The composition of Ni-Mo phases obtained by NiMoOx-SiO2 reduction and their catalytic properties in anisole hydrogenation

Article abstract of DOI:10.1016/j.apcata.2016.01.025

The specific features of the formation of nickel- and molybdenum-containing phases during the reduction of the oxide precursor of the NiMoO_x-SiO₂ catalyst with hydrogen at three different temperatures (470, 570, and 750 °C) were studied. The reduction behavior was investigated and the reduction temperature of oxide forms was determined with the use of the methods of temperature-programmed reduction, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. It was shown that, at a reduction temperature from 470 to 570 °C, one can observe the formation of NiMoO_x particles with the NiO-type structure, Ni-Mo alloys of different composition, and MoO₂, which pass into the metallic phases Mo, Ni₃Mo, and Ni_xMo_1-x at 750 °C. Nickel located at the surface is completely reduced to the metallic state in the temperature range of 300-750 °C, the Mo° content increases with the growing of treatment temperature and reaches 100% at 750 °C. Based on the data obtained, a reduction scheme for the catalytic system is proposed. The catalytic properties of the systems obtained are studied in the anisole hydrogenation reaction at a temperature of 300 °C and a hydrogen pressure of 6 MPa. The results of catalytic experiments showed that the 750-NiMo-SiO₂ catalyst possesses the highest specific activity in the anisole hydrogenation, which is probably due to the complete reduction of nickel oxide forms and molybdenum to metallic forms, which are highly active in the hydrogenation of C-O bonds and aromatic rings. The highest selectivity in the formation of oxygen-free products can be attributed to the catalysts reduced at 470-570 °C and whose active component contains coordinatively unsaturated molybdenum atoms. The most stable during the thermal treatment in acetic acid is the 750-NiMo-SiO₂ catalyst, which can be explained by the fact that it contains Ni-Mo alloys highly stable in the acid medium.

Full text of DOI:10.1016/j.apcata.2016.01.025

Applied Catalysis A: General 514 (2016) 224–234
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
The composition of Ni-Mo phases obtained by NiMoO -SiO reduction
x
2
and their catalytic properties in anisole hydrogenation
A.A. Smirnov , S.A. Khromova , D.Yu. Ermakov , O.A. Bulavchenkoa,b, A.A. Saraeva,b
a,∗
a,b
a
,
a
a,b
a,b,c
P.V. Aleksandrov , V.V. Kaichev , V.A. Yakovlev
Boreskov Institute of Catalysis SB RAS, Lavrenteva Ave., 5, 630090 Novosibirsk, Russia
Novosibirsk State University, Pirogova Str. 2, 630090 Novosibirsk, Russia
UNICAT Ltd., Lavrentieva Ave. 5, 630090 Novosibirsk, Russia
a
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 July 2015
Received in revised form 15 January 2016
Accepted 19 January 2016
Available online 21 January 2016
The specific features of the formation of nickel- and molybdenum-containing phases during the reduction
of the oxide precursor of the NiMoOx-SiO2 catalyst with hydrogen at three different temperatures (470,
◦
5
70, and 750 C) were studied. The reduction behavior was investigated and the reduction temperature of
oxide forms was determined with the use of the methods of temperature-programmed reduction, X-ray
diffraction analysis, and X-ray photoelectron spectroscopy. It was shown that, at a reduction temperature
◦
from 470 to 570 C, one can observe the formation of NiMoOx particles with the NiO-type structure, Ni-Mo
Keywords:
Ni-Mo alloys
Hydrodeoxygenation
Hydrogenation
Anisole
alloys of different composition, and MoO2, which pass into the metallic phases Mo, Ni3Mo, and NixMo1-x
◦
at 750 C. Nickel located at the surface is completely reduced to the metallic state in the temperature
◦
◦
range of 300–750 C, the Mo content increases with the growing of treatment temperature and reaches
◦
100% at 750 C. Based on the data obtained, a reduction scheme for the catalytic system is proposed.
NiMo-based catalysts
The catalytic properties of the systems obtained are studied in the anisole hydrogenation reaction at a
temperature of 300 C and a hydrogen pressure of 6 MPa. The results of catalytic experiments showed that
◦
the 750-NiMo-SiO2 catalyst possesses the highest specific activity in the anisole hydrogenation, which is
probably due to the complete reduction of nickel oxide forms and molybdenum to metallic forms, which
are highly active in the hydrogenation of C O bonds and aromatic rings. The highest selectivity in the
◦
formation of oxygen-free products can be attributed to the catalysts reduced at 470–570 C and whose
active component contains coordinatively unsaturated molybdenum atoms. The most stable during the
thermal treatment in acetic acid is the 750-NiMo-SiO2 catalyst, which can be explained by the fact that
it contains Ni-Mo alloys highly stable in the acid medium.
©
2016 Elsevier B.V. All rights reserved.
1
. Introduction
rial obtained by this method make it impossible to use the final
treatment products as motor fuels without the use of an additional
step, which is hydrotreating. The main objectives of this process are
to reduce the oxygen content by the hydrodeoxygenation (HDO)
and to increase the hydrogen content by means of the hydro-
genation (HYD). Since the study of the pyrolysis oil hydrotreating
process is very difficult due to the diversity of the composition of
this raw material, so most of the works on the hydrodeoxygenation
are devoted to studying the process not with real pyrolysis oil, but
with its model compounds [2–4] or their mixtures [5–8]. One of the
simplest oxygen-containing model compounds is anisole, which
was studied in a number of articles [9–11]. Due to its simple struc-
ture and a small amount of derivatives, it is also well-suited for
studying the kinetics of the process [12].
An interest in the alternative energy sources, particularly in the
alternative fuels, increases every year, which is primarily due to
such factors as rising prices for oil products and decreasing stocks of
natural resources. This is why more and more attention has recently
been paid to renewable and cheap raw materials, for example,
biomass can act as a partial or complete replacement of the nat-
ural oil. One of the most common ways of biomass treatment is fast
pyrolysis that allows obtaining high product yields at high heating
rates and short contact times [1]. However, the multi-component
composition and the high oxygen content of up to 40% in the mate-
The most frequently examined HDO catalysts commercially
∗ Corresponding author.
E-mail address: asmirnov@catalysis.ru (A.A. Smirnov).
used for petroleum hydrotreatment products are NiMo/Al O3 and
2
http://dx.doi.org/10.1016/j.apcata.2016.01.025
0
926-860X/© 2016 Elsevier B.V. All rights reserved.

A.A. Smirnov et al. / Applied Catalysis A: General 514 (2016) 224–234
225
Table 1
CoMo/Al O [2–4]. Commercial sulfided catalysts are deactivated
due to sulfur removal from the catalysts composition and oxi-
dation of the active sulfide phase is occurred. At the same time,
2
3
The elemental composition of NiMoOx-SiO2.
Ni (wt%)
28
Mo (wt%)
43
SiO2 (wt%)
2
Ni/Mo
addition of sulfur-containing agents (H S, CS ) for maintaining of
2
2
1
catalyst activity results to sulfur contamination of products. As
an alternative for the sulfided catalysts mentioned above, non-
sulfided systems based on transition metals (Ni, Cu, and Mo) were
considered earlier [11–13]. The activity of unsulfided NiMo/Al O
cursor for active component. The 35 g of NiCO ·3Ni(OH) ·2.7H O
3
2
2
2
3
(
Taurus, 98%) and 65 g (NH ) Mo7O ·4H O (Laverna, 99%) were
4
6
24
2
catalysts in the reduced form was also studied in the hydrodeoxy-
genation. In a reaction with a model compound (glacial acetic acid)
a high activity was manifested by a reduced Mo-10Ni/␥-Al O cata-
stirred with an 100 ml ammonia solution at room tempera-
ture. The amounts of the metal precursors were calculated to
obtain a required Ni/Mo ratio—1:1. While stirring for 1 h the 2 ml
ethylsilicate-32 was added to the suspension. The obtained precip-
2
3
lyst (33.2% conversion). After pyrolysis oil is treated in the presence
of the same catalyst, its pH value rose from 2.16 to 2.84 and the
hydrogen content increased from 6.61 to 6.93 wt%. Thus, it was
shown that it is possible to improve the pyrolysis oil properties
during hydrodeoxygenation and esterification of carboxyl groups
of the compounds included in its composition [14]. The high con-
tent of organic acids in pyrolysis oil not only causes its corrosive
properties, such as high corrosiveness and acidity, but also intro-
duces a number of limitations to its application. The pyrolysis oil
hydrodeoxygenation catalysts should possess a sufficient stability
to an acidic environment. The formation of the nickel-molybdenum
alloys results in increasing the corrosion and thermal stability of the
material and improves its hydrogenation activity. Such alloys are
used as heat- and acid-resistant construction materials [15]. Thus, it
was mentioned that the activity of Raney nickel increased twice in
the glucose hydrogenation while doping it with molybdenum [16].
The activity of molybdenum-doped Ni-ZrO2 catalysts was studied
in the hydrodeoxygenation of octanoic acid. It was shown that the
introduction of Mo improves the adsorption ability of hydrogen
and the acid properties of the catalyst. In the case of the bimetal-
◦
itate was filtered, dried during 24 h and calcined at 500 C for 1 h in
air. The elemental composition of NiMoOx-SiO2 is given in Table 1.
The SiO was used as a stabilizing agent, which has no activity in
the hydrogenation process. Before the reaction the catalysts were
activated by reduction with hydrogen; the reduction temperatures
300, 470, 570, and 750 C) were determined from the TPR data.
2
◦
(
2.2. Catalyst characterization
Temperature programmed reduction. Catalyst precursor
NiMoOx-SiO2 (0.1 g) was placed in a U-tube quartz reactor and
treated in a reducing atmosphere (10 vol.% of H2 balanced in Ar
at a flow rate of 20 ml/min) with a constant heating rate of approx-
imately 4 C/min up to 900 C. The hydrogen concentration in the
outlet stream during reduction was measured with a thermal con-
ductivity detector.
◦
◦
The amount of H2 consumed in the runs was quantified by the
peak-area integration method. NiO, which was prepared by calci-
◦
lic catalyst 10Mo/Ni-ZrO , the main product of the octanoic acid
nation of NiCO ·3Ni(OH) ·2.7H O (Taurus, 98%) for 2 h at 600 C in
2
3
2
2
conversion was the C8 alkane with a 77% yield, whereas, in the
air flow, was used to calibrate the TCD response.
presence of Ni-ZrO , the acid converted primarily to the C7 alkane
X-ray diffraction. The phase composition of the spent catalysts
was studied using a D8 X-ray diffractometer (Bruker, Germany)
equipped with the Goebel mirror, generating a parallel X-ray beam
of the CuK˛ radiation (ꢀ = 1.5418 Å).
2
with a 70% yield. Thus, the introduction of molybdenum allows the
hydrodeoxygenation process to be more profitable way in terms of
conservation of the number of carbon atoms [17].
The simplest way to prepare such catalytic systems is the
reduction of nickel molybdate, which is also a precursor of active
structures in the sulfided form. Depending on the reduction
conditions, the result is stable NiMo structures with different com-
position. Thus, Tsurov et al. [18] investigated the composition of the
catalyst and its catalytic properties depending on the ␣-NiMoO4
reduction temperature. It was noted therein that the formation of
a Ni-Mo alloy suppresses hydrogenation, but not hydrogenolysis.
In the present work we studied the activity and stability of Ni-,
Mo-containing catalysts in the hydrotreating of pyrolysis oil using
anisole as a model compound. The catalysts are multicomponent
systems resulting from the reduction of NiMoOx-SiO2 sample in
The chemical analysis of the catalyst surface was performed
using X-ray photoelectronspectroscopy. The XPS measurements
were performed on a SPECS’s Surface Nano Analysis GmbH
(Germany) photoelectron spectrometer equipped with a PHOIBOS-
150-MCD-9 hemispherical electron energy analyzer, a FOCUS-500
X-ray monochromator, and an XR-50M X-ray source with a double
Al/Ag anode. The spectrometer was also equipped with a high-
pressure cell (HPC) which enables to heat samples before analyzing
in gaseous mixtures at pressures up to 0.5 MPa. The core-level
spectra were obtained using the monochromatic AlK˛ radiation
(hn = 1486.74 eV) and fixed analyzer pass energy of 20 eV under
ultrahigh vacuum conditions. The charge correction was performed
by setting the Ni2p3/2 peak at 852.7 eV corresponding to nickel in
the metallic state. Such correction is justified at least for reduced
catalysts with high content of metals [12]. The C1s binding energy of
adventitious carbon surface impurities changed between 284.3 and
284.4 eV that confirmed the suitability of our approach. Relative
element concentrations were determined from the integral intensi-
ties of XPS peaks using the cross-sections according to Scofield [19].
For detailed analysis the spectra were fitted into several peaks after
the background subtraction by the Shirley method. The fitted pro-
cedure was performed using the CasaXPS software. The line shapes
were approximated by the convolution of Gaussian and Lorentz
functions. Before the XPS analysis, the catalysts were additionally
◦
the temperature range of 300–750 C (the sample is prepared by the
sol-gel method, and its main component is NiMoO ). The reduction
4
temperatures were determined according to the temperature-
programmed reduction (TPR) data. To determine the composition
of the active phase after reduction, these systems have been studied
by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy
(
XPS).
2
. Experimental
2.1. Catalyst preparation
◦
reduced in 1 bar H2 at 300 and 400 C for 30 min in the HPC.
A sol-gel method was applied to synthesize NiMoOx-SiO2.
The metallic surface area of the reduced samples was deter-
To obtain a homogeneous system and to avoid the effect of
nickel and molybdenum oxides on reduction processes, the ratio
Ni/Mo = 1 was used. It allowed forming nickel molybdate as a pre-
mined by CO pulse chemisorption measurements using
a
Chemosorb analyzer (“Modern laboratory equipment”, Russia). CO
◦
◦
uptakes were measured at 25 C after prereduction at 350 C. A sto-

2
26
A.A. Smirnov et al. / Applied Catalysis A: General 514 (2016) 224–234
Fig. 1. Set-up scheme:V1–V5—valves; DPC—downstream pressure controller; MFC—mass flow controller; SP—safety pressure rupture disk; DCM—DC Motor; R—reactor;
EF—electric furnace; M—manometer; BPR—back pressure regulator; CV1 and CV2—control valves.
ichiometry of M:CO = 1:1 was assumed, where М was active site
20–22]
The specific surface area (Sco) and average particle size (d) were
respectively. The following temperature program was used for
◦
◦
◦
[
analysis: 70 C hold for 10 min, 15 C/min for 4 min, 280 C hold
for 6 min. A 0.3 ␮l sample was injected into the GC/MS spectrom-
eter with a chromatographic syringe; argon was used as a carrier
gas. The reaction mixture components were identified by retention
times on the chromatogram, which were determined separately for
each component in the calibration process. The internal normal-
ization was used for the quantitative calculation of the component
concentrations in the mixture.
calculated as follows:
ꢀ
ꢁ
m2
g
V
n × am
100
w
Sco
=
N
Av
×
×
22414
m
ꢂ
ꢃ
Vm × m × ×
00 × M × am × V × n
d = 6
1
The deoxygenation selectivity (HDO) was calculated as follows:
23
where N is Avogadro’s number (6.022 × 10 ); V is the adsorbate
Av
ꢄ
3
volume required to form a monolayer coating (cm ); n is the stoi-
0
n
× X −
ni × ai
anisole
chiometric factor of CO adsorption; m is the sample mass (g); am is
i
2
the surface area occupied by the surface atoms (m ); w is the metal
HDO(%) =
0
n
× X
⎞
mass fraction (%); M is the atomic mass of metal (g/mol); Vm is the
anisole
3
⎛
ꢄ
volume occupied by the metal atom (m ).
ni × ai
× X
⎜
⎟
i
2.3. Experimental setup
×100 = ⎜1 −
⎟ × 100
⎝
0
⎠
n
anisole
Catalytic hydrotreatment of anisole was carried out in a high-
pressure setup (Autoclave Engineers, USA) in a sealed 300-ml
stainless steel batch reactor (EZE Seal type). The reactor was
equipped with a magnetic stirrer, a thermocouple, a pressure sen-
sor, and a system for controlling stirring rate, temperature, and
pressure (Fig. 1). Before the reaction, the catalysts (1 g of a fine
0
final
n
− n
anisole
anisole
X(%) =
× 100
0
n
anisole
where n0
is the initial amount of anisole (mol), nfinal is the
powder) were activated directly in the reactor by the reduction in a
anisole
anisole
◦
final amount of anisole (mol), ni is the amount of i-product (mol) in
flow of 100% H (100 ml/min) for 1 h at 350 C and 0.1 MPa. After the
2
the liquid phase (except for unreacted anisole), and a is the number
i
activation, 100 ml of 15 wt% anisole (ACROS Organics, 99%) in unde-
cane (Sigma–Aldrich, 99%) was placed into the reactor at 0.1 MPa
of oxygen atoms in the molecule of i-product.
◦
and 25 C without access of air to prevent the catalyst oxidation.
2.5. Corrosion resistance test
The reactions of anisole were carried out under isothermal condi-
◦
tions (300 C) and a total pressure of 6 MPa. The hydrogen pressure
The catalysts resistance to corrosion in acidic medium was
was kept at the same level in the all experiments. The reaction con-
ditions were selected in terms of the required hydrogen excess to
provide the first-order kinetics with respect to the organic reagents.
During the reaction, liquid products were taken at certain intervals
and analyzed. The stirring rate was 2000 rpm, the catalysts were
used in the form of fine powder, the reaction was carried out in a
tenfold excess of hydrogen with respect to anisole.
determined by the treatment with glacial acetic acid. The catalysts
in the reduced form (1 g) were treated in glacial acetic acid (100 ml)
◦
at 118 C for 2 h, and then the samples were separated from the
solution. The corrosion resistance was calculated from the Ni and
Mo concentrations in the solution and the samples mass loss (wt%)
after the acidic treatment.
2.4. Product analysis
3. Results and discussion
Qualitative analysis of liquid products of the hydrodeoxy-
3.1. Catalyst characterization results
genation and hydrogenation of anisole was carried out using a
Varian Saturn 2000 GC/MS spectrometer equipped with an ion
trap and an HP-5 quartz capillary column (stationary phase: 5%
phenyl—95% dimethylpolysiloxane, column length 30 m, inner
diameter 0.25 mm). Quantitative analysis of the liquid products
was performed using a Hromos GC 1000 chromatograph equipped
with a Zebron ZB-35HT capillary column (stationary phase: 35%
phenyl—65% dimethylpolysiloxane, 30 m × 0.32 mm × 0.25 ␮m).
Temperature programmed reduction technique was applied to
study the reduction behavior of the oxide precursor NiMoOx-SiO2.
The TRP profile is presented in Fig. 2. Reduction of ␣-NiMoO4
was widely discussed in the literature, but there is no consensus
about the sequence of phase transformations and the intermediate
state composition. According to different authors, at the first step
◦
300–600 C NiMoO reduced to Ni and MoO [23]. Ni, MoO , Ni Mo
4
2
2
4
◦
The injector and detector temperatures were 280 and 260 C,
[24], Ni and Mo O , NiMo alloy and MoO [18,25] or to the mixed
2 3 2

A.A. Smirnov et al. / Applied Catalysis A: General 514 (2016) 224–234
227
oxide—NiMoOx [26]. The second stage occurs in a temperature
◦
range of 600–800 C and results in the formation of various metallic
compounds: Mo, NiMo alloys, intermetallics Ni Mo, Ni Mo [24,26].
3
4
The TPR profile also can have various positions of the peaks in dif-
ferent experiments, it depends on the heating rate, crystallite size,
crystallite size, etc [27]. Madeira et al [24] and Brito et al. [27] got a
◦
similar TPR profile, which had two maxima at about 575 and 730 C.
The TPR profile of the calcined sample on Fig. 2 consists of a narrow
◦
◦
peak at 450 C and two broad peaks at 570 and 750 C. The hydrogen
◦
◦
consumption begins at 400 C and has maximum at 450 C. Accord-
ing to this picture, this peak may be assigned to the Ni reduction
28]. In works [27,29] no peak at 450 C was detected, however the
small shoulder at 320–400 C, which then transform to the broad
2+
◦
[
◦
◦
peak at 520–550 C, was observed. A clear shape of this peak in
6+
our case might indicate also the reduction of Mo to the metallic
state, and the transition of Mo6+ to Mo . Probably, the major part of
4+
◦
the process takes place at a temperature of 570 C. It is worth con-
Fig. 2. H2-TPR profile of catalyst precursor NiMoOx-SiO2.
sidering that reduced metallic nickel could activate the hydrogen
molecule, which promoted the reduction of Mo [27]. According
6+
◦
6+
to [29] the peak at 575 C belongs to the reduction of Mo to ␣-
NiMoO while in the case of ␤-NiMoO that peak shifts to the higher
be not homogeneous it could contain individual molybdenum oxide
particles, so the main TPR profile is a superposition of NiMoO4 and
4
4
◦
◦
temperature (635 C). When the reduction performed up to 680 C,
the third peaks appeared. Reduction of residual forms of molybde-
num oxide passes at 750 C. Additionally, the ratios of the first to
◦
MoO /MoO2 profile. That is why there is a shoulder around 800 C.
3
◦
The reduction temperatures 470, 570 and 750 C were chosen
◦
according to the results of TPR experiments: the TPR profile exhibits
maxima near these temperatures. Therefore, it was reasonable to
test the composition of the Ni-Mo-O system after reduction namely
the second signals are larger (S570/S750 = 2.3), suggesting that more
molybdenum is reduced in the first step. Because the sample could
Fig. 3. XRD patterns of catalysts: NiMoOx-SiO2 (a, b), 300-NiMo-SiO2 (c), 470-NiMo-SiO2 (d), 570-NiMo-SiO2 (e), 750-NiMo-SiO2 (f).

2
28
A.A. Smirnov et al. / Applied Catalysis A: General 514 (2016) 224–234
at these temperatures, to elucidate the mechanism of the reduction
of such systems. The reduction of NiMoO4 at these temperatures
results in the formation of different Ni- and Mo- containing phases.
Subsequently, catalytic activity tests were performed to under-
stand the effect of these phases.
In order to identify the reduction products XRD analysis was per-
formed after the reduction at selected temperatures corresponding
◦
to the maxima in the TPR profile and 300 C. Fig. 3 shows the XRD
patterns of the non-reduced catalyst NiMoO -SiO (a, b) and the
4
2
same catalyst activated in H2 at 300 (c), 470 (d), 570 (e), and 750
◦
(
f) C.
The XRD patterns of the NiMoO -SiO2 catalyst in the oxidized
4
state were recorded when the sample was fixed (3a) and when
it rotated at 15 rpm (3b). In those experiments, the only differ-
ences could be found in the relative intensity of the three reflections
(
interplanar distances d = 6.92, 3.47, 2.31 Å) belonging to the phase
MoO ·2H O (JCPDS card No. 01-07-01513). Their varying intensity,
3
2
with and without rotation, indicates that the sample contains few
Fig. 4. Unit cell parameter as a function of Ni-Mo alloy composition.
big grains of MoO ·2H O textured in the [0k0] direction. Hereby the
3
2
sample contains a few big grains of textured MoO ·2H O and non-
3
2
textured oxide MoO ·2H O. At a certain orientation of the sample,
3
2
tion led many authors to conclude that there are different kinds of
intermediates that in the most cases correspond to the composi-
tion of NiMoOx or Ni Mo O [30]. For instant, Rodrigues et al. [31]
large textured MoO ·2H O particles make a big contribution to the
3
2
diffraction pattern (Fig. 3a). Rotation leads to a better averaging (a
larger sample volume). So the contribution of a small amount of
2
3
8
suggested that the intermediate is a mixture of Ni Mo, Ni, and NiO.
4
big grains of textured MoO ·2H O reduces. As a result the intensity
3
2
Moreover, in addition to the reflections of MoO , NiMoO , and
2
y
of the corresponding reflections of MoO ·2H O decreases. More-
◦
3
2
NixMo1-x, the XRD pattern of the catalyst reduced at 570 C showed
the peaks of molybdenum in the metallic state (Fig. 3e). In this case,
the metallic solution has the composition Ni0.84Mo0.16, and its lat-
over, the diffraction pattern contains peaks corresponding to the
NiMoO phase (JCPDS card No. 330948). The analysis of the sample
4
◦
reduced at 300 C showed that the sample contains only the nickel
◦
tice parameter is 3.595 Å. Reduction of the catalyst at 750 C leads
molybdate phase, while the MoO ·2H O phase is absent (Fig. 3c).
3
2
to the formation of Mo, Ni Mo, and Ni Mo
(Fig. 3f). The lattice
3
x
1-x
This is most likely due to the fact that the water evaporates and the
crystalline destructs during heating.
parameter of NixMo1-x is 3.618 Å, which corresponds to the compo-
sition Ni0.79Mo0.21 of the solid solution. Table 2 shows the overall
phase composition data for all samples under the study.
◦
The XRD patterns of the catalyst reduced at 470 C (Fig. 3d) con-
tains the reflections of MoO , however the position of the other
2
Fig. 5 shows the proposed scheme of the catalyst reduction.
peaks is very different from the original angle values. The reduced
catalyst contains a NixMo1-x metallic solid solution of Ni modified
by molybdenum ions. The composition of Ni-Mo solid solutions
was estimated by the linear dependence of the unit cell param-
eter of the known compounds: Mo (JCPDS card No. 421120), Ni
◦
The first stage consists of heating to 300 C, which leads to the
decomposition of the crystalline hydrate and the formation of an
amorphous molybdenum oxide. When nickel molybdate is reduced
◦
in hydrogen at 470 C, NiMoO converts to a NiMoOx oxide with the
4
NiO-type structure and the formation of MoO2 and the NixMo1-x
(
JCPDS card No. 040850), Mo0.09Ni0.91 (JCPDS card No. 105048),
2+
solid solution. In this case, Ni reduced to a metallic nickel acti-
Mo0.36Ni0.64 (JCPDS card No. 105045), and Mo0.984Ni0.016 (JCPDS
card No. 105049) on the content of “x” in NixMo1-x (Fig. 4). The
unit cell parameter (3.575 Å) can be used to determine the com-
vates H2 and contributes to the reduction of Mo6+ to Mo (MoO2)
4+
[32] with a subsequent formation of an alloy. Upon activation of
◦
the catalyst at 570 C, MoO is partially reduced to molybdenum in
2
position of the solid solution, which corresponds to Ni0.88Mo0.12
.
the metallic state. At the final stage corresponding to the reduction
The other peaks can be attributed to the Ni-Mo-oxide phase with a
NiO-type structure whose reflections are displaced toward distant
angles with respect to NiO. The composition of this phase is still
not completely determined. Thus, the study of the NiMoO4 reduc-
◦
temperature of 750 C, the alloy is partially reduced to Ni Mo and
3
MoO2 is completely reduced. The formation of Ni Mo may occur
3
from NixMo1-x alloy or NiO-type particles. To determine the forma-
tion way we decided to carry out the additional XRD study of sample
Fig. 5. Catalyst reduction scheme. The crystalline hydrate reduction is shown in italic.

A.A. Smirnov et al. / Applied Catalysis A: General 514 (2016) 224–234
229
Table 2
The phase composition of the catalyst.
Catalyst
NiMoOx-SiO2
300-NiMo-SiO2
NiMoO4
470-NiMo-SiO2
570-NiMo-SiO2
750-NiMo-SiO2
The phase composition
NiMoO4
MoO3·2H2O
MoO2, NiMoOx
Ni0.88 Mo0.12
MoO2, NiMoOy
Ni0.84Mo0.16
Mo
Mo
Ni0.79Mo0.21
Ni3Mo
the XPS data are shown in Table 4. As can be seen, the atomic ratio
of Ni/Mo for the catalysts increases along with the temperature of
pre-treatment in hydrogen, which can be associated with the nickel
segregation to the surface. It also shows that molybdenum is in the
◦
oxide form on the surface at a temperature of 300 C, and it is mainly
in the metallic state at 750 C.
◦
Fig. 7 shows the Ni2p and Mo3d spectra of the catalysts. The
shape of Ni2p spectra indicates that nickel in the catalysts is in the
metallic state. Indeed, the Ni2p spectra contain two sharp Ni2p3/2
and Ni2p1/2 peaks at 852.7 and 869.9 eV, which correspond to nickel
in the metallic state. This is also indicated by the shape of the Ni2p
spectra and by the value of the spin-orbit splitting (difference in the
Ni2p1/2 and Ni2p3/2 binding energies) equal to 17.2 eV (Table 5). For
nickel in the oxidized state Ni2+, this value is 17.6–17.8 eV [35–38].
Moreover, the Ni2+ compounds have the higher Ni2p3/2 binding
energies and shake-up satellites, which are ∼6 eV higher on the
binding energy scale from the main peak. The presence of these
satellites determined by multielectron processes [34–36] is charac-
teristic only for Ni2+ compounds. For example, the intense shake-up
satellites are observed in the spectra of NiO, Ni(OH)2, NiSiO3, etc.
◦
Fig. 6. XRD patterns of catalysts NiMoOx-SiO2 reduction at 700 C.
◦
reduced at 700 C (Fig. 6). According to the data obtained the heat-
ing of sample at 700 C causes to formation of two metallic phases:
significant amount of Mo and the Ni0.81Mo0.19 solid solution. The
content of Mo and MoO2 at 570 C is very small and it cannot give
enough quantity of molybdenum at 700 C. Also the sequence of for-
mation Ni0.88Mo0.12–Ni0.84Mo0.16–Ni0.81Mo0.19 requires increasing
of molybdenum content. These facts suggest that the molybdenum
◦
[
39–41]. At the same time, the spectra of metallic nickel and of Ni3+
◦
◦
compounds do not have these satellites [33,42]. The decomposition
of the spectra into individual components indicates that nickel is
completely reduced to the metallic state.
◦
In the 470-NiMo-SiO2 catalyst, molybdenum is partly reduced
◦
to the metallic state. When reduction is carried out at 750 C,
can be formed from the NiMoOx structure. In addition, the XRD data
◦
molybdenum is reduced completely. Thus, we observe the single
Mo3d5/2-Mo3d3/2 doublet in its spectra with the binding energy
of Mo3d5/2 equal to 227.4 eV, which corresponds to molybdenum
in the metallic state, for which the Mo3d5/2 binding energies are
given in the literature in the range 227.7–227.9 eV [43–45]. The
value 227.4 is different from the literature data; it is due to the
chemical shift of Mo3d5/2 peak.
at 700 C shows that Ni Mo is produced from the NixMo alloy.
3
1-x
The XRD results are consistent with TPR data. The amount of H2
consumed in the TPR runs indicates that the oxide form of cata-
lysts is completely reduced to the metallic state. Indeed, TPR data
for the NiMoOx-SiO2 sample (see Table 3) show that the total H2
consumption is 17.6 mmol/g, which is close to the calculated value
7.9 mmol/g required to reduce the total amount of NiMoO4 in
the sample. The small amount of amorphous MoO3 was not taken
into account during the calculation. The reduction of the catalyst at
50 C resulted in a H uptake of 1.5 mmol/g, which is equivalent to
1
In the Mo3d spectrum of the catalyst 470-NiMo-SiO , we
2
observe two doublets Mo3d5/2-Mo3d3/2 with the Mo3d5/2 bind-
ing energies equal to 227.8 and 229.6 eV. The first doublet can be
attributed to molybdenum in the metallic state, and the second
◦
4
2
the reduction of less than 30% of nickel assuming, 1) the stoichiom-
4+
2+
◦
one—to molybdenum in the Mo state. The Mo3d5/2 binding ener-
etry for the direct reduction of Ni to Ni and 2) the reduction of
molybdenum with the formation of an alloy Ni0.88Mo0.12. This indi-
cates that most of nickel is reduced at higher temperatures. The
reduction of the catalyst at 570 C resulted in the H2 consumption
of 11.3 mmol/g, which is sufficient for the partial reduction of Ni
Mo and Mo . According to the XRD, nickel at this temperature
is not completely reduced, which can be due to strong interaction
of Ni with Mo in NiO-type structures. Besides, the content of Mo
gies of Mo4+, Mo , and Mo are given in the literature varies in the
ranges of 229.2–229.9, 230.8–231.6, and 232.7–233.2 eV, respec-
tively [43–47]. There are two Mo3d5/2-Mo3d3/2 doublets observed
for the catalyst 300-NiMo-SiO2 with the Mo3d5/2 binding energies
equal to 229.0 and 231.3 eV. These values correspond to molybde-
num in the Mo4+ and Mo states, respectively.
5+
6+
◦
2
+
,
6+
4+
5+
◦
◦
and MoO2 at 570 C is very small while the Ni content in the NiMo
3.2. Catalytic activity of NiMoOx-SiO2 in anisole hydrotreatment
alloy is very high. Thus, the amount of NiO in NiMoOx is very low.
◦
It can be assumed that the TPR peak at 750 C corresponds mostly
The main product obtained during the hydrotreatment
of anisole is cyclohexane; the intermediate components are
methoxycyclohexane, cyclohexanol, benzene, and methylanisoles.
According to mass-spectrometric data, unidentified products that
may appear because of polymerization or other side reactions were
not formed. According to the results of the composition of liquid
products after the reaction, we proposed an anisole conversion
scheme that includes three reaction pathways (Fig. 8). The first
reaction pathway is for the hydrodeoxygenation of anisole with
a cleavage Car. O bound and the formation of benzene, which then
converts to cyclohexane. The second pathway is meant for the
to the reduction of molybdenum oxide. For the complete reduction
of molybdenum from Mo4+ to Mo in the sample NiMoO -SiO , the
◦
4
2
necessary consumption of H2 would be 9.1 mmol/g. Therefore, the
H2 uptake of 4.8 mmol/g, which was observed in the third peak, is
equivalent to the reduction of 52% of Mo to Mo .
To study the chemical composition of the near-surface layer,
the samples were investigated by XPS. Before recording spectra,
the samples were pre-reduced directly in the high-pressure cell of
4+
◦
◦
the spectrometer in hydrogen at 300 C. The relative atomic con-
centrations of the detected elements determined on the basis of

2
30
A.A. Smirnov et al. / Applied Catalysis A: General 514 (2016) 224–234
Table 3
TPR data of NiMoO4-SiO2 samples.
Tonseta
(
◦
C)
Tmaxb
(
◦
C)
Ttermc
( C)
◦
H2 consumption (mmol/gcat)
Peak
1st peak
2nd peak
3rd peak
350
480
670
450
570
750
480
665
840
1.5
11.3
4.8
Total H2 consumption (mmol/gcat) −17.6
a
Temperature of the onset of a reduction peak.
Temperature of the peak maximum.
Temperature of termination of a reduction peak.
b
c
Table 4
The relative elements concentrations in the surface layer of the investigated catalysts.
◦
◦ a
Catalyst
[Ni]/[Mo]
[Ni ]/[Niall] (%)
[Mo ] /[Moall] (%)
[Si]/[Mo]
300-NiMo-SiO2
470-NiMo-SiO2
570-NiMo-SiO2
750-NiMo-SiO2
0.08
0.38
0.39
0.57
100
100
100
100
0
–
68
81
100
0.35
0.66
0.57
a
The peak position in the region 227.5–227.8 eV, corresponding molybdenum in the metallic state.
Fig. 7. The Ni2p and Mo3d spectra of the catalysts studied. The Ni2p spectra are normalized to the integral intensity of the corresponding Mo3d spectra.
Table 5
The of Mo3d5/2, Ni2p3/2, and O1s binding energies (eV) determed for the catalysts.
Catalyst
Mo3d5/2 (ox.)
Mo3d5/2 (metal.)
Ni2p3/2
ꢁNi2pa
O1s
3
00-NiMо-SiO2
229.0
–
852.7
17.2
530.1
531.0
231.3
5
32.1
4
5
7
70-NiMо-SiO2
70-NiMо-SiO2
50-NiMо-SiO2
229.6
227.8
228.1
227.4
–
852.70
852.7
852.7
853.8
852.7
17.2
17.2
17.2
17.7
17.2
530.2
5
32.7
229.2
530.5
5
32.8
–
–
–
530.1
5
32.9
NiOb
529.5
5
–
31.6
Nic
–
a
The value of the spin-orbit splitting equal to the difference in the Ni2p1/2 and Ni2p3/2 binding energies.
Nickel oxide previously obtained by oxidizing a nickel foil in oxygen directly in HPC of the spectrometer.
Pre-cleaned nickel foil (Ni 99.99%).
b
c

A.A. Smirnov et al. / Applied Catalysis A: General 514 (2016) 224–234
231
Fig. 8. The proposed scheme of anisole conversion pathways (ki is the first-order rate constants).
hydrogenation of the aromatic ring of anisole with the formation
of methoxycyclohexane. The third pathway includes an additional
reaction of methyl substitution of anisole in the benzene ring with
subsequent processes of hydrogenation and hydrodeoxygenation
of methylanisoles obtained. The third pathway includes an addi-
tional reaction of methyl substitution of anisole in the benzene ring
with subsequent processes of hydrogenation and hydrodeoxygena-
tion of methylanisoles obtained. In this case, there is a possibility
of reverse demethylation. Thus, Odebunmi and Ollis [48] studied
k1 that an increase of the catalyst reduction temperature lowers
the contribution of the HDO pathway. For the 750-NiMo-SiO cata-
2
lyst, the reaction rate constant along the pathway of methylanisole
formation equals zero, though methylanisoles were found in their
composition during the analysis of the reaction products. This is due
to the fact that, during the heating of the reaction medium in the
absence of hydrogen, the methylation of anisole also takes place.
For the 470-NiMo-SiO2 and 570-NiMo-SiO2 catalysts, the forma-
tion of methyl-substituted products occurs at a higher rate with the
subsequent formation of methylcyclohexane, which indicates that
these catalysts are easier to methylate as compared to the sample
the hydrodeoxygenation of m-, o-, and p-cresols on CoO-MoO /␥-
3
Al O sulfided catalysts, in which case the main product was
2
3
◦
methylcyclohexane.
reduced at 750 C.
The kinetic modeling was based on the proposed scheme of
reactions, and calculations were carried out with the use of the
To determine the specific activity of the catalysts, we studied
their metal surface by the CO chemisorption method. The results
are presented in Table 7. The HDO pathway corresponds to the
hydrogenolysis of the Car. O bond in the anisole molecule without
hydrogenation of the aromatic ring. The HYD pathway corresponds
to the hydrogenation of the aromatic ring in anisole without oxygen
removal.
The average particle size increases with an increase in the reduc-
tion temperature, which is caused by the sintering of the particles
during reduction. There is no certain dependence of the specific
activity on the reduction temperature. For example, the activity of
the sample 570-NiMo-SiO2 is lower than that of the sample 470-
following model:
ꢄ
dC
n
i
=
R , R =
rm, rm = kmCm ,where km is the rate constant,
i
i
dt
m
C and Cm are the mole fractions of each component, R is the reac-
i
i
tion rate, n is the order of the reaction (n = 1 for all reactions except
the reaction of the formation of methylanisole from anisole, where
n = 2). An experimental point serves as t = 0, are equal to the mole
fractions of the corresponding compounds at the first point.
The system of equations was solved by the numerical integration
using the Runge-Kutta method, and the kinetic parameters were
found by the minimization of the sum of squared differences of
the estimated and experimental values of the mole fraction of each
compound for each experimental point. The minimizing function
has the form:
NiMo-SiO . At the same time, the specific catalytic activity of the
2
◦
sample reduced at 750 C exceeds several times the specific activ-
ity of the other catalysts. This is true for the specific activity in
both HDO and HYD. The high specific activity of the sample 750-
NiMo-SiO2 may be due to the nature of its active component: all
metallic particles in this catalyst are in the reduced state. Thus, the
complete reduction of nickel to the metallic state leads to a higher
activation of molecular hydrogen on the catalyst surface, which
causes the high specific activity in the hydrogenation of anisole. At
ꢀ
ꢁ
2
ꢄꢄ
Cijexp − Cijcalc
F =
C
ijexp
i
j
where j is the number of the experimental point;
◦
the same time, in the samples reduced at 470 and 570 C, nickel
i is the serial number of the compound from the reaction scheme
is respectively in the form of alloys Ni0.88Mo0.12 and Ni0.84Mo0.16
.
(
anisole, benzene, cyclohexane, cyclohexanol, methylcyclohexane,
Its content in the composition of the alloy decreases, resulting in a
slight decrease in the specific activity.
methoxycyclohexane, and methylanisole). The concentration vari-
ations of the species in the reaction mixture as a function of reaction
time and kinetic modeling results are shown in Fig. 9.
Fig. 9 shows that the concentration of transitional products
for each sample does not exceed 8 mol%, which indicates a high
hydrogenating activity of catalysts under these conditions, and that
leads to a high yield of the final product (cyclohexane). The studies
have shown that an increase in the reduction temperature reduces
the yield of byproducts formed during the methylation of anisole
In contrast, the effective activity, which is defined via unnor-
malized constants k , was the higher, the lower was the reduction
i
temperature. The activity decreases with an increase in the par-
ticle size, but this dependence is nonlinear. For example, for the
samples 570-NiMo-SiO2 and 750-NiMo-SiO , the 12-fold increase
2
in the particle size leads to the 2-fold decrease in the activity, while
for the samples 470-NiMo-SiO and 570-NiMo-SiO , an increase in
2
2
the particle size as low as 1.2-fold leads to the 1.6-fold decrease in
the activity. Thus, the particle size is not the main reason for the
activity decrease.
(
methylcyclohexane and methylanisole) and reached with the use
of the 750-NiMo-SiO2 catalyst.
Table 6 presents the estimated values of the constants of the
reaction rates of anisole conversion. It follows from the values of

2
32
A.A. Smirnov et al. / Applied Catalysis A: General 514 (2016) 224–234
◦
Fig. 9. Concentration profiles of the reactant and products as a function of reaction time. Reaction conditions: 300 C, 6 MPa, mcatalyst = 1 g. The points are experimental data
and the lines are calculated from the first-order kinetics model.
Table 6
◦
The values of the reaction rate constants for anisole conversion at 300 C, PH2 = 6 MPa.
k1 (min 1 103)
−
k2 (min
−1
102)
k3 (min
−1
102)
k4 (min
−1
)
k5 (min
−1
103)
k6 (min
−1
)
k7 (l min
−1
mol 105)
−1
−1
102)
k8 (min
Catalyst
470-NiMo-SiO2
570-NiMo-SiO2
750-NiMo-SiO2
2.4 ± 0.2
2.33 ± 0.04
1.22 ± 0.01
1.197 ± 0.006
3.3 ± 0.1
0.99 ± 0.04
0.78 ± 0.02
0.22 ± 0.01
5.1 ± 0.4
12 ± 1
0.270 ± 0.002
0.74 ± 0.03
0.13 ± 0.01
4.01 ± 0.05
2.34 ± 0.05
0
3.11 ± 0.04
1.95 ± 0.05
0.48 ± 0.02
1.57 ± 0.09
1.12 ± 0.07
1.11 ± 0.02
0.27 ± 0.02
8.4 ± 0.2
Table 7
Textural characteristics of the catalyst by CO chemisorption and general and specific activity in HDO and HYD pathway in anisole conversion. kHDO = k1/mcat, kHYD = (k3 + k5)/mcat,
kHDO + HYD = (k1 + k3+ k5)/mcat, k ´ı i = ki mcat/Sco.
2
Catalyst
Sco (m /g)
Average
size (nm)
kHDO
(min
k ´ı HDO
(min
kHYD
(min
k ´ı HYD
(min
kHDO + HYD
k ´ı HDO + HYD
(min
−1
−1
102)
−1
−2
102)
−1 −1
102)
−1
−2
102)
−1 −1
102)
−1
−2
102)
m
g
m
g
m
(min
g
470-NiMo-SiO2
570-NiMo-SiO2
750-NiMo-SiO2
6.3
5.4
0.4
106
124
1503
0.24
0.157
0.112
0.038
0.029
0.28
3.81
2.31
1.11
0.60
0.43
2.775
4.0
2.5
1.23
0.64
0.46
3.075

A.A. Smirnov et al. / Applied Catalysis A: General 514 (2016) 224–234
233
Fig. 11. The dependence of the Ni and Mo mass loss and Mo content on the catalyst
surface vs. the catalyst reduction temperature.
Fig. 10. HDO selectivity of different catalysts.
3
.3. The catalysts stability
The HDO selectivity was calculated according to the formula
referred to in Section 2.4. The data obtained for the catalyst are
shown in Fig. 10. As seen from the picture, the best HDO selectivities
To determine the corrosion resistance of the catalysts, the
reduced forms of the original sample were subjected to desalination
in a solution of concentrated acetic acid at 118 C. As shown by XPS
and XRD, the reduction of nickel molybdate causes the formation of
the oxide of the NiMoOx and MoO2 compounds within and Ni on
the surface of catalysts that can be subjected to the partial dissolu-
tion in acetic acid. Fig. 11 shows that the corrosion resistance of the
reduced NiMoOx-SiO samples (estimated by acetic acid treatment)
increases with rising the catalysts reduction temperature, which is
accounted for by the increase of Ni-Mo alloys content in the sam-
ples. Moreover, it is known that the molybdenum content in the
alloy increases along with its corrosion resistance. If the molybde-
num content is higher than 15% in the nickel-molybdenum alloy
of stands in the solution of mineral acids, the alloy corrosion rate
reduces 16 times in 10% HCl at 70 C with increasing the molyb-
denum content from 5% to 25% [52]. This explains the small mass
loss of the 750-NiMo-SiO2 sample that contains the Ni0.79Mo
and Ni Mo alloys. In the case of catalysts reduced at 470 and 570 C
alloys and pure molybdenum was observed, nevertheless mass loss
value for them was at 2–4 times higher than one was for 750-NiMo-
SiO . This may be due to the fact that significant metal dissolution
occurs during the reaction of the oxide forms of Ni and Mo with
acetic acid. Fig. 11 shows that the catalyst stability increases with
increasing of Mo form on the catalyst surface. Thus, when real
were achieved when the NiMoO -SiO system was reduced at 470
4
2
◦
◦
◦
and 570 C. The selectivity is lower for the sample reduced at 750 C.
It is practically in agreement with the values of kHDO for all samples.
Actually, the HDO selectivity is determined not only by the HDO
constant of anisole conversion but also by the sum of all possible
◦
pathways. For example, conversion of cyclohexanol (k ) leads to
4
the formation of non-oxygenate cyclohexane, the concentration of
which is taken into account in the calculation of the HDO selectivity.
2
The high HDO selectivity for the 470-NiMo-SiO and 570-NiMo-
2
SiO2 catalysts can be due to the fact that the surface of these
catalysts contains a significant amount of molybdenum in the oxide
form. Thus, according to the XRD data, the catalyst contains the
MoO2 and NiMoOx particles in which molybdenum may be in dif-
◦
ferent charge states, though the XPS data suggests that the surface
of these two samples only contains Mo4+ whose concentration
reaches 32% and 19%, respectively. This, in its turn, leads to a high
0.21
◦
degree of hydrodeoxygenation as compared to the 750-NiMo-SiO
3
2
◦
◦
system containing only Mo and Ni [49]. In this case, the 470-
NiMo-SiO2 catalyst demonstrates a higher effective activity and
selectivity to oxygen removal due to a higher content of coordi-
natively unsaturated molybdenum. The effect of a metal oxide on
the catalyst activity in oxygen removal is well-described by the
Mars—van Krevelen mechanism [50]. according to which a reduc-
ing agent (hydrogen) adsorbs on the surface of the oxide catalyst
and removes the surface oxygen in the form of water, thereby creat-
ing a vacancy for the adsorption of oxygen-containing molecules.
The second stage is replenishing the oxygen vacancies from the
anisole molecule (in this case, with a cleavage of Car O bond). Also
of great importance is the amount of nickel on the catalyst surface,
which contributes to the dissociative adsorption of the hydrogen
molecule and further spillover of hydrogen from the metal surface
onto the molybdenum oxide [51]. This is also a reason for the similar
activity and selectivity of catalysts obtained in the reduction of the
2
◦
material with high pH value is used, the 750-NiMo-SiO2 sample,
which also has a very high specific activity, has significant advan-
tage compared to other catalysts.
4
. Conclusions
The catalytic activity and selectivity of the samples reduced at
◦
4
70–750 C in the anisole hydrogenation were studded. The data
obtained showed that the most specific activity is possessed by the
50-NiMo-SiO2 catalyst, which is possibly related to the complete
7
◦
original sample at 470 and 570 C, and the ratio Ni/Mo for these two
reduction of oxide forms of nickel and molybdenum to the metal-
lic forms having a high activity both in the hydrogen adsorption
and the hydrogenation of the C O bonds and the aromatic ring. In
addition to that, the high selectivity in the formation of oxygen-
free products is possessed by the catalysts reduced at 470–570 C,
which can be explained by a high content of molybdenum in the
systems is 0.38 and 0.39 compared with the data of XRD showed
the ratio Ni/Mo in alloy 0.88 and 0.84, respectively. As noted above,
the 750-NiMo-SiO2 catalyst has the largest specific activity, which
indicates a high effect of the spillover as the ratio Ni/Mo for this
sample is 0.57.
Thus, it was shown that the reduction temperature of the
NiMoOx form significantly affects the composition of the products
of the hydrogenation of anisole and the selectivity toward oxygen-
free products.
◦
4+
form of Mo . It is also shown that the yield of side products (methy-
lanisoles) decreases with an increase of the reduction temperature.
The 750-NiMo-SiO2 sample is the most stable catalyst, which is
due to a high resistance to corrosion of NiMo alloys. Since the

2
34
A.A. Smirnov et al. / Applied Catalysis A: General 514 (2016) 224–234
main requirement for the HDO catalyst is the total oxygen removal,
which is characterized by HDO selectivity, the most suitable cata-
lysts are the systems reduced at 470 and 570 C. However, the use
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