Highly efficient and durable platinum nanocatalysts stabilized by thiol-terminated poly(N-isopropyl acrylomide) for selective hydrogenation of halonitrobenzene to haloaniline

Article abstract of DOI:10.1039/c6ra24773c

In this paper, the selective hydrogenation of halonitrobenzenes (HNBs) to haloanilines (HANs) under mild conditions catalyzed by well-dispersed Pt nanoparticles protected by thiol-terminated poly(N-isopropyl acrylomide) (PNIPAM-SH) was firstly investigated. The polymer not only protected the Pt nanoparticles, but also inhibited the highly active Pt catalyst from producing undesired hydrodehalogenation products through anchoring the thiol groups to the surface of Pt nanoparticles. Thus high selectivities to HANs were achieved over this modified Pt catalyst for a variety of HNBs with satisfactory catalytic activities. Especially, the selectivity to HANs showed no obvious loss with the prolonging of the reaction time. Moreover, the recycling experiment showed that this Pt nanocatalyst was easier to recover and reuse based on the cononsolvency of PNIPAM-SH. Excellent stability and reusability were presented over this catalyst, and both the catalytic activity and selectivity were well maintained after fourteen runs.

Full text of DOI:10.1039/c6ra24773c

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Highly efficient and durable platinum nanocatalysts
stabilized by thiol-terminated poly(N-isopropyl
acrylomide) for selective hydrogenation of
halonitrobenzene to haloaniline
Cite this: RSC Adv., 2017, 7, 751
ab
ab
ab
ab
ab
ab
Wenjun Yu, Lan-Lan Lou,* Shanshan Li, Tianyuan Ma, Lezi Ouyang, Li Feng
abc
and Shuangxi Liu*
In this paper, the selective hydrogenation of halonitrobenzenes (HNBs) to haloanilines (HANs) under mild
conditions catalyzed by well-dispersed Pt nanoparticles protected by thiol-terminated poly(N-isopropyl
acrylomide) (PNIPAM-SH) was firstly investigated. The polymer not only protected the Pt nanoparticles,
but also inhibited the highly active Pt catalyst from producing undesired hydrodehalogenation products
through anchoring the thiol groups to the surface of Pt nanoparticles. Thus high selectivities to HANs
were achieved over this modified Pt catalyst for a variety of HNBs with satisfactory catalytic activities.
Especially, the selectivity to HANs showed no obvious loss with the prolonging of the reaction time.
Moreover, the recycling experiment showed that this Pt nanocatalyst was easier to recover and reuse
based on the cononsolvency of PNIPAM-SH. Excellent stability and reusability were presented over this
catalyst, and both the catalytic activity and selectivity were well maintained after fourteen runs.
Received 5th October 2016
Accepted 3rd November 2016
DOI: 10.1039/c6ra24773c
www.rsc.org/advances
1
8,19
20,21
as alloying,
using bimetallic catalysts,
adjusting metal/
1
. Introduction
22–26
support interaction,
surface modication via ligands or
Among these strategies, the last one
27–33
Haloanilines (HANs) are an important class of ne chemicals modier reagents.
and are widely used in the synthesis of pharmaceuticals, dyes, represented a widely used and powerful tool for improving the
1
herbicides, pesticides, and so on. These compounds are selectivity to HANs through control of the electronic properties
generally produced by selective hydrogenation of haloni- of the catalytically active sites. Yang and Liu reported that some
2
+
3+
2+
trobenzenes (HNBs) catalyzed by transition metals, which is metal cations such as Ni , Fe and Co introduced to PVP–Pt
regarded as a high atom efficiency and environmentally friendly colloidal clusters had a favorable effect on the selectivity to o-
2
27
process. However, catalytic hydrodehalogenation of HNBs as CAN in the catalytic hydrogenation of o-CNB. Motoyama et al.
a side reaction oen occurs over most metal catalysts, which applied n-octylamine as poisoning reagent for Pt nanoparticles
signicantly limits the selectivity to HANs, especially for iodo- dispersed on nanocarbon ber and high selectivities were ob-
29
nitrobenzenes (INBs) and bromonitrobenzenes (BNBs) with tained in the hydrogenation of HNBs. Recently, Lara et al.
a weaker carbon–halogen bond than chloronitrobenzenes reported the Pt nanoparticles stabilized by N-heterocyclic
carbine for the selective hydrogenation of different nitro-
and Co, Pt has been one of the aromatics under mild conditions and high levels of activity and
most promising metal catalysts for selective hydrogenation of selectivity were obtained. However, these modiers usually
3,4
(
CNBs). Compared with other transition metals such as Pd,
Au, Ag, Ir,
5–7
8
9–11
12
13–15
16
Ru, Ni,
33
HNBs due to high catalytic activity in nitro reduction and increased the complexity of the reaction system and could not
17
a certain degree of selectivity to HANs. Several strategies have be completely avoided leaching into the products. Therefore,
been developed to improve the selectivity of Pt catalyst, new surface modication of Pt nanocatalyst with excellent
although at the expense of catalytic activity in many cases, such catalytic performance and high reusability is highly signicant
in the selective hydrogenation of HNBs.
Poly(N-isopropylacrylamide) (PNIPAM) is the most widely
a
Institute of New Catalytic Materials Science and Key Laboratory of Advanced Energy
studied thermosensitive polymer, and exhibits a lower critical
Materials Chemistry (Ministry of Education), School of Materials Science and
solution temperature (LCST) of ꢀ32 ꢁC, at which the single-
Engineering, Nankai University, Tianjin 300350, China. E-mail: lllou@nankai.edu.
chain polymer undergoes a reversible change from a soluble
cn; sxliu@nankai.edu.cn; Fax: +86 22 23509005; Tel: +86 22 8535 8599; +86 22
34
2
b
350 9005
coil to an insoluble globule in water. This polymer has
National Institute for Advanced Materials, Nankai University, Tianjin 300350, China received more and more attention due to its widely applications
c
35,36
37–40
Collaborative Innovation Center of Chemical Science and Engineering (Tianjin),
in targeted drug delivery,
catalysis,
and so on. It was
Tianjin 300072, China
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Scheme 1 Synthesis of PNIPAM-SH by RAFT polymerization.
particularly necessary to point out that PNIPAM exhibits con- the spectra were recorded with an Al Ka X-ray source using C 1s
onsolvency in mixed aqueous solutions, that is to say, the LCST as a reference for binding energy. Inductively coupled plasma-
of aqueous PNIPAM solution is remarkably decreased when atomic emission spectrometry (ICP-AES) analysis was
being added an appropriate proportion of polar organic measured with a PerkinElmer Optima 8300 spectrometer for the
41,42
solvents such as methanol, ethanol and tetrahydrofuran.
Pt contents in the catalysts and metal leaching into products.
Thus, in this case, PNIPAM is easily precipitated from the The products of selective hydrogenation reaction were analyzed
reaction system at room temperature and below it. The by gas chromatography (GC) on a FL9790II gas chromatograph
phenomenon seems very interesting and surprising, because equipped with a ame ionization detector and a weak polarity
PNIPAM is well soluble in water as well as in polar solvents capillary column (SE-30, 30 m  0.53 mm  0.50 mm). The
separately. This cononsolvency property of PNIPAM has few injection and detector temperatures were set at 543 K with the
application in the recovery of colloid catalysts, which provides column temperature of 383–413 K.
an effective and simple way to recycle the PNIPAM related
colloid catalysts in polar organic solvents.
2
.2 Catalyst preparation
.2.1. Synthesis of polymers PNIPAM-SH and PNIPAM. The
thiol-terminated polymer PNIPAM-SH was prepared as described
Here we would like to report the selective hydrogenation of
HNBs catalyzed by colloidal Pt catalyst stabilized by thiol-
terminated PNIPAM (PNIPAM-SH). The polymer here can not
only stabilize the Pt nanoparticles, but also inhibit the highly active
catalyst from producing hydrodehalogenation products through
the strong interaction between the thiol groups and unsaturated
surface of Pt nanoparticles. To the best of our knowledge, this is
the rst report on the utilization of thermosensitive polymer-
modied Pt catalyst for selective hydrogenation of HNBs. High
and steady selectivity to HANs was achieved over this Pt nano-
catalyst. In addition, this catalyst could be easily recovered based
on the cononsolvency of PNIPAM-SH and exhibited high durability
in the selective hydrogenation reaction due to the strong interac-
tion between PNIPAM-SH and Pt nanoparticles.
2
43
previously. Briey, dithiobenzoate-terminated PNIPAM was
rstly prepared by reversible addition fragmentation chain

transfer (RAFT) polymerization of NIPAM using AIBN as initiator
in the presence of cumyl dithiobenzoate as RAFT agent, nally
the PNIPAM-SH was obtained by reducing the dithiobenzoate
moiety with n-butylamine (Scheme 1). The as-synthesized poly-
mer PNIPAM-SH had a mean molecular weight of 16 290 with
a polydispersity of 1.59 as determined by GPC.
For comparison, PNIPAM was also prepared by polymeriza-
tion of NIPAM under the same conditions in the absence of
RAFT agent. The obtained PNIPAM sample possessed a mean
molecular weight of 28 130 with a polydispersity of 2.32 as
determined by GPC.
2. Experimental
2.2.2. Synthesis of polymer-modied Pt nanoparticles. A
simple method was employed to prepare polymer-modied Pt
nanoparticles through alcohol reduction. In a typical synthesis,
PNIPAM-SH (44 mg) was added to a solution of H PtCl $6H O
2
.1 General
Hexachloroplatinic acid hexahydrate (H
isopropylacrylamide (NIPAM) of analytical grade were supplied
by Aldrich, and the monomer was recrystallized from n-hexane.
2
6 2
PtCl $6H O) and N-
2
6
2
À2
(
1.93 Â 10 mmol) in water (2.0 mL) and ethanol (8.0 mL), then
ꢁ
the mixture was heated to 100 C and reuxed for 3 h. The
reaction mixture was evaporated under reduced pressure, and
then the resulting black powder, marked as Pt@PNIPAM-SH,
was dispersed in 10 mL of ethanol. For comparative purposes,
Pt@PNIPAM with the same ratio of polymeric monomer to Pt
was prepared under the same conditions.
2,2-Azobisisobutyronitrile (AIBN) was purchased from Wako
Pure Chemical Ind and recrystallized from pure ethanol before
use. Halonitrobenzenes (HNBs) of analytical grade were ob-
tained from J&K Chemical and used without further purication.
The mean molecular weight and polydispersity of polymers
were measured by gel permeation chromatography (GPC)
system equipped with a Waters 1525 pump and Waters Styragel
À1
2.3 Catalytic reaction
columns (MW range 3000–600 000 g mol ), using tetrahydro-
ꢁ
À3
furan as eluent at 35 C and polystyrenes as calibration stan- Typically, the required amount of Pt colloid (1.9 Â 10 mmol Pt)
dards. Transmission electron microscopy (TEM) photographs dispersed in 2.0 mL of ethanol and HNBs (2 mmol) were added
were taken by using a Philips Tecnai G2F20 electron microscope into a glass liner tube, then transferred to a stainless steel auto-
operated at 200 kV. X-ray photoelectron spectroscopy (XPS) clave (30 mL) and purged with pure hydrogen. Aer that, the
analysis was performed on an Axis Ultra DLD instrument, and reactor was conducted at 313 K with 10 bar of hydrogen and the
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reaction was lasted for a proper time. When the reaction was over,
a certain amount of water was added to precipitate the colloid Pt
catalyst from the reaction system based on the cononsolvency of
polymer. The catalyst was subjected to a new run without further
treatment aer phase separation. The products were obtained by
simple ethyl ether extraction, and the conversion of HNB and the
selectivity to HAN were determined by GC-FID.
3. Results and discussion
3.1 Catalyst characterization
The as-synthesized polymer protected Pt nanocatalysts
Pt@PNIPAM-SH and Pt@PNIPAM were submitted to TEM
characterization. As shown in Fig. 1, these two catalysts were
uniformly dispersed and no aggregation of Pt nanoparticles was
observed. Fig. 1b and d showed these two catalysts have sharp
Fig. 2 High-resolution XPS spectra of Pt 4f region for Pt@PNIPAM-SH
and Pt@PNIPAM.
size distribution curves in the range of 0.6–3.0 nm, suggesting with hydrogen pressure of 10 bar and reaction temperature of
a very narrow size distribution of Pt particles. The average Pt 313 K. For comparison, Pt@PNIPAM was also investigated
particle diameters were about 1.7 nm and 1.8 nm for under the same reaction conditions.
Pt@PNIPAM-SH and Pt@PNIPAM, respectively.
The catalytic performance of the two catalysts Pt@PNIPAM-SH
The two Pt nanocatalysts Pt@PNIPAM-SH and Pt@PNIPAM and Pt@PNIPAM was compared with p-CNB as a model substrate.
were characterized by XPS. Fig. 2 shows the high-resolution Pt 4f As shown in Fig. 3, Pt@PNIPAM showed a higher conversion of
XPS spectra of Pt@PNIPAM-SH and Pt@PNIPAM. It could be 36.4% in 15 min and a complete conversion was achieved in
observed that the binding energies of Pt 4f5/2 and Pt 4f7/2 in 90 min. Compared with Pt@PNIPAM, Pt@PNIPAM-SH exhibited
Pt@PNIPAM were 74.7 and 71.4 eV, respectively. There were no a decrease reaction rate and a lower conversion of 26.7% was
2
+
Pt 4f5/2 and Pt 4f7/2 peaks derived from Pt species in the Pt 4f attained in 15 min. Thus the TOF values of Pt@PNIPAM and
2
+
0
À1
À1
spectrum, which indicated that Pt was entirely reduced to Pt . Pt@PNIPAM-SH were 1508 h and 1106 h , respectively, and
Similar results were observed for Pt@PNIPAM-SH with a slightly the inferior catalytic activity for the latter could be attributed to
negative shi of the Pt 4f5/2 and Pt 4f7/2 binding energies (by 0.2 the partial poisoning of Pt catalytic sites by thiol groups. In term
and 0.1 ev, respectively).
of selectivity of products, the selectivity to p-CAN over
Pt@PNIPAM-SH remained stable at 99.9% within 2 h. While for
Pt@PNIPAM, the selectivity was gradually decreased with reaction
time and a relatively low selectivity to p-CAN of 85.7% was ob-
tained aer 1.5 h of reaction time. In summary, the modication
with PNIPAM-SH could improve the selectivity of Pt nanocatalyst,
although at a slight expense of reactivity, compared to PNIPAM.
The other results of selective hydrogenation of HNBs are
summarized in Table 1. It could be found that the selectivity to
the undesired dechlorination product over Pt@PNIPAM for
selective hydrogenation of p-CNB increased to 42.3% (Table 1,
entry 2) when the reaction time was prolonged to 8 h. In addi-
tion, it is notable that Pt@PNIPAM-SH could effectively prevent
the dechlorination of p-CAN and the selectivity to p-CAN was
maintained 99.6% from 99.9% when prolonging the reaction
time to 8 h (Table 1, entries 3 and 4). These results indicated
that the catalytically active Pt sites in Pt@PNIPAM-SH, which
were modied by the polymer PNIPAM-SH through the strong
interaction between the thiol groups and unsaturated surface of
Pt nanoparticles, were more suitable for selective hydrogena-
tion of HNBs with a high and steady selectivity to HANs. The
obtained high selectivity was mainly attributed to the moderate
poisoning of Pt catalytically active sites by thiol groups in the
terminal of polymer. Apart from these, the steric hindrance
effect of Pt surface that was modied by PNIPAM-SH would
prevent the at adsorption of the substrate via the benzene
3.2 Catalytic performance
The as-synthesized catalyst Pt@PNIPAM-SH was evaluated in
the selective hydrogenation of HNBs under mild conditions
32
ring, and consequently avoid the exposure of the C–Cl groups
Fig. 1 TEM micrographs and particles size distributions of Pt nano-
particles in (a and b) Pt@PNIPAM-SH and (c and d) Pt@PNIPAM.
toward the active sites during hydrogenation of nitro groups.
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Table 1 Selective hydrogenation of HNBs to HANs over Pt@PNIPAM-
a
SH and Pt@PNIPAM catalysts
Selectivity
(%)
b
Time Conversion
Fig. 3 Dependence of conversion and selectivity on the reaction time
in the selective hydrogenation of p-CNB. Reaction conditions: 2.0 mL
Entry
X
Catalyst
(h)
(%)
HAN AN
À3
ꢁ
EtOH; 2 mmol p-CNB, 1.9 Â 10 mmol Pt, 10 bar H
2
, 40 C.
1
2
3
4
5
6
7
8
9
p-Cl
p-Cl
p-Cl
p-Cl
Pt@PNIPAM
Pt@PNIPAM
Pt@PNIPAM-SH
Pt@PNIPAM-SH
1.5
8
2
8
2
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
85.7
57.7
99.9
99.6
99.8
92.1
99.7
98.8
83.3
98.8
98.6
97.3
73.3
92.9
83.7
10.5
42.3
0.1
0.4
0.2
7.9
0.3
1.2
16.8
1.2
1.4
2.7
26.7
7.1
16.3
With the same reaction conditions, we extended the scope of
substrate to various HNBs to examine the generality of the
reaction. In all cases, the desired HANs were obtained in
satisfactory and high selectivity over Pt@PNIPAM-SH. Especially
for a series of CNBs and BNBs, high selectivities of 98.5% above
were obtained for CANs and BANs, respectively, along with
a complete conversion achieved within 3 h (Table 1, entries 3, 5,
m-Cl Pt@PNIPAM-SH
m-Cl Pt@PNIPAM
o-Cl
p-Br
p-Br
m-Br Pt@PNIPAM-SH
o-Br
p-I
1.5
Pt@PNIPAM-SH 2.5
Pt@PNIPAM-SH
Pt@PNIPAM
2
2
2
3
4
4
6
10
11
12
13
Pt@PNIPAM-SH
Pt@PNIPAM-SH
Pt@PNIPAM
Pt@PNIPAM-SH
Pt@PNIPAM-SH 10
7, 8, 10 and 11). The selective hydrogenation of INBs (Table 1,
p-I
m-I
o-I
entries 12, 14 and 15) was slightly worse than CNBs and BNBs, 14
15
which could be due to the weaker C–I bond compared with C–Br
and C–Cl bonds. Inferior selectivities of 83.7–93.7% to IANs
were furnished with a longer reaction time of 4–10 h.
a
À3
Reaction conditions: 2.0 mL EtOH; 2 mmol HNB, 1.9 Â 10 mmol Pt,
ꢁ
b
10 bar H
2
, 40 C. Conversion of HNB.
In addition, the position of halogeno substituent was found
to have an obvious effect on the catalytic activity and product
selectivity. It could be seen that the hydrogenation of o-HNBs reduced to À7.5 C when the volume fraction of methanol is
ꢁ
41
required a longer reaction time and afforded more dehaloge- 0.55. This phenomenon has been called “cononsolvency”. In
nation side products, compared with p-HNBs or m-HNBs. The this case, PNIPAM polymers are insoluble and precipitated in
spatial adjacence of two reducible functional groups in o-HNBs mixed solvent at room temperature and below it. The catalyst
would increase the contact probability between halogeno group Pt@PNIPAM-SH also showed cononsolvency in the mixture of
and catalytically active site, which resulted in dehalogenation water and ethanol. It could be observed that Pt@PNIPAM-SH was
during the hydrogenation of nitro-group. Apart from this, o- well soluble in ethanol (Fig. 4A), and a phase separation behavior
HNBs, especially o-INB, possessed comparatively larger mole- occurred when water was added at room temperature (Fig. 4B).
cule bulks, which would lead to higher steric hindrance for the Thus aer each hydrogenation reaction, the catalyst could be
reaction of o-HNBs on the surface of polymer-modied Pt easily separated from the reaction mixture by adding deionized
nanoparticles, resulted in declined catalytic activity.
water at room temperature, and then well redispersed in ethanol
The comparison experiments showed that besides p-CNB, for a new run. The cononsolvency of PNIPAM polymers provides
other substrates catalyzed by Pt@PNIPAM also gave obviously a convenient and effective method to recycle Pt nanocatalysts in
inferior selectivity to HANs compared with Pt@PNIPAM-SH polar organ solvent.
(
Table 1, entries 6, 9 and 13 vs. 5, 8 and 12). This further veri-
ed that the thiol groups played an irreplaceable role in
inhibiting the dehalogenation side reaction.

3.3 Catalyst recycling and stability
The thermosensitive polymers PNIPAMs are well soluble in
ꢁ
aqueous solution below the LCST at about 32 C. Compared to
water, these polymers are more easily soluble in many polar
organic solvents such as alcohol, tetrahydrofuran, dioxane and
acetic acid, however they show no thermosensitivity in these pure
solvents. While in a mixture of water and polar organic solvent,
a uniquely thermosensitive behavior was observed for PNIPAM
polymers with a distinctly depressed LCST. For instance, the
Fig. 4 Photographs of Pt@PNIPAM-SH in ethanol (A) and in a water/
LCST of PNIPAM in a mixture solvent of water and methanol was ethanol mixture at room temperature (B).
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could be seen that the catalyst Pt@PNIPAM-SH could be reused
for twelve runs and no decrease in both p-CNB conversion and
p-CAN selectivity was observed. Aer twelve runs, the conver-
sion gradually decreased, but the selectivity to p-CAN remained
stable and higher than 99%. The results suggested that the
Pt@PNIPAM-SH was highly stable and durable for the reaction.
For the purpose of comparison, the Pt@PNIPAM catalyst was
also studied in the recycling experiment. As shown in Fig. 5B,
Pt@PNIPAM displayed obviously inferior catalytic stability for
the selective hydrogenation of p-CNB. Both the p-CNB conver-
sion and p-CAN selectivity decreased in the h run. The
compared recycling experiments demonstrated that the thiol-
terminated polymer can efficiently promote the stability and
reusability of Pt nanocatalysts. As far as we know, the reusability
achieved over Pt@PNIPAM-SH is among the best ones obtained
by transition metal catalysts for selective hydrogenation of
2,9,15,21,28,30
HNBs.
The excellent stability and durability of
Pt@PNIPAM-SH could be owing to the strong interaction
between thiol group in the terminal of polymer and unsaturated
surface of Pt nanoparticles as well as the good cononsolvency of
thermosensitive polymer.
In order to further explore the stability of the Pt nano-
catalysts during the reaction process, Pt@PNIPAM-SH aer ve
and ten runs were characterized by TEM (Fig. 6a and b). It could
be found that several particles formed small aggregates along
th
with many monodispersed particles aer the 5 run, and
Fig. 5 Recycle studies of Pt@PNIPAM-SH (A) and Pt@PNIPAM (B) in dozens of particles formed large aggregates along with much
th
the selective hydrogenation of p-CNB. Reaction conditions: 2 mmol less monodispersed nanoparticles aer the 10 run. While only
À3
HNB, 1.9 Â 10 mmol Pt, H
2
pressure of 10 bar, reaction temperature
a very slight increase in particle size from 1.7 Æ 0.3 nm to 2.0 Æ
ꢁ
of 40 C, reaction time of 2 h for Pt@PNIPAM-SH and 1.5 h for
Pt@PNIPAM, respectively.
0
.4 nm was observed aer ten runs (Fig. 6c). Therefore, this
form of aggregation could be due to the formation of polymer
aggregates and does not mean Pt nanoparticles was obviously
The recycling experiment of catalyst was carried out using p- grow larger. This suggested that the Pt nanoparticles in
CNB as a model substrate, in order to assess the reusability of Pt@PNIPAM-SH were highly stable during the recycling process,
the Pt@PNIPAM-SH, and the results are shown in Fig. 5A. It which could explain the excellent reusability of this catalyst. In
Fig. 6 TEM images of Pt@PNIPAM-SH after five (a) and ten (b) runs, and Pt@PNIPAM after two (d) and five (e) runs; particle size distributions of
Pt@PNIPAM-SH after ten runs (c) and Pt@PNIPAM after five runs (f).
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the case of Pt@PNIPAM, it was found that large aggregates
formed only aer two runs (Fig. 6d), but the Pt particle size
had no obvious change. Aer ve runs, the catalyst was
seriously aggregated to form a superstructure completely
including hundreds of particles, and the histogram of
particle size distribution showed an increased Pt particle size
of 4.3 Æ 1.0 nm. These results implied that the thiol-
terminated polymer could efficiently stabilize the Pt nano-
particles, and thus enhance the reusability of the catalyst
Pt@PNIPAM-SH.
The contents of metal leaching are of vast importance for
industrial applications, so the Pt leaching into products during
the recycling experiment over Pt@NIPAM-SH was tested by ICP-
AES. Aer each run, the liquid phase was separated from the
precipitated Pt catalyst and combined together. Then the solu-
tion was vaporized to remove the solvents, and the non-volatile
organics was removed by high temperature calcination. Finally,
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2
We have demonstrated that PNIPAM-SH can not only stabilize
the Pt nanoparticles, but also inhibit the highly active Pt
catalyst from producing hydrodehalogenation products
through anchoring the thiol groups to unsaturated surface of
Pt nanoparticles. The catalytic site poisoning and steric
hindrance effect of Pt@PNIPAM-SH catalyst were suitable for
selective hydrogenation of HNBs with high and steady selec-
tivities to HANs, and the conclusion was further conrmed by
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1
1
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1
a
series of HNBs. Moreover, the recycling process of
9
Pt@PNIPAM-SH is rather simple and practical based on the
cononsolvency of PNIPAM-SH. Excellent stability and reus-
ability were presented over Pt@PNIPAM-SH, and no decrease
in catalytic activity and selectivity was observed for rst twelve
runs with extremely low metal leaching, which was one of the
best results obtained over Pt catalysts. TEM characterization of
reused catalyst revealed that the Pt nanoparticles in
Pt@PNIPAM-SH were not obviously enlarged, the formation of
polymer aggregates took place. These inspiring results
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