Room Temperature Synthesis and Characterization of Hybrid Nanoparticles of NiMo over the Surface of Mixed Oxides (Al2O3-TiO2 and Al2O3-ZrO2) Using Ultrasound Radiation

Article abstract of DOI:10.1007/s10562-014-1410-6

Two novel catalysts of nano-hybridized Ni-Mo over Al₂O₃/TiO₂ and Al₂O₃/ZrO₂ were synthesized through a newly designed procedure by using ultrasonic irradiation and characterized by X-ray diffraction, UV-Vis diffuse reflectance spectra, FT-IR, energy dispersive X-ray spectroscopy and transmission electron microscopy. Then, the catalytic activities of these catalysts were examined in the oxidation of toluene by O₂ in various conditions of pressure, time and temperature. The products were analyzed by GC and GC-MS. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-014-1410-6

Catal Lett
DOI 10.1007/s10562-014-1410-6
Room Temperature Synthesis and Characterization of Hybrid
Nanoparticles of NiMo over the Surface of Mixed Oxides
(Al2O3–TiO2 and Al2O3–ZrO2) Using Ultrasound Radiation
•
Elham Morteza Gholizadeh Mehran Ghiaci
Received: 10 August 2014 / Accepted: 25 October 2014
Ó Springer Science+Business Media New York 2014
Abstract Two novel catalysts of nano-hybridized Ni–Mo
over Al2O3/TiO2 and Al2O3/ZrO2 were synthesized through
a newly designed procedure by using ultrasonic irradiation
and characterized by X-ray diffraction, UV–Vis diffuse
reflectance spectra, FT-IR, energy dispersive X-ray spec-
troscopy and transmission electron microscopy. Then, the
catalytic activities of these catalysts were examined in the
oxidation of toluene by O2 in various conditions of pressure,
time and temperature. The products were analyzed by GC and
GC–MS.
suitable way for tailoring particle size at the nano level [5].
The particles prepared in a reverse micellar solution are
generally very fine and mono dispersed. Many kinds of
nanoparticles have been obtained in reverse micellar
solution [6–8], including metals, metal oxides, polymers,
metal sulfides, and metal selenides.
Furthermore, one of the most common techniques for
deposition of nanoparticles over different supports is using
ultrasound irradiation. Ultrasound has a frequency between
2 9 104 and 2 9 106 Hz. When ultrasonic wave passes
through a liquid medium, a large number of micro bubbles
form, grow, and collapse in a very short time about a few
microseconds, which is called ultrasonic cavitation [9]. The
advantages of ultrasound in chemical processes are the
possibility of lower reaction temperature, increasing kinetic
reaction rates; higher yields and selectivity. Ultrasonic
cavitation is well known to be the origin of these chemical
advantages [10].
Keywords Nano-hybridized Ni–Mo Á Sonochemical Á
Mixed oxide Á Sol–gel Á Reverse micelle
1 Introduction
Nano catalysis is one of the most exiting subfields of nano
science. These kinds of catalysts are thought to be a bridge
between homogeneous and heterogeneous systems which
offer distinct and tunable chemical activity, specificity and
selectivity [1–4]. The high activity of nano catalysts has
been attributed mostly to the formation of well-dispersed
nanoparticles over the support. Also, preparation of uni-
form sized nanoparticles has become a very important
research issue, and various techniques have been used for
this purpose.
Besides, metal molybdates are of great technological
interest due to their attractive properties, especially
potential applications in catalysis [11–16]. Among differ-
ent kinds of metal molybdates, nickel molybdates have
become more important because of their application in
catalysis such as oxidative dehydrogenation of light
alkanes [15], hydrodesulfurization, hydrodenitrogenation
[17, 18], hydrodeoxygenation [19–21], etc. Up to now,
many investigations have been carried out on the synthesis
of nickel molybdate materials [14, 22–24]. The most
common method used for preparation of the nickel
molybdate is the co-precipitation technique which the
effects of various parameters on the resulting product have
been investigated [14, 22]. Furthermore, other techniques
including reactive puttering [23], thermal treatment of
organic salts [24], and sonochemical synthesis [25] have
also been used.
Among various methods which have been used to syn-
thesize nanoparticles with controlled morphology and
structure, using reverse microemulsions seems particular
E. Morteza Gholizadeh (&) Á M. Ghiaci
Department of Chemistry, Isfahan University of Technology,
84156-83111 Isfahan, Iran
e-mail: elham.gh1985@gmail.com
123

E. M. Gholizadeh and M. Ghiaci
Scheme1 Model for
preparation of catalysts
Nevertheless, sometimes embedding nanoparticles over
the supports cause nanoparticle aggregation. So based on
this drawback, in this study we report a new procedure to
fabricate nano-hybridized NiMo catalyst by deposition
ultrasonically on two different mixed oxides (Al2O3/TiO2
and Al2O3/ZrO2), before taking them out of a reverse
micelle solution. Finally, the activity of these catalysts was
measured in the liquid phase oxidation of toluene with
molecular oxygen (see Scheme 1). To the best of our
knowledge, there is no report on this method and study on
the supported nanoparticles of NiMoO4. Also, this is the
first report regarding the use of NiMo nanoparticles for the
liquid phase oxidation of toluene by O2. As a matter of fact,
although several articles have described the use of a het-
erogeneous catalyst for the oxidation of toluene [26–28],
none of them have used supported NiMo nanoparticles for
toluene oxidation. However, NiMo containing catalysts
have been used for oxidation of toluene where a 70 % yield
of benzaldehyde was achieved in fixed bed reactor with
NiMoO4 activated in 450 °C [29]. This is therefore the first
report regarding the use of NiMo nanoparticles for the
liquid oxidation of toluene.
Aluminum tri-bisbutylate (97 %) and 0.01 mol (2.96 mL)
Titanium (IV) i-propoxide (99 %) as precursors, were
dissolved in the solvent, n-butanol. The solution was
heated to 80 °C. The components were thoroughly mixed.
Then, the solution was cooled down to room temperature,
and 2,4-pentandione (H-acac) as the complexing agent was
added [1, 5, 30]. This clear solution was hydrolyzed with
deionized water. The solutions were left overnight to
hydrolyze the alkoxides yielding transparent gels. The
transparent gels were dried at 120 °C to remove water and
solvent, and then calcined at 500 °C for 5 h to remove the
organics.
Al2O3/ZrO2 support was prepared in a similar manner
as mentioned above, but only 0.01 mol (3.1 mL) Zirco-
nium (IV) isopropoxide (70 wt% solution in 2-propanol)
was used instead of Titanium (IV) i-propoxide.
2.3 Preparation of Nano-Hybridized NiMo
A general protocol was also used to prepare hybridized
NiMo nanoparticles by the water-in-oil microemulsion.
Reverse microemulsion solution was prepared by dissolv-
ing 26 mmol of anionic surfactant bis-(2-ethylhexyl) sul-
fosuccinate (AOT) in 500 mL dry n-hexane. Only doubly
distilled and deionized water was used in this experiment.
The clear appearance of the solution implicates the for-
mation of the microemulsion.
2 Experimental
2.1 Materials
Catalysts were prepared using a solution of ammonium
heptamolybdate (NH4)6Mo7O24Á4H2O (7 wt%) and nickel
nitrate Ni(NO3)2Á6H2O (3 wt%). Equal amounts of these
solutions (5 mL) mixed together and 2 mmol of these
metals overall was added to the reverse micelle solution
and was stirred slowly until the appearance of a clear blue
solution.
Aluminum tri-bisbutylate (97 %), Titanium (IV) i-prop-
oxide (99 %), methanol, n-butanol, toluene, ammonium
heptamolybdate, n-hexane and 2,4-pentandione (H-acac)
were purchased from Merck. The Zirconium (IV) iso-
propoxide (70 wt% solution in 2-propanol) was obtained
from Fluka. All other chemicals used in this study were of
analytical grade.
2.4 Preparation of Catalyst and Characterization
2.2 Preparation of Support
0.02 mol of Al2O3/TiO2 or Al2O3/ZrO2 was added to n-
hexane solution that contains hybrid NiMo nanoparticles in
reverse micelle, and the flask was put in ultrasonic bath for
The reference mixed-oxide, i.e., Al2O3/TiO2 (1/1) was
prepared by the sol–gel method. 0.01 mol (2.56 mL) of
123

Characterization of Hybrid Nanoparticles of NiMo
CH3
3 Analysis and Characterization
The X-ray diffraction (XRD) patterns were recorded by using
a Philips Xpert MPD diffractometer equipped with a Cu Ka
˚
anode (k = 1.51418 A, 40 kV, 30 mA) in 2h range of 0°–60°
at the speed of 0.05°/min (dimension of examined area:
1 9 1 cm2). Transmission Electron Microscopy (TEM) was
carried out on the powder samples with a Philips CM 120
TEM operating at an accelerating voltage of 100 kV. In
addition, energy dispersive X-ray analysis was conducted on
each sample. The solid-state UV–Vis spectra were recorded
usingaUV/Vis/NIRspectrophotometer, JASCO,V-570inthe
spectral range between 200 and 800 nm. FT-IR spectra of the
catalysts were recorded on Jasco-680 (Japan) spectrometer by
using pressed KBr pellets, and scanned at wavenumber range
CH3
CHO
CH2OH
COOH
+
+
+
OH
400–4,000 cm-1
.
(2)
(3)
(4)
(1)
Scheme2 Liquid phase oxidation of toluene with molecular oxygen
over Ni-Mo based heterogeneous catalysts
4 Results and Discussion
4 h. Immediately after, the solvent was removed and the
All fresh catalysts were characterized with respect to XRD,
UV–Vis, FT-IR, EDX and TEM, to study the physico-
chemical properties of the catalyst. The detailed discussion
on these analyses is given below.
catalyst calcined at 700 °C for 12 h.
2.5 Oxidation of Toluene
The oxidation reaction was performed in a 200 mL tita-
nium batch reactor composed of 316 L stainless-steel
oxygen inlet and outlet ports, a one-way valve (check
valve) also made from 316 L stainless steel in the inlet
port, an analog pressure gauge, an electric belt-like heater,
and a PT-100 temperature sensor. The oxygen (99.98 %
purity) consumed during the reaction was passed into the
reactor through the inlet port and its pressure set to a fixed
value using a high pressure gas regulator. The effect of
partial oxygen pressure was therefore neglected. After the
reaction, the internal pressure was released by venting the
gases through the outlet port, and then the reactor was
cooled and opened. Also a magnetic stir bar was used as
impeller in mixture with the speed of 500 rpm. Moreover,
the components of the reaction mixture were identified at
the end of the reaction time by using GC–MS.
4.1 X-ray Diffraction Analysis (XRD)
XRD patterns of the Al2O3–TiO2/NiMo and Al2O3–ZrO2/
NiMo catalysts after calcinations are presented in Fig. 1. In
the XRD patterns of both catalysts, the presence of crys-
talline NiMoO4 is evident. So, the NiMo particles have
constructed NiMoO4 nanoparticles over the supports.
Several phases including the Al2O3 (JCPDS 02-1373
Rhombohedral and JCPDS 02-1422), ZrO2 (JCPDS
37-1413 tetragonal and JCPDS 14-0534 tetragonal) in
Al2O3–ZrO2/NiMo sample and TiO2 (JCPDS 04-0477
tetragonal anatase and JCPDS 02-0514), Al2O3 (JCPDS
02-1373 Rhombohedral), NiTiO3 (JCPDS 17-0617 Rhom-
bohedral) in Al2O3–TiO2/NiMo sample can be detected.
XRD was used to investigate the structure and phase of
the prepared NiMoO4 (Fig. 1). The observed diffraction
peaks at 2h = 14.5, 23.5, 25.8, 29.3, 32.9, 39.2, 41.3, 44.1,
47.7, 53.5, 56.4, 57.6 for the sample are well matched with
the standard NiMoO4 (JCPDS card No. 09-0175).
According to its JCPDS card, the crystal system is
unknown but the reference has reported that it seems to fit
most closely into the tetragonal system [31].
The stainless steel reactor was charged with 5 mL tol-
uene and 50 mg catalyst under 15 bar oxygen pressure in
190 °C for 2 h. After cooling the reaction mixture to room
temperature, 10 mL methanol was added to it to dis-
solve benzoic acid. Then, the catalyst was filtered off.
Then, the progress of the reaction was monitored by gas
chromatography (Agilent technologies 6890N, HP-50
capillary column). Identification of products was done by
comparing the GC retention times of expected products
with those of standard samples. Finally, the products (see
Scheme 2) were analyzed using GC–MS (UK Fisons Trio
1000).
Under atmospheric pressure, three phases of stoichi-
ometric NiMoO4 can exist usually designated as a, b and
the hydrate. In all three compounds, Ni2? ions occupy sites
with octahedral coordination. The structural type depends
on condition of synthesis, temperature and pressure. a-
NiMoO4 is stable at room temperature and b-NiMoO4 is
123

E. M. Gholizadeh and M. Ghiaci
the high temperature phase. The coordination of Mo6? ions
is octahedral in a-phase while it is tetrahedral in both the b-
as well as the hydrate phase [32].
Ti4O7
Al2O3
ZrO2
NiTiO3
TiO2
According to JCPDS patterns, the pure a-NiMoO4
shows characteristic XRD lines at 2h = 14.5, 24.3, 26.1,
29, 32.8, 38.7, 41.3, 43.9 and 47.6, the strongest being that
at 29° while the diffraction lines of pure b-NiMoO4
obtained by high temperature XRD studies, may be
observed at 2h = 23.4, 25.6, 26.7, 27.4, 28.8, 32.7, 33.9,
43.8 and 47.5, the strongest being at 26.7° [33]. Although
the crystal structure of this detected NiMoO4 (JCPDS
09-0175) is unknown, the XRD analysis of these two cat-
alysts indicates diffraction lines of a phase besides b-Ni-
MoO4. In fact, a-NiMoO4 transforms into the high-
temperature modification b-NiMoO4 at about 700 °C [34].
In light of this, it seems calcination procedure and chilling
after that can cause changes in the phase of NiMoO4. In
both of these catalysts, the peaks characteristics of detected
NiMoO4 indicate no full conversion under these reaction
conditions. Likewise, this fact may be consequence of the
formation of tetrahedral Mo sites following the interaction
between acid species containing molybdenum and the basic
sites of mixed oxide. As a matter of fact, it seems that both
kinds of NiMoO4 exist in these catalysts; a phase is
apparently most prevalent in Al2O3–TiO2/NiMo catalyst,
and the strongest peak being still at the 29° accompanied
with the peak at 14.5°.
Comparing these results with the reference X-ray
diffraction pattern of standard nickel powder, a very
slight reduction in Bragg’s angle can be found for most
of NiMo nano-crystals. This can be attributed to the
expansion of Ni lattice through the introduction of Mo
into the Ni lattice. The average size of the NiMoO4
nanoparticles in these catalysts is calculated by Debye–
Scherrer formula (D = 0.9 k/b Cos h) and 63, 74 nm
attained for Al2O3–TiO2/NiMo and Al2O3–ZrO2/NiMo,
respectively.
NiMoO4
Fig. 1 XRD pattern of (a) Al2O3–TiO2/Ni–Mo, (b) Al2O3–ZrO2/Ni–
Mo
The UV–Vis Drs spectra of the prepared catalysts were
obtained in the region between 200 and 800 nm. No
absorptions arise from alumina, which is transparent in this
region of the UV–Vis spectrum (not shown) [38]. On the
other hand, UV–Vis spectra of pure TiO2 and ZrO2 display
absorption edges around 390 nm for TiO2 and 240 nm for
ZrO2, that in both cases are due to ligand to-metal charge
transfer (LMCT) between the O2 ligand and the metal ion
[38, 39]. In the region 200–400 nm in Al2O3–TiO2/NiMo,
the tetrahedral (260–280 nm) and octahedral (300–320 nm)
molybdenum species can be observed [40] which could
overlap with those originated from TiO2 in the region
200–400 nm. Therefore, it is not possible to judge on the
structure of Mo in this Ti based catalyst. However,
regarding to the structure of the Mo and Ni species existing
on the catalysts containing Ti, it has been well established in
literatures that the presence of TiO2 on the surface induces
the formation of Mo in octahedral coordination [40]. It
seems in parallel with the XRD results about excess of a
phase in the case of Al2O3–TiO2 based catalyst. In the case
of Al2O3–ZrO2/NiMo, the peaks around 240 nm are ascri-
bed to ZrO2. Also the peaks in 300–450 nm may be
attributed to other forms of ZrO2 instead of Mo ions
(260–320 nm), because of their existence in the UV–Vis
spectra of both catalyst and support.
4.2 UV–Vis Analysis
The UV–Vis spectra of Al2O3–TiO2/NiMo and Al2O3–
ZrO2/NiMo and Al2O3–ZrO2/Mo catalysts are shown in
Fig. 2i, ii and iii, respectively. The UV–Vis spectra of the
supported catalysts contain peaks in the range of
600–800 nm. They show that nanoparticles of the targeted
metals have been immobilized over the supports.
According to the published literatures, Mo and Ni ions
show ligand-to-metal charge transfer (LMCT) bands
around 200–400 nm [6, 8, 35] and 623–736 nm [36, 37]
based on their configuration, respectively. Consequently,
on the basis of these findings and from comparing of
Fig. 2i, ii with Fig. 2iii, the absorbance presented in visible
region of Fig. 2i, ii attributed to the NiO or NiMoO4.
The presence of a shoulder in the 600–650 nm and the
small band at 598 nm [41] suggests that Ni2? exists in
tetrahedral symmetry [42]. The bands at 598 and 636 nm
123

Characterization of Hybrid Nanoparticles of NiMo
Fig. 2 UV–Vis spectra of
i (a) Al2O3–TiO2, (b) Al2O3–
TiO2/Ni–Mo ii (a) Al2O3–ZrO2,
(b) Al2O3–ZrO2/Ni–Mo iii
(a) Al2O3–ZrO2, (b) Al2O3–
ZrO2/Mo
has been reported [44, 45] that tetrahedral symmetry of
Ni2? could be resulted to a large Ni-support association.
XRD studies confirm the formation of NiTiO3 which can
be attributed to bands at 598 and 636 nm. The peaks at
720 nm are characteristics of the NiO crystals and they are
arises from octahedral Ni2? in NiO [46]. Ni2? ions in all
phases of the NiMoO4 are in octahedral configuration as
well. So, their peaks could also correspond with NiO.
In addition, a band at 720 nm is associated with Ni2?
ions in an octahedral symmetry [41], however, the shoul-
ders at 598 and 636 nm were less intense than those
observed at 720 nm. This indicates that Ni2? ions mainly
prefer an octahedral symmetry. In light of this, it seems that
in the Al2O3–TiO2 base catalysts, Ni2? ions prefer octa-
hedral symmetry more than them in Al2O3–ZrO2 base
catalyst. This difference may be result of support charac-
teristics; however, this assertion needs more consideration.
4.3 FT-IR Analysis
The FT-IR spectra of prepared catalysts are shown in
Fig. 3. According to the literatures, the pure ZrO2 displays
an absorption band at around 480 cm-1 and Al2O3 shows
two absorption bands at 595 and 440 cm-1. Formation of
ZrO2–Al2O3 could be explained by the shift of the two Zr–
O and Al–O absorption bands into lower frequencies [47].
In light of this, in this current work embedding NiMo
nanoparticles on the support caused even more shifting.
Likewise, construction of Al2O3–TiO2 and embedding
NiMo nanoparticles over it may result in observing bands
at 408 and 420 cm-1 for Ti–O and 615–638 cm-1 for
Fig. 3 FT-IR spectra of (a) Al2O3–TiO2/NiMo, (b) Al2O3–ZrO2/
NiMo, (c) Al2O3–ZrO2/Mo
are indication of Ni2? in the tetrahedral sites. All the
samples show that these bands prove the presence of Ni2?
ions in the tetrahedral vacant sites of the support [43]. It
123

E. M. Gholizadeh and M. Ghiaci
Fig. 4 EDX pattern of the
(a) Al2O3–TiO2/NiMo,
(b) Al2O3–ZrO2/NiMo
a-NiMoO4 where the bands in the 800–880 cm-1 region
ascribed to the b-phase [52]. In fact, the bands at
930–970 cm-1 present in the a-NiMoO4 are assigned to
vibration of the distorted MoO4 present in a-NiMoO4. The
bands in the range of 600–700 cm-1 are attributed to
vibrations of the same units [52]. In as much as previous
articles determined Mo–O–Mo or MoO3 frequencies
820–880 cm-1 in b-NiMoO4 [53], bands in 841 and
868.7 cm-1 assigned to these interactions.
Table 1 Results of the EDX analysis
Sample Catalysts
(wt%)
Molar ratio Catalysts
(wt%)
Molar ratio
Al
M
Al/M
Ni
Mo
Ni/(Ni ? Mo)
AT
AZ
4.33 16.74 0.46
0.63 1.24 1.7
46.04 32.9 0.7
14.83 83.3 0.2
AT: Al2O3–TiO2/NiMo, AZ: Al2O3–ZrO2/NiMo, M: Zr or Ti
The band at 1,100 cm-1 represents Al–O stretching
vibration of alumina [54]. Likewise, MoO4 bands [53] in
963 cm-1 can be shifted to higher frequencies because of
standing over the support and interference by Al–O vibra-
tions. Consequently, the bands in 1099, 1124 and 1125 cm-1
in three samples can be explained by MoO4 structure.
The regions 3,000–4,000 and 900–1800 cm-1 are
termed as the hydroxyl stretching region and vibration of
Al–O stretching, respectively [54].
Al–O (Fig. 3a) whereas in literatures 438, 480, 499 cm-1
bands are attributed to TiO2, Ti2O3 and Ti–O–Ti, respec-
tively [48, 49]. As comparing of Fig. 3a and b, those peaks
which are just exist in the Fig. 3a may be attributed to Ti–
O bands. Additionally, two strong bands characteristic in
the spectra of TiO2 supported NiMoO4 has been reported
for the support at 520 and 675 cm-1 [50] and it is com-
pletely fit with this current report.
Due to cite to other literatures, the peaks in
615–617 cm-1 and 638–645 cm-1 were ascribed to a-Ni-
MoO4 while they may overlap by Al–O peaks in
612–618 cm-1 [51]. Likewise, the peaks in 841–868 cm-1
are assigned to b-NiMoO4. Existence of both a and b phase
of NiMoO4 are consistent with the XRD results. Truly, the
bands at 610, 935 and 958 cm-1 are characteristic of
4.4 Energy-Dispersive X-ray Analysis (EDX)
Stoichiometric and chemical compositions of the prepared
nanomaterial were examined by energy-dispersive X-ray
analysis (EDX). EDX provides an elemental analysis of the
123

Characterization of Hybrid Nanoparticles of NiMo
Fig. 5 TEM image of (a, b) Al2O3–TiO2/Ni–Mo (c, d) Al2O3–ZrO2/Ni–Mo
samples, showing the presence and relative distribution of
the present elements. The EDX spectrum (Fig. 4), obtained
for both catalysts indicates successful deposition of NiMo
nanoparticles on the surface of the support.
The modification of the surface of alumina with TiO2
eliminated most of the reactive hydroxyl groups and
avoided the formation of tetrahedral Mo oxide species,
resulting in an increase of octahedral Mo [55]. Therefore, a
phase of NiMoO4 is expected more in Al2O3–TiO2 and it is
consistent with the XRD and UV–Vis results.
The approximate compositions of all catalysts evaluated
by EDX microanalysis are given in Table 1. SEM-EDX
TESCAN equipped with INCA software has been used for
this purpose. The numbers of scans were 2,048 in 20 s. and
the size of scanned area was 1 9 1lm2. The atomic ratio of
Ni:Mo was 1:3.4 determined by energy dispersive X-ray
spectroscopy (EDX) on the Al2O3–TiO2 sample and 2.3:1
on the Al2O3–ZrO2 sample.
4.5 TEM Data
Transmission electron microscopy (TEM) images (Fig. 5)
were used to show that these catalysts have nano structure.
These pictures clearly show that NiMo particles are nearly
mono dispersed and that their shape is spherical. The metal
particle diameters are between 20 and 70 nm which is fit by
the particle diameter calculated by using XRD analysis. It
appears that this method produces smaller discrete particles
directly over the support. To the best of our knowledge,
there have been no previous reports concerning the prep-
aration of NiMoO4 nanoparticles directly over the support.
Theoretical amount of Al:M (M:Ti or Zr) while all the
metals participate in the composition of the support was 2:
1, however, this ratio alter to 1:2.17 in Al2O3–TiO2 and
1.7:1 in Al2O3–ZrO2 samples. These results indicate that in
the case of Al2O3–ZrO2, the support’s composition com-
patible with theoretical ratio. Additionally, although we
had expected to attain Ni/(Ni ? Mo) = 0.3 ratio, 0.2 ratio
in Al2O3–ZrO2 and 0.7 in Al2O3–TiO2 has been attained. It
reveals that in Al2O3–ZrO2 catalyst smaller amount of Ni
has been deposited over the support. On the other hand, the
amount of Mo nanoparticles over the support is lower than
the expected limit. These results may be attributed to the
surface characteristics such as acidity. It also confirms the
presence of various species such as NiO, MoO3, MoO4,
NiTiO3 and NiMoO4.
4.6 Studies of Toluene Oxidation
In the present study, the catalytic activities of Al2O3–TiO2/
NiMo and Al2O3–ZrO2/NiMo and Al2O3–ZrO2/Mo cata-
lysts were examined in the oxidation of toluene by O2 in
various conditions of pressure, time and temperature. The
results are shown in Table 2. Some main beneficial
123

E. M. Gholizadeh and M. Ghiaci
Table 2 Conversion and selectivity data during oxidation of toluene in various conditions
Entry
Catalyst
Temperature (°C)
O2 Pressure (atm)
Time (h)
Conversion (%)
Selectivity (%)
1a
2b
3c
4d
Others
1
Al2O3–TiO2/NiMo
190
190
190
190
190
190
190
190
150
150
190
190
190
190
190
190
190
190
150
150
190
190
150
15
15
15
15
30
30
30
30
15
15
15
15
15
15
30
30
30
30
15
15
15
30
15
12
8
25
15
10
2
19 \1
21 \1
23 \1
11
4
57
53
41
34
45
44
43
35
5
12
21
23
6
4
12
8
2
51
9
1
12
8
23
11
8
2
6
38
29
55
32
20
16
38
24
–
17
19
22
67
69
2
2
8
4
3
9
2
12
2
2
9
12
2
8
–
2
10
1
2
3
2
Al2O3–ZrO2/NiMo
12
8
66
15
\1
8
8
51
34
–
23
–
–
19
–
4
–
2
45
19
12
15
21
78
16
26
23
81
15
5
10
8
19
47
68
43
35
7
11
21
14
11
31
11
6
12
8
12
23
7
2
4
4
28
10
4
3
2
15
2
3
12
2
\1
1
1
76
2
\1
50
50
–
3
Al2O3–ZrO2/Mo
12
12
2
17
8
10
4
12
20
19
3
\1
–
–
a
Benzaldehyde
b
c
d
Benzyl alcohol
Cresol (para, ortho, meta)
Benzoic acid
characteristics of these reactions are that the oxidation
reaction is carried out using O2 as oxidant under solvent
free conditions with high selectivity to benzaldehyde and
high conversion of toluene. Merely, 50 mg of catalysts was
used in oxidation reactions whereas only 10 % of the cat-
alysts’ supports were loaded by Ni–Mo nanoparticles.
From the data in Table 2, it could be observed that in
most cases, increasing the O2 pressure causes the conver-
sion of the reactant was decreased probably due to satu-
ration of surface of the catalyst by O2 and inaccessibility of
toluene to these active positions.
of b phase of NiMoO4 to a phase in this catalyst prob-
ably causes this improvement. In fact, the surface char-
acteristics of the catalysts such as acidity of the surface
may affect the final results. Truly, increase of the content
of b-NiMoO4 leads to a decrease of the acidity [56], due
to the fact that in the structure of this phase the Ni sites
which are responsible for the base character are more
exposed.
A decrease in the reaction temperature also causes to
lower conversions, but higher selectivity for benzaldehyde.
As illustrated, under the condition of 12 h and 15 bar
pressure by Al2O3–TiO2/NiMo, the conversion and selec-
tivity was altered from 25 to 2 and 19 to 67 percent,
respectively when the temperature is changed from 190 to
150 °C.
Comparing among the results of Al2O3–ZrO2/NiMo and
Al2O3–ZrO2/Mo at the same conditions, it could be con-
cluded that the presence of Ni in the catalyst structure
increases the selectivity of benzaldehyde, although, the
conversion is decreased.
Additionally, the conversion of the reactions is
increased in parallel to time increasing. As the reaction
time increased, the exposure time of toluene to the cat-
alyst is increased. Subsequently, toluene is more inclined
to oxidize into benzoic acid instead of benzaldehyde. The
best conversion related to Al2O3–ZrO2/NiMo catalyst in
reaction time and 15 bar O2 pressure and the best
selectivity to benzaldehyde attributed to this catalyst with
2 h reaction time and the same pressure. The higher ratio
123

Characterization of Hybrid Nanoparticles of NiMo
loading in this study is compared with those published in
the literatures, it can be observed that the catalyst
employed here behaves in an outstanding way. In order to
compare the influence of these various catalysts, their TON
(mmol of converted toluene/mmol of catalysts used) and
TOF (TON/time) parameters were calculated. Tremendous
difference among these results demonstrates effectiveness
of these new catalysts.
Table 3 Comparison of the data obtained in the present work with
other reported catalysts
Catalyst
Conversion Selectivity
(%)
TONe TOFf Ref
(%)
CHO COOH
(h-1
)
CuCo/
Al2O3
0.7
12.4 29.9
8.2
4.1
26
CoCu/C
1.1
1.1
57
0
0
7.4
3.7
6.5
26
26
CuZn/
Al2O3
86.6
12.9
5 Conclusions
CuMn/C 1.4
71.7
0
13.2
22.3
6.6
26
26
CuMn/
Al2O3
1.9
1.2
1.8
74.9 3.2
41.5
27.2 5.2
11.2
In summary, we have developed a clean, efficient and rapid
protocol for the synthesis of nanoparticles on the surface of
two mixed oxides using ultrasonic waves. The NiMoO4
nanoparticles prepared and deposited over the supports
through decomposition of reverse micelles by using ultra-
sound waves with spherical shapes of 20–70 nm size. The
advantage of this approach is better control over the size
and shape of the final nickel molybdate nanoparticles in
comparison to other methods. Likewise, the dispersion of
nanoparticles over the supports using ultrasound radiation
in room temperature is highlighted. Additionally, the cur-
rent method by employing non-toxic materials and facile
procedure is an important step regarding green chemistry.
These two catalysts were shown to be active for oxidation
of toluene with only 10 percent of metal nanoparticles over
the supports. Some points to be emphasized in regard to
these reactions are that the oxidation reaction is carried out
using O2 as oxidant under solvent free conditions with
rather good selectivity for benzaldehyde and high conver-
sion of toluene.
CuFe/
MgO
0
0.9
1.7
0.45
0.85
26
26
CuFe/
TiO2
c-MnOa2
17.6
13.5
–
–
21
1.05
62.7
27
28
Au/c-
64.1 16.8
501.6
MnOb2
NiMo/
Al2O3–
TiO2
2
51
69
19
45
78
2
34
3
60
30
Present
work
NiMo/
Al2O3–
TiOc2
2
60
30
Present
work
NiMo/
Al2O3–
TiOd2
25
8
57
19
7
666.6
307.7
69.2
55.6
Present
work
NiMo/
Al2O3–
ZrO2
153.9 Present
work
NiMo/
Al2O3–
ZrOc2,d
2
5.8
Present
work
Acknowledgments Thanks are due to the Iranian Nanotechnology
Initiative, the Research Council of Isfahan University of Technol-
ogy and Center of Excellence in the Chemistry Department of Isfahan
University of Technology for supporting of this work.
NiMo/
Al2O3–
ZrOd2
66
17
51
50
2307.7 192.3 Present
work
Mo/
Al2O3–
ZrOd2
26
500
41.7
Present
work
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