Gold nanoparticles supported on magnesium oxide nanorods for oxidation of alcohols

Article abstract of DOI:10.1166/jnn.2016.10778

Gold nanoparticles supported on magnesium oxide nanorods (Au-MgO) have been synthesised by a solution based chemical reduction method. Au-MgO nanorods were found to be an efficient heterogeneous catalyst for oxidation of alcohols with hydrogen peroxide in aqueous medium at room temperature. To find out the best reaction conditions for oxidation, optimization of catalyst quantity, solvent, mole equivalence of hydrogen peroxide were carried out. The scope of the reaction was extended to several aromatic and aliphatic alcohols, product yields were quantified by gas chromatography (GC) and GC/mass spectroscopy. Heterogeneity and reusability tests were performed. The use of water as a solvent and hydrogen peroxide as co-catalyst at room temperature makes the reaction interesting from sustainable development point of view.

Full text of DOI:10.1166/jnn.2016.10778

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Nanoscience and Nanotechnology
Vol. 16, 2517–2526, 2016
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Gold Nanoparticles Supported on Magnesium Oxide
Nanorods for Oxidation of Alcohols
P. Emayavaramban1ꢀ∗, S. Ganesh Babu2, R. Karvembu3, K. Kadirvelu4, and N. Dharmaraj1
1Inorganic and Nanomaterials Research Laboratory, Department of Chemistry, Bharathiar University, Coimbatore 641046, India
2SRM Research Institute, SRM University, Kattankulathur 603203, India
3Department of Chemistry, National Institute of Technology, Tiruchirappalli 620015, India
4DRDO-BU CLS, Bharathiar University Campus, Coimbatore 641046, India
Gold nanoparticles supported on magnesium oxide nanorods (Au–MgO) have been synthesised by
a solution based chemical reduction method. Au–MgO nanorods were found to be an efficient het-
erogeneous catalyst for oxidation of alcohols with hydrogen peroxide in aqueous medium at room
temperature. To find out the best reaction conditions for oxidation, optimization of catalyst quantity,
solvent, mole equivalence of hydrogen peroxide were carried out. The scope of the reaction was
extended to several aromatic and aliphatic alcohols, product yields were quantified by gas chro-
matography (GC) and GC/mass spectroscopy. Heterogeneity and reusability tests were performed.
The use of water as a solvent and hydrogen peroxide as co-catalyst at room temperature makes
the reaction interesting from sustainable development point of view.
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Keywords: Gold Nanoparticles, Magnesium Oxide Nanorods, Oxidation, Alcohols,
Copyright: American Scientific Publishers
Heterogeneous Catalyst, Hydrogen Peroxide.
1. INTRODUCTION
nanoparticles is the most promising candidate due to their
outstanding catalytic performance and selectivity.9–14 Oxi-
dation of alcohols over gold catalysts in the presence of
base can promote the abstraction of hydrogen from the
substrate and also capturing of free carboxylic acid formed
at the reaction that suppresses efficiency of gold cata-
lyst due to catalyst poisoning.15 Recently, gold contain-
ing catalysts have been developed for the effective aerobic
oxidation of alcohols under base-free conditions.16–18 On
the other hand, magnesium oxide (MgO) is an important
oxide material with assuring activity in catalysis, toxic
waste remediation, refractory or adsorbents. Particularly in
catalysis, it can either be used as a sole catalyst or as a
solid support for metal catalysts owing to its high tem-
perature superconducting behaviour.19–22 Moreover, in the
crystalline lattice it possess high concentration of reactive
surface ions with various cationic and anionic vacancies
with Mg2+ (Lewis acidic) or O2− (Lewis basic).23 Fur-
thermore, it can be easily converted into Mg(OH)2 in the
presence of water, especially under acidic conditions.24–26
Recently, gold nanoparticles supported on magnesium
oxide (Au–MgO) was used as an active catalyst for var-
ious catalytic reactions such as CO oxidation, reduction
of nitroarenes, synthesis of propargylamines and Ullmann
Oxidation of alcohols to aldehydes and ketones plays a
vital role in industry as these carbonyl compounds are
key intermediates for the synthesis of many drugs, fine
chemicals and fragrances.1ꢀ2 Although traditional methods
are available for oxidation of alcohols they suffer from
the involvement of toxic, corrosive and expensive oxidants
such as Cr(VI), Mn(VII), heptavalent iodine and DMSO-
coupled reagents and all of them create environmentally
hazardous wastes.3–5 Few studies have been reported for
the oxidation of alcohols by metal supported catalyst
namely Cu boehmite,6 Pd on CNT7 and NiO-HAP8 with
periodic acid and sodium hypochlorite as co-catalysts but
they are harmful to the environment. Hence, researchers
show much interest to replace the current strategies and
to develop a new catalytic oxidation processes concern-
ing green chemistry. In this connection, hydrogen peroxide
was utilised as an effective oxidant because it is cheap,
safer and produces only water as the sole by-product. Sev-
eral metal based nanocatalysts with oxidants were car-
ried out for oxidation of alcohols. Among them, gold
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2016, Vol. 16, No. 3
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doi:10.1166/jnn.2016.10778
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Gold Nanoparticles Supported on Magnesium Oxide Nanorods for Oxidation of Alcohols
Emayavaramban et al.
coupling of aryl iodides.27–30 Additionally, Au–MgO was
found to be an effective catalyst for oxidative methoxyla-
O
OH
Au-MgOnanorods, H2O2
H2O,room temperature
R
R'
R
R'
tion of benzyl alcohol as well as the oxidation of alcohols
in the absence of base.31ꢀ32 However, there is no liter-
ature available on gold nanoparticles supported magne-
sium oxide nanorods (Au–MgO nanorods) for oxidation of
alcohols using hydrogen peroxide in aqueous medium. In
this work, we report the solution based chemical reduc-
tion method was adopted for the formation of Au–MgO
nanorods and its potential for oxidation of alcohols using
hydrogen peroxide under base free condition in aqueous
medium at room temperature.
R = alkyl or aryl.
R' = H, alkyl or aryl.
Scheme 1. Oxidation of alcohols using Au–MgO nanorods.
a laser Raman spectrometer (Horiba Jobin-LabRam-HR-
UV) using a 20 mW argon laser operating at 514 nm. The
thermal decomposition behaviour of sample was studied
by simultaneous thermogravimetry and differential thermal
analysis (TG/DTA) using a PerkinElmer Pyris Diamond
TG/DTA under a flow of synthetic air (50 mL per min)
ꢀ
at a heating rate of 10 C per min. The nitrogen adsorp-
2. EXPERIMENTAL DETAILS
tion/desorption experiments were carried out at 77 K using
an ASAP 2020 system of micromeritics the autosorp-iQ
(Quantachrome instruments). The sample was de-gassed
under vacuum at 423 K for 24 h before the adsorption
of nitrogen. GC analysis was done in Shimadzu-2010 gas
chromatograph. Gas chromatographic analysis and mass
spectroscopy were recorded in PerkinElmer Clarus 600
instrument.
2.1. Materials and Methods
Reagent grade magnesium chloride hexahydrate was
obtained from Loba Chemie and oxalic acid was purchased
from HiMedia, was used as received. All other chemicals
and reagents purchased from Sigma Aldrich were used
without further purification. Commercial grade solvents
were obtained from Merck India.
2.2. Preparation of Au–MgO Nanorods
2.4. Procedure for Alcohol Oxidation
A typical reaction scheme for the alcohol oxidation is
given in Scheme 1. Au–MgO nanorods (30 mg) and H2O2
The magnesium oxide (MgO) support was prepared
according to the literature method.33 Magnesium chloride
hexahydate (0.1 M) was dissolved in 100 mL of dou-
(945 ꢅL, 15 equivalence) were stirred in 20 mL of water
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ble distilled water and excess of oxalic acid (0.12 M)
was added to it under continuous stirring. Then, the solu-
tion was neutralized by adding ammonium hydroxide and
stirred for 6 h under ambient temperature. The obtained
precipitate was filtered and dried at 100 ꢀC in hot air
oven. The dried magnesium oxalate powder was calcined
at 500 ꢀC to obtain magnesium oxide as white powder.
Gold ions were incorporated on the surface of MgO by ion
exchange reaction using 5 mM of HAuCl4 and hydrated
MgO (1 g), and then the exchanged gold ions were reduced
with 0.1 M of sodium borohydride and subjected for cal-
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and the substrate alcohol (1 mM) was slowly added to the
Copyright: American Scientific Publishers
reaction mixture and continuously stirred at room temper-
ature. After the requisite time, the catalyst was separated
by centrifugation. The centrifugate was extracted using
diethyl ether. The ether extract was dried over anhydrous
sodium sulphate and evaporated. Then the product was dis-
solved in ethyl acetate and then analysed by GC. Authentic
samples of reactants and respective products were used to
verify the retention time and to confirm the product for-
mation. The used catalyst was washed with ethyl acetate
ꢀ
cination at 500 C.
2.3. Characterization Techniques
Powder X-ray diffraction (XRD) patterns of the sam-
ples were recorded using a PAN analytical X’PERT-PRO
X-ray diffractometer (Cu-Kꢁ radiation, ꢂ = 1ꢃ54056 Å)
employing a scan rate of 0.02ꢀ sec in the 2ꢄ range from
15ꢀ to 82ꢀ. UV-visible absorption spectra of the sam-
ples were recorded with a double beam UV/vis. and
UV-DRS-JASCO (model V550) spectrophotometer. Field
emission scanning electron microscopic (FE-SEM) image
were performed with FEI Quanta-250 instrument. TEM
measurements were carried out on a FEI model Tec-
nai sprit instrument operated at an accelerating voltage
of 110 kV. For TEM analysis, 0.2 mg of samples was
dispersed in 10 mL of ethanol in an ultrasonicator for
25 min. and a drop of the solution was placed on a car-
bon coated copper grid. Raman spectra was recorded from
Figure 1. XRD patterns of as-prepared samples (a) Au3+ ions incorpo-
rated hydrated MgO (b) Au–Mg(OH)2 reduced with NaBH4 and (c) the
same sample calcined at 500 ꢀC.
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Emayavaramban et al.
Gold Nanoparticles Supported on Magnesium Oxide Nanorods for Oxidation of Alcohols
150 ꢀC at the rate of 10 ꢀC/min. and then increased to
220 ꢀC at the rate of 40 ꢀC per min. and N2 was used as a
carrier gas. The temperature of the injection port and FID
ꢀ
were kept constant at 150 and 250 C respectively during
product analysis.
3. RESULTS AND DISCUSSION
The phase composition of the as-prepared samples was
studied by XRD. Figure 1(a) shows the XRD patterns
of Au3+ ions incorporated MgO (hydrated). The peaks
observed at 18.3ꢀ, 37.8ꢀ, 49.1ꢀ, 57.4ꢀ, 57.4ꢀ, 59.1ꢀ and
62.1ꢀ corresponding to planes (001), (101), (102), (110),
(003) and (111) respectively, are in good agreement with
JCPDS file no. (44-1482) for hydrated MgO. The sec-
ondary peaks observed at 23.3ꢀ, 28.2ꢀ, 35.5ꢀ, 36.3ꢀ, 36.7ꢀ,
43.5ꢀ, 44.4ꢀ and 60.6ꢀ are due to the presence of calcium
impurities confirmed with JCPDS file no. (04-0733). The
results revealed that the MgO support was hydrated with
aqueous solution of auric chloride.34 This conversion pro-
cess was accelerated by the presence of the strong acidic
condition. The Figure 1(b) clearly shows the diffraction
patterns of Au–Mg(OH)2. The peaks observed at 18.3ꢀ,
37.8ꢀ, 49.1ꢀ, 57.4ꢀ, 57.4ꢀ, 59.1ꢀ and 62.1ꢀ corresponding to
planes (001), (101), (102), (110), (003) and (111) respec-
tively. Figure 1(c) shows the XRD patterns of calcined
Au–MgO nanorods. The characteristic peaks of MgO are
Figure 2. UV-DRS spectra of (a) freshly prepared MgO and (b) Au–
MgO nanorods.
and driꢀed under vacuum. The dried catalyst was calcined
at 500 C before reuse.
2.5. Product Analysis
Gas chromatographic analysis was carried out with the
instrument equipped with a 5% diphenyl and 95%
dimethyl polysiloxane, Restek-5 capillary column (60 m
length, 0.32 mm dia) and a flame ionization detector (FID).
The initial column temperature was increased from 60 to
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Figure 3. Field-emission scanning electron microscopic images of Au–MgO nanorods with lower and higher magnification (a)–(d).
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Gold Nanoparticles Supported on Magnesium Oxide Nanorods for Oxidation of Alcohols
Emayavaramban et al.
observed at 36.8ꢀ, 43ꢀ, 62.3ꢀ, 74.3ꢀ and 78.5ꢀ which cor-
respond to the diffraction planes (111), (200), (220), (311)
and (222) respectively. The calcined sample was hexag-
onal phase of MgO similar to previous reports.35ꢀ36 The
XRD profile were well matched with the JCPDS file no.
(07-0612) for the formation of Au–MgO nanorods. The
Diffuse reflectance spectra of the as-prepared MgO
and Au–MgO nanorods were depicted in Figure 2. The
broad absorption band observed in the range from 225
to 300 nm (inset in Fig. 2) were assigned to the opti-
cal excitation of 4- and 3-coordinated surface anions of
MgO present in both synthesised MgO and Au–MgO
nanorods.37 In addition, the UV-DRS spectrum of the pre-
pared Au–MgO nanorods showed the optical absorption
band at 520 nm due to the surface plasmon resonance.38
This clearly indicated the formation of gold nanoparti-
cles on the surface of MgO nanorods. However, no such
ꢀ
result revealed that calcination at 500 C dehydrated the
Mg(OH)2 phase to MgO phase. Since the AuNPs formed
on MgO nanorods was relatively very small fractions,
appearance of AuNPs was not observed in diffraction
pattern.
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Figure 4. TEM images of gold nanoparticles supported on magnesium oxide nanorods prepared at 500 ꢀC.
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Emayavaramban et al.
Gold Nanoparticles Supported on Magnesium Oxide Nanorods for Oxidation of Alcohols
absorption band was observed in the spectrum of exclusion
MgO.
The morphological study of nanostructured Au–MgO
roads obtained after calcination of Au–Mg(OH)2 at 500 ꢀC
was investigated by electron microscopy. The FE-SEM
images of Au–MgO under different magnification are
shown in Figures 3(a)–(d) with cube like morphol-
ogy visualized under high magnification. Figures 4(a)
and (b) shows the low magnification TEM images of
Au–MgO nanorods. The presence of gold nanoparti-
cles was identified as black spots on the surface of
MgO nanorods. Figures 4(c)–(e) are higher magnifica-
tion images of Au–MgO nanorods. A single nanorod with
approximately 876 nm length and 22 nm diameters is
shown in Figure 4(f).
Figure 6. (a) TG and (b) DTA curves of as-synthesised gold nanopar-
ticles on magnesium hydroxide.
Figures 5(a) and (b) shows the Raman spectra of
Au–Mg(OH)2 and Au–MgO nanorods. The Raman lines
observed (Figure 5(a)) at 519, 848, 915, 1095 cm−1 and
1490 cm−1 are characteristics of Mg(OH)2 which are well
matched with previous report.39 The spectrum of the sam-
of Au–Mg(OH)2. The endothermic weight loss observed
around 200 ꢀC indicated the elimination of hydroxyl
moiety present in the Au–Mg(OH)2. These results from
TG/DTA confirmed that Au–Mg(OH)2 was formed as an
intermediate during the preparation of Au–MgO nanorods.
Similar observations were also made from powder XRD
and Raman studies.
The surface area of the prepared Au–MgO nanorods
determined by BET and Langmuir methods was found
to be 45.8 and 56.7 m2g−1 respectively. As can be seen
ꢀ
ple after calcined at 500 C showed well resolved bands
at 279, 590 and 1092 cm−1 confirming the formation of
Au–MgO nanorods (Fig. 5(b)). The bands observed at 279
and 590 cm−1 were assigned to transverse acoustic (TA)
phonon mode at the zone boundary and transverse opti-
cal (TO) phonon mode at the zone center respectively.
Another broad band at 1092 cm−1 was assigned to the sur-
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from the Figure 7(a), Au–MgO nanorods presented a
type IV isotherm characteristic of mesoporous materials.
face phonon modes in a transverse to longitudinal optical
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phonon mode TO-LO phonon gap.40−42
Copyright: American Scientific Publishers
The surface area and pore volume of Au–MgO nanorods
determined by density functional theory (DFT) method
were 44.6 m2g−1 and 0.152 cm3g−1 respectively. The pore
size distribution derived from the N2-adsorption isotherms
using DFT method revealed that the prepared Au–MgO
nanorods possess various pore sizes such as 2, 4, 6, 14, 18
and 26 nm.
Figure 6(a) shows the TG weight loss curve of Aꢀu–
Mg(OH)2. The initial weight loss observed up to 200 C
was attributed to the removal of crystalline water. The
rapid weight loss monitored in the temperature range
from 350 to 380 ꢀC was attributed to dehydration of
Au–Mg(OH)2. The weight loss observed above 380 ꢀC
may be due to the removal of impurities in the prepared
sample. Figure 6(b) shows the endothermic DTA curve
3.1. Catalysis
3.1.1. Optimization of Reaction Conditions
In order to identify an efficient catalytic system for the oxi-
dation of alcohols, reactions were carried out with different
catalyst quantity, changing the equivalence of hydrogen
peroxide and nature of solvent. In a typical experiment,
oxidation of 1-phenylethanol was taken as model reaction
by varying the quantity of Au–MgO nanorods from 10
to 60 mg. A gradual improvement in the yield of ace-
tophenone was realised with increasing the quantity of
Au–MgO nanorods from 10 to 30 mg. Further loading of
catalyst quantity to 50 mg did not show any improvement
in the yield of the product. But, surprisingly, the use of
60 mg of Au–MgO nanorods catalyst decreased the yield
of acetophenone.
The effect of hydrogen peroxide equivalence on the oxi-
dation of alcohols was also studied. Among the differ-
ent hydrogen peroxide quantities (5 to 20 equivalence),
Figure 5. Raman spectra of (a) Au–Mg(OH)2 and (b) Au–MgO
nanorods.
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Gold Nanoparticles Supported on Magnesium Oxide Nanorods for Oxidation of Alcohols
Emayavaramban et al.
Figure 8. Effect of hydrogen peroxide equivalence on the oxidation of
1-phenylethanol.
3.1.2. Extension of Scope
To check the generality of this study, a series of primary
and secondary alcohols were oxidized with hydrogen per-
oxide in the presence of Au–MgO nanorods to give cor-
responding carbonyl compounds in good yield and the
results are shown in Table I (entries 1–17). Oxidation of
alcohols is a dehydrogenation process but the removal of
H from CH or CH2 group of an alcohol is difficult. When
an electron withdrawing group is attached with CH or CH
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2
group, then these proton(s) become(s) more acidic and
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6
Copyright: American Scientific Publishers
highly reactive so that they could be easily removed. In
our investigation, 1-phenylethanol was converted to ace-
tophenone within 5 h and yielded 68% but substitution of
–Cl and –Br in the phenyl ring of 1-phenylethanol reduced
the yield to 21 and 4% (Table I, entries 1–3) respectively,
due to mesomeric effect.
Oxidation of ꢁ-methyl-2-naphthalenemethanol and
diphenylmethanol (Table I, entries 4 and 5) yielded 98 and
41% (m/z is 182), without oxidation of the naphthalene
ring unlike CrO3/H5IO6 oxidation.43 For the conversion of
Figure 7. (a), (b) and (c) N2-adsorption/desorption isotherms of Au–
MgO nanorods with DFT pore size distribution curve and multipoint
BET.
the 15 equivalence showed a maximum yield of 68%
(Fig. 8). It is important to note here that in the absence of
hydrogen peroxide, no oxidation of 1-phenylethanol was
observed.
Oxidation of 1-phenylethanol was carried out in dif-
ferent reaction medium like water, toluene, acetonitrile
and dichloromethane with 30 mg of the catalyst and the
corresponding yields are given in Figure 9. From this
result, it is understood, that water served as a best solvent
for the oxidation of alcohols compared to other solvents
tested.
Figure 9. Effect of solvent on the oxidation of 1-phenylethanol.
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Emayavaramban et al.
Gold Nanoparticles Supported on Magnesium Oxide Nanorods for Oxidation of Alcohols
Table I. Oxidation of alcohols using Au–MgO nanorods.a
Entry
1
Substrate
OH
Product
Reaction time (h)
5
Yield (%)b
68
Selectivityd
100
O
OH
OH
2
3
24
24
21
100
100
O
Cl
Br
Cl
4
O
Br
OH
4
5
6
7
5
5
98
100
100
100
99
O
41c
OH
O
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O
6
4
90
OH
O
OH
76
8
9
24
24
12
1c
98
OH
O
100
OH
O
10
11
4
50
99
OH
O
24
15c
100
OH
O
H3CO
H3CO
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Gold Nanoparticles Supported on Magnesium Oxide Nanorods for Oxidation of Alcohols
Emayavaramban et al.
Table I. Continued.
Entry
12
Substrate
Product
Reaction time (h)
3
Yield (%)b
Selectivityd
99
99
OH
OH
O
O
O2N
Cl
O2N
Cl
13
14
4
6
50
97
67
100
OH
O
Br
Br
15
16
17
24
24
24
4
2c
2
100
100
100
OH
O
H3CO
H3CO
S
S
O
O
OH
OH
a
ꢀ
b
Determined from GC; cDetermined from
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Notes. Reaction condition: Au–MgO nanorod (30 mg), substrate (1 mM), H2O2 (15 equivalence), H2O (20 mL), at 27
GC-MS; dSelectivity = [(peak area of substrate + peak area of product)/total peak area]×100.
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Copyright: American Scientific Publishers
1-indanol to 1-indanone (Table I, entry 6), present Au–
3.1.3. Heterogeneity of the Catalyst
MgO nanorods catalytic system (with the yield of 90%
after 3 h) was better compared to Ru-catalyzed oxidation.44
Oxidation of 1-cyclopropylethanol yielded 76% (Table I,
entry 7) but in the case of oxidation of cyclopentanol
and 1-cyclohexylethanol only poor yield was observed
(Table I, entries 8 and 9). It is worth to mention that oxi-
dation of benzyl alcohol proceeds well with this system
and yielded 50% of benzaldehyde without any appreciable
oxidation to the corresponding carboxylic acid (Table I,
entry 10). Electron donating (–OCH3ꢆ and electron with-
drawing (–NO2ꢆ groups present in benzyl alcohol influ-
enced the conversion yield to 15% (m/z = 135) and 99%
respectively (Table I, entries 11 and 12). The oxida-
tion of 4-(chloromethyl)benzyl alcohol, 2-(4-bromophenyl)
ethanol and 2-(4-methoxyphenyl)ethanol yield 50, 97
and 4% of the corresponding carbonyl compounds
which were given in the Table I, entries 13–15.
In the case of 2-thiophenemethanol, the yield of
2-thiophenecarboxaldehyde was very less (Table I, entry
16) with corresponding m/z value of 113. The oxidation
of DL-isoborneol was very difficult due to the steric hin-
drance at bridge head position and only 2% yield of the
carbonyl compound was achieved over a period of 24 h
(Table I, entry 17).
Heterogeneous nature of the catalyst was tested by filtering
the catalyst after 2 h of reaction. The filtrate was con-
tinued to proceed further without catalyst and monitored
at every 1 h for another 3 h using GC and the results
are given in Figure 10. From the Figure 10, it was clear
that no progress occurred in the conversion of 1-indanol to
Figure 10. Heterogeneity test for oxidation of 1-indanol.
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Emayavaramban et al.
Gold Nanoparticles Supported on Magnesium Oxide Nanorods for Oxidation of Alcohols
using solution based chemical reduction method and char-
acterized by XRD, Raman and TG/DTA which confirmed
the formation of intermediate Au–Mg(OH)2 in the reaction
mixture. Further, higher temperature annealing resulted
in the formation of homogenous nanorods AuNPs sup-
ported on MgO nanorods as verified from the results
of XRD, UV-DRS, FE-SEM and TEM. Nitrogen adsorp-
tion/desorption experiment established the mesoporous
nature of catalyst. An effective and base free approach
was adopted for oxidation of alcohols including various
aliphatic and aromatic alcohols to aldehydes or ketones.
AuNPs supported on MgO nanorods is a highly active and
reusable catalyst for the oxidation of alcohols with H2O2
in water at room temperature. The catalyst was reused for
five cycles with consistent activity and selectivity.
Figure 11. Proposed mechanism for the oxidation of alcohols with Au–
Acknowledgment: The authors wish to thank the Uni-
versity Grants Commission (UGC), New Delhi (UGC F.
No. 37-98/2009 (SR) dated 19th December 2009 for the
financial support in the form of a major research project.
MgO nanorods.
1-indanone without catalyst even after 3 h. These results
proved that the reaction is feasible only on the catalyst
surface and also the nanoparticle was not leached out from
the support during the catalysis.
References and Notes
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Reusability of heterogeneous catalysts is an important
advantage that makes them suitable for industrial applica-
tions. Recycling activity of the Au–MgO nanorods catalyst
towards oxidation reaction was tested with 1-indanol as
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The possible mechanism for the oxidation of alcohols
using Au–MgO nanorods is given in Figure 11. The reac-
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alcohol with the oxygen of surface –OH group (basic sites)
present in MgO. Consecutively, the AuNPs on the surface
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alkoxide ion of the alcohol. On the other hand, the H2O2
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supported on MgO nanorods was successfully prepared
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Received: 30 July 2014. Accepted: 5 January 2015.
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