High catalytic activity of a new Ag phosphorus ylide complex supported on montmorillonite: synthesis, characterization, and application for room temperature nitro reduction

Article abstract of DOI:10.1007/s13738-017-1230-x

In this work, the phosphorus ylide, [PPh₃CHC(O)CH₂Cl], was reacted with AgNO₃ to give the [Ag{C(H)PPh₃C(O)CH₂Cl}₂]⁺NO₃^? as the product. Then, it was supported on the modified montmorillonite nanoclay to prepare a new catalyst for the reduction reaction. The structure and morphology of the nanoclay catalyst were characterized by FT-IR, X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray analysis and transmission electron microscopy techniques; also, the content of silver was obtained by inductively coupled plasma analyzer. This composition was exploited to study its catalytic activity in the reduction in aromatic nitro compounds; it displayed the high catalytic activity. Factors such as catalyst amount, solvent, temperature and reaction time were all systematically investigated to elucidate their effects on the yield of catalytic reduction in nitroarenes. This catalytic system exhibited high activity toward aromatic nitro compounds under mild conditions. The catalyst was reused five times without any significant loss in its catalytic activity.

Full text of DOI:10.1007/s13738-017-1230-x

J IRAN CHEM SOC
DOI 10.1007/s13738-017-1230-x
ORIGINAL PAPER
High catalytic activity of a new Ag phosphorus ylide complex
supported on montmorillonite: synthesis, characterization,
and application for room temperature nitro reduction
1
1
1
Kazem Karami · Mahzad Rahimi · Mohammad Dinari
Received: 23 May 2017 / Accepted: 30 October 2017
©
Iranian Chemical Society 2017
Abstract In this work, the phosphorus ylide,
titania, [12], polymeric materials [13, 14], and clay materi-
als [15, 16]. However, clay particles at the nanosize possess
some unique characteristics diferent ꢀrom those oꢀ the other
supports. Thus, they are turned into the platelet ꢀorm with
the thickness oꢀ only 1 nm and the width oꢀ 70–150 nm [17].
Clay minerals can be divided into ꢀour major groups
including the kaolinite group, the montmorillonite (MMT)/
smectite group, the illite group, and the chlorite group.
MMT nanoclay, due to high cation-exchange capacity, large
speciꢁc surꢀace, and colloidal properties that give rise to
the optimum adsorbents oꢀ organic and inorganic substances
[18, 19], has received much attention; it has been used as a
heterogeneous catalyst ꢀor several reactions [20, 21]. These
catalysts enjoy several advantages over their homogeneous
counterparts in terms oꢀ recovery and recycling, as well as
minimization oꢀ the undesired toxic wastes [22].
[
[
PPh CHC(O)CH Cl], was reacted with AgNO to give the
3 2 3
+
−
Ag{C(H)PPh C(O)CH Cl} ] NO as the product. Then,
3
2
2
3
it was supported on the modiꢁed montmorillonite nanoclay
to prepare a new catalyst ꢀor the reduction reaction. The
structure and morphology oꢀ the nanoclay catalyst were
characterized by FT-IR, X-ray powder difraction, scanning
electron microscopy, energy-dispersive X-ray analysis and
transmission electron microscopy techniques; also, the con-
tent oꢀ silver was obtained by inductively coupled plasma
analyzer. This composition was exploited to study its cata-
lytic activity in the reduction in aromatic nitro compounds; it
displayed the high catalytic activity. Factors such as catalyst
amount, solvent, temperature and reaction time were all sys-
tematically investigated to elucidate their efects on the yield
oꢀ catalytic reduction in nitroarenes. This catalytic system
exhibited high activity toward aromatic nitro compounds
under mild conditions. The catalyst was reused ꢁve times
without any signiꢁcant loss in its catalytic activity.
Aromatic amines are important intermediates used ꢀor
the manuꢀacture oꢀ dye stufs, pharma, agricultural chemi-
cals, photographic chemicals, additives, surꢀactants textile
auxiliaries, chelating agents, and polymers [23–26]. These
are essentially prepared by the reduction in nitroarene with
metals [27–31]. Thus, the reduction in aromatic nitro com-
pounds to their corresponding anilines is one oꢀ the most
important transꢀormations in the synthetic organic chemistry
[32]. A plethora oꢀ methods has been used ꢀor the reduction
in nitroaromatic compounds to their corresponding amines
[33–35]. Among these methods, the nanocatalysts oꢀten
exhibit speciꢁc physical and chemical properties [36], giv-
ing rise to their high catalytic activity ꢀor the reduction in
nitrobenzenes [37].
Keywords Silver phosphorus ylide · Montmorillonite
(
MMT) · Nanocatalyst · Nitroarenes · Reduction reaction
Introduction
In the last decade, silver has been immobilized onto various
supports such as silica [1, 2], MCM and zeolite [3, 4], car-
bon nanotubes and activated carbon [5–8], alumina [9–11],
In the present work, nanoclay (MMT) was used as a
green, readily available and non-expensive support ꢀor Ag
phosphorus ylide complex and the resulting hybrid material
was used ꢀor hydrogen transꢀer reactions oꢀ aromatic nitro
compounds at room temperature. According to the obtained
*
Kazem Karami
karami@cc.iut.ac.ir
1
Department oꢀ Chemistry, Isꢀahan University oꢀ Technology,
Isꢀahan 84156/83111, Iran
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1
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J IRAN CHEM SOC
data, the newly prepared nanocatalyst exhibited excellent
activity ꢀor the hydrogenation oꢀ a series oꢀ nitro compounds
and conversion oꢀ them to their corresponding amino deriva-
tives. The reactions were perꢀormed at the room temperature
and short reaction times. As a result, less energy and time
were consumed in comparison with many other catalytic
reductions oꢀ nitroarenes. At least, the catalyst was reusable
[PPh CHC(O)CH Cl] was reacted with AgNO (2:1) in
3
2
3
acetone (10 mL) at room temperature in dark. The result-
ing solution was stirred ꢀor 4 h; then, the reaction mixture
was concentrated under reduced pressure to yield a white
solid. The residue was puriꢁed by re-precipitation ꢀrom ethyl
acetate and n-hexane, which were collected and air-dried
(Scheme 1). Yield is 64%.
ꢁ
ve times. Please insert the reaction Scheme here.
Preparation of the Ag complex/MMT nanohybrid
catalyst
Experimental
Materials
The original MMT-K10 powder samples were sieved, and
the ꢀraction < 40 mm was used as a host matrix ꢀor the
preparation oꢀ the Ag/MMT. The clay mineral sample was
stirred in 30 mL DI water ꢀor 8 h at 90 °C. Then, it was dis-
persed in the 0.1 M aqueous solution oꢀ Ag complex, and the
mixture was stirred at 60 °C ꢀor 6 h. The product was ꢁltered
through a plug oꢀ glass ꢁber ꢁlter paper and washed with
distilled water several times. It was dried ꢀor 24 h at 80 °C.
Starting materials and solvents were purchased ꢀrom Merck
and Aldrich; they were used without puriꢁcation. MMT-K10
with the cation-exchange capacity oꢀ 0.119 eq/100 g was
provided by Aldrich chemical Co.
Characterization
General procedure for the reduction in nitroarenes
Inꢀrared spectra were recorded on a FT-IR JASCO 680 spec-
−
1
trophotometer in the range oꢀ 400–4000 cm using KBr
pellets. Gas chromatography (GC) data ꢀor the reduction
reaction were recorded by 6890 N Technologies ꢀrom Agi-
First, NaBH (1 mmol) was used as a reducing agent ꢀor
4
the conversion oꢀ Ag (+ 1) to Ag (0) in methanol at room
temperature ꢀor 2 h. Aꢀter that, the Ag/MMT was ꢁltered and
used as a catalyst. Then, in a typical procedure, a mixture
oꢀ 4-nitrophenol (0.1 mmol), KOH (0.15 mmol), isopropyl
alcohol (3 mL), and Ag/MMT catalyst (50 mg) 1.01 wt%
was stirred at room temperature ꢀor an appropriate time
(Scheme 2). Aꢀter the completion oꢀ the reaction (monitored
by GC), the catalyst was separated by ꢁltration. The ensu-
ing product was extracted with ethyl acetate and repeatedly
washed with water (3–4 times) to remove KOH. The result-
ing solvent was evaporated to dryness in vacuum.
lent Company, using the FID detector and N as the carrier
2
gas. Column chromatography with 28.5 m length, 320 µm
inner diameter, and 0.25 µm thickness (the HP + 5 types)
was used. X-ray difraction (XRD) analysis was carried out
to measure the change in the interlayer spacing oꢀ the clay
mineral based on Bragg’s law ꢀor conꢁrming the intercala-
tion oꢀ complexes into the galleries oꢀ the Ag/MMT nano-
catalyst. The XRD analyses were perꢀormed via the X-ray
difractometer (Bruker, D8 Advance) with CuKa character-
istic radiation (wavelength k = 0.154 nm at 45 kV, 100 mA,
with a step size oꢀ 0.02° and at the range oꢀ 2θ = 1.2–10°).
The dispersion morphology oꢀ the samples was observed
using ꢁeld-emission scanning electron microscope [(FE-
SEM) HITACHI: S-4160]. Energy-dispersive X-ray analysis
Results and discussion
1
13
H NMR and C NMR spectra oꢀ the Ag complex were
1
(
EDX) results were obtained at 20 kV using Philips (Model
recorded in CDCl . The H NMR spectrum oꢀ Ag com-
3
XL-30) instrument. Transmission electron microscopy
plex displayed two sets oꢀ signals ꢀor the methylene pro-
1
3
(
TEM) images were obtained using a Philips CM 120 micro-
tons and acrylic protons. The C NMR spectrum oꢀ the
Ag complex showed aliphatic and aromatic regions. MMT
had a crystal lattice unit ꢀormed by one alumina octa-
hedral sheet sandwiched between two silica tetrahedral
sheets. The elementary structural units were silica tetra-
scope with an accelerating voltage oꢀ 100 kV. NMR spectra
were recorded in DMSO-d at room temperature on a Bruker
6
1
13
spectrometer at 400.13 MHz ( H) and 100.61 MHz ( C).
The silver content oꢀ the catalyst was measured by induc-
tively coupled plasma (ICP) analyzer (Varian-vista-pro-CCD
simultaneous ICP-OES inductive genoppeltes plasma).
+
4
hedron and aluminum octahedral [39, 40]. The cation Si
was ꢀourꢀold and possessed tetrahedral coordination with
+
3
oxygen, while the cation, Al , occurred in the sixꢀold or
octahedral coordination. The ion substitution or the site
vacancies at the tetrahedral and/or octahedral sheets could
result in a negatively charged surꢀace. The exchangea-
ble cations between the layers could compensate ꢀor the
Preparation of the Ag phosphorus ylide complex
First, the phosphorus ylide, [PPh CHC(O)CH Cl], was
3
2
prepared according to our previous study [38]. Then, the
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J IRAN CHEM SOC
Scheme 1 Preparation oꢀ the
Ag complex
Scheme 2 Hydrogen transꢀer reactions oꢀ aromatic nitro compounds
on the modiꢁed Ag/MMT-K10 nanocatalyst
Fig. 1 FT-IR spectra oꢀ (a) MMT-K10 and (b) Ag/MMT hybrid
negative charge and might be easily exchanged by other
metal cations accounting ꢀor the high ion-exchange capac-
ities oꢀ these clay minerals [41]. Due to this crystalline
arrangement, MMT could expand and contract the inter-
layer while maintaining the two-dimensional crystallo-
graphic integrity. The interlayer between units contained
positive cations and water molecules.
FT‑IR analysis
The FT-IR spectrum oꢀ the MMT-K10 and Ag/MMT hybrid
is shown in Fig. 1. The FT-IR spectra ꢀor MMT-K10 showed
−
1
a broadband in the range oꢀ 2700–3600 cm that was
related to the interlayer absorbed water molecules (Fig. 1a).
−
1
According to ICP analysis, the silver content oꢀ the
catalyst was obtained to be 1.01 wt%.
A weak band that appeared at 1645 cm was related to the
OH bending vibration. The Si–O stretching band was in the
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J IRAN CHEM SOC
−
1
−1
range oꢀ 1300–900 cm . The bands at 463 and 529 cm
could be regarded as a good sign, revealing that complex had
entered into the interlayer space oꢀ MMT.
were related to Mg–O and Al–O bonds, respectively [42].
The FT-IR spectrum oꢀ Ag/MMT showed characteristic
−
1
bands due to the clay mineral (Si–O) at 1100 cm . The IR
TEM analysis
−
1
spectrum oꢀ ligand showed a band at 1575 cm that could
be assigned to ν (C=O); ꢀor the Ag complex, the absorption
Figure 3 shows the TEM images oꢀ the Ag/MMT nanocata-
lyst. In the TEM image oꢀ the hybrid, the presence oꢀ Ag (0)
nanoparticles based on the sizes more than 235 resulted in
45.89-nm particles in the presence oꢀ MMT platelet ꢀrag-
ments; however, they were separated ꢀrom each other. Proba-
bly, they originated ꢀrom the collapse oꢀ MMT-K10 structure
during the ion-exchange process, conꢁrming the damage oꢀ
the MMT-layered morphology by the ion-exchange process,
as already shown by XRD analysis.
−
1
was in the range oꢀ 1670–1675 cm in the region typical
ꢀ
or the C-bonded phosphorus ylides [43]. The three bands
−
1
corresponded to P–C bonds at 700–800 cm (Fig. 1b).
Carbonyl-stabilized phosphorus ylides could behave as C
or O donors owing to the delocalization oꢀ the ylidic electron
pair The FT-IR spectra conꢁrmed that the ligand was bound
through the carbon oꢀ ylide to the Ag (I) center. The FT-IR
data exhibited that the Ag complex and then MMT/Ag were
synthesized, conꢁrming the presence oꢀ the Ag complex
intercalated between the MMT layers.
FE‑SEM analysis
X‑ray diꢀraction analysis
The FE-SEM images oꢀ the Ag/MMT catalyst were stud-
ied by the SEM technique (Fig. 4). According to the SEM
images, the Ag/MMT catalyst had a layer structure.
Figure 2 shows the XRD pattern oꢀ pristine MMT and Ag/
MMT hybrids. The pristine MMT showed a diꢀꢀraction
peak at 2θ = 8.7° with the d-spacing oꢀ 1.051 nm (Fig. 2a).
Aꢀter the treatment oꢀ MMT by cation-exchange with the
Ag complex, the X-ray reꢂections were shiꢀted to a lower
angle position. The XRD pattern oꢀ the Ag/MMT exhibited
a difraction peak at about 2θ = 2.3° that corresponded to
an interlayer distance oꢀ 3.84 nm (Fig. 2b). An increase in
the interlayer distance led to a shiꢀt oꢀ the difraction peak
toward the lower angles, conꢁrming that the intercalation
reaction and surꢀace modiꢁcation oꢀ MMT had occurred.
This implied that the basic structures oꢀ the MMT were kept,
the layers were only propped open, and the basal distances
were increased signiꢁcantly, thereby providing evidence
that the intercalation reaction had occurred successꢀully. It
Energy‑dispersive X‑ray spectroscopy
The energy-dispersive X-ray spectroscopy (EDX) showed
the presence oꢀ Ag and P atoms as well as Al, Si, Fe, Cl, and
O atoms in the structure oꢀ the MMT-supported Ag catalyst
(Fig. 5).
Catalytic activity of Ag/MMT for the reduction
in aromatic nitro compounds
The Ag/MMT material was explored as a nanocatalyst ꢀor
hydrogen transꢀer reactions oꢀ aromatic nitro compounds
using isopropyl alcohol (IPA) as the hydrogen donor
(
Table 1). First, the catalytic activity oꢀ the prepared nano-
catalyst was tested ꢀor the reduction in 4-nitrophenol to
yield 4-aminophenol under various reaction conditions. In
the hydrogen transꢀer reaction, diferent parameters includ-
ing the efects oꢀ the type oꢀ bases, temperature, solvent,
and the amount oꢀ the catalyst were tested. So, three difer-
ent amounts oꢀ catalyst 1 (25, 50, and 100 mg) were used,
keeping all other reaction parameters including room tem-
perature, IPA (3 mL), KOH, and reaction time (2 h) ꢁxed
(
Table 2, entries 5, 11, and 12). Consequently, 50 mg oꢀ
the catalyst 1 was taken to be ideal with higher conversion.
Diferent reactions were used in order to choose the suit-
able base in the reduction reaction (Table 2, entries 6–10).
Thereꢀore, a high yield was gained in the presence oꢀ KOH
in IPA. Moreover, we tested various solvents in the pres-
ence oꢀ KOH, using the appropriate time reaction; it was
evident that the catalytic activity in isopropanol was greater
than that in CH CN, CH Cl , CH OH, and ethanol (Table 2,
Fig. 2 X-ray powder difraction pattern oꢀ (a) MMT-K10 and (b) Ag/
3
2
2
3
MMT
entries 1–4) and IPA was the best selection ꢀor this reduction
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J IRAN CHEM SOC
Fig. 3 TEM images oꢀ Ag/MMT at diferent magniꢁcations oꢀ a 150 nm, b 80 nm, and histogram illustrating the Ag nanoparticles size distribu-
tion
reaction (Table 2, entry 5). In addition, the efect oꢀ reaction
temperature was investigated at two diferent temperature
intervals (room temperature and 60 °C) (Table 2, entries 5,
product, thereby minimizing the eforts to separate the unre-
acted starting compounds. As the solvent used was IPA,
without any harmꢀul group such as Cl, the reaction was saꢀe.
The nature and position oꢀ the substituents on the aromatic
nitro compounds did not signiꢁcantly inꢂuence the catalytic
perꢀormance oꢀ the synthesized nanocatalyst. For example,
electron-donating and electron-withdrawing groups such
as –Cl, –F, –Br, –NO , –NHNH , and –OCH did not have
6
). At room temperature, the reaction showed the ideal yield
aꢀter 2 h (Table 2, entries 6). Aꢀter the optimization oꢀ the
reaction conditions, the catalytic activity oꢀ the catalyst with
other nitro substrates was ꢀurther explored. Notably, transꢀer
hydrogenation over the modiꢁed clay mineral as the nano-
catalyst exhibited excellent activity ꢀor the hydrogenation oꢀ
a series oꢀ nitrobenzenes. All nitroarenes were reduced in
excellent yields (Table 1, yield 80–98%) afording a single
2
2
3
any signiꢁcant inꢂuence on the reduction reaction. Notably,
transꢀer hydrogenation over Ag/MMT nanocatalyst exhibited
excellent activity and selectivity (Table 2, entries 4–6, 8–10)
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J IRAN CHEM SOC
Fig. 4 FE-SEM images corresponding to the Ag (0) complex/MMT beꢀore reaction
Fig. 5 EDX spectrum oꢀ the
MMT-supported Ag catalyst
Table 1 Optimizing o the
reaction conditions ꢀor the
reduction in 4-nitrophenol,
using the Ag/MMT nanocatalyst
Entry
Solvent
Catalyst (g)
Base
Temp. (°C)
Time (h)
Conv. (%)a
1
2
3
4
5
6
7
8
9
CH CN
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.1
KOH
KOH
KOH
KOH
KOH
KOH
60
60
60
60
6
6
4
5
2
2
4
3
40
45
70
60
97
95
85
90
30
87
95
75
3
CH OH
3
Ethanol
CH Cl
2
2
Isopropanol (IPA)
60
IPA
IPA
IPA
IPA
IPA
IPA
IPA
R.T
R.T
R.T
R.T
R.T
R.T
R.T
Na CO
2
3
NaOAC
NaOH
K CO
4
3.5
2
10
11
12
2
3
KOH
KOH
0.025
2
Reaction conditions: 4-nitrophenol (0.1 mmol), base (0.15 mmol), solvent (3 mL), and catalyst
a
Determined by GC
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J IRAN CHEM SOC
Table 2 Ag (0) complex/
montmorillonite catalyzed by
the hydrogen transꢀer reaction
oꢀ aromatic nitroarene
Entry
Nitro compound
Amines
Time
h)
Yield
TOF
(%)a
(h–1
(
)
1
2
2.5
98
8.64
2
97
10.82
3
4
8.64
7.22
2
.5
3
95
90
5
2
.5
93
8.64
6
5
.4
4
98
7
8
6
4
.21
.81
3
.5
90
95
4.5
9
1
0.82
2
93
88
10
8
7
.64
.22
2
.5
11
3
2
80
80
12
1
0.82
Reaction conditions: nitroarene (0.1 mmol), KOH (0.15 mmol), IPA (3 mL),
and 50 mg oꢀ catalyst 1.01 (wt%) Ag
b
Determined by GC
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J IRAN CHEM SOC
Fig. 6 FE-SEM images corresponding to the Ag (0) complex/MMT aꢀter the ꢁꢀth run
Scheme 3 The possible mechanism ꢀor hydrogen transꢀer reactions over Ag complex/montmorillonite
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J IRAN CHEM SOC
VALUE]
[
was tested by recycling and reusing the catalyst (ꢁve times)
without any signiꢁcant loss in the catalytic activity. Aꢀter
each cycle, the catalyst was separated and used ꢀor the next
cycle to check the eꢃciency oꢀ this protocol in the reduction
in 4-nitrophenol. Aꢀter using this catalyst ꢀor nitro reduc-
tion, the SEM images did not show any changes in the sur-
9
6
100
90
8
6
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
80
ꢀ
ace morphology and the layered structure was conꢁrmed
Fig. 6).
(
In order to show the improvement in this heterogeneous
reaction, a typical experiment was conducted. The model
reaction oꢀ the reduction in 4-nitrophenol was proceeded.
The mixture was stirred without the catalyst ꢀor 24 h. No
ꢀormation oꢀ product was observed. Also, a standard reaction
oꢀ the reduction was proceeded by 4-nitrophenol in the pres-
ence oꢀ the Ag complex. The mixture was stirred ꢀor 12 h;
notably, no product was observed even aꢀter 12 h, indicating
that no homogeneous catalyst was involved in the reaction.
The reduction in 4-nitrophenol was done without the inter-
calated Ag complex, such that no ꢀormation oꢀ the product
was observed.
1
2
3
4
5
Run
Fig. 7 Recyclability tests ꢀor the catalyst in the reduction in 4-nitro-
phenol (reaction conditions were the same as those given in Table 2)
The proposed mechanism ꢀor the reduction in aromatic
nitro compounds is depicted in the Scheme 3 [44]. Aꢀter the
reaction between NaBH and the prepared complex and the
4
conversion oꢀ Ag (+ 1) to Ag (0), as a result oꢀ the adsorp-
tion oꢀ IPA on the Ag/MMT nanocatalyst surꢀace, a hydride
was transꢀerred to the nitro group with the concomitant ꢀor-
mation oꢀ acetone 1, 2. Meanwhile, the rate oꢀ reaction could
show the dependence on the strength oꢀ the adsorption oꢀ
both isopropanol and the nitro compound. The nitroso inter-
mediate 3, which was ꢀormed upon the elimination oꢀ water
adsorbed on the Ag/MMT nanocatalyst, was again reduced
by the hydride transꢀer ꢀrom IPA to the hydroxylamine 4,
which was ꢀurther reduced to the amine group 5. Mainly,
phosphorus ylides show interesting properties such as high
stability and resistance as ligands. Phosphorus ylides could
be used as the chiral auxiliary reagents, reaction intermedi-
ates, or starting materials in a wide variety oꢀ processes due
to their nucleophilic nature, particular bonding properties,
and diverse coordination modes. In our work, it is shown
that the phosphorus ylide could be a stable agent ꢀor the
Ag nanoparticles. Notably, we synthesized a heterogeneous
catalyst by using the Ag phosphorus ylide complex that was
Fig. 8 Kinetic proꢁles oꢀ the Ag catalyst in the reduction reaction.
(
a) Normal reaction kinetics in the presence oꢀ catalyst; (b) reaction
kinetics in the absence oꢀ the catalyst. Reaction conditions: nitroarene
0.1 mmol), KOH (0.15 mmol), IPA (3 mL), 50 mg oꢀ catalyst, room
temperature, 2 h
(
ꢀ
or the hydrogenation oꢀ a series oꢀ halogenated nitroben-
zenes to their corresponding halogenated amines, without
any dehalogenation product. The stability and reusability oꢀ
the catalyst at room temperature could be important ꢀrom the
viewpoint oꢀ a green sustainable protocol, in the heterogene-
ous catalysis. So, the stability oꢀ the Ag/MMT nanocatalyst
Table 3 Comparison with
Entry
Catalyst
Reaction conditions solvent/
base/temp./time/oxidant
Yields (%)
Reꢀerences
the reported results ꢀor the
reduction reaction on the
supported Ag catalysts
1
2
3
Ag–Ni core–shell nanoparticles
AgNPs@CeO2
Ag-MPTA
IPA/KOH/80 °C/2 h
Dodecane/110 °C/24 h/H2
96
98
96
[44]
[45]
[46]
NaOH/i-PrOH/80 °C/10 h/N
2
atmosphere
4
5
6
SiO Ag (nano), NaBH , H O
Ag/HT (Ag: 0.02 mmol)
Complex 1/clay
H O/NaBH /Reꢂux/1 h/-
100
> 99
98
[47]
[48]
This work
2
4
2
2
4
DMA, H O/150 °C/CO/3 h
2
IPA/KOH/RT/2 h/-
1
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J IRAN CHEM SOC
ꢀ
acile, simple, and inexpensive; it could be used in a green
Acknowledgments We wish to express our gratitude to the Research
Afairs Division oꢀ Isꢀahan University oꢀ Technology (IUT), Isꢀa-
han, ꢀor the partial ꢁnancial support. Further ꢁnancial support ꢀrom
Iran Nanotechnology Initiative Council (INIC) is also grateꢀully
acknowledged.
protocol ꢀor nitro reduction.
Recycle procedure
To conꢁrm the recyclability oꢀ the nanocatalyst in the reduc-
tion in nitroarenes, 4-nitrophenol was used. Aꢀter the com-
pletion oꢀ the ꢁrst reaction cycle, the catalyst was separated
and washed several times with ethyl acetate and water. The
catalyst was dried overnight at 80 °C beꢀore being reused.
For the other runs, the ꢀresh 4-nitrophenol was added while
the other conditions were the same as the ꢁrst reaction cycle.
A little decrease in the conversion was observed with
no signiꢁcant change in selectivity, which exhibited that
the catalyst was stable and could be reused. The results are
shown in Fig. 7.
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