The colloidal synthesis of unsupported nickel-tin bimetallic nanoparticles with tunable composition that have high activity for the reduction of nitroarenes

Article abstract of DOI:10.1016/j.catcom.2015.02.026

Abstract Ni-Sn bimetallic nanoparticles with controllable size and composition were prepared by facile method in ambient air using inexpensive metal salts. Adjusting stoichiometric ratio of Ni and Sn precursors afforded nanoparticles with different compositions, such as Ni₁₀₀, Ni₇₄-Sn₂₆, Ni₅₉-Sn₄₁, and Ni₅₀-Sn₅₀. The characterization of nanoparticles was performed by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM), and energy dispersive X-ray analysis (EDX). Ni₇₅-Sn₂₅ and Ni₆₀-Sn₄₀ nanoparticles showed enhanced catalytic activity towards 2-nitroaniline reduction as compared with Ni nanoparticles. Furthermore, Ni₇₅-Sn₂₅ nanocatalyst exhibited excellent activity for the reduction of a number of nitro aromatic compounds under mild conditions along with high level of reusability.

Full text of DOI:10.1016/j.catcom.2015.02.026

Catalysis Communications 65 (2015) 85–90
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
The colloidal synthesis of unsupported nickel‐tin bimetallic nanoparticles
with tunable composition that have high activity for the reduction
of nitroarenes
⁎
⁎
Mazloom Shah, Qing-Xiang Guo , Yao Fu
Department of Chemistry, University of Science and Technology of China, Hefei 230026, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 January 2015
Received in revised form 20 February 2015
Accepted 21 February 2015
Available online 25 February 2015
Ni‐Sn bimetallic nanoparticles with controllable size and composition were prepared by facile method in ambient
air using inexpensive metal salts. Adjusting stoichiometric ratio of Ni and Sn precursors afforded nanoparticles
with different compositions, such as Ni100, Ni74‐Sn26, Ni59‐Sn41, and Ni50‐Sn50. The characterization of nanopar-
ticles was performed by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolu-
tion transmission electron microscopy (HR-TEM), and energy dispersive X-ray analysis (EDX). Ni75‐Sn25 and
Ni60‐Sn40 nanoparticles showed enhanced catalytic activity towards 2-nitroaniline reduction as compared with
Ni nanoparticles. Furthermore, Ni75‐Sn25 nanocatalyst exhibited excellent activity for the reduction of a number
of nitro aromatic compounds under mild conditions along with high level of reusability.
Keywords:
Nanoparticles
Nickel
© 2015 Published by Elsevier B.V.
Nickel‐tin
Nitroarene
Reduction
1. Introduction
chemical behavior of the bimetallic system. In these works, Ni‐Sn alloy
nanoparticles were mostly prepared directly on catalyst supports or
In recent years, research has been directed towards the synthesis
and application of metal nanoparticles owing to their unique properties
compared to bulk materials [1]. Among various metal nanoparticles,
nickel nanoparticles have received considerable attention because of
their applications as catalytic and magnetic materials [2]. The magnetic
properties of nickel nanoparticles make them to be effective and easily
separated from the reaction mixture by applying an external magnetic
field. The nanoparticles composed of two metals are of great importance
from the scientific and technological points of view for the enhance-
ment of the catalytic activities of monometallic nanoparticles for indus-
trial production of chemicals. The enhancement derived from the
combination of two metal elements into bimetallic nanoparticles can
arise from an ensemble effect, a modified electronic structure, or the for-
mation of new catalytic sites [3–6]. Nanoparticles composed of a noble
metal and a non-noble metal have an increasing interest among re-
searchers because of their high possibility of tailoring electronic and
geometric structures, which in turn can enhance the catalytic
activity [7–9]. Bimetallic nanoparticles involving tin and late transition
metals are useful industrial catalysts for various hydrocarbon reactions.
Several authors have studied the deposition of tin on nickel which
highlighted its actual importance for the bimetallic system [10–13].
The formation of surface alloys appears to be determinant in the
substrates by coimpregnation, sequential impregnation or surface or-
ganometallic chemistry [10–14]. On the contrary side, reports on the
colloidal synthesis of unsupported Ni‐Sn bimetallic nanoparticles with
advanced structural, size or composition control are very limited. There-
fore, the synthesis of Ni‐Sn nanoparticles with narrow size-distribution
and well controlled composition/structure still remains a challenge. The
nickel nanoparticles exhibit lower activity than bimetallic Ni‐Sn nano-
particles but higher selectivities for the production of hydrogen by
aqueous phase reforming of oxygenated hydrocarbons [15,16]. Adding
tin to nickel catalysts influence the dehydrogenation of cyclohexane,
hydrogenation of acetylene, H2-D2 equilibration and H‐D exchange be-
tween C2D4 and H2 [17,18]. The addition of tin to modify metal catalysts
prevents metal carbide formation and therefore, it reduces cooking [19].
The reduction of nitro compounds to amino compounds is industrially
important as the amines obtained are versatile synthetic intermediates
due to their application in the preparation of dyes, pharmaceuticals, ag-
ricultural products, surfactants and polymers [20–22]. In this regard, a
variety of methods and catalyst system have been well documented
for the catalytic reduction of nitro compounds [23–30], however,
some of these protocols bear drawbacks such as long reaction time,
high reaction temperature, use of complicated method for catalyst syn-
thesis, use of toxic and expensive catalyst, carcinogenic solvent, and un-
availability and reusability of the catalyst. Therefore, development of
fast, cost effective, and mild catalytic route for the reduction of
nitroaromatics is needed. In the present study, the Ni‐Sn nanoparticles
⁎
Corresponding authors.
E-mail addresses: qxguo@ustc.edu.cn (Q.-X. Guo), fuyao@ustc.edu.cn (Y. Fu).
http://dx.doi.org/10.1016/j.catcom.2015.02.026
1566-7367/© 2015 Published by Elsevier B.V.

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M. Shah et al. / Catalysis Communications 65 (2015) 85–90
Table 1
Reaction conditions for the preparation of nanoparticles.
Nanoparticles
Precursors (mol L‐1
)
PVP (g)
NaBH4 (g)
T1 (°C)
T2 (°C)
Reaction time (min)
Ni
Ni‐Sn
Nickel (II) formate dehydrate (0.03)
Nickel (II) formate dehydrate (0.03)
Tin (II) chloride dehydrate (0.01)
Nickel (II) formate dehydrate (0.036)
Tin (II) chloride dehydrate (0.02)
Nickel (II) formate dehydrate (0.03)
Tin (II) chloride dehydrate (0.03)
Tin (II) chloride dehydrate (0.03)
0.35
0.35
0.15
0.17
69
50
195
198
150
150
Ni‐Sn
Ni‐Sn
Sn
0.35
0.35
0.25
0.17
0.17
0.15
50
50
25
198
198
25
150
150
60
with tunable composition having different particle sizes were prepared
by facile method using inexpensive metal salts such as nickel format
dihydrate (Ni (HCOO)2·2H2O) and tin chloride dihydrate (SnCl2·2H2O).
Furthermore, Ni‐Sn nanoparticles with different particle sizes and metal
compositions were tested for reduction of 2-nitroaniline by NaBH4 in
water. The nanocatalyst which exhibited best performance was used
for the reduction of a number of nitro aromatic compounds under
mild reaction conditions.
was stirred at room temperature until the yellow solution became col-
orless. After the completion of the reaction, the reaction mixture was fil-
tered. Then, the residue was extracted with ethyl acetate. The organic
layer was dried over Na2SO4 and the solvent was removed under vacu-
um. The products were identified with GC‐MS analysis.
3. Results and discussion
The nickel‐tin nanoparticles with tunable composition were synthe-
sized in air using Ni (HCOO)2·2H2O and SnCl2·2H2O as precursors and
NaBH4 as reducing agent. Nanoparticles composed up of reactive
metals such as Ni and Sn typically degrade in the presence of air. How-
ever, Ni-Sn nanoparticles described here were synthesized, dried and
stored in ambient condition. It is well known that the morphology and
size distribution of metallic particles produced by the reduction of pre-
cursor salts in solution depend on various reaction conditions such as
concentration, temperature, time, molar ratio of precursor salt/reducing
agent, mode and order of addition of reagents, presence and type of pro-
tective agents, degree and type of agitation, and whether nucleation is
homogeneous or heterogeneous [31]. The synthesis conditions used
for the production of nanoparticles are summarized in Table 1. The
nominal particle-composition was controlled by varying the ratio be-
tween the nickel and tin precursors. The compositions of Ni‐Sn nano-
2. Experimental
2.1. Materials
Tin chloride dihydrate (SnCl2·2H2O ≥ 98%), sodium borohydride
(NaBH4 ≥ 96%), ethylene glycol (HOCH2CH2OH 99%), polyvinylpyrroli-
done with an average molecular weight of 10,000 (PVP 100%), nitroben-
zene (NO2C6H5 ≥ 99%), 3-nitroaniline (NH2C6H4NO2 ≥ 98.5%), 4-
chloronitrobenzene (ClC6H4NO2), acetone (CH3COCH3 ≥ 99%) and
ethanol (C2H5OH ≥ 99%) were purchased from Sinopherm chemical
reagent Co. Ltd., 4-nitroaniline (NH2C6H4NO2) from Aladdin,
petafluoronitrobenzene (NO2C6F5) and 4-nitroanisole (CH3OC6H4NO2)
from TCI Mark and nickel (II) formate dihydrate (Ni (HCOO)2·2H2O),
2-nitroaniline (NO2C6H4NH2 98%) from Alfa Aesar.
particles, as determined by EDX analysis, were Ni74-Sn26, Ni59-Sn41
,
2.2. Methods
and Ni50-Sn50 which corresponded to the precursor Ni/Sn molar ratios
of 3:1, 3:2, and 1:1, respectively shown in Table 2. The XRD patterns
of as-synthesized Ni and Ni‐Sn nanoparticles are shown in Fig. 1.
Three main characteristic diffraction peaks at 2θ = 44.38, 51.67, and
76.57° correspond to the (111), (200), and (220) crystal planes of me-
tallic Ni, confirming the formation of Ni nanoparticles with no visible
impurity phases such as NiO. The broadening of peaks in the XRD
diffractogram is inversely correlated with short crystallite size of the
nanoparticles. X-ray diffraction patterns of Ni‐Sn show a crystalline
structure, where two broad diffraction lines at 30.41° and 43.05° were
clearly observed. The broadening of peaks in the diffraction patterns is
because of very small crystallite size [32–34]. The Ni‐Sn XRD patterns
indicated the presence of hexagonal Ni3Sn and orthorhombic Ni3Sn2
phases. Although, the hexagonal Ni3Sn phase showed diffraction lines
2.2.1. Preparation and catalytic application of nanoparticles
For preparation of Ni nanoparticle 0.24 g Ni (HCOO)2·2H2O was dis-
solved in 35 mL of ethylene glycol. Calculated amount of PVP was added
and the solution was heated to 342 K while stirring until the formation
of a completely homogeneous blue solution. Once at this temperature,
0.15 g of NaBH4 was added under magnetic stirring. The resultant solu-
tion was refluxed at 468 K for 2.5 h. In case of Ni‐Sn nanoparticle prep-
aration calculated amount of Ni (HCOO)2·2H2O, SnCl2·2H2O and PVP
were added in 35 mL of ethylene glycol and the solution was heated
to 323 K while stirring until the formation of a completely homoge-
neous blue solution. Once at this temperature, 0.18 g of NaBH4 was
added under magnetic stirring. The resultant solution was refluxed at
470 K for 2.5 h. The nanoparticles were precipitated in acetone, washed
with acetone, ethanol and dried in air at room temperature.
In a typical reduction, 0.0019 g of catalyst was dispersed in 15 mL of
aqueous solution containing 0.5 mmol of NaBH4. The mixture was vigor-
ously stirred for 10 min at room temperature. 10 mL of 0.0036 M 2-
nitroaniline aqueous solution was added and the resulting mixture
Table 2
Particle size and composition as determined by TEM‐EDX for the as prepared Ni‐Sn
nanoparticles.
Entry
Sample
name
Average particle
size (nm)
Nominal
composition
(atom % Ni)
Ni‐Sn composition
determined by EDX
(atom % Ni)
1
2
3
Ni‐Sn (3:1)
Ni‐Sn (3:2)
Ni‐Sn (1:1)
4.5
8
7.2
75
60
50
73.6
58.8
49.5
Fig. 1. Powder XRD patterns for Ni, Sn and Ni‐Sn nanoparticles.

M. Shah et al. / Catalysis Communications 65 (2015) 85–90
87
corresponding to the (0 0 2) and (2 0 1) planes at 42.54 and 44.95°, re-
spectively that may account for the broad peaks observed at 43.41, the
line at 30.41 cannot be associated to this phase since the closer possible
diffraction line corresponding to the (1 0 1), (2 2 0) and (3 1 0) plane
appears at 28.61, 71.21 and 74.67 respectively far away from that exper-
imentally observed. However, the Ni3Sn2 phase revealed diffraction
lines corresponding to the (1 1 2), (2 1 1), (0 2 0), (1 2 2) and (3 0 2),
appears at 30.32, 32.36, 34.35, 42.96 and 44.07, respectively. With a
gradual increase in tin content, the peaks progressively shifted to higher
intensity and low 2θ values without forming any discrete Sn reflections,
which suggested that the nanoparticles were bimetallic alloys, as op-
posed to a physical mixture of separately nucleated monometallic Ni
and Sn particles. Representative TEM images and the corresponding
particle size distributions of the as-prepared, Ni74-Sn26, Ni59-Sn41, and
Ni50-Sn50 nanoparticles are shown in Figs. 2, 3 (a, b) and Fig. 3 (c, d), re-
spectively. Ni, Ni74-Sn26, Ni59-Sn41, and Ni50-Sn50 nanoparticles were
observed to have a mixture of irregular shape and spherical morphology
with an estimated average size of 13 nm, 4.5 nm, 8 nm and 7.2 nm, re-
spectively. The mean diameter of the nanoparticles was estimated by
counting about 100 metal particles. The size estimated from TEM micro-
graphs agrees well with the crystallite size calculated from XRD, which
may reveal nearly single crystalline character of metallic Ni nanoparti-
cles. However in case of Ni-Sn nanoparticles, well-dispersed nanoparti-
cles are single crystals while the elongated particles are polycrystals.
The EDX analysis of the Ni-Sn nanoparticles showed that Sn concentra-
tion on the agglomerated particles was higher than on the well dis-
persed nanoparticles. It means that the material formed is quite
heterogeneous having particles with different compositions. It is found
that the reducibility of Ni2+ in the synthesis conditions was easier
than that of Sn2+ favouring the initial formation of nickel rich particles.
Furthermore, a closer observation of Ni74-Sn26 nanoparticles in
Fig. 2(d) indicated that they are crystalline with visible lattice fringes
of d = 0.20 nm and 0.228 nm, correspond to Ni3Sn (201) and (200)
planes, respectively.
To investigate the catalytic performance of Ni74‐Sn26, Ni59‐Sn41, and
Ni50‐Sn50 nanoparticles as compared to Ni nanoparticles, the reduction
of 2-nitroaniline using sodium borohydride as the hydrogen source was
initially studied. The reduction of 2-nitroaniline does not occur without
coinage metals [35]. The peak at 411 nm completely diminished when
all the 2-nitroaniline was converted to 1,2-benzenediamine in Fig. 4.
In the presence of the Ni and Sn nano-catalysts, it takes about 6.5 min,
and 42 min respectively to complete a reduction reaction. While using
the Ni74‐Sn26, Ni59‐Sn41, and Ni50‐Sn50 nano-catalyst, the reaction lasts
only about 2.5 min, 5.0 min and 8.0 min respectively shown in Fig. 5
and Table S.1. Ni74-Sn26 and Ni59–Sn41, nano-catalysts reported here ex-
hibited higher catalytic activity for the reduction of 2-nitroaniline as
compared to Ni, Sn and Ni50‐Sn50 nano-catalysts. When the reaction
temperature was decreased from room temperature to 8 °C, Ni74‐Sn26
nano-catalyst takes 34 min, for the reduction reaction to complete.
The order of activity at room temperature was Ni74‐Sn26 N Ni59
‐
Sn41 N Ni N Ni50‐Sn50 N Sn nano-catalyst in water. With the increase in
the concentration of tin up to 41 mol% the catalytic activity towards
the reduction of 2-nitroaniline was increased, and further increase in
the tin concentration up to 50% decreases catalytic activity of Ni‐Sn
nanoparticles as compared with nickel nanoparticles. The high catalytic
activity of Ni74‐Sn26 nano-catalyst is because of having small crystallite
size, small particle size and high surface area as compared to other
nano-catalysts. The Ni50‐Sn50 nano-catalyst has low crystallite size,
low particle size and high surface area as compare to Ni59‐Sn41 and Ni
nano-catalysts. But the catalytic activity of Ni50‐Sn50 nano-catalyst is
lower than Ni59‐Sn41 and Ni nanocatalysts mean that addition of tin
up to some extent enhances catalytic activity of Ni‐Sn nanoparticle.
Fig. 2. (a) The TEM images of Ni‐Sn nanoparticles with different magnifications, (b) size distribution histogram of Ni‐Sn nanoparticles obtained from the TEM micrographs (c) EDX profile
of Ni‐Sn nanoparticles (d) HR-TEM image of Ni‐Sn nanoparticles.

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M. Shah et al. / Catalysis Communications 65 (2015) 85–90
Fig. 3. (a) and (c) The TEM micrographs of Ni‐Sn (3:2) and Ni‐Sn (1:1) nanoparticles respectively, (b) and (d) size distribution of Ni‐Sn (3:2) and Ni‐Sn (1:1) respectively; obtained from
the TEM micrographs.
The reduction of 2-nitroaniline by NaBH4 in the absence of catalyst did
not show any conversion after 72 h. Subsequently, the catalyst which
showed the best performance towards reduction of 2-nitroaniline,
was tested for the reduction of a number of nitro aromatic compounds
under mild reaction conditions. Results, in Table 3, show that different
nitro aromatic compounds can be converted to the corresponding
amines at high yields and selectivity, regardless of the electron-
donating or electron-withdrawing ability of the substituent group.
When nitrobenzene was subjected to hydrogenation it yielded 98% of
aniline in 8.5 min (Table 3, entry 1). The rate of reaction was increased
by increasing concentration of sodium borohydride (NaBH4). As its con-
centration was increased from 3-equivalent to 4-equivalent the time of
reduction reaction decreased significantly from 8.5 min to 4.5 min with
99% product yield (Table 3, entry 1 and entry 2). Clearly, the presence of
Fig. 5. Comparison of reduction of 2-nitroaniline into benzene-1,2-diamine at various
nano-catalysts in water. Where Ni‐Sn 1 (3:1), Ni‐Sn 2 (3:2), Ni‐Sn 3 (1:1). Reaction condi-
tions; 37 mmol 2-nitroaniline aqueous solution, 19 mg catalysts, 0.4 mol NaBH4 aqueous
solution, room temperature.
Fig. 4. Absorption spectra of aqueous solution of, A; 2-nitro-aniline; B, C, D, E and F; after
reaction completion by using bimetallic Ni‐Sn (3:1), Ni‐Sn (3:2), Ni‐Sn (1:1), Ni and Sn
nanoparticles as catalyst, respectively.

M. Shah et al. / Catalysis Communications 65 (2015) 85–90
89
Table 3
Reduction of various nitro aromatic compounds into corresponding amines with NaBH4 catalyzed by Ni‐Sn a
.
Entry
1
Reactant
Product
NaBH4 (Equiv.)
3
Time (min)
8.5
Yieldb (%)
98
99
95
98
2
3
4
4
4
4
4.5
12
7
5
6
4
4
15
30
91
95
7
8
4
4
7
5
91
92
Reaction conditions: substrate (1 mmol), a (Ni74:Sn26) Catalyst (0.026 g), NaBH4(4 mmol), H2O (5 mL), room temperature. bIsolated yield.
an amino group at different positions on the phenyl ring afforded the
corresponding aniline in excellent yields (Table 3, entries 3‐5).
Nitroarenes possessing electron donating groups such as 4-
nitroanisole (Table 3, entry 6) was also reduced to the desired amines
in high yield (N95%). Similar reduction of 1-chloro-4-nitrobenzene
and petafluoronitrobenzene compounds containing the electron-
acceptor group (Table 3, entries 7 and 8) gives above 91% of the corre-
sponding amines. Notably, we have not observed any secondary reac-
tion affecting the dehalogenation functionalities under the selected
reaction conditions, suggesting the high chemoselectivity of the present
Ni74‐Sn26/ NaBH4 reduction system.
respectively. The well-dispersed Ni‐Sn nanoparticles were found to
have single crystals while the elongated particles have polycrystals.
The Ni74‐Sn26 nanoparticles exhibited excellent catalytic performance
as compared with Ni, Ni59‐Sn41, and Ni50‐Sn50 nanoparticles. The re-
placement of the nickel content with tin up to 41% improved catalytic
performance while further its addition decreased catalytic activity of
the nickel‐tin nanoparticle for the reduction of 2-nitroaniline as com-
pared with nickel nanoparticles. Furthermore, Ni74‐Sn26 nanocatalyst
showed excellent activity for the reduction of a number of nitroarenes
carrying activated and deactivated groups under mild conditions.
Acknowledgments
4. Conclusions
This work is supported by the NSFC (21325208, 21172209,
21272050), CAS (KJCX2-EW-J02) and FRFCU (WK2060190025,
WK2060190033).
The unsupported Ni‐Sn bimetallic nanoparticles with controllable
size and composition were successfully prepared by a simple method
using nickel formate dihydrate (Ni (HCOO)2·2H2O), tin chloride
dihydrate (SnCl2·2H2O) and sodium borohydride (NaBH4). The obtain-
ed nanoparticles have been confirmed by XRD, TEM, HR-TEM and EDX
analysis. Ni, Ni74‐Sn26, Ni59‐Sn41, and Ni50‐Sn50 nanoparticles were ob-
served to have a mixture of irregular shape and spherical morphology
with an estimated average size of 13 nm, 4.5 nm, 8 nm and 7.2 nm,
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2015.02.026.

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M. Shah et al. / Catalysis Communications 65 (2015) 85–90
[21] K. Stella, F.C. Lynch, M. Xiaomei, L. Won Jin, A. Jane, H.H. Carol, C.A. Gabriella, F. Laura
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