Pd Nanoparticles Confined in the Porous Graphene-like Carbon Nanosheets for Olefin Hydrogenation

Article abstract of DOI:10.1021/acs.langmuir.8b02785

As a novel type of defective graphene, porous graphene has been considered an excellent support material for metal clusters, as the interaction between defective carbon atoms surrounded with the metal nanoparticles (NPs) is very different from that on the ordinary supported catalyst. In this work, we reported a facile three-step method to confine the Pd NPs and grow the graphene-like carbon nanosheets (GLCs) in the same interlayer space of the layered silicate, generating embedded Pd NPs in the pores of porous GLCs in situ. The Pd@GLC nanocomposite exhibited not only high activity and stability than the common commercial Pd/C catalyst for the hydrogenation of olefins but also superior ability of resisting high temperature, which benefitted from the two-dimensional structure of layered GLCs, the confinement of Pd, and the increased edge and defect of the unsaturated carbon atoms in GLCs.

Full text of DOI:10.1021/acs.langmuir.8b02785

Subscriber access provided by Kaohsiung Medical University
Interfaces: Adsorption, Reactions, Films, Forces, Measurement Techniques, Charge
Transfer, Electrochemistry, Electrocatalysis, Energy Production and Storage
Pd nanoparticles confined in the porous Graphene-
like carbon nanosheets for olefin hydrogenation
Zhe Chen, Weixue Wang, Yifei Zhang, Yu Liang, Zhi-Min Cui, and Xiangke Wang
Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b02785 • Publication Date (Web): 29 Sep 2018
Downloaded from http://pubs.acs.org on September 29, 2018
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 21
Langmuir
1
2
3
4
5
6
7
8
9
Pd nanoparticles confined in the porous Graphene-
like carbon nanosheets for olefin hydrogenation
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
Zhe Chen,a Weixue Wang,a Yifei Zhang, a Yu Liang,a Zhimin Cui *,b and Xiangke Wang *, a
a College of Environmental Science and Engineering, North China Electric Power University,
Beijing, 102206, PR China
b School of Chemistry, Beihang University, Beijing 100191, PR China
KEYWORDS: Palladium, confined, porous graphene, hydrogenation, catalysis
ABSTRACT: As a novel type of defective graphene, porous graphene has been considered an
excellent support material for metal clusters, as the interaction between defective carbon atoms
surrounding with the metal NPs is very different from that on ordinary supported catalyst. In this
work, we reported a facile three-step method to confine the Pd NPs and grow the graphene-like
carbon nanosheets (GLCs) in the same interlayer space of layered silicate, generating embedded
Pd NPs in the pores of porous GLCs in situ. The Pd@GLCs nanocomposite not only exhibited
highly active activity and stability than common commercial Pd/C catalyst for the hydrogenation
of olefins, but also superior ability of resisting high temperature, which benefitted from the two
dimensional structure of layered GLCs, the confinement of Pd and the increased edge and defect
of the unsaturated carbon atoms in GLCs.
ACS Paragon Plus Environment
1

Langmuir
Page 2 of 21
1
2
3
4
Introduction
5
6
7
8
Supported metal nanoparticles (NPs) are the most widely investigated heterogeneous catalysts
in catalysis community. The interaction between the metal and support materials have great
influence on the stability and adsorption properties of catalysts, which lead to different activity
and selectivity.1-4 Among the common catalyst supports, carbon materials, such as active carbon,
graphene and carbon nanotubes (CNTs) are widely employed as support due to their high surface
areas, excellent structure stability, and non-toxicity.5-9 However, the migration, agglomeration,
and sintering of metal NPs on the surface of pristine graphene (or CNTs, etc.) are always
unavoidable because the functional groups as the anchoring sites are absent on the carbon
support.10,11 How to solve this problem becomes a significant topic of the catalyst design based
on carbon materials.12 Take graphene as an example, many approaches have been proposed to
improve the interaction of metal NPs and carbon support, such as by introducing oxygen or
nitrogen-containing groups, doping heteroatom on graphene, and fabricating pores with defective
sites on the graphene.13-20
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
As a novel type of defective graphene, porous graphene has been considered an excellent
support material for metal clusters, as the interaction between defective carbon atoms
surroundings with the metal NPs is very different from that on ordinary supported catalyst.21,22
Banhart et.al demonstrated that defects in graphene and CNTs could trap metal atom and prevent
it from diffusing effectively,23 thus improving the stability of the composite as a catalyst. Not
just in regard to the stability, the electron character of metal also might be influenced a lot when
metal clusters were embedded in the porous graphene, which was revealed by theoretical
calculations research particularly. Wang et.al investigated electronic structures of metal clusters
(Pd, Ir, and Rh) supported on pristine graphene and porous graphene with density functional
ACS Paragon Plus Environment
2

Page 3 of 21
Langmuir
1
2
3
4
5
6
7
8
9
theory (DFT) calculations, and reported that graphene with nanopores could stabilize the metal
clusters, downshift the d-band center of the metal clusters and change the binding energy of
reagents substantially.24
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
What’s more, the porous graphene itself exhibit special electron or adsorption properties due to
the abundant defective carbon atoms along the pores. For example, several works proved that the
reaction rate of methane decomposition catalyzed by defective carbon materials was linearly
dependent on the number of -CH=CH- defective sites.25,26 In brief, as the support of catalyst, the
enriched unsaturated carbon atoms on porous graphene will bring significant effect to the
catalyst’ performance.
Although several exciting theoretical reports have proved the significant impact of porous
graphene on catalysis, the related experimental studies are limited. The severe mismatches may
derive from the difficulty to synthesize porous graphene with subnano-sized pores,23,27 as well as
the difficulty of the precise control to embed all the metal NPs into the pores on porous graphene
perfectly.
Herein, we reported a facile three-step method to confine the Pd NPs and grow the graphene-
like carbon nanosheets (GLCs) in the same interlayer space of layered silicate, generating
embedded Pd NPs in the pores of porous GLCs in situ. The Pd@GLCs nanocomposite not only
exhibited highly active activity and stability than common commercial Pd/C catalyst for the
hydrogenation of olefins, but also superior ability of resisting high temperature. The two-
dimensional structure of layered GLCs and the intimate contact between the confined Pd and
GLCs was supposed to account for the superior performance of the Pd@GLCs nanocomposite.
Experimental Methods
Synthesis of RUB-15 nanoplates
ACS Paragon Plus Environment
3

Langmuir
Page 4 of 21
1
2
3
4
5
6
7
8
9
In a typical process, 17.78 g TMAOH (Tetramethylammonium hydroxide, 25 wt% solution)
was mixed with 12.22 g TEOS (Tetraethyl orthosilicate) at room temperature under stirring.
After stirred overnight, the solution was transferred to a 50 mL Teflon-lined autoclave, which
next would be kept in the oven at the temperature of 140 ◦C for 7 days. Lastly, the product was
collected by filtration and washed with acetone till the pH decreased to 7, and then dried at 60
◦C.
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
Synthesis of Pd@GLCs
100 mg RUB-15 was dispersed in 50mL distilled water and stirred for 20 min. At the
same time, 0.1 g SnCl2 was dissolved in 20 mL 0.02 M HCl solution. Then the SnCl2
solution was added into RUB-15 suspension under stirring for 10 min. Afterwards the
suspension was centrifuged and washing with distilled water for five times. The
precipitate was dispersed in 50 mL distilled water, and mixed with 500 ꢀL PdCl2 (0.0564
mol/L) solution. Ten min later, 10 mL of 0.15 mol/L NaCOOH solution was added
following stirring for 5 h. After centrifugation and washing with distilled water five times,
the precipitate Pd/RUB-15 was obtained and dried at 60 ºC for 12 h.
100 mg Pd/RUB-15 and 150 mg of glucose were dispersed in 5mL of distilled water and
stirred overnight. Then, 30 ꢀL of concentrated sulfuric acid was added. Afterward, the mixture
was stirred for another 10 min and heated at 110 °C for 10 h. The black product was collected
carefully and calcined at 900 °C in Ar flow for 4 h (rate: 5 °C/min) to remove oxygen and
organic species and improve the graphitization of GLCs. Then, the graphitized Pd@GLCs-RUB-
15 was stirred with 5 mol/L NaOH solution tenderly for 12 h. After the etching of RUB-15, the
Pd@GLCs was harvested.
Olefin hydrogenation
ACS Paragon Plus Environment
4

Page 5 of 21
Langmuir
1
2
3
4
5
6
7
8
9
A 25 mL steel autoclave was charged with Pd@GLCs (4.6 wt%, 5 mg), an olefin (2.5 mmol),
1,3,5-trimethylbenzene (internal standard, 285 mL, 2.0 mmol) and 5 mL ethanol. The autoclave
was evacuated and backfilled with H2 (3 cycles, 1.0 MPa). Then, the mixture was stirred in a 25
°C water bath under 1.0 MPa H2 atmosphere for the desired time. Gas chromatograph (Shimadzu
GC-2010Plus) equipped with a flame ionization detector (FID) and a Rtx-5 capillary column
(0.25 mm in diameter, 30 m in length) was used to analyzed the yield of product, and the product
identity was ascertained by GC-MS (Shimadzu GCMS-QP2010S). The commercial Pd/C
catalyst (5 wt%) was purchased in Sigma-Aldrich.
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
Characterization
The crystal structure of the Pd@GLCs was characterized using an X-ray diffraction meter
(XRD-Rigaku) with Cu Kα radiation (λ = 1.54 Å). Scanning electron microscopy (operated on
JEOL JSM-7800F), transmission electron microscope, high resolution TEM images and energy
dispersive absorption X-ray (EDAX) spectroscopy (operated on JEM-ARM200F) was used to
examine the size and morphology of RUB-15 and Pd@GLCs. The concentrations of Pd2+ loss in
the reaction were analyzed using inductively coupled plasma atomic emission spectroscopy
(ICP-AES; Shimadzu ICPE-9000). The X-ray photoelectron spectroscopy (XPS) spectra was
performed on Thermo VG RSCAKAB 250X with VG SCIENTA KKLaser.
Results and discussion
The Pd@GLCs composite was fabricated in a three-step in situ carbonization method in the
interlayer space of layered silicate as shown in Scheme 1. The layered silicate RUB-15 was a
layered silicate ([N(CH3)4]8[Si24O52(OH)4]·20H2O) with side length of 5−10 ꢀm and thickness of
28
100 nm approximately (Figure S1). In the structure of RUB-15, the Tetramethylammonium
(TMA) cations as well as water molecules were filled in the hemihedral cavities inside the
ACS Paragon Plus Environment
5

Langmuir
Page 6 of 21
1
2
3
4
5
6
7
8
9
interlayer, which stabilized the layered structure. With the basal d spacing of 1.4 nm, the ion-
exchange between TMA+ inside the layered silicate RUB-15 and other metal cations was
feasible. In this synthesis route, the SnCl2 solution was added into RUB-15 suspension, as the
ion-exchange between TMA+ and Sn2+ took place. Then Sn2+ could act as the reductive site for
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
2-
PdCl4 , which assured that all the Pd NPs were loaded inside the interlayer of RUB-15.
Afterwards, the glucose was intercalated in the interlamellar space of RUB-15 and then the
carbon nanosheets were generated from the carbonization of glucose. At last, the Pd@GLCs
nanocomposite was obtained after the graphitization of carbon nanosheets and the removal of
RUB-15.
Scheme 1 The preparation of Pd@GLCs composite in three steps.
As shown in Figure 1, the uniform Pd nanoparticles with particle size of 5 2 nm were
successfully obtained on the GLCs without any agglomeration. The average size of Pd
nanoparticles was found to be 4.5 nm inspired by the size distribution (inset of Figure 1c). From
the SEM image (Figure 1a) and TEM images (Figure 1b-c) of Pd@GLCs, the GLCs looked like
monolayer-patched graphene and quite a number of GLCs were exfoliated as single or few-
layers graphene. The Pd NPs were located and confined in the pores of GLCs, as obvious vacant
regions existed around Pd NPs (Figure 1c). It was believed that the confined structure endowed
ACS Paragon Plus Environment
6

Page 7 of 21
Langmuir
1
2
3
4
5
6
7
8
9
Pd superior stability and efficient electron/ions transport on the GLCs. Figure 1d was the
HRTEM of a selected section Pd NPs. The lattice fringes of (111) planes with a d spacing of
0.225 nm indicated good crystallization of Pd nanoparticles. From the ICP-AES analysis, the Pd
content in the Pd@GLCs was calculated to be 4.6 wt%. Energy dispersive spectroscopy (EDS)
mapping of Pd@GLCs using STEM (Figure 1e) revealed the homogeneous and highly-uniform
distribution of Pd NPs on the Pd@GLCs.
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
b
2 µm
100 nm
35
30
25
20
15
10
5
c
d
0.225 nm
0
0
1 2 3 4 5 6 7 8 9 10
Pd(111)
50 nm
5 nm
e
100 nm
C
k
α1
O kα1
Pd Lα1
Figure 1 (a) The SEM image, (b-c) TEM images, (d) HRTEM images and (e) compositional
EDS mapping of Pd@GLCs composite.
Figure 2a displayed the XRD pattern of the Pd@GLCs composite. The wide peaks around 25.0
degree and the weak peak at 44.8 degree were attributed to the GLCs. No peaks belong to Pd
were observed at XRD patterns, which might due to the ultra-small size of the Pd NPs. He et.al
also reported the absence of Pt-phase diffraction peak of Pt/TiO2 in their XRD patterns, and
ACS Paragon Plus Environment
7

Langmuir
Page 8 of 21
1
2
3
4
5
6
7
8
9
attributed it to the strong metal interaction between the Pt and the TiO2 support.29 Control
experiments were carried out by preparation of GLCs that intercalated in RUB-15 first and then
loading Pd NPs on the GLCs afterwards (denoted as Pd@out-GLCs). The XRD patterns of
Pd@out-GLCs composite showed the apparent peak at 39.6 degree which was well assigned to
Pd (111) plane (Figure S2). The difference of the XRD patterns between the Pd@GLCs and
Pd@out-GLCs further proved that there was strong interaction between Pd and GLCs in the
Pd@GLCs composite. The Raman spectra of Pd@GLCs (Figure 2b) showed the disordered band
at∼1356 cm-1 (D-band), the graphitic band at ∼1587 cm-1 (G-band), and a wide 2D-band around
2870 cm-1. The measured intensity ID/IG ratio is about 0.735. The low intensity ratio of ID/IG
suggested that the sp2 carbon atoms domain and the GLCs was largely graphitized.30
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 (a) The XRD patterns (b) Raman spectra of Pd@GLCs (c) The N2
adsorption−desorption curve of Pd@GLCs (d) The pore distribution of the Pd@GLCs based on
NLDFT method.
ACS Paragon Plus Environment
8

Page 9 of 21
Langmuir
1
2
3
4
5
6
7
8
9
Figure 2c revealed the N2 adsorption−desorption curve of Pd@GLCs and it belonged to type-
IV isotherm according to IUPAC classification. The Brunauer− Emmett−Teller (BET) surface
area was calculated as 517.6 m2 g−1. The relatively large surface area indicated that the obtained
GLCs has sufficient diffusion paths for mass transfer and abundant active sites to combine
reagents. At the same time, the pore diameter of the GLCs based on Nonlocal density functional
theory (NLDFT) method is∼1 nm (Figure 2d), which were consisted with the fact that interlayer
spacing of the GLCs was caused by the removal of layered silicate RUB-15. The two-
dimensional Pd@GLCs structure and the ∼1 nm spacing ensured mass-transfer rates and high
catalytic permeation for species involved in the catalysis.
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 The XPS survey spectrum of Pd 3d in (a) Pd@GLCs composite and (b) commercial
Pd/C catalyst.
The XPS spectrum of Pd 3d was shown in Figure 3. The spectrum of Pd 3d could be
deconvoluted into four single peaks in both Pd@GLCs composite and commercial Pd/C catalyst
(Figure 3). The peaks at 335.4 eV and 340.6 eV were assigned to Pd (0), and the other two peaks
at 337.2 eV and 342.3 eV were the characteristic peaks of Pd (II) due to the partially oxided
Pd31,32. The intensity of Pd (II) in Pd@GLCs composite was much weaker than that of
ACS Paragon Plus Environment
9

Langmuir
Page 10 of 21
1
2
3
4
5
6
commercial Pd/C, indicating that there was strong interaction between the Pd nanoparticles and
the GLCs, which further protected the Pd nanoparticles from oxidation.
7
8
9
The hydrogenation of styrene was chosen as a model reaction to evaluate the catalytic
performance of the Pd@GLCs composite under 1 MPa hydrogen pressure and at room
temperature. It is observed that the as-prepared Pd@GLCs exhibited outstanding catalytic
performance for the hydrogenation of various kinds of olefins, as shown in Table 1. The
conversion of styrene, 4-methylstyrene, 4-chlorostyrene and 4-methoxystyrene achieved almost
100 % in 15 minutes (Table 1, entry 1-4), giving the corresponding hydrogenated products that
be confirmed by GC and GC-MS. The turnover frequency (TOF) quantifies the specific activity
of a catalytic centre by the number of molecular reactions occurring at the centre per unit time.
The turnover frequency (TOF) was calculated to be 21284 h-1 for entry 1-4. The olefins
conversion in Entry 5 indicated that the hydrogenation rate of cyclohexene was slower than that
of styrene (Table 1, entry 5). The relatively inert reactivity of cyclohexene and its larger tri-
dimensional size might attribute to the lower reaction rate (entry 5). According to the TOF value,
the catalytic performance of Pd@GLCs was better than reported Pd catalyst, such as
Pd@Fe@meso-SiO2 composite33 (TOF=7918 h-1 for styrene hydrogenation) and the commercial
Pd/C in this work (TOF=16180 h-1) at same experiment condition. In addition, the selectivity of
all the reagents was nearly 100%, as no by-product was detected in GC-MS.
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
ACS Paragon Plus Environment
10

Page 11 of 21
Langmuir
1
2
3
4
Table 1 Olefin hydrogenation catalyzed by Pd@GLCs
5
6
7
8
9
Run
1
Olefin
Product Time (min)
15
Conversion (%)
TOF (h-1)
2.1×105
﹥99
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
15
15
60
30
2.1×105
2.1×105
2.1×105
5.3×104
1.0×105
﹥99
﹥99
﹥99
﹥99
﹥99
2
3
4
5
6
Reaction conditions: Olefin (2.5 mmol), Pd @GLCs (5 mg), EtOH (5 mL), 25 °C, under 1.0 MPa H atmosphere. [b] The conversion of
2
reagents was determined by GC, and the identity of the product was ascertained by GC-MS.
Stability is another important parameter for a heterogeneous catalyst. Figure 4a displayed the
conversion of styrene at 15 minutes catalyzed by Pd@GLCs and commercial Pd/C in cycling
tests of styrene hydrogenation. Note that the amount of Pd in Pd@GLCs and commercial Pd/C
was kept to be equal. It can be found that the activity of fresh Pd/C was comparable with fresh
ACS Paragon Plus Environment
11

Langmuir
Page 12 of 21
1
2
3
4
5
6
7
8
9
Pd@GLCs, and 76% conversion was achieved at 15 minutes catalyzed by Pd/C. However, the
conversion of styrene catalysed by commercial Pd/C decreased significantly in the followed
reaction runs, and the conversion dropped to about 32% in the 8th runs. In sharp contrast, the
Pd@GLCs composite showed much better stability in the consecutive reaction runs. The
conversion of styrene still maintained higher than 90 % after eight reaction cycles. In addition,
the concentration of Pd in the supernatant of the hydrogenation reaction system catalyzed by
Pd@GLCs and commercial Pd/C after the reaction was measured by ICP-AES, and it was found
the concentration of Pd was around 316 ppb and 20 ppb in the Pd/C and Pd@GLCs systems,
respectively, indicating that the leaching Pd could be much reduced by the confinement of Pd
NPs in the porous GLCs.
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
100
80
60
40
20
0
a
1
2
3
4 5
Run times
6
7
8
35
30
25
20
15
10
5
pristine Pd@GLCs
After 1st calcination
After 2nd calcination
b
c
100
90
0
0
1 2 3 4 5 6 7 8 9 10
80
70
100 nm
60
1
2
3
4
Run times
5
6
7
8
ACS Paragon Plus Environment
12

Page 13 of 21
Langmuir
1
2
3
4
5
6
7
8
9
Figure 4 (a) The cycling performance of the Pd@GLCs (yellow columns) and commercial Pd/C
(blue columns) catalyst catalyzed styrene hydrogenation as a model reaction. (b) The TEM
image and the size distribution of Pd@GLCs after calcination for two times. (c) The catalytic
activity of Pd@GLCs in the designed cycle experiment.
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
It was known that the surface restructuring and sintering of Pd nanoparticles was prone to
occurring after annealing even at relatively low temperature (above 400 °C ) on support, either
on silica, alumina or graphene.34,35 Supported metal nanoparticles, especially for noble metal
NPs, showed rapid growth if the reaction temperature was very high. We further investigated the
ability of resisting high temperature of Pd@GLCs. In this work, the Pd@GLCs was fabricated
by carbonization at 900 °C for 4 hours under nitrogen atmosphere, thus the Pd@GLCs was
speculated to possess superior thermal stability. In a designed experiment, the fresh Pd@GLCs
was used as catalyst for hydrogenation of styrene once, then calcined at 900 °C for 1 hours under
Ar atmosphere and worked for three times. Next, the Pd@GLCs was calcined for the second
time, and used as catalyst for the following four catalytic reaction. Figure 3b displayed the TEM
image of the final Pd@GLCs after calcination at 900 °C for two times. No obvious change of Pd
NPs (sintering or grownup) could be found on the calcined Pd@GLCs. The diameter of Pd NPs
still kept at 5 2 nm, and the average size was calculated to be 5.3 nm by the size distribution.
The Figure 3c showed the catalytic performance of fresh and calcined Pd@GLCs in eight
consecutive hydrogenation of styrene reaction. The conversion of styrene catalyzed by fresh
Pd@GLCs was 98.2 %, whereas the conversion of styrene was still higher than 88.7% with the
calcined Pd@GLCs catalyst in the 8th reaction runs. The superb ability of resisting high
temperature was closely related with the structure of the Pd@GLCs composite. The confinement
ACS Paragon Plus Environment
13

Langmuir
Page 14 of 21
1
2
3
4
5
6
of the porous GLCs could prevent the Pd NPs from shifting and agglomeration on the surface of
GLCs, and thus help to maintain their high catalytic activity.
7
8
9
The high catalytic activity and superb stability of the Pd@GLCs were attributed to the specific
formation process and structure of the final product with Pd NPs embedded in the graphene-like
carbon. (1) the specific structure that Pd NPs embedded in the GLCs endowed it with
outstanding activity and stability. Lee reported that the edges of graphene layers were the
activated chemisorption sites in the hydrogenation of acetylene.36 The dramatically increased
edge and defects of GLCs layers could adsorb the olefins reagents. The GLCs with nanopores
exhibited stronger binding energies than pristine graphene, and the interactions of graphene with
nanopores and confined Pd NPs were better comparing with the supported metal cluster on
pristine graphene. The intimate contact between GLCs and Pd impacted on the properties of Pd
NPs and promoted the catalytic reaction a lot. (2) The unsaturated carbon atoms exhibited act as
anchor sites to immobilize Pd nanoparticles, which efficiently prevents the Pd NPs aggregation
and leaching. The porous graphene confined the Pd NPs strongly like a pliers, assuring the
cycling and stability of Pd@GLCs. (3) the graphene-like carbon nanosheets generated in the
layered silicate had relatively large surface area. The measured BET surface area of Pd@GLCs
composite was 517.6 m2/g. The large surface area and hydrophobic nature of the GLCs would
adsorb H2 and olefins, facilitating the effective contact between reagents and the spread out of
the products.
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
Conclusions
In summary, the Pd@GLCs composite with the structure that Pd NPs embedded in the pores of
porous GLCs were fabricated by growth and graphitization of carbon source around Pd NPs in
the interlamellar space of layered silicate. The Pd@GLCs composite exhibited not only high
ACS Paragon Plus Environment
14

Page 15 of 21
Langmuir
1
2
3
4
5
6
7
8
9
activity to the hydrogenation of olefins, but also superb stability. The conversion of styrene in
the hydrogenation reaction maintained higher than 91.7% even after calcination of Pd@GLCs at
900 °C for 2 times in the 8th reaction cycle, which was much better than the commercial Pd/C.
The superior catalytic performance of the Pd@GLCs was benefited from their specific structure.
The increased edge and defect of GLCs layers provided more adsorption sites for reagents, while
the interaction between Pd NPs and GLCs enhanced the activity, and the confinement of Pd NPs
by the GLCs much increased their catalytic stability.
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
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI:
Details on the SEM and TEM images of RUB-15, the XRD patterns of Pd@out-GLCs, and the
N2 adsorption−desorption curve of Pd@GLCs..
AUTHOR INFORMATION
Corresponding Author
* Email: xkwang@ncepu.edu.cn
cuizhm@buaa.edu.cn
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
The authors gratefully acknowledge financial support from National Natural Science Foundation
of China (NSFC 51502089, 51772010) and the National Key Research and Development
Program of China (2017YFA0207002).
ACS Paragon Plus Environment
15

Langmuir
Page 16 of 21
1
2
3
4
ABBREVIATIONS
5
6
GLCs, graphene-like carbon nanosheets.
7
8
9
REFERENCES
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)
Qiao, B. T.; Wang, A. Q.; Yang, X. F.; Allard, L. F.; Jiang, Z.; Cui, Y. T.; Liu, J.
Y.; Li, J.; Zhang, T. Single-atom catalysis of CO oxidation using Pt-1/FeOx. Nature Chemistry
2011, 3, 634-641.
(2)
Liang, Y.; Chen, Z.; Yao, W.; Wang, P. Y.; Yu, S. J.; Wang, X. K. Decorating of
Ag and CuO on Cu Nanoparticles for Enhanced High Catalytic Activity to the Degradation of
Organic Pollutants. Langmuir 2017, 33, 7606-7614.
(3)
Zhao, M. T.; Yuan, K.; Wang, Y.; Li, G. D.; Guo, J.; Gu, L.; Hu, W. P.; Zhao, H.
J.; Tang, Z. Y. Metal-organic frameworks as selectivity regulators for hydrogenation reactions.
Nature 2016, 539, 76-80.
(4)
Zhao, M. T.; Deng, K.; He, L. C.; Liu, Y.; Li, G. D.; Zhao, H. J.; Tang, Z. Y.
Core-Shell Palladium Nanoparticle@Metal-Organic Frameworks as Multifunctional Catalysts
for Cascade Reactions. Journal of the American Chemical Society 2014, 136, 1738-1741.
(5)
Bonarowska, M.; Rarog-Pilecka, W.; Karpinski, Z. The use of active carbon
pretreated at 2173K as a support for palladium catalysts for hydrodechlorination reactions.
Catalysis Today 2011, 169, 223-231.
(6)
Chen, Z.; Lu, J. F.; Ai, Y. J.; Ji, Y. F.; Adschiri, T.; Wan, L. J.
Ruthenium/Graphene-like Layered Carbon Composite as an Efficient Hydrogen Evolution
Reaction Electrocatalyst. Acs Applied Materials & Interfaces 2016, 8, 35132-35137.
(7)
Siamaki, A. R.; Khder, A. E. S.; Abdelsayed, V.; El-Shall, M. S.; Gupton, B. F.
Microwave-assisted synthesis of palladium nanoparticles supported on graphene: A highly active
ACS Paragon Plus Environment
16

Page 17 of 21
Langmuir
1
2
3
4
5
6
and recyclable catalyst for carbon-carbon cross-coupling reactions. Journal of Catalysis 2011,
279, 1-11.
7
8
9
(8)
Liu, H. Y.; Zhang, L. Y.; Wang, N.; Su, D. S. Palladium Nanoparticles Embedded
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 the Inner Surfaces of Carbon Nanotubes: Synthesis, Catalytic Activity, and Sinter Resistance.
Angewandte Chemie-International Edition 2014, 53, 12634-12638.
(9)
Jing, Y. Q.; Gui, C. X.; Qu, J.; Hao, S. M.; Wang, Q. Q.; Yu, Z. Z. Silver
Silicate@Carbon Nanotube Nanocomposites for Enhanced Visible Light Photodegradation
Performance. Acs Sustainable Chemistry & Engineering 2017, 5, 3641-3649.
(10) Gan, Y. J.; Sun, L. T.; Banhart, F. One- and two-dimensional diffusion of metal
atoms in graphene. Small 2008, 4, 587-591.
(11) Jin, Z.; Nackashi, D.; Lu, W.; Kittrell, C.; Tour, J. M. Decoration, Migration, and
Aggregation of Palladium Nanoparticles on Graphene Sheets. Chemistry of Materials 2010, 22,
5695-5699.
(12) Xi, J. B.; Sung, H. Y.; Wang, D.; Zhang, Z. Y.; Duan, X. M.; Xiao, J. W.; Xiao,
F.; Liu, L. M.; Wang, S. Confined-interface-directed synthesis of Palladium single-atom
catalysts on graphene/amorphous carbon. Applied Catalysis B-Environmental 2018, 225, 291-
297.
(13) Li, Y. Z.; Yu, Y.; Wang, J. G.; Song, J.; Li, Q.; Dong, M. D.; Liu, C. J. CO
oxidation over graphene supported palladium catalyst. Applied Catalysis B-Environmental 2012,
125, 189-196.
(14) Chen, N.; Huang, X. K.; Qu, L. T. Heteroatom substituted and decorated
graphene: preparation and applications. Physical Chemistry Chemical Physics 2015, 17, 32077-
32098.
ACS Paragon Plus Environment
17

Langmuir
Page 18 of 21
1
2
3
4
5
6
7
8
9
(15) Liu, X.; Meng, C. G.; Han, Y. Defective Graphene Supported MPd12 (M = Fe,
Co, Ni, Cu, Zn, Pd) Nanoparticles as Potential Oxygen Reduction Electrocatalysts: A First-
Principles Study. Journal of Physical Chemistry C 2013, 117, 1350-1357.
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
(16) Su, C. L.; Acik, M.; Takai, K.; Lu, J.; Hao, S. J.; Zheng, Y.; Wu, P. P.; Bao, Q.
L.; Enoki, T.; Chabal, Y. J.; Loh, K. P. Probing the catalytic activity of porous graphene oxide
and the origin of this behaviour. Nature Communications 2012, 3.
(17) Xi, J. B.; Xie, C. Y.; Zhang, Y.; Wang, L.; Xiao, J.; Duan, X. M.; Ren, J. H.;
Xiao, F.; Wang, S. Pd Nanoparticles Decorated N-Doped Graphene Quantum Dots@N-Doped
Carbon Hollow Nanospheres with High Electrochemical Sensing Performance in Cancer
Detection. Acs Applied Materials & Interfaces 2016, 8, 22563-22573.
(18) Dong, Z. P.; Le, X. D.; Liu, Y. S.; Dong, C. X.; Ma, J. T. Metal organic
framework derived magnetic porous carbon composite supported gold and palladium
nanoparticles as highly efficient and recyclable catalysts for reduction of 4-nitrophenol and
hydrodechlorination of 4-chlorophenol. Journal of Materials Chemistry A 2014, 2, 18775-18785.
(19) Cui, X. L.; Long, Y.; Zhou, X.; Yu, G. Q.; Yang, J.; Yuan, M.; Ma, J. T.; Dong,
Z. P. Pd-doped Ni nanoparticle-modified N-doped carbon nanocatalyst with high Pd atom
utilization for the transfer hydrogenation of nitroarenes. Green Chemistry 2018, 20, 1121-1130.
(20) Yin, H. J.; Tang, H. J.; Wang, D.; Gao, Y.; Tang, Z. Y. Facile Synthesis of
Surfactant-Free Au Cluster/Graphene Hybrids for High-Performance Oxygen Reduction
Reaction. Acs Nano 2012, 6, 8288-8297.
(21) Zhang, Z. Y.; Dong, Y.; Wang, L.; Wang, S. Scalable synthesis of a Pd
nanoparticle loaded hierarchically porous graphene network through multiple synergistic
interactions. Chemical Communications 2015, 51, 8357-8360.
ACS Paragon Plus Environment
18

Page 19 of 21
Langmuir
1
2
3
4
5
6
7
8
9
(22) Ye, R. Q.; Peng, Z. W.; Wang, T.; Xu, Y. N.; Zhang, J. B.; Li, Y. L.; Nilewski, L.
G.; Lin, J.; Tour, J. M. In Situ Formation of Metal Oxide Nanocrystals Embedded in Laser-
Induced Graphene. Acs Nano 2015, 9, 9244-9251.
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
(23) Rodriguez-Manzo, J. A.; Cretu, O.; Banhart, F. Trapping of Metal Atoms in
Vacancies of Carbon Nanotubes and Graphene. Acs Nano 2010, 4, 3422-3428.
(24) Zhou, H.; Chen, X. L.; Wang, L.; Zhong, X.; Zhuang, G. L.; Li, X. N.; Mei, D.
H.; Wang, J. G. Effect of graphene with nanopores on metal clusters. Physical Chemistry
Chemical Physics 2015, 17, 24420-24426.
(25) Zhong, B. W.; Zhang, J.; Li, B.; Zhang, B. S.; Dai, C. L.; Sun, X. Y.; Wang, R.;
Su, D. S. Insight into the mechanism of nanodiamond catalysed decomposition of methane
molecules. Physical Chemistry Chemical Physics 2014, 16, 4488-4491.
(26) Huang, L. P.; Santiso, E. E.; Nardelli, M. B.; Gubbins, K. E. Catalytic role of
carbons in methane decomposition for CO- and CO(2)-free hydrogen generation. Journal of
Chemical Physics 2008, 128.
(27) Jang, D.; Idrobo, J. C.; Laoui, T.; Karnik, R. Water and Solute Transport
Governed by Tunable Pore Size Distributions in Nanoporous Graphene Membranes. Acs Nano
2017, 11, 10042-10052.
(28) Chen, Z.; Jia, D. S.; Zhou, Y.; Hao, J.; Liang, Y.; Cui, Z. M.; Song, W. G. In situ
generation of highly dispersed metal nanoparticles on two-dimensional layered SiO2 by
topotactic structure conversion and their superior catalytic activity. Applied Surface Science
2018, 434, 1137-1143.
ACS Paragon Plus Environment
19

Langmuir
Page 20 of 21
1
2
3
4
5
6
7
8
9
(29) Zhang, C. B.; He, H.; Tanaka, K. Catalytic performance and mechanism of a
Pt/TiO2 catalyst for the oxidation of formaldehyde at room temperature. Applied Catalysis B-
Environmental 2006, 65, 37-43.
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
(30) Li, X. H.; Kurasch, S.; Kaiser, U.; Antonietti, M. Synthesis of Monolayer-Patched
Graphene from Glucose. Angewandte Chemie-International Edition 2012, 51, 9689-9692.
(31) Duan, X.; Xiao, M.; Liang, S.; Zhang, Z.; Zeng, Y.; Xi, J.; Wang, S. Ultrafine
palladium nanoparticles supported on nitrogen-doped carbon microtubes as a high-performance
organocatalyst. Carbon 2017, 119, 326-331.
(32) Liu, J.; Hao, J.; Hu, C.; He, B.; Xi, J.; Xiao, J.; Wang, S.; Bai, Z. Palladium
Nanoparticles Anchored on Amine-Functionalized Silica Nanotubes as a Highly Effective
Catalyst. Journal of Physical Chemistry C 2018, 122, 2696-2703.
(33) Yang, S. L.; Peng, L.; Cao, C. Y.; Wei, F.; Liu, J.; Zhu, Y. N.; Liu, C.; Wang, X.
S.; Song, W. G. Preparation of Magnetic Tubular Nanoreactors for Highly Efficient Catalysis.
Chemistry-an Asian Journal 2016, 11, 2797-2801.
(34) Cao, A.; Veser, G. Exceptional high-temperature stability through distillation-like
self-stabilization in bimetallic nanoparticles. Nature Materials 2010, 9, 75-81.
(35) Zhang, Q.; Jiang, L.; Wang, H.; Liu, J. L.; Zhang, J. F.; Zheng, Y. Q.; Li, F. T.;
Yao, C. X.; Hou, S. F. Hollow Graphitized Carbon Nanocage Supported Pd Catalyst with
Excellent Electrocatalytic Activity for Ethanol Oxidation. Acs Sustainable Chemistry &
Engineering 2018, 6, 7507-7514.
(36) Lee, S. Y.; Kwak, J. H.; Han, G. Y.; Lee, T. J.; Yoon, K. J. Characterization of
active sites for methane decomposition on carbon black through acetylene chemisorption.
Carbon 2008, 46, 342-348.
ACS Paragon Plus Environment
20

Page 21 of 21
Langmuir
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
Table of Contents and Synopsis
The confinement of Pd and the increased edge and defect of the unsaturated carbon atoms in
graphene-like carbon nanosheets endowed high efficiency on the hydrogenation of olefins and
outstanding ability of resisting high temperature.
pristine Pd@GLCs
After 1st calcination
After 2nd calcination
100
90
80
70
60
1
2
3
4
Run times
5
6
7
8
50 nm
Pd@GLCs
ACS Paragon Plus Environment
21