Temperature-induced enhancement of catalytic performance in selective hydrogen generation from hydrous hydrazine with Ni-based nanocatalysts for chemical hydrogen storage

Article abstract of DOI:10.1002/ejic.201100083

We demonstrate here that Ni nanoparticles, which are inactive for the decomposition of hydrous hydrazine at room temperature, can exhibit drastically enhanced catalytic performance with an increase in reaction temperature to 323 K. At this reaction temperature, complete conversion of hydrous hydrazine with 100 % H₂ selectivity can be achieved by alloying Ni and Pt with a Pt content as low as 1 mol-%. This significant temperature effect coupled with the uniform alloy composition of Ni-Pt nanocatalysts results in the observed enhanced catalytic performance of the Ni-Pt nanocatalyst for hydrogen generation from hydrous hydrazine. In addition, evidence suggests that the Ni-based bimetallic catalysts can be used to release five equivalents of H₂ and one equivalent of N₂ from an aqueous solution of hydrazine borane N₂H₄BH₃.

Full text of DOI:10.1002/ejic.201100083

FULL PAPER
DOI: 10.1002/ejic.201100083
Temperature-Induced Enhancement of Catalytic Performance in Selective
Hydrogen Generation from Hydrous Hydrazine with Ni-Based Nanocatalysts
for Chemical Hydrogen Storage
[a]
[a]
[a]
Sanjay Kumar Singh, Zhang-Hui Lu, and Qiang Xu*
Keywords: Nickel / Hydrogen / Hydrazine / Nanostructures / Temperature effects
We demonstrate here that Ni nanoparticles, which are inac-
tive for the decomposition of hydrous hydrazine at room tem-
perature, can exhibit drastically enhanced catalytic perform-
ance with an increase in reaction temperature to 323 K. At
this reaction temperature, complete conversion of hydrous
composition of Ni–Pt nanocatalysts results in the observed
enhanced catalytic performance of the Ni–Pt nanocatalyst for
hydrogen generation from hydrous hydrazine. In addition,
evidence suggests that the Ni-based bimetallic catalysts can
be used to release five equivalents of H
of
2
and one equivalent
hydrazine with 100% H
2
selectivity can be achieved by al-
N
2
from an aqueous solution of hydrazine borane
loying Ni and Pt with a Pt content as low as 1 mol-%. This
significant temperature effect coupled with the uniform alloy
N
2
H
4
3
BH .
H
2
NNH
2
Ǟ N
2
+ 2H
2
(1)
Introduction
Development of new materials that can provide an alter-
native to fossil fuels for clean energy production, conver-
sion, and storage is of paramount importance. Hydrogen
has emerged as an alternative clean fuel, which produces
However, the key to exploit effectively the hydrogen-stor-
age properties of hydrazine is to avoid its incomplete de-
composition by an undesired reaction pathway [Equa-
tion (2)].
[
1]
only water when burning with oxygen or used in fuel cells.
However, safe and efficient hydrogen storage is one of the
most difficult tasks on the path toward a hydrogen-energy- 3H
2
NNH
2
Ǟ N
2
+ 4NH
3
(2)
based society. However, despite extensive exploration over
several decades, no single material investigated to date of-
fers high volumetric and gravimetric hydrogen capacities,
A large number of metal catalysts have been investigated
so far for the decomposition of hydrazine, and it has been
shown that the reaction pathways for hydrazine decomposi-
tion strongly depend on the catalyst used and the reaction
safe handling pressure and temperature, and effective re-
cycling of byproducts.[
1,2]
Hydrous hydrazine, such as hy-
drazine monohydrate, H NNH ·H O, a liquid at room tem-
[6–10]
2
2
2
conditions.
However, the development of highly active,
[
3]
perature, has a hydrogen content available for hydrogen
generation as high as 8.0 wt.-%, thus making it a promising
candidate and safe in handling. Notably, nitrogen, the only
byproduct produced in addition to hydrogen by hydrazine
decomposition, can be transformed to ammonia by the Ha-
ber–Bosch process, homogeneous catalytic processes, or an
low-cost, and efficient catalysts is of significant importance
for the practical use of hydrous hydrazine as a potential
[7]
hydrogen-storage material. Here, emphasis is placed on
the development of suitable reaction conditions for hydraz-
ine decomposition to hydrogen by using low-cost nanocata-
lysts such as Ni-based nanoparticles. We have observed that
Ni nanoparticles/nanocrystallites, which are inactive for the
decomposition of hydrous hydrazine at room temperature,
can show drastically enhanced catalytic activity with an H2
selectivity of 33% when the reaction temperature is raised
to 323 K. This significant temperature effect can be suitably
[
4]
electrolytic process; and subsequently to hydrazine on a
[
5]
large scale, or perhaps transformed directly to hydrazine
by means of an electrolytic process similar to that for am-
monia synthesis.[ Recent explorations in this direction
have shown that hydrazine can be decomposed completely
to hydrogen and nitrogen through Equation (1).[
4c]
6–8]
exploited to achieve 100% H selectivity at 323 K by alloy-
2
ing Ni and Pt with a Pt content as low as 1 mol-%. The
present results indicate that a suitable reaction temperature
may make it possible to achieve high catalytic performance
for hydrogen generation by decomposition of hydrous hy-
drazine with Ni-based nanocatalysts with low content of
noble metals.
[
a] National Institute of Advanced Industrial Science and Technol-
ogy (AIST),
Ikeda, Osaka, Japan
Fax: +81-72-751-7942
E-mail: q.xu@aist.go.jp
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100083.
2232
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 2232–2237

Temperature-Induced Enhancement of Catalytic Performance
Results and Discussion
served at higher temperatures, whereas the reaction comple-
tion time was significantly reduced (i.e., 150 min at 333 K
and 90 min at 343 K). From the volumetric observations,
the overall reaction for the hydrogen decomposition over
From our recent studies devoted to bimetallic-nanoparti-
cle-catalyzed hydrous hydrazine conversion to hydrogen,
nickel has emerged as a central component for all the active
bimetallic catalysts.[ However, in the past, we found that
the monometallic Ni nanoparticles themselves are catalyti-
cally inactive for the decomposition of hydrous hydrazine at
room temperature (298 K),[ and therefore it is significantly
important to make clear their activity in detail, for example,
at various temperatures. Ni nanoparticles were prepared
using our previously reported method;[ their catalytic ac-
tivity for hydrous hydrazine decomposition were examined
at different reaction temperatures (298–343 K). In contrast
[6]
Ni nanoparticles can be expressed as [Equation (3)].
7]
H
2
NNH
2
Ǟ 0.55N
2
(g) + 0.66H
2
(g) + 0.89NH
3
(3)
Having established that the Ni nanoparticles are able to
catalyze the hydrous hydrazine decomposition to hydrogen
6]
with a maximum of 33% H selectivity by increasing the
2
reaction temperature from room temperature to 323 K, we
have extensively explored the effect of temperature on the
catalytic performance of the Ni nanoparticles alloyed with
a very low content of Pt. Bimetallic Ni0.99Pt0.01 nanopar-
ticles were obtained by alloying Ni and Pt with a Pt content
as low as 1 mol-% by using an aqueous-phase co-reduction
6]
[
6,7]
to the catalytic inactivity of Ni nanoparticles at 298 K,
a significant enhancement in the catalytic performance of
Ni nanoparticles for hydrous hydrazine decomposition has
been observed with an increase in the reaction temperature.
As shown in Figure 1, a release of 1.2 equiv. of gases was
observed over 210 min at 323 K with monometallic Ni
2+
2+
process of the chloride salts of Ni and Pt in the pres-
ence of hexadecyltrimethyl ammonium bromide (CTAB).
Catalytic decomposition reaction of hydrous hydrazine was
initiated with the addition of hydrazine monohydrate into
nanoparticles, which corresponds to an H selectivity of
2
the reaction flask, and the relation between H selectivity
2
33%. However, no further increase in H selectivity was ob-
2
and the reaction temperature was studied by conducting the
catalytic decomposition reaction of hydrous hydrazine in
the temperature range of 298–333 K. At 323 K, a release of
3.0 equiv. of gas was observed in 120 min with the
Ni0.99Pt0.01 nanocatalyst (Figure 2), which is in agreement
with 100% selectivity for hydrogen and nitrogen according
to Equation (1), thus indicating the complete decomposi-
tion of hydrazine into hydrogen and nitrogen in aqueous
solution at 323 K. Moreover, the reaction completion time
could be reduced to 70 min with 100% H selectivity by
2
increasing the reaction temperature from 323 to 333 K,
whereas low H selectivity and long reaction times were ob-
2
served by decreasing the reaction temperatures to 313 K
(88%, 5 h) or 298 K (80%, 7 h). Therefore, moderate tem-
peratures are important for enhancing the catalytic per-
formance of the bimetallic Ni–Pt nanocatalysts with low
content of noble metals. It is worth noting that raising the
reaction temperature to 323 K, only slightly higher than
room temperature, makes it possible to achieve 100% H2
selectivity for the Ni–Pt nanocatalyst with a Pt content as
low as 1 mol-%, whereas at room temperature one needs to
use a Ni–Pt nanocatalyst with much higher Pt content (7–
[
7a]
3
4 mol-%) to achieve 100% H selectivity.
2
Arrhenius treatment of the temperature-dependent rate
data for hydrogen release from the decomposition of hy-
drous hydrazine in the presence of Ni and Ni0.99Pt0.01 nano-
catalysts exhibits straight lines for both the catalysts (Fig-
ure S1 in the Supporting Information). The apparent acti-
vation energy (E ) for hydrogen release from this reaction
a
in the presence of bimetallic Ni0.99Pt0.01 nanocatalyst [E ≈
a
–1
(
49.95Ϯ5) kJmol ] is significantly lower than that for the
–1
monometallic Ni nanocatalyst [E ≈ (81.08Ϯ5) kJmol ].
a
Figure 1. (a) Time-course plots of hydrogen generation by decom- The large difference in activation energy itself suggests a
position of hydrazine in aqueous solution (0.5 m) catalyzed by Ni
facile complete decomposition of hydrous hydrazine in the
nanoparticles (catalyst/H
tures of (i) 298, (ii) 313, (iii) 323, (iv) 333, and (v) 343 K. (b) Tem-
perature dependence of H selectivity from hydrous hydrazine de-
2 2
NNH = 1:10) at the reaction tempera-
presence of Ni0.99Pt0.01 nanocatalyst. In contrast to the high
activity of the Ni0.99Pt0.01 nanocatalyst, the effect of tem-
perature does not introduce a significant enhancement in
2
composition catalyzed by Ni nanoparticles.
Eur. J. Inorg. Chem. 2011, 2232–2237
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2233

S. K. Singh, Z.-H. Lu, Q. Xu
FULL PAPER
Figure 3. Time-course plots for hydrogen generation by the decom-
position of hydrazine in aqueous solution (0.5 m) catalyzed by (i)
Ni0.99Pt0.01, (ii) Ni, and (iii) Pt nanocatalysts (catalyst/H NNH =
2 2
1:10) at 323 K.
1:1) in the presence of the Ni0.99Pt0.01 nanocatalyst [catalyst/
(
H NNH2 + NH BH ) = 1:10] at room temperature
2 3 3
(
6
298 K) and 323 K (Figure 4). A release of around
.0 equiv. of gas from the mixture of hydrazine (1.0 equiv.)
and ammonia borane (1.0 equiv.), which corresponds to
n(H + N )/n(H NNH + NH BH ) = 3.0, at 323 K sug-
2
2
2
2
3
3
gested the complete decomposition of hydrous hydrazine
and hydrolysis of ammonia borane through the total reac-
tion [Equation (4)].
Figure 2. (a) Time-course plots for hydrogen generation by the de-
composition of hydrazine in aqueous solution (0.5 m) catalyzed by
Ni0.99Pt0.01 nanocatalyst (catalyst/H
temperatures of (i) 298, (ii) 313, (iii) 323, and (iv) 333 K. (b) Tem-
perature dependence of H selectivity from hydrous hydrazine de-
2 2
NNH = 1:10) at the reaction
2
composition catalyzed by Ni0.99Pt0.01 nanocatalyst.
the catalytic performance of Pt nanoparticles, which exhibit
only around 7% H selectivity at 323 K for hydrazine de-
2
composition in aqueous solution (Figure 3). In comparison
to the low H selectivity observed for the monometallic Ni
2
and Pt counterparts (around 33% and around 7% for Ni
and Pt nanoparticles, respectively) at 323 K, the 100% H2
selectivity exhibited by the Ni0.99Pt0.01 nanocatalyst sug-
gested the involvement of the bimetallic phase as active cen-
ters on the catalyst surface, and that the significant interac-
Figure 4. Time-course plots for hydrogen generation from a mix-
tion between Ni and Pt is necessary for the observed cata- ture of H
2
NNH
2 2 3 3 2 2
·H O (0.25 m) and NH BH (0.25 m) (H NNH /
[
7a]
NH BH = 1:1) in aqueous solution in the presence of Ni0.99Pt
lytic activity. The turnover frequency for the catalytic de-
composition reaction of hydrazine in aqueous solution for
Ni0.99Pt0.01 is 6 h at 323 K, which is three times the value
for Ni0.93Pt0.07 at 298 K.[ In addition, we have examined
the activity and selectivity of the Ni0.99Pt0.01 for the decom-
position of hydrazine in aqueous solution during repeated
3
3
0.01
nanocatalyst [catalyst/(H
b) 323 K.
2
NNH
2
+ NH
3
BH
3
) = 1:10] at (a) 298 and
(
–
1
7a]
2 2 3 3 2 2 2 4 2
H NNH + NH BH + 2H O Ǟ N (g) + 5H + BO
(g) + NH +
–
(
4)
use and found no change in the H selectivity (Figure S2 in
the Supporting Information).
It is noteworthy that the hydrolysis of ammonia borane
has fast kinetics in comparison with the decomposition of
2
In addition, we have investigated the hydrogen-genera- hydrazine over the Ni–Pt nanocatalyst. The present results
tion reaction from a mixture of hydrazine (H NNH ·H O) suggest that an active catalyst such as the bimetallic Ni–
2
2
2
and ammonia borane (NH BH ) (H NNH /NH BH =
Pt nanocatalysts can be used for the hydrogen release from
3
3
2
2
3
3
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 2232–2237

Temperature-Induced Enhancement of Catalytic Performance
aqueous hydrazine boranes, for example [Equation (5)],
which can release 6.0 equiv. of gas from hydrazine borane
(HB).
H
2
NNH
2
BH
3
+ 2H
2
O Ǟ N
2
+ 5H
2
+ HBO
2
(5)
As it is reasonable to consider that the hydrolysis of the
BH group in hydrazine boranes is relatively easy, a cata-
–
3
lyst that can completely decompose hydrazine to N and H2
2
should be a key candidate for hydrogen release from aque-
ous hydrazine boranes as new hydrogen-storage materi-
als.[
11]
The X-ray photoelectron spectroscopic (XPS) analysis
(Figure S3 in the Supporting Information) of Ni nanopar-
ticles revealed that the Ni 2p3/2 and Ni 2p1/2 core levels
show binding energies of 853.59 and 870.80 eV, respec-
[
12]
tively. A peak that appeared at 858.16 eV, assigned to the
oxide of Ni, could be readily removed by 36 min of argon
sputtering. The powder X-ray diffraction (XRD; Figure S4
in the Supporting Information) data illustrates the crystal- Figure 5. (a–c) TEM images at different magnifications [scale bar
line nature of Ni nanoparticles, in which the major diffrac- (a) 20, (b) 10, and (c) 5 nm] with (d) corresponding SAED pattern
of Ni nanoparticles after the hydrazine decomposition reaction in
aqueous solution at 323 K.
tion peak at the 2θ value of 45.38° can be indexed to the
(111) diffraction plane of face-centered cubic (fcc) unit cell
of Ni (PDF #65-0380). Consistent with the analogous XPS
and XRD analysis results, SEM images (Figure S5 in the major peak at 2θ value of 44.56°. The observed XRD dif-
Supporting Information) of Ni nanoparticles before and af- fraction pattern is analogous to that of the (111) plane for
ter the reaction suggest a slight aggregation of Ni nanopar- nickel and is consistent with other Ni–Pt alloy nanocata-
ticles during the catalytic reaction at 323 K. The Brunauer– lysts with higher nickel content.
Emmett–Teller (BET) surface areas (Figure S6 in the Sup-
TEM and HRTEM images for Ni0.99Pt0.01 nanocatalysts
porting Information) of the Ni nanoparticles before and af- shown in Figure 6 reveal the presence of partially aggre-
2
–1
ter the reaction are 47.8 and 28.4 m g , respectively. Trans- gated nanoparticles of irregular shape with an average par-
mission electron microscopic (TEM) images of the Ni nano- ticle size of around 5 nm and are consistent with the pre-
particles after the reaction show an average particle size of vious observations with Ni–Pt nanoparticles for which the
around 5 nm (Figure 5). High-angle annular dark-field nanoparticle size is independent of the composition of Ni–
[
7a]
scanning TEM (HAADF-STEM) along with energy-dis- Pt nanocatalysts.
In addition, the TEM observations
persed X-ray spectroscopic (EDS) analysis from several (Figure 6) of the Ni0.99Pt0.01 nanocatalysts before and after
points of the Ni nanoparticles reveals the presence of nickel the reaction show no appreciable change in particle size
element (see Figure S7 in the Supporting Information). The (around 5 nm). HAADF-STEM measurements along with
selected area electron diffraction (SAED) measurements EDS analysis from several points of the nanoparticles
suggest the crystalline nature of the Ni nanoparticles (Fig- reveal the presence of both Ni and Pt elements (Figures S10
ure 5).
and S11 in the Supporting Information). The SAED
XPS, TEM, and EDS measurements were performed for measurements suggest the crystalline nature of the
the Ni0.99Pt0.01 nanocatalyst. The XPS analysis (Figure S8 Ni0.99Pt0.01 nanocatalysts (Figure 6). The BET surface area
2
–1
in the Supporting Information) of Ni0.99Pt0.01 nanocatalysts of Ni0.99Pt0.01 is 50.03 m g .
reveals that the Ni 2p3/2 and 2p1/2 core levels show binding
The release of around 1.2 equiv. of gas from the hydraz-
energies of 853.28 and 870.48 eV, respectively, whereas the ine decomposition at 323 K, which corresponds to a H2
Pt 4f7/2 and 4f5/2 core levels show binding energies of 71.44 selectivity of 33%, suggests that the catalyst surface of Ni
and 75.16 eV, respectively.[ A thin oxide cover, presum- nanoparticles activates the hydrazine decomposition
ably formed during exposure to air, was observed, which through both the reaction pathways in Equations (1) and
can be readily removed by argon sputtering. Consistent (2) simultaneously. One can understand that the bonding
with other Ni–Pt compositions, the Pt 4f7/2 core level for pattern and stability of the different adsorbed species of the
the Ni0.99Pt0.01 nanocatalyst shifts to a higher binding en- reactant on the catalyst surface are key factors that deter-
12]
[
12]
ergy than that for the monometallic Pt (Pt 4f7/2 70.9 eV).
mine the performance of a catalyst. However, the mobility
Argon-sputtering experiments over a period of 0 to 186 min and chances of the interaction of the reactant to the catalyst
for the Ni0.99Pt0.01 nanocatalyst confirmed the uniform dis- can be enhanced with the increase in the reaction tempera-
tribution of Ni and Pt atoms in the nanoparticle with an ture. As the electronic and structural properties of the sur-
alloy composition. The powder XRD profile (Figure S9 in face of the catalysts are significantly tuned with the intro-
the Supporting Information) of Ni0.99Pt0.01 nanocatalyst duction of a second component, a bimetallic catalyst might
shows a face-centered cubic (fcc) diffraction pattern with a exhibit enhanced activity to those of the corresponding mo-
Eur. J. Inorg. Chem. 2011, 2232–2237
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2235

S. K. Singh, Z.-H. Lu, Q. Xu
FULL PAPER
product N to hydrazine by an electrolytic process, similar
2
[
4c]
to that for ammonia synthesis,
could significantly en-
hance the practical application of hydrous hydrazine as a
highly promising hydrogen-storage material.
Experimental Section
Commercial chemicals were used as received for catalyst prepara-
tion and hydrazine decomposition experiments. Hydrazine mono-
hydrate (H
9%), and hexadecyltrimethyl ammonium bromide (CTAB, 95%)
were obtained from Aldrich. Ammonia borane (NH BH , 97%)
was purchased from AVIABOR. Potassium tetrachloroplatinate(II)
PtCl , 99.9%) and nickel chloride hexahydrate (NiCl ·6H O,
9.9%) were obtained from Wako. Powder X-ray diffraction (XRD)
studies were performed with a Rigaku RINT-2000 X-ray dif-
fractometer (Cu-K ). A scanning electron microscope (SEM, Hita-
chi S-5000) and transmission electron microscope (TEM, FEI
TECNAI G ) equipped with selected area electron diffraction
SAED) and energy dispersed X-ray detector (EDS) were used to
2 2 2 4
NNH ·H O, 99%), sodium borohydride (NaBH ,
9
3
3
(
K
2
4
2
2
9
α
2
(
Figure 6. (a,c) TEM and (b,d) HRTEM images with corresponding
(
(
inset) SAED patterns of Ni0.99Pt0.01 nanocatalysts (a,b) before and
c,d) after the hydrazine decomposition reaction in aqueous solu-
collect the detailed microstructure information. The SEM and
TEM samples were prepared by depositing few droplets of the nan-
oparticle suspension onto amorphous carbon-coated copper grids,
which were dried under an argon atmosphere. The surface-area
tion at 323 K.
measurements were performed by N
perature with automatic volumetric adsorption equipment (Belsorp
2 2
adsorption at liquid N tem-
nometallic components.[13] The significant temperature ef-
fect, which led to a drastic enhancement of the catalytic II). XPS analysis was carried out with a Shimadzu ESCA-3400
performance of Ni nanoparticles, has been extended to the X-ray photoelectron spectrometer using an Mg-K source (10 kV,
α
Ni–Pt alloy nanocatalysts. A 100% H selectivity for the 10 mA). The Ar-sputtering experiments were carried out under the
2
–
6
conditions of background vacuum 3.2ϫ10 Pa, sputtering acceler-
ation voltage 1 kV.
decomposition of hydrous hydrazine has been achieved with
Ni0.99Pt0.01 nanocatalysts, which have a Pt content as low
as 1 mol-%. Considering the uniform composition of the Preparation of the Monometallic Ni Nanocatalyst: An aqueous
Ni0.99Pt0.01 nanocatalyst, which indicates the co-existence of solution (1.5 mL) of NaBH (0.020 g, 0.526 mmol) was added
dropwise to an aqueous suspension (2.5 mL) of NiCl ·6H
0.047 g, 0.02 mmol) and CTAB (0.050 g, 0.142 mmol), obtained
4
2
2
O
bimetallic phase on the active sites of the catalyst surface,
(
and the temperature effect, the observed 100% H selectiv-
2
by sonication and stirring for 5 min. The content of the flask was
vigorously shaken for 2 min, thereby resulting in the generation of
Ni nanoparticles as a black suspension, which was used as prepared
for the catalytic reaction.
ity exhibited by the Ni0.99Pt0.01 nanocatalyst results from
the activation of hydrazine bonds towards its complete de-
composition for selective release of hydrogen and nitrogen
through decomposition reaction pathway in Equation (1).
Preparation of the Monometallic Pt Nanocatalyst: An analogous
synthetic procedure as for the Ni nanoparticles was adapted.
2 4 2 2
K PtCl (0.083 g, 0.02 mmol) was used instead of NiCl ·6H O.
Conclusion
Preparation of the Ni0.99Pt0.01 Nanocatalyst: Ni0.99Pt0.01 nanopar-
We have demonstrated that the catalytic performance of
ticles were prepared following a surfactant-aided co-reduction pro-
the Ni nanoparticles for the decomposition of hydrazine in cess analogous to that reported previously.[ In brief, an aqueous
7a]
aqueous solution can be enhanced appreciably from inac- suspension that contained NiCl
2
·6H
2
O and K
2
PtCl
4
in 99:1 molar
in
tive at 298 K to active with around 33% H selectivity at ratio was co-reduced by using an aqueous solution of NaBH
4
2
the presence of CTAB, thereby resulting in the generation of
Ni0.99Pt0.01 nanocatalyst as a black suspension, which was used as
prepared for the catalytic reaction.
3
23 K. Furthermore, this significant temperature effect has
also been applied to bimetallic Ni–Pt nanocatalysts, which
were prepared by alloying Ni and Pt with a Pt content as
low as 1 mol-%, and for which the temperature effect cou- Catalytic Reaction for Hydrogen Release from Hydrous Hydrazine:
Catalytic reactions were carried out at room temperature and ele-
vated temperatures using a two-necked, round-bottomed flask with
one of the flask openings connected to a gas burette and another
pled with the uniform alloy composition of the bimetallic
Ni–Pt phase results in 100% H selectivity from catalytic
2
decomposition of hydrazine in aqueous solution at 323 K.
used for the introduction of hydrazine monohydrate. Catalytic de-
The present system, which includes much lower Pt content,
composition reaction of hydrazine for the release of hydrogen
shows promise in the development of low-cost, high-per-
formance catalysts for the decomposition of hydrazine to
hydrogen. We believe that in combination with our process
(
along with nitrogen) was initiated by stirring the mixture of hy-
drazine monohydrate (0.1 mL, 1.97 mmol), which was introduced
with a syringe to the reaction flask that contained the aqueous
for highly efficient catalytic decomposition of hydrous hy- suspension (4.0 mL) of the as-prepared nanocatalysts (catalyst/
drazine to hydrogen, an energy-efficient recycling of the by- NNH = 1:10; prepared as described above). The gases released
H
2
2
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Eur. J. Inorg. Chem. 2011, 2232–2237

Temperature-Induced Enhancement of Catalytic Performance
during the reaction were passed through a trap that contained hy-
drochloric acid (1.0 m) to ensure the absorption of ammonia, if
produced, the volume of which was monitored using the gas bu-
rette. Catalyst-stability experiments were conducted over the same
catalyst by adding an additional equivalent amount of N H ·H O
2 4 2
to the reaction vessel after the completion of previous catalytic run.
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[
[
(
0.05 mL) and ammonia borane (0.031 g) in 1:1 molar ratio and
the as-prepared Ni0.99Pt0.01 nanocatalyst [catalyst/(H NNH
NH BH ) = 1:10] at 298 and 323 K.
2
2
+
3
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Received: January 24, 2011
Published Online: March 29, 2011
Eur. J. Inorg. Chem. 2011, 2232–2237
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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