RETRACTED ARTICLE: A Recycling-Free Nanocatalyst System: The Stabilization of in Situ-Reduced Noble Metal Nanoparticles on Silicone Nanofilaments via a Mussel-Inspired Approach

Article abstract of DOI:10.1021/acscatal.6b03185

The recovery and reuse of costly nanocatalysts is an essential operation in modern nanocatalysis, and improvements in catalyst reusability can contribute significantly to the economic viability and sustainable development of nanocatalysis. Herein, starting with the application of a silicone nanofilament (SNF) coating on a target substrate, a mussel-inspired approach in the form of polydopamine (PDA) deposition on the SNF surface was used to form in situ-reduced Pd nanoparticles (Pd NPs) and to stabilize them on the SNFs. This PDA-mediated approach enabled a high integrity nanocatalyst system to be built on a free-standing SNF support while retaining the porosity in the original SNF architecture. The SNFs-Pd nanocomposites prepared as such were applied to the inside walls of laboratory chemical reactors and used as recycling-free nanocatalyst systems for Pd-catalyzed organic reactions without the laborious conventional catalyst recovery and redispersion processes. The SNFs-Pd catalyst system exhibited high activity and high selectivity in single and successive Heck coupling reactions; and a reusability as high as 90% was still possible in the 20th cycle. This mussel-inspired approach is highly versatile and can be applied to laboratory chemical reactors in different shapes, sizes, and configurations to scale up the nanocatalyst applications. Furthermore, the general utility of the chemistry involved allows this surface modification technique to apply to other supported noble metal (e.g., Ag, Au, and Pt) catalysts, thereby increasing the usability and the performance of nanocatalyst systems.

Full text of DOI:10.1021/acscatal.6b03185

Subscriber access provided by University of Newcastle, Australia
Article
A Recycling-Free Nanocatalyst System: The Stabilization
of In-Situ Reduced Noble Metal Nanoparticles on
Silicone Nanofilaments via a Mussel-Inspired Approach
Xiang Fei, Wangqing Kong, Xin Chen, Xuejiao Jiang, Zhengzhong Shao, and Jim Yang Lee
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b03185 • Publication Date (Web): 17 Feb 2017
Downloaded from http://pubs.acs.org on February 18, 2017
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street
N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 18
ACS Catalysis
1
2
3
4
5
6
7
8
9
A Recycling-Free Nanocatalyst System: The Stabilization of In-Situ
Reduced Noble Metal Nanoparticles on Silicone Nanofilaments via a
Mussel-Inspired Approach
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Xiang Fei,†,§,* Wangqing Kong,‡ Xin Chen,# Xuejiao Jiang,# Zhengzhong Shao,# and
Jim Yang Lee§
† Department of Chemistry, University of Zurich, Winterthurerstrasse 190, CHꢀ8057 Zurich,
Switzerland
‡ Laboratory of Synthesis and Natural Products, Institute of Chemical Sciences and Engineering, Ecole
Polytechnique Fédérale de Lausanne, EPFLꢀSBꢀISICꢀLSPN, BCH5304, CHꢀ1015 Lausanne,
Switzerland
# State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science
and Laboratory of Advanced Materials, Fudan University, Shanghai, 200433, P. R. China
§
Department of Chemical and Biomolecular Engineering, National University of Singapore, 10
Kent Ridge Crescent, Singapore 119260, Republic of Singapore
ABSTRACT: The recovery and reuse of costly nanocatalysts is an essential operation
in modern nanocatalysis, and improvements in catalyst reusability can contribute
significantly to the economic viability and sustainable development of nanocatalysis.
Herein, starting with the application of a silicone nanofilament (SNF) coating on a
target substrate, a musselꢀinspired approach in the form of polydopamine (PDA)
deposition on the SNF surface was used to form in-situ reduced Pd nanoparticles (Pd
NPs) and to stabilize them on the SNFs. This PDA mediated approach enabled a high
integrity nanocatalyst system to be built on a freeꢀstanding SNF support while
retaining the porosity in the original SNF architecture. The SNFsꢀPd nanocomposites
prepared as such were applied to the inside walls of laboratory chemical reactors and
used as recyclingꢀfree nanocatalyst systems for Pdꢀcatalyzed organic reactions
without the laborious conventional catalyst recovery and redispersion processes. The
SNFsꢀPd catalyst system exhibited high activity and high selectivity in single and
successive Heck coupling reactions; and a reusability as high as 90% was still
possible in the 20th cycle. This musselꢀinspired approach is highly versatile, and can
be applied to laboratory chemical reactors in different shapes, sizes and configurations
to scale up the nanocatalyst applications. Furthermore, the general utility of the
1
ACS Paragon Plus Environment

ACS Catalysis
Page 2 of 18
1
2
3
4
5
6
7
8
chemistry involved allows this surface modification technique to apply to other
supported noble metal (e.g. Ag, Au, and Pt) catalysts; thereby increasing the usability
and the performance of nanocatalyst systems.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
KEYWORDS: recyclingꢀfree, nobleꢀmetal nanocatalyst, polydopamine, reusability,
silicone nanofilament, Heck reaction
INTRODUCTION
The high activity and selectivity of noble metal nanoparticles (NMNs) for catalyzing
chemical reactions has made them the workhorse of modern nanocatalysis.1ꢀ3 The
current emphasis on sustainable chemistry has also increased the interest in the
recovery and reuse of the costly NMNs after catalytic reactions.4ꢀ8 Catalyst recycling
is made easier by immobilizing the nanocatalyst on a support material (e.g. silica,
carbon, polymer and metalꢀorganic framework (MOF)) which can be separated from
the reaction mixture by physical means (e.g. centrifugation and filtration).9ꢀ12 For
example, the use of an external magnetic field to facilitate the separation of catalysts
supported on superparamagnetic oxides (e.g. Fe, Co, Ni, FePt, Fe3O4, ɤꢀFe2O3).13ꢀ17
Often, a laborious and wasteful workꢀup (washing and redispersion) is required after
the separation to restore the catalyst to its initial form; during which some catalyst
may be lost. The eluted catalyst may also introduce unknown environmental, and
safety and health issues. All of these can undermine the economic and environmental
viability of nanocatalysts in largeꢀscale operations.4,18ꢀ20
Intuitively, for the sustainable use of catalysts, an ideal supported nanocatalyst
system should be immobilized on the inside walls of the catalytic reactor and hence
can be reused without the aforementioned onerous recovery and redispersion
processes.21 Unfortunately, such a strategy to the development of a recyclingꢀfree
nanocatalyst system, to the best of our knowledge, has yet to be developed and
demonstrated.
Among the available support materials, silicone nanofilaments (SNFs) appear to
hold the most promise because they can be applied as a chemically and thermally
stable coating, with sufficient porosity to support good reactant accessibility.22,23
2
ACS Paragon Plus Environment

Page 3 of 18
ACS Catalysis
1
2
3
4
5
6
7
8
9
Specifically, SNFs several µm in lengths and ~50 nm in diameters can be grown as a
microꢀscale freeꢀstanding “carpet” on a variety of surfaces (e.g. glass, aluminum,
polyethylene) by a convenient gas or liquid phase method,24ꢀ31 thereby allowing their
use as a nanocatalyst support on the chemical reactor interior. On the other hand, the
direct synthesis of nanomaterials on SNFs as a supported nanocatalyst system has
proved to be extremely challenging, due to the complexity in their structural
configurations and the inert nature of polysiloxanes. Up to now, only a limited
number of nanomaterials (TiO2, Ni(OH)2 and Ag) can be supported on SNFs by
highly systemꢀspecific procedures.32ꢀ34 For example, TiO2 or Ni(OH)2 nanomaterials
can only be deposited on SNFs by using chemical additives to compatilize the surface
chemistries of silicone and metal precursors.32,33 In other instances a chemical linker
(e.g. (3ꢀmercaptopropyl)trimethoxysilane) is required to attach NaBH4ꢀreduced Ag
nanoparticles to the SNF surface.34 Hence, it is highly desirable to develop simple and
generalizable methods which can be applied to noble and nonꢀnoble metal
nanoparticles as well as other functional nanomaterials on a SNF support with good
control of nanoparticle size, dispersion and loading.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
A biomimetic surface functionalization approach may be used to address the
challenge in the preparation of SNFsꢀsupported systems. Inspired by the adhesive
proteins in mussels (3,4ꢀdihydroxyꢀphenylalanine, DOPA),35ꢀ37 polydopamine (PDA)
with multiple functional moieties analogous to those in DOPA, is recently gaining
attention as a novel surface modification material which can be formed on virtually all
types of inorganic and organic surfaces with controllable film thickness and high
durability.38,39 The catechol, amine, and imine moieties in PDA are also useful as the
functional platforms to reduce transition metal ions, and to immobilize the ensuing
metal nanoparticles to form a variety of hybrid nanomaterials.38ꢀ40
Herein, a musselꢀinspired surface functionalization with PDA was used to form
metallic Pd NPs in-situ on porous SNFs which preserves the high specific surface area
and intrinsic catalytic activity of the Pd NPs. The method also leveraged on PDA’s
strong metal binding ability to reduce the loss of catalytic metal by leaching.38 The
SNFsꢀPd nanocomposite prepared as such could be easily immobilized on the
3
ACS Paragon Plus Environment

ACS Catalysis
Page 4 of 18
1
2
3
4
5
6
7
8
9
chemical reactor inside walls to provide a recyclingꢀfree nanocatalyst system which
can be reused without the routine recovery and redispersion processes. A significant
improvement of reusability was achieved relative to the conventional supported
nanocatalysts. High reactivity, selectivity, and scalability were also shown in common
Pdꢀcatalyzed organic reactions. The general utility of this method was also
demonstrated in other noble metal (Ag, Au and Pt) nanocatalysts by simply changing
the metal precursors.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
RESULTS AND DISCUSSION
The procedure began with the deposition of SNFs on the target substrates (glass slides
and laboratory flasks in our case) via a liquid phase method by using trifunctional
silane CH3SiCl3 as the precursor (Figure S1). The deposition conditions were
optimized to produce a porous SNF coating with high surface area suitable to be used
as a catalyst support (Figure S2 and S3). Scanning electron microscope (SEM)
(Figure 1a,b) and transmission electron microscope (TEM) images (Figure 1c) show
good uniformity of the SNF coating. The loose, fractalꢀlike network of the optimized
~3.5 ꢁm thick SNF coating (Figure 1d) was formed by the extensive entanglements of
1D nanofilaments ~50 nm in diameters. A PDA coating was then applied to the SNF
surface via dopamine selfꢀpolymerization to provide the functionality for in-situ NMN
formation and stabilization. The following describes the three major steps in the
preparation of a typical SNFsꢀPd nanocomposite (Figure 1e): (i) the O2ꢀplasma
“activation” of the SNF coating to form an abundance of hydroxyl groups on the SNF
surface, (ii) immersion of the SNF coating in an aqueous dopamine solution, buffered
to a pH typical of the marine environment (2 mg of dopamine per milliliter of 10 mM
tris, pH=8.5) for 5 h to deposit a uniform PDA layer on the SNFs through the
spontaneous oxidative selfꢀpolymerization of dopamine (Figure S4),38,39 and (iii)
immersion of the coated SNFs in an aqueous potassium tetrachloropalladate(II)
(K2PdCl4) solution at room temperature (see Experimental Section in the Supporting
Information). The adsorbed Pd precursor was reduced to Pd nanoparticles (Pd NPs)
4
ACS Paragon Plus Environment

Page 5 of 18
ACS Catalysis
1
2
3
4
by the catechol moieties in the PDA coating, which also bound the PdNPs. The in-situ
5
6
formed Pd NPs were therefore simultaneously stabilized by the SNF coating.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. SEM images of the SNF coating (a, b) surface and (c) crossꢀsectional views; (d) TEM
image of the 1D SNFs; (e) Schematic illustration of the steps in the preparation of SNFsꢀPd
nanocomposite by the musselꢀinspired approach.
In this procedure, the PDA layer has sufficient reducing power to eliminate the
need for an exogenous reducing agent for K2PdCl4. In addition, the strong metal
binding property of the PDA layer also renders an additional chemical stabilizer
redundant. The benefits of in-situ reduction and stabilization are obvious; and are in
compliance with the green chemistry principles of waste minimization and the use of
safer chemicals. The stability of the SNFsꢀPd nanocatalyst coating also contributes to
an overall lower lifeꢀcycle cost.
Figure 2aꢀc show the typical TEM images of the SNFsꢀPd nanocomposite
fabricated as such. The surface of the 1D SNFs was found to be populated with
nanoparticles ~2 nm in diameters. Highꢀresolution TEM (HRTEM) images and the
5
ACS Paragon Plus Environment

ACS Catalysis
Page 6 of 18
1
2
3
4
5
6
7
8
9
corresponding selected area electron diffraction (SAED) pattern indicate that the
small Pd NPs are crystalline; with an interꢀplanar distance of ~0.23 nm in the lattice
fringes which correspond well with the diffraction from the Pd (111) planes (Figure
2d). Furthermore, highꢀangle annular darkꢀfield scanning TEM (HAADFꢀSTEM) and
energyꢀdispersive Xꢀray (EDX) spectroscopy (Figure 2e,f) also indicated the
immobilization of Pd NPs on the SNFs. The existence of the PDA layer and Pd was
independently confirmed by Xꢀray photoelectron spectroscopy (XPS) (Figure 2gꢀi)
where N 1s peak (Figure 2h and Figure S5) and metallic Pd peaks (3d5/2 = 335.3 eV;
3d3/2 = 340.5 eV) (Figure 2i) were found only after the treatment of SNFs with PDA
and Pd precursor salt.41,42
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. Characterization of SNFsꢀPd nanocomposite. (aꢀc) TEM images and (d) HRTEM image
of Pd NPs with the inset showing their SAED pattern. (e) STEM image and (f) corresponding
EDX spectra. (g) XPS survey spectrum and (h, i) highꢀresolution N 1s and Pd 3d spectra of the
SNFsꢀPd nanocomposite.
6
ACS Paragon Plus Environment

Page 7 of 18
ACS Catalysis
1
2
3
4
5
6
7
8
9
The preservation of the SNFs porosity is crucial to their use as a catalyst support.
The PDA coating is known to be nanoscale tunable by simply varying the immersion
time,38 and is therefore useful for preserving the porosity in its 3D nanostructure. In
order to confirm the uniform surface modification of SNFs with PDA, and also to
examine the structural features of the SNFsꢀPd nanocomposite, tomographic focused
ion beam scanning electron microscopy (FIBꢀSEM) was used to generate the images
in Figure 3.43,44 Figure 3a shows an overview SEM image of a SNFsꢀPd
nanocomposite trenchꢀcarved by FIB. The porous nanostructure and the architecture
of the parent SNFs were not altered by the PDA surface modification and the
incorporation of Pd NPs, and the thickness (~3.5 ꢁm, Figure 3aꢀe, and Figure S6) was
the same as that of the pristine SNFs (Figure 1d). The porous nanostructure remains
visible even in the denser bottom region in contact with the substrate (Figure 3e). It is
noteworthy to mention that Pd NPs could not be revealed by FIBꢀSEM analysis due to
their small size. The internal fine structure was further investigated via the 3D
reconstruction of the SNFsꢀPd tomograms collected over an imaged sample volume of
3.3 × 3.5× 3.7 ꢁm (Figure 3f, Figure S7aꢀd, movies S1 to S3 and Supporting
Information). The SNFsꢀPd component of the 3D nanostructure occupied an average
volume fraction of ~15%, i.e. a porosity of ~85% (Figure S7eꢀg). The 1D architecture
of the SNFs was found to be very well preserved in the composite (Figure 3g,h). The
3D reconstruction exercise shows very little changes to the porosity originally created
by the highly entangled 1D SNFs in the SNFsꢀPd nanocomposite (Figure 3i,j and
Movie S4 in Supporting Information). This is clearly a desirable feature which
increases the availability and accessibility of the catalytically active sites.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
7
ACS Paragon Plus Environment

ACS Catalysis
Page 8 of 18
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. Tomographic FIB–SEM analysis of SNFsꢀPd nanocomposite. (a) A SEM overview of
the sample trenchꢀcarved by spatially directed FIB milling. (b) Expanded crossꢀsectional views.
The frames in (b) show the regions subjected to further analysis: (c) the top region (red), (d) the
middle region (green), and (e) the bottom region (yellow). (f) Orthogonal crossꢀsections used for
the 3D reconstruction of the FIB–SEM tomograms of the SNFs–Pd nanocomposite. (g, h) 3D
reconstruction for one single 1D SNFꢀPd nanofilament. (i, j) The rendered surface view of the 3D
reconstructed SNFsꢀPd nanocomposite.
The simplicity of fabrication and immobilization of SNFsꢀsupported
nanocomposites is valuable to the development of a recyclingꢀfree nanocatalyst
system. The unique application value of the latter was demonstrated in a 10 mL
roundꢀbottom glass flask laboratory chemical reactor. The SNFsꢀPd nanocomposite
was applied to the reactor interior walls by the previously described procedures to a
Pd loading of 0.22 ± 0.01 mg with good reproducibility (as determined by inductively
coupled plasma atomic emission spectroscopy, ICPꢀAES). With the careful control of
the experimental conditions such as the thickness of the SNF coating and PDA layer;
and the Pd precursor concentration, the catalyst loading would only vary with the size
of the reactor. The reactor fabricated as such was named as the SNFsꢀPd device. The
Heck reaction, i.e. the Pdꢀcatalyzed coupling of aryl halides and alkene was used as
the model reaction to evaluate the catalytic performance of Pd NPs in this device
(Figure 4a and Figure S8).41,45ꢀ49 Specifically, 1.0 mmol iodobenzene (1a), tertꢀbutyl
acrylate (2a) (1.2 equiv.), trimethylamine (Et3N) (2 equiv.), tetrabutylammonium
acetate (TBAA) (0.2 equiv.) and 3 mL nꢀbutanol were added to the SNFsꢀPd device at
100oC. The coupling reaction was almost 100% completed in 60 min with a 0.2 mol%
8
ACS Paragon Plus Environment

Page 9 of 18
ACS Catalysis
1
2
3
4
5
6
7
8
9
Pd loading (relative to iodobenzene) (Figure 4b and Figure S8c), whereas a
commercial Pd/C nanocatalyst with the same amount of Pd could only achieve ~80%
conversion in 60 min. The SNFsꢀPd device also showed very good cycle stability in
terms of conversion kinetics: the near complete conversion in 60 min could be
sustained for the first five cycles, whereas the activity of the Pd/C benchmark catalyst
showed a significant 35% decrease in the 2nd cycle (Figure S9). For the evaluation of
the reusability of the SNFsꢀPd device, the reaction time was extended to 12 h to
ensure complete conversion. The reactor contents were then emptied out and analyzed
to determine the product yields, while the device was reused after simple washings
with ethyl acetate (EtOAc) and ethanol (EtOH). The reaction conditions were kept
identical in all batches. Figure 4c shows the good cycle stability and reusability of the
SNFsꢀPd device ꢀ the catalysis of the coupling reactions proceeded with high and
stable activity to give tertꢀbutyl cinnamate (3aa) in 98%, 97% and 96% yields after 5,
10 and 15 reuses respectively. The excellent yield of the 3aa product (90%) even for
the 20th reuse (Figure 4c) has significantly surpassed the performance of supported
nanocatalysts in a variety of chemical reactions reported in the literature (see Table S1
in Supporting Information). We have also characterized our catalytic device after
repeated uses in organic reactions. SEM images showed no changes in the
microstructure after the 20th reuse in the Heck reaction (Figure S10), thereby
demonstrating the good structural stability and reusability of the SNFsꢀbased devices
for the organic reactions in this study. The extent of Pd leaching during the cycling
reactions was also measured by ICPꢀAES. No Pd loss was detected from the 2nd, 5th
and 10th reuse, and only a < 2% Pd loss was registered after 20 reuses. The
leachability of Pd in the SNFsꢀPd device was therefore very low, which can be
credited to the strong PDA binding of the Pd NPs.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
9
ACS Paragon Plus Environment

ACS Catalysis
Page 10 of 18
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. The cycling stability of the SNFsꢀPd device in catalysis. (a) The Heck coupling reaction
of iodobenzene (1a) with tertꢀbutyl acrylate (2a) in a 10 mL SNFsꢀPd device (with ~ 0.2 mol% of
Pd based on iodobenzene). (b) The kinetics of the Heck reaction in the SNFsꢀPd device for the
initial few cycles as monitored by GCꢀMS analysis. (c) Reusability test of the SNFsꢀPd device.
Table 1 shows the Heckꢀcoupling reactions using homologues with different
substitution patterns (electronꢀdeficient and electronꢀrich substituted aryl halides and
alkenes) which occurred in good to excellent yields (i.e. in the range of 80% to 99%)
in SNFsꢀPd devices, as a test of the versatility of these devices (Table 1, entries 1–9).
10
ACS Paragon Plus Environment

Page 11 of 18
ACS Catalysis
1
2
3
4
Table 1: Heck coupling reactions of aryl halides with olefins in the SNFsꢀPd devices
5
6
7
8
(with 0.2 mol% Pd based on the aryl halide used)
X
R'
SNFsꢀPd (0.2 mol%)
R
+
R
9
R'
Conditions
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
3
2
1
entry
yield of 3 (%)
2
X
I
R
1
2
3
4
5
6
7
8
9
R = pꢀF (1b)
R = pꢀCN (1c)
R = pꢀNO2 (1d)
R = pꢀCF3 (1e)
R = pꢀOMe (1f)
R = H (1a)
2a (R’ = COOBu-t)
3ba (99)[a]
3ca (95) [a]
3da (97) [a]
3ea (98) [a]
3fa (90) [a]
3ab (80) [a]
3ga (85) [b]
3ha (90) [b]
3ia (80) [b]
I
2a
I
2a
I
2a
I
2a
I
2b (R’ = Ph)
Br
Br
Br
R = H (1g)
2a
2a
2a
R = pꢀCHO (1h)
R = pꢀOMe (1i)
[a] Conditions A: 1 (1.0 mmol), 2 (1.2 equiv.), Et3N (2.0 equiv.), TBAA (20 mol %), nꢀBuOH (3.0
mL), 100 oC, 12 h; [b] Conditions B: 1 (1.0 mmol), 2 (2 equiv.), NaOAc (2.0 equiv.), TBAB (30
mol %), DMF (3.0 mL), 140 oC, 12 h.
Encouraged by these results, a preliminary study on catalytic selectivity was
carried out by performing the sequential coupling of 1ꢀbromoꢀ2ꢀiodobenzene (1j) with
tertꢀbutyl acrylate (2a) in the same SNFsꢀPd device. oꢀBromocinnamate 3ja was first
formed in 90% yield by the selective coupling of iodobenzene with one molecule of
2a under condition A. Subsequently, in the same device but with the condition
changed to B, a further coupling reaction occurred selectively to form diacrylates 4ja
in 75% yield (Figure 5). Besides the convenience of a recyclingꢀfree catalyst system,
the ability to execute specific catalytic reactions selectively and sequentially in the
same device is highly valuable to the chemistry industry to facilitate the production of
more complex and diverse products.
11
ACS Paragon Plus Environment

ACS Catalysis
Page 12 of 18
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5. Sequential and selective catalysis of the coupling of 1ꢀbromoꢀ2ꢀiodobenzene (1j) with
tertꢀbutyl acrylate (2a) in the same SNFsꢀPd device.
In order to probe the catalytic activity of the catalytic device for the
heterogeneous catalysis of the Heck reaction, a 100 mL SNFsꢀPd device with a much
lower Pd loading (5.1 µg according to ICPꢀAES) was fabricated (Figure S11) by using
a larger flask (i.e. 100 mL flask) and a significantly reduced Pd precursor
concentration (1 µM), while keeping all other preparation conditions the same (see
Experimental Section in the Supporting Information). The coupling reactions 1a and
2a were performed in this SNFsꢀPd device at the 10 mmol scale (with 0.48 mmol %
Pd relative to 1a) using TBAA, Et3N at 100 ºC for 24 h. The desired product 3aa was
obtained at the gramꢀlevel (2.0 g) in 98% yield (Figure S11). This shows that the
catalytic activity of our SNFsꢀPd device can reach a 4.8 mol ppm Pd with the turnover
number (TON) and turnover frequency (TOF) values of 204500 and 8520 hꢀ1
respectively, which is comparable to most of the heterogeneous Pd catalysts used for
the Heck reactions.49 At the same time, the ability to scale the coupling reactions for
gramꢀlevel production was unambiguously demonstrated. Hence we are hopeful that
this catalyst immobilization technique can be useful to pilotꢀscale or industrial reactor
operations, although this has to be demonstrated.
The versatility of the SNFsꢀPd nanocatalyst system was also tested in other
important organic transformations. The hydrogenation of stilbene to
1,2ꢀdiphenylethane in a SNFsꢀPd device equipped with a H2 balloon could occur to
12
ACS Paragon Plus Environment

Page 13 of 18
ACS Catalysis
1
2
3
4
5
6
7
8
9
99% yield without changes in the catalytic activity and product yield for 10 cycles
(Figure 6a). The reduction of 3ꢀnitroꢀpꢀcresol to 4ꢀaminoꢀmꢀcresol could also occur
under the same condition to 98% yield (Figure 6b). Another example is the synthesis
of amides from aryl halides with isocyanides,50 where Nꢀtertꢀbutylbenzamide could be
produced in 85% yield (Figure 6c).51,52 A three component coupling of aryl iodide,
2ꢀamniophenol and tertꢀbutylꢀisocyanide could also be carried out in the SNFsꢀPd
device to form 2ꢀphenylꢀbenzoxazole in 86% yield (Figure 6d).53 These experimental
results indicate that the SNFsꢀPd nanocatalytic system can endure different reaction
conditions (different reagents, temperature and pH) without the loss of its high
catalytic activity, and it is generally applicable to a large number of chemical
reactions.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
99% (1 th)
a
97% (2 nd)
99% (3 rd)
98% (5 th)
97% (10 th)
SNFsꢀPd (0.2 mol %)
Ph
Ph
H2 (ballon)
EtOH, 70oC, 12 h
NH2
NO2
b
SNFsꢀPd (0.2 mol %)
Me
Me
H2 (ballon)
EtOH, 70oC,12 h
HO
HO
(98%)
O
I
c
SNFsꢀPd (0.2 mol %)
Cs2CO3 (2 equiv.)
N
H
+ CN
DMSO/H2O
80oC, 12 h
(85%)
d
I
SNFsꢀPd (0.2 mol %)
Cs2CO3 (2 equiv.)
toluene, 100 oC,12 h
OH
O
N
+
+ CN
NH2
(86%)
Figure 6. Further catalytic applications of the SNFsꢀPd system: (a) hydrogenation of alkene; (b)
reduction of nitrobenzene; (c) amidation of phenyl iodide with tertꢀbutylꢀisocyanide; (d) the
threeꢀcomponent coupling of phenyl iodide, tertꢀbutylꢀisocyanide, and 2ꢀaminophenol.
Benefiting from high porosity, the SNFsꢀPd system provides easily accessible,
Pdꢀcatalytic active sites, leading to its high catalytic activity. The impressive cycling
stability of this new nanocatalyst system can be attributed to a number of factors: (1)
the use of porous SNFs with exceptional thermal and chemical stability as the
13
ACS Paragon Plus Environment

ACS Catalysis
Page 14 of 18
1
2
3
4
5
6
7
8
9
foundation of a highꢀintegrity nanocatalyst system; (2) the use of a uniform PDA
coating with good metalꢀbinding ability to stabilize the Pd NPs against the leaching of
Pd into the reaction mixture; (3) the ability to apply this novel nanocatalyst system as
a reactor wall coating, thereby allowing the SNFsꢀPd nanocatalyst system to be easily
reused with practically no loss, circumventing the onerous and wasteful catalyst
recovery and redispersion processes which are standard in the reuse of a conventional
nanocatalyst systems. In this regards this is perhaps the first successful demonstration
of a recyclingꢀfree nanocatalyst system.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In addition, this musselꢀinspired surface functionalization technique for
producing SNFsꢀsupported nanocomposites can also be extended to other noble
metals (Ag, Au and Pt) by simply changing the noble metal precursors (AgNO3,
HAuCl4•4H2O and H2PtCl6•6H2O) (Figures S12ꢀS14). The resulting SNFsꢀsupported
NMN nanocomposites could also be applied to common types of reactors for
organocatalysis (e.g. glass tubes, flasks and Schlenk tubes) with different shapes and
sizes and configurations (Figure S15). It is therefore a viable technology that can be
used to advance applications which are based on heterogeneous catalytic reactions.
CONCLUSION
In summary, starting with a SNF substrate as the nanocatalyst support, we
incorporated catalytically active Pd NPs via a musselꢀinspired approach which
provides the facility for the in-situ reduction of the noble metal precursor and the
stabilization of the MNPs formed on SNFs. Specifically, a PDA layer was overlaid on
the SNF support after a simple surface modification of the latter with no changes in
the porosity of the SNFs. The PDA layer contains multiple moieties that could reduce
the Pd precursor and stabilize the Pd NPs against dissolution. The simplicity of these
processes enables the SNFsꢀPd nanocatalyst to be coated on the interior walls of a
chemical reactor; and to serve as a recyclingꢀfree nanocatalyst system which can be
reused without the laborious and wasteful recovery and redispersion operations
common to the reuse of conventional nanocatalyst systems. The SNFsꢀPd
nanocatalyst system showed excellent catalytic performance (activity, selectivity and
14
ACS Paragon Plus Environment

Page 15 of 18
ACS Catalysis
1
2
3
4
5
6
7
8
9
scalability) with good cycling stability in Pdꢀcatalyzed chemical reactions, including
the Heck reaction, alkene hydrogenation, nitrobenzene reduction, and cascading
reactions involving isocyanide. The versatility of the SNFsꢀbased nanocatalyst system
was demonstrated by using chemical reactors of different shapes, sizes and
configurations; and other noble metals besides Pd; and may offer new and more
effective alternatives for implementing nanocatalytic systems.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ASSOCIATED CONTENT
Supporting Information.
Details of experimental procedures, materials and methods, Figures S1ꢀS15, Table S1,
NMR spectra and Movies S1ꢀS4. These materials are available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author: chefeix@nus.edu.sg
ACKNOWLEDGMENTS
This work is supported by Swiss National Science Foundation, the
AlfredꢀWernerꢀLegat, and the University of Zurich. The authors thank A. Kaech and
M. Kirschmann (University of Zurich) for the support in FIBꢀSEM analysis from the
Center for Microscopy and Image Analysis. A. Sologubenko (ETH Zurich) is
gratefully acknowledged for acquiring HRTEM data in ScopeM. The authors further
thank Prof. S. Seeger (University of Zurich) for his valuable discussion.
REFERENCES:
1. Lewis, L. N. Chem. Rev. 1993, 93, 2693ꢀ2730.
2. Roucoux, A.; Schulz, J.; Patin, H. Chem. Rev. 2002, 102, 3757ꢀ3778.
3. Turner, M.; Golovko, V. B.; Vaughan, O. P.; Abdulkin, P.; BerenguerꢀMurcia, A.; Tikhov, M.
S.; Johnson, B. F.; Lambert, R. M. Nature 2008, 454, 981ꢀ983.
4. Astruc, D., Ed.; Nanoparticles and Catalysis; WileyꢀVCH: Weinheim, 2008.
5. Benaglia, M., Ed,; Recoverable and recyclable catalysts; WileyꢀVCH: Weinheim, 2009.
6. Bell, A. T. Science 2003, 299, 1688ꢀ1691.
7. Schlögl, R.; Abd Hamid, S. B. Angew. Chem., Int. Ed. 2004, 43, 1628ꢀ1637.
8. Chng, L. L.; Erathodiyil, N.; Ying, J. Y. Acc. Chem. Res. 2013, 46, 1825-1837.
9. Herzing, A. A.; Kiely, C. J.; Carley, A. F.; Landon, P.; Hutchings, G. J. Science 2008, 321,
1331ꢀ1335.
15
ACS Paragon Plus Environment

ACS Catalysis
Page 16 of 18
1
2
3
4
5
10. Joo, S. H.; Park, J. Y.; Tsung, C.ꢀK.; Yamada, Y.; Yang, P.; Somorjai, G. A. Nat. Mater.
2008, 8, 126ꢀ131.
6
7
11. Molnar, A. Chem. Rev. 2011, 111, 2251ꢀ2320.
12. Wang, G.ꢀH.; Hilgert, J.; Richter, F. H.; Wang, F.; Bongard, H.ꢀJ.; Spliethoff, B.;
Weidenthaler, C.; Schüth, F. Nat. Mater. 2014, 13, 293ꢀ300.
13. Jeong, U.; Teng, X.; Wang, Y.; Yang, H.; Xia, Y. Adv. Mater. 2007, 19, 33ꢀ60.
14. Yan, J.; Zhang, X.; Han, S.; Shioyama, H.; Xu, Q. Angew. Chem., Int. Ed. 2008, 47,
2287ꢀ2289.
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
15. Jun, Y.ꢀw.; Seo, J.ꢀw.; Cheon, J. Acc. Chem. Res. 2008, 41, 179ꢀ189.
16. Shylesh, S.; Schünemann, V.; Thiel, W. R. Angew. Chem., Int. Ed. 2010, 49, 3428ꢀ3459.
17. Polshettiwar, V.; Luque, R.; Fihri, A.; Zhu, H.; Bouhrara, M.; Basset, J.ꢀM. Chem. Rev.
2011, 111, 3036ꢀ3075.
18. Bhanage, B. M.; Arai, M. Cat. Rev. 2001, 43, 315ꢀ344.
19. Nel, A.; Xia, T.; Mädler, L.; Li, N. Science 2006, 311, 622ꢀ627.
20. Lu, A.ꢀH.; Salabas, E. L.; Schüth, F. Angew. Chem., Int. Ed. 2007, 46, 1222ꢀ1244.
21. Somorjai, G. A.; Li, Y. Introduction to Surface Chemistry and Catalysis, 2nd ed.; Wiley:
New York, 2010.
22. Artus, G. R.; Seeger, S. Adv. Colloid Interface Sci. 2014, 209, 144ꢀ162.
23. Chu, Z.; Seeger, S. Chem. Soc. Rev. 2014, 43, 2784ꢀ2798.
24. Artus, G. R.; Jung, S.; Zimmermann, J.; Gautschi, H. P.; Marquardt, K.; Seeger, S. Adv.
Mater. 2006, 18, 2758ꢀ2762.
25. Gao, L.; McCarthy, T. J. J. Am. Chem. Soc. 2006, 128, 9052ꢀ9053.
26. Zimmermann, J.; Reifler, F. A.; Fortunato, G.; Gerhardt, L. C.; Seeger, S. Adv. Funct.
Mater. 2008, 18, 3662ꢀ3669.
27. Zhang, J.; Seeger, S. Angew. Chem., Int. Ed. 2011, 50, 6652ꢀ6656.
28. Zhang, J.; Seeger, S. Adv. Funct. Mater. 2011, 21, 4699ꢀ4704.
29. Zhang, J.; Wang, A.; Seeger, S. Adv. Funct. Mater. 2014, 24, 1074ꢀ1080.
30. Zhang, J.; Wang, A,; Seeger, S. Polym. Chem. 2014, 5, 1132ꢀ1139.
31. Chu, Z.; Seeger, S. Adv. Mater. 2015, 27, 7775ꢀ7781.
32. Meseck, G. R.; Kontic, R.; Patzke, G. R.; Seeger, S. Adv. Funct. Mater. 2012, 22,
4433ꢀ4438.
33. Meseck, G. R.; Fabbri, E.; Schmidt, T. J.; Seeger, S. Adv. Mater. Interfaces 2015, 2,
1500216.
34. Meier, M.; Suppiger, A.; Eberl, L.; Seeger, S. Small, 2016, doi: DOI:
10.1002/smll.201601072.
35. Waite, J. H.; Tanzer, M. L. Science 1981, 212, 1038ꢀ1040.
36. Harrington, M. J.; Masic, A.; HoltenꢀAndersen, N.; Waite, J. H.; Fratzl, P. Science 2010,
328, 216ꢀ220.
37. Waite, J. H.; Qin, X. Biochemistry 2001, 40, 2887ꢀ2893.
16
ACS Paragon Plus Environment

Page 17 of 18
ACS Catalysis
1
2
3
4
5
6
7
8
38. Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B. Science 2007, 318, 426ꢀ430.
39. Liu, Y.; Ai, K.; Lu, L. Chem. Rev. 2014, 114, 5057ꢀ5115.
40. Li, B.; Wu, L.; Li, L.; Seeger, S.; Zhang, J.; Wang, A. ACS Appl. Mater. Interfaces 2014, 6,
11581ꢀ11588.
41. Yamada, Y.; Yuyama, Y.; Sato, T.; Fujikawa, S.; Uozumi, Y. Angew. Chem., Int. Ed. 2014,
53, 127ꢀ131.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
42. Yang, S.; Cao, C.; Sun, Y.; Huang, P.; Wei, F.; Song, W. Angew. Chem., Int. Ed. 2015, 54,
2661ꢀ2664.
43. Uchic, M. D.; Holzer, L.; Inkson, B. J.; Principe, E. L.; Munroe, P. MRS Bulletin 2007, 32,
408ꢀ416.
44. Meseck, G. R.; Käch, A.; Seeger, S. J. Phys. Chem. C 2014, 118, 24967ꢀ24975.
45. Mizoroki, T.; Mori, K.; Ozaki, A. Bull. Chem. Soc. Jpn. 1971, 44, 581ꢀ581.
46. Heck, R.; Nolley Jr, J. J. Org. Chem. 1972, 37, 2320ꢀ2322.
47 Mehnert, C. P.; Weaver, D. W.; Ying, J. Y. J. Am. Chem. Soc. 1998, 120, 12289ꢀ12296.
48. Dams, M.; Drijkoningen, L.; Pauwels, B.; Van Tendeloo, G.; De Vos, D. E.; Jacobs, P. A. J.
Catal. 2002, 209, 225ꢀ236
49. Yin, L.; Liebscher, J. Chem. Rev. 2007, 107, 133ꢀ173.
50. Humphrey, J. M.; Chamberlin, A. R. Chem. Rev. 1997, 97, 2243ꢀ2266.
51. Vlaar, T.; Ruijter, E.; Maes, B. U.; Orru, R. V. Angew. Chem., Int. Ed. 2013, 52,
7084ꢀ7097.
52. Qiu, G.; Ding, Q.; Wu, J. Chem. Soc. Rev. 2013, 42, 5257ꢀ5269.
53. Vlaar, T.; Cioc, R. C.; Mampuys, P.; Maes, B. U.; Orru, R. V.; Ruijter, E. Angew. Chem.,
Int. Ed. 2012, 51, 13058ꢀ13061.
17
ACS Paragon Plus Environment

ACS Catalysis
Page 18 of 18
1
2
3
4
Table of Contents Graphic
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
18
ACS Paragon Plus Environment