Supported nano-sized gold catalysts for selective reduction of 4,4′-dinitrostilbene-2,2′-disulfonic acid using different reductants

Article abstract of DOI:10.1016/j.dyepig.2012.03.009

Gold nanoparticles supported on three metal oxides, TiO₂, Al₂O₃ and Fe₂O₃, were prepared by a modified precipitation-deposition method using urea as an additive. These catalysts were tested in chemoselective reduction of 4,4′-dinitrostilbene- 2,2′-disulfonic acid to 4,4′-diaminostilbene-2,2′-disulfonic acid. Three reagents, hydrogen, carbon monoxide, and sodium formate, were employed as reductants. It was found that >94% of the nitrostilbene was transformed into the aminostilbene without the reduction of olefinic group. In addition, these catalysts exhibited stable performance after regeneration by calcination at 400 °C for 5 h. This clean approach provides a promising application for synthesis of amino substituted stilbene sulfonic acid on an industrial scale.

Full text of DOI:10.1016/j.dyepig.2012.03.009

Dyes and Pigments 95 (2012) 215e220
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Supported nano-sized gold catalysts for selective reduction of 4,40-dinitrostilbene-
2,20-disulfonic acid using different reductants
,
,
c
,
,
Ying Chen b 1, Wenchao Peng a 1, Shaobin Wang c, Fengbao Zhang a, Guoliang Zhang a, Xiaobin Fan a
*
a School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, China
b Department of Chemical Engineering, Renai College of Tianjin University, Tianjin 301636, China
c Department of Chemical Engineering, Curtin University, GPO Box U1987, WA 6845, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
Gold nanoparticles supported on three metal oxides, TiO2, Al2O3 and Fe2O3, were prepared by a modified
precipitation-deposition method using urea as an additive. These catalysts were tested in chemoselective
reduction of 4,40-dinitrostilbene-2,20-disulfonic acid to 4,40-diaminostilbene-2,20-disulfonic acid. Three
reagents, hydrogen, carbon monoxide, and sodium formate, were employed as reductants. It was found
that >94% of the nitrostilbene was transformed into the aminostilbene without the reduction of olefinic
group. In addition, these catalysts exhibited stable performance after regeneration by calcination at
400 ꢀC for 5 h. This clean approach provides a promising application for synthesis of amino substituted
stilbene sulfonic acid on an industrial scale.
Received 12 January 2012
Received in revised form
9 March 2012
Accepted 9 March 2012
Available online 1 April 2012
Keywords:
Heterogeneous catalysis
Chemoselective
Reduction
Ó 2012 Elsevier Ltd. All rights reserved.
Gold
Supported catalysis
Catalyst regeneration
1. Introduction
cost of industrial production. Therefore, development of a facile
and environmentally friendly chemoselective process has attracted
4,40-Diaminostilbene-2,20-disulfonic acid (DSD), a typical amino
substituted stilbene sulfonic acid, is an important industrial inter-
mediate used widely in production of direct dyes, fluorescent
brighteners and mothproofing agents [1]. Generally, it is produced
from the reduction of 4,40-dinitrostilbene-2,20-disulfonic acid
(DNS) with stoichiometric reducing agents, such as sodium
hydrosulfite [2]. In addition, metals such as either iron, tin or zinc in
ammonium hydroxide have been successfully applied in the
reduction with high yields of w98% [3]. However, these reducing
agents are not environmentally sustainable, and generate signifi-
cant amounts of solid wastes which are difficult to be disposed of
[4]. Catalytic hydrogenation is a green and effective way, but
commercial catalysts (Raney Ni) can also result in the reduction of
olefinic and nitro groups [5]. A Pd supported on C (Pd/C) has shown
high selectivity, but large quantities of additives are required for the
reaction [6]. Separation of the additive from products increases the
substantial interest.
Gold nanoparticles supported on metal oxides have been used
as catalysts for a number of reactions, including addition of
multiple CeC bonds, cyclization reactions, rearrangements, CeC
coupling reactions, oxidation reactions, and hydrogenations [7].
Selective reduction of nitro compounds in the presence of reducible
functions is more challenging and has attracted tremendous
interest. Corma et al. have shown that gold nanoparticles supported
on TiO2 and Fe2O3 can successfully catalyze selective reduction of
nitro aromatic compounds containing olefinic bonds with H2 [8].
Cao et al. used CO/H2O as a hydrogen source and Au/TiO2 for the
selective reduction of nitro aromatic compounds containing
olefinic bonds and achieved high chemoselectivity [9]. Formate is
another hydrogen carrier, and ammonium formate has been used in
the reduction of nitro compounds by copper nanoparticles.
However, the selectivity for nitro aromatic compounds containing
olefinic bonds was low at only w57% [10].
In this study, we prepared a serial of Au NPs-based catalysts using
a depositioneprecipitation method [11]. These catalysts were eval-
uated in the chemoselective reduction of DNS to DSD. H2, CO and
sodium formate were used as reductants for a comparative study.
Excellent yields and high stability were achieved on these catalysts.
* Corresponding author.
E-mail address: xiaobinfan@tju.edu.cn (X. Fan).
1
Ying Chen and Wenchao Peng contributed equally to this article.
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2012.03.009

216
Y. Chen et al. / Dyes and Pigments 95 (2012) 215e220
2. Experimental
HCOONa as a reductant was also used for the reduction of DNS at
130 ꢀC with HCOONa (0.3 g). In those tests, the reactor was purged
with N2 at 5 bar.
2.1. Materials and reagents
Sample analysis was carried out on a Finnigan Surveyor HPLC
integrated with quaternary gradient pumps, photodiode array
detector, auto injector, degasser and system controller (Thermo-
Fisher Scientific, USA). A reversed-phase Hypersil ODS-2 C18 column
P25 titanium dioxide (ca. 80% anatase, 20% rutile; BET area ca.
50 m2
g
ꢁ1) was obtained from Degussa Co. (Germany).
a
eFe2O3
(30 nm, BET area ꢂ50 m2
g geAl2O3 (10 nm, BET area
ꢁ1), and
ꢃ200 m2 gꢁ1) were obtained from Aladdin (China). 4,40-Dini-
trostilbene-2,20-disulfonic acid (DNS), 4,40-diaminostilbene-2,20-
disulfonic acid (DSD), 4,40-diaminobibenzyl-2,20-disulfonic acid
(DAD) and Raney Ni were provided by Huayu Chemical Company
(Cangzhou, China). All chemicals and solvents (Merck) were either
analytical or chromatography grade and were used without further
purification.
(250 ꢄ 4.6 mm i.d., 5
mm particle size, Thermo Scientific, US) was used
for separation. HPLC conditions: 5:95 acetonitrile:watere0.01 M
ammonium acetate, 254 nm (flow: 1 mL minꢁ1).
2.5. Catalyst stability
The catalyst stability of Au/TiO2 was tested in the reduction of
DNS with the three reductants. Firstly the catalyst (0.02 g) was used
in a 40 mL reaction (fresh catalyst). After the first run reaction, the
catalyst was recovered, filtered and washed three times with
distilled water. Then, they were dried under vacuum at 100 ꢀC for
2 h and calcined at 400 ꢀC for 5 h. Secondly recycled catalyst
(0.015 g) was tested in a 30 mL solution for second run reaction.
After recovered, recycled catalyst (0.01 g) was tested in a 20 mL
solution for the third run reaction.
2.2. Catalyst preparation
The catalysts were prepared using the depositioneprecipitation
method with urea (DP urea) [11,12]. Typically, the nano-sized metal
oxides either TiO2, Al2O3 or Fe2O3 (1.0 g) was added to an aqueous
solution of HAuCl4 (100 mL, 0.9 ꢄ 10ꢁ3 M) with urea (0.42 M). The
suspension was heated to 85 ꢀC and kept for 6 h with vigorously
stirring. Then the suspension was separated from the precursor
solution by centrifugation (15000 rpm for 10 min). The obtained
soꢁlids were washed three times with water to remove the residual
Cl , and dried under vacuum at 100 ꢀC for 3 h. After that, they were
calcined at 300 ꢀC for 4 h and reduced for 2 h at 250 ꢀC in a flow of
5% H2/N2.
3. Results and discussion
3.1. Catalyst characterization
Fig. 1 shows the TEM images of the three catalysts. Al2O3 is non-
reducible and it is different from other two supports. The diameters
of the Au NPs on these supports had some differences. Size distri-
butions of Au NPs on the catalysts are presented in Fig. 2. The d of
Au NPs on Al2O3 was 3.8 nm and most particles were in size of
2e4 nm. Other two catalysts had similar d (Au/TiO2 4.7 nm, Au/
Fe2O3 4.6 nm), and the Au particles ranged from 4 to 6 nm. Due
to the reduction by H2/Ar, the supported gold species are metallic
states determined by XPS (Fig. 3). In addition, the gold loadings
on these catalysts were found to be w1.5% by Inductively Coupled
Plasma (ICP).
2.3. Catalyst characterization
Catalysts were examined by transmission electron microscopy
(TEM) with a JEOL2010F microscope. The histograms of particle size
of Au NPs were obtained from the measurement of w300 particles.
The size limit for the detection of the gold particle is 1 nm. The
average particle diameter
d was calculated from the for-
P
P
mula:d ¼
nidi= ni, where ni is the number of particles of
diameter di. The Au weight loading was determined by an induc-
tively coupled plasma (ICP) technique, and the chemical state of the
Au species on the catalysts was determined by X-ray Photoelectron
Spectroscopy (XPS).
3.2. Reduction of DNS to DSD
3.2.1. Hydrogen as a reductant
2.4. Catalytic activity tests
Hydrogen is an ideal and powerful reductant with water as
a product. Hydrogen is always used to reduce nitro compounds
with satisfactory yields on commercial catalysts. However, other
functional groups can also be reduced, resulting in low selectivity to
the reduction of nitro groups. For the reduction of DNS, the olefinic
groups will be simultaneously reduced using commercial catalysts
[13]. Corma et al. found that gold nanoparticles (3.8 ꢅ 1.5 nm)
supported on TiO2 or Fe2O3 can produce high selectivities towards
hydrogenation of 3-nitrostyrene [8]. Herein, three supported gold
The hydrogenation of DNS was performed in a 50 mL autoclave.
For each reaction, water (10 mL), DNS (0.05 g) were charged into
the autoclave together with the catalyst (0.005 g). Before reaction,
the reactor was flushed five times with hydrogen at 5 bar to remove
air. Then the autoclave was heated to 120 ꢀC and pressurized at
5 bar. After 5 h, the products were analyzed by a HPLC. The
reduction process was also performed by CO at 100 ꢀC. In addition,
Fig. 1. TEM images of Au/TiO2 (a), Au/g eAl2O3 (b), and Au/a eFe2O3 (c).

Y. Chen et al. / Dyes and Pigments 95 (2012) 215e220
217
30
25
20
15
10
5
⎯
γ⎯
a
b
35
Au/ Al O
c
Au/α Fe O
Au/TiO
40
30
25
20
15
10
5
30
20
10
0
0
0
2
3
4
5
6
7
8
2
3
4
5
6
7
2
3
4
5
6
7
Partical size (nm)
Partical size (nm)
Partical size (nm)
Fig. 2. Size distributions of Au NPs in (a) Au/TiO2, (b) Au/
g
eAl2O3, and (c) Au/
a
eFe2O3.
nanoparticles were used in the reduction of DNS, and the results are
shown in Table 1. A commercial catalyst-Raney Ni was also evalu-
ated in the reduction of DNS for a comparison. It was found that the
Raney Ni did not show any selectivity in the reduction of DNS to
DSD and that the product was only 4,40-diaminobibenzyl-2,20-
disulfonic acid (DAD) (Fig. 4). For supported Au NPs, Au/Al2O3 was
the most efficient catalyst with selectivity to DSD of 98.7%. Au/TiO2
and Au/Fe2O3 were also efficient with selectivities to DSD at more
than 90%. The determination of the reduction products was per-
formed by HPLC-ESI-MS, and the identification was further
confirmed by comparing their retention times with those of high
purity standards (Fig. 5).
realized more easily with CO/H2O on gold nanoparticles [9,14]. It
was proposed that the nitro groups could be reduced by the
hydrogen gas generated from the low-temperature wateregas shift
(WGS) reaction. However, it was found that supported gold for low-
temperature wateregas shift (WGS) reaction (CO þ H2O ¼ CO2 þ H2)
was effective in the temperature range of 150e250 ꢀC, which is
higher than the reduction temperature of DNS (100 ꢀC) [14e16]. In
addition, a control experiment with DAD <1% also indicated the
WGS reaction could not occur under the current experimental
conditions. Commercial Raney Ni has no selectivity towards DSD
with CO/H2O, the same result as that for hydrogen as the reductant.
3.2.3. Sodium formate as a reductant
3.2.2. CO as a reductant
Sodium formate is an important hydrogen source. Sodium
formate is mild in nature and conveniently available, and it has
been proved effective in hydrogenation of nitro compounds in
following reaction equation:
CO is a very attractive industrial reductant due to its low-cost,
accessibility, and wide range of applications in the chemical
industry [9]. The reduction of nitro groups using CO/H2O has been
known for many years. Herein, the reduction of DNS by CO/H2O
catalyzed by supported Au NPs was also investigated and the results
are listed in Table 2. All three Au NPs containing catalysts could
achieve selectivities of more than 99%, which are higher than those
in H2 reduction on the same catalysts. The results indicated that
selective reduction of the nitro group over olefinic groups can be
cat:
ArNO þ 3HCOONa þ H O
ArNH þ 3NaHCO
(1)
ꢀ!
2
2
2
3
It was found that the reduction proceeded in the form of direct
hydrogen transfer between the sodium formate and the nitro
acceptor rather than a dehydrogenation-hydrogenation sequence
[17]. Therefore, the selectivities during the catalytic reduction of
DNS with sodium formate should be different from hydrogen
reduction. The results of DNS reduction with HCOONa on supported
Au NPs are listed in Table 3. All three metal oxide supported Au
catalysts can provide selectivities of >99%, similar to CO/H2O. The
results indicated that reduction by HCOONa on gold catalysts is
relatively mild.
Au0(83.3)
Au+(84.7)
Au0(87.0)
Au+(88.5)
It should be noted that formic acid and ammonium formate
might also be effective, however, formaic acid has high corrosive
effect and ammonium formate can be decomposed to hydrogen
cyanide (HCN) at a relative high temperature [17]. Commercial
Raney Ni was also investigated with HCOONa as a reductant, and no
DSD production could be observed during the reduction of DNS.
Table 1
Reduction of DNS with H2 by varies catalysts.
Catalysts e xa
T/ꢀC
Au loading
(wt.%)
Conv./%
Sel.(DSD)/%
Sel.(DAD)/%
80
82
84
86
88
90
Au/TiO2 e 4.7
Au/Fe2O3e 4.6
Au/Al2O3e 3.8
Raney Ni
120
120
120
120
1.7
1.6
1.5
1.6
100
100
100
100
97.8
94.6
98.7
0
<2.0
3.6
1.2
Binding Energy / eV
>99.0
Fig. 3. XPS spectra (Au 4f) of Au/TiO2 catalyst after reduction with H2/Ar (the three
catalysts have very similar results, so we take the spectra of Au/TiO2 as an example).
a
The d of Au NPs supported on each metal oxides.

218
Y. Chen et al. / Dyes and Pigments 95 (2012) 215e220
Fig. 4. The reduction of DNS to DSD and DAD.
a
9.16
6.95
DSD
DAD
0
3
6
9
12
15
RT/ min
b
c
371.1
[M-H]-
6.95
DAD
m/z
371
369.1
[M-H]-
9.16
DSD
m/z 369
0
3
6
9
12
15
200 250 300 350 400 450 500
m/z
RT/ min
Fig. 5. The HPLC chromatography of DAD and DSD (a); mass spectrum and m/z information of DAD (b) and DSD (c).
H2, CO and HCOONa are all industrial-wide used reductants due
DSD using hydrogen was found to be the lowest based on the
foregoing results. Higher selective reduction of nitro over olefinic
groups could be ascribed to (1) preferable absorption of nitro group
to the supported gold particles than carbonecarbon double bonds;
(2) higher intrinsic rate for nitro group reduction than that of the
to their clean, ready accessibility and low cost. CO is more toxic to
human health and HCOONa is more expensive. Hydrogen is low-
cost and environmental benign, and thus it is the best reductant
in an industrial scale application. However, the selectivity of DNS to
Table 2
Table 3
Reduction of DNS with CO by varies catalysts.
Reduction of DNS with HCOONa by varies catalysts.
Catalysts e xa
T/ꢀC
Au loading
(wt.%)
Conv./%
Sel.(DSD)/%
Sel.(DAD)/%
Catalysts e xa
T/ꢀC
Au loading
(wt.%)
Conv./%
Sel.(DSD)/%
Sel.(DAD)/%
Au/TiO2 e 4.7
Au/Fe2O3e 4.6
Au/Al2O3e 3.8
Raney Ni
100
100
100
100
1.7
1.6
1.5
1.6
100
100
100
100
>99.0
>99.0
>99.0
0
<1.0
<1.0
<1.0
Au/TiO2 e 4.7
Au/Fe2O3e 4.6
Au/Al2O3e 3.8
Raney Ni
130
130
130
130
1.7
1.6
1.5
1.6
100
100
100
100
>99.0
>99.0
>99.0
0
<1.0
<1.0
<1.0
>99.0
>99.0
a
a
The d of Au NPs supported on each metal oxides.
The d of Au NPs supported on each metal oxides.

Y. Chen et al. / Dyes and Pigments 95 (2012) 215e220
219
Fig. 6. Stability of the Au/TiO2 catalyst for the DNS hydrogenation after recycling and regeneration of the catalyst. While activity needs an appropriate thermal treatment to recover
the original level, no loss of conversion was observed for a third recycle (a), keeping high selectivity values (b).
Fig. 7. The TEM image (a) and size distributions of Au NPs (b) of Au/TiO2 (after the 2nd re-use bath); the average diameter ðdÞ of the Au NPs is w4.8 nm.
olefinic group [18]. The lower selectivity to DSD by hydrogen sug-
gested that is probably due to similar intrinsic rate for reduction of
nitro and olefinic groups occurred in H2 reduction.
be maintained at a high level for a third recycle. However, some
active sites of the used catalyst might be poisoned by the organic
molecules, and this could lead to the decrease of the yield. The
calcination process at 400 ꢀC can help restore the activity of the
catalysts and maintain high yield [8].
3.3. Catalyst stability
4. Conclusion
TiO2-P25 is a commercially available support, so TiO2 supported
gold NPs (Au/TiO2) can be produced on an industrial scale. The
catalyst stability was thus evaluated in Au/TiO2 system for the
hydrogenation of DNS. The results are shown in Fig. 6. A decrease in
DSD yield was observed (Fig. 6a) in 5 h reaction for non-calcined
Au/TiO2. While for the catalyst treated at 400 ꢀC for 5 h, little
decrease in yield could be observed for all three reductants. This
indicated that some active sites of the catalyst might be poisoned
by the organic molecules, and the activity can be recovered by
calcined at 400 ꢀC [8]. On the other hand, Fig. 6b showed that no
changes in selectivity to DSD were observed for the non-calcined
and 400 ꢀC-treated catalysts. For the Au/TiO2 with 400 ꢀC treat-
ment, more than 98% selectivity could be obtained after three run
regenerations.
Gold nanoparticles supported on three metal oxides were
prepared and evaluated in the chemoselective reduction of DNS to
DSD using H2, CO and HCOONa as reductants. Compared with the
commercial Raney Ni catalyst under the same conditions, excellent
selectivity (>94%) was obtained on the three Au NPs containing
catalysts. In addition, the catalysts maintained stability in three-run
tests after regeneration by calcination at 400 ꢀC for 5 h.
References
[1] Peng WC, Chen Y, Fan SD, Zhang FB, Zhang GL, Fan XB. Use of 4,4 0-dini-
trostilbene-2,2 0-disulfonic acid wastewater as a raw material for paramycin
production. Environ Sci Technol 2010;44:9157e62.
The selectivity to the nitro and olefinic group reduction was
related to the size of supported Au NPs. The change of Au NPs
diameters was also investigated in the H2 reduction. It was found
that the average diameter of Au NPs slightly increased (from 4.7 to
4.8 nm) after two calcinations (Fig. 7). Therefore, the selectivity can
[2] Peng WC, Zhang FB, Zhang GL, Liu B, Fan XB. Selective reduction of 4,4
0-dinitrostilbene-2,2 0-disulfonic acid catalyzed by supported nano-sized gold
with sodium formate as hydrogen source. Catal Commun 2011;12:568e72.
[3] Burawoy A, Critchley JP, Coll M. Electronic spectra of organic molecules and
q
their interpretationeV : effect of terminal groups containing multiple bonds
on the K-bands of conjugated systems. Tetrahedron 1959;5:340e51.

220
Y. Chen et al. / Dyes and Pigments 95 (2012) 215e220
[4] Sirijaruphan A, Goodwin JG, Rice RW. Investigation of the initial rapid deac-
[12] Sudsakorn K, Goodwin JG, Adeyiga AA. Effect of activation method on FeFTS
catalysts: investigation at the site level using SSITKA. J Catal 2003;213:204e10.
[13] Panpranot J, Goodwin JG, Sayari A. Effect of H-2 partial pressure on surface
reaction parameters during CO hydrogenation on Ru-promoted silica-sup-
ported Co catalysts. J Catal 2003;213:78e85.
[14] Panpranot J, Goodwin JG, Sayari A. Synthesis and characteristics of MCM-41
supported CoRu catalysts. Catal Today 2002;77:269e84.
[15] Jongsomjit B, Panpranot J, Goodwin JG. Co-support compound formation in
alumina-supported cobalt catalysts. J Catal 2001;204:98e109.
tivation of platinum catalysts during the selective oxidation of carbon
monoxide. J Catal 2004;221:288e93.
[5] Panpranot J, Kaewkun S, Praserthdam P, Goodwin JG. Effect of cobalt
precursors on the dispersion of cobalt on MCM-41. Catal Lett 2003;91:
95e102.
[6] Zhao XB, Chen HB, Zhang SF. J Chem Ind Eng 2003;54:1138.
[7] Corma A, Garcia H. Supported gold nanoparticles as catalysts for organic
reactions. Chem Soc Rev 2008;37:2096e126.
[8] Corma A, Serna P. Chemoselective hydrogenation of nitro compounds with
supported gold catalysts. Science 2006;313:332e4.
[16] Kim SY, Goodwin JG, Farcasiu D. The effects of reaction conditions and catalyst
deactivation on the mechanism of n-butane isomerization on sulfated
zirconia. Appl Catal A-Gen 2001;207:281e6.
[17] Kim SY, Goodwin JG, Olindo R, Pinna F. Alumina-promotion of sulfated
zirconia for n-butane isomerization: impact on surface intermediates. Abstr
Pap Am Chem S 2000;220. U241-U.
[18] Shimizu K, Miyamoto Y, Kawasaki T, Tanji T, Tai Y, Satsuma A. Chemoselective
hydrogenation of nitroaromatics by supported gold catalysts: mechanistic
reasons of size- and support-dependent activity and selectivity. J Phys Chem C
2009;113:17803e10.
[9] Hammache S, Goodwin JG. Characteristics of the active sites on sulfated
zirconia for n-butane isomerization. J Catal 2003;218:258e66.
[10] Saha A, Ranu B. Highly chemoselective reduction of aromatic nitro
compounds by copper nanoparticles/ammonium formate. J Org Chem 2008;
73:6867e70.
[11] Jongsomjit B, Goodwin JG. Co-support compound formation in Co/Al2O3
catalysts: effect of reduction gas containing CO. Catal Today 2002;77:
191e204.