Hydrolysis of Ammonia-Borane over Ni/ZIF-8 Nanocatalyst: High Efficiency, Mechanism, and Controlled Hydrogen Release

Article abstract of DOI:10.1021/jacs.7b06859

Non-noble metal nanoparticles are notoriously difficult to prepare and stabilize with appropriate dispersion, which in turn severely limits their catalytic functions. Here, using zeolitic imidazolate framework (ZIF-8) as MOF template, catalytically remark

Full text of DOI:10.1021/jacs.7b06859

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Article
Hydrolysis of ammonia-borane over Ni/ZIF-8 nanocatalyst:
high efficiency, mechanism and controlled hydrogen release
Changlong Wang, Jimena Tuninetti, Zhao WANG, Chen Zhang, Roberto
Ciganda, Lionel Salmon, Sergio Moya, Jaime Ruiz, and Didier Astruc
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 01 Aug 2017
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Hydrolysis of ammonia-borane over Ni/ZIF-8 nanocatalyst:
high efficiency, mechanism and controlled hydrogen release
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Changlong Wang,§,ǁ Jimena Tuninetti,♯ Zhao Wang,♩ Chen Zhang,§ Roberto Ciganda,ǁ
Lionel Salmon,§ Sergio Moya,♯ Jaime Ruiz,ǁ Didier Astrucǁ,*
§ Laboratoire de Chimie de Coordination, UPR CNRS 8241, 31077 Toulouse Cedex,
France
ǁ ISM, UMR CNRS N。5255, Univ. Bordeaux, 33405 Talence Cedex, France
♯ CIC biomaGUNE, Unidad Biosuperficies, Paseo Miramon No 182, Edif “C”, 20009
DonostiaꢀSan Sebastian, Spain
♩
Sorbonne Universités, UPMC Univ Paris 06, UMR CNRS 7197, Laboratoire de
Réactivité de Surface, 4 Place Jussieu, Tour 43ꢀ33, 3ème étage, Case 178, Fꢀ75252
Paris, France
Abstract
Nonꢀnoble metal nanoparticles are notoriously difficult to prepare and stabilize with
appropriate dispersion, which in turn severely limits their catalytic functions. Here
using zeolitic imidazolate framework (ZIFꢀ8) as MOF template, catalytically
remarkably efficient ligandꢀfree firstꢀrow late transitionꢀmetal nanoparticles are
prepared and compared. Upon scrutiny of the catalytic principles in the hydrolysis of
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ammoniaꢀborane, the highest total turnover frequency among these firstꢀrow late
transition metals is achieved for the templated Ni nanoparticles with 85.7
molH2·molcatꢀ1·minꢀ1 at room temperature, which overtakes performances of previous
nonꢀnoble metal nanoparticles systems, and is even better than some noble metal
nanoparticles systems. Mechanistic studies especially using kinetic isotope effects
show that cleavage by oxidative addition of an O–H bond in H2O is the rate
determining steps in this reaction. Inspired by these mechanistic studies, an attractive
and effective “onꢀoff” control of hydrogen production is further proposed.
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Introduction
Catalytic hydrogen generation from hydrogen storage materials is considered as a
convenient, inexpensive, and effective approach to address the energy and
environmental concern.1ꢀ4 Among various chemical hydrogen storage materials,
ammoniaꢀborane (AB) has a high hydrogen content (19.6 wt%), high stability in the
solid state and solution under ambient conditions, nontoxicity, and high solubility.
Therefore it is considered as one of the most leading contender in promising chemical
hydrogenꢀstorage materials for various applications.5ꢀ15
Until now, effective catalysts for hydrolysis of AB are typically based on expensive
and rare noble metal nanocatalysts (e.g., Rh, Pt, Ru). Considerable efforts have been
devoted to the design of highꢀperformance noble metalꢀfree nanocatalysts,16ꢀ25 On the
other hand, the hydrolysis of AB under mild conditions by cheap and earthꢀabundant
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first row metal nanoparticles (Fe, Co, Ni and Cu, “BM”) with practical efficiency and
sustainability remains extremely challenging, largely due to their labile nature,
complex mechanistic manifolds and low catalytic efficiencies.26
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Supported nanoparticle (NP) catalysts have shown remarkable catalytic efficiencies. It
has also been found, however, that the activities were significantly influenced or/and
eventually determined by the NP supports.27ꢀ37 In this regard, metal organic
frameworks (MOFs) are outstanding emerging porous nanomaterials that are
advantageous compared to other conventional inorganic supports.38ꢀ43 MOFs allow
confining and stabilizing catalytically active metal NPs within their frameworks,
which controls the nucleation and growth of NPs, thus preventing their aggregation
and prolonging their stabilities.44ꢀ51 Moreover, the high specific surface areas and
tunable pore sizes ensured good NP dispersion, which allows exposing active sites
and facilitates the accessibility of substrates to the active NP surface by reducing
diffusion resistance.44ꢀ51 On the other hand, the direct use of nanoconfinement effect
by MOFs provides a facile method to prepare ligandꢀfree and ultrafine NP/MOF
nanocatalysts, which is significant but also crucial for the design of highly efficient
heterogeneous catalysts. However, the comparison of the catalytic efficiencies of
BMNPs using the same MOF template have not yet been disclosed.
In addition to the rational design of new nanocatalysts, insights to the mechanistic
aspects of the hydrolysis reaction would be essential for the enhancement of the
catalytic efficiencies of the BMNPs/MOFs nanocatalysts. The details of the reaction
process of AB hydrolysis over BMNPs/MOFs nanocatalysts again have rarely been
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experimentally examined, however. In order to address these challenging issues, we
now report the synthesis, characterization and catalytic functions of the
BMNPs/zeolitic imidazolate framework (ZIFꢀ8; [Zn(MeIM)2]n) nanocatalysts,
especially with efforts to further improve the catalytic activity by understanding the
mechanistic aspects of the hydrolysis reaction. First, the supporting nanomaterial of
ZIFꢀ8 is synthesized and characterized. Then we highlight the efficiency of
Ni NPs/ZIFꢀ8 nanocatalyst by comparing the catalytic activities of firstꢀrow late
transitionꢀmetals NPs/ZIFꢀ8 catalysts in the hydrolysis of AB in water under mild
conditions. Subsequently we scrutinize the catalytic behavior of Ni NPs/ZIFꢀ8
nanocatalysts for the hydrolysis of AB in water, the mechanistic aspects of this
reaction using kinetic isotope effects (KIEs), and an anion effect for the control of
hydrogen release. The catalytic activity of the nanocatalyst Ni NPs/ZIFꢀ8 surpassed
all the nonꢀnoble metal NP systems for the hydrolysis of AB.
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Result and discussion
Synthesis and characterizations of the nanocatalysts: The ZIFꢀ8 nanoparticles52
are first rapidly synthesized in water using a modified method (SI).53 Transmission
electron microscope (TEM) image indicates that the ZIFꢀ8 NPs are nanocrystals with
sharp hexagonal facets, and the average size of ZIFꢀ8 NPs is around 75 nm (Figure
S1). Powder Xꢀray diffraction (PXRD) proves the pure phase of ZIFꢀ8 nanomaterial
(Figure S2). ZIFꢀ8 NPs show a type I isotherm in the N2 adsorption measurement. The
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presence of micropores results in volume increase adsorbed at very low relative
pressures, whereas a second uptake at a high relative pressure indicates the existence
of textural meso/macroporosity formed by the packing of NPs (Figure S3). The
BrunauerꢀEmmettꢀTeller (BET) surface area of ZIFꢀ8 NPs is 1663.3 m2 g−1. Refluxing
the ZIFꢀ8 NPs in either methanol or water during one day does not change the
framework structure, as evidenced from the unchanged PXRD patterns (Figure S2),
showing the thermal and chemical stabilities of ZIFꢀ8 NPs.52,53
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The nanocatalysts BMNPs/ZIFꢀ8 are prepared using the depositionꢀprecipitation (DP)
method with fast reduction by NaBH4, then collected by centrifugation followed by
washing and drying in vacuo (Scheme 1 and SI). These nanomaterials are clearly
distinguished by their colors (compare the photographs in Figure S4); for instance Ni
NPs/ZIFꢀ8 appears grey, whereas Cu NPs/ZIFꢀ8 is completely black. No diffractions
are detected for Ni NP species from PXRD patterns after reduction in Ni NPs/ZIFꢀ8
compared to ZIFꢀ8 NPs, which indicates that Ni loadings are too low or Ni NPs are
too small.49,54 The metal loading is determined by inductively coupled plasmaꢀoptical
emission spectroscopy (ICPꢀAES); for instance the Ni loading in Ni NPs/ZIFꢀ8 is 2.2
wt%. The metal oxidation state is then identified by XꢀRay photoelectron
spectroscopy (XPS). Binding energies (B.E.) of 1021.4 and 1044.5 eV are observed
for the 2p3/2 and 2p1/2 levels of the Zn2+ ion in the ZIFꢀ8 framework, respectively
(Figure S5). Moreover the wellꢀdefined peaks with B.E. of 852.2 and 870.1 eV are
detected for the 2p3/2 and 2p1/2 levels (Figure S6), respectively, of metallic Ni0 in the
Ni NPs.17,21
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Scheme 1. Preparations of the nanocatalysts BMNP/ZIFꢀ8.
Interestingly, after the deposition of the BMNPs, the nanocatalysts BMNPs/ZIFꢀ8
become more spherical, as exemplified by NiNPs/ZIFꢀ8 (Figures 1a and 1b). The
measurements of the NP size by TEM encounters problems, however, probably due to
their small sizes and lack of contrast over ZIFꢀ8 framework. In order to release the
BMNPs from the nanocatalysts BMNPs/ZIFꢀ8 for direct TEM characterization, the
ZIFꢀ8 framework was then digested using a solution of ethylenediaminetetraacetic
acid (EDTA)55 in the presence of poly(vinylpyrrolidone) (PVP, Mw = 10,000) to
stabilize the ultrasmall NPs. In this way the sizes of the BMNPs are successfully
measured by TEM (Table 1). The size of the released NiNPs is 2.7 nm, and other size
distributions of FeNPs, CoNPs, and CuNPs are shown in Table 1 and in the SI
(Figures S7ꢀS10). On the other hand, nitrogen sorption experiments of the
nanocatalysts show type I shape and considerable decrease of pore volume and BET
surface areas (Table 1 and Figure S3). This indicates blocking of the windows of the
ZIFꢀ8 framework cavities by highly dispersed NPs within the locally distorted
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environment or/and the location of NPs at the surface; the latter was also shown by
TEM in Figure 1b, for instance for NiNPs/ZIFꢀ8.
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Table 1. Physical properties and catalytic efficiencies of the nanocatalysts.
Sample
Sizea
(nm)
BET surface Pore volume
TOFb
area
(cm3 g−1)
(molH2·molcatꢀ1·minꢀ1)
(m2 g−1)
ZIFꢀ8
75±3
1663.3
0.6614
ꢀꢀ
FeNPs/ZIFꢀ8
CoNPs/ZIFꢀ8
NiNPs/ZIFꢀ8
3.0±0.4
2.9±0.3
2.7±0.3
3.2±0.4
1313.3
1313.8
1324.3
1367.3
0.4491
0.4539
0.4255
0.4110
2.5
19.4
35.3/85.7c
5.6
CuNPs/ZIFꢀ8
b
a TEM size. Hydrolysis of AB in water at room temperature (25 ± 0.5°C), TOF =
c
molH2 released / (molcatalyst × reaction time(min)). TOF is obtained in the presence of
0.3M NaOH.
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Figure 1. TEM images of NiNPs/ZIFꢀ8: (a) at 500 nm scale. (b) at 20 nm scale. (c)
NiNPs in NiNPs/ZIFꢀ8 after digestion using EDTA and capping with PVP.
High efficiency of NiNPs/ZIF-8 in the hydrolysis of AB and mechanistic studies.
The catalytic performances of the BMNPs/ZIFꢀ8 are evaluated for the hydrolysis of
AB reaction in water. Hydrolysis of AB starts in water by employing 3 mol% of the
various late transition metal nanocatalysts BMNPs/ZIFꢀ8 (measured by ICPꢀAES).
The reaction profile in the presence of the nanocatalysts BMNPs/ZIFꢀ8 is shown in
Figure S11. The volumes of gas collected represent nearly 3 equiv. H2 per AB with no
detectable NH3 (SI),56 indicating that hydrolysis of AB catalyzed by the nanocatalyst
BMNPs/ZIFꢀ8 proceeds according to Equation (1):
BMNPs/ZIFꢀ8 nanocatalysts
ꢀ
NH4+ + BO2 + 3 H2
H3NBH3
2 H2O
(1)
+
r.t., H2O
This comparison demonstrates the best activity of NiNPs/ZIFꢀ8 in terms of turn over
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frequency (TOF) among the four nanocatalysts BMNPs/ZIFꢀ8 (Table 1 and Figure
S11). Therefore the catalytic system NiNPs/ZIFꢀ8 was chosen for further studies.
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Figure S12 shows the logarithmic plot of the hydrogen generation rate vs
.
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concentration of NiNPs/ZIFꢀ8; the slope is 0.98, indicating that the hydrolysis of AB
catalyzed by NiNPs/ZIFꢀ8 is firstꢀorder with respect to the catalyst concentration. On
the other hand hydrolysis of AB catalyzed by NiNPs/ZIFꢀ8 is zeroꢀorder with respect
to the AB concentration, as a nearly horizontal line (slope of 0.086) is observed
(Figure S13). This implies that under the present reaction conditions, AB is easily
activated, and thus the possibility of the activation of AB in the rateꢀdetermining step
(RDS) is ruled out. This also is in accordance with the KIE results (vide infra). The
activation energy (Ea) of AB hydrolysis, determined by measuring the time
dependence of H2 generation at various temperatures, is approximately 42.7 kJ/mol
(Figure S14 and calculation). This value also is lower than those found for several
known noble metalꢀbased nanocatalysts (Table S1).
Although the catalytic rates in the hydrolysis of AB catalyzed by NiNPs/ZIFꢀ8 is
independent of the AB concentration, the KIE57ꢀ59 was further investigated in order to
shed light on the RDS of hydrolysis of AB catalyzed by NiNPs/ZIFꢀ8. Indeed in this
reaction the KIE value should tell if N−H or B−H or both bonds are broken during the
RDS.16,60ꢀ63
The hydrolysis of the deuterated products of AB (for their synthesis, see S.I.) in the
presence of NiNPs/ZIFꢀ8 shows slower reaction rates (Figure S17). A KIE of 1.33 is
determined for deuteration at the boron site (NH3BD3), indicating a similar
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dehydrogenation behavior to that of AB in H2O. This indicates that the absence of
large KIE for hydrolysis of AB deuterated at the boron site (NH3BD3). On the other
hand, the KIE value of 2.49 is calculated according to the H2 generation rates in
ND3BH3 (NH3BH3–D2O system), suggesting that the O–H bond cleavage of H2O
might be in the RDS. This would be similar to the metalꢀcatalyzed borohydride
hydrolysis, in which half of the hydrogen comes from water.64 Previously, it has been
suggested that the water activation by means of oxidative addition of a OꢀH bond on
noble metal NP surfaces easily occurs, forming adsorbed –OH and –H species. For
instance Pt NPs have been known as the redox catalyst for water photoꢀsplitting.65,66
That Ni is the best metal found here for the hydrolysis reaction among those four
firstꢀrow late transition metals is in accord with oxidative addition of water as the
RDS, because Ni(0) is known by far the best firstꢀrow metal catalyst of reactions
involving oxidative addition.67 In addition the involvement of water activation in the
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RDS may be partially explained by the higher OꢀH bond energy (
～
493 kJ molꢀ1)68
than that of B–N and B–H bond ( 117 and
～
～
430 kJ molꢀ1, respectively).69 Thus it is
mostly likely that the water molecule is activated by an indirect O–H bond cleavage to
form –H and –OH species promoted by AB in the presence of the nanocatalyst
NiNPs/ZIFꢀ8. Since the NH3 group does not participate in the hydrolysis, the B–N
bond dissociates in AB, followed by H2 release (Figure 2).
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Figure 2. Proposed mechanism for the hydrolysis of AB catalyzed by NiNPs/ZIFꢀ8.
Remarkable improvement of the catalytic performance by ion effect allowing the
controlled release of hydrogen. From the mechanistic studies, it can be assumed that
if OHꢀ is directly adsorbed on the surface of the Ni nanocatalyst, a bifunctional
catalyst with both H and OH adsorptions should be highly expected to provoke the
surface reaction. Thus the presence of surface OHꢀ should be of great value for the
enhancement of the catalytic activity. To verify this hypothesis, various concentrations
of NaOH (0.1ꢀ0.4 M), a conventional OHꢀ provider in aqueous solution, were
separately added to the reaction media that only contained NiNPs/ZIFꢀ8. After stirring
for 30 min, the aqueous solution of AB was added, and the catalytic activities were
examined. Surprisingly, as shown in Figure S18, the H2 generation rates greatly
improved as compared to the one in the absence of NaOH. The H2 generation rates
first increased with the increased NaOH concentrations (0.1ꢀ0.3 M), then decreased
with higher NaOH concentration (0.4 M). It is suggested that the accumulation of too
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much OHꢀ beyond the optimum level (0.3 M) could significantly reduce the beneficial
effect, resulting in the decrease of the H2 generation rate. The highest reaction rate in
term of TOF is 85.7 molH2·molcatꢀ1· minꢀ1 with 0.3 M NaOH, showing the best activity
among all the nonꢀnoble metal NP systems. This is even more efficient than noble
metal NPs systems (Table S1); for instance the utilization of commercial 40 wt %
Pt/C catalyst only had a TOF of 55.56 molH2·molcatꢀ1· minꢀ1. Control experiment
shows that the addition of NaOH has no effect on AB in aqueous solution in the
absence of catalyst, as no H2 release is observed, as also confirmed by the 1H and 11B
NMR spectra.70 On the other hand, other bases such as Na2CO3 and NaHCO3 have no
influence or slow down the H2 generation rate (SI).
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In parallel the hydrolysis reaction was also conducted under identical conditions,
except that NaOH was replaced by HCl (0.3 M solution for the final concentration),
and it was surprisingly found that there was no hydrogen release. Thus in the present
study, the contribution from OHꢀ predominated. The influence of OHꢀ and H+
disclosed here is different from the very recent work involving AB hydrolysis by
single Rh atoms/VO2 nanorods, which showed positive correlation between the H+
concentration and the reaction rate.71
Density functional theory (DFT) calculations on the interaction of H and OH with
(111) metal Ni surface suggested that H forms an essentially covalent bond with the
metal, whereas OH forms a largely ionic bond.72 The weaker covalent interaction and
a stronger Pauli repulsion of the OH with the metal
d electrons result in the preference
of binding molecular hydroxyl to Ni surface rather than H.73,74 Moreover, Ni is more
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oxophilic than Pt, so that it can better promote surface OH adsorption than Pt.75 To
confirm this, XPS is reꢀcalled to measure the surface binding energy of Ni 2p upon
treatment with NaOH. As shown in Figure S23, upon treatment with NaOH, the
binding energy at 855.6 eV that associates with Ni(OH)2 species76 becomes
predominant, verifying the coordination of OH group to the Ni surface. On the other
hand, a ca. 0.76 eV Ni 2p binding energy downshift was also observed. Thus upon
coordination of OH group to the Ni surface, the OH adsorbates donate electrons to the
Ni surface. This results in an increased electron density around the Ni surface, which
facilitates the interaction with the reactant, AB. The Ea of AB hydrolysis in the
presence 0.3 M NaOH was considerably decreased to 28.0 kJ/mol (Figure S24).
Therefore the overall reaction activity is significantly improved.
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The reason for the switch off of hydrogen generation possibly comes from two
aspects. One of them is the negative effect of H+ on the selfꢀionization of water that
suppresses the OHꢀ formation and occupation of OHꢀ absorption sites on the NiNP
surface. The other one is the ion effect, because Clꢀ ligands are known to limit the
catalytic activity of NPs by strongly bonding to NPs surface, which inhibits access to
the surface active sites. We thus first conducted the initial reaction by adding NaCl
solution (0.3 M), and found that the H2 generation rate was slower than that without
NaCl solution. H2 was released smoothly, however, with a TOF of 16.67
molH2·molcatꢀ1· minꢀ1 (Figure S25). This result suggests the possible ion effect in the
reaction. To confirm this ion effect, other aqueous solutions of for instance NaI,
NaBF4, NaBr, NaF, and Na2SO4 were then added to the reaction media with final
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concentration of 0.3 M (SI). The H2 generation rates were considerably slowed down
compared with the initial reaction preformed with only NiNPs/ZIFꢀ8, and the TOFs
were 10.3, 13.7, 16.2, 18.5 and 21.4 molH2·molcatꢀ1·minꢀ1 for NaI, NaBF4, NaBr, NaF
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2ꢀ
and Na2SO4, respectively. Interestingly, the catalytic activities follow the order: SO4 >
Fꢀ > Clꢀ > Brꢀ > Iꢀ, which also follows the direct Hofmeister series. Significant ion
effects occurred and showed correlations with the catalytic activities obtained in the
hydrolysis of AB reaction, a characteristic fingerprint of the Hofmeister effects. It is
suggested that H+ plays a very negative effect in the hydrolysis reaction. On the other
hand, ions such as Clꢀ, Fꢀ, Brꢀ et al present in the solution prefer to bind to the surface
active sites of NiNPs, leaving less active surface sites available to OHꢀ generated from
water activation in the RDS of hydrolysis. Thus the negative synergistic effects
switched off the hydrogen release. Therefore here we establish for the first time that
the anion effect tuned hydrolysis of AB catalyzed by the nanocatalyst NiNPs/ZIFꢀ8 in
water, allowing the hydrogen generation to reversibly turn “off” and “on”. This
property is of great practical importance for onꢀboard hydrogen applications under
ambient conditions (vide infra).
The “onꢀoff” control of hydrogen generation is achieved by addition of an equimolar
amount of aqueous solution of HCl and NaOH to the reaction media (Figure 3).
Through the studies above, OHꢀ facilitates the hydrolysis reaction, while H+ and Clꢀ
play negative roles in the hydrolysis of AB. At the beginning of the hydrolysis
reaction, H2 generation can be completely stopped by adding 0.3 M HCl solution, and
the H2 generation is released again by adding the same NaOH molarity. In this way,
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the H2 generation is controlled. In addition, in each “onꢀoff” cycle, a gradual decrease
in the H2 generation is also observed. Indeed the poisoning effect of H+ dominates the
switch off of the H2 generation. The subsequent addition of NaOH neutralizes the HCl
solution, however. The effect of NaCl production (from NaOH + HCl) was also
observed in the medium, also considerably slowing down the H2 generation (vide
supra).
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Figure 3. “Onꢀoff” control of H2 production in the AB hydrolysis in water.
Finally, we examined the reusability of the nanocatalyst NiNPs/ZIFꢀ8, which is a
critical issue for further practical applications. The reusability tests were conducted
under the present conditions by continuous addition of a new proportion of AB
aqueous solution when the previous run was completed. As shown in Figure 4, the
activity of NiNPs/ZIFꢀ8 is essentially retained until the fifth runs, where a slight drop
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in reaction rate is observed. The nanocatalyst was then characterized after the fifth
runs by PXRD and TEM techniques, PXRD showing the unchanged nanostructure
(Figure S30), while TEM showed the increase of NiNP size (Figure S31). Thus the
decrease in the activity is ascribed to the diluted reactant in water, the deactivation
effect of the hydrolysis product metaborate,77ꢀ79 and to the increased NiNP size,
especially for NPs at the surface of ZIFꢀ8.
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Figure 4. Plots of volume of H2 vs. time for the hydrolysis of AB catalyzed by the 3%
NiNPs/ZIFꢀ8 during the reusability test.
Concluding remarks. In summary, highly dispersed ligandꢀfree Fe NPs, Co NPs, Ni
NPs and Cu NPs have been successfully synthesized using ZIFꢀ8 as nanocatalyst
template, and the highest catalytic activity for hydrogen generation upon hydrolysis of
AB is shown to be that of NiNPs/ZIFꢀ8 showing a TOF value of 85.7
molH2·molcatꢀ1·minꢀ1. This represents the best TOF value ever reported for noble
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metalꢀfree catalysts. Detailed mechanistic investigations, especially KIE
measurements, show that the RDS for AB hydrolysis is the cleavage of an O–H bond
in H2O by means of oxidative addition of such a bond on Ni NP surfaces. Inspired by
this approach, we further disclosed the ion effect in this reaction, which allowed a
remarkable improvement of the catalytic performance and the controlled release of
hydrogen. The principles and results obtained here may not only provide insights into
the rational design of highly efficient nonꢀnoble metalꢀbased nanocatalysts, but also
demonstrate a promising step towards the application of chemical hydrogen storage
materials in a fuelꢀcellꢀbased hydrogen economy.
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ASSOCIATED CONTENT
1
Supporting Information. Syntheses and characterization of the nanocatalysts. H
NMR spectra of the products. Profiles of hydrolysis of the AB hydrolysis reactions.
This material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Author to whom correspondence should be addressed.
Eꢀmail: didier.astruc@uꢀbordeaux.fr
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENT
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Record of an XPS spectrum of NiꢀZIFꢀ8 nanomaterial from and helpful discussion
with Luis Yate (CIC biomaGUNE) and financial support from the China Scholarship
Council (CSC) of the People’s Republic of China (grant to C.W.), the Universities of
Toulouse 3 and Bordeaux, the Centre National de la Recherche Scientifique (CNRS),
and CIC biomaGUNE (FP7ꢀPEOPLEꢀIRSESꢀ HIGRAPHEN Project ID: 612704
gratefully acknowledged.
) are
REFERENCES
1 Armaroli, N.; Balzani, V. ChemSusChem 2011, 4, 21–36.
2 Yang, J.; Sudik, A.; Wolverton, C.; Siegel, D. J. Chem. Soc. Rev. 2010, 39, 656–
675.
3 Li, Z.; Xu, Q. Acc. Chem. Res. 2017, 50, 449–1458.
4 He, T.; Pachfule, P.; Wu, H.; Xu, Q.; Chen, P. Nat. Rev. Mater. 2016, 1, 16059.
5 Chandra, M.; Xu Q. J. Power Sources 2006, 156, 190ꢀ194.
6 Hamilton, C. W.; Baker, R. T.; Staubitz, A.; Manners, I. Chem. Soc. Rev. 2009, 38,
279–293.
7 Staubitz, A.; Robertson, A. P. M.; Manners, I. Chem. Rev. 2010, 110, 4079–4124.
8 Zhu, Q. L.; Xu, Q. Energy Environ. Sci. 2015, 8, 478–512.
18
ACS Paragon Plus Environment

Page 19 of 24
Journal of the American Chemical Society
1
2
3
4
5
6
9 Rossin, A.; Peruzzini, M. Chem. Rev. 2016, 116, 8848ꢀ8872.
10 Zhu, Q. –L.; Xu, Q. Chem 2016, 1, 220ꢀ245.
7
8
9
11 Zhan, W. ꢀW.; Zhu, Q. –L.; Xu, Q. ACS Catal. 2016, 6, 6892–6905.
12 Akbayrak, S.; Özkar S. In Hydrogen Production Technologies, pp. 207ꢀ230,
Sankir, M. and Sankir, N. D.; ed.; WileyꢀVCH: Weinheim, Germany, 2017.
13 Yang, Q. H.; Xu, Q.; Yu, S. H.; Jiang, H. L. Angew.Chem., Int .Ed. 2016, 55,
3685ꢀ3689.
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
14 Khalily, M. A.; Eren, H.; Akbayrak, S.; Susapto, H. H.; Biyikli, N.; Özkar, S.;
Guler, M. O. Angew. Chem. Int. Ed. 2016, 55, 12257 –12261.
15 J. –X. Kang, T. –W. Chen, D. –F. Zhang, L. Guo, Nano Energy 2016, 23, 145–152.
16 Li, Z.; He, T.; Liu, L.; Chen, W.; Zhang, M.; Wu, G.; Chen, P. Chem. Sci. 2017, 8,
781ꢀ788.
17 Mahyari, M.; Shaabani, A. J. Mater. Chem. A, 2014, 2, 16652–16659.
18 Yu, C.; Fu, J.; Muzzio, M.; Shen, T.; Su, D.; Zhu, J.; Sun, S. Chem.
Mater., 2017, 29, 1413–1418.
19 Zhou, L.; Meng, J.; Li, P.; Tao, Z.; Mai, L.; Chen, J. Mater. Horiz., 2017, 4,
268ꢀ273.
20 Bulut, A.; Yurderi, M.; Ertas, I. E.; Celebi, M.; Kaya, M.; Zahmakiran, M. Appl.
Catal. B: En. 2016, 180, 121–129.
21 Yin, H.; Kuwahara, Y.; Mori, K.; Cheng, H.; Wen, M.; Yamashita, H. J. Mater.
Chem. A 2017, 5, 8946ꢀ8953.
22 Liu, P.; Gu, X.; Kang, K.; Zhang, H.; Cheng, J.; Su, H. ACS Appl. Mater.
19
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 20 of 24
1
2
3
4
Interfaces 2017, 9, 10759–10767.
5
6
7
8
9
23 Zhang, H.; Gu, X.; Liu, P.; Song, J.; Cheng, J.; Su, H. J. Mater. Chem. A 2017, 5,
2288ꢀ2296.
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
24 Tang, C.; Xie, L.; Wang, K.; Du, G.; Asiri, A. M.; Luo, Y.; Sun, X. J. Mater.
Chem. A 2016, 4, 12407ꢀ12410.
25 Feng, K.; Zhong, J.; Zhao, B.; Zhang, H.; Xu, L.; Sun, X.; Lee, S. ꢀT. Angew.
Chem., Int. Ed. 2016, 55, 11950ꢀ11954.
26 Wang, D.; Astruc, D. Chem. Soc. Rev. 2017, 46, 816ꢀ854.
27 Yang, Q.; Xu, Q.; Jiang, H.–L. Chem. Soc. Rev. 2017, DOI: 10.1039/C6CS00724D.
28 Astruc, D.; Lu, F.; Ruiz, J. Angew. Chem., Int. Ed. 2005, 44, 7852ꢀ7872.
29 Navalon, S.; Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. Coord. Chem. Rev.
2016, 312, 99–148.
30 Fihri, A.; Bouhrara, M.; Nekoueihahraki, B.; Basset, J. M.; Polhettiwar, V. Chem.
Soc. Rev. 2011, 40, 5181ꢀ5203.
31 Gross, E.; Liu, J. H. ꢀC.; Toste, F. D.; Somorjai, G. A. Nat. Chem. 2012, 4,
947ꢀ952.
32 Bai, C.; Liu, M. Nano Today 2012, 7, 258ꢀ281.
33 Scholden, J. D.; Leal, B. C.; Dupont, J. ACS Catal. 2012, 2, 184ꢀ200.
34 Sankar, M.; Dimitratos, N.; Miedjack, P. J.; Wells, P. P.; Kiely, C. J.; Hutchings, G.
J. Chem. Soc. Rev. 2012, 41, 8099ꢀ8139.
35 Haruta, M. Angew. Chem. Int. Ed. 2014, 53, 52ꢀ56.
36 Amiens, C.; CiuculescuꢀPradines, D.; Philippot, K. Coord. Chem. Rev. 2016, 308,
20
ACS Paragon Plus Environment

Page 21 of 24
Journal of the American Chemical Society
1
2
3
4
409ꢀ432.
5
6
7
8
9
37 Xia, Y.; Gilroy, K. D.; Peng, H.–C.; Xia, X. Angew. Chem., Int. Ed. 2017, 56,
60ꢀ95.
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
38 Lee, J.Y.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Chem.
Soc. Rev. 2009, 38, 1450ꢀ1459.
39 Farrusseng, D.; Aguado, S.; Pinel, C. Angew. Chem., Int. Ed. 2009, 48, 7502ꢀ7513.
40 Zeng, L.; Guo, X.; He, C.; Duan, C. ACS Catal. 2016, 6, 7935–7947.
41 Liu, J.; Chen, L.; Cui, H.; Zhang, J.; Zhang, L.; Su, C. –Y. Chem. Soc. Rev. 2014, 43,
6011ꢀ6061.
42 Chughtai, A. H.; Ahmad, N.; Younus, H. A.; Laypkov, A.; Verpoort, F. Chem. Soc. Rev.
2015, 44, 6804ꢀ6849.
43 Dhakshinamoorthy, A.; Garcia, H. Chem. Soc. Rev. 2012, 41, 5262ꢀ5284.
44 Lu, G.; Li, S.; Guo, Z.; Farha, O. K.; Hauser, B. G.; Qi, X.; Wang, Y.; Wang, X.; Han, S.;
Liu, X.; DuChene, J. S.; Zhang, H.; Zhang, Q.; Chen, X.; Ma, J.; Loo, S. C. J.; Wei, W. D.;
Yang, Y.; Hupp, J. T.; Huo, F. Nat. Chem. 2012, 4, 310–316.
45 Choi, K. M.; Na, K.; Somorjai, G. A.; Yaghi, O. M. J. Am. Chem. Soc. 2015, 137,
7810ꢀ7816.
46 Na, K.; Choi, M.; Yaghi, O. M.; Somorjai, G. A. Nano Lett. 2014, 14, 5979ꢀ5983.
47 Rungtaweevoranit, B.; Baek, J.; Araujo, J. R.; Archanjo, B. S.; Choi, K. M.; Yaghi,
O. M.; Somorjai, G. A. Nano Lett. 2016, 16, 7645–7649.
48 Aijaz, A.; Karkamkar, A.; Choi, Y. J.; Tsumori, N.; Rönnebro, E.; Autrey,
T.; Shioyama, H.; Xu, Q. J. Am. Chem. Soc. 2012, 134, 13926–13929.
21
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Journal of the American Chemical Society
Page 22 of 24
1
2
3
4
5
6
49 Zhao, M.; Yuan, K.; Wang, Y.; Li, G.; Guo, J.; Gu, L.; Hu, W.; Zhao, H.; Tang, Z.
Nature 2016, 539, 76–80.
7
8
9
50 An, B.; Zhang, J.; Cheng, K.; Ji, P.; Wang, C.; Lin, W. J. Am. Chem. Soc. 2017, 139,
3834–3840.
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
51 Choi, K. M.; Kim, D.; Rungtaweevoranit, B.; Trickett, C. A.; Barmanbek, J. T.
D.; Alshammari, A. S.; Yang, P.; Yaghi, O. M. J. Am. Chem. Soc. 2017, 139, 356–362.
52 Park, K. S.; Ni, Z.; Cote, A. P.; Choi, J. Y.; Huang, R.; UribeꢀRomo, F. J.; Chae, H.
K.; O’Keeffe, M.; Yaghi, O. M. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 10186–
10191.
53 Pan, Y.; Liu, Y.; Zeng, G.; Zhao, L.; Lai, Z. Chem. Commun. 2011, 47, 2071–2073.
54 Yurderi, M.; Bulut, A.; Zahmakiran, M.; Gülcan, M.; Özkar, S. Appl. Catal. B:
Environ. 2014, 160, 534–541.
55 Lu, G.; Hupp, J. T. J. Am. Chem. Soc. 2010, 132, 7832–7833.
56 Metin, Ö.; Mazumder, V.; Özkar, S.; Sun, S. J. Am. Chem. Soc. 2010, 132,
1468ꢀ1469.
57 Westaway, K. C. J. Labelled Compd. Radiopharm. 2007, 50, 989–1005.
58 Guella, G.; Patton, B.; Miotello, A. J. Phys. Chem. C 2007, 111, 18744–18750.
59 Simmons, E. M.; Hartwig, J. F. Angew. Chem., Int. Ed. 2012, 51, 3066–3072.
60 Keaton, R. J.; Blacquiere, J. M.; Baker, R. T. J. Am. Chem. Soc. 2007, 129, 1844–
1845.
61 Bhattacharya, P.; Krause, J. A.; Guan, H. J. Am. Chem. Soc. 2014, 136,
11153−11161.
22
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Page 23 of 24
Journal of the American Chemical Society
1
2
3
4
5
6
62 Buss, J. A.; Edouard, G. A.; Cheng, C.; Shi, J.; Agapie, T. J. Am. Chem. Soc. 2014,
136, 11272−11275.
7
8
9
63 Chen, W.; Li, D.; Wang, Z.; Qian, G.; Sui, Z.; Duan, X.; Zhou, X.; Yeboah, I.;
Chen, D. AIChE J. 2017, 63, 60–65.
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
64 Liu, B. H.; Li, Z. P. J. Power Sources 2009, 187, 527–534.
65 Lehn, J. ꢀM.; Sauvage, J. ꢀP. Nouv. J. Chim. 1977, 1, 449–451.
66 Hagfeldt, A.; Grätzel, M. Chem. Rev. 1995, 95, 49–68.
67 Astruc, D. Organometallic chemistry and catalysis; Springer: Berlin, New York,
2007.
68 Rablen, P. R. J. Am. Chem. Soc. 1997, 119, 8350–8360.
69 Peebles, L. R.; Marshall, P. J. Chem. Phys. 2002, 117, 3132–3138.
70 Fu, Z.ꢀC.; Xu, Y.; Chan, S. L.ꢀF.; Wang, W.ꢀW.; Li, F.; Liang, F.;Chen, Y.; Lin, Z.ꢀS.;
Fu, W.ꢀF.; Che, C.ꢀM. Chem. Commun. 2017, 53, 705ꢀ708.
71 Wang, L.; Li, H.; Zhang, W.; Zhao, X.; Qiu, J.; Li, A.; Zheng, X.; Hu, Z.; Si, R.;
Zeng, J. Angew. Chem., Int. Ed. 2017, 56, 4712 –4718.
72 Koper, M. T. M.; van Santen, R. A. J. Electroanal. Chem. 1999, 472,126–136.
73 Gómez, E. del V.; AmayaꢀRoncancio, S.; Avalle, L. B.; Linares, D. H.; Gimenez,
M. C. Appl. Sur. Sci. 2017, 420, 1–8.
74 Bengaard, H. S.; Nørskov, J. K.; Sehested, J.; Clausen, B. S.; Nielsen, L. P.;
Molenbroek, A. M.; RostrupꢀNielsen, J. R. J. Catal. 2002, 209, 365–384.
75 Wang, C.; Chi, M.; Wang, G.; van der Vliet, D.; Li, D.; More, K.; Wang, H.ꢀH.;
Schlueter, J. A.; Markovic, N. M.; Stamenkovic, V. R. Adv. Funct. Mater. 2011, 21,
23
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1
2
3
4
147−152.
5
6
7
8
9
76 Grosvenor, A. P.; Biesinger, M. C.; St.C. Smart, R.; McIntyre, N. S. Surf. Sci. 2006,
600, 1771ꢀ1779.
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
77 Zhu, Q. –L.; Li, J.; Xu. Q. J. Am. Chem. Soc. 2013, 135, 10210−10213.
78 Rakap, M. Appl. Catal. B: En. 2015, 163, 129–134.
79 Chen, W.; Ji, J.; Feng, X.; Duan, X.; Qian, G.; Li, P.; Zhou, X.; Chen, D.; Yuan, W.
J. Am. Chem. Soc. 2014, 136, 16736–16739.
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