Controlled Synthesis of MOF-Encapsulated NiPt Nanoparticles toward Efficient and Complete Hydrogen Evolution from Hydrazine Borane and Hydrazine

Article abstract of DOI:10.1021/acs.inorgchem.7b01910

The catalytic dehydrogenation of hydrazine borane (N₂H₄BH₃) and hydrous hydrazine (N₂H₄·H₂O) for H₂ evolution is considered as two of the pivotal reactions for the implementation of the hydrogen-based economy. A reduction rate controlled strategy is successfully applied for the encapsulating of uniform tiny NiPt alloy nanoclusters within the opening porous channels of MOFs in this work. The resultant Ni_0.9Pt_0.1/MOF core-shell composite with a low Pt content exerted exceedingly high activity and durability for complete H₂ evolution (100% hydrogen selectivity) from alkaline N₂H₄BH₃ and N₂H₄·H₂O solution. The features of small NiPt alloy NPs, strong synergistic effect between NiPt alloy NPs and the MOF, and open pore structure for freely mass transfer made NiPt/MIL-101 an excellent catalyst for highly efficient H₂ evolution from N₂H₄BH₃ or N₂H₄·H₂O.

Full text of DOI:10.1021/acs.inorgchem.7b01910

Article
pubs.acs.org/IC
Controlled Synthesis of MOF-Encapsulated NiPt Nanoparticles
toward Efficient and Complete Hydrogen Evolution from Hydrazine
Borane and Hydrazine
Zhujun Zhang, Shiliang Zhang, Qilu Yao, Xiangshu Chen, and Zhang-Hui Lu*
Institute of Advanced Materials, College of Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang 330022,
China
*
S Supporting Information
ABSTRACT: The catalytic dehydrogenation of hydrazine borane (N H BH ) and
2
4
3
hydrous hydrazine (N H ·H O) for H evolution is considered as two of the pivotal
2
4
2
2
reactions for the implementation of the hydrogen-based economy. A reduction rate
controlled strategy is successfully applied for the encapsulating of uniform tiny NiPt alloy
nanoclusters within the opening porous channels of MOFs in this work. The resultant
Ni Pt /MOF core−shell composite with a low Pt content exerted exceedingly high
0.9 0.1
activity and durability for complete H evolution (100% hydrogen selectivity) from
2
alkaline N H BH and N H ·H O solution. The features of small NiPt alloy NPs, strong
2
4
3
2
4
2
synergistic effect between NiPt alloy NPs and the MOF, and open pore structure for freely
mass transfer made NiPt/MIL-101 an excellent catalyst for highly efficient H evolution
2
from N H BH or N H ·H O.
2
4
3
2
4
2
1
. INTRODUCTION
harvest high catalytic activity as well as prominent stability for
dehydrogenation of N H BH is of fundamental importance.
2
4
3
Hydrogen is generally regarded as one of the cleanest and most
reliable energy resources because it has high energy capacity
N H BH (aq) + 3H O(l)
−1
1−4
2
4
3
2
(143 MJ·kg ) and is environmentally friendly.
However,
the implementation of the H -based economy is still hindered
→ N H (aq) + H BO (aq) + 3H (g)
2
2
4
3
3
2
(1)
(2)
(3)
by the lack of reliable and efficient hydrogen storage and
5
−7
evolution technology.
N compound with qualities of high hydrogen content (15.4 wt
) and the potential of 100% hydrogen utilization efficiency
and thus has been proposed as a potential hydrogen storage
Hydrazine borane (N H BH ) is a B-
N H (aq) → N (g) + 2H (g)
2
4
3
2
4
2
2
%
3N H (aq) → 4NH (aq) + N (g)
2
4
3
2
8
−12
In general, metal nanoparticles (MNPs) with extremely
narrow sizes have exceedingly large surface areas and a great
medium.
The hydrogen atoms of N H BH can be
2 4 3
completely converted to H from the BH group hydrolysis
2
3
13−21
number of edge and corner atoms, which is highly desired for
(
eq 1) and the N H moiety decomposition (eq 2).
To
2
4
30,31
boosting the catalytic properties.
However, the increased
achieve a 100% hydrogen utilization efficiency of N H BH as a
2
4
3
surface energy of tiny MNPs often leads to their serious
aggregation and fusion during a catalytic process, thus resulting
in the loss of catalytic activity. Immobilizing metal NPs to
porous materials can not only reduce particle aggregation but
also control the particle nucleation and growth to the confined
hydrogen storage media, the incomplete and undesired product
of NH from decomposition of N H via eq 3 should be
avoided. Though much effort has been invested, the catalytic
dehydrogenation of hydrazine borane for H evolution is still
characterized by significant challenges. To fully dehydrogenate
N H BH , the catalysts adopted should be both active and
selective for the hydrolysis (eq 1) and decomposition process
3
2
4
2
32
pores. Besides, the electronic structure and surface state of
noble metal can be tailored by alloying with foreign elements,
such as transition non-noble metals, which can be beneficial to
the adsorption and excitation of reaction substrates and
2
4
3
(
eq 2). Thus far, most reported catalysts are only effective for
13−16
the first hydrolysis step,
while the selective decomposition
27−29
eventually improve the catalytic properties.
On the basis
of N H is still highly dependent on the utilization of noble-
metal (Pt and Rh) based catalysts.
2
4
1
7−29
of the above consideration, incorporating tiny alloy NPs within
porous materials with appropriate pore channels and open
windows for mass transfer would be a possible strategy to
increase the efficiency and stability of noble metals.
Noble metal catalysts
have received extensive research interest for decades because of
their versatility in a variety of areas, especially in catalysis.
Although they have incomparable advantages in catalytic
activity for chemistry reactions, their high prices and scarcity
limitation should be basically considered. In this regard, to
maximally enhance their utilization efficiency and meanwhile
Received: July 26, 2017
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b01910
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Inorganic Chemistry
Article
Metal−organic frameworks (MOFs) are constructed via the
self-assembly of organic linkers and secondary building blocks
with tunable and uniform pore structures. The properties of
high surface areas and special open pore structure made it an
consisting of Ni0.9Pt0.1/MIL-101_A, Ni0.9Pt0.1/MIL-101_B, and
Ni Pt /MIL-101_C, respectively. The preparation of Ni Ptx/
0.9 0.1
1−x
MIL-101_A catalysts (x = 0, 0.01, 0.04, 0.07, 0.1, 0.13, 0.16, 0.25, 1.0)
with different Pt molar contents follows the similar process for the
synthesis of Ni0.9Pt0.1/MIL-101_A catalysts only by adjusting the
molor ratio of platinum and nickle salts.
33
ideal host for the spatial confinement of MNPs. The
encapsulating of tiny alloy NPs within the cavities of MOFs
would avoid the agglomeration of the confined MNPs, and thus
form a stable and accessible structure for freely mass
2.4. Catalysis. The catalytic performances of all the samples
toward dehydrogenation of N H BH or N H ·H O for H evolution
2
4
3
2
4
2
2
were tested on a water-filled graduated buret system as our previous
3
4−40
27−29
transfer.
A facile and general approach that can effectively
work reported.
Typically, a flask reactor containing the
control the encapsulating of tiny MNPs, especially noble metal
based MNPs, within MOFs is significant for practical
application.
Herein in this paper, a reduction rate controlled strategy is
reported to tailor the size and spatial distribution of NiPt alloy
clusters in a MOF crystal as highly efficient catalyst for
synthesized catalyst suspension and NaOH (0.5 M, 5 mL) was placed
in a water bath at a certain temperature. The buret and reactor is
connected by a trap filled with HCl solution (0.1 M) to absorb
ammonia (NH ) if generated. The catalytic reaction is started by the
3
injection of N H BH ((Pt + Ni)/(N H BH ) = 0.1) or N H ·H O
2
4
3
2
4
3
2
4
2
(
(Pt + Ni)/(N H ·H O) = 0.1) to the above catalyst suspension.
2 4 2
Then, the volume of H along with N is measured by the gas buret
2
2
complete H evolution from alkaline aqueous N H BH or
2
2
4
3
and recorded at sequential times. Finally, we can calculate the molar
N H ·H O solution. MIL-101(Cr) is selected as the host MOF
ratio λ = n(H + N )/n(N H BH ) by the total volume of H and N .
2
4
2
2
2
2
4
3
2
2
for NiPt alloy NPs in this work due to its large pore sizes and
The hydrogen selectivity for N H BH dehydrogenation (N H BH +
2
4
3
2
4
3
2
−1
window sizes, its large specific surface area (up to 5900 m ·g ),
3H
2
O → B(OH)
3
+ (3 + 2α)H
2
+ (2α + 1)/3N
2
+ 4(1 − α)/3NH )
3
can be obtained on the basis of the following equation:
and high thermal (up to 300 °C) and good chemical resistance
4
1
to water. The MOFs encapsulated tiny NiPt alloy NPs with
only 10% Pt (molar ratio: Pt/(Ni + Pt)) exerts exceedingly
higher activity than ordinary NiPt alloy NPs for complete
dehydrogenation of N H BH or N H ·H O solution for H
2
⎡
⎢
⎣
⎤
⎥
⎦
α = 3
λ − 10
λ =
n(H + N ) ⎛10
≤ λ ≤ 6
⎞
2
2
⎜
⎟
8
n(N H BH ) ⎝ 3
⎠
2
4
3
2
4
4
2
4
2
evolution even at room temperature.
3. RESULTS AND DISCUSSION
.1. Synthesis and Characterization of MIL-101
3
2
. EXPERIMENTAL SECTION
Supported MNPs. A general and facile impregnation method
combined with a reduction rate controlled strategy was
implemented for the synthesis of MIL-101(Cr) supported
NiPt alloy nanoparticles (NPs) with size and location control
2
.1. Chemicals and Materials. K PtCl (99.95%, Aladdin), NiCl ·
2 4 2
6
9
2
H O (≥98.0%, Sinopharm Chemical Reagent Co., Ltd.), Cr(NO ) ·
2
3 3
H O (99.95%, Aladdin), NaBH (98%, J&KCHEMICAL), N H ·1/
2
4
2
4
H SO4 (Sigma-Aldrich), HCl (36−37%, Sinopharm Chemical
2
2+
2+
(
Scheme 1). Typically, the Ni and Pt precursors were first
Reagent Co., Ltd.), HF (37 wt %, J&KCHEMICAL), NaOH
(
≥96.0%, Sinopharm Chemical Reagent Co., Ltd.), terephthalic acid
(
HO CC H CO H, 99%, Aladdin), 1,4-dioxane (99.8%, J&KCHEM-
Scheme 1. Schematic Representation of Preparing MIL-101
Supported NiPt NPs with Size and Location Control
2
6
4
2
ICAL), n-pentane (99.5%, Sigma-Aldrich), and ethanol (≥99.7%,
Tianjin Fuchen Chemical Reagent) were used as received. The
ultrapure water was prepared by reversed osmosis, ion exchange, and
filtration.
2
.2. Instrumentation. The crystal structure of the synthesized
samples was analyzed by powder X-ray diffraction (XRD) with a
Rigaku RINT-2200 X-ray diffractometer (Cu Kα source, 40 kV, 20
mA). The N2 adsorption/desorption isotherms at 77 K (liquid
nitrogen temperature) were obtained by a BELSORP-mini II. The
microstructures and elemental contents of the synthesized samples
were analyzed on a transmission electron microscope (TEM, Tecnai
G2 F20) and scanning electron microscope (SEM, SU8020 cold field-
emission instrument). Inductively coupled plasma atomic emission
spectroscopy (ICP-AES, 725-ES) was adopted to detect the detail
components of the samples. The surface valence state of the NiPt alloy
NPs was determined by X-ray photoelectron spectroscopy (XPS)
measurement (Thermo Scientific ESCALAB 250). The evolved gases
from dehydrogenation of N H BH over Ni Pt /MIL-101 catalyst
incorporated into the pore channels of MIL-101 via capillary
force during an impregnation process. Then, a reduction rate
controlled strategy by changing the NaBH /(Ni + Pt) molar
4
ratio was applied to obtain the confined NiPt alloy NPs in the
MOF with size and location control. The metal precursors
deposited inside the MOF can be reduced completely and
promptly due to the increase of reduction rate when providing
more reducing agent. The instantaneously swelled NiPt NPs
can be confined by MOF ligands, and thus the agglomeration of
NiPt alloy NPs can be minimized. In contrast, the reduction of
metal precursors inside the cages was not timely when
providing less reducing agent, thus leading a part of the
metal precursors redissolved and diffused to the outside of the
pores and aggregated to large metal clusters on the external
surface.
2
4
3
0.9 0.1
1
was analyzed by a Balzers Prisma QMS 200 mass spectrometer. H
solution-state nuclear magnetic resonance (NMR) was adopted to
determine the purity of the synthesized hydrazine borane on a Bruker
1
4
00 M liquid HNMR using CD CN as solvent.
3
2
.3. Synthesis of NiPt/MIL-101. NiPt/MIL-101_A−C catalysts
were synthesized via a general and facile impregnation method
combined with a reduction rate controlled strategy. Typically, a
solution containing H O (5 mL), MIL-101 (50 mg), NiCl ·6H O
2
2
2
(
0.09 mmol), and K PtCl (0.01 mmol) was sonicated for several
2 4
minutes to get a fully dispersed suspension. Then, the above
suspension was vigorously stirred for 8 h at 20 °C to impregnate
the metal ions into the pores of the MOF. Finally, NaBH4 with
The nanocomposites obtained with a NaBH /(Ni + Pt)
different NaBH /(Ni + Pt) molar ratios (10:1, 7:1, and 4:1) was
4
4
quickly poured into the above solution, followed by vigorous stirring
for 20 min, leading to the generation of a celadon suspension
molar ratio of 10:1, 7:1, and 4:1 are named as NiPt/MIL-
101_A, NiPt/MIL-101_B, and NiPt/MIL-101_C, respectively.
B
DOI: 10.1021/acs.inorgchem.7b01910
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Inorganic Chemistry
Article
The typical SEM, TEM, and high-angle annular dark-field
scanning TEM (HAADF-STEM) images of the obtained NiPt/
MIL-101_A−C catalysts are illustrated in Figure 1. The
demonstrates the uniformity of NiPt alloy NPs in the Cr-based
MOF. The detail composition of the catalysts can be further
determined by using the ICP-AES instrument (Table S1).
The parent MIL-101 and NiPt/MIL-101_A−C catalysts with
2
−1
specific surface areas of 2794, 1411, 1533, and 1670 m ·g
Table 1), respectively, are determined by N adsorption/
(
2
Table 1. Physical Properties and Activities of Ni Pt /MIL-
0
.9 0.1
1
01_A−C Catalysts Synthesized via a Reduction Rate
Controlled Strategy
SBET [m g−1]
2
D
a
[nm]
size [nm] TOF [h−1
]
b
sample
NiPt/MIL-
1411
2.98/1.45/1.05
3.00/1.53/1.05
3.11/1.62/1.05
2.5
1515
1
01_A
NiPt/MIL-
01_B
1533
1670
4.5
732
1
NiPt/MIL-
01_C
5−25
500
1
a
Micropore size obtained by using the QSDFT method (slit/
b
cylindrical pore model). TOF values for dehydrogenation of
N H BH are calculated based on the number of full metal (Ni +
2
4
3
Pt) atoms in catalysts.
desorption isotherms measurement using the Brunauer−
Emmett−Teller (BET) model (Figure 2a). The pore size of
NiPt/MIL-101_A−C is slightly smaller than that of the parent
MIL-101 (Figure 2b). The decrease in N sorption and pore
2
sizes compared with the parent MIL-101 is probably because
the cavities are occupied by the NiPt alloy NPs. The N2
sorption capacity of NiPt/MIL-101_A is a little lower than that
of NiPt/MIL-101_B and C, which is probably due to that more
metal NPs are deposited inside the pore channels after a rapid
reduction process. The low-angle XRD patterns show no
crystallinity loss for the MOF after the formation of NiPt/MIL-
101 catalysts (Figure 2c), further demonstrating the integrity of
the MIL-101 crystal during the catalyst synthesis process. It can
be seen from the wide-angle powder XRD patterns that both
NiPt/MIL-101_B and C composites exhibit a weak and broad
peak at around 2θ = 41.8°, which is between the characteristic
peaks for Pt(111) (PDF# 05-0685) and Ni(111) (PDF# 04-
0850) (Figure 2d), verifying the nanoalloy structure of NiPt
NPs. In comparison with NiPt/MIL-101_B and NiPt/MIL-
101_C samples, NiPt/MIL-101_A has a unconspicuous NiPt
alloy signal due to its smaller particle sizes inside the MOF. X-
ray photoelectron spectroscopic (XPS) measurement on the
NiPt/MIL-101_A with Ar sputtering was carried out to
determine the surface valence state of the metal NPs (Figure
3). The Ni species are present in both the oxide and the
metallic forms. The binding energies (BEs) at 852.8 and 870.2
Figure 1. SEM, TEM, and HAADF-STEM images of Ni Pt /MIL-
0.9 0.1
1
1
01_A (a, d, g), Ni Pt /MIL-101_B (b, e, h), and Ni Pt /MIL-
01_C (c, f, i), respectively.
0.9 0.1 0.9 0.1
octahedral framework of MIL-101 (Figure S1) kept complete
and uniform after the loading of NiPt NPs via the reduction
rate controlled strategy. It can be seen from the SEM (Figure
1
a), bright-field TEM (Figure 1d and Figure S2a), and
HAADF-STEM images (Figure 1g) that the NiPt NPs obtained
through a rapid reduction process (NaBH /(Ni + Pt) molar
4
ratio = 10:1) are highly distributed into the framework of MIL-
1
01 (NiPt/MIL-101_A). The mean particle size of the NiPt
NPs is 2.5 nm (Figure S2a). As the MOF MIL-101 used in this
work has mesoporous cavities with sizes of ∼3.2 nm and
41
windows with sizes of ∼1.2 and 1.6 nm, it is reasonable that
the obtained NiPt NPs (2.5 nm) can be accommodated into
the mesoporous cavities confined by the windows. However,
larger metal clusters on the surface of the MOF crystal are
observed from both the SEM, bright and dark TEM images of
NiPt/MIL-101_B and NiPt/MIL-101_C (Figure 1 and Figure
S2c,d). For the NiPt/MIL-101_B sample, a part of NiPt NPs
with particle sizes of about 4.5 nm are aggregated to large
clusters on the surface of the MOF crystal (Figure S2c). When
0
eV that are attributed to Ni could be detected after the thin
the NaBH /(Ni + Pt) molar ratio was further decreased to 4:1,
more NiPt NPs with sizes bigger than 5 nm are aggregated
oxidized layer was eliminated by Ar sputtering in 60 s.
Meanwhile, the characteristic signals of Pt 4f centered at
binding energies (BEs) of around 70.6 and 73.9 eV can be
4
together as larger clusters (∼25 nm) on the surface of the MIL-
0
1
01 framework (NiPt/MIL-101_C) (Figure S2d). These
assigned to Pt .
results reveal that the reduction rate controlled process is
effective to control the size and spatial distribution of NiPt NPs
in a MOF framework, which can be easily expanded to the
synthesis of other heterogeneous catalysts with similar porous
structures. The high-resolution TEM (HRTEM) image of
NiPt/MIL-101_A (Figure S2b) confirms the crystalline alloy
nature of Ni-Pt NPs, as the d-spacing (∼0.219 nm) is between
the Pt(111) plane (0.227 nm) and the Ni(111) plane (0.203
nm). In addition, the corresponding energy dispersive X-ray
detector (EDX) pattern of NiPt/MIL-101_A (Figure S3)
3.2. Catalytic Performance. The obtained NiPt/MIL-
101_A catalysts with different molar contents of Pt have been
tested for the catalytic dehydrogenation of alkaline N H BH
3
2
4
solution (0.5 M NaOH) at 323 K as shown in Figure 4. NaOH
27−30
was used to promote the decomposition of N H .
The
2
4
optimum concentration of NaOH for dehydrogenation of
N H BH was measured to be 0.5 M in the present reaction
2
4
3
system (Figure S4). Obviously, both the monometallic Ni/
MIL-101_A and Pt/MIL-101_A catalysts showed a certain
activity for H evolution from the BH group hydrolysis and the
2
3
C
DOI: 10.1021/acs.inorgchem.7b01910
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Inorganic Chemistry
Article
Figure 2. (a) N sorption isotherms, (b) the pore size distribution curves, (c) the low-angle and (d) wide-angle powder XRD patterns for the as-
2
synthesized MIL-101, Ni Pt /MIL-101_A, Ni Pt /MIL-101_B, and Ni Pt /MIL-101_C.
0.9 0.1
0.9 0.1
0.9 0.1
Figure 3. XPS spectra of the electron binding energies for (a) Ni 2p and (b) Pt 4f in the Ni Pt /MIL-101_A catalyst before (0 s) and after argon
0.9 0.1
sputtering for 60 s.
N H moiety decomposition with a total of 4.97 and 4.34 equiv
2
4
(
H2 + N ) per N H BH released in 68 and 3.6 min,
2 2 4 3
respectively. The activity and H selectivity for the N H
2
2
4
moiety decomposition were significantly increased by Ni-Pt
alloying with a very little amount of Pt (Figure 4). The
bimetallic NiPt/MIL-101_A catalysts with low Pt contents of
7
−13 mol % showed 100% H selectivity and excellent activity
2
(
Figure 4). Among them, the best catalytic performance is
observed for the Ni Pt /MIL-101_A sample, with which the
0.9 0.1
reaction was completed in only 1.92 min, which corresponds to
−
1
a total turnover frequency (TOF) of 1515 mol ·mol ·
h
H
2
(Ni+Pt)
−1
(inset of Figure 4). This is 84-fold higher than that of the
reported catalyst Ni0.89Pt0.11 NPs stabilized by CTAB (Table
22
S2). Further increase or decrease of Pt content in NiPt/MIL-
01_A catalyst leads to the decrease of catalytic activity and H2
Figure 4. Time course plots for H generation from alkaline aqueous
2
1
N H BH solution (1.0 mmol, 5.0 mL, 0.5 M NaOH) at 323 K
2
4
3
productivity, suggesting the Ni Pt /MIL-101_A with a Ni:Pt
catalyzed by the Ni1−xPt /MIL-101_A. Inset: the corresponding TOF
0.9 0.1
x
values of the catalysts with different Pt molar contents and the
molar ratio of 9:1 can optimize the synergy between Ni and Pt
simulated diagram of NiPt/MIL-101_A.
based on their electronic and geometric effects in the present
D
DOI: 10.1021/acs.inorgchem.7b01910
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Inorganic Chemistry
Article
reaction conditions. The H /N ratio of the evolved gases from
can be achieved. It is also found that both the NiPt/MIL-101_B
and C catalysts, which were synthesized via a mild reduction
2
2
dehydrogenation of N H BH over Ni Pt /MIL-101_A
2
4
3
0.9 0.1
catalyst was determined by mass spectrometric analysis (Figure
process, display high catalytic activity for H evolution from
2
S5), indicating the 100% H selectivity.
dehydrogenation of N H BH with a total TOF value of 732
2
2
4
3
−1
For comparison, the parent MIL-101 and Ni Pt NPs were
and 500 h , respectively (Figure 6). However, their catalytic
activities were still much lower than that of NiPt/MIL-101_A
0
.9 0.1
separately applied to the dehydrogenation of N H BH at the
2
4
3
−1
same conditions. Obviously, only 5.4 equiv (H + N ) per
2
2
catalyst (1515 h ). The NiPt alloy NPs in NiPt/MIL-101_A
have smaller particle sizes and the confined active sites in the
pore channels of MOF are more accessible than that of the
aggregated one in the outer surface of MOF. The enhanced
catalytic activity of NiPt/MIL-101_A may mostly due to its
smaller NiPt particle sizes encapsulated in the pores of the
MOF and stronger interaction between bimetallic NPs and the
MOF matrix.
N H BH was released in more than 40 min by Ni Pt NPs,
2
4
3
0.9 0.1
while MIL-101 was inactive (Figure 5). The Ni Pt /MIL-
0
.9 0.1
The catalytic activity of Ni Pt /MIL-101_A has also been
0.9 0.1
tested for dehydrogenation of N H BH at different temper-
2
4
3
atures. The reactions were completed in 1.42, 1.95, 3.67, and
.50 min at temperatures ranging from 333, 323, 313, and 303
K, corresponding to total TOF values of 2113, 1515, 817, and
7
−1
−1
4
00 mol ·mol
·h , respectively (Figure 7a). It should
H
2
(Ni+Pt)
be noted that Ni Pt /MIL-101_A has a tremendously high
0.9 0.1
TOF value even at room temperature. The TOF value
Figure 5. Time course plots for H generation from alkaline aqueous
evaluated by the noble-metal content reaches 4000 mol ·
2
H
2
N H BH solution (1.0 mmol, 5.0 mL, 0.5 M NaOH) at 323 K
−1 −1
2
4
3
molPt ·h , which is much higher than that of MSC-30
catalyzed by the parent MIL-101, the Ni Pt NPs, and Ni Pt /
0.9 0.1
0.9 0.1
−1 −1
supported Ni Pt NPs (TOF: 1667 mol ·mol ·h ), the
0
.6 0.4
H
2
Pt
2
MIL-101_A. Inset: The corresponding TOF values of Ni Pt and
0
.9 0.1
5
Ni Pt /MIL-101_A, respectively.
best catalyst reported so far at room temperature. The highly
efficient utilization of noble metal endows this catalyst with
more possibility for practical application. The activation energy
0
.9 0.1
1
01_A shows a marked, more than 21-fold increase in activity
value for hydrolysis of the BH group (Part 1 in Figure 7a) and
and a much higher selectivity compared with the parent
Ni Pt NPs (that is, TOF of 68 h and selectivity of 77.5%)
3
−1
decomposition of the N H moiety (Part 2 in Figure 7a) of
2
4
0.9 0.1
N H BH over Ni Pt /MIL-101_A can be estimated to be
(
inset of Figure 5). Thus, the strong interaction of the MOF
2
4
3
0.9 0.1
1
8.6 and 44.6 kJ/mol, respectively, by using the Arrhenius plot
crystal and Ni-Pt alloy NPs is highly required for the better
catalytic performance. Due to the multiple advantages of the
synthesized Ni Pt /MIL-101_A catalyst, namely, the smaller
fitted by the corresponding H generation rate at different
2
reaction temperatures (Figure 7b).
0.9 0.1
particle sizes of NiPt alloy NPs provide more active sites, the
enrichment of substrates inside the pores of the MOF highly
boost the adsorption of N H BH by the active sites, and the
Hydrous hydrazine is a promising liquid hydrogen storage
42−45
material with high hydrogen content.
decomposition (100% selectivity calculated by Eq S1) of
·H O over Ni0.9Pt0.1/MIL-101_A at 333, 323, 313, and
The complete
2
4
3
open pore structure of the catalyst endows the freely mass
transfer in and out of catalysts during the heterogeneous
catalytic process, the greatly enhanced catalytic performance
N
H
2
4
2
303 K can be finished in 1.3, 1.9, 4.1, and 8.6 min,
corresponding to total TOF values of 922, 621, 296, and 140
Figure 6. Catalytic performance of Ni Pt /MIL-101 catalysts with different active sites locations for H generation from alkaline aqueous
0.9 0.1
2
N H BH solution (1.0 mmol, 5.0 mL, 0.5 M NaOH). Inset: the corresponding simulated diagrams of different Ni Pt /MIL-101 catalysts.
2
4
3
0.9 0.1
E
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Inorganic Chemistry
Article
Figure 7. (a) Time course plots for H generation from aqueous solution of N H BH and (c) N H ·H O over Ni Pt /MIL-101_A catalyst at
2
2
4
3
2
4
2
0.9 0.1
temperatures ranging from 303 to 333 K. Plot of ln k versus 1/T during the releasing of H from (b) the hydrolysis of BH group (Part 1) and
2
3
decomposition of the N H moiety (Part 2) and (d) decomposition of N H ·H O over Ni Pt /MIL-101_A catalyst at different temperatures.
2
4
2
4
2
0.9 0.1
Figure 8. Durability test for the H generation from alkaline aqueous N H BH solution catalyzed by Ni Pt /MIL-101_A (a) and Ni Pt /MIL-
2
2
4
3
0.9 0.1
0.9 0.1
1
01_C (b) at 323 K.
−
1
−1
mol ·mol ·h , respectively. The activation energy value
(Ni+Pt)
genation of N H BH as well as in decomposition of N H ·
2 4 3 2 4
H
2
H O (Figure S6). Without the stabilization of MOF ligands, the
for decomposition of N H ·H O is estimated to be 48.4 kJ/mol
Figure 7c,d), a little higher than that for decomposition of the
N H moiety of N H BH . These TOF and activation energy
values are comparable to those of state-of-the-art catalysts
Table S3). The NiPt/MIL-101_A showed a little higher
catalytic activity for H evolution from N H BH than that
from N H ·H O. A plausible explanation is that the quick
hydrolysis of the BH group of N H BH (Figure 7a,b) can
2
2
4
2
NiPt NPs on the outer surface of Ni Pt /MIL-101_C turned
(
0.9 0.1
46
to be easily aggregated after reaction (Figure S7). The MOF
2
4
2
4
3
frameworks of Ni Pt /MIL-101_A were not well retained
0.9 0.1
during the durability test according to the SEM image and XRD
pattern of the sample after 7 cycles of reactions in
(
2
2
4
3
dehydrogenation of N H BH (Figures S8 and S9), probably
2
4
3
2
4
2
due to the long-time corrosion by high concentration of NaOH
in the reaction solution. However, the micropore and mesopore
features of MOF were well retained as verified by the
3
2
4
3
highly accelerate the transfer of the resulting N H moiety to
the active sites and promote the kinetic for decomposition of
N H .
2
4
corresponding N sorption isotherms (Figure S10a) and pore
2
4
2
The stability of a catalyst is of great importance for practical
size distribution curves (Figure S10b). From the TEM and
HAADF-STEM images of the sample after 20 cycles of
application. Therefore, the durability of the Ni Pt /MIL-
0
.9 0.1
1
01_A catalyst for H evolution from dehydrogenation of
reactions in dehydrogenation of N H BH , the NiPt alloy NPs
2 4 3
2
N H BH at 323 K was tested (Figure 8a). After 20 cycles of
are still highly dispersed in the resulting fragments and the
serious aggregation of metal NPs is not observed (Figure S11).
Consequently, we believe that the favorable activity of NiPt/
MIL-101_A retained during the durability test in dehydrogen-
2
4
3
reactions, the H productivity was kept at 100% with a slight
2
decrease in catalytic activity, indicating that the Ni Pt /MIL-
0
.9 0.1
101_A catalyst has prominent durability in catalytic dehydro-
F
DOI: 10.1021/acs.inorgchem.7b01910
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Inorganic Chemistry
Article
ation of alkaline N H BH (Figure 8a) or N H ·H O (Figure
(5) Zhu, Q.-L.; Xu, Q. Liquid organic and inorganic chemical
hydrides for high-capacity hydrogen storage. Energy Environ. Sci. 2015,
2
4
3
2
4
2
S6) is mainly due to the fact that the ligands of MIL-101 can
avoid the particle aggregation during the heterogeneous
catalytic process.
8
(
, 478−512.
6) Yang, J.; Sudik, A.; Wolverton, C.; Siegel, D. J. High capacity
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4
. CONCLUSION
(
7) Sevilla, M.; Mokaya, R. Energy storage applications of activated
In summary, a series of catalysts that comprise tiny NiPt alloy
NPs encapsulated within a MOF have been successfully
synthesized via a reduction rate controlled strategy, which is
proved to be effective to tailor the size and spatial distribution
of bimetallic alloy NPs in porous materials. When a rapid
carbons: supercapacitors and hydrogen storage. Energy Environ. Sci.
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(
̈ ̈
8) Hugle, T.; Kuhnel, M. F.; Lentz, D. Hydrazine borane: a
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7
(
reduction process with a higher NaBH /metals molar ratio was
4
applied, most of the bimetallic NiPt alloy NPs with a tiny size
(
(
2.5 nm) would be encapsulated within the pore channels of
Zhang, T.; Chen, P. Borohydride hydrazinates: high hydrogen content
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MOFs without agglomeration on the external surface of the
host. The resulting low Pt content Ni Pt /MIL-101_A
0
.9 0.1
catalyst exhibited outstanding activity and durability for
complete H evolution from dehydrogenation of N H BH or
(11) Wu, H.; Zhou, W.; Pinkerton, F. E.; Udovic, T. J.; Yildirim, T.;
Rush, J. J. Metal hydrazinoborane LiN
2N BH : crystal structures and high-extent dehydrogenation. Energy
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H BH and LiN H BH ·
3 3 2 3 3
2
2
4
3
2
N H ·H O and, thus, may promote the practical use of
2
H
4
3
2
4
2
N H BH and N H ·H O as chemical hydrogen storage
2
4
3
2
4
2
(
materials for H evolution. The MOF ligands stabilized NiPt
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S.; Petit, E.; van der Lee, A.; Miele, P. Hydrazine borane: synthesis,
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NPs displayed excellent durability in 20 cycles of reactions
without obvious activity loss and MNPs aggregation, though
the MOF frameworks were not well retained during the long-
time corrosion by high concentration of NaOH in the reaction
solution.
̈
(13) Karahan, S.; Zahmakiran, M.; Ozkar, S. Catalytic hydrolysis of
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ASSOCIATED CONTENT
(14) Hannauer, J.; Demirci, U. B.; Geantet, C.; Herrmann, J.-M.;
Miele, P. Transition metal-catalyzed dehydrogenation of hydrazine
borane N H BH via the hydrolysis of BH and the decomposition of
■
*
S
Supporting Information
2
4
3
3
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b01910.
N H . Int. J. Hydrogen Energy 2012, 37, 10758−10767.
2
4
̈
(15) Karahan, S.; Zahmakiran, M.; Ozkar, S. Catalytic methanolysis
of hydrazine borane: a new and efficient hydrogen generation system
under mild conditions. Dalton Trans. 2012, 41, 4912−4918.
Additional information as noted in text (PDF)
(
16) Yao, Q.; Lu, Z.-H.; Zhang, Z.; Chen, X.; Lan, Y. One-pot
synthesis of core-shell Cu@SiO nanospheres and their catalysis for
hydrolytic dehydrogenation of ammonia borane and hydrazine borane.
2
AUTHOR INFORMATION
■
Sci. Rep. 2014, 4, 7597.
Corresponding Author
(17) Çakanyildirim, Ç.; Demirci, U. B.; Şener, T.; Xu, Q.; Miele, P.
*E-mail: luzh@jxnu.edu.cn.
Nickel-based bimetallic nanocatalysts in high-extent dehydrogenation
of hydrazine borane. Int. J. Hydrogen Energy 2012, 37, 9722−9729.
(18) Chen, J.; Yao, Q.; Zhu, J.; Chen, X.; Lu, Z.-H. Rh−Ni
nanoparticles immobilized on Ce(OH)CO3 nanorods as highly
efficient catalysts for hydrogen generation from alkaline solution of
hydrazine. Int. J. Hydrogen Energy 2016, 41, 3946−3954.
ORCID
Zhang-Hui Lu: 0000-0001-6342-0879
Notes
The authors declare no competing financial interest.
(19) Singh, S. K.; Zhang, X.-B.; Xu, Q. Room-temperature hydrogen
ACKNOWLEDGMENTS
generation from hydrous hydrazine for chemical hydrogen storage. J.
Am. Chem. Soc. 2009, 131, 9894−9895.
■
This work was financially supported by the National Natural
Science Foundation of China (Nos. 21763012 and 21463012)
and the Natural Science Foundation of Jiangxi Province of
China (Nos. 20171ACB21021 and 2016BAB203087).
(20) Singh, S. K.; Xu, Q. Complete conversion of hydrous hydrazine
to hydrogen at room temperature for chemical hydrogen storage. J.
Am. Chem. Soc. 2009, 131, 18032−18033.
(21) Wang, J.; Li, W.; Wen, Y.; Gu, L.; Zhang, Y. Rh-Ni-B
nanoparticles as highly efficient catalysts for hydrogen generation from
hydrous hydrazine. Adv. Energy Mater. 2015, 5, 1401879.
(22) Hannauer, J.; Akdim, O.; Demirci, U. B.; Geantet, C.;
Herrmann, J.-M.; Miele, P.; Xu, Q. High-extent dehydrogenation of
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