Ni-Pt nanoparticles growing on metal organic frameworks (MIL-96) with enhanced catalytic activity for hydrogen generation from hydrazine at room temperature

Article abstract of DOI:10.1039/c5dt00493d

Well-dispersed bimetallic Ni-Pt nanoparticles (NPs) with different compositions have been successfully grown on the MIL-96 by a simple liquid impregnation method using NaBH₄ as the reducing agent. Powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, N₂ adsorption-desorption, and inductively coupled plasma-atomic emission spectroscopy measurements were employed to characterize the NiPt/MIL-96. Catalytic activity of NiPt/MIL-96 catalysts was tested in the hydrogen generation from the aqueous alkaline solution of hydrazine at room temperature. These catalysts are composition dependent on their catalytic activity, while Ni₆₄Pt₃₆/MIL-96 exhibits the highest catalytic activity among all the catalysts tested, with a turnover frequency value of 114.3 h^-1 and 100% hydrogen selectivity. This excellent catalytic performance might be due to the synergistic effect of the MIL-96 support and NiPt NPs, while NiPt NPs supported on other conventional supports, such as SiO₂, carbon black, γ-Al₂O₃, poly(N-vinyl-2-pyrrolidone) (PVP), and the physical mixture of NiPt and MIL-96, all of them exhibit inferior catalytic activity compared to that of NiPt/MIL-96. This journal is

Full text of DOI:10.1039/c5dt00493d

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Ni–Pt nanoparticles growing on metal organic
frameworks (MIL-96) with enhanced catalytic
activity for hydrogen generation from hydrazine at
room temperature†
Cite this: DOI: 10.1039/c5dt00493d
Lan Wen,a Xiaoqiong Du,a Jun Su,b Wei Luo,*a,c Ping Cai*a and Gongzhen Chenga
Well-dispersed bimetallic Ni–Pt nanoparticles (NPs) with different compositions have been successfully
grown on the MIL-96 by a simple liquid impregnation method using NaBH4 as the reducing agent.
Powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, N2
adsorption–desorption, and inductively coupled plasma-atomic emission spectroscopy measurements
were employed to characterize the NiPt/MIL-96. Catalytic activity of NiPt/MIL-96 catalysts was tested in
the hydrogen generation from the aqueous alkaline solution of hydrazine at room temperature. These
catalysts are composition dependent on their catalytic activity, while Ni64Pt36/MIL-96 exhibits the highest
catalytic activity among all the catalysts tested, with a turnover frequency value of 114.3 h−1 and 100%
hydrogen selectivity. This excellent catalytic performance might be due to the synergistic effect of the
MIL-96 support and NiPt NPs, while NiPt NPs supported on other conventional supports, such as SiO2,
carbon black, γ-Al2O3, poly(N-vinyl-2-pyrrolidone) (PVP), and the physical mixture of NiPt and MIL-96, all
of them exhibit inferior catalytic activity compared to that of NiPt/MIL-96.
Received 3rd February 2015,
Accepted 15th February 2015
DOI: 10.1039/c5dt00493d
www.rsc.org/dalton
liquid-based distribution infrastructure, making it more com-
petitive, compared with the solid chemical hydrogen storage
Introduction
Hydrogen, as a globally accepted clean fuel, has emerged as an materials such as sodium borohydride (NaBH4) and ammonia
ideal alternative to petrochemical energy. However, the borane (NH3BH3) derivatives.8–13 However, from the perspec-
development of safe and effective hydrogen storage materials tive of hydrogen storage application, the incomplete decompo-
is still one of the most challenging obstacles for the develop- sition to ammonia which is toxic to the fuel cell catalysts by
ment of hydrogen economy. During the past few decades, a the other pathway (eqn (2)) should be avoided. Up to now,
number of chemical hydrogen storage materials, such as metal much progress in developing heterogeneous nanocatalysts for
hydrides,1 sorbent materials,2,3 and chemical hydride systems selective dehydrogenation of hydrazine under mild conditions
have been widely explored.4 Among them, hydrous hydrazine has been made,14,15 however, in view of practical applications,
(N2H4·H2O) is considered as a promising chemical hydrogen the improvement of their catalytic kinetics at room tempera-
material because of its high hydrogen content (8.0 wt%), easy ture is highly desirable for the development of hydrous hydra-
recharging ability, and production of only nitrogen as the zine as a potential hydrogen storage material.
byproduct, which does not need on-board collection for recy-
H2NNH2 ðlÞ ! N2 ðgÞ þ 2H2 ðgÞ
ð1Þ
cling, via a complete decomposition route as shown in eqn
(1).5–7 Moreover, hydrous hydrazine is a liquid-phase material
which is easy to handle and transport using the existing
3H2NNH2 ðlÞ ! N2 ðgÞ þ 4NH3 ðgÞ
ð2Þ
Recently, binary NiPt NPs have been developed as efficient
catalysts toward dehydrogenation of hydrous hydrazine. It is
known that the catalytic performance of metal NPs is highly
dependent on their dispersion. Hence, to prevent the NPs
from aggregation and increase their catalytic performance,
appropriate supports have been designed for restraining the
agglomeration. For example, Xu’s group reported the synthesis
of NiPt in the presence of hexadecyltrimethyl ammonium
bromide (CTAB) with an initial turnover frequency (TOF) of
aCollege of Chemistry and Molecular Sciences, Wuhan University, Wuhan, Hubei
430072, P. R. China. E-mail: wluo@whu.edu.cn, applecaiping@163.com;
Tel: +86 2768752366
bWuhan National Laboratory for Optoelectronics, Huazhong University of Science
and Technology, Wuhan, Hubei 430074, P. R. China
cSuzhou Institute of Wuhan University, Suzhou, Jiangsu 215123, P. R. China
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
c5dt00493d
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7.9 h−1 at room temperature,15 and dendrimer-encapsulated cation. We used ordinary distilled water as the reaction
1.1 nm NiPt NPs with TOF of 240 h−1 at 70 °C.16 Yan and co- solvent.
workers reported Ce2O3 supported NiPt NPs with TOF of
28.1 h−1 at room temperature,17 Zhang and co-workers
Synthesis of MIL-96
reported Al2O3 supported NiPt with a TOF value of 16.5 h−1 at
MIL-96 was hydrothermally synthesized by following the
30 °C.18 Our group reported graphene supported flower-like
NiPt nanoclusters with TOF of 68 h−1 at room temperature.19
Owing to their high surface area, porosity, and chemical tun-
ability, metal organic frameworks (MOFs) have been emerging
as very promising materials for gas storage,20 heterogeneous
catalysis21 and drug delivery.22 Given the similarity to zeolites,
using MOFs as the support is expected to control the growth of
metal NPs, and increase their catalytic performance.23 Very
recently, we have reported the immobilization of 1.8 nm NiPt
NPs inside the pores of MIL-101(Cr) as efficient catalysts for
dehydrogenation of alkaline solution of hydrazine with a TOF
value of 65.2 h−1 at room temperature. MIL-96, a new
reported method.25 Trimethyl 1,3,5-benzenetricarboxylate
(C6H3(CO2CH3)3) (328 mg), aluminium nitrate (Al(NO3)3·9H2O)
(110 mg), sodium hydroxide (NaOH) (80 mg) and de-ionized
water (5 mL) were placed in a 50 mL Teflon-lined autoclave
and heated at 210 °C for 12 h. After natural cooling, the sus-
pension was centrifuged to separate the white powder of
MIL-96 with the formula: (Al12O(OH)18(H2O)3(Al2(OH)4)
[btc]6·24H2O), and then further purified by solvothermal treat-
ment in anhydrous dimethylformamide (DMF) at 150 °C for
5 h. The separated resulting solid was refluxed overnight in a
suspension of water at 100 °C for 12 h and immediately fil-
tered. The resulting white solid was finally dried overnight at
100 °C for further use.
aluminium
trimesate
Al12O(OH)18(H2O)3(Al2(OH)4)[btc]6·
24H2O possessing a unique 3D framework with three different
types of cages, high thermal and chemical stability has been
used as an efficient material to support Ru NPs for catalytic
hydrolysis of ammonia boranes.24 The pore size in MIL-96 is
about 1.2 nm, which is much smaller than that of MIL-101
(2.9 nm), as a result, most of the metal NPs are expected to
stay on the surface of MIL-96 instead of going inside the pores.
As a continuous work on the study of the effect of different
types of MOFs and the position of metal NPs in MOFs (inside
the pores or outside the surface), herein, we have reported
MIL-96 supported NiPt NPs for the catalytic dehydrogenation
of hydrazine in alkaline solution. Compared with previously
reported catalysts, Ni64Pt36/MIL-96 exhibited the highest cataly-
tic activity, with a TOF value of 114.3 h−1 and 100% hydrogen
selectivity at room temperature.
Preparation of catalysts
The NiPt/MIL-96 catalysts were synthesized by a simple liquid
impregnation method. A typical synthetic procedure for cata-
lysts has been described here. Activated MIL-96 (100 mg) was
mixed with 0.10 mmol NiCl2·6H2O and 0.10 mmol K2PtCl6
solution in 10 mL de-ionized water. The solution was continu-
ously stirred for 12 h at 25 °C to impregnate metal salts. After
the impregnation, the suspension was concentrated under
vacuum. The resulting mixture was then reduced by sodium
borohydride (NaBH4, 37.8 mg) solution with vigorous stirring
at 0 °C to yield Ni64Pt36/MIL-96. The preparation of Ni95Pt5/
MIL-96, Ni81Pt19/MIL-96, Ni42Pt58/MIL-96, Ni15Pt85/MIL-96, Ni/
MIL-96, and Pt/MIL-96 was by following the analogous
process.
Hydrous hydrazine decomposition test
Experimental section
Chemicals and materials
In a typical experiment, Ni–Pt/MIL-96 (100 mg) and NaOH
(80 mg) were dissolved in 4 mL of water kept in a two-necked
round-bottom flask with vigorous stirring. One neck was con-
nected to a gas burette to monitor the volume of gas evolution,
and the other neck for the introduction of hydrous hydrazine
(0.1 mL, 1.96 mmol). A water bath was used to control the
temperature of the reaction solution at 25 °C. The gas released
during the reaction was passed through HCl solution (1.0 M)
before being measured volumetrically. The selectivity towards
H2 generation (X) can be calculated using eqn (3).
All chemicals were commercially available and used without
further purification. Nitrate (Al(NO3)3·9H2O, Sinopharm
Chemical Reagent Co., Ltd, 99%), trimethyl(1,3,5-benzenetri-
carboxylate) (C6H3(CO2CH3)3, 98%, Aldrich), sodium hydroxide
(NaOH, Sinopharm Chemical Reagent Co., Ltd, 96%), nickel
chloride hexahydrate (NiCl2·6H2O, Sinopharm Chemical
Reagent Co., Ltd, 99%), potassium chloroplatinate (K2PtCl6,
Wuhan Greatwall Chemical Co., Ltd, 99%), Ketjenblack
EC-300J (Triquo Chemical Co., Ltd), neutral silica powder
(SiO2, Branch of Qingdao Haiyang Chemical Co., Ltd), neutral
aluminum oxide (γ-Al2O3, Sinopharm Chemical Reagent Co.,
Ltd, FCP), poly(N-vinyl-2-pyrrolidone) (PVP, Aladdin Chemistry
Co., Ltd, M = 58 000), hydrazine monohydrate (H4N2·H2O, TCI
Shanghai Co., Ltd, >98%), sodium borohydride (NaBH4, Sino-
pharm Chemical Reagent Co., Ltd, 96%), dimethylformamide
X ¼ ð3λ ꢀ 1Þ=8½λ ¼ nðH2 þ N2Þ=nðH2NNH2Þꢁ
ð3Þ
To obtain the activation energy (Ea), the catalytic reaction
temperature varied from 25 °C to 50 °C (catalyst = 100 mg;
N2H4·H2O = 0.1 mL).
Recycle stability tests
(C3H7NO, Sinopharm Chemical Reagent Co., Ltd, 96%), For a recycle stability test, catalytic reactions were repeated
ethanol (C2H5OH, Sinopharm Chemical Reagent Co., Ltd, 4 times by adding another equivalent of hydrous hydrazine
>99.8%) were used as received without any further purifi- (2 mmol) into the mixture after the previous cycle.
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Recycle stability and reusability tests
(Table S1†). The powder X-ray diffraction (PXRD) patterns of
all the NiPt/MIL-96 samples matched with those of the parent
MIL-96 (Fig. 1a), indicating that the structural integrity of
MIL-96 was maintained well after the Ni–Pt loading. Further-
more, from the wide-angle PXRD (Fig. 1b), the diffraction peak
of NiPt/MIL-96 is between Pt (111) (39.8°), and the Ni (010)
(39.1°), indicating the formation of the Ni–Pt alloy. The N2
adsorption–desorption isotherms of MIL-96 and Ni64Pt36/
MIL-96 are shown in Fig. 2a. The specific areas were 263.8 and
153.6 m2 g−1 for MIL-96 and Ni64Pt36/MIL-96, respectively. The
significant decrease in the amount of N2 adsorption and the
pore volume (Fig. 2b, Table S2†) of Ni64Pt36/MIL-96 strongly
indicates that the cavities of MIL-96 were either occupied or
blocked by the well dispersed NiPt NPs.26 In the X-ray photo-
electron spectroscopy (XPS) (Fig. 3), the 4f peaks of Pt appear-
ing at 71.2 and 74.2 eV, and 2p peaks of Ni appearing at 856.2
and 874.8 eV were observed, indicating the coexistence of both
metals. The formation of oxidized Ni may have been caused
during the sample preparation process for the XPS measure-
ments.27 The morphologies of MIL-96 supported Ni–Pt NPs
were further characterized by transmission electron
microscopy (TEM) and energy-dispersive X-ray spectroscopy
(EDS) measurements. TEM images of NiPt/MIL-96 indicate
that the NiPt NPs are well dispersed on the surface of the
framework with a mean diameter of 3.2 nm (Fig. 4a and b,
Fig. S1†), which are too large to immobilize into the pores of
MIL-96. The EDX spectra further confirmed the presence of Ni
and Pt (Fig. 4d).
For a recycle stability test, catalytic reactions were repeated
4 times by adding another equivalent of hydrous hydrazine
(2 mmol) into the mixture after the previous cycle.
For a reusability test, after the decomposition of hydrazine
was complete, the catalyst was separated from the reaction
solution by centrifugation and washed with water several
times. The washed catalyst was re-dispersed in 4 mL water con-
taining 80 mg NaOH and 0.1 mL hydrous hydrazine. Such
reuse tests were repeated 4 times.
Characterization
The morphologies and sizes of the samples were observed by
using a Tecnai G20 U-Twin transmission electron microscope
(TEM) equipped with an energy dispersive X-ray detector (EDX)
at an acceleration voltage of 200 kV. Powder X-ray diffraction
(XRD) patterns were measured by a Bruker D8-Advance X-ray
diffractometer using
a Cu Kα radiation source (λ =
0.154178 nm) with a velocity of 1° min−1. X-ray photoelectron
spectroscopy (XPS) measurements were performed using a
Kratos XSAM 800 spectrophotometer. The surface area
measurements were performed with N2 adsorption/desorption
isotherms at liquid nitrogen temperature (77 K) after de-
hydration under vacuum at 150 °C for 18
h using
Quantachrome NOVA 4200e. The inductively coupled plasma-
atomic emission spectroscopy (ICP-AES) was performed on
IRIS Intrepid II XSP (Thermo Fisher Scientific, USA). MS of the
generated gases were collected by using an Ametek Dycor mass
spectrometer under an Ar atmosphere.
The catalytic dehydrogenation of aqueous alkaline solution
of hydrazine was performed for all the samples at 25 °C in the
presence of NaOH (0.5 M) as shown in Fig. 5. The catalytic
activity of the catalysts strongly depends on the Ni–Pt compo-
sitions. Among all the bimetallic NiPt/MIL-96 samples investi-
gated, Ni64Pt36/MIL-96 exhibited the highest catalytic activity,
with the TOF value of 114.3 h−1 at room temperature, which is
among the highest reported values (Table 1). Interestingly,
monometallic Ni/MIL-96 and Pt/MIL-96 were catalytically in-
active, while Ni95Pt5/MIL-96 presented poor catalytic activity
Results and discussion
The NiPt/MIL-96 catalysts were synthesized by a simple liquid
impregnation method using NaBH4 as the reductant at 0 °C.
The final ratio of Ni and Pt in the catalysts was determined
based on the inductively coupled plasma atomic emission
spectroscopic (ICP-AES), which were close to the initial loading
Fig. 1 (a) Powder X-ray diffraction patterns of samples; (b) the wide-angle PXRD of patterns of samples. (a–i) MIL-96, Ni95Pt5/MIL-96, Ni81Pt19
/
MIL-96, Ni64Pt36/MIL-96, Ni42Pt58/MIL-96, Ni15Pt85/MIL-96, Ni64Pt36/MIL-96 after 4 runs, Pt/MIL-96, Ni/MIL-96.
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Fig. 2 (a) N2 sorption isotherms of activated MIL-96 and Ni64Pt36/MIL-96 at 77 K. (b) The pore diameter distribution of MIL-96 and Ni64Pt36/MIL-96.
Fig. 3 XPS spectra for catalyst Ni64Pt36/MIL-96 showing Ni 2p (a) and Pt 4f (b).
Fig. 5 Time course plots for the decomposition of hydrazine in
aqueous NaOH solution (0.5 M) over NiPt/MIL-96 (catalyst = 0.100 g;
N2H4·H2O = 0.1 mL).
(only about 2 equiv. gas with 64% hydrogen selectivity was
released over 1 h). The H2 selectivity and completeness of
Fig. 4 (a,b) TEM images of Ni64Pt36/MIL-96 with different magnifi-
cations, (c)TEM image of Ni64Pt36/MIL-96 after four runs; (d) EDX of
hydrazine decomposition over Ni64Pt36/MIL-96 were further
Ni64Pt36/MIL-96.
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confirmed by mass spectroscopy (Fig. 6), indicating the 100%
H2 selectivity. In addition, to study the effects of the supported
materials on the catalytic performances of the as-synthesized
NiPt catalysts, NiPt NPs supported on different support
materials, such as γ-Al2O3, SiO2, carbon black, PVP and the
physical mixture of NiPt with MIL-96 were prepared and their
catalytic activities toward dehydrogenation of alkaline solution
of hydrazine at room temperature were studied. As shown in
Fig. 7, their catalytic activities are all inferior to that of
Ni64Pt36/MIL-96, in the physical mixture of NiPt and MIL-96,
only 2.4 equiv. gas with 78% hydrogen selectivity were released
over 1 h, and almost no reactivity was observed for MIL-96,
highlighting the dominant factor of MIL-96 in facilitating
dehydrogenation of aqueous solution of hydrazine in our
system and the synergistic effect between MIL-96 and NiPt
NPs. This result may be caused by the intrinsic activity of the
Fig. 7 Decomposition of hydrous hydrazine to H2 over time by
Ni64Pt36/MIL-96, MIL-96, Ni64Pt36 NPs and MIL-96 physically mixed,
Ni64Pt36/C black, Ni64Pt36/γ-Al2O3, Ni64Pt36/SiO2, Ni64Pt36/PVP and a
physical mixture of Ni/MIL-96 and Pt/MIL-96 in the presence of NaOH
(0.5 M) at 25 °C.
Table 1 Comparison of activities and Ea of different catalysts for hydro-
gen generation by H2NNH2·H2O decomposition
T
(°C)
Ea
TOF
Catalyst
(kJ mol−1
)
(h−1
)
Reference
active sites, potential effects of adsorption and pore confine-
ment of MIL-96, which could help to pre-activate the reactants
and/or stabilize the reaction transition states. Furthermore,
the physical mixing of Ni/MIL-96 to Pt/MIL-96 does not facili-
tate their catalytic performance, demonstrating that the syner-
gistic effect of Ni and Pt in the same materials play a decisive
role in enhancing the catalytic activity. It is known that NaOH
has a great effect on the catalysts’ performance. We investi-
gated the dehydrogenation of hydrazine with/without adding
NaOH. As shown in Fig. 8, the dehydrogenation rate and
selectivity of hydrazine in the presence of NaOH were much
higher than those without NaOH. The reason is that NaOH
can accelerate the rate-determining step (N2H4 → N2H3* + H*)
RANEY® Ni-300
NiPt0.057/Al2O3
Ni/Al2O3
Ni1.5Fe1.0-alloy/(MgO)3.5
Ni–Pt
Ni64Pt36/MIL-96
Ni3Pt7/graphene
NiPt@MIL-101
Ni0.9Pt0.1/Ce2O3
Rh4Ni/graphene
Rh4Ni
30
30
30
26
25
25
25
25
25
25
25
25
25
25
44.4
49.3
34
—
—
51.7
49.36
51.29
42.3
39.3
—
114
16.5
2.2
1.9
150
114.3
68
65.2
28.1
20
9.6
3
2.8
1.6
29
19
19
30
31
This study
20
32
18
29
33
15
34
35
Ni0.93Pt0.07
Rh
Ni0.95Ir0.05
—
—
—
Fig. 6 MS profile for the gases released from the decomposition reac-
tion of hydrazine in aqueous NaOH solution (0.5 M) over Ni64Pt36
MIL-96 (catalyst = 0.100 g; N2H4·H2O = 0.1 mL) under an argon atmos-
phere at 25 °C.
/
Fig. 8 Time course plots for the decomposition of hydrazine with or
without aqueous NaOH solution (0.5 M) over Ni64Pt36/MIL-96 solution
(catalyst = 0.100 g; N2H4·H2O = 0.1 mL).
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Fig. 9 (a) Time course plots for hydrogen generation by the decomposition of hydrazine by Ni64Pt36/MIL-96 at 25 °C, 30 °C, 40 °C and 50 °C.
(b) Plot of ln k versus 1/T during the hydrazine decomposition over Ni64Pt36/MIL-96 at different temperatures.
of hydrazine decomposition and alkaline NaOH suppresses dispersed in the same amount of hydrazine for the next cycle,
the formation of basic NH3.28
more than 90% of their initial activities were preserved even in
In order to obtain the activation energy (Ea) of the dehydro- the fifth run (Fig. S2†). The PXRD of Ni64Pt36/MIL-96 after the
genation of aqueous solution of hydrazine catalyzed by 4th cycle exhibited no loss of crystallinity (Fig. 1), indicating
Ni64Pt36/MIL-96, the catalytic reactions were carried out at that the integrity of MIL-96 was maintained well during the
temperatures ranging from 25 °C, 30 °C, 40 °C, 50 °C (Fig. 9), catalytic process. The representative TEM images of Ni64Pt36/
and Ea was determined to be 51.7 kJ mol−1, which is consistent MIL-96 after the 4th cycle is shown in Fig. 4c, while some of
with the reported values (Table 1). In addition, the as-syn- the NiPt NPs were already aggregated into big size on the
thesized Ni64Pt36/MIL-96 was tested for the durability four surface of MIL-96, which may be the reason for the decrease of
times after all of the hydrazine present in solution was con- catalytic performance. Furthermore, studies on the enhance-
sumed for each cycle. As shown in Fig. 10, the catalytic activity ment of the stability of the as-synthesized catalyst for hydrogen
decreased after 4 cycles, but the hydrogen selectivity had no generation from hydrazine are underway.
change at all. However, after the decomposition of hydrazine
was complete, when the catalysts were separated from the reac-
tion by centrifugation, washed with water several times and re-
Conclusion
In summary, we have developed a highly efficient catalyst for
dehydrogenation of alkaline solution of hydrazine using
MIL-96 supported NiPt NPs. Thanks to the unique 3D structure
and synergistic effect, the catalytic activity of NiPt NPs have
been significantly increased after loading onto the surface of
MIL-96, which exhibited the highest catalytic activity toward
dehydrogenation of alkaline solution of hydrazine at room
temperature up to now. The combination of high activity and
selectivity makes Ni64Pt36/MIL-96 a potential catalyst for de-
hydrogenation of aqueous solution of hydrazine, and further
strongly encourages the practical applications of hydrous
hydrazine as a chemical hydrogen storage material in the
hydrogen economy.
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (21101121, 21201134), the
Fig. 10 Durability test of Ni64Pt36/MIL-96 for decomposition of hydra-
Natural Science Foundation of Jiangsu Province (BK20130370),
the Natural Science Foundation of Hubei Province
zine in aqueous NaOH solution (0.5 M) at 25 °C (catalyst = 0.100 g;
N2H4·H2O = 0.1 mL).
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(2013CFB288), the Creative Research Groups of Hubei Province 18 L. He, Y. Q. Huang, A. Q. Wang, Y. Liu, X. Y. Liu,
(2014CFA007) and the Large-scale Instrument and Equipment
Sharing Foundation of Wuhan University.
X. W. Chen, J. D. Juan, X. D. Wang and T. Zhang, J. Catal.,
2013, 298, 1–9.
19 N. Cao, L. Yang, C. Du, J. Su, W. Luo and G. Z. Cheng,
J. Mater. Chem. A, 2014, 2, 14344–14347.
20 K. K. Tanabe and S. M. Cohen, Chem. Soc. Rev., 2011, 40,
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