Platinum nanoparticles confined in imidazolium-based ionic polymer for assembling a microfluidic reactor with enhanced catalytic activity

Article abstract of DOI:10.1016/j.apcata.2019.117186

A synthetic strategy is developed to grow Pt nanoparticles supported by imidazolium-based ionic polymers (Pt/ImIP-2BrB) on the inner surface of fused-silica capillary. The imidazolium-based ionic polymers ImIP-2BrB are prepared from condensation of tetrakis[4-(1-imidazolyl)phenyl]methane and 1,4-bis-bromomethyl-benzene and are employed to support Pt nanoparticles. The capillary coated with Pt/ImIP-2BrB is further assembled to achieve a catalytic micro?uidic reactor. The catalytic activity is probed in either the reduction of nitrobenzene derivatives or the hydrosilylation of phenylacetylene with triethylsilane by flowing through the micro?uidic reactor. The catalytic micro?uidic reactor demonstrates significantly enhanced activity about 2–8 times in comparison with the corresponding reactions under batch conditions. The reactor greatly reduces the amount of Pt upon achieving similar yields. It also shows good recyclability without significant decrease of the activity.

Full text of DOI:10.1016/j.apcata.2019.117186

Accepted Manuscript
Title: Platinum nanoparticles confined in imidazolium-based
ionic polymer for assembling a microfluidic reactor with
enhanced catalytic activity
Authors: Haobin Fang, Junxing Chen, Yali Xiao, Jianyong
Zhang
PII:
DOI:
Article Number:
S0926-860X(19)30341-2
https://doi.org/10.1016/j.apcata.2019.117186
117186
Reference:
APCATA 117186
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
9 May 2019
27 July 2019
30 July 2019
Please cite this article as: Fang H, Chen J, Xiao Y, Zhang J, Platinum nanoparticles
confined in imidazolium-based ionic polymer for assembling a microfluidic
reactor with enhanced catalytic activity, Applied Catalysis A, General (2019),
https://doi.org/10.1016/j.apcata.2019.117186
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Platinum nanoparticles confined in imidazolium-based ionic polymer for assembling a
microfluidic reactor with enhanced catalytic activity
Haobin Fang, Junxing Chen, Yali Xiao, Jianyong Zhang*
MOE Laboratory of Polymeric Composite and Functional Materials, School of Materials Science
and Engineering, Sun Yat-Sen University, Guangzhou 510275, China.
*
Correspondence author.
E-mail addresses: zhjyong@mail.sysu.edu.cn (J. Zhang).
Graphical Abstract
Highlights



 Fused-silica capillary is modified by ionic polymer loaded with well-dispersed Pt
nanoparticles.
 A catalytic microfluidic reactor is assembled for nitroreduction and
hydrosilylation.
The microfluidic reactor shows improved activity and multiple uses.
Abstract
A synthetic strategy is developed to grow Pt nanoparticles supported by imidazolium-based
ionic polymers (Pt/ImIP-2BrB) on the inner surface of fused-silica capillary. The
imidazolium-based ionic polymers ImIP-2BrB are prepared from condensation of
tetrakis[4-(1-imidazolyl)phenyl]methane and 1,4-bis-bromomethyl-benzene and are employed to

support Pt nanoparticles. The capillary coated with Pt/ImIP-2BrB is further assembled to achieve a
catalytic microfluidic reactor. The catalytic activity is probed in either the reduction of
nitrobenzene derivatives or the hydrosilylation of phenylacetylene with triethylsilane by flowing
through the microfluidic reactor. The catalytic microfluidic reactor demonstrates significantly
enhanced activity about 2-8 times in comparison with the corresponding reactions under batch
conditions. The reactor greatly reduces the amount of Pt upon achieving similar yields. It also
shows good recyclability without significant decrease of the activity.
Keywords: platinum nanoparticles, ionic polymers, microfluidic reactor, nitroreduction
1. Introduction
Noble metals like Au, Pd, Pt are widely applied as catalysts in a number of organic
transformations such as nitroreduction [1,2], aerobic oxidation [3], coupling reaction [4,5],
hydrogenation reaction [6,7], etc. Altough the high cost limits their application, it is still
irreplaceable. Metal nanoparticles (NPs) loaded on porous materials have been developed as
efficient heterogeneous catalysts because reduced metal dosage and downsizing nanoparticles can
achieve a large proportion of active surface atoms [8-24]. Among various porous materials,
imidazolium-based ionic polymers incorporating ionic building blocks can load kinds of metal
nanoparticles through electrostatic interaction or ion exchange with corresponding metal salts
[25-29]. Stable and well-dispersed nanoparticles may be encapsulated in the imidazolium-based
ionic polymers to result in improved catalytic efficiency and stability. However, heterogeneous
catalysts generally suffer from decreased catalytic efficiency compared with homogeneous
catalysts, and specific technology is needed to improve the catalytic efficiency [30].
Microfluidic reactors have been extensively explored to improve the efficiency of organic
synthesis in recent years [31-35]. In comparison with the reactions performed under batch
conditions, the microfluidic systems have a range of advantages such as easy automatical control
of reaction temperature and reagent consumption, improved transfer efficiency of heat, mass and
kinetics of diffusion-limited reactions [36-40]. Catalysts in a confined region offer a large number
of active sites exposed to reagents and precise selection for products [41-45]. In addition the
reaction in microfluidic reactors is safer for hazardous chemicals. So the high reaction efficiency,

environmental sustainability, and easy control make the microfluidic systems promising in various
fields [46-54].
Based on the above considerations, an open-tubular microfluidic system with coating Pt NPs
supported on imidazolium-based organic polymer is herein reported. Imidazolium-based ionic
polymer (ImIP-2BrB) [55] is coated on the inner surface of microfluidic capillary to support Pt
2
-
NPs. The positive network of ImIP-2BrB can entrap PtCl
6
ions for subsequent formation of Pt
NPs. In the capillary, the polymer acts as a carrier allowing Pt NPs to be stably loaded on the
capillary wall. In the catalytic process, the polymer can stabilize Pt NPs and prevent the loss or
agglomeration of Pt NPs. The open-tubular capillary reactor with Pt/ImIP-2BrB coating is applied
to catalyze nitroreduction [56-59] and hydrosilylation reactions [60-67]. The technology greatly
reduces the amount of Pt with remarkably improved catalytic activity and recyclability.
2
2
. Experimental section
.1 Materials and methods
Chemicals and solvents were obtained from commercial sources and used as received without
further purification unless otherwise stated. (3-Bromo-propyl)triethoxysilane [68] and
tetrakis[4-(1H-imidazole-1-yl)phenyl]methane [55] were synthesized according to the previous
reports. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX)
analysis was carried out using an ultra-high resolution SU8010 FE-SEM. For SEM measurements,
the material was dispersed in EtOH using sonication, and then deposited on aluminum foil.
Transmission electron microscopy (TEM) investigations were performed on a FEI Tecnai G2
Spirit 120 kV or 300 kV TEM system. For TEM measurement, the material was dispersed in
EtOH with the aid of sonication, and then dropped on a carbon coated copper grid. Powder X-ray
diffraction (XRD) data was collected on a Rigaku Smart Lab diffractometer (Cu-Kα
1
radiation, λ =
1.54056 Å). NMR spectra were obtained on a Bruker Avance 400 MHz Superconducting Fourier
Transform Nuclear Magnetic Resonance Spectroscopy instrument. Pt analysis was performed
using a Thermo ScientifiCAP RQ ICP-MS instrument. Before the analysis, the material on the
o
coated capillary was digested by aqua regia at 150 C for 3 d. Infrared spectra were recorded on a
-1
Perkin Elmer Frontier FT-IR spectrometer with KBr pellets in the range 4000-400 cm . X-ray
photoelectron spectroscopy (XPS) was using X-ray Photoelectron Spectroscopy/ESCA

(ESCALAB 250). Thermo analyses were using a NETZSCH TG STA 449 F3 Jupiter system under
N
2
atmosphere.
2.2 Coating of Pt/ImIP-2BrB in capillary
Pre-bromination of the inner surface of capillary. A capillary (ID = 0.53 mm, L = 30.0 m)
-1
-1
was rinsed with acetone for 30 min, 3 mol L NaOH for 2 h, and 3 mol L HCl aqueous solution
for 2 h, in turn. Then the capillary was rinsed with distilled water for 10 min and EtOH for 10 min
in turn, and dried in Ar stream for 2 h. Subsequently the capillary was filled with a solution of
o
3
-bromopropyl-triethoxysilane in dry toluene (2%, v:v) and kept for 1 d at 80 C. The solution was
removed and the capillary was rinsed with dry toluene for 10 min and EtOH for 10 min in turn,
and dried in Ar stream for 4 h.
Coating of ImIP-2BrB in the capillary. The above pre-treated capillary (L = 1000 mm) was
filled with a mixed solution of tetrakis[4-(1-imidazolyl)phenyl]methane (TIM) and 1,4-bis-
-1
-1
bromomethyl-benzene (2BrB) in CHCl
3
(cTIM = 0.046 mol L , c2BrB = 0.091 mol L , mixed in a
-1
1
:1 volume ratio). The injection speed was controlled by a syringe at 0.2 mL min . The capillary
o
was sealed and kept for 2 d at 80 C. Then the solution was removed by flushing the capillary with
Ar. The capillary was rinsed with CHCl for 10 min.
The above processes (pre-bromination and ImIP-2BrB coating) were repeated for three times.
3
-1
Pt NPs incorporating in capillary. H
2
PtCl
4
in EtOH (2.5 mmol L ) was injected into the
-1
above capillary at 0.2 mL min . The capillary was sealed and kept for 1 d at RT. NaBH
4
solution
-1
-1
in EtOH (0.2 mol L ) was injected into the capillary at 0.2 mL min continuously during 1.5 h.
The solution was removed by flushing the capillary with Ar. The capillary was rinsed with water
for 10 min and ethanol for 10 min in turn. The coating thickness was ca. 31.7 ± 0.7 µm according
to SEM. ICP showed that the Pt content was 0.00025 mmol for 1000 mm capillary.
2.3 Nitroarene reduction in capillary reactor and recyclability
Typical procedure: A solution of nitrobenzene (0.062 g, 0.5 mmol) in THF (4 mL) was mixed
with a solution of reducing agent, NaBH (0.095 g, 2.5 mmol) in water (2 mL). 1 mL of the
4
resulting mixture was taken to be continuously introduced into the coated capillary (ID = 0.53 mm,
L = 1000 mm) using a syringe, and the mixture passed through the capillary with constant flow

-1
o
rate (6 µL min ) at RT (~25 C). The reaction time in the coated capillary was about 1.0 h. Then
the effluent was collected and extracted with ethyl acetate (0.5 mL). The organic layer (1 μL) was
tested using gas chromatography. For subsequent use, the capillary reactor was rinsed with H
EtOH and dried by flushing the capillary with Ar.
2
O,
2.4 Nitroarenereduction under batch conditions
General procedure: Nitroarene derivatives (1.0 mmol) in THF (4 mL) and NaBH (0.189 g,
4
5.0 mmol) in water (2 mL) were mixed, and Pt/ImIP-2BrB-2.5 catalyst (10.0 mg, 0.6 mol% Pt
based on ICP analysis) was added. The mixture was stirred at RT under Ar atmosphere. For GC
analysis, the mixture (0.2 mL) was taken and extracted with H O (1 mL) and ethyl acetate (1 mL)
2
in turn, and the organic layer (1 μL) was tested. After the mixture was stirred at RT for 2 h, and
filtered, the filtrate was extracted with ethyl acetate (3×10 mL) and washed by 10 mL water. The
combined organic phase was dried by anhydrous MgSO and the crude product was further
4
purified by flash column chromatography on silica gel. The product was dried in vacuum and
confirmed by NMR. 4-Toluidine (0.091 g, 85%), 3-toluidine (0.085 g, 79%), 2-toluidine (0.080 g,
75%), 4-aminophenol (0.076 g, 70%), 1,4-phenylenediamine (0.089 g, 82%), 4-tert-butylaniline
(0.118 g, 79%), 4-anisidine (0.107 g, 87%).
2.5 Hydrosilylation in capillary reactor and recyclability test
Typical procedure: Phenylacetylene (0.102 g, 1.0 mmol) and triethylsilane (0.116 g, 1.0
mmol) were mixed in 5 mL toluene. The resulting solution was taken to be continuously
o
introduced into the coated capillary (ID = 0.53 mm, L = 2000 mm) using a syringe at 80 C. The
-
1
reaction was kept for 4 h (flow rate, 2 μL min ) and then cooled down to RT. The 0.5 mL effluent
from the end of the coated capillary was collect at intervals and evaporated to dryness in vacuum
1
and analyzed by H NMR using 1,4-dioxane (0.1 mmol) as the standard. After the reaction, the
capillary was rinsed with toluene for subsequent use and the residual solution was removed by Ar.
2.6 Hydrosilylation under batch conditions
Typical procedure: Phenylacetylene (0.102 g, 1.0 mmol), triethylsilane (0.116 g, 1.0 mmol),
o
2
0, 10 or 5 mg catalyst (1.2, 0.6 or 0.3 mol%) were mixed in toluene (5 mL) under Ar at 80 C.

The reaction mixture was stirred for 4 h and then cooled down to RT. The reaction mixture was
1
dried in vacuum, extracted with 0.5 mL CDCl
3
, filtrated and analyzed by H NMR spectroscopy
with 1,4-dioxane as standard. The isomeric content was determined based on the alkene coupling
1
constants in the H NMR spectra and/or analysis of chemical shifts.
3
3
. Results and discussion
.1 Preparation of the coating capillary
The synthetic route for the growth of Pt/ImIP-2BrB on the surface of fused-silica capillary is
presented in Fig. 1. First, the inner surface of a capillary is brominated by (3-bromo-
propyl)triethoxysilane treatment [56]. The resulting capillary is denoted as C-Br. Subsequently, the
imidazole groups of tetrakis[4-(1H-imidazole-1-yl)phenyl]methane (TIM) are alkylated on its N
atoms with 1,4-bis(bromomethyl)-benzene (2BrB) to generate extended imidazolium-based ionic
polymer with cationic imidazolium crosslinks, ImIP-2BrB. In the meantime, the coupling reaction
of TIM with the dangling -Br groups on the capillary surface leads to strong covalent linkage
between ImIP-2BrB and capillary, which benefits a uniform and stable modified layer. Finally, due
to the cationic nature, ImIP-2BrB layer grown on the capillary surface readily adsorbs PtCl 2
-
6
anions. Following an in situ reduction induced by NaBH solution, Pt NPs are formed and
4
stabilized within the porous channels of the ImIP-2BrB layer.
a)
Br-
N
N
N
Br-
N
N
SiO
N
N
O
Si
N
Br-
SiO
SiOH
O
SiOH
N
N
N
N
1
B
N
)
H
Br-
N
r(
C
Br-
2 P
tC
H
N
l
6
2
)
Pt
N
3
S
i(
O
N
2
)
E
NaBH
Pt Br-
N
N
t)
3
N
4
Br
SiO
N
N
O
Si
Br-
Br
SiO
C-ImIP-2BrB
Pt
Br
SiO
N
Br-
O
Si
SiO
N
Pt
C-Pt/ImIP-2BrB

Fig. 1. a) Synthetic route to C-Pt/ImIP-2BrB, and b) schematic representation of the microfluidic
reactor assembled from Pt/ImIP-2BrB-coated capillary.
Fig. 2. a-d) SEM and e) TEM images of Pt/ImIP-2BrB layer on the capillary, and f) particle size
-1
-1
distribution (Pt/ImIP-2BrB growth parameters, cTIM = 0.023 mol L and c2BrB = 0.091 mol L in
CHCl in 1:1 volume ratio). The bars represent 40.0, 30.0, 10.0, 2.00, and 5 nm, respectively, from
a to e.
3
3.2 Characterization of the coating capillary
The morphology of the resulting Pt NPs supported on ImIP-2BrB within the microfluidic
capillary (denoted as C-Pt/ImIP-2BrB) is characterized using SEM and TEM (Fig. 2). SEM of the
capillary cross section confirms the growth of a Pt/ImIP-2BrB layer with a thickness of 42.3±4.0
μm. The morphology of the material on the capillary was macroscopically composed of
interconnected spheres which is in agreement with that of the material obtained under batch
conditions. TEM reveals nanoparticles of 1.8±0.2 nm for C-Pt/ImIP-2BrB which is close to the
size of the Pt NPs (1.92±0.33 nm) obtained under batch conditions according to our previous
study [55]. High resolution TEM shows atomic lattice fringes of Pt NPs with a spacing of 0.23 nm

which corresponds to Pt(111) planes and proves the existence of crystalline Pt NPs in ImIP-2BrB
within the microfluidic capillary (Fig. S1) [69,70]. Energy dispersive X-ray spectroscopy (EDX)
analysis of the coating layer shows the Pt, C, N and Br elements indicating the successful coating
of the polymer on the capillary (Fig. S2). Powder X-ray diffraction (PXRD) shows that the
polymer ImIP-2BrB is amorphous before loading Pt NPs (Fig. S3). After loading of Pt NPs, the
signal at 2θ ≈ 40° ascribed to the Pt(111) lattice plane of Pt NPs is too broad to be observed clearly,
which is presumably attributed to the small size and high dispersion of crystalline Pt NPs [59, 60].
FT-IR of Pt/ImIP-2BrB scraped from the capillary shows characteristic peaks at around 1665
-1
and 1615 cm , which are attributed to the imidazolium C=C and C=N stretching vibrations,
respectively (Fig. S4) [61]. The polymer after Pt loading shows almost identical spectrum to the
corresponding polymer before Pt loading, indicating that the polymeric structure is well
maintained [55,59,60]. X-ray photoelectron spectroscopy (XPS) survey spectra of Pt/ImIP-2BrB
on the capillary possess characteristic signals of Pt 4f, Br 3d, Si 2p, C 1s, N 1s, and O 1s (Fig. S5).
The Pt 4f region is divided into two spin-orbital pairs. The binding energy peaks at 75.0 eV (Pt
4f5/2) and 71.7 eV (Pt 4f7/2) are assigned to Pt(0) species [60,62,63]. The results indicate successful
coating of the polymer on the capillary.
Thermogravimetric analysis (TGA) profile shows that Pt/ImIP-2BrB and ImIP-2BrB scraped
from the capillary show similar thermal stability (Fig. S6). For ImIP-2BrB the continuous weight
o
loss before 100 C is related to the removal of moisture or free solvent. Both the materials
o
decompose when the temperature is above about 200 C.
3.3 Assembling of the microfluidic reactor
The microfluidic equipment includes a syringe pump, an injector, a capillary coated by
Pt/ImIP-2BrB and a vessel for collecting the product. The injector and coated capillary were
connected by a Luer taper. The starting solution mixture in the injector was injected into the
coating capillary by the syringe pump that controls the flow rate. The flow rate of the solution
mixture and the length/volume of the coated capillary (ID = 0.53 mm, L = 1000 mm) determine
the reaction time (of passing through the capillary) (Fig. 1). For the hydrosilylation reaction, an oil
bath is needed to heat the coating capillary. The Pt NPs in the reactor was determined to be 2.5×

1 -
4
0 mmol m by ICP. The Pt NPs in the reactor has similar size but lower content in comparison
-1
with the material prepared under the batch conditions.
3
.4 Reduction of nitroarene derivatives
The catalytic performance of the microfluidic reactor was evaluated in the reduction of
nitroarene derivatives to corresponding anilines, which is an important transformation in organic
chemistry. The reaction was first performed under batch conditions for optimized conditions
(Table 1). First, the molar ratio of nitrobenzene:NaBH
4
was optimized. The selectivity was only
64% (azobenzene/azoxybenzene compounds are main by-products) when the molar rate of
nitrobenzene:NaBH
4
was 1:3, while it was higher up to 99% when nitrobenzene:NaBH
4
was 1:5
(with >98% conversion after 2 h). It indicates that insufficient NaBH
4
results in poor selectivity.
Next the activity of the material with different size of Pt NPs was also studied. Pt/ImIP-2BrB-2.5
with smaller size of Pt NPs (1.92 ± 0.33 nm) showed better selectivity (e.g., ＞99% for the
reduction of nitrobenzene) and shorter reaction time (e.g., 1 h for the reduction of
1
-chloro-4-nitrobenzene) than Pt/ImIP-2BrB-5.0 (2.86 ± 0.56 nm). Therefore the optimized
reaction was performed with 1:5 molar ratio of nitrobenzene and NaBH and 10 mg of
O (v:v = 2:1) at RT (~25 C)
4
o
Pt/ImIP-2BrB (Pt 0.64 mol% to the nitrobenzene) in 6 mL THF/H
under Ar atmosphere.
2
The reaction was then performed in the microfluidic reactor. The reaction mixture (e.g.,
nitrobenzene (0.17 mmol) and NaBH (0.83 mmol) in THF-H O (v:v = 2:1)) was taken to be
4
2
introduced into the capillary using a syringe pump. Nitrobenzene was catalytically reduced and the
product was collected at the end of the capillary and tested using gas chromatography and NMR
(
Fig. S7-S26). The Pt amount in the reactor was determined using inductively coupled plasma, and
apparent turnover frequency (TOF) for all the catalytic reactions was calculated as the amount of
nitrobenzene that a mole of Pt can convert per unit time [64]. Then the TOF for the reactions
performed in the microfluidic reaction system was compared with the reactions under batch
conditions. Most of the nitrobenzene derivatives catalysed by C-Pt/ImIP-2BrB showed about 2-4
times higher TOF when compared with those by Pt/ImIP-2BrB under batch conditions. For
example, the reduction of 2-nitrotoluene (46 vs. 284) and 1-tert-butyl-4-nitrobenzene (75 vs. 594)

by C-Pt/ImIP-2BrB showed about 8 times higher TOF compared with those by Pt/ImIP-2BrB
under batch conditions. The substrates bearing electron-donating groups, such as 2-nitrotoluene,
3-nitrotoluene, 4-nitrotoluene and 4-nitroanisole, provided good conversion and selectivity to
corresponding products (98% and 99% for 2-nitrotoluene, 94% and 89% for 3-nitrotoluene, 92%
and 93% for 3-nitrotoluene, 98% and 95% for 4-nitroanisole). The steric hindrance at ortho-,
meta- and para-positions of nitrotoluene has little effect on the catalytic reactions. Additionally the
reduction of 1-tert-butyl-4-nitrobenzene also gave 92% conversion and 96% selectivity indicating
that the bulky steric effect was also little. Functional groups, such as -OH and -NO
tolerated in the catalytic system and gave good conversion and selectivity.
2
, were well
1
4
-Chloro-4-nitrobenzene gave 90% conversion and only 76% selectivity of 4-chloroaniline, and
-nitrobenzaldehyde gave only 82% conversion and 62% selectivity of 4-aminobenzyl alcohol due
to the electron-withdrawing groups like -Cl and -CHO [64, 65]. The TOFs are also much higher
than those under batch conditions. The present Pt catalyst in microfluidic reactor showed higher
TOFs than the reported Pt NPs-based catalysts for nitroreduction (Table S1) [8-11]. The reported
-1
TOFs range from 2 to 262 h for several nitrobenzene derivatives, while the present microfluidic
-1
reactor achieves more than 600 h for most of the nitrobenzene derivatives. The higher TOFs may
be caused by the larger proportion of Pt NPs that are exposed to the substrates. When the Pt NPs
catalyst is transformed into a confined ionic polymer layer of the microfluidic channel, the contact
is significantly enhanced between substrates and the Pt NPs catalytically active sites [66, 67].
Table 1 Reduction of nitrobenzene derivatives to anilines catalyzed by Pt/ImIP-2BrB
.
Cat. , NaBH4
NO2
NH2
THF/H O, RT
2
R
R
Pt content
Entry
R
Catalysta
Time/h
Conv./% Sel./%
TOFmax/h-1
/
mmol
1
2
3c
4
5
6
4-H
Pt/ImIP-2BrB-2.5
Pt/ImIP-2BrB-5.0
Pt/ImIP-2BrB-5.0
C-Pt/ImIP-2BrB
Pt/ImIP-2BrB-2.5
0.0064
1
1
2
＞99
＞99
98
＞99
94
156
-
-
-
64
-
0.00025 1
＞99
95
＞99
67
666
99
4-Cl
0.0064
-
1
3
Pt/ImIP-2BrB-5.0
97
62
-

7
8
C-Pt/ImIP-2BrB
Pt/ImIP-2BrB-2.5
0.00025 2
0.0064
0.00025 1
0.0064
0.00025 2
0.0064
90
99
76
96
233
74
4
-Me
2
9
1
1
1
C-Pt/ImIP-2BrB
Pt/ImIP-2BrB-2.5
C-Pt/ImIP-2BrB
98
99
94
99
90
89
660
46
0
1
2
2-Me
3
284
3
4
-Me
-OH
Pt/ImIP-2BrB-2.5
C-Pt/ImIP-2BrB
Pt/ImIP-2BrB-2.5
3
98
92
98
99
93
93
50
1
1
3
4
0.00025 2
291
285
0.0064 0.5
0.00025 1
1
1
1
5
6
7
C-Pt/ImIP-2BrB
Pt/ImIP-2BrB-2.5
C-Pt/ImIP-2BrB
95
99
98
99
640
155
646
4-NO
2
0.0064
0.00025 1
0.0064
0.00025 5
0.0064
0.00025 1
0.0064
0.00025 3
1
＞99
97
1
8e
4
4
-CHO
Pt/ImIP-2BrB-2.5
C-Pt/ImIP-2BrB
Pt/ImIP-2BrB-2.5
6
79
40
62
96
8
1
2
9e
0
82
69
75
-CMe
3
2
＞99
2
2
2
1
2
3
C-Pt/ImIP-2BrB
Pt/ImIP-2BrB-2.5
C-Pt/ImIP-2BrB
92
95
594
52
4-OMe
3
＞99
98
＞99
95
211
a
b
Pt/ImIP-2BrB-2.5 and Pt/ImIP-2BrB-5.0 were synthesized according to ref [41]. Batch reaction
(5.0 mmol), Pt/ImIP-2BrB-2.5 (0.64 mol%) in 6 mL
O (2:1, v/v) at RT; Microfluidic reaction conditions: 1.0 m capillary (Pt, 0.16 mol%),
conditions: nitroarene (1.0 mmol), NaBH
THF-H
4
2
C-Pt/ImIP-2BrB with a coating thickness of 31.7±0.7 μm, nitroarene (0.17 mmol) and NaBH
4
c
(0.83 mmol) in 1 mL or 2 mL H
2
O-THF (2:1, v/v) at RT. the molar ratio of nitroarene and NaBH
4
d
e
was 1:3. Conversion [%] and selectivity [%] were determined by GC and NMR. The product
was determined to be 4-aminobenzyl alcohol.
Conversion
Selectivty
TOF
100
350
300
250
200
150
100
50
0
80
60
40
20
0
1
2
3
4
5
6
7
8
Cycle
Fig. 3. Histogram of the multiple uses of C-ImIP-2BrB for the nitroreduction of nitrobenzene.

Reaction conditions: nitrobenzene (0.083 mmol), NaBH
8:3:1, v:v:v) at RT for 1 h.
4
(0.42 mmol) in 2 mL THF-H O-EtOH
2
(
100
80
60
40
20
0
Solution in Pt capillary
to raw capillary
Fresh solution added
to Pt capillary
0
2
4
6
8
10
12
Time/min
Fig. 4. Three-phase test plots for the nitroreduction of nitrobenzene. A solution of nitrobenzene
0.5 mmol) in THF (4 mL) was mixed with a solution of reducing agent, NaBH (2.5 mmol) in 2
mL H O/EtOH (v:v = 2:1). The reaction mixture flowed through the Pt/ImIP-2BrB capillary (10
(
4
2
-1
cm) with reaction time of 2 min (11 μL min ), and conversion was monitored. (a) When
conversion reach 68%, the solution collected from the Pt/ImIP-2BrB capillary was introduced into
a raw capillary with no catalyst loaded (black line); (b) Fresh solution was introduced into the first
Pt/pIM-2BrB capillary, and conversion was monitored (red line).
Multiple uses were performed in the capillary reactor for the nitroreduction of nitrobenzene.
The catalytic activity of C-Pt/ImIP-2BrB maintained for at least 8 recycling runs (Fig. 3). Initial
time-conversion plots also showed that no significant activity loss was observed (Fig. S27). The Pt
-1
content after 8 runs was experimentally measured to be 0.00021 mmol m and the size of Pt NPs
-
1
was 2.0±0.4 nm, which are close to those prior to initiating the reduction (0.00025 mmol m and
1.8 ±0.2 nm), and a spacing of atomic lattice fringes of Pt NPs was still 0.24 nm which
corresponds to Pt (111) planes, showing that the Pt NPs catalyst was stable (Fig. S28-S30). SEM
of the capillary cross section showed the Pt/ImIP-2BrB layer with a thickness of 39.7±6.7 μm
which is close to that before the catalytic reaction (42.3±4.0 μm) and the morphology of polymer
on the capillary did not change after 10 runs. Further verification that the Pt NPs were not leaching
was carried out with a three-phase test for the nitroreduction of nitrobenzene. With reaction time

-1
of 2 min and 4 min (10 cm, 11 μL min ), the conversion reached 43% and 68% respectively. After
68% conversion was reached, the reaction solution from the Pt/ImIP-2BrB capillary was injected
to a new raw capillary which did not contain any catalyst, and the solution did not react and
remains at 68% conversion (Fig. 4). This indicates that no active Pt NPs leached from the
Pt/pIM-2BrB capillary, otherwise an increase in conversion would have been observed for the
solution from the raw capillary [71]. The microfluidic reactor remains its catalytic activity after
the multiple uses. This proves that Pt NPs and polymer in the capillary is stable after modification
of the capillary using the present method together with other evidences. Polymers do not fall off
from the capillary wall and Pt NPs are captured firmly within the polymers during the reactions.
Thus the microfluidic reactor continues to catalyze the reactions without clogging or degradation.
3.5 Hydrosilylation reaction
Hydrosilylation was performed in the microfluidic reactor and the reactions were detected by
1H NMR [53, 68-70]. The hydrosilylation of phenylacetylene and triethylsilane was chosen as a
model hydrosilylation system. Reaction conditions were first optimized under batch conditions,
and the best performance was observed when toluene was chosen as the solvent and the Pt content
of Pt/ImIP-2BrB was 0.6 mol% (Table S2, Fig. S31, S32). The yield was 66% with the α:β-(E)
-1
isomeric ratio 40:60 (no β-(Z) isomer was observed) and the TOF was calculated to be 28 h . The
1
hydrogen signals on the alkene of both products were detected according to H NMR (α product,
6.2, 5.9 ppm; β-(E) product, 7.3, 6.8 ppm). Then the hydrosilylation of phenylacetylene and
triethylsilane was performed in the microfluidic reactor with the coated capillary (ID = 0.53 mm,
o
-1
L = 2000 mm) at 80 C. The flow rate was about 2 μL min and the reaction time was about 4 h.
The yield was 79% and the α:β-(E) isomeric ratio was 56:44 after 4 h in toluene. The TOF was
-1
3
95 h , which is over ten times higher than that under batch conditions.
The microfluidic reactor (C-Pt/ImIP-2BrB) was also assessed in other hydrosilylation
reactions. When 1-phenyl-1-propyne or 4-ethynyltoluene was chosen to react with triethylsilane,
characteristic signals were detected at 6.1 ppm (α product) and 6.7 ppm (β-(E) product) for
1-phenyl-1-propyne (Fig. S33) and at 5.9, 5.6 ppm (α product) and 6.9, 6.4 ppm (β-(E) product)
for 4-ethynyltoluene (Fig. S34). The yield and isomeric ratio was 65%, 29:71, and 50% 50:50 with
-1
TOF was 217 and 167 h , respectively. They are remarkably higher than those under batch

-1
conditions (yield 45% and 39%, TOF 13 and 11 h ). NMR signals were detected at 5.9, 5.6 ppm
α product) and 6.9, 6.4 ppm (β-(E) product) for 1-ethynyl-4-fluorobenzene, at 6.1, 5.8 ppm (α
product) and 7.1, 6.7 ppm (β-(E) product) for 4-ethynylanisole (Fig S35). For
(
-1
1
-ethynyl-4-fluorobenzene, low yield (6%) and TOF (20 h ) was observed, while no product was
detected for 4-ethynylanisole (Fig S36). These results suggest that the presence of
electron-withdrawing substituent groups of CH O and F inhibits the catalytic efficiency. Therefore
3
the microfluidic reactor efficiently catalyzes the hydrosilylation reaction between triethylsilane
and phenylacetylene and its derivatives with electron-donating groups.
Table 2. Hydrosilylation of alkynes with triethylsilane.
R1
R1
R2
R2
Cat.
H
R1
R2
SiEt3
HSiEt3
SiEt3
H
α
β-(E)
Pt content
Yield TOF Isomeric ratio
Entry Alkyne
Cat.
Time/h
4
/mmol
/%c
/h-1
α:β-(E)c
1a
1
Pt/ImIP-2BrB 6×10-3
R = H,
66
28
40:60
2
R = H
2b
3a
C-Pt/ImIP-2BrB 5×10-4
Pt/ImIP-2BrB 6×10-3
4
6
79
45
395
13
56:44
27:73
1
R = H,
2
4b
5a
R = CH
3
3
C-Pt/ImIP-2BrB 5×10-4
Pt/ImIP-2BrB 6×10-3
6
6
65
39
217
11
29:71
37:63
1
R = CH
,
6b
2
C-Pt/ImIP-2BrB 5×10-4
6
50
167
50:50
R = H
7a
8b
9a
1
Pt/ImIP-2BrB 6×10-3
C-Pt/ImIP-2BrB 5×10-4
Pt/ImIP-2BrB 6×10-3
10
6
10
6
1.7
20
30:70
28:72
0:100
R = F,
2
R = H
1
24
1
0.03
R = CH
3
O,
0b
2
C-Pt/ImIP-2BrB 5×10-4
1
R = H
24
-
-
-
a
Batch reaction conditions: Triethylsilane (1.0 mmol), alkyne (1.0 mmol) and 10 mg
o
b
Pt/ImIP-2BrB (0.6 mol% Pt) in toluene (5 mL) at 80 C. Microfluidic reaction conditions:
Triethylsilane (1.0 mmol), alkyne (1.0 mmol) in toluene (5 mL) using the capillary reactor (ID =
-4
c
0
.53 mm, L = 2000 mm) coated by Pt/ImIP-2BrB (5×10 mmol Pt). Yield and isomeric ratio
1
were determined by H NMR using 1,4-dioxane as the standard.
The microfluidic reaction system could be reused as shown in the hydrosilylation of

phenylacetylene and triethylsilane (Fig. 5). The catalytic activity of C-Pt/ImIP-2BrB maintained
for at least 5 recycling runs with around 79-72 yields and α:β-(E) isomeric ratio 55:45 (TOF
-1
3
95-360 h ), indicating good recyclability for the reactor under heating conditions. In comparison
with other Pt-based catalyst systems [17-19, 25], the present system is easy to be recycled with
controllable reaction conditions, and it may be potentially applied in automated control field.
Yield
TOF
100
400
350
300
250
200
150
100
50
0
80
60
40
20
0
1
2
3
4
5
Cycle
Fig. 5. Histogram of the recyclability test of C-ImIP-2BrB for hydrosilylation between
triethylsilane and phenylacetylene. Reaction conditions: triethylsilane (1.0 mmol) and
o
phenylacetylene (1.0 mmol) in toluene (5 mL) at 80 C.
4. Conclusion
In summary, a novel strategy has been developed to fabricate a catalytic microfluidic reactor
via coating Pt/ImIP-2BrB along the inner surface of microfluidic capillary. The inner surface of
the fused-silica capillary was coated with dangling bromo groups as anchors for the ImIP-2BrB
and subsequent in situ growth of ImIP-2BrB along the surface was performed. The ImIP-2BrB
layer is prepared from nucleophilic substitution reactions between TIM and 2BrB, and employed
to support Pt NPs. Then the coated capillary is further assembled into an open-tubular microfluidic
reactor and the thickness of the Pt/ImIP-2BrB in the capillary was 31.7±0.7 μm and the Pt NPs
-4
-1
was 1.8±0.2 nm and 2.5×10 mmol m . The Pt/ImIP-2BrB microfluidic reactor shows various
catalytic applications as shown in either the nitroreduction or the hydrosilylation reaction. The
microfluidic reactor shows significantly higher catalytic efficiency in terms of TOFs (about 2-10
folds) than the corresponding catalyst under batch conditions. The significantly enhanced TOFs

suggest that capillary confinement plays a crucial role in increasing the efficiency of catalytic
active sites and reducing the amount of noble metal catalysts. It is also noticed that the selectivity
is improved in some reactions under microfluidic conditions. Additionally the microfluidic reactor
exhibits good recyclability for multiple uses without significant activity decrease for the reduction
of nitroarene and the hydrosilylation reaction. These results demonstrate the significance of
improving the current catalytic activity of supported noble metal catalysts by combination with
microfluidic technology and porous materials.
Acknowledgements
We gratefully acknowledge the NSFC (51573216) for financial support.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.org/xxxxxx.

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