mo3d level showed
It was found on the basis of the statistical process-
ing during the analysis of several micrographs of the
MoS2–TiO2 sulfided catalyst that the average length of
that about 29% molybdenum was in the oxide phase the particles of the active component of the catalyst
МoOx (Мo6+) (Table 1). Molybdenum was also
detected in the form of initial hexacarbonyl and metal-
lic molybdenum Mo0 being formed during the hydro-
genation reaction of naphthalene in the atmosphere of
H2 on the surface of TiO2 (227.6 eV, 4.2%). The spec-
trum presented peaks at 229.2 (29.8%) and 232.0 eV
(37.5%) which, according to [29], correspond to the
initial precursor Mo(CO)6 (3d5/2) and Mo(CO)6
(3d3/2) adsorbed on the surface of TiO2.
was 4.5 nm, while the average number of layers in the
multilayer agglomerate was four.
Catalytic Properties
The dependence of the conversion of the substrate
on the substrate/molybdenum and TiO2/Mo(CO)6
ratios in the raw materials is presented in Fig. 3 by the
example of hydrogenation of 2-methylnaphthalene in
the presence of the Mo–TiO2 catalyst at 400°С and
2 MPa for 2 h. The highest conversion of the substrate
is achieved at a TiO2/Mo(CO)6 ratio of 7.5 : 1 and a
substrate/molybdenum ratio of 18.4 : 1 (44.6%)
and 36.8 : 1 (43.9%). The main reaction products are
2- and 6-methyltetralines; no decalins are formed in
The electron states Ti2p1/2 and Ti2p3/2 correspond
to two peaks with the bond energy of 464.3 (32.1%)
and 458.6 eV (67.9%), which confirms the presence of
Ti4+ in the lattice of TiO2 [27].
In the MoS2–TiO2 sulfided catalyst, molybdenum
can exist on its surface both in the form of molybde- the system; here, 6-methyltetraline is predominantly
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Table 1. Data of XPS for the Mo3d, Ti2p, and S2p levels for the Mo–ТiO2 and MoS2–TiO2 catalysts
Catalyst
Element
Bond energy, eV weight fraction, %
State
MoOx (Мo6+)
Mo–TiO2
(Ti/Mo = 3.8 : 1)
Mo3d
3d5/2
3d3/2
3d5/2
3d3/2
3d3/2
2p3/2
2p1/2
3d5/2
3d3/2
3d5/2
3d3/2
3d5/2
3d3/2
2p3/2
2p1/2
2p3/2
2p1/2
2p3/2
2p1/2
232.8 (22.5%)
235.9 (6.0%)
229.2 (29.8%)
232.0 (37.5%)
227.6 (4.2)
Мo(СO)6 (Мo6+
)
Mo0
TiO2 (Ti4+
)
Ti2p
458.6 (67.9%)
464.3 (32.1%)
228.4 (57.3%)
231.6 (37.0%)
230.1 (0%)
Sulfided MoS2–TiO2,
(Ti/Mo = 3.8 : 1, 2.5% S)
Mo3d
MoS2
MoOxSy
MoOx
233.2 (0%)
232.1 (0%)
235.2 (0%)
S2–
S2p
161.4 (73.1%)
162.6 (26.9%)
S22–
163.5 (0%)
164.3 (0%)
TiO2 (Ti4+
)
Ti2p
458.8 (61.4%)
464.1 (38.4%)
formed (the 6-methyl-/2-methyl- ratio = 80 : 20).
Increasing the reaction time from 1 to 6 h leads to a
Increasing the pressure to 5 MPa promotes an increase small growth in the conversion of 2-methylnaphtha-
in the conversion of the substrate by 15–20%, an lene from 37 to 44% (Fig. 4), which is due to the high
insignificant decrease in the selectivity of the forma- reaction temperature and structure of the substrate.
tion of 6-methyltetraline (the 6-methyl-/2-methyl- Also, the main reaction products are 2- and 6-meth-
ratio = 70 : 30), as well as the formation of decalins (up yltetralins. Even when conducting the reaction for 6 h,
to 14%).
the concentration of decalins does not exceed 2%.
Mo
TiO2
TiO2
Mo
Mo
TiO2
Mo
Mo
Mo
Mo
10 nm
100 nm
Fig. 1. Micrographs of the Mo–TiO catalyst prepared in situ from the Mo(CO) and TiO precursors (Ti/Mo = 3.8 : 1).
2
6
2
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26
ZAKHARYAN et al.
MoS2
50 nm
10 nm
Fig. 2. Micrographs of the sulfided MoS –TiO catalyst prepared in situ from the Mo(CO) and TiO precursors in the presence
2
2
6
2
of elemental S (Ti/Mo = 3.8 : 1, 2.5% S).
50
40
30
20
10
0
2-methylnaphthalene
n-hexadecane
sub/Mo: 18.4 18.4
18.4
18.4
36.8
36.8
36.8
Ti/Mo: 7.5 : 1 3.8 :1 2.5 : 1 1.5 : 1 7.5 : 1 5.0 : 1 3.0 : 1
Fig. 3. The effect of the substrate/Мо and TiO /Mo(CO) ratios on the conversion of 2-methylnaphthalene (400°С, 2 MPa, 2 h).
2
6
The effect of the structural features of the substrate
50
40
30
20
10
0
2-methylnaphthalene
is demonstrated in Figs. 5a and 5b. In the case of the
use of Mo–TiO2 (substrate/Мo = 18.4 and Ti/Mo =
3.8 : 1) as the catalyst in hydrogenation of unsubsti-
tuted naphthalene, the maximum conversion is
achieved at both 400 and 380°С, 69 and 99%, respec-
tively. The presence of a methyl group in position 1 of
naphthalene substantially decreases the yield of tetra-
lins (to 39 and 41%), which is due to the steric hin-
drances during the approach and adsorption of a sub-
strate molecule by the active sites on the surface of the
catalyst. The presence of a substituent in position 2 of
naphthalene no longer has the same effect on the
decrease in the degree of conversion (by just 7%).
n-hexadecane
1 h
2 h
3 h
4 h
6 h
Fig. 4. The kinetics of the conversion of the model mixture
of a 10% solution of 2-methylnaphthalene in n-hexadec-
A substantial effect on hydrogenation of naphtha-
lenes is also caused by the process temperature and
pressure. Thus, for example, when 2,3-dimethylnaph-
thalene is hydrogenated at 400°С and 2 MPa, the yield
of the products is 43%, while in the case of a decrease
by just 20°С and an increase by 3 MPa, it already
is 80%. 2,3- and 6,7-dimethyltetralines are formed as
the products; the fraction of decalins at 400°С and
2 MPa is 6%, while at 380°С and 5 MPa, 3%; the pre-
dominant formation of the 6,7-dimethyl isomer (the
ane at 400°С and 2 MPa over the Mo/TiO catalyst (sub-
2
strate/Мо = 18.4, substrate/Ti = 4.9, and Ti/Mo = 3.8 : 1).
benzene ring is hydrogenated, is an interesting charac-
teristic feature of the processes under these conditions.
The small fraction of the second isomeric product
being formed, 2,3-dimethyltetraline, is explained by
the steric hindrances created by the methyl substitu-
ents in the benzene ring during the adsorption of the
selectivity of up to 80%), in which the unsubstituted substrate on the surface of the catalyst.
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PROMOTED CATALYSTS FOR HYDROGENATION
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(a)
(b)
100
100
75
50
25
0
2-methylnaphthalene
n-hexadecane
naphthalenes
n-hexadecane
75
50
25
0
Fig. 5. The dependence of the conversion over the Mo–TiO catalyst on the substrate type: (a) 400°С, 2 MPa, 2 h,
2
substrate/Мо = 18.4, Ti/Mo = 3.8 : 1 and (b) 380°С, 5 MPa, 2 h, substrate/Мо = 18.4, Ti/Mo = 3.8 : 1.
100
naphthalenes
n-hexadecane
75
50
25
0
1 h
2 h
1 h
2 h
1 h
2 h
1 h
2 h
Fig. 6. The effect of the reaction time on the hydrocracking of 10% solutions of 1- and 2-methylnaphthalenes and 1,5- and 2,3-
dimethylnaphthalenes in n-hexadecane over the Mo–TiO catalyst at 380°С and 5 MPa (substrate/Мо = 18.4 and Ti/Mo =
2
3.8 : 1).
Figure 6 shows the effect of the reaction time
The partial and complete replacement of TiO2 by
(1 and 2 h) and presence of substituents in the sub- acidic Al2O3 during the formation of the catalyst leads
strate on the degree of its conversion. Like in the pre-
vious cases (Figs. 5a and 5b), the position of the sub-
stituent determines the activity of the catalyst and the
yield of the product; the difference in the conversion
of 1- and 2 methyl-substituted naphthalenes is 51%
(the reaction time is 2 h). Such a great difference is
determined by the fact that a competing process,
isomerization of the substrate to 2-methylnaphtha-
lene, occurs during hydrogenation of 1-methylnaph-
thalene [4]. The main products are 5- and 6-methylte-
tralines (the ratio is 75 : 25); the fraction of decalins in
this process, in comparison with 2-methylnaphtha-
lene, reaches 16%. Here, with the increase in the reac-
tion time to 6 h, up to 61% decalins is formed (380°С,
5 MPa, Mo/TiO2: substrate/Мo = 18.4, Ti/Mo =
3.8 : 1). The difference in the reaction times of 1 h has
an unsubstantial effect on the yield of the process of
hydrogenation of all the four substrates.
to a decrease in the conversion of 2-methylnaphtha-
lene (380°С, 5 MPa, 2 h) from 91.8 to 71.3% (Table 2)
and a decrease in the fraction of decalins, from 15.9 to
7.4%. The acidic OH groups on the surface of Al2O3
strongly interact with the OH groups of МoO3, the
main molybdenum phase of the Mo–Al2O3 catalyst,
which leads to a change in the electron structure of the
catalytic surface, thus increasing the acidity of the
final catalyst, which adversely affects the adsorption of
a substrate molecule. According to the published data,
in the case of supported catalysts for hydrodesulfuriza-
tion, CoMo/Al2O3 catalysts exhibit higher activity
than CoMo/TiO2 catalysts [38]. The addition of Сo,
Ni, and Zr promoters also promotes a decrease in the
yield of the product, which acts conversely in the case
of supported catalysts, namely, increases the catalytic
activity of the catalysts [39]. Such a difference in the
catalytic activity between unsupported and supported
catalysts is possibly associated with the structural fea-
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28
ZAKHARYAN et al.
Table 2. The effect of additives on hydrogenation of 2-methylnaphthalene*
Substrate
to metal, mol/mol
Metal 1/metal 2,
mol/mol
Ydec, % Y2-mt, % Y6-mt, % C2-mn, % Cn-С16, %
Catalyst
Mo(СO)6
TiO2
Mo 18.4
Ti 4.9
Ti/Mo,
3.8 : 1
15.9
8.9
23.8
23.2
52.3
58.9
91.8
86.9
3.5
2.4
Mo(СO)6
TiO2 + Al2O3
Mo 18.4
Ti 7.4
Al 7.4
Ti/Al/Mo,
1.9 : 1.9 : 1
Mo(СO)6
Al2O3
Mo 18.4
Al 4.9
Al/Mo,
3.8 : 1
7.4
27.8
26.1
64.8
58.7
71.3
85.6
2.4
2.1
Mo(СO)6 + TiO2
Mo 18.4
Zr 70.2
Ti 4.9
Zr/Ti/Mo
1 : 14.4 : 3.8
10.9
· 6H2O
ZrO(NO3)2
Mo(СO)6+ TiO2 + СoC16H30O4 Mo 18.4
Ti/Mo/Co
7.6 : 2 : 1
12.7
6.7
23.9
21.3
49.3
46
72.3
91.4
3.1
1.9
Ti 4.9
Co 37.2
Mo(СO)6 + TiO2 + NiC16H30O4 Mo 18.4
Ti/Mo/Ni
7.6 : 2 : 1
Ti 4.9
Ni 37.2
*The substrate is a 10% solution of 2-methylnaphthalene in n-hexadecane, 1.25 mmol. Reaction conditions: 2 h, 5 MPa Н , and Т =
2
380°С. C
is the conversion of 2-methylnaphthalene, %; C
is the conversion of 2-methylnaphthalene, %; Y is the yield of
2-mn
n-С16 dec
decalins, %; Y
is the yield of 2-methyltetraline, %; and Y
is the yield of 6-methyltetraline, %.
2-mt
6-mt
tures and properties of nanocrystalline oxides
When conducting the hydrogenation reaction of
TiO2 and Al2O3. In this case, the degree of conversion 2-methylnaphthalene (400°С, 2 MPa, 2 h), the
replacement of TiO2 by Al2O3 also promotes an
increase in the conversion in the case of the use of both
Mo(CO)6 and W(CO)6 precursors (Fig. 8). The use of
oil-soluble tungsten carbonyl leads to a significant
decrease in the conversion, which is possibly
explained by the change in its catalytic properties
during the interaction with nanocrystalline oxides
TiO2 and Al2O3. A similar catalytic activity is also
exhibited by sulfided Мo and W catalysts in hydroge-
nation of naphthalene [40].
of n-hexadecane does not exceed 3.5%, which is due
to the low reaction temperature.
Unlike the case of 2-methylnaphthalene, the par-
tial replacement of TiO2 by Al2O3 (the ratio of 1 : 1) in
the processes of transformation of 1-methylnaphtha-
lene and 1,5- and 2,3-dimethylnaphthalenes promotes
an insignificant increase in the conversion of the sub-
strate by 2–4% (Fig. 7) and a decrease in the degree of
conversion of n-hexadecane to 1.2%.
2
100
75
50
25
0
1
50
2
1
naphthalenes
2-methylnaphthalene
n-hexadecane
n-hexadecane
40
2
1
30
20
10
0
TiMo
AlMo
TiW
AlW
Fig. 7. The effect of the Al O additive on the conversion
2
3
of 10% solutions of 1-methylnaphthalene and 1,5-
Fig. 8. The effect of precursors on the conversion of
2-methylnaphthalene (400°С, 2 MPa, 2 h). Reaction con-
and 2,3-dimethylnaphthalenes in n-hexadecane over the
Mo–TiO catalyst: (1) substrate/Мо = 18.4 and Ti/Mo =
ditions: Mo–TiO , Мо–Al O , W–TiO , and W–Al O ,
2 2 3 2 2 3
2
3.8 : 1 and (2) substrate/Мо = 18.4, Ti/Mo = Al/Mo =
1.9 : 1, and Ti/Al = 1 : 1 at 380°С and 5 MPa.
substrate/Мо = substrate/W = 18.4, Ti/Mo = Al/Mo =
Ti/W = Al/W = 3.8 : 1.
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PROMOTED CATALYSTS FOR HYDROGENATION
29
sharply decreases, which is due to the effect of steric
hindrances (MoS2–TiO2, substrate/Мo = 18.4 : 1,
Ti/Mo = 3.8 : 1, 400°С, 2 MPa, 2 h). The conversion
of n-hexadecane under these conditions does not
exceed 4–7%.
In the case of a decrease in the temperature and an
increase in the pressure (Fig. 11b), the conversion
of naphthalene increases to 96%, the conversion of
2-methylnaphthalene, to 80%, and the conversion of
2,3-dimethylnaphthalene, to 90% (380°С, 5 MPa,
2 h), while the degree of conversion of n-hexadecane
decreases to 2–3%. The effect of the position of the
substituents is also seen from Fig. 11, namely, in the
case of hydrogenation of 1-methylnaphthalene,
during which the percent of isomerization of the sub-
strate to 2-methylnaphthalene is significant.
100
80
60
40
20
0
MoS2-TiO2 Mo-TiO2 MoS2-TiO2 Mo-TiO2
Fig. 9. The effect of the sulfidation of the catalyst on
the conversion of 10% solutions of 1- and 2-methylnaph-
thalenes (Mo–TiO and MoS –TiO catalysts, sub-
2
2
2
strate/Мо = 18.4 : 1, Ti/Mo = 3.8 : 1, 380°С, 5 MPa, 2 h).
Also, the effect of the nature of the additives
(Table 3) and precursors (Fig. 12) was studied by the
example of hydrogenation of 2-methylnaphthalene
(MoS2–TiO2, 400°С, 2 MPa, 2 h). The use of the pre-
cursor of zirconium oxide, ZrO(NO3)2 · 6H2O, (sub-
strate/Zr = 70.2) promotes a decrease in the conver-
sion of the substrate by 24%, while in the case of the
addition of oil-soluble nickel ethylhexanoate
NiC16H30O4 (substrate/Ni = 37.2), the conversion
increases to 53.3%, and the yield of decalins, to 8.1%.
In comparison with molybdenum hexacarbonyl
Mo(CO)6, the use of the W(CO)6 precursor did
not show high results (Fig. 12) (substrate/Мo = sub-
strate/W = 18.4 : 1, Ti/Mo = Al/Mo = Ti/W = Al/W =
3.8 : 1).
The sulfided catalysts prepared in situ were also
studied in the hydrogenation reactions of various
naphthalenes. Molybdenum sulfide MoS2 particles
localized on the surface of TiO2 nanoparticles served
as the active catalytic sites in these catalysts (Fig. 2).
As is seen from Fig. 9, the MoS2–TiO2 unsupported
sulfided catalyst is characterized by lower activity,
thus, 1- and 2-methylnaphthalenes are converted to a
smaller extent in comparison with Mo–TiO2 (380°С,
5 MPa, 2 h); here, the effect of the position of the sub-
stituent in the substrate is preserved. The yield of
decalins did not exceed 10%.
The effect of the substrate/Мo ratio is presented in
Fig. 10 by the example of the MoS2–TiO2 catalyst. The
highest conversion was reached at the substrate/Мo
ratio of 18.4 : 1 and the Ti/Mo ratio of 3.8 : 1 and
2.5 : 1 (400°С, 2 MPa, 2 h). The conversion declined
substantially with the increase in the substrate/Мo
ratio.
The replacement of TiO2 by more acidic Al2O3 also
led to a decrease in the conversion of the substrate as
opposed to the unsulfided catalysts, in which the use
of nanocrystalline Al2O3 promoted an increase in the
conversion (Fig. 8).
With the increase in the reaction time from 2 to 6 h,
When passing from unsubstituted naphthalene to the conversion of 2-methylnaphthalene increases
2,3-dimethylnaphthalene (Fig. 11a), the conversion from 38 to 46.8%, and the conversion of n-hexadec-
50
2-methylnaphthalene
n-hexadecane
40
30
20
10
0
sub/Mo: 18.4
Ti/Mo: 3.8 : 1
18.4
2.5 : 1
18.4
1.5 : 1
36.8
7.5 : 1
36.8
5.0 : 1
36.8
3.0 : 1
Fig. 10. The effect of sub/Мо and Ti/Мо ratios on the conversion of 2-methylnaphthalene (MoS –TiO , 400°С, 2 MPa, 2 h).
2
2
PETROLEUM CHEMISTRY Vol. 58 No. 1 2018

30
ZAKHARYAN et al.
100
(a)
(b)
100
75
50
25
0
naphthalenes
naphthalenes
n-hexadecane
n-hexadecane
75
50
25
0
Fig. 11. The dependence of the conversion over the MoS –TiO catalyst on the substrate type: (a) 400°С, 2 MPa, 2 h, sub-
2
2
strate/Мо = 18.4 : 1, Ti/Mo = 3.8 : 1 and (b) 380°С, 5 MPa, 2 h, substrate/Мо = 18.4 : 1, Ti/Mo = 3.8 : 1.
ane, from 6.1 to 7.3% (MoS2–TiO2, substrate/Мo = sulfide MoS2, which suggests a 100% sulfidation of the
36.8, 400°С, 2 MPa, 2 h).
metal. The formation of highly dispersed MoS2 parti-
cles located on the surface of TiO2 has been found by
transmission electron microscopy. It has been shown
that the catalysts exhibit high activity in the hydroge-
nation reactions of unsubstituted naphthalene, 1- and
2-methyl-naphthalenes, and 1,5- and 2,3-dimethyl-
naphthalenes and selectivity towards the formation of
tetralins. The effect of aluminum and zirconium oxide
CONCLUSIONS
Unsupported Mo–TiO2 and W–TiO2 catalysts pro-
moted by nickel and cobalt, as well as their sulfided
analogues, have been obtained in the work by the
in situ method. It has been found by X-ray photoelec-
tron spectroscopy that, in the MoS2–TiO2 sulfided additives has been studied. The effect of the sub-
catalysts, all the molybdenum is in the composition of strate/precursor and precursor/acidic oxide ratios
Table 3. The effect of additives to the sulfided catalyst on hydrogenation of 2-methylnaphthalene*
Substrate to metal, Metal 1/metal 2,
Ydec, % Y2-mt, % Y6-mt, % C2-mn, % Cn-С16, %
Precursors
mol/mol
mol/mol
Mo(СO)6
TiO2
Mo 18.4
Ti 4.9
Ti/Mo,
3.8 : 1
4
3
14
12
29
31
48.3
34.1
6.2
5.9
Mo(СO)6 + TiO2
Mo 18.4
Ti 4.9
Zr 70.2
Zr/Ti/Mo,
1 : 14.4 : 3.8
+
· 6H2O
ZrO(NO3)2
Mo 18.4
Zr 70.2
Co 37.2
Mo 18.4
Zr 70.2
Ni 37.2
Mo 18.4
Ti 4.9
Co 37.2
Zr/Co/Mo,
1 : 2 : 4
5
2
3
8
12
7
29
15
19
32
45.4
24.6
28.4
53.3
6.4
8.5
6.5
2.9
Mo(СO) +
+ СoC16H30O4
· 6H2O
· 6H2O
ZrO(NO3)2
6
Zr/Ni/Mo,
1 : 2 : 4
Mo(СO) +
ZrO(NO3)2
6
+ NiC16H30O4
Mo(СO)6 + TiO2
+ СoC16H30O4
Ti/Mo/Co,
7.6 : 2 : 1
7
Mo(СO)6 + TiO2
+ NiC16H30O4
Mo 18.4
Ti 4.9
Ni 37.2
Ti/Mo/Ni,
7.6 : 2 : 1
14
*The substrate is a 10% solution of 2-methylnaphthalene in n-hexadecane, 1.25 mmol. Reaction conditions: 2 h, 2 MPa Н , Т = 400°С.
2
C
is the conversion of 2-methylnaphthalene, %; C
is the conversion of 2-methylnaphthalene, %; Y
is the yield of 6-methyltetraline, %.
is the yield of
2-mn
n-С16
6-mt
dec
decalins, %; Y
is the yield of 2-methyltetraline, %; and Y
2-mt
PETROLEUM CHEMISTRY
Vol. 58
No. 1
2018

PROMOTED CATALYSTS FOR HYDROGENATION
31
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Translated by E. Boltukhina
PETROLEUM CHEMISTRY Vol. 58 No. 1 2018