Facile fabrication of Cu-based alloy nanoparticles encapsulated within hollow octahedral N-doped porous carbon for selective oxidation of hydrocarbons

Article abstract of DOI:10.1039/c8sc03531h

Hollow carbon materials with versatile chemical compositions and complicated shell architectures hold great promise in heterogeneous catalysis. However, it is a daunting challenge to synthesize metal alloy nanoparticles (NPs) supported by hollow nanostruc

Full text of DOI:10.1039/c8sc03531h

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Facile fabrication of Cu-based alloy nanoparticles encapsulated
within hollow octahedral N-doped porous carbon for selective
oxidation of hydrocarbons
Received 00th January 20xx,
Accepted 00th January 20xx
ab
a
a
a
b
a
Hong Zhong, Yangxin Wang, Caiyan Cui, Feng Zhou, Shuangqi Hu and Ruihu Wang*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Hollow carbon materials with versatile chemical compositions and complicated shell architectures hold great promises in
heterogeneous catalysis, it is a daunting challenge to synthesize metal alloy nanoparticles (NPs) supported by the hollow
nanostructures. Herein, we present a simple approach for facile fabrication of Pd-Cu alloy NPs embedded in hollow
octahedral N-doped porous carbon (Pd-Cu@HO-NPC). The hollow material is derived from HKUST-1 coated by
imidazolium-based ionic polymer (ImIP). Water-sensitive HKUST-1 is simultaneously removed in the process of anion
exchange between bromide in the ImIP shell and tetrachloropalladate in aqueous medium. The released Cu(II) ions and
exchanged Pd(II) ions serve as Cu and Pd sources in subsequent pyrolysis. The resultant Pd-Cu@HO-NPC exhibits high
catalytic activity, selectivity, stability and recyclability in the aerobic oxidation of hydrocarbons. More attractively, the
synthetic strategy is of excellent generality, and could be extended to the synthesis of Cu-based bimetallic and trimetallic
alloy NPs, such as Pt-Cu@HO-NPC and Pd-Pt-Cu@HO-NPC. This work highlights the superiority of water-sensitive metal-
organic frameworks in the ingenious design of hollow carbon materials incorporated with well-dispersed metal alloy NPs.
desirable to develop a simple yet effective strategy to
integrate metal alloy NPs into hollow heteroatom-doped
carbon materials for the design of advanced nanocatalysts.
Introduction
Supported metal nanocatalysts have captured increasing
interests in fine chemical industry, environmental protection
The templating methods are considered as straightforward
1-4
and energy conversion. Hollow carbon materials with large
and versatile approaches for the synthesis of hollow carbon
18-20
nanostructures,
the compatability between template
internal voids and porous shells are one type of promising
5-8
surface and carbon precursors has pivotal influences on the
supports of metal nanoparticles (NPs).
function as a barrier to prevent coalescence of the embedded
metal NPs, and the pores in the shell could provide a highway
The shell could
5
homogenity of carbon shells and the dispersion of metal NPs.
The deliberate selection and modification of carbon precursors
5,9-11 play crucial roles in the final physical and chemical properties
for free diffusion of substrates to access metal active sites.
Considerable progresses have been achieved in the
21
of resulting carbon shells. In the context, the main-chain
12-14
imidazolium-based ionic polymers (ImIPs) are one type of
promising precursors to synthesize heteroatom-doped carbon
materials. The counter halide anions could facilely exchange
preparation of hollow porous materials,
and the
application of several hollow nitrogen-doping carbon materials
incorporated with noble metal NPs has also been explored in
6,15
heterogeneous catalysis. Alloying a parent noble metal with
with various heteroatom-containing and/or metal-containing
22-24
anions,
which provides great opportunities to control the
a non-precrious metal holds a great promise to improve the
loading amount and the types of metal precursors in ImIPs.
Metal and/or metal alloy NPs could be expected after
subsequent pyrolysis without the extra addition of other
heteroatoms and metal ions. Importantly, ImIPs could serve as
robust physical barriers to effectively resist the sintering of
metal NPs during pyrolysis, resulting in uniform distribution
and high dispersion of metal NPs. The incorporated
heteroatoms in the carbon lattice not only modify their
chemical and electrical properties, but also enhance the
interactions between the carbon support and the embedded
catalytic performance and minimize the usage of noble
16,17
metals,
but metal alloy NPs supported by hollow carbon
materials have not been reported owing to their the
complicated fabrication processes with harsh reaction
conditions and/or the use of expensive additives. It is highly
14
metal NPs to trigger superior catalytic performance. Despite
these attractive advantages, as far as we are aware, there is no
report on ImIPs-based hollow materials, one of main reasons is
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that the flexible backbone of ImIPs is liable to deformation and only sustains the original shape of ImIPs shells, but also serves
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DOI: 10.1039/C8SC03531H
even collapse after the removal of templates. It is a daunting as the precursors of carbon and/or metal NPs. After the
challenge to construct hollow ImIPs for promising application carbonization, the hollow ImIPs containing modifiable metal
as the precursors of supported metal nanocatalysts.
ions and heteroatoms could be topotactically transformed into
Metal-organic frameworks (MOFs), assembled by metal heteroatom-doped porous carbon materials containing
ions/clusters and organic ligands, are suitable templates for homogeneously embedded metal alloy NPs, which brings out
the construction of hollow structures owing to their facile unique chemical and physical properties that are not
synthesis, fascinating morphologies, various compositions and attainable from single MOF or ImIPs precursors.
25,26
tuneable particle sizes.
Although MOFs have been
As a proof-of-concept study, herein, we developed a facile
extensively used as sacrificial templates to fabricate hollow and versatile method for the synthesis of well-dispersed M-Cu
27-30
metal and/or metal oxide composites,
hollow carbon alloy NPs embedded in hollow octahedral nitrogen-doped
materials derived from MOFs templates have been rarely porous carbon (M-Cu@HO-NPC, M = Pd, Pt and Pd-Pt) using
reported, more efforts are needed to explore the advantages water-sensitive HKUST-1 as a template. They were readily
of MOFs templates in the synthesis of hollow carbon materials prepared through topotactic transformation of hollow M-
with versatile chemical compositions and complicated shell Cu@HO-ImIPs, which were obtained through anion exchange
architectures. It is well known that most of MOFs are instable of core-shell-structured HKUST-1@ImIP with metal-containing
in water, the instability provides tremendous opportunity for anions in water. To the best of our knowledge, this is first
disassembly of MOFs cores in MOF@ImIP core-shell structures report about metal alloy NPs supported by hollow nitrogen-
during anionic exchange of ImIPs under mild conditions, doped carbon materials. Pd-Cu@HO-NPC exhibits high
requiring no additional procedures for the removal of MOFs catalytic activity, selectivity and recyclability in the oxidation of
31,32
templates.
The released metal ions and organic ligands hydrocarbons using air as an oxidant in the absence of co-
could be located in the pores of the hollow shell, which not catalysts and additives.
Results and Discussion
Scheme 1. Schematic illustration for the synthesis of Pd-Cu@HO-NPC.
HKUST-1 has been widely employed as a self-sacrificial
Scanning electron microscopy (SEM) images reveal that
33,34
template in the preparation of metal oxide composites,
but HKUST-1 is octahedron-shaped nanocrystals with the edge
its application in the synthesis of hollow carbon materials has lengths in the range from 200 to 400 nm (Fig. 1a). After coated
not reported so far. As shown in Scheme 1, HKUST-1 was with ImIP, the octahedral morphology is retained in HKUST-
prepared through the assembly of 1,3,5-benzenetricarboxylic 1@ImIP, but the edge lengths are increased to 300-600 nm
35
acid (H3BTC) and Cu(NO3)2·3H2O. ImIP was readily coated on (Fig. 1b). Thus, the thickness of the ImIP shell in HKUST-
the surface of HKUST-1 through the quaternization reaction of 1@ImIP is in the range of 50-100 nm. Notably, the morphology
1,2,4,5-tetrakis(bromomethyl)benzene
and
1,3,5-tri(1H- and size of Pd-Cu@HO-ImIP are almost identical with that of
imidazol-1-yl)benzene to give rise to HKUST-1@ImIP core-shell HKUST-1@ImIP, indicating the shell structure is well
material, subsequent anion exchange between bromide in the maintained after the decomposition of HKUST-1 (Fig. 1c).
ImIP shell and tetrachloropalladate generated hollow Pd- Transmission electron microscopy (TEM) images show that
Cu@HO-ImIP, in which the HKUST-1 template was HKUST-1@ImIP possesses an octahedral core-shell structure
decomposed simultaneously during anion exchange, no (Fig. 1d). ImIP is homogenously coated on the surface of
tedious steps and hazardous reagents were employed for the HKUST-1 nanocrystals with a thickness of 50-100 nm, which is
removal of templates when compared with conventional hard- consistent with the SEM results. Interestingly, Pd-Cu@HO-ImIP
5,6,12
template methods.
exhibits a hollow octahedral structure (Fig. 1e), no HKUST-1
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residues are observed. The shape and size of the inner cavity HKUST-1@ImIP (Fig. 2b), no additional diffractioVniepweAartikcsle fOrnolimne
DOI: 10.1039/C8SC03531H
are matched well with those of the original HKUST-1 the ImIP shell are detected. However, the characteristic
nanocrystals, no structural collapse and/or deformation are diffraction peaks of HKUST-1 totally disappear in the XRD
observed in the external shells after the removal of kernel pattern of Pd-Cu@HO-ImIP, which further reveals that the
template. To the best of our knowledge, this is first report decomposition of HKUST-1 octahedral nanocrystals after anion
about hollow ionic polymers with flexible backbones. The exchange.
outstanding stability of hollow Pd-Cu@HO-ImIP is probably
The porous properties of HKUST-1, HKUST-1@ImIP and Pd-
attributed to the assistance of released metal ions and organic Cu@HO-ImIP were investigated by N2 adsorption/desorption
ligands from HKUST-1, they reside in the pores of the shell at 77 K (Fig. 2c). A rapid nitrogen uptake at very low relative
through electrostatic and coordination interactions to sustain pressure (P/P0 < 0.01) in HKUST-1 and HKUST-1@ImIP indicates
22,36
37
Notably, the that the presence of extensive micropores, while the
the original shape of hollow ImIP shells.
hollow octahedral structure was dramatically squashed when nitrogen uptake in Pd-Cu@HO-ImIP is negligible. The BET
Pd-Cu@HO-ImIP was washed with aqueous EDTA-2Na solution surface areas of HKUST-1 and HKUST-1@ImIP are 1776 and
2
). The high-annular dark-field 816 m /g, respectively. As expected, the BET surface area of
to remove metal ions (Fig. S1
†
2
-1
scanning TEM (HAADF-STEM) images further confirm hollow Pd-Cu@HO-ImIP is as low as 37 m g owing to both the
octahedral structure of Pd-Cu@HO-ImIP (Fig. 1f). The flexibility of ImIP shell and the pores filling by metal ions and
22
corresponding element mapping images show that Cu (orange) counter anions. The pore size distribution reveals that the
and Pd (green) are co-existent in the octahedral shell (Fig. 1g), predominant pores in HKUST-1 and HKUST-1@ImIP are
they are derived from exchanged tetrachloropalladate ions micropores (Fig. 2d), while the pores in Pd-Cu@HO-ImIP are in
2+
and released Cu
ions in HKUST-1, respectively. The the range of mesopores, which are consistent with the results
distribution between Pd and Cu is identical with each other, of their nitrogen adsorption-desorption isotherms.
which is conducive to in situ growth of Pd-Cu alloy NPs during
22
subsequent pyrolysis.
Fig. 2 (a) FTIR spectra, (b) XRD patterns, (c) N adsorption/desorption isotherms
2
and (d) pore size distribution for HKUST-1, HKUST-1@ImIP and Pd-Cu@HO-ImIP.
Fig. 1 SEM images for (a) HKUST-1, (b) HKUST-1@ImIP and (c) Pd-Cu@HO-ImIP.
Considering unique hollow octahedral structure, high
(d) TEM image of HKUST-1@ImIP. (e) TEM image, (f) HAADF-STEM and (g) EDX
mapping images of Pd-Cu@HO-ImIP.
concentrations of carbon and nitrogen species as well as
homogeneous distribution of Pd and Cu in Pd-Cu@HO-ImIP, its
o
topotactic transformation at 500 C under an inert atmosphere
gave rise to hollow octahedral nitrogen-doped porous carbon
incorporated with Pd-Cu alloy NPs (Pd-Cu@HO-NPC). SEM and
TEM analyses indicate that Pd-Cu@HO-NPC possesses a similar
hollow octahedral morphology to Pd-Cu@HO-ImIP (Fig. 3), but
the edge lengths and the shell thickness are decreased to 250-
In the Fourier-transform infrared (FTIR) spectrum of HKUST-
1@ImIP, the simultaneous appearance of the characteristic
peaks of HKUST-1 and ImIP reveals their successful
combination in the core-shell material (Fig. 2a). An extra peak
-1
at 1711 cm , which corresponds to the carboxylate group of
35
BTC, occurs in the FTIR spectrum of Pd-Cu@HO-ImIP,
500 nm and 30-60 nm, respectively, which is probably
indicating the decomposition of HKUST-1 and the
incorporation of the released BTC into the polymer shell,
which serves as adsorption site of Cu(II). Thermogravimetric
analysis (TGA) curves show that HKUST-1@ImIP possesses a
lower thermal stability than HKUST-1 owing to the presence of
the ImIP shell, and Pd-Cu@HO-ImIP begins to decompose after
38,39
attributed to volume shrinking during pyrolysis.
HAADF-
STEM images of Pd-Cu@HO-NPC further confirm the
maintenance of the hollow structure with an octahedral cavity
(Fig. 3d). The metal NPs in the carbon shells are assigned to Pd-
Cu alloy formed by the co-reduction of Pd and Cu cations
during pyrolysis. The average size of well-dispersed Pd-Cu alloy
o
200 C (Fig. S2
22
). Powder X-ray diffraction (XRD) patterns
†
NPs is 8.2 ± 0.8 nm (Fig. S3
†
), which is comparable with those
indicate that the crystallinity of HKUST-1 is well retained in
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in metal NPs prepared through the pyrolysis of carbon Pd(0) to Pd(II) is 1.26 as determined by the rVaietwioArtoicfle Othnelinier
6,40
precursors without using extra reductive agents.
Pd-Cu alloy NPs are uniformly embedded in the porous carbon peaks are ascribed to Cu 2p3/2 and Cu 2p1/2 of Cu(0) and Cu(II)
shell, no metals NPs are observed on the exterior surface of species, respectively (Fig. 4c). The binding energy peaks at
the carbon shell and/or in the hollow cavity, which is 932.18 and 957.23 eV are assigned to Cu(0) 2p3/2 and 2p1/2
Notably, relative peak areas. In Cu 2p XPS spectruDmO,I:t1w0o.10s3e9t/sC8oSfCd0o3u53b1lHe
,
conducive to suppressing the leaching and agglomeration of respectively, while the peaks at 934.61 and 954.40 eV
6
active species in the catalytic reactions. The corresponding correspond to Cu(II) 2p3/2 and 2p1/2, respectively. Impressively,
element mapping images show that the distribution between the Pd(0) 3d5/2 and Cu(0) 2p3/2 peaks shift negatively by 0.06
Pd and Cu is identical with each other, revealing the alloying and 0.11 eV, respectively, when compared with those in free
45
state of bimetallic Pd-Cu NPs, which is further demonstrated Pd (335.4 eV) and Cu (932.29 eV). The negative shift probably
by their line-scan analyses (Fig. 3e).The high-resolution TEM results from the strong interaction between Pd-Cu alloy NPs
image shows the intervals between adjacent lattice fringes are and nitrogen-doped carbon, which makes Pd(0) and Cu(0)
14
0.219 nm (Fig. 3c), which corresponds to the (111) lattice plane species more electron-rich than free Pd and Cu. In the high-
41
of Pd-Cu alloy. In the XRD pattern of Pd-Cu@HO-NPC (Fig. S4 resolution N 1s XPS spectrum (Fig. 4d), the presence of
†
), the diffraction peaks at 41.1, 48.2, 69.7 and 83.9 can be pyridinic N (398.5 eV), pyrrolic N (399.7 eV) and graphitic N
46
indexed as the (111), (200), (220) and (311) facets of face- (401.1 eV) could be clearly identified. Raman spectrum
42,43
centered cubic (fcc) Pd-Cu alloy, respectively.
Inductively shows the characteristic D-band and G-band at 1345 and 1577
-1
coupled plasma (ICP) analyses show that Cu and Pd contents cm , respectively (Fig. S6
†
). The relative ratio of ID/IG is 0.98,
-1
are 0.83 and 0.39 mmol·g , respectively. The N content in Pd- indicating that the carbon species in Pd-Cu@HO-NPC possess a
-1
Cu@HO-NC is 5.8 mmol·g as determined by elemental high graphitization degree, which is favorable for electron
analysis.
mobility and stabilization of the reactive intermediates in the
47
radical-involved catalytic systems.
Fig. 3 (a) SEM image, (b, c) TEM images, (d) HAADF-STEM and EDX mapping
images, and (e) the line-scan analyses of Pd-Cu@HO-NPC.
The N2 adsorption/desorption isotherms and relevant pore
size distribution show that Pd-Cu@HO-NPC possesses
predominantly mesopores (Fig. 4a), the BET surface area and
Fig. 4 (a) N adsorption/desorption isotherms and pore size distribution (inset),
2
(b) Pd 3d, (c) Cu 2p and (d) N 1s XPS spectra for Pd-Cu@HO-NPC.
2
-1
3
-1
total pore volume are 121 m g and 0.21 cm g , respectively.
The combination of the mesopores with large hollow cavity
generated by the self-sacrificial HKUST-1 is favorable for mass
transfer, resulting in ready availability of the catalytic active
sites to substrate molecules and rapid release of the products
The attractive advantages of the hollow octahedral
nanostructure incorporated with well-dispersed Pd-Cu alloy
NPs have encouraged us to explore its catalytic application.
The selective oxidation of hydrocarbons is an essential
reaction in organic synthesis and industrial chemistry, it has
usually required the use of various oxidants, such as toxic
20
in heterogeneous catalytic reaction. The surface composition
and valence state of Pd-Cu@HO-NPC were examined by X-ray
photoelectron spectroscopy (XPS) measurements. In the XPS
48
metal oxides, peroxides and ozone. Compared with those
survey spectrum (Fig. S5
†
), the binding energy peaks around
oxidants, air is undoubtedly the most ubiquitous, atom-
economical and environmentally benign oxidant. However, air
284.1, 335.9, 399.7, 532.0 and 931.9 eV are assigned to C 1s,
44
Pd 3d, N 1s, O 1s and Cu 2p, respectively. The deconvolution
3
is unreactive and difficult to activate strong sp C-H bonds of
of Pd 3d XPS spectrum presents two sets of double peaks
corresponding to Pd 3d5/2 and Pd 3d3/2 (Fig. 4b). The binding
energy peaks at 335.34 and 340.68 eV correspond to Pd(0)
3d5/2 and 3d3/2, respectively, while the peaks at 337.44 and
342.68 eV are attributed to Pd(II) species. The ratio of surface
hydrocarbon in the transformation. Recently, various
supported noble metal nanocatalysts, such as palladium,
platinum, ruthenium and gold, have been reported in selective
oxidation of hydrocarbons, but the catalytic systems are
subjected to high temperatures, high pressures and/or the use
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47,49-51
of the additives.
Alloying a parent noble metal with a aggregation and migration of Pd-Cu alloy NPs in the
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DOI: 10.1039/C8SC03531H
second metal offers numerous opportunities to improve hydrocarbon oxidation.
catalytic activities, but the application of alloy metal NPs in this
52
chemical tranformation has seldom been reported.
The oxidation of indane was evaluated initially using air as
an oxidant in the presence of 0.2 mol% palladium under
solvent-free conditions. Kinetic profiles show that indane
consumption and 1-indanone formation increased rapidly in
the first 8 h, and 86 % conversion of indane was achieved in 24
h (Fig. 5a). The selectivity of 1-indanone remains above 99% in
the entire catalytic process. The control experiments were also
performed. When the indane oxidation was carried out either
in the absence of Pd-Cu@HO-NPC (Table 1, entry 2) or under
N2 atmosphere (entry 3), negligible product was detected in 24
h. As expected, the indane conversion decreased to 50% when
hollow Pd-Cu@HO-NPC was replaced by dense Pd-Cu@NPC
Fig. 6 (a) SEM, (b, c, d) TEM, (e) HAADF-STEM images and (f) the line-scan
(entry 4). The use of the commercial Pd/C afforded a 33 % analyses for Pd-Cu@HO-NPC-5run.
conversion of indane under the same conditions (entry 5). The
heterogeneous behavior of this catalytic system was verified
To extend application scope of the catalytic system, the
by hot filtration experiment. After the reaction was carried out
for 6 h, the catalyst was quickly removed by filtration, and the
reaction of the filtrate was continued for additional 18 h, both
conversion and selectivity show negligible variation (entries 6
and 7).
oxidation reactions of various hydrocarbons were examined
using air as an oxidant. As shown in Table 1, a conversion of
75 % was obtained in the oxidation of tetralin, a key
intermediate in the commercial production of α-naphthol
48,52
(entry 8).
Diphenylmethane and fluorene with a large
molecular size could be transformed into diphenylmethanone
and fluorenone in good conversions of 71 % and 89 %,
respectively (entries 9 and 10). Impressively, the C-H bond of
ethylbenzene was also selectively oxidized, acetophenone was
obtained in a 38 % GC yield (entry 11). The electron-rich 1-
ethyl-4-methoxybenzene and electron-deficient 1-ethyl-4-
nitrobenzene provided the corresponding procucts in 44 % and
29 % GC yields, respectivley (entries 12 and 13), indicating the
electron-donating groups in ethylbenzene are more favorable
for C-H bond activation than the electron-withdrawing groups
in this catalytic system. Besides aromatic molecules, Pd-
Cu@HO-NPC is also effective for the oxidation of aliphatic
molecules. 48 % conversion and 89 % selectivity were achieved
in 24 h when cyclohexene was used as a substrate (entry 14).
These results show that Pd-Cu@HO-NPC is a promising catalyst
Fig. 5 (a) The kinetic curve and (b) recyclability for Pd-Cu@HO-NPC in the
oxidation reaction of indane. Reaction conditions: indane (8.77 mmol), catalyst
-1
o
([Pd] = 0.2 mol%), air flow (5 mL min ), 120 C and 24 h.
Pd-Cu@HO-NPC shows excellent recyclability and stability in
the aerobic oxidation of indane. After the reaction finished,
the catalyst was separated by centrifugation, and directly used
for next run. Pd-Cu@HO-NPC could be used at least five runs
without detectable loss of catalytic activity and selectivity (Fig.
5b), the total turnover number (TON) exceeds 2125. The
recovered Pd-Cu@HO-NPC after the consecutive reaction for
five runs is denoted as Pd-Cu@HO-NPC-5run. As shown in Fig.
3
for the aerobic oxidation of allylic- or benzyl sp C-H bonds.
Interestingly, when the oxidation of indane was tested in the
presence of p-benzoquinone, which is
a typical radical
scavenger. The reaction was totally suppressed to give a
negligible conversion (entry 15), indicating that the reaction
proceeds through radical intermediates. The attractive
catalytic performance of Pd-Cu@HO-NPC in selective aerobic
oxidation of hydrocarbons is mainly attributed to its favorable
structure features: 1) The hollow cavity and mesoporous shell
are beneficial for mass transfer/diffusion of substrates and
products; 2) The uniform distribution of Pd-Cu alloy NPs in
mesoporous shell makes them readily interact with
hydrocarbons and oxygen molecules; 3) The incorporation of
nitrogen atoms into carbon shell not only makes Pd-Cu alloy
NPs electron-rich, but also significantly enhances the
interactions between the carbon shell and the embedded
metal NPs; 4) The high graphitization of the carbon shell
6 and S7
†
, the Raman spectrum, SEM and TEM images of Pd-
Cu@HO-NPC-5run are almost identical with that of as-
prepared sample. The most strikingly, Pd-Cu alloy NPs are still
uniformly embedded in hollow carbon material with the
retention of their original size (Fig. S8
†
), there are no metals
NPs on the exterior of the porous carbon shell and/or in the
hollow cavity. Inductively coupled plasma (ICP) analyses show
Pd and Cu contents in Pd-Cu@HO-NPC-5run are the same as
those in as-synthesized catalyst. These results have
demonstrated that hollow HO-NPC could effectively inhibit the
leaching of catalytic active species and prevent the
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benefits the electron mobility and radical stabilization during and trimetallic Pd-Pt-Cu alloy NPs supported by hollow
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catalytic oxidation of hydrocarbons.
nitrogen-doped carbon shells. TEM analDyOseI:s10in.1d03ic9a/Cte8StCh0a3t53P1tH-
Cu@HO-NPC and Pd-Pt-Cu@HO-NPC also possess hollow
octahedral morphology, the edge lengths and shell thickness
are in the range of 200-500 nm and 30-60 nm, respectively (Fig.
7). The alloy NPs are tightly embedded in the HO-NPC shell,
their size, location and distribution are very similar to those in
Pd-Cu@HO-NPC.
Table 1. The aerobic oxidation of hydrocarbons catalysed by Pd-Cu@HO-NPC.
b
b
Conv.
(%)
Select.
Entrya
Substrate
Product
(%)
1
86
< 1
-
>99
c
2
-
-
d
3
e
4
50
>99
f
5
33
96
g
6
31
31
75
71
>99
>99
>97
>99
g
7
Fig. 7 TEM images for (a) Pt-Cu@HO-ImIP, (b, c) Pt-Cu@HO-NPC, (d) Pd-Pt-
Cu@HO-ImIP and (e, f) Pd-Pt-Cu@HO- NPC.
8
9
Conclusions
HKUST-1@ImIP core-shell materials have been fabricated and
employed as promising precursors of Cu-based alloy NPs
embedded in hollow nitrogen-doped porous carbon. HKUST-1
is simultaneously decomposed when metal-containing anions
are introduced into the ImIP shell through anion exchange in
water, no tedious steps and hazardous reagents are required
for the removal of templates, the morphology and size of the
flexible shell are well maintained. To the best of our
knowledge, this is first report on hollow polymers with flexible
backbones. The released Cu ions and exhanged metal ions
reside in the pore of the ImIP shell, subsequent topotactic
transformation generates hollow nitrogen-doped porous
carbon incorporated with Cu-based bimetallic or trimetallic
alloy NPs. The unique hollow structure endows metal alloy NPs
with high catalytic activity and outstanding durability in
selective aerobic oxidation of hydrocarbons. In summary, this
study develops a simple, green and general method for facile
synthesis of Cu-based alloy NPs supported by hollow carbon
materials, the synthetic strategy holds great promises for the
synthesis of a broad range of hollow carbon nanostructures
owing to the availability of a large family of MOFs and ionic
polymers, further investigation for other metal alloy NPs
supported by various hollow heteroatom-doped carbon
materials is on progress.
10
89
>99
11
12
38
44
>99
>93
13
14
29
>95
48
89
h
15
< 0.3
-
a
Reaction conditions: hydrocarbons (1 mL), catalyst ([Pd] = 0.2 mol%), air
-1
flow (5 mL min ), 120 C and 24 h. GC yield. The absence of catalysts;
o
b
c
d
e f
Pd-Cu@NPC was used as catalyst; Under N2 atmosphere; Pd/C was used
g h
as catalyst; Filtration experiment; p-Benzoquinone was added (1 mmol).
This strategy for the synthesis of Pd-Cu@HO-NPC exhibits
excellent generality, and can be extended to the fabrication of
other Cu-based bimetallic and trimetallic alloy NPs. The
treatment of HKUST-1@ImIP with aqueous K2PtCl6 and
Na2PdCl4/K2PtCl6 solutions generated hollow Pt-Cu@HO-ImIP
and Pd-Pd-Cu@HO-ImIP, respectively (Fig. 7a and 7d). Their
morphology and size are almost identical with that of Pd-
Cu@HO-ImIP, suggesting the change of exchanged metal ions
has no obvious effects on the flexible ImIP shells. Notably, the
pyrolysis of Pt-Cu@HO-ImIP and Pd-Pd-Cu@HO-ImIP under
inert atmosphere gave rise to corresponding bimetallic Pt-Cu
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21603228, 21673241 and 21471151),
and the Strategic Priority Research Program of the Chinese
Academy of Sciences (XDB20000000).
6 | J. Name., 2012, 00, 1-3
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ARTICLE
29 X. Zhang, W. Qin, D. Li, D. Yan, B. Hu, Z. Sun andVLie.wPAarntic,leCOhnelmine.
Notes and references
Commun. 2015, 51, 16413-16416.
DOI: 10.1039/C8SC03531H
1
G. H. Wang, J. Hilgert, F. H. Richter, F. Wang, H. J. Bongard, B.
Spliethoff, C. Weidenthaler and F. Schüth, Nat. Mater., 2014,
13, 293-300.
30 J. Yang, F. Zhang, H. Lu, X. Hong, H. Jiang, Y. Wu and Y. Li,
Angew. Chem. Int. Ed., 2015, 127, 11039-11043.
31 P. Guo, D. Dutta, A. G. Wong-Foy and D. W. Gidley, J. Am.
Chem. Soc., 2015, 137, 2651-2657.
2
X. H. Li and M. Antonietti, Chem. Soc. Rev., 2013, 42, 6593-
6604.
32 Z. Hasan and S. H. Jhung, J. Hazard. Mater., 2015, 283, 329-
339.
3
4
L. Liu and A. Corma, Chem. Rev., 2018, 118, 4981-5079.
S. Li, A. Tuel, D. Laprune, F. Meunier and D. Farrusseng, Chem.
Mater., 2015, 27, 276-282.
33 S. Zhang, H. Liu, P. Liu, Z. Yang, X. Feng, F. Huo and X. Lu,
Nanoscale, 2015, 7, 9411-9415.
5
H. Yang, S. J. Bradley, A. Chan, G. I. N. Waterhouse, T. Nann, P.
E. Kruger and S. G. Telfer, J. Am. Chem. Soc., 2016, 138,
11872-11881.
34 C. Yu, J. Cui, Y. Wang, H. Zheng, J. Zhang, X. Shu, J. Liu, Y.
Zhang and Y. Wu, Appl. Surf. Sci., 2018, 439, 11-17.
35 J. L. Zhuang, D. Ceglarek, S. Pethuraj and A. Terfort, Adv. Funct.
Mater., 2011, 21, 1442-1447.
6
7
8
L. Chen, L. Zhang, Z. Chen, H. Liu, R. Luque and Y. Li, Chem. Sci.,
2016, 7, 6015-6020.
36 H. Zhao, X. Li, L. Li and R. Wang, Small, 2015, 11, 3642-3647.
37 H. Zhong, C. Liu, Y. Wang, R. Wang and M. Hong, Chem. Sci.,
2016, 7, 2188-2194.
B. Li, H. Nam, J. Zhao, J. Chang, N. Lingappan, F. Yao, T. H. Lee
and Y. H. Lee, Adv. Mater., 2017, 29, 1605083.
W. Zhang, X. Jiang, Y. Zhao, A. Carne-Sanchez, V. Malgras, J.
Kim, J. H. Kim, S. Wang, J. Liu, J. S. Jiang, Y. Yamauchi and M.
Hu, Chem. Sci., 2017, 8, 3538-3546.
38 J. S. Jang, W. T. Koo, S. J. Choi and I. D. Kim, J. Am. Chem. Soc.,
2017, 139, 11868-11876.
39 J. Tang, R. R. Salunkhe, J. Liu, N. L. Torad, M. Imura, S.
Furukawa and Y. Yamauchi, J. Am. Chem. Soc., 2015, 137,
1572-1580.
9
J. Liu, N. P. Wickramaratne, S. Z. Qiao and M. Jaroniec, Nat.
Mater., 2015, 14, 763-774.
10 C. Chen, A. Wu, H. Yan, Y. Xiao, C. Tian and H. Fu, Chem. Sci.,
2018, 9, 4746-4755.
40 Z. P. Dong, X. D. Le, Y. S. Liu, C. X. Dong and J. Ma, J. Mater.
Chem. A, 2014, 2, 18775-18785.
11 W. Luo, M. Sankar, A. M. Beale, Q. He, C. J. Kiely, P. C. A.
Bruijnincx and B. M. Weckhuysen, Nat. Commun., 2015, 6,
6540.
41 K. Mori, H. Tanaka, M. Dojo, K. Yoshizawa and H. Yamashita,
Chem. Eur. J., 2015, 21, 12085-12092.
42 M. Yuan, A. Liu, M. Zhao, W. Dong, T. Zhao, J. Wang and W.
Tang, Sens. Actuators, B Chem., 2014, 190, 707-714.
43 F. Yang, Y. Zhang, P. F. Liu, Y. Cui, X. R. Ge and Q. S. Jing, Int. J.
Hydrogen Energy, 2016, 41, 6773-6780.
12 H. Pan, Z. Cheng, Z. Xiao, X. Li and R. Wang, Adv. Funct. Mater.,
2017, 27, 1703936.
13 J. Yang, F. Zhang, H. Lu, X. Hong, H. Jiang, Y. Wu and Y. Li,
Angew. Chem. Int. Ed., 2015, 54, 10889-10893.
14 L. He, F. Weniger, H. Neumann and M. Beller, Angew. Chem.
Int. Ed., 2016, 55, 12582-12594.
44 M. Hronec, K. Fulajtárová, I. Vávra, T. Soták, E. Dobrocka and
M. Micusík, Appl. Catal. B: Environ., 2016, 181, 210-219.
45 X. Du, S. Luo, H. Du, M. Tang, X. Huang and P. K. Shen, J.
Mater. Chem. A, 2016, 4, 1579-1585.
15 R. Jia, J. Chen, J. Zhao, J. Zheng, C. Song, L. Li and Z. Zhu, J.
Mater. Chem., 2010, 20, 10829-10834.
46 L. Li, L. Li, C. Cui, H. Fan and R. Wang, ChemSusChem, 2017, 10,
4921-4926.
16 Q. L. Zhu, J. Li and Q. Xu, J. Am. Chem. Soc., 2013, 135, 10210-
10213.
47 X. Lin, Z. Nie, L. Zhang, S. Mei, Y. Chen, B. Zhang, R. Zhu and Z.
Liu, Green Chem., 2017, 19, 2164-2173.
17 L. T. Guo, Y. Y. Cai, J. M. Ge, Y. N. Zhang, L. H. Gong, X. H. Li, K.
X. Wang, Q. Z. Ren, J. Su and J. S. Chen, ACS Catal., 2015, 5,
388-392.
48 P. Zhang, Y. Gong, H. Li, Z. Chen and Y. Wang, Nat. Commun.,
2013, 4, 1593.
18 J. Tang, J. Liu, R. R. Salunkhe, T. Wang and Y. Yamauchi, Chem.
Commun., 2016, 52, 505-508.
49 T. Maegawa, A. Akashi, K. Yaguchi, Y. Iwasaki, M. Shigetsura, Y.
Monguchi and H. Sajiki, Chem. Eur. J., 2009, 15, 6953-6963.
50 L. Kesavan, R. Tiruvalam, M. H. A. Rahim, M. I. B. Saiman, D. I.
Enache, R. L. Jenkins, N. Dimitratos, J. A. Lopez-Sanchez, S. H.
Taylor, D. W. Knight, C. J. Kiely and G. J. Hutchings, Science,
2011, 331, 195-199.
19 Y. Wang, L. Yu and X. W. Lou, Angew. Chem. Int. Ed., 2016, 55,
14668-14672.
20 S. Yang, L. Peng, P. Huang, X. Wang, Y. Sun, C. Cao and W.
Song, Angew. Chem. Int. Ed., 2016, 55, 4016-4020.
21 S. Yang, Y. Zhu, C. Cao, L. Peng, S. Li, D. Zhai and W. Song,
Nanoscale, 2017, 9, 13538-13545.
51 D. Deng, Y. Yang, Y. Gong, Y. Li, X. Xu and Y. Wang, Green
Chem., 2013, 15, 2525-2531.
22 Y. Gong, H. Zhong, W. Liu, B. Zhang, S. Hu and R. Wang, ACS
Appl. Mater. Interfaces, 2018, 10, 776-786.
52 M. Takahashi, H. Koizumi, W. J. Chun, M. Kori, T. Imaoka and K.
Yamamoto, Sci. Adv., 2017, 3, e1700101.
23 B. Xin and J. Hao, Chem. Soc. Rev., 2014, 43, 7171-7187.
24 B. Xin, C. Jia and X. Li, Curr. Org. Chem., 2016, 20, 616-628.
25 L. Zhang, H. B. Wu and X. W. Lou, J. Am. Chem. Soc., 2013, 135,
10664-10672.
26 J. Chun, S. Kang, N. Park, E. J. Park, X. Jin, K. D. Kim, H. O. Seo,
S. M. Lee, H. J. Kim, W. H. Kwon, Y. K. Park, J. M. Kim, Y. D. Kim
and S. U. Son, J. Am. Chem. Soc., 2014, 136, 6786-6789.
27 F. Zou, Y. M. Chen, K. Liu, Z. Yu, W. Liang, S. M. Bhaway, M.
Gao and Y. Zhu, ACS Nano, 2016, 10, 377-386.
28 J. Shao, Z. Wan, H. Liu, H. Zheng, T. Gao, M. Shen, Q. Qu and H.
Zheng, J. Mater. Chem. A, 2014, 2, 12194-12200.
This journal is © The Royal Society of Chemistry 20xx
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Chemical Science
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DOI: 10.1039/C8SC03531H
Table of Contents
HKUST-1 serves as a template of imidazolium-based ionic polymer, anion exchange and
subsequent topotactic transformation generate hollow nitrogen-doped porous carbon
incorporated with Cu-based alloy nanoparticles.
1