Palladium Separation by Pd-Catalyzed Gel Formation via Alkyne Coupling

Article abstract of DOI:10.1021/acs.chemmater.9b02031

Selective entrapment of precious metals from industrial wastes containing various metals is a most challenging branch of environmental science. Developed methods like solvent or solid-phase extraction, ion exchange, co-precipitation, membrane filtration, and adsorption rely on chelation, electrostatic attraction, or ion exchange, and these methods present limited selectivity and require post-treatment for further application. Herein, an original concept is reported involving the utilization of the superior catalytic properties of Pd selectively for efficient entrapment of Pd from other metals. Specifically, side chains of poly(vinyl alcohol) (PVA) functionalized with alkynyl groups are catalytically dimerized using Pd(II), which forms gels. The Pd(II) ions are coordinatively encapsulated into the gel networks, while the other metal ions are excluded from the networks, thus allowing the separation and immobilization of Pd. The entrapped Pd(II) is also reduced to Pd(0) nanoparticles (PdNPs) forming PdNPs@alkyne-PVA aerogels that exhibit a high catalytic activity for the Suzuki-Miyaura cross-coupling reaction. PdNPs@alkyne-PVA aerogels are further carbonized to PdNPs@C networks for the efficient electrochemical hydrogen evolution reaction. This method provides an effective way not only to selectively separate Pd but also to utilize the entrapped Pd resources for multiple catalyses without further post-treatment of the entrapped Pd source.

Full text of DOI:10.1021/acs.chemmater.9b02031

Subscriber access provided by Nottingham Trent University
Article
Palladium Separation by Pd-Catalyzed Gel Formation via Alkyne Coupling
Xiaojiao Yang, Jinfan Chen, Liangsheng Hu, Jianyu Wei, Maobin Shuai,
Deshun Huang, Guozong Yue, Didier Astruc, and Pengxiang Zhao
Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.9b02031 • Publication Date (Web): 09 Aug 2019
Downloaded from pubs.acs.org on August 17, 2019
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 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 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.
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 10
Chemistry of Materials
1
2
3
4
5
6
7
8
9
Palladium Separation by Pd-Catalyzed Gel Formation via Alkyne
Coupling
10
11
12
Xiaojiao Yang,† Jinfan Chen,† Liangsheng Hu,‡ Jianyu Wei,†, § Maobin Shuai,*, † Deshun Huang, †
Guozong Yue,† Didier Astruc,*, § and Pengxiang Zhao*, †
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
† Institute of Materials, China Academy of Engineering Physics No. 9, Huafengxincun, Jiangyou City, Sichuan Province, 621908,
P.R. China
‡ Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structural Materials of Guangdong
Province, Shantou University, Guangdong, 515063, P. R. China
§ ISM, UMR CNRS Nº 5255, Univ. Bordeaux, 33405 Talence Cedex, France
ABSTRACT: Selective entrapment of precious metals from industrial wastes containing various metals is a most challenging
branch of environmental science. Developed methods like solvent or solid-phase extraction, ion exchange, co-precipitation,
membrane filtration and adsorption rely on chelation, electrostatic attraction or ion exchange, and these methods present limited
selectivity and require post-treatment for further application. Herein, an original concept is reported involving utilization of the
superior catalytic properties of Pd selectively for efficient Pd entrapment from other metals. Specifically, side chains of polyvinyl
alcohol (PVA) functionalized with alkynyl groups are catalytically dimerized using Pd(II), which forms gels. The Pd(II) ions are
coordinatively encapsulated into the gel networks, while the other metal ions are excluded from the networks, thus allowing to
separate and immobilize Pd. The entrapped Pd(II) is also reduced to Pd(0) nanoparticles (PdNPs) forming PdNPs@alkyne-PVA
aerogels that exhibit a high catalytic activity for the Suzuki-Miyaura cross-coupling reaction. PdNPs@alkyne-PVA aerogels are
further carbonized to PdNPs@C networks for efficient electrochemical hydrogen evolution reaction (HER). This method provides
an effective way not only to selectively separate Pd, but also to utilize the entrapped Pd resources for multiple catalysis without
further post-treatment of entrapped Pd source.
encapsulation of ions in porous structures such as MOFs6, 21-24
INTRODUCTION
or COFs.25 However, the recycle processes using
aforementioned methods mainly depend on the chemical and
physical properties of host materials. Consequently, these
methods are considered as “passive” methods with a relatively
low selectivity. In other words, the common disadvantage of
these strategies is the difficult selective “recognition” of each
metal ion from the others. Hence, designing a smart and
“positive” method that allows distinguishing a metal from
others in a group of metal ions using its own “unique feature”
is greatly desired. Pd is one of the most popular catalytic
metals with outstanding activities in numerous chemical
reactions.26-29 Therefore it is possible to devise a way to
separate and entrap Pd via the use of its “unique feature”,
superior catalytic activities.
Among the Pt-group metals, Pd is the most widely used in
industry due to its specific physical and chemical properties,
and in particular its high catalytic activity.1-4 This causes Pd
traces in industrial wastes to be usually higher than those in
natural minerals, making waste electric and electronic
equipment considerable secondary raw Pd sources.5 Therefore,
effective entrapment of Pd sources from industrial wastes is of
great significance to ecological and economical full utilization
of Pd.6-10 In general, the recycle of Pd sources follows two
steps: (i) dissolving Pd and other metals derived from solid
wastes in strong acid, and (ii) separation of Pd from other
metal ions in solution. There are several methods, e.g., solvent
extraction,11-13 ion-exchange,14 membrane separation15-17 and
adsorption18-20 that are available in the literature for the second
step. Basically, these methods work obeying two main
principles: (i) the preparation and functionalization of guest
materials; (ii) the “entrapping” of metal ions using the
functionalized features of host materials like chelation,
electrostatic attraction, ion exchange, or physical
Inspired by this concept, we propose a new strategy for the
separation and entrapment of Pd(II) ions from solutions
containing mixtures of various non-precious metal ions based
on the high catalytic activity of Pd for the Glaser coupling
reaction.30-32 In brief, terminal alkynes functionalized with side
chains of polyvinyl alcohol (PVA) are synthesized, and then
1
ACS Paragon Plus Environment

Chemistry of Materials
Page 2 of 10
cross-linked to bis-alkyne-PVA by fast Pd(II)-catalyzed Glaser
Pd(II)@alkyne-PVA gel is prepared via a spontaneous Pd2+-
1
2
3
4
5
6
7
8
coupling, which forms the gel. Following dimerization
catalysis, the Pd ions remain coordinated in the bis-alkynyl
environment, i.e. embedded in the network, whereas the other
metal cations that are not located in the catalytic site
environment remain free in the solution. Finally, Pd(II) ions
are selectively screened out and embedded in the gel by
immersion of the gel into ion-free water and washing away
other metal ions that are only physically absorbed. Meanwhile,
theses entrapped Pd(II) sources that are homo-dispersed in the
bis-alkynyl network were directly reduced by NaBH4 to Pd0
nanoparticles (PdNPs). Subsequently they efficiently catalyze
the Suzuki-Miyaura cross-coupling reaction33-35 and
electrochemical hydrogen evolution reaction (HER) without
further treatment.
induced gelation of Alkyne-PVA in a DMF/H2O solution at
room temperature (r.t.) (Scheme 1). The Pd(II)@alkyne-PVA
aerogel, ZZM-1, is obtained by freeze-drying of the
Pd(II)@alkyne-PVA gel. The PdNPs@alkyne-PVA aerogel,
rZZM-1, is fabricated through reduction of Pd(II)@alkyne-
PVA gel with NaBH4 and followed by freeze-drying.
Scheme 1. Preparation of Pd(II)@alkyne-PVA aerogel (ZZM-
1) and PdNPs@alkyne-PVA aerogel (rZZM-1)
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
EXPERIMENTAL SECTION
Preparation of Alkyne-Substituted PVA: Alkyne-Substituted
PVA (Alkyne-PVA) was prepared according to previous reports.36 In
brief, 400 mg PVA was dissolved in 10 mL DMF stirred at 80 oC for
2 h. After cooling to room temperature, 1.22 g (7.5 mmol) CDI was
added in one portion to the PVA solution under nitrogen atmosphere.
After the reaction mixture was stirred under nitrogen at room
temperature for another 3 h, 413 mg (7.5 mmol) propargylamine was
added. Stirring was continued at room temperature for 16 h.
Afterward 4 mL of a concentrated aqueous ammonia solution was
added, and then the mixture was stirred at room temperature for
another 1 h. The solvent was reduced to ~5 mL volume by rotary
evaporation. Finally, the alkynes substituted polymer was precipitated
from the residual DMF solution by adding to 50 mL ethanol drop by
drop. The precipitation was washed by ethanol and diethyl ester and
dried in vacuum at 70 oC to give a light yellow powder.
Preparation of Pd(II)@alkyne-PVA gels: 50 mg Alkyne-PVA
was dissolved in 0.8 mL DMF in a vial. A certain amount of
Na2PdCl4 was dispread in mixture of DMF and water (or a certain
concentration of HCl aqueous solution) (200 μL, 1:1, v/v). The
Na2PdCl4 solution was dropped into Alkyne-PVA solution and
wobbled to a homogenized mixture. The resulting solution was sealed
to form a gel under natural light and air at room temperature. The
obtained wet gel was subjected to solvent exchange with 15 mL
deionized water for 24 h. The gelation possibility of other metal ions
was investigated by using the same method as that used for the
Pd(II)@alkyne-PVA gel.
The microstructure of ZZM-1 was first investigated using
scanning electron microscopy (SEM), and the result showed
that it was an intensive network with a porous structure
(Figure 1a). The Brunauer, Emmett and Teller (BET) test
confirmed the porous feature revealing a surface area of 46 m2
g−1 (Figure S1). Further thermogravimetry analysis (TGA) data
(Figure 1b) showed that Pd was entrapped by ZZM-1 and
rZZM-1. The differences of thermogravimetry in Alkyne-PVA,
ZZM-1 and rZZM-1 after 500 oC are because of the introduct-
ion of Pd.
Preparation
of
PdNPs@alkyne-PVA
aerogels:
The
Figure 1. SEM images of ZZM-1 (a); TG curve of Alkyne-
PVA, ZZM-1 and rZZM-1 (b).
PdNPs@alkyne-PVA aerogel was in situ reduced from
Pd(II)@alkyne-PVA gel by NaBH4. In briefly, Pd(II)@alkyne-PVA
gel was soaked in 5 mL water with 10 equivalents of NaBH4. Black
Pd(0)@alkyne-PVA gel was obtained until no bubbles were generated
from the solution. The black gel washed with water (10 mL × 6), and
finally freeze-drying to obtained aerogel catalyst.
Preparation of PdNPs@CNWs: The PdNPs@alkyne-PVA
aerogel was annealed at 700 oC for 6 h in a Ar filled tube furnace with
a heating rate of 2 oC min-1 to foam PdNPs embedded carbon
networks (designated PdNPs@CNWs).
NMR analysis of Pd(II)-catalyzed N-Methyl proparylamine: N-
Methyl propargylamine (0.25 mmol) and Na2PdCl4 (0.5 mol%) were
dissolved in 400 μL d6-DMSO and 40 μL D2O. The mixture was
transferred to a NMR tube and monitored by 1H NMR spectroscopy.
Separation of Palladium: A series of solution of Pd2+ mixed with
another metal ions (3 times Pd2+ concentration) were prepared by
DMF/HCl(aq) (400 μL, 1:1, v/v) in advance. Then, the above mixture
was added into the prepared alkyne-PVA solution (50 mg in 0.8 mL
DMF). After gelation the gels were washed by water a several times
and freeze dried to Pd-entrapped aerogels.
To take insight into the mechanism and specificity of the
gelation processes, a series of experiments and theoretic
calculations have been carried out. First, various metal ions
including Pd2+, Ru3+, Rh3+, Fe3+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+,
Al3+ and Mn2+ have been introduced into the Alkyne-PVA
solution to estimate if these ions can trigger the Alkyne-PVA
polymerization. Only Pd2+ induces the gelation within 2 min to
form the Pd(II)@alkyne-PVA gel (Figure 2), whereas no
obvious changes were observed from the solutions containing
the other metal ions even for 6 months, suggesting that the
gelation processes were preferably conducted in the presence
of Pd(II). Additionally, PdCl2 that is regarded as another Pd(II)
source also shows a process of gelation comparable to that of
Na2PdCl4 (Figure S2). Based on the outstanding catalytic
performance of Pd(II), one might assume that other noble
metal ions, such as Au(III) and Pt(IV), could also display
some catalytic activities towards the Glaser coupling-induced
RESULTS AND DISCUSSION
2
ACS Paragon Plus Environment

Page 3 of 10
Chemistry of Materials
gelation. However, we found that Au(III) and Pt(IV) are not
able to induce gelation even after 72 h (Figure S3).
1
2
3
Accordingly, in our case, it appears that Pd(II) is an extremely
selective catalyst among all metals.
4
5
6
7
8
9
Figure 2. Comparison of the gelation process induced by
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
different metal ions through this strategy.
To explain this gelation processes, Density Functional Theory
(DFT) calculations (Figure 3) have been conducted taking the
Co2+, Ni2+ and Pd2+ ions as examples for research models. The
interaction between metal ions and alkyne (C≡C) forming π-
type complexes has been previously reported.37-38 The results
show that the binding energies of the metals bonded with the
neighboring ethynyl group of one Alkyne-PVA chain are
about 50 kcal/mol more positive than those of metals bonded
with two ethynyl groups in two different Alkyne-PVA chains
(Figure 3a and 3b) . This means that the above metals link
with the ethynyl groups in two different Alkyne-PVA chains
to achieve more stable structures. Meanwhile, the π-type
binding strength between two ethynyl groups in different
Alkyne-PVA chains and metal ions follows the order Ni2+
>Pd2+ > Co2+ (Figure 3a). Alkynes are slightly more strongly
coordinated with Ni2+ than with Pd2+ and Co2+, which means
that Ni2+ would induce the gelation more easily than Pd2+ and
Co2+ if coordination was responsible for the reaction. The
experiments show the opposite, however, i.e. only Pd2+
induced the gelation, (Figure 2). Hence, the gelation process
was kinetically controlled rather than simply related to the
coordination of ligands to metal ions. Nevertheless, it has been
reported that Pd(II), in the presence of Cu(I), is a good catalyst
1
Figure 4. H NMR of N-methyl propargylamine at different
reaction times (a); signal of proton 2 in methane (b); signal of
proton 3 in methyl (c); and XPS spectra of ZZM-1 (d).
for the Glaser reaction that involves the coupling of two
terminal alkynes, forming diynes.32 Thus, the gelation process
is taken into account by the Glaser crosslinking of alkynes in
PVA with the expectation that Pd(II) is also playing the role of
Cu(I) in the catalytic process. The Glaser-coupling reaction
between alkynyl-terminated side chains of ZZM-1 was
confirmed by FT-IR spectroscopy (Figure S4a). Compared to
Alkyne-PVA, the peak belonging to the stretch of C≡C
terminal alkyne at 2130 cm-1 disappears in ZZM-1. In addition,
the 13C solid-state NMR spectrum of ZZM-1 (Figure S4b)
exhibits a strong shift of the signal corresponding to the
carbon-carbon triple bond of alkyne at 73 ppm in ZZM-1. This
clearly shows the formation of a new carbon-carbon bond
upon Glaser-coupling reaction. To further confirm the Glaser-
coupling catalyzed by Pd(II) under ambient conditions, N-
methyl propargylamine, that is similar to the side chain of
Alkyne-PVA, was utilized as a test example. The dimerization
reaction of N-methyl propargylamine catalyzed by PdCl2 was
monitored by 1H NMR (Figure 4a, 4b and 4c). The intensity of
the signal of proton 1 in the terminal alkyne at 3.0 ppm
decreases as the reaction progresses. Meanwhile, the signals of
proton 2 of the methyl group at 2.24 ppm and proton 3 of the
methylene group at 3.22 ppm are slightly shifted upfield.
These results are in good agreement with previous literature39
confirming alkyne dimerization to N, N'-dimethylhexa-2,4-
diyne-1,6-diamine via Glaser coupling. Subsequently, the
Figure 3. Two Alkyne-PVA chains (a); one single Alkyne-
PVA chain (b). The binding energies of the
ligands/components to the metal ions are also listed. Colors in
the figure: orange-metal ion, red-O, blue-N, grey-C, white-H.
3
ACS Paragon Plus Environment

Chemistry of Materials
Page 4 of 10
Pd(II)-catalyzed alkyne coupling for gelation is followed by closely related to the concentration of Pd(II), as the gelation
1
2
3
4
reductive elimination (Scheme 2), since both Pd(II) (located at
337 and 342.1 eV) and Pd(0) (located at 339 and 344.2 eV)
were found in the XPS of ZZM-1 (Figure 4d). Finally, the
gelation rate of Pd(II)@alkyne PVA gel was shown to be
process was much accelerated by increasing the concentration
of Pd(II), confirming that Pd(II) catalyzed the gelation (Table
S1).
5
6
7
8
9
Scheme 2. General mechanism for the Pd(II)-catalyzed homocoupling of N-methyl-propargylamine
PdIIX2L
PdX2L2
PdIIX2L
Pd0L4
2
HN
2
HN
2
H2N
PdIIX2L2
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
Step 1
Step 6
[PdIL4]+[PdIIX3L]-
(without acid)
step 5:
Step 2
NH
-
2 [PdIL4]+O2
I
+
II
-
-
+
a
+
2HO2
2 [Pd L4] [Pd X3L]
+
HN
NH
NH2[PdIIX3L]-
NH2[PdIIX3L]-
2 [PdIL4]+[PdIIX3L]-
+
+
+
O2
H2O2
HN
Product
Product
Step 5
PdIIL2
H2O2
(with acid)
step 5:
a
NH
2 [PdIL ]+O
2 [PdIL ]+[PdIIX L]-
+ 2
4 3
-
4H+
+
a
+
H2O2
+
4
2
-
[PdIL4]+O2
HN
Product
Step 3
step 6:
Step 4
O2
2L
2[PdIL4]+[PdIIX3L]-
[PdIIL4]2+2[PdIIX3L]-
+
Pd0L4
Pd0L4
NH2[PdIIX3L]-
X = Cl
3PdIIX2L2
Pd0L4
+
L = DMF
-[LX3PdII]H2N
a
The long-known Glaser coupling is usually carried out under
aerobic conditions, as it is here, because O2 is consumed
stoichiometrically in the reaction. The reaction is generally
catalyzed by a mixture of Pd and Cu salts, because the Cu salt
is necessary to mediate Pd(0) re-oxidation by O2 to Pd(II) in
the catalytic cycle, as in the Wacker process.40 Here, only Pd(II)
is present, thus Pd(II) must also play the role of responsible for
alkyne deprotonation and transmetallation agent as in the
Sonogashira reaction41-42 and as oxidation mediator. It is also
found that the presence of acid (Table S2) accelerates the
process of gelation, which corresponds well to step 5 (Scheme
2) in our mechanism. Therefore, as shown in Scheme 3, Pd(II)
catalyzes cross-linking of Alkyne-PVA. Then it becomes
encapsulated inside the alkyne network of PVA, because the
alkyne group contains π electrons and herewith strongly
coordinates to Pd(II).
Given the mechanism of this gelation process and the
location of Pd(II) inside the cross-linked Alkyne-PVA, a new
strategy based on Alkyne-PVA gel was performed for
separation and entrapment of Pd(II) from a mixture of various
metal ions. In brief, the appropriate amount (50 mg) of
Alkyne-PVA was added into a series of solutions of Pd(II)
(0.017 mmol) mixed with another metal ion. Residual metal
ions inside the gel were determined by ICP-OES. As shown in
Figure 5, after gelation, most of Pd(II) was obviously
separated from the mixture and strongly immobilized inside
the gel, while only a trace amount of another corresponding
completive ion was found in each sample. Besides, the
experiment was also extended to more complex solutions that
included Pd2+ together with Fe3+, Co2+, Ni2+, Zn2+and Al3+. In
this case, a large amount of Pd(II) (79%) was successfully
entrapped by the gel, achieving a significant efficiency for
separation and entrapment of Pd(II) from a mixture solution.
The entrapment performance of this gelation based strategy
was also investigated. (Table S3) The result indicates that with
the increase of the concentration of Pd(II), the maximal ratio
of gelation entrapped Pd(II) ions is 152.37 mg/g, which is
comparable to the conventional adsorption based strategy.
(Table S4).
Scheme 3. Proposed mechanism of the gelation process for
Pd(II)@alkyne-PVA
Strong acids are always utilized as lixiviants to dissolve Pd(II)
from waste or mineral, which results in high acidic conditions
for the dissolved Pd(II) solution. Thus, an ideal material which
would be able to directly separate and immobilize Pd(II) from
the acidic solution should be searched.43 In this work,
Pd(II)@alkyne-PVA is shown to be able to effect rapid
gelation in a wide range of pH values. In addition, the state-of-
art methods are all “passive”, relying on the chelation,
electrostatic attraction, ion exchange, or unique hollow
4
ACS Paragon Plus Environment

Page 5 of 10
Chemistry of Materials
PdNPs have long been shown to be excellent catalysts.44-45
1
2
3
4
5
6
7
8
Thus, entrapped Pd(II) inside Alkyne-PVA was reduced by
NaBH4 followed by dry freezing, yielding the rZZM-1. The
TEM image of the rZZM-1 (Figure 6a) shows that the PdNPs
inside the gels are nearly monodispersed with a diameter of
~1.9 nm. The small size and relative monodispersity of the
PdNPs is attributed to the confinement effect of alkyne ligands
that encapsulate Pd(0) inside the network. This aerogel
composite exhibited a remarkable catalytic activity towards
Suzuki-Miyaura cross coupling without further treatment. The
recycled rZZM-1 that contains 0.005 mmol Pd source has been
investigated for coupling between iodobenzene and 4-
methoxyphenyl boronic acid in various solvents, and
EtOH/H2O (2:1) has been the most favorable solvent for this
system (Table S5). In order to screen the optimal reaction
conditions, bromobenzene and 4-methoxy phenyl boronic acid
have been probed under various conditions.
9
10
11
12
13
14
15
16
17
18
19
Scheme 5. Suzuki-Miyaura coupling catalyzed by rZZM-1
Br
B(OH)2
R
rZZM-1,
EtOH/H2O, 80 o
K2CO3
+
Figure 5. Metal residual rate of Pd(II) gel formed from binary
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
C
metallic mixture (a); multi-metallic mixture (b).
R
MeO
F
structure of guest materials. On the contrary, the strategy
shown here represents an “active” way that mainly relies on
process of Glaser coupling catalyzed by Pd(II). The Pd(II) ions
that are entrapped inside the alkyne network of PVA during
the gelation are difficult to remove, while other completive
metal ions are located outside the network and easily washed
out (Scheme 4).
20 min 97%
14550 h-1
27 min 98%
10333 h-1
27 min 95%
10555 h-1
18 min 93%
15500 h-1
Reaction conditions: aryl halide (0.65 mmol), arylboronic acid
(0.5 mmol), K2CO3 (2.0 mmol), rZZM-1 (0.35 mg, 0.02 mol%
Pd), EtOH (96%) (2 ml), deionized water (1 mL). Yields are
isolated yields.
Scheme 4. Possible mechanism for Pd2+ entrapped in the gel.
When the catalytic amount was reduced to 200 ppm, rZZM-
1 still achieved an excellent catalytic performance with a TOF
value at 14550 h-1 at 80 oC (Table S6), and no obvious
decrease of the catalyst activity was observed during the first 6
cycles (Figure S5). In addition, rZZM-1 also catalyzed C-C
coupling between various substrates with high yields and high
TOF values including upon recycling (Scheme 5 and Table
S7). Meanwhile, the separated rZZM-1, after entrapped Pd(II)
from mixed metallic solution, also performed well
catalytically, as initial rZZM-1 (Table 1).
Table 1. Comparison of turnover frequencies reported for other Pd(0) catalyst in the Suzuki cross-coupling reaction.
X
B(OH)2
O
+
R2
R1
Entry
Catalyst
X/R1/R2
Reaction conditions
TOF(h-1)
14550
Ref.
rZZM-1
Br/H/OMe
EtOH:H2O/K2CO3/0.02
mol%/353 K/20 min
This
work
1
2
Pd/PDA
Br/H/OMe
EtOH/ K2CO3/0.031 mol%/298
580
[46]
5
ACS Paragon Plus Environment

Chemistry of Materials
Page 6 of 10
K/3 h
1
2
3
4
5
6
7
Pd@Hal-pDA-NPC
I/H/OMe
I/OMe/H
EtOH:H2O/K2CO3/1
mol%/373K/110 min
49
[47]
[48]
3
4
Fe3Pd2(OH)2[PA]8(H2O)4
DMF:H2O/ K2CO3/TBAB/0.11
mol%/353K/20 min
2612
PdAS
Br/OMe/H
H2O/ Na2CO3//0.05
mol%/373K/24 h
82
[49]
5
8
9
Pd@CNPCs
Pd/PIC
Br/OMe/H
Br/H/OMe
Br/OMe/H
Br/OMe/H
Br/OMe/H
Br/OMe/H
Br/OMe/H
Br/H/OMe
I/OMe/H
DMF:H2O/ K2CO3/ 0.1
mol%/323K/1 h
946
4950
63
[50]
[51]
[52]
[53]
[54]
[55]
[56]
[57]
[58]
[59]
6
7
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
H2O/Na2CO3/TBAB/0.01
mol%/373K/2 h
SMNPs-Salen Pd
DMF:H2O/ K2CO3/ 0.5
mol%/323K/373K/3 h
8
Fe3O4/SiO2-Met-
Pd(OAc)2
EtOH:H2O/K2CO3/0.14
mol%/353 K/1 h
671
64
9
Pd0-Mont
Pd@SAB-15
SA-15/CCPy/Pd(II)
KCC-1-NH2/Pd
XG-Pd
H2O/K2CO3/0.07 mol%/333
K/-
10
11
12
13
14
15
H2O/K2CO3/0.08 mol%/353
K/1 h
1200
320
41
EtOH:H2O/K2CO3/0.3
mol%/353 K/1 h
EtOH:H2O/K3PO4/0.5
mol%/373 K/4 h
H2O/K2CO3/0.15 mol%/363
K/12 h
32
Pd-Gel
I/OMe/H
EtOH:H2O/K2CO3/1 mol%/323
K/18 h
8
The electrocatalytic HER activity of PdNPs@CNWs was
investigated in 0.5 M H2SO4 using a three-electrode cell by
linear sweep voltammetry (LSV) with a scan rate of 5 mV s-1.
For comparison, the activity of commercial Pd on activated
carbon (Pd/C)-modified GCE was also evaluated. Figure 7
presents the polarization curves of PdNPs@CNWs (left) and
the commercial Pd/C (right) promotors modified on the GCE
in 0.5 M H2SO4. PdNPs@CNWs exhibits a very good HER
activity with a low onset potential of 18 mV and an
overpotential at 10 mA cm-2 current density of 146 mV as well
as a small Tafel slope of 97 mV dec-1, which is comparable to
those of commercial Pd/C. Remarkably, the stability of
fabricated PdNPs@CNWs is much higher than that of Pd/C.
Figure 6. TEM image of rZZM-1 (a); SEM images of rZZM-1 (b) and PdNPs@CNWs (c).
The LSV curves of the first cycle and after scanning cyclic
voltammetry (CV) at a scanning rate of 100 mV s-1 for 1,000
and 3,000 cycles are presented in Figure 7. It reveals just 7 and
14 mV shift in the overpotential after 1,000 and 3,000 CV
cycles for PdNPs@CNWs, which compares with shifting
values as large as 41 and 107 mV obtained with Pd/C. The
negligible overpotential shifts observed from PdNPs@CNWs
after continuous scanning indicate an excellent stability in
long-term performance. This is ascribed to the protection gen
erated by the carbon network preventing the PdNPs from
6
ACS Paragon Plus Environment

Page 7 of 10
Chemistry of Materials
detachment away from the carbon matrices and precluding the
PdNPs from corrosion in the electrolyte.
Didier Astruc: 0000-0002-2258-3126
1
ACKNOWLEDGMENT
2
3
4
5
6
7
8
9
Financial support from the Science and Technology Department
of Sichuan Province (2018JY0287), the Discipline Development
Foundation of Science and Technology on Surface Physics and
Chemistry Laboratory (XKFZ201505), Natural Science
Foundation of China (51573172, 21806151, 21806099), the
University of Bordeaux and the Centre National de la Recherche
Scientifique (CNRS) is gratefully acknowledged.
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
REFERENCES
(1) Chen, A.; Ostrom, C. K. Palladium-Based Nanomaterials:
Synthesis and Electrochemical Applications. Chem. Rev. 2015, 115,
11999-12044.
(2) Gao, G.; Jiao, Y.; Waclawik, E. R.; Du, A. Single Atom (Pd/Pt)
Supported on Graphitic Carbon Nitride as an Efficient Photocatalyst
for Visible-Light Reduction of Carbon Dioxide. J. Am. Chem. Soc.
2016, 138, 6292-6297.
Figure 7. Polarization curves of PdNPs@CNWs and
commercial Pd/C before and after CV scanning (a).
Corresponding Tafel plots of PdNPs@CNWs and commercial
Pd/C (b).
CONCLUSION
(3) Uehling, M. R.; King, R. P.; Krska, S. W.; Cernak, T.;
Buchwald, S. L. Pharmaceutical Diversification via Palladium
Oxidative Addition Complexes. Science 2019, 363, 405-408.
(4) Astruc, D.; Lu, F.; Ruiz. J. Nanoparticles as Recyclable
Catalysts: The Frontier Between Homogeneous and Heterogeneous
Catalysis. Angew. Chem., Int, Ed. 2005, 44, 7852-7872.
(5) Gurung, M.; Adhikari, B. B.; Kawakita, H.; Ohto, K.; Inoue, K.;
Alam, S. Selective Recovery of Precious Metals from Acidic Leach
Liquor of Circuit Boards of Spent Mobile Phones Using Chemically
Modified Persimmon Tannin Gel. Ind. Eng. Chem. Res. 2012, 51,
11901-11913.
(6) Lin, S.; Zhao, Y.; Bediako, J. K.; Cho, C. W.; Sarkar, A. K.;
Lim, C. R.; Yun, Y. S. Structure Controlled Recovery of Palladium
(II) from Acidic Aqueous Solution Using Metal-Organic Frameworks
of MOF-802, UiO-66 and MOF-808. Chem. Eng. J. 2019, 362, 280-
286.
(7) Ling, L.; Huang, X.; Zhang, W. Enrichment of Precious Metals
from Wastewater with Core-Shell Nanoparticles of Iron. Adv. Mater.
2018, 30, 1705703.
(8) Gauthier, D.; Sobjerg, L. S.; Jensen, K. M.; Lindhardt, A. T.;
Bunge, M.; Finster, K.; Meyer, R. L.; Skrydstrup, T. Environmentally
Benign Recovery and Reactivation of Palladium from Industrial
Waste by Using Gram-Negative Bacteria. Chemsuschem 2010, 3,
1036-1039.
In conclusion, a new, facile and efficient strategy for
precious palladium metal separation and entrapment was
designed based on the high and specific catalytic activity of
Pd(II) in the Glaser coupling reaction that is not observed with
other ions. Pd(II) selectively catalyzed the crosslinking of
alkyne-PVA and Pd(II)@alkyne-PVA gels rapidly formed
during the process.
The Pd(II) ions are coordinately entrapped inside the “alkyne
network” of the gels, which screens them from other non-
precious metal ions including Fe2+, Co2+, Ni2+, Zn2+ and Al3+.
The obtained Pd(II)@alkyne-PVA gels were also reduced, and
after freeze-drying Pd0NPs@alkyne-PVA (rZZM-1) aerogels
formed. These aerogels were directly utilized as a remarkably
efficient and recyclable heterogeneous catalyst without any
post-treatment. Fundamentally, this strategy provides a general
means for metal ion separation and entrapment. Indeed, the
PVA (or other polymer) with special functionality may be
regarded as template for a unique entrapment of specific metal
ion catalysts crosslinking the functionality in the PVA or
potentially other polymers. Further investigations should
concentrate on the separation of other metal ions using this
strategy.
(9) Troupis, A.; Hiskia, A.; Papaconstantinou, E. Selective
Photocatalytic
Polyoxometallates. Appl. Catal. B-Environ. 2004, 52, 41-48.
Reduction-Recovery
of
Palladium
Using
ASSOCIATED CONTENT
Supporting Information
Physical, calculation and catalysis data. The Supporting
Information is available free of charge on the ACS Publications
website.
(10) Zhou, C.; Ontiverosvalencia, A.; Wang, Z.; Maldonado, J.;
Zhao, H.; Krajmalnikbrown, R.; Rittmann, B. E. Palladium Recovery
in a H2-Based Membrane Biofilm Reactor: Formation of Pd(0)
Nanoparticles Through Enzymatic and Autocatalytic Reductions.
Environ. Sci. Technol. 2016, 50, 2546-2555.
(11) Nguyen, T. H.; Chong, H. S.; Man, S. L. Separation of Pt(IV),
Pd(II), Rh(III) and Ir(IV) from Concentrated Hydrochloric Acid
Solutions by Solvent Extraction. Hydrometallurgy 2016, 164, 71-77.
(12) Lee, J. Y.; Raju, B.; Kumar, B. N.; Kumar, J. R.; Park, H. K.;
Reddy, B. R. Solvent Extraction Separation and Recovery of
Palladium and Platinum from Chloride Leach Liquors of Spent
Automobile Catalyst. Sep. Purif. Technol. 2010, 73, 213-218.
(13) Yue, C.; Sun, H.; Liu, W.; Guan, B.; Deng, X.; Zhang, X.;
Yang, P. Environmentally Benign, Rapid and Selective Extraction of
Gold from Ores and Waste Electronic Materials. Angew. Chem., Int.
Ed. 2017, 56, 9331-9335.
AUTHOR INFORMATION
Corresponding Authors
* shuaimaobin@caep.cn
* didier.astruc@u-bordeaux.fr
* zhaopengxiang@caep.cn
ORCID
(14) Godlewskażylkiewicz, B.; Leśniewska, B.; Gąsiewska, U.;
Hulanicki, A. Ion-Exchange Preconcentration and Separation of Trace
mounts of Platinum and Palladium. Anal. Lett. 2000, 33, 2805-2820.
(15) Zhiwei, T.; Gang, H.; Yue, C.; Jie, G.; Tai-Shung, C.; Yung, C.
S.; Shawn, W. Novel Nanofiltration Membranes Consisting of a
Pengxiang Zhao: 0000-0002-4685-0751
Liangsheng Hu: 0000-0002-4133-2090
7
ACS Paragon Plus Environment

Chemistry of Materials
Page 8 of 10
Sulfonated Pentablock Copolymer Rejection Layer for Heavy Metal
(34) Deraedt, C.; Astruc, D., "Homeopathic" Palladium Nanoparticle
Removal. Environ. Sci. Technol. 2014, 48, 13880-13887.
(16) Kim, D. I.; Gwak, G.; Dorji, P.; He, D.; Phuntsho, S.; Hong, S.;
Shon, H. K. Palladium Recovery Through Membrane Capacitive
Deionization from Metal Plating Wastewater. ACS Sustain. Chem.
Eng. 2017, 6, 1692-1701.
(17) Gwak, G.; Kim, D. I.; Hong, S. New Industrial Application of
Forward Osmosis (FO): Precious Metal Recovery from Printed
Circuit Board (PCB) Plant Wastewater. J. Membrane Sci. 2018, 552,
234-242.
(18) Fujiwara, K.; Ramesh, A.; Maki, T.; Hasegawa, H.; Ueda, K.
Adsorption of Platinum(IV), Palladium(II) and Gold(III) from
Aqueous Solutions onto L-Lysine Modified Crosslinked Chitosan
Resin. J. Hazard. Mater. 2007, 146, 39-50.
(19) Kim, S.; Song, M. H.; Wei, W.; Yun, Y. S. Selective
Biosorption Behavior of Escherichia Coli Biomass toward Pd(II) in
Pt(IV)-Pd(II) Binary Solution. J. Hazard. Mater. 2015, 283, 657-662.
(20) Kawakita, H.; Parajuli, D., Recovery of Gold(III),
Palladium(II), and Platinum(IV) by Aminated Lignin Derivatives.
Ind. Eng. Chem. Res. 2006, 45, 6405-6412.
(21) Lin, S.; Reddy, D. H. K.; Bediako, J. K.; Song, M. H.; Wei, W.;
Kim, J. A.; Yun, Y. S. Effective Adsorption of Pd(II), Pt(IV) and
Au(III) by Zr(IV)-based Metal-Organic Frameworks from Strongly
Acidic Aolutions. J. Mater. Chem. A 2017, 5, 13557-13564.
(22) Mon, M.; Ferrandosoria, J.; Grancha, T.; Forteaperez, F. R.;
Gascon, J.; Leyvaperez, A.; Armentano, D.; Pardo, E. Selective Gold
Recovery and Catalysis in a Highly Flexible Methionine-Decorated
Metal-Organic Framework. J. Am. Chem. Soc. 2016, 138, 7864-7867.
(23) Zhang, Q.; Cui Y.; Qian G. Goal-directed design of metal-
organic frameworks for liquid-phase adsorption and separation.
Coord. Chem. Rev. 2017, 378, 310-332.
(24) Liu Y.; Lin S.; Liu Y.; Sarkar A. K.; Bediako J. K., Kim H. Y.;
Yun Y. S. Super-Stable, Highly Efficient, and Recyclable Fibrous
Metal-Organic Framework Membranes for Precious Metal Recovery
from Strong Acidic Solutions. Small 2019, 15, 1805242.
(25) Zhou, Z.; Zhong, W.; Cui, K.; Zhuang, Z.; Li, L.; Li, L.; Bi, J.;
Yu, Y., A Covalent Organic Framework Bearing Thioether Pendant
Arms for Selective Detection and Recovery of Au from Ultra-low
Concentration Aqueous Solution. Chem. Commun. 2018, 54, 9977-
9980.
(26) Zhao, S.; Gensch, T.; Murray, B.; Niemeyer, Z. L.; Sigman, M.
S.; Biscoe, M. R., Enantiodivergent Pd-Catalyzed C–C Bond
Formation Enabled Through Ligand Parameterization. Science 2018,
362, 670-674.
(27) Wang, D.; Weinstein, A. B.; White, P. B.; Stahl, S. S., Ligand-
Promoted Palladium-Catalyzed Aerobic Oxidation Reactions. Chem.
Rev. 2017, 118, 2636-2679.
(28) Ye, J.; Lautens, M., Palladium-Catalysed Norbornene-Mediated
C-H Functionalization of Arenes. Nat. Chem. 2015, 7, 863-870.
(29) Yin, L.; Liebscher, J., Carbon-Carbon Coupling Reactions
Catalyzed by Heterogeneous Palladium Catalysts. Chem. Rev. 2007,
107, 133-173.
(30) Chen, L.; Lemma, B. E.; Rich, J. S.; Mack, J., Freedom: a
Copper-Free, Oxidant-Free and Solvent-free Palladium-Catalysed
Homocoupling Reaction. Green Chem. 2014, 16, 1101-1103.
(31) Peng, H.; Xi, Y.; Ronaghi, N.; Dong, B.; Akhmedov, N. G.;
Shi, X., Gold-Catalyzed Oxidative Cross-Coupling of Terminal
Alkynes: Selective Synthesis of Unsymmetrical 1,3-diynes. J. Am.
Chem. Soc. 2014, 136, 13174-13177.
Catalysis of Cross Carbon-Carbon Coupling Reactions. Acc. Chem.
Res. 2014, 47, 494-503.
(35) Su, S.; Yue, G.; Huang, D.; Yang, G.; Lai, X.; Zhao, P., Parts
per Million Level, Green, and Magnetically-recoverable Triazole
Ligand-stabilized Au and Pd Nanoparticle Catalysts. RSC Adv. 2015,
5, 44018-44021.
(36) Ossipov, D.; Hilborn, J., Poly(vinyl alcohol)-Based Hydrogels
Formed by “Click Chemistry”. Macromolecules 2006, 39, 1709-1718.
(37) And, X. W.; Andrews, L., Side-Bonded Pd-η2-(C2H2)1,2 and
Pd2-η2-(C2H2) Complexes: Infrared Spectra and Density Functional
Calculations. J. Phys. Chem. A 2002, 107, 337-345.
1
2
3
4
5
6
7
8
9
(38) Han-Gook, C.; Lyon, J. T.; Lester, A., Infrared Spectra of M-η2-
(C2H2) and HM-C ≡ CH Produced in Reactions of Laser-Ablated
Group 6 Metal Atoms with Acetylene. J. Phys. Chem. A 2012, 116,
11880-11887.
(39) Derosa, J.; Cantu, A. L.; Boulous, M. N.; Duill, M. O.;
Turnbull, J. L.; Liu, Z.; La Torre, D. M. D.; Engle, K. M.,
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
Palladium(II)-Catalyzed
Directed
anti-Hydrochlorination
of
Unactivated Alkynes with HCl. J. Am. Chem. Soc. 2017, 139, 5183-
5193.
(40) Astruc, D., Electron Transfer and Radical Processes in
Transition-Metal Chemistry. Wiley-VCH, New York, 1995.
(41) Méry, D.; Heuze, K.; Astruc, D., A Very Efficient, Copper-Free
Palladium Catalyst for the Sonogashira Reaction with Aryl Halides.
Chem. Commun. 2003, 34, 1934-1935.
(42) Chinchilla, R.; Najera, C., Recent Advances in Sonogashira
Reactions. Chem. Soc. Rev. 2011, 40, 5084-5121.
(43) Lin, S.; Wei, W.; Wu, X.; Zhou, T.; Mao, J.; Yun, Y., Selective
Recovery of Pd(II) from Extremely Acidic Solution Using Ion-
Imprinted Chitosan Fiber: Adsorption Performance and Mechanisms.
J. Hazard. Mater. 2015, 299, 10-17.
(44) Dai, Y.; Liu S.; Zheng, N. C2H2 Treatment as a Facile Method
to Boost the Catalysis of Pd Nanoparticulate Catalysts. J Am. Chem.
Soc. 2014, 136, 5583-5586.
(45) Wei, T.; Sun, J.; Zhang, F.; Zhang, J.; Chen, J.; Li, H.; Zhang,
X. Acetylene Mediated Synthesis of Au/Graphene Nanocomposite for
Selective Hydrogenation. Catal. Commun. 2017, 93, 43-46.
(46) Kunfi, A.; May, Z.; Nemeth, P.; London, G. Polydopamine
Supported Palladium Nanoparticles: Highly Efficient Catalysts in
Suzuki
Cross-Coupling
and
Tandem
Suzuki
Cross-
Coupling/Nitroarene Reductions under Green Reaction Conditions. J.
Catal. 2018, 361, 84-93.
(47) Samahe, S.; Giuseppe, L.; Masoumeh, M.; Heravi, M. M. Pd
nanoparticles immobilized on the poly-dopamine decorated halloysite
nanotubes hybridized with N-doped porous carbon monolayer: A
versatile catalyst for promoting Pd catalyzed reactions. J. Catal. 2018,
361, 84-93.
(48) Hamid, A.; Yadollah, Y.; Maryam, S.; Maryam, K. M.; Akbar,
H. Architectured Fe3Pd2(OH)2[Picolinic acid]8(H2O)4 hybrid nanorods:
a remarkably reusable and robust heterogeneous catalyst for Suzuki–
Miyaura and Mizoroki-Heck cross-coupling reactions. ACS Sustain.
Chem. Eng. 2018, 6, 12613-12620.
(49) Yamada, Y. M.; Takeda, K.; Takahashi, H.; Ikegami, S. Highly
active catalyst for the heterogeneous Suzuki-Miyaura reaction:
assembled complex of palladium and non-cross-linked amphiphilic
polymer. J. Org. Chem. 2003, 68, 7733-7741.
(50) Peng, Z.; Weng, Z.; Jia, G.; Wang, C. Solution-Dispersible,
Colloidal, Conjugated Porous Polymer Networks with Entrapped
Palladium Nanocrystals for Heterogeneous Catalysis of the Suzuki–
Miyaura Coupling Reaction. Chem. Mater. 2011, 23, 5243-5249.
(51) Yu, Y.; Hu, T.; Chen, X.; Xu, K.; Zhang, J.; Huang, J. Pd
nanoparticles on a porous ionic copolymer: a highly active and
recyclable catalyst for Suzuki–Miyaura reaction under air in water.
Chem Commun. 2011, 47, 3592-3594.
(32) Fairlamb, I. J. S.; Bauerlein, P. S.; Marrison, L. R.; Dickinson,
J. M., Pd-Catalysed Cross Coupling of Terminal Alkynes to Diynes in
the Absence of a Stoichiometric Additive. Chem. Commun. 2003, 34,
632-633.
(33) Astruc, D., Palladium Catalysis Using Dendrimers: Molecular
Catalysts Versus Nanoparticles. Tetrahedron Asym. 2010, 21, 1041-
1054.
(52) Jin, X.; Zhang, K.; Jian, S.; Jia, W.; Dong, Z.; Rong, L.
Magnetite nanoparticles immobilized Salen Pd (II) as a green catalyst
for Suzuki reaction. Catal. Commun. 2012, 26, 199-203.
8
ACS Paragon Plus Environment

Page 9 of 10
Chemistry of Materials
(53) Beygzadeh, M.; Alizadeh, A.; Khodaei, M. M.; Kordestani, D.
efficient heterogeneous nanocatalyst for Suzuki-Miyaura coupling
reactions. J. Mol. Catal. A Chem. 2014, 395, 25-33.
(57) Fihri, A.; Cha, D.; Bouhrara, M.; Almana, N.; Polshettiwar, V.
Fibrous nano-silica (KCC-1)-supported palladium catalyst: Suzuki
coupling reactions under sustainable conditions. Chemsuschem 2012,
5, 85-89.
(58) Maity M.; Maitra U. An easily prepared palladium-hydrogel
nanocomposite catalyst for C-C coupling reactions. J. Mater. Chem. A
2014, 2, 18952-18958.
(59) Slavík, P.; Kurka D. W.; Smith D. K. Palladium-scavenging
self-assembled hybrid hydrogels-reusable highly-active green
catalysts for Suzuki-Miyaura cross-coupling reactions. Chem. Sci.
2018, 9, 8673-8681.
Biguanide, Pd(OAc)2 immobilized on magnetic nanoparticle as a
recyclable catalyst for the heterogeneous Suzuki reaction in aqueous
media. Catal. Commun. 2013, 32, 86-91.
(54) Borah, B. J.; Borah, S. J.; Saikia, K.; Dutta, D. K. Efficient
Suzuki-Miyaura coupling reaction in water: Stabilized Pd0-
Montmorillonite clay composites catalyzed reaction. Appl. Catal. A
Gen. 2014, 469, 350-356.
(55) Zhi, J.; Song, D.; Li, Z.; Lei, X.; Hu, A. Palladium
nanoparticles in carbon thin film-lined SBA-15 nanoreactors: efficient
heterogeneous catalysts for Suzuki-Miyaura cross coupling reaction in
aqueous media. Chem. Commun. 2011, 47, 10707-10709.
(56) Veisi, H.; Hamelian, M.; Hemmati, S. Palladium anchored to
SBA-15 functionalized with melamine-pyridine groups as a novel and
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
9
ACS Paragon Plus Environment

Chemistry of Materials
Page 10 of 10
1
TOC graphic
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
10
ACS Paragon Plus Environment