Influence of preparation conditions of hollow silica-nickel composite spheres on their catalytic activity for hydrolytic dehydrogenation of ammonia borane

Article abstract of DOI:10.1016/j.jallcom.2013.11.134

In this paper, we investigated influence of preparation conditions of hollow silica-nickel composite spheres on their morphology and catalytic activity for hydrolytic dehydrogenation of ammonia borane. In the preparation method of this study, when silica-nickel composite shells were coated on polystyrene templates by the sol-gel method using L(+)-arginine as the promoter for the reaction to form silica-nickel composite shell, the polystyrene templates were dissolved subsequently, even synchronously, in the same medium to form hollow spheres. The as-prepared silica-nickel composite spheres were characterized by transmission electron microscopy and scanning electron microscopy. The effects of Si+Ni content on the morphology were systematically evaluated. All the as-prepared hollow silica-nickel composite spheres have the similar morphology as identified by SEM and TEM measurement. Homogeneity of the hollow silica-nickel composite spheres increases with the increase in the Si+Ni content as shown by the laser diffraction particle size analysis. The catalytic activities of the hollow silica-nickel composite spheres for hydrolytic dehydrogenation of ammonia borane prepared with different Si+Ni contents were compared. The catalytic activity for the hydrogen evolution in the presence of the hollow spheres increases with the increase of Si+Ni content. The results of FTIR spectra of the hollow silica-nickel composite spheres indicate that a certain amount of residual PS templates exists in hollow silica-nickel composite spheres. The residual PS templates was able to be reduced by procedure of as-prepared samples with toluene solvent. The catalytic activity of hollow silica-nickel composite spheres increases with decrease in the amount of residual PS templates.

Full text of DOI:10.1016/j.jallcom.2013.11.134

Accepted Manuscript
Influence of preparation conditions of hollow silica-nickel composite spheres
on their catalytic activity for hydrolytic dehydrogenation of ammonia borane
Tetsuo Umegaki, Ayano Seki, Qiang Xu, Yoshiyuki Kojima
PII:
S0925-8388(13)02875-2
DOI:
http://dx.doi.org/10.1016/j.jallcom.2013.11.134
JALCOM 29963
Reference:
To appear in:
Received Date:
Revised Date:
Accepted Date:
29 March 2013
11 November 2013
21 November 2013
Please cite this article as: T. Umegaki, A. Seki, Q. Xu, Y. Kojima, Influence of preparation conditions of hollow
silica-nickel composite spheres on their catalytic activity for hydrolytic dehydrogenation of ammonia borane,
(
2013), doi: http://dx.doi.org/10.1016/j.jallcom.2013.11.134
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Influence of preparation conditions of hollow silica-nickel composite
spheres on their catalytic activity for hydrolytic dehydrogenation of
ammonia borane
a
a
b
a
Tetsuo Umegaki *, Ayano Seki , Qiang Xu , Yoshiyuki Kojima
a
Department of Materials & Applied Chemistry, College of Science & Engineering,
Nihon University, 1-8-14, Kanda-Surugadai, Chiyoda-Ku, Tokyo 101-8308, Japan,
b
National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31
Midorigaoka, Ikeda, Osaka, 563-8577, Japan
*
Corresponding Author: E-mail: umegaki.tetsuo@nihon-u.ac.jp (Tetsuo Umegaki)
TEL: +81-3-3259-0810, Fax: +81-3-3293-7572
Abstract
In this paper, we investigated influence of preparation conditions of hollow
silica-nickel composite spheres on their morphology and catalytic activity for hydrolytic
dehydrogenation of ammonia borane. In the preparation method of this study, when
silica-nickel composite shells were coated on polystyrene templates by the sol-gel
1

method using L(+)-arginine as the promoter for the reaction to form silica-nickel
composite shell, the polystyrene templates were dissolved subsequently, even
synchronously, in the same medium to form hollow spheres. The as-prepared
silica-nickel composite spheres were characterized by transmission electron microscopy
and scanning electron microscopy. The effects of Si+Ni content on the morphology
were systematically evaluated. All the as-prepared hollow silica-nickel composite
spheres have the similar morphology as identified by SEM and TEM measurement.
Homogeneity of the hollow silica-nickel composite spheres increases with the increase
in the Si+Ni content as shown by the laser diffraction particle size analysis. The
catalytic activities of the hollow silica-nickel composite spheres for hydrolytic
dehydrogenation of ammonia borane prepared with different Si+Ni contents were
compared. The catalytic activity for the hydrogen evolution in the presence of the
hollow spheres increases with the increase of Si+Ni content. The results of FTIR spectra
of the hollow silica-nickel composite spheres indicate that a certain amount of residual
PS templates exists in hollow silica-nickel composite spheres. The residual PS
templates was able to be reduced by procedure of as-prepared samples with toluene
solvent. The catalytic activity of hollow silica-nickel composite spheres increases with
decrease in the amount of residual PS templates.
2

Keywords: Hollow silica-nickel composite spheres; L(+)-arginine; Hydrolytic
dehydrogenation; Ammonia borane
1
. Introduction
There have been intensive efforts for developing safe and efficient methods for
controlled storage and release of hydrogen, a key issue of a fuel-cell-based hydrogen
-1
economy [1-3]. Owing to its low molecular weight (30.9 g mol ), high hydrogen
content (19.6 wt%), high stability at room temperature, and nontoxicity, ammonia
borane (NH BH ) is has been identified as an attractive candidate for chemical
3
3
hydrogen storage application [4-25]. Moreover, NH BH can be handled at room
3
3
temperature and can release hydrogen gas upon catalytic hydrolysis under mild
conditions [4]. The hydrolysis occurs at appreciable rate in the presence of a suitable
acid or a suitable catalyst at ambient temperature [12-25]. For the viewpoint of practical
application, the development of efficient, low-cost, and stable catalysts to further
improve the kinetic properties under moderate conditions is therefore very important. It
is reported that nickel based catalyst is one of highly active catalysts for this reaction
[
14, 17, 19-25], and several reports have studied supported or composite effect with
3

metal oxides on nickel based catalysts [14, 17, 21, 22, 24, 25].
In recent years, the preparation and study of core-shell solid and hollow microspheres
with well-defined structures have attracted substantial interest because of their potential
applications in controlled drug delivery system, lightweight fillers, catalysis,
chromatography, vessels for confined reactions, and photonic band gap material [26-29].
A number of efforts to find new methods have been devoted to generating colloids with
the core-shell structure, such as template-assisted sol-gel process [30-35], layer by layer
(
LBL) techniques [36-40], microemulsion/interfacial polymerization strategies [41-45].
Microsized, monodisperse, hollow silica [32] and titania [46] spheres were fabricated
via a one-step process, which means that the formation of the inorganic shells and the
dissolution of core particles occur in the same medium. In that method, microsized,
monodisperse, positively charged polystyrene (PS) particles were prepared by
dispersion
polymerization
using
the
cationic
monomer
2
-(methacryloyl)-ethyltrimethylammonium chloride (MTC) as the comonomer [47] or
by emulsifier-free emulsion polymerization using α,α’-azodiisobutyramidine
dihydrochloride (AIBA) as the initiator and poly(vinyl pyrrolidone) (PVP) as the
stabilizer [32, 48]. These small PS template particles without a positively charged
comonomer could also be dissolved in the same medium subsequently, even
4

simultaneously, during the coating of silica shells to directly form hollow spheres.
Neither additional dissolution nor a calcination process was used to remove the PS cores
to form hollow spheres.
Our resent studies reveal that hollow metal oxide-nickel composite spheres have been
able to be fabricated by the similar method [49, 50]. We firstly fabricated the hollow
silica-nickel composite spheres using L(+)-arginine, a kind of basic amino acid, as the
promoter for hydrolysis of tetraethoxysilane (TEOS) [51] and for dissolution of PS
templates [50]. The hollow spheres shows higher catalytic activity for hydrolytic
dehydrogenation of ammonia borane than the hollow spheres prepared using aqueous
ammonia solution as the promoter for hydrolysis of tetraethoxysilane (TEOS) and for
dissolution of PS templates [50].
In the present study, we investigated the influence of preparation conditions, such as
Si+Ni content, aging temperature, and procedure for reduction of residual PS templates,
of the hollow silica-nickel composite spheres by PS template method using
L(+)-arginine on their morphology and catalytic activity for hydrolytic dehydrogenation
of ammonia borane.
2
. Experimental
5

2
.1 Catalyst preparation
Hollow silica-nickel composite spheres were prepared by polystyrene beads template
method as follows [50]. The monodisperse PS particles were prepared by
emulsifier-free emulsion polymerization as follows: 10.0 g of styrene (Kanto Chem.
Co.), 1.5 g of poly(vinyl pyrrolidone) (PVP) K30 (M ≈ 40 000, Fluka), 0.26 g of
w
Cationic initiator 2,2’-azobis-(isobutyramidine) dihydrochloride (AIBA, Kanto Chem.
Co.), and 100.0 g of distilled water were charged into a 250-mL three-neck flask
equipped with a mechanical stirrer, a thermometer with a temperature controller, a N2
inlet, a Graham condenser, and a heating oil bath. The reaction solution was
deoxygenated by bubbling nitrogen gas at room temperature for 60 min. Then, under a
stirring rate of 150 rpm, the reaction was carried out at 343 K for 24 h. The obtained PS
suspension was centrifuged (6000 rpm, 5 min) and washed in ethyl alcohol for 3 times,
and content of the PS suspension could be tailored through the addition of ethanol. The
mixed aqueous solution of 0.03, 0.09, 0.15, and 0.30 g of Ni(NO )・6H O (Kanto Chem.
3
2
2
Co., > 99.0 %), 0.3093 g of L(+)-arginine (Kanto Chem. Co.), and 160 mL of ethyl
alcohol were added into 20.0 g of the PS suspension, to which added was 0.215, 0.646,
1
.076, and 2.152 mL of tetraethoxysilane (Kanto Chem. Co., > 99.9 %). The sol-gel
reaction was carried out at 323 K, and the hollow silica-nickel composite spheres could
6

be directly obtained. After drying in a desiccator overnight, the obtained light blue fine
powders were used as catalysts.
2
.2. Characterization
The morphologies of hollow silica-nickel composite spheres were observed using a
Hitachi S-450 scanning electron microscope (SEM) operating at an acceleration voltage
of 15 kV and a Hitachi FE2000 transmission electron microscope (TEM) operating at an
acceleration voltage of 200 kV. The particle size distribution of the hollow silica-nickel
composite spheres dispersed in water was analyzed by laser diffraction method using a
Shimadzu SALD-2000A analyzer. The TPR–TGA (temperature-programmed
reduction–thermogravimetric analysis) investigations were performed on a Rigaku
TG8120 instrument. TPR profiles were recorded by passing a 10 vol% H in Ar (260
2
-1
-1
mL min ) through the sample (≈ 2 mg) heated at a constant rate of 5 K min up to 1173
K. FTIR spectra of hollow metal oxide-nickel composite spheres were recorded using a
Fourier transform infrared spectrophotometer (FTIR-8400S, Shimadzu Co., Ltd.) with a
-1
resolution of 4 cm .
2
.3. Experimental procedures for hydrolysis of ammonia borane
A mixture of sodium borohydride (NaBH , 5 mg, Kanto Chemical Reagent Co., >
4
9
8.5 %), ammonia borane (NH BH , 27.5 mg, Aldrich, 90 %), and catalyst
3
3
7

(
NH BH /NaBH /Ni = 1/0.17/0.05) was kept in a two-necked round-bottom flask. One
3 3 4
neck was connected to a gas burette, and the other was fitted with a septum inlet to
introduce distilled water (5 mL). The reaction started when distilled water was
introduced to the mixture of NaBH , NH BH , and the catalyst, and the evolution of gas
4
3
3
was monitored using the gas burette. The reactions were carried out at room temperature
in air. All the samples after hydrolysis of NH BH were centrifugally separated from the
3
3
reaction solution, and then dried in desiccator under vacuum condition for
characterizations. For obtaining the activation energy, we carried out the hydrogen
generation reaction at 298, 323 and 343 K.
3
. Results and discussion
The morphologies of hollow silica-nickel composite spheres with different Si+Ni
contents before hydrolysis of NH BH were examined using TEM and SEM. From the
3
3
TEM image of hollow silica-nickel composite spheres prepared with Si+Ni content =
-3
1
.06 × 10 mol (Figure 1(a)), the spherical particles with their hollow feature indicated
by the arrows were obtained. All the SEM images of the hollow silica-nickel composite
spheres reveal that the samples prepared with Si+Ni content = 1.06, 3.19, 5.32, and
-3
1
0.64 × 10 mol consist of spherical particles (Figure 1(b)-(e)). Figure 2 shows laser
8

diffraction size distribution profile of the hollow silica-nickel composite spheres
-3
prepared with Si+Ni content = 1.06, 3.19, 5.32, and 10.64 × 10 mol. There are two
main peaks at around 300 and 680 nm in the particle size distribution profile of the
-3
hollow spheres prepared with Si+Ni content = 1.06 × 10 mol (Figure 2(a)). The peak at
around 300 nm in the profile of the hollow spheres prepared Si+Ni content = 3.19, 5.32,
-3
and 10.64 × 10 mol is narrower and larger than that in the profile of the hollow spheres
-3
prepared with Si+Ni content = 1.06 × 10 mol, while the number of the particle of
around 680 nm in diameter drastically decreases with increase of Si+Ni content. The
results indicate that homogeneity of the hollow silica-nickel composite spheres
increases with the increase of Si+Ni content.
Figure 3 shows the time course of the hydrogen evolution from aqueous
NaBH /NH BH solution in the presence of hollow silica-nickel composite spheres. The
4
3
3
reaction rate and the amount of hydrogen evolution significantly depend on the catalysts.
The evolution of 54, 55, 56, and 56 mL hydrogen from aqueous NaBH solution were
4
finished in 32, 30, 22, and 18 min in the presence of hollow silica-nickel composite
-3
spheres prepared with Si+Ni content = 1.06, 3.19, 5.32, and 10.64 × 10 mol,
respectively. In the present reaction system, NaBH was mixed with H O, NH BH , and
4
2
3
3
catalyst. Hydrogen is evolved via following two reactions (reactions (2) and (3)) besides
9

reaction (1);
2
+
-
-
+
4
Ni + BH + 2H O → 4Ni + BO + 8H
(1)
(2)
(3)
4
2
2
+
-
NaBH + 2H O → Na + BO + 4H
2
4
2
2
+
-
NH BH + 2H O → NH + BO + 3H
2
3
3
2
4
2
-4
Under the present reaction condition, about 12 mL of hydrogen (4.8 × 10 mol) is
generated via reactions (2) from residual amount of NaBH consumed via the reaction
4
-4
-4
(
1) (1.3 × 10 (total amount of NaBH ) - 0.1 × 10 (amount of NaBH consumed via
4
4
-4
-4
the reaction (1)) = 1.2 × 10 mol) , and about 59 mL of hydrogen (24.0 × 10 mol) is
generated via reaction (3), experimentally. The molar ratios of the hydrolytically
generated hydrogen to the initial NH BH in the presence of hollow silica-nickel
3
3
-3
composite spheres prepared with Si+Ni content = 1.06, 3.19, 5.32, and 10.64 × 10 mol
are 2.3, 2.3, 2.4, and 2.4, respectively. These results indicate that hydrogen evolution
rate from aqueous NaBH /NH BH solution in the presence of hollow silica-nickel
4
3
3
composite spheres increases with the increase of Si+Ni content.
In order to obtain information about reducibility of active nickel species, the
temperature programmed reduction (TPR) profiles observed upon treatment of the
as-prepared samples in H are obtained by TGA. Figure 4 shows the DTG curves of the
2
as-prepared samples. The curves involved three main domains that point to the presence
1
0

of different kinds of nickel species with diverse reducibility: one reduced at the lower
temperature (Tmax at about 550 K) and another reduced at higher temperatures (Tmax at
about 724 K). From the reduction profile of hollow silica-nickel composite spheres
-3
prepared with Si+Ni content = 1.06 × 10 mol (Figure 4(a)), the clearly defined peaks at
around 724 K appear in the DTG curve. This peak is assigned to nickel species
contacting with silica matrix [52-54]. Contrary to the sample, a low temperature peak at
about 550 K which is ascribed to the presence of clustered nickel species [53] appears in
the reduction profiles of silica-nickel composite spheres prepared with Si+Ni content =
-3
3
.19 and 5.32 × 10 mol in addition to the high temperature peak at around 724 K. With
increase of Si+Ni content, the intensity of the low temperature peak increases and the
intensity of the high temperature peak decreases, and then only low temperature peak
appears in the reduction profiles of silica-nickel composite spheres prepared with Si+Ni
-3
content = 10.64 × 10 mol. These results indicate that clustered nickel species in hollow
silica-nickel composite spheres increase with increase of Si+Ni content, and more
reducible nickel species exist in the hollow spheres prepared with higher Si+Ni content.
The as-prepared hollow silica-nickel composite spheres were characterized by using
FTIR spectroscopic methods to confirm that the difference in the catalytic activity
depends on the amount of residual PS templates. Figure 5(a) shows FTIR spectra for
11

-3
hollow silica-nickel composite spheres prepared with Si+Ni content = 1.06 × 10 mol at
3
1
23 K. These hollow spheres display the characteristic bands of PS at around 1600,
-1
492, 1449, 754, and 698 cm [55]. These bands indicate that the PS segments are
included in the shell of hollow spheres. In order to reduce the amount of residual PS
templates in the hollow silica-nickel composite spheres, we investigate the effect of the
various conditions of procedures during or after preparation. Figure 5(b) and (c) show
the spectra of the hollow silica-nickel composite spheres prepared at 343 K and treated
in toluene after preparation of the hollow spheres. In addition to the characteristic bands
of PS described above, these samples display the stretch vibration bands of the Si-O-Si
-1
bond at around 1077 cm [55]. These bands indicate that the shell of hollow spheres is
composed of both silica and PS segments. The ratio of the peak intensity for the
-1
characteristic band of PS at around 698 cm to the peak intensity for the Si-O-Si band
depends on the procedure. The ratios, IPS/ISiO , of the hollow silica-nickel composite
2
spheres prepared at 323 and 343 K, and treated in toluene after preparation of the
hollow spheres are 1.34, 1.12, and 0.43, respectively, indicating that the stirring
procedure in toluene is effective for reducing the amount of residual PS templates.
The morphologies of hollow silica-nickel composite spheres prepared at 323 and 343
K, and treated in toluene after preparation of the hollow spheres were examined using
1
2

SEM (Figure 6). All the SEM images reveal that all the samples consist of
homogeneous spherical particles and that the morphology of hollow silica-nickel
composite spheres was not significantly different with the preparation conditions or
treatment procedure of as-prepared sample.
Figure 7 shows the catalytic activity over the hollow silica-nickel composite spheres
prepared or treated in various conditions. The reaction rate does not depend on the
catalysts, however, the amount of hydrogen evolution depend on the catalysts. The
evolution of 54, 53, and 57 mL hydrogen were finished in 32, 36, and 34 min in the
presence of the hollow silica-nickel composite spheres prepared at 323 and 343 K, and
treated in toluene after preparation of the hollow spheres, respectively. The molar ratios
of the hydrolytically generated hydrogen to the initial NH BH in the presence of the
3
3
hollow silica-nickel composite spheres prepared at 323 and 343 K, and treated in
toluene after preparation of the hollow spheres are 2.3, 2.2, and 2.4, respectively. The
results indicate that the catalytic activity of hollow silica-nickel composite spheres
increases when the amount of residual PS templates decreases.
Figure 8 shows FTIR spectra of hollow silica-nickel composite spheres prepared with
various amount of silica-nickel composite following the treatment in toluene. The
results indicate that all the spectra consist of the characteristic bands of PS at around
1
3

-1
6
98 cm with negligible intensity, thus, all the samples treated in toluene include
negligible amount of residual PS templates.
The morphologies of hollow silica-nickel composite spheres prepared with various
amount of silica-nickel composite following treatment in toluene were examined using
SEM (Figure 9). All the SEM images reveal that all the samples consist of
homogeneous spherical particles and that the morphology of all the hollow spheres were
not significantly changes compared with the sample without the treatment in toluene.
Figure 10 shows the catalytic activity over the hollow silica-nickel composite spheres
prepared with various amount of silica-nickel composite following treatment in toluene.
The reaction rate depends on the catalysts. The evolution of 57, 58, 60, and 61 mL
hydrogen from aqueous NaBH solution were finished in 31, 30, 29, and 22 min in the
4
presence of hollow silica-nickel composite spheres prepared with Si+Ni content = 1.06,
-3
3
.19, 5.32, and 10.64 × 10 mol, respectively. The molar ratios of the hydrolytically
generated hydrogen to the initial NH BH in the presence of hollow silica-nickel
3
3
-3
composite spheres prepared with Si+Ni content = 1.06, 3.19, 5.32, and 10.64 × 10 mol
are 2.4, 2.5, 2.6, and 2.6, respectively. These results indicate that the amount and rate of
hydrogen evolution from aqueous NaBH /NH BH solution in the presence of hollow
4
3
3
silica-nickel composite spheres increases with the increase of Si+Ni content. The results
1
4

in Figure 4 indicate that clustered nickel species in hollow silica-nickel composite
spheres increase with increase of Si+Ni content, and more reducible nickel species exist
in the hollow spheres prepared with higher Si+Ni content. The results in Figure 4 and 10
suggest that the amount of clustered nickel species in the hollow spheres increases with
increase of Si+Ni content, and then, the catalytic activity increases with increase of
Si+Ni content.
The hollow silica-nickel composite spheres catalyzed hydrolysis of NH BH was
3
3
carried out at various temperatures in the range of 298-343 K.
3d[NH BH ]/dt = d[H ]/dt = k (4)
-
3
3
2
Under our experimental conditions, the reaction rate constant, k, is constant for a given
temperature, implying zero order kinetics for the NH BH hydrolysis reaction. This
3
3
suggests that the hydrogen generation rate is controlled within a surface reaction. The
reaction rate equation can be written as follows:
k = k exp(−E /RT)
(5)
0
a
−
1
where k is the reaction constant (ml min ), E the activation energy for the reaction, R
0
a
the gas constant and T is the reaction temperature. Following the above mentioned
equation, the values of rate constant k at different temperatures for hydrolysis of
NH BH catalyzed by the hollow spheres were calculated from the linear part of time
3
3
1
5

courses of the hydrogen evolution in the presence of the hollow spheres with various
Si+Ni contents at various temperatures in the range of 298-343 K. The Arrhenius plots
are shown in Fig. 11. They were also used to calculate the activation parameters: E =
a
-1
4
4, 54, 49, and 45 kJ mol for the hollow spheres with Si+Ni content = 1.06, 3.19, 5.32,
-3
and 10.64 × 10 mol, respectively. The activation energies obtained for the hydrolysis
of NH BH catalyzed hollow silica-nickel composite spheres do not significantly
3
3
depend on the Si+Ni contents.
4
. Conclusion
In this paper, we investigated influence of preparation conditions of hollow
silica-nickel composite spheres in their morphology and catalytic activity for hydrolytic
dehydrogenation of ammonia borane. In the preparation method of this study, when
silica-nickel composite shells were coated on polystyrene templates by the sol-gel
method using L(+)-arginine as the promoter for the reaction to form silica-nickel
composite shell, the polystyrene templates were dissolved subsequently, even
synchronously, in the same medium to form hollow spheres. All the as-prepared hollow
silica-nickel composite spheres have the similar morphology identified by SEM and
TEM measurement. Homogeneity of the hollow silica-nickel composite spheres
1
6

increases with the increase of Si+Ni content as observed by laser diffraction particle
size analysis. The catalytic activity for the hydrogen evolution in the presence of the
hollow spheres increases with the increase of Si+Ni content. The results of FTIR spectra
of the hollow silica-nickel composite spheres indicate that a certain amount of residual
PS templates exists in hollow silica-nickel composite spheres. The residual PS
templates was able to be reduced by procedure of as-prepared samples with toluene
solvent. The catalytic activity of hollow silica-nickel composite spheres increases when
the amount of residual PS templates decreases.
1
7

References
[
1] Basic research needs for the hydrogen economy, report of the basic energy sciences
workshop on hydrogen production, storage and use, May 13-15, 2003, Office of
Science, U.S. Department of Energy, www.sc.doe.gov/bes/hydrogen.pdf.
2] J. Turner, G. Sverdrup, M.K. Mann, P.G. Maness, B. Kroposki, M. Ghirardi, R. J.
Evans, D. Blake, Int. J. Energy Res. 32(5) (2008) 379-407.
[
[
[
3] A.W.C.V. Berg, C.O. Areán, Chem. Commun. 27 (2008) 668-681.
4] Basic research needs catalysis for energy, report from the U.S. Department of Energy,
basic
energy
sciences
workshop
report,
August
6-8,
2007,
<http://www.sc.doe.gov/bes/reports/ list.html>.
[
5] A. Gutowska, L.Y. Li, Y.S. Shin, C.M.M. Wang, X.H.S. Li, J.C. Linehan, et al. ,
Angew. Chem. Int. Ed. 44(23) (2005) 3578-3582.
[
[
6] V. Sit, R.A. Geanangel, W.W. Wendlandt, Thermochim. Acta 113 (1987) 379-382.
7] M.E. Bluhm, M.G. Bradley, R. Butterick III, U. Kusari, L.G. Sneddon, J. Am. Chem.
Soc. 128(24)(2006) 7748-7749.
[
[
8] M.C. Denney, V. Pons, T.J. Hebden, D.M. Heinekey, K.I. Goldberg, J. Am. Chem.
Soc. 128(37) (2006) 12048-12049.
9] F.H. Stephens, R. Tom Baker, M.H. Matus, D.J. Grant, D.A. Dixon, Angew. Chem.
1
8

Int. Ed. 46(5) (2007) 746-749.
[
[
10] A. Paul, C.B. Musgrave, Angew. Chem. Int. Ed. 46(43) (2007) 8153-8156.
11] R.J. Keaton, J.M. Blacquiere, R.T. Baker, J. Am. Chem. Soc. 129(7) (2007)
1
844-1845.
[
[
[
[
[
12] M. Chandra, Q. Xu, J. Power Sources 156(2) (2006) 190-194.
13] M. Chandra, Q. Xu, J. Power Sources 159(2) (2006) 855-860.
14] Q. Xu, M. Chandra, J Power Sources 163(1) (2006) 364-370.
15] M. Chandra, Q. Xu, J. Power Sources 168(1) (2007) 135-142.
16] J.M. Yan, X.B. Zhang, S. Han, H. Shioyama, Q. Xu, Angew. Chem. Int. Ed. 47(12)
(2008) 2287-2289.
[
[
17] S.B. Kalidindi, M. Indirani, B.R. Jagirdar, Inorg. Chem. 47(16) (2008) 7424-7429.
18] S.B. Kalidindi, U. Sanyal, J B.R. Jagirdar, Phys. Chem. Chem. Phys. 10(38) (2008)
5
870-5874.
19] J.M. Yan, X.B. Zhang, S. Han, H. Shioyama, Q. Xu, Inorg. Chem. 48(15) (2009)
389–7393.
[
[
[
7
20] T. Umegaki, J.M. Yan, X.B. Zhang, H. Shioyama, N. Kuriyama, Q. Xu, Int. J.
Hydrogen Energy 34(9) (2009) 3816-3822.
21] T. Umegaki, J.M. Yan, X.B. Zhang, Shioyama, N. Kuriyama, Q. Xu, J. Power
1
9

Sources 191(2) (2009) 209-216.
[
[
22] H.L. Jiang, T. Umegaki, T. Akita, X.B. Zhang, M. Haruta, Q. Xu, Chem. Eur. J.
1
6(10) (2010) 3132-3137.
23] O . Metin, V. Mazumder, S. O zkar, S. Sun, J. Am. Chem. Soc. 132(5) (2010)
468–1469.
1
[
[
[
24] O . Metin, S. O zkar, S. Sun, Nano Res. 3(9) (2010) 676-684.
25] P.Z. Li, K. Aranishi, Q. Xu, Chem. Commun. 48(26) (2012) 3173-3175.
26] M. M. Ren, R. Ravikrishna, K. T. Valsaraj, Environ. Sci. Technol. 40(22) (2006)
7
029-7033.
[
[
[
27] P. Jiang, J. F. Bertone, V. L. Colvin, Science 291 (2001) 453-457.
28] Y. Li, J. Shi, Z. Hua, H. Chen, M. Ruan, D. Yan, Nano Lett. 3(5) (2003) 609-612.
29] U. Jeong, Y. L. Wang, M. Ibisate, Y. N. Xia, Adv. Funct. Mater. 15(12) (2005)
1
907-1921.
[
[
[
30] P. Wang, D. Chen, F. Q. Tang, Langmuir 22(10) (2006) 4832-4835.
31] A. Imhof, Langmuir 17(12) (2001) 3579-3585.
32] Z. Z. Yong, Z. W. Niu, Y. F. Lu, Z. B. Hu, C. C. Han, Angew. Chem. Int. Ed.
4
2(17) (2003) 1943–1945.
[
33] M. Chen, L. M. Wu, S. X. Zhou, B. You, Adv. Mater. 18(6) (2006) 801-806.
2
0

[
[
[
34] Y. N. Xia, B. Gates, Y. D. Yin, Y. Lu, Adv. Mater. 12(10) (2000) 693-713.
35] Z. Y. Zhong, Y. D. Yin, B. Gates, Y. N. Xia, Adv. Mater. 12(3) (2000) 206-209.
36] H. Nakamura, M. Ishii, A. Tsukigase, M. Harada, H. Nakano, Langmuir 21(19)
(2005) 8918-8922.
[
[
[
[
37] F. Caruso, R. A. Caruso, H. Möhwald, Science 282 (1998) 1111-1114.
38] D. Y. Wang, F. Caruso, Chem. Mater. 14(5) (2002) 1909-1913.
39] A. Yu, Y. Wang, E. Barlow, F. Caurso, Adv. Mater. 17(14) (2005) 1737-1741.
40] H. W. Duan, D. Y. Wang, N.S. Sobal, M. Giersig, D. G. Kurth, H. Mohwald, Nano
Lett. 5(5) (2005) 949-952.
[
[
41] K. Zhang, X. H. Zhang, H. T. Chen, X. Chen, L. L. Zheng, J. H. Zhang, B. Yang,
Langmuir 20(26) (2004) 11312-11314.
42] M. Zhang, G. Gao, D. C. Zhao, Z. Y. Li, F. Q. Lu, J. Phys. Chem. B 109(19) (2005)
9
411-9415.
[
[
[
[
[
43] W. J. Li, M. O. Coppens, Chem. Mater. 17(9) (2005) 2241-2246.
44] I. Csetneki, G. Filipcsei, M. Zrinyl, Macromolecules 39(5) (2006) 1939-1942.
45] T. Nakashima, N. Kimizuka, J. Am. Chem. Soc. 125(21) (2003) 6386-6387.
46] X. Cheng, M. Chen, L. Wu, G. Gu, Langmuir 22(8) (2006) 3858-3863.
47] M. Chen, S. Zhou, B. You, L. Wu, Macromolecules 38(15) (2005) 6411-6417.
2
1

[
[
48] Z. Deng, M. Chen, S. Zhou, B. You, L. Wu, Langmuir 22(14) (2006) 6403-6407.
49] T. Umegaki, C. Takei, Q. Xu, Y. Kojima, Int. J. Hydrogen Energy 38(3) (2013)
1
397-1404.
50] T. Umegaki, C. Takei, Y. Watanuki, Q. Xu, Y. Kojima, J. Mol. Catal. A, 371 (2013)
-7.
[
[
[
[
1
51] T. Yokoi, Y. Sakamoto, O. Terasaki, Y. Kubota, T. Okubo, T. Tatsumi, J. Am.
Chem. Soc. 128(42) (2006) 13664-13665.
52] K.-Q. Sun, E. Marceau, M. Che, Phys. Chem. Chem. Phys. 8(14) (2006)
1
731-1738.
53] V. Mavrodinova, M. Popova, Ch. Minchev, R. Nickolov, M. Linden, J. Porous
Mater. 14(2) (2007) 213-218.
[
[
54] J. Li, G. Lu, Appl. Catal. A: Gen. 273(1-2) (2004) 163-170.
55] W. Leng, M. Chen, S. Zhou, L. Wu, Langmuir 26(17) (2010) 14271–14275.
2
2

Figure captions
Figure 1 (a) TEM image of as-prepared hollow silica-nickel composite spheres prepared
-3
with Si+Ni content = 1.06 × 10 mol (aging time = 17 h) and SEM images of
as-prepared hollow silica-nickel composite spheres prepared with Si+Ni content = (b)
-3
1
.06, (c) 3.19 (aging time = 40 h), (d) 5.32 (aging time = 50 h), and (e) 10.64 × 10 mol
(aging time = 100 h).
Figure 2 Particle size distribution of hollow silica-nickel composite spheres prepared
with Si+Ni content = (a) 1.06 (aging time = 17 h), (b) 3.19 (aging time = 40 h), (c) 5.32
-3
(
aging time = 50 h), and (d) 10.64 × 10 mol (aging time = 100 h).
Figure 3 Hydrogen generation from the mixture of sodium borohydride and ammonia
borane in the presence of hollow silica-nickel composite spheres prepared with Si+Ni
content = (a) 1.06 (aging time = 17 h), (b) 3.19 (aging time = 40 h), (c) 5.32 (aging time
-3
=
50 h), and (d) 10.64 × 10 mol (aging time = 100 h).
Figure 4 DTG curve registered upon H -TPR of hollow silica-nickel composite spheres
2
prepared with Si+Ni content = (a) 1.06 (aging time = 17 h), (b) 3.19 (aging time = 40 h),
-3
(
c) 5.32 (aging time = 50 h), and (d) 10.64 × 10 mol (aging time = 100 h).
Figure 5 FT-IR spectra of as-prepared hollow silica-nickel composite spheres prepared
2
3

at (a) 323 K (aging time = 17 h) and (b) 343 K (aging time = 7 h), and (c) hollow
silica-nickel composite spheres prepared at 323 K following the treatment in toluene.
Figure 6 SEM images of as-prepared hollow silica-nickel composite spheres prepared at
(a) 343 K (aging time = 7 h) and (b) hollow silica-nickel composite spheres prepared at
3
23 K following the treatment in toluene.
Figure 7 Hydrogen generation from the mixture of sodium borohydride and ammonia
borane in the presence of hollow silica-nickel composite spheres prepared at (a) 323
K(aging time = 17 h) and (b) 343 K (aging time = 7 h), and (c) hollow silica-nickel
composite spheres prepared at 323 K following the treatment in toluene.
Figure 8 FTIR spectra of as-prepared hollow silica-nickel composite spheres prepared
with Si+Ni content = (a) 1.06 (aging time = 17 h), (b) 3.19 (aging time = 40 h), (c) 5.32
-3
(
aging time = 50 h), and (d) 10.64 × 10 mol (aging time = 100 h) following treatment
of the samples in toluene.
Figure 9 SEM images of as-prepared hollow silica-nickel composite spheres prepared
with Si+Ni content = (a) 1.06 (aging time = 17 h), (b) 3.19 (aging time = 40 h), (c) 5.32
-3
(
aging time = 50 h), and (d) 10.64 × 10 mol (aging time = 100 h) following treatment
of the samples in toluene.
2
4

Figure 10 Hydrogen generation from the mixture of sodium borohydride and ammonia
borane in the presence of hollow silica-nickel composite spheres prepared with Si+Ni
content = (a) 1.06 (aging time = 17 h), (b) 3.19 (aging time = 40 h), (c) 5.32 (aging time
-3
=
50 h), and (d) 10.64 × 10 mol (aging time = 100 h) following treatment of the
samples in toluene.
Figure 11 Arrenius plots for the hydrolysis of NH BH catalyzed by the hollow spheres
3
3
with Si+Ni contents = (a) 1.06 (aging time = 17 h), (b) 3.19 (aging time = 40 h), (c) 5.32
-3
(
aging time = 50 h), and (d) 10.64 × 10 mol (aging time = 100 h) following treatment
of the samples in toluene catalyzed hydrolysis of NH BH .
3
3
2
5

Fig. 1
2
6

Fig. 2
2
7

Fig. 3
2
8

Fig. 4
2
9