Liquid phase selective oxidation of aromatic alcohols employing nanoparticles of Zirconia supported on nickel manganese oxide: Synthesis, characterization and catalytic evaluation

Article abstract of DOI:10.14233/ajchem.2013.14911

Zirconia nanoparticles supported on nickel manganese mixed oxide were synthesized by co-precipitation method. The catalytic properties of these materials were investigated for the oxidation of benzyl alcohol using molecular oxygen as oxidant. It was obser

Full text of DOI:10.14233/ajchem.2013.14911

Asian Journal of Chemistry; Vol. 25, No. 16 (2013), 8927-8932
http://dx.doi.org/10.14233/ajchem.2013.14911
Liquid Phase Selective Oxidation of Aromatic Alcohols Employing Nanoparticles of Zirconia
Supported on Nickel Manganese Oxide: Synthesis, Characterization and Catalytic Evaluation
*
SAAD ALABBAD, S.F. ADIL, ABDULRAHMAN ALWARTHAN and M. RAFIQ H. SIDDIQUI
Department of Chemistry, College of Science, King Saud University, P.O. 2455, Riyadh 11451, Kingdom of Saudi Arabia
*
Corresponding author: E-mail: rafiqs@ksu.edu.sa
Received: 4 December 2012;
(
Accepted: 9 September 2013)
AJC-14082
Zirconia nanoparticles supported on nickel manganese mixed oxide were synthesized by co-precipitation method. The catalytic properties
of these materials were investigated for the oxidation of benzyl alcohol using molecular oxygen as oxidant. It was observed that calcina-
tion temperature plays an important role in the process. The catalyst calcined at 400 ºC showed the highest catalytic activity for the
oxidation of benzyl alcohol. Molecular oxygen was found to be the most efficient oxidant in the catalytic performance of the synthesized
catalyst.
Key Words: Zirconia nanoparticles, Nickel manganese mixed oxide, Benzyl alcohol, Oxidation catalyst.
Herein, we reported the synthesis of nano zirconia
supported nickel-manganese mixed oxide as oxidation catalyst
for aromatic alcohols, using benzyl alcohol as the model
compound. The synthesized catalyst was characterized by
SEM, TEM, EADX, XRD, BET and TGA. The catalyst was
tested for various substituted benzyl alcohol and the conversion
was monitored using gas chromatography.
INTRODUCTION
Oxidation of aromatic alcohols to corresponding
aldehydes is an important area of research for scientist around
the world as they play a significant role of building blocks for
1-3
many organic compounds .A large number of heterogeneous
4
-12
catalyst have been reported in literature with regard to the
conversion of alcohols to aldehydes using noble metals such
as Pt, Ru, Au, Pd and their derivatives using oxygen as an
oxidant. Platinum-based catalysts can be easily poisoned which
make them sensitive and hence can be used only in mild
conditions while gold catalysts have also been reported for
EXPERIMENTAL
Preparation of zirconia supported on nickel manga-
nese oxide by deposition method: 95 mL of 0.2 M solutions
of nickel nitrate and manganese nitrate were mixed in a round
bottomed flask. To it was added 10 mL of 0.2 M solution of
zirconium nitrate solution. The resulting solution was heated
to 80 ºC, while stirring using a mechanical stirrer and 1 M
13
their high selectivity towards aldehydes . Silica supported
1
catalysts have been reported widely in literature
4,15
for gas-
phase oxidations of ethylene and for methanol oxidations.
Nickel-manganese combination has been known to chemists
for a long time, owing to their use as major components in
3
solution of NaHCO was added drop wise until the solution
1
6-18
alloys , high-energy and high-power electrode material for
attained a pH 9. The solution was continued to stir at the same
temperature for 3 h and then left on stirring over night at room
temperature. The solution was filtered using a Buchner funnel
under vacuum and dried at 70 ºC overnight. The product
obtained was characterized using SEM, TEM, EADX, XRD,
BET and TGA. The resulting powder was then calcined at
different temperatures and was evaluated for its oxidation
activity using benzyl alcohol as starting material.
19
20
alkaline cells , lithium ion batteries , fuel cells and super
21
2
capacitors . Nickel and manganese as catalyst have been
2
reported in literature for their use in deprotonative arene dimeri-
2
3
24
zation , oxidation of many precursors such as cyclohexene ,
2
5-27
28
CO, hydrocarbons , partial oxidation of methane , electro
2
oxidation of methanol , oxidative degradation of volatile
9
30
31
organic compounds hydration of acrylonitrile and xylene
32
to terphthalic acid . In order to investigate the possible appli-
cation of nickel manganese mixed oxide as oxidation catalyst
for the conversion of benzyl alcohol to benzaldehyde, we have
earlier reported the synthesis of the nickel manganese oxide
Preparation of zirconia supported on nickel manganese
oxide by modified deposition method: In this method of
preparation of catalyst is divided into two parts: (a) Hydro-
thermal synthesis of zirconia nanoparticles, (b) Zirconia supported
on nickel manganese oxide using deposition method.
33
supported gold nanoparticles .

8
928 Alabbad et al.
Asian J. Chem.
Hydrothermal synthesis of zirconia nanoparticles: It
shown in Figs. 1 and 2. It suggest that the morphology of the
synthesized catalysts is like a bunch of nano flowers. The 1 %
Zr-NiMnO showed some nano-rods which were absent in the
3 % Zr-NiMnO. It was also interesting to find that the catalyst
5 % Zr-NiMnO synthesized by the modified deposition method
had a very different morphology. It was found to be spherical
in shape and regular in size. The stoichiometric amount of
doping could be confirmed from the EDX analysis to be
approximately near to the calculated value.
was carried out using zirconium oleate as starting material,
which was synthesized by reacting zirconium nitrate and
sodium oleate. The zirconium oleate was then transferred into
a PARR autoclave along with Triton X-100 and triethylene
glycol and heated at 180 ºC, for 3 h. After the autoclave was
cooled, the sample was transferred into a centrifuge tube and
centrifuged several times washing it with acetone and water
to get rid of the organic impurities and other water soluble
impurities. The isolated particles were then calcined at 250 ºC.
Deposition synthesis of zirconia supported on nickel
manganese oxide: The stoichiometric amount of the synthe-
sized zirconia nanoparticles were dispersed in 95 mL of 0.2
M solutions of nickel nitrate and manganese nitrate were mixed
in a round bottomed flask. The resulting solution was heated
to 80 ºC, while stirring using a mechanical stirrer and 1 M
3
solution of NaHCO was added drop wise until the solution
attained a pH 9. The solution was continued to stir at the same
temperature for 3 h and then left on stirring over night at room
temperature. The solution was filtered using a Buchner funnel
under vacuum and dried at 70 ºC overnight. The product
obtained was characterized using SEM, TEM, EADX, XRD,
BET and TGA. The resulting powder was then calcined at
different temperatures and was evaluated for its oxidation
activity using benzyl alcohol as starting material.
Fig. 1. SEM of the catalyst (a) 1 % Zr-NiMnO (b) 3 % Zr-NiMnO at 400 ºC
Catalyst characterization: Scanning electron micro-
scopy (SEM), elemental analysis and energy dispersive
X-Ray analysis (EDX) were carried out using Jeol SEM model
JSM 6360A (Japan). This was used to determine the morpho-
logy of nanoparticles and its elemental composition. Trans-
mission electron microscopy (TEM) was carried out using Jeol
TEM model JEM-1101 (Japan), which was used to determine
the shape and size of nanoparticles. Powder X-ray diffraction
studies were carried out using Altima IV: Regaku X-ray
diffractometer. Fourier Transform Infrared Spectroscopy (FT-
IR) the infrared spectra were recorded as KBr pellets using a
Perkin-Elmer 1000 FT-IR spectrophotometer. BET surface area
was measured on a NOVA 4200e surface area & pore size
analyzer. ThermogravimetricAnalysis (TGA) was carried out
using Perkin-Elmer Thermogravimetric Analyzer 7.
Fig. 2. SEM of the catalyst (a) 5 % Zr-NiMnO (b) 5 % Zr-NiMnO
modified) calcined at 400 ºC
(
The TEM image of the catalyst 5 % Zr-NiMnO was carried
out to know about the shape and size of the particles as shown
in Fig. 3. The particle size distribution was calculated by using
the general-purpose image processing program Image J soft-
ware. It was found that the synthesized catalyst 1 % Zr-NiMnO
possessed particle size of 0.61 nm, while 3 % Zr-NiMnO was
found to contain particles of size 1.59 nm. When similar studies
were carried out for 5 % Zr-NiMnO, calcined at 300, 400 and
Catalyst testing: In a typical reaction run, 300 mg of
catalyst was loaded in a glass flask pre-charged with 0.2 mL
(
mixture was then heated to 100 ºC with vigorous stirring.
2 mmol) benzyl alcohol with 10 mL toluene as solvent; the
5
00 ºC, it was found that the particle size was found to be
.53, 0.46, 0.43 nm, respectively. The particle size of the
3
-1
Oxygen was bubbled at a flow rate of 20 mL min into the
mixture once the reaction temperature was attained. After
reaction, the solid catalyst was separated by centrifugation and
the liquid samples were analyzed by gas chromatography to
evaluate the conversion of the desired product by (GC, 7890A)
Agilent Technologies Inc, equipped with a flame ionization
detector (FID) and a 19019S-001 HP-PONA column.
catalyst 5 % Zr-NiMnO synthesized by the modified synthetic
procedure was found to be 0.69 nm.
RESULTS AND DISCUSSION
The synthesized catalyst was characterized by electron
microscopy to evaluate the morphology and particle size of
the catalyst. The scanning electron microscopy of the synthe-
sized catalyst X % Zr-NiMnO, where X = (1, 3 and 5) pre-
calcined at 400 ºC was carried out and the micrographs are
Fig. 3. TEM of the catalyst (a) 5 % Zr-NiMnO (400 ºC) (b) 5 % Zr-NiMnO
(500 ºC)

Vol. 25, No. 16 (2013)
Liquid Phase Selective Oxidation of Aromatic Alcohols Employing Nanoparticles of Zirconia 8929
Fig. 4 illustrates the X-ray diffraction pattern of 5 %
Zr-NiMnO calcined at 300, 400 and 500 ºC. The symbols in
the Fig. 4 indicate the peaks of the corresponding phase.
4
000
3500
3000
2500
Wavenumber (cm
2000
–
1500
1000
500
1
)
Fig. 5. FT-IR spectrum of the synthesized catalyst (a) 1 % Zr-NiMnO (b)
% Zr-NiMnO (c) 5 % Zr-NiMnO (d) 5 % Zr-NiMnO (modified)
3
1
6
24
32
40
(°)
48
56
64
possibly due to the metal-oxygen bond vibrations on the
-1
surface. The peaks in the region 700-550 cm can be due to
2
θ
Fig. 4. XRD pattern of the synthesized 5 % Zr-NiMnO catalyst
a) 300 ºC (b) 400 ºC (c) 500 ºC
the stretching frequencies between the metal and oxygen atom.
The catalyst with different % loading of zirconia
nanoparticles were subjected to TGA analysis to learn out about
the thermal stability of the synthesized catalyst. Temperature
was programmed from 25-1000 ºC at a heating rate of 10 ºC/
min. It was observed that the almost all the synthesized catalyst
is thermally stable, yielding a maximum loss of weight to be
(
Observations made in the XRD spectrum (Fig. 4) indicates
that the catalyst 5 % Zr- NiMnO, calcined at 300 ºC contains
a mixture of cubic hexanickel manganese(IV) oxide (ICSD #
4
4
#
0584), orthorhombic β-manganese oxide (3/4) (ICSD #
0110) and orthorhombic dinickel dioxide hydroxide (ICSD
202427). The catalyst calcined at 400 ºC was found to contain
16.4 % at 1000 ºC found in the case 3 % zirconia nanoparticles
loaded catalyst making it to be the least thermally stable among
the synthesized catalyst, while the catalyst with 5 % Zr
nanoparticles can be assumed to be the best thermally stable
catalyst with a least weight loss % of just 7.6 % at 1000 ºC. A
graphical illustration is given in Fig. 6.
peaks corresponding to a mixture of cubic hexa nickel
manganese(IV) oxide (ICSD # 40584),orthorhombic dinickel
dioxide hydroxide (ICSD # 202427) and a single peak of
orthorhombic β-manganese oxide (3/4) (ICSD # 40110). The
catalyst calcined at 500 ºC was found to contain peaks corres-
ponding to a mixture orthorhombic dinickel dioxide hydroxide
with traces of cubic zirconium nickel oxide (4/2/1) (ICSD #
100
7
1964) and tetragonal zirconia (ICSD # 93028). When similar
study of the XRD spectrum of X % Zr-NiMnO, where X = (1,
and 5) pre-calcined at 400 ºC was carried out it was found
that the 1 % Zr-NiMnO, 3 % Zr-NiMnO and 5 % Zr-NiMnO
modified) contains peaks corresponding to cubic hexanickel
3
95
(
manganese(IV) oxide, while the spectrum of 5 % Zr-NiMnO
contains mixtureof cubic hexanickel manganese(IV) oxide and
orthorhombic dinickel dioxide hydroxide. The presence of
different phases of oxide along with the orthorhombic dinickel
dioxide hydroxide may be attributed to the increase in catalytic
activity of the catalyst 5 % Zr-NiMnO pre-calcined at 40 ºC
among the rest of the synthesized catalyst.
90
85
0
0
200
400
600
Temperature (ºC)
800
1000
The synthesized catalyst was subjected to FT-IR spec-
troscopy and the spectrum was obtained (Fig. 5). From the %
Fig. 6. TGA curves of the synthesized catalyst (a) 1 % Zr-NiMnO (b) 3 %
Zr-NiMnO (c) 5 % Zr-NiMnO (d) 5 % Zr-NiMnO (modified)
-
1
transmittance peaks in the region between 3450-3350 cm
characteristic of the OH group stretching vibration it can be
concluded the presence of OH groups on the surface of the
catalyst which may be due to the presence of moisture on the
surface while the peak corresponding to OH in the IR spectrum
of 5 % Zr-NiMnO catalyst could be due the presence of dinickel
dioxide hydroxide which was established by observations of
the XRD spectrum. While the peaks in the region 1600-1300
In order to optimize the percentage of zirconia nanoparticles
to be supported on the nickel-manganese mixed oxide for the
best catalytic performance as oxidation catalyst, a series of
catalyst with varying percentage of zirconia nanoparticles were
synthesized and evaluated for their catalytic property using
the oxidation of benzyl alcohol to benzaldehyde as a model
reaction. The reaction was carried out at 100 ºC, while passing
-
1
cm are due to the metal/surface binding characteristics

8
930 Alabbad et al.
Asian J. Chem.
O
2
gas as a source of molecular oxygen. During the study it
When the similar conversion was carried out to ascertain
the optimum calcination temperature for the best catalytic
performance of the synthesized catalyst, the 5 % Zr: NiMnO
catalyst was calcined at different temperatures i.e., 300, 400
and 500 ºC. All the catalysts was subjected to the conversion
of benzyl alcohol to benzaldehye while maintaining similar
reaction conditions as mentioned above. It was observed that
the catalyst calcined at 300 ºC the reaction starts off by yielding
a 40 % conversion product after a time of 0.5 h and when the
reaction was continued for another 150 min the conversion
product obtained was 70 %, while in the case of 400 ºC calcined
catalyst the reaction starts off with 94 % conversion after 0.5 h
and reaction is complete at 1 h with 100 % conversion product.
When the 500 ºC calcined catalyst was used a 51 % conver-
sion product was obtained after 0.5 h of reaction time, while
81 % conversion was obtained at the end of 3 h of reaction
time. The results are summarized in Table-2 and a graphical
illustration is given in Fig. 8.
was found that the 1 % zirconia doped nickel manganese mixed
oxide (1 % Zr-NiMnO) yielded a conversion of 70 %, while
the catalyst with 3% zirconia doped nickel manganese mixed
oxide (3 % Zr-NiMnO) yielded 67 %. A 100 % conversion of
benzyl alcohol to benzaldehyde was obtained with the catalyst
containing 5 % zirconia doped nickel manganese mixed oxide
(
5 % Zr-NiMnO). The selectivity in all the above reactions
was found to be >99 %. In order to evaluate the effect of
synthetic procedure on the catalytic performance of the
synthesized catalyst, the catalyst synthesized with modified
deposition method was used for the conversion and the
conversion product obtained was 56 % and since the result
obtained is not comparable as the rest, this method of synthesis
was not employed further in the synthesis of catalysts. The
results have been summarized in Table-1. A graphical illus-
tration is given in Fig. 7.
TABLE-1
EFFECT ON THE CATALYTIC PROPERTIES
BY WEIGHT % OF Zr IN THE CATALYST
Entry
Zr (%)
Conversion (%)
1
2
3
4
5
0
48
71.21
67.35
100
1
3
5
5 (Modi)
56
Reaction conditions: Amount of catalyst 300 mg; calcination
temperature 400 °C; reaction temperature 100 ºC; oxygen flow rate 20
mL min ; benzyl alcohol 2 mmol; toluene 10 mL; reaction time 2 h.
-1
Time (min)
Fig. 8. Graphical illustration of the conversion of benzyl alcohol to
benzaldehyde using of the synthesized catalyst 5 % Zr: NiMnO
calcined at different temperatures (a) 300 ºC (b) 400 ºC (c) 500 ºC
In order to check the compatibility and the effect of source
of oxygen on catalytic performance of the synthesized catalyst
5
% Zr-NiMnO calcined at 400 ºC, a few other sources of
oxygen reported for similar conversion were employed and it
was found that the catalyst displayed excellent performance
with 100 % conversion and > 99 % selectivity when molecular
oxygen is used, when dibenzoyl peroxide and hydrogen
peroxide were used 20 and 7 % conversion product was
obtained, respectively.A graphical illustration is given in Fig. 9.
The results have been summarized in Table-3.
Time (min)
Fig. 7. Graphical illustration of the conversion of benzyl alcohol to
benzaldehyde using of the synthesized catalyst (a) 1 % Zr-NiMnO
(
b) 3 % Zr-NiMnO (c) 5 % Zr-NiMnO (d) 5 % Zr-NiMnO (modified)
TABLE-2
EFFECT OF CALCINATION TEMPERATURE ON THE CATALYTIC PROPERTIES
2
SA (m g )
-1
Entry
Catalyst
Temperature (ºC)
Conversion (%)
48.00
Selectivity (%)
1
2
3
4
NiMnO
400
300
400
500
–
>99
>99
>99
>99
5 % Zr-NiMnO
5 % Zr-NiMnO
5 % Zr-NiMnO
143.723
57.008
148.329
52.67
100.00
64.32
-1
Reaction conditions: Amount of catalyst 300 mg; reaction temperature 100 ºC; oxygen flow rate 20 mL min ; benzyl alcohol 2 mmol; toluene 10
mL; reaction time 2 h.

Vol. 25, No. 16 (2013)
Liquid Phase Selective Oxidation of Aromatic Alcohols Employing Nanoparticles of Zirconia 8931
was studied. It was found that conversion product obtained
was > 60 % and selectivity displayed by the catalyst was >
99 %. The results have been summarized in Table-4.
TABLE-4
SELECTIVE OXIDATION OF BENZYL ALCOHOL
AND ITS DERIVATIVES INTO CORRESPONDING
ALDEHYDES IN THE PRESENCE OF O AS CLEAN OXIDANT
2
R.
No.
Conversion
(%)
Selectivity
(%)
Reactants
Products
OH
O
1
2
100
63
>99
>99
OH
O
H
Sources of oxygen
Fig. 9. Graphical illustration of the conversion of benzyl alcohol to
benzaldehyde using of the synthesized catalyst 5 % Zr: NiMnO
using different sources of oxygen
CH3
OH
CH3
H
O
TABLE-3
EFFECT OF DIFFERENT SOURCES OF OXYGEN ON THE
CATALYTIC PERFORMANCE OF 5 % Zr: NiMnO
3
4
5
100
100
100
>99
>99
>99
Entry
Oxidant
O2
Conversion (%)
OCH3
OH
OCH3
H
1
2
3
100
20
7
O
O
Dibenzyl peroxide
Hydrogen peroxide
Reaction conditions: Amount of catalyst 300 mg; reaction temperature
100 ºC; benzyl alcohol 2 mmol; toluene 10 mL; reaction time 2 h.
Cl
Cl
H
In order to understand the effect of catalyst on the solvent
OH
used, which is toluene in the present study, a blank reaction
was carried out without the substrate benzyl alcohol using 5 %
Zr-NiMnO as catalyst and no product was formation was
observed. Hence it can be concluded that the conversion
product benzaldehyde obtained is from the catalytic conversion
of benzyl alcohol and not from toluene.
NO2
OH
NO2
H
O
From the conversion of benzyl alcohol to benzaldehyde
which was used as a model reaction it was ascertained that the
best catalytic activity was displayed by 5 % Zr: NiMnO,
calcined at 400 ºC, which was established by spectral studies
to contain mixture of cubic hexanickel manganese (IV) oxide
and orthorhombic dinickel dioxide hydroxide. It can be
concluded that the presence of orthorhombic dinickel dioxide
hydroxide on the surface of the catalyst plays a crucial role. It
was also found that the catalyst 5 % Zr: NiMnO (400 ºC)
possess least surface area according to the BET surface area
analysis results, but yet has displayed best catalytic perfor-
mance among the synthesized catalyst which could be due to
the absence of orthorhombic dinickel dioxide hydroxide on
the surface. As all the other catalyst synthesized were found
to possess other phases of nickel manganese salts, which could
not produce comparable catalytic performance. It was also
confirmed that the catalyst performs best in the presence of
molecular oxygen as source of oxygen. In order to determine
the catalytic performance of 5 % Zr: NiMnO (400 ºC), the
reaction was carried out under similar conditions using a
6
65.12
>99
OH
O
F
H
7
8
95
>99
>99
F
F
F
F
F
OH
O
H
100
NO2
NO2
Reaction conditions: Catalyst 5 % Zr: NiMnO (400 ºC): Amount of
catalyst 300 mg; reaction temperature 100 ºC; benzyl alcohol 2 mmol;
toluene 10 mL; reaction time 2 h.
Conclusion
Nano zirconia supported nickel manganese oxide show
series of substituted benzyl alcohols, containing, 4-CH
-Cl, 4-NO , 4-C(CH , 4-CF and 3-NO groups as different
substrates and their conversion to corresponding aldehydes
3 3
, 4-OCH ,
4
2
3
)
3
3
2
high activity and stability for the oxidation of benzyl alcohol
using molecular oxygen as a source of oxygen. A synergistic

8
932 Alabbad et al.
Asian J. Chem.
1
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oxygen has substantial influence on the catalytic performance
of the synthesized catalyst. It can be believed that this catalyst
can be further used for the evaluation of its oxidative property
for the synthesis of other important aromatic and aliphatic
aldehydes can be explored.
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This project was supported by King Saud University,
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