Kinetics of Ru-promoted sulphated zirconia catalysed hydrogen generation by hydrolysis of sodium tetrahydroborate

Article abstract of DOI:10.1016/j.molcata.2007.09.025

Pure hydrogen can be catalytically generated by hydrolysis of sodium tetrahydroborate NaBH₄. The present paper reports the kinetics of hydrolysis of aqueous alkaline solution of NaBH₄. The investigated catalyst was 1 wt% Ru-promoted sulphated zirconia. The reaction orders for both NaBH₄ and NaOH, the reaction order for Ru and the apparent activation energy were determined. The hydrogen generation rate can be written following a power law: r = k[NaBH₄]^0.23[NaOH]^-0.35[Ru]^1.27. The activation energy for the hydrogen generation reaction is of 76 kJ mol^-1. Otherwise, the present paper shortly reviews the kinetic data that are available in the open literature and notices the discrepancies that exist for these data. The kinetic data of the present study also contribute to these discrepancies.

Full text of DOI:10.1016/j.molcata.2007.09.025

Available online at www.sciencedirect.com
Journal of Molecular Catalysis A: Chemical 279 (2008) 57–62
Kinetics of Ru-promoted sulphated zirconia catalysed hydrogen
generation by hydrolysis of sodium tetrahydroborate
U.B. Demirci∗, F. Garin
LMSPC, ECPM, ULP, CNRS, 25 rue Becquerel, 67000 Strasbourg, France
Received 23 June 2007; received in revised form 25 September 2007; accepted 27 September 2007
Available online 2 October 2007
Abstract
Pure hydrogen can be catalytically generated by hydrolysis of sodium tetrahydroborate NaBH4. The present paper reports the kinetics of
hydrolysis of aqueous alkaline solution of NaBH4. The investigated catalyst was 1 wt% Ru-promoted sulphated zirconia. The reaction orders for
both NaBH4 and NaOH, the reaction order for Ru and the apparent activation energy were determined. The hydrogen generation rate can be
written following a power law: r = k[NaBH4]0.23[NaOH]−0.35[Ru]1.27. The activation energy for the hydrogen generation reaction is of 76 kJ mol−1
.
Otherwise, the present paper shortly reviews the kinetic data that are available in the open literature and notices the discrepancies that exist for
these data. The kinetic data of the present study also contribute to these discrepancies.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Hydrogen; Kinetics; Ru-promoted sulphated zirconia; Sodium tetrahydroborate
1. Introduction
and provides a safe method of hydrogen storage/transport [7].
The basic hydrogen reaction producing reaction (hydrolysis) is
NaBH4 + 4H2O → NaB(OH)4 + 4 H2 + heat (−300 kJ mol−1).
The hydrolysis reaction is controllable since the hydrogen gen-
eration only occurs in the presence of catalyst [7]. Generating
hydrogen catalytically from NaBH4 solution has several advan-
tages [7], e.g., generated hydrogen is high purity (no CS, no
S) and humidified; hydrogen can be generated even at 0 ◦C;
the reaction products, H2O and NaB(OH)4, are environmentally
safe; and, NaB(OH)4 can be recycled. The main problem of
NaBH4 is its cost and the main research activity in this area
is in the development of alternative processes for regenerating
NaBH4 from dehydrated NaB(OH)4 that is NaBO2 [8].
Catalysts are essential and the catalysts used are transi-
tion metal-based: metal salts [9]; metal borides [10]; La- and
Ni-based intermetallic compounds (LaNi4.5M0.5, M: metal)
[11]; fluorinated metals [12]; bulk metals [13]; Raney metals
[14]; and metal-promoted metal oxides [15]. In the course of
examining the interaction of NaBH4 with heavy metals, Prof.
H.C. Brown and his namesake and collaborator C.A. Brown
[9] observed that many of these exerted a powerful catalytic
effect on the NaBH4 hydrolysis; the Pt family were effective:
Ru, Rh > Pt > Co > Ni > Os > Ir > Fe ꢀ Pd. Besides the authors
noticed that NaBH4 reduced these metals to the elementary state,
in a form, which exhibited high-catalytic activity for hydrolysis.
Prof. Herbert C. Brown (1912–2004) won the Nobel Prize
in Chemistry 1979 [1] “for the development of the use of
boron-containing compounds, into important reagents in organic
synthesis” [2] as well as the inventor (with the late Prof. H.I.
Schlesinger) of sodium tetrahydroborate NaBH4 [3]. Although
rather overlooked in recent years, this chemical has been known
as a viable hydrogen generator since the 1950s [3].
Hydrogen is an energy carrier that has a great potential as an
environmentally clean energy fuel. It has the highest energy con-
tent of any common fuel by weight (about three times more than
gasoline), but the lowest energy content by volume (about four
times less than gasoline) [4]. This presents great transportation
and storage hurdles. Storage systems being developed include
compressed hydrogen, liquid hydrogen, adsorption on solids of
large surface area, metal hydrides, and light hydrides [5]. NaBH4
is a light solid hydride (or chemical hydride) [6]. It increasingly
interests because its hydrogen content is of 10.7 wt%. An aque-
ous alkaline solution of NaBH4 is non-flammable and stable
∗
Corresponding author. Tel.: +33 390 2427 58; fax: +33 390 2427 61.
E-mail addresses: umitbilgedemirci@yahoo.fr,
umit.demirci@ecpm.u-strasbg.fr (U.B. Demirci).
1381-1169/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2007.09.025

58
U.B. Demirci, F. Garin / Journal of Molecular Catalysis A: Chemical 279 (2008) 57–62
1 M, Aldrich) solution of NaBH4 (Aldrich) filled a sealed flask.
Nomenclature
The sealed flask was fitted with an outlet tube for collecting
evolved hydrogen. The temperature T was varied and then main-
tained thanks to a water bath. Ru–SZ was added to the solution
under stirring (not to have external diffusion effects, 400 rpm).
Theoutlettubeexhaustwasconnectedtoawater-filledgraduated
U-type glass cylinder and generated hydrogen was measured by
monitoring water displacement from the cylinder as the reac-
tion proceeded. The initial hydrogen generation rate (HGR) was
calculated in the time range 1–5 min. The relative error on the
measured volume was of about 2%.
A
Ea
k
pre-exponential factor
activation energy (J mol−1
rate constant
)
[NaBH4] molar concentration of NaBH4
[NaOH] molar concentration of NaOH
r
R
[Ru]
T
HGR (mol(H2) L−1
)
gas constant, 8.31451 J K−1 mol−1
molar concentration of Ru
temperature (K)
2.3. Kinetic study
Greek symbols
α
β
χ
reaction order with respect to NaBH4
reaction order with respect to NaOH
reaction order with respect to Ru
In such a way to get a maximum of information, the
experiments were performed as follows. All kinetic data were
measured using fresh Ru–SZ. Studies were carried out over a
NaBH4 concentration range from 0.132 to 0.661 M and a NaOH
concentration range from 0.1 to 1.3 M. The amount of cata-
lyst was varied from 0.05 to 0.45 g. Besides, the Ru loading
was varied from 0.5 to 4 wt%. HGRs were measured at a low-
temperature range of 281–297 K, where thermal hydrolysis of
stabilised NaBH4 solutions is approximately zero [17]. Initial
HGRs were measured. Theoretically the maximum HGR occurs
at the beginning of the reaction since the concentration of the
reactant NaBH4 is the highest and the concentration of the by-
product NaB(OH)4 is the lowest. Note that the production of
NaB(OH)4 is detrimental to the HGR. For instance, Shang and
Chen [21] showed that, when NaB(OH)4 was saturated in the
solution, the HGR significantly decreased, most probably due
to its blockage of the catalytic sites. Hence, the HGRs were
measured during the initial 5 min of hydrolysis.
On the basis of this study, Ru was selected to be the active metal
of the catalyst of the present study.
Guella et al. [16] justly wrote that the state of knowledge was
depleted for metal-catalysed NaBH4 hydrolysis. As for Zhang et
al. [17], they commented that kinetic studies were rather limited.
Kinetics studies are essential because they can provide informa-
tion concerning the reactant(s) role and the catalyst behaviour.
In this study, kinetics of catalytic hydrolysis of aqueous alka-
line solution of NaBH4 was studied over a novel catalyst, 1 wt%
Ru-promoted sulphated zirconia.
2. Experimental
2.1. Catalyst
3. Results and discussion
2−
Sulphated zirconia ZrO2–SO4 (SZ) was prepared accord-
ing to a one-step sol–gel method [18]. An n-propyl alcohol
(Aldrich) solution of 10 wt% zirconium n-propoxide (Aldrich)
and an aqueous solution of sulphuric acid (Aldrich) were dis-
tinctly prepared. The amount of sulphuric acid was determined
in order to have 5 wt% of sulphur in the catalyst prior the cal-
cination stage. The solution of sulphuric acid was added to the
solution of zirconium n-propoxide under vigorous stirring. A gel
formed. The gel was stirred for 2 h and was dried at 80 ◦C for
18 h. The solid was then calcined at 625 ◦C for 4 h. As prepared,
SZ had a specific surface area of 88 m2 g−1 and final sulphur
content (after calcination) of 1.31 wt% and it showed a tetrago-
nal crystalline phase (unpublished results), what is in accordance
with to data already reported [18,19]. The impregnation of Ru
onto SZ was as follows. The desired amount of Ru (0.5, 1, 2, 3 or
4 wt%) was added from an aqueous solution of RuCl3 (Strem).
The mixture was stirred for 1 h and was dried in an oven for 12 h.
The catalyst is denoted Ru–SZ.
3.1. Preliminaries
NaBH4 self-hydrolyses (in the absence of a catalyst) in aque-
ous solution but it can be stabilised by addition of NaOH.
Under our selected experimental conditions, the HGR was of
< 0.01 mL h−1 (<0.2 ␮L min−1), what is negligible. Hydrogen
generation with SZ was assessed and, in our selected experimen-
tal conditions, it was of 0.04 mL h−1 (0.7 ␮L min−1). SZ can be
regarded as being inactive. In all the experiments of the present
study, the hydrogen generation started immediately without any
induction time, as was the case with Guella et al. [16], Mitov et
¨
al. [22] and Ozkar and co-worker [23].
Zhang et al. [17] studied the kinetics of hydrolysis
of stabilised NaBH4 solutions for a Ni-metal supported
catalyst and represented the HGR by the expression
r = k[NaBH4]−0.41[NaOH]0.13[H2O]0.68. The reaction order for
H2O was determined from the variations of H2O concentration
during the course of an experiment but was checked for several
experiments. This order of 0.68 showed the importance of water
management for effective NaBH4 hydrolysis since water is the
key reactant for hydrogen generation and the key solvent for the
by-product NaB(OH)4. The authors did not investigate the effect
2.2. Apparatus
In typical hydrogen generation experiments (apparatus
adapted from Ref. [20]), 20 mL of an aqueous alkaline (NaOH,

U.B. Demirci, F. Garin / Journal of Molecular Catalysis A: Chemical 279 (2008) 57–62
59
Table 1
Hydrogen generation rates (in bold the varying parameters)
Temperature (◦C)
Ru–SZ weight (mg)
Ru loading (wt%)
[NaBH4] (M)
[NaOH] (M)
r (10−4 mol(H2) L−1
)
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
8
250
250
250
250
250
250
250
250
250
250
50
150
250
350
450
250
250
250
250
250
250
250
250
250
250
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0.5
1
2
3
4
1
1
1
1
1
0.132
0.264
0.397
0.529
0.661
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
0.529
1
1
1
1
6.3
7.3
8.4
8.5
9.1
19.6
12.8
10.8
8.5
8.1
1.0
5.4
8.5
13.7
16.9
2.5
1
0.1
0.4
0.7
1
1.3
1
1
1
1
1
1
1
1
1
1
1
1
1
8.5
17.6
30.0
37.4
1.6
2.2
3.6
11
15
19
24
1
1
6.5
8.5
of the catalyst concentration on the HGR. In the present study,
the reaction order for H2O was not determined because, in our
selected experimental conditions, the variation of the concentra-
tion of H2O during the time range 1–5 min was found as being
nil (by calculations). In fact, in our experimental conditions, the
molar ratio [H2O]/[NaBH4] was of ∼100.
co-worker [29]. Positive orders, i.e., first-order, were reported
˜
by Shang and Chen [21] (3 wt% Ru–C) and Pena-Alonso et al.
[30] (PtPd–carbon nanotubes).
Fig. 1 shows the plot of the data in Table 1 (lines 1–5),
which slope provides an estimate of the reaction order for
NaBH4, found as being of 0.23. With 1 wt% Ru–SZ, an increase
of the initial concentration of NaBH4 has a positive effect
on the, HGRs as was the case with Shang and Chen 3 wt%
Ru–C [21]. In our selected experimental conditions, the molar
ratio [H2O]/[NaBH4] was of ∼100; it was probably not opti-
mum and therefore an increase of the NaBH4 concentration
improved the HGR. The first group of researchers discussed
above determined the reaction order for NaBH4 from the plot
‘volume of hydrogen generated versus time’. Fig. 2 shows such
In the present study, the HGR is given following a power
law r = k[NaBH4]α[NaOH]β[Ru]x where k = A exp(−Ea/RT).
Table 1 shows all the HGRs that were obtained and used to
determine the orders and the apparent activation energy.
3.2. Reaction order for NaBH4
In the existing literature, the reaction order with respect to
NaBH4 was obtained in two ways. A first group of researchers
determined the order from variation of HGR with time in
the course of an experiment. Often, the volume of hydrogen
increased linearly with time, implying then zero-order kinetics
[14,20,22–28]. Hence, Amendola et al. [20] proposed that the
first-step involved a surface reaction, most likely BH4− adsorp-
tion on Ru. For Kojima et al. [25], an order of 0 indicated that
HGR was controlled by the catalyst (1.5 wt% Pt–LiCoO2). A
second group of researchers determined the order for NaBH4
from variation of the initial concentration of NaBH4. There was
a discrepancy between the orders found. Negative orders were
reported by Zhang et al. [17] (−0.41 with Ni-supported catalyst)
or were implied by Mitov et al. [22] (CoMnB on Ni foam) and Ye
et al. [27] (9 wt% Co–␥Al2O3). The latter authors explained their
observation by an increase in solution viscosity as first suggested
¨
by Amendola et al. [20]. A zero-order was reported by Ozkar and
Fig. 1. Determination of the reaction order with respect to NaBH4.

60
U.B. Demirci, F. Garin / Journal of Molecular Catalysis A: Chemical 279 (2008) 57–62
Fig. 2. Volume of hydrogen generated as a function of time for 1 wt% Ru–SZ
(250 mg; 24 ◦C; [NaBH4] = 0.529 M; [NaOH] = 1 M).
Fig. 3. Determination of the reaction order with respect to NaOH.
(Ni-supported catalyst), who remarked that it was not clear how
NaOH affected rates but they surmised that NaOH might affect
desorption of B(OH)4− from the catalyst surface, thus affecting
the active site renewal rate. Variations of the order for NaOH
with the variation of NaOH concentration were observed by
Jeong et al. [24] (CoB) and Ye et al. [27] (9 wt% Co–␥Al2O3),
i.e., increase of the HGR with the increase of the NaOH concen-
tration from 1 to 10 wt% but decrease with further increase. For
Ye et al. [27], the effect of NaOH concentration on the NaBH4
hydrolysis was greatly dependent on the catalyst. As for Liu et
al. [14], they ascribed a decrease in water activity to the drop
of the HGR above 20 wt% of NaOH. In fact, it seems that the
reaction order with respect to NaOH is greatly dependent on the
selected experimental conditions as well as the catalysts.
Fig. 3 shows the plot of the data in Table 1 (lines 6–10),
which slope provides an estimate of reaction order for NaOH,
i.e., −0.35. A negative order was reported by Hua et al. [31]
with 2 wt% Ru–C and Shang and Chen [21] with 3 wt% Ru–C.
The effect of NaOH concentration on the NaBH4 hydrolysis is
likely dependent on the catalyst [27] and the increase of NaOH
concentration might have negative effects on the Ru-based cat-
alysts. Besides, an increase of the solution viscosity might be
ascribed to this negative effect [20].
a plot, which was monitored for the conversion of NaBH4
over 1 wt% Ru–SZ. The volume of hydrogen increases lin-
early with time and this observation suggests an order of zero
for NaBH4 [14,20,22–28]. All of the experiments reported in
Table 1 showed the same result. Zhang et al. [17] emphasised
that the zero-order kinetics contradicted observed HGR vari-
ations with increases in initial NaBH4 concentrations. These
contradictory orders are difficult to explain but it is important
to note that the features of the reaction medium in the course
of the hydrolysis experiment change with time (e.g., NaBO2
production, variation of pH, change in viscosity and increase of
the temperature) while the features of the reaction medium for
experimentsvarying the initialconcentration ofNaBH4 areiden-
tical. Zhang et al. [28] developed an interesting methodology for
determining the kinetics of the hydrolysis reaction since they
analysed their experimental data by regarding various kinetic
models: namely zero-order kinetic, first-order kinetic, nth-order
kinetic and Langmuir–Hinshelwood models. This latter model
assumed that the reaction consisted of two important steps: the
equilibrated adsorption of NaBH4 on the surface of the cata-
lyst and the reaction of the adsorbed species on the catalyst
surface. This model successfully captured the zero-order reac-
tion behaviour of the reaction. Our data, for example those in
Fig. 2, were then analysed in this way. According to the infor-
mation given by Zhang et al. [28], we tried the four models. The
zero-order model, the nth-order model with n ∼ 0–0.24 and the
Langmuir–Hinshelwood model fitted our data well. This analy-
sis confirmed the zero-order behaviour at 24 ◦C and as Kaufman
and Sen [10] one may suggest pseudo-zero-order kinetics.
3.4. Reaction order for Ru
Guella et al. [16] investigated the kinetics of NaBH4 hydrol-
ysis for 10 wt% Pd–C by 11B NMR measurements. With this
catalyst, the hydrogen production showed a first-order kinetic
dependence on Pd concentration. An order of one was also
¨
3.3. Reaction order for NaOH
reported by Ozkar and co-workers [23,29] for Ru and Ni nan-
oclusters, respectively. Kojima et al. [25] reported the expression
k = 0.0436 + 0.00917.c, with c the content of the Pt–LiCoO2 cat-
alyst. In fact, the few studies that report a reaction order for the
catalyst report a positive order.
Fig. 4 shows the plot of the data in Table 1 (lines 11–15 and
lines 16–20). The reaction order for the active component of the
catalyst, i.e., Ru, was determined in two ways: variation of the
weight of the Ru–SZ catalyst from 50 to 450 mg; for 250 mg
of Ru–SZ, variation of the Ru loading from 0.5 to 4 wt%. The
Hua et al. [31] reported that, with the increase of the NaOH
concentration from 0 to 20 wt%, the HGRs with NixB increased
while the HGRs with 2 wt% Ru–C decreased, implying pos-
itive and negative orders with respect to NaOH, respectively.
The authors admitted then that these contradictory results were
difficult to explain. For Shang and Chen [21] (3 wt% Ru–C),
the addition of NaOH slowed down the HGR (negative order).
A positive order, i.e., 0.13, was reported by Zhang et al. [17]

U.B. Demirci, F. Garin / Journal of Molecular Catalysis A: Chemical 279 (2008) 57–62
61
Fig. 5. Determination of the apparent activation energy.
Fig. 4. Determination of the reaction order with respect to Ru: (a) from the
variation of the weight of 1 wt% Ru–SZ and (b) from the variation of the Ru
loading (wt%) for 250 mg of Ru–SZ.
ture for NaBH4 hydrolysis over transition metal-based catalysts
[10,14,17,20–24,26–31]. Table 2 shows them. The values are
scattered and disparate; they vary from 19 to 75 kJ mol−1, most
likely due to differences in the experimental conditions as well as
in the intrinsic physical–chemical properties of the metals (geo-
metric effect like, e.g., dispersion of the metal, metallic particles
size and surface area; electronic effect induced by a support or
a second metal). The 1 wt% Ru–SZ catalyst appears less active
compared to all of these solid catalysts (Table 2) since increased
activation energy suggests lower catalytic activity [17,31]. It
shows apparent activation energy that is similar to that of Zhang
orders are identical: namely 1.28 and 1.26, respectively; hence
an order of 1.27 is retained. This suggests that the nature of
the Ru active sites on the catalyst surface is unchanged with the
increase of the Ru loading and that the increase of the Ru loading
only affects the concentration of the Ru surface sites. A reaction
order of 1.27 for Ru agrees with those reported in the literature
[16,23,29].
3.5. Apparent activation energy
¨
et al. 3 wt% Ru–C [28]. Note that Ozkar and co-workers reported
Fig. 5 shows the plot of the data in Table 1 (lines 21–25)
that enables the determination of the apparent activation energy.
Apparent activation energy of 76 kJ mol−1 is found. This
value is higher than those reported through the open litera-
two different values for the apparent activation energy obtained
with Ru nanoclusters namely 29 [23] and 41 kJ mol−1 [26]. Ru
nanoclusters were prepared following a procedure adapted from
a method referenced by the authors and these data seems to have
Table 2
Apparent activation energies reported through the open literature
Catalyst
Ea (kJ mol−1
)
Experimental conditions for Ea NaBH4–NaOH
References
Ni
Ni
Ni
71
63
73
54
52
63
51
38
54
75
42
53
33
46
65
55
47
29
41
43
37
69
19
5.10−3 mol–0
1–10
0.15 mol L−1–0
0.15 mol L−1 –0
5.53–0.79 mol L−1
5.10−3 mol–0
1–10
1.6–10 in wt%
1–10
5.10−3 mol–0
1–10
[10]
[14]
[29]
[29]
[17]
[10]
[14]
[31]
[14]
[10]
[14]
[14]
[27]
[27]
[24]
[22]
[20]
[23]
[26]
[26]
[21]
[28]
[30]
Ni nanoclusters
Ni-supported
Raney Ni
Raney Ni
NixB
Raney Co
Co
Co
Raney Ni50Co50
9 wt% Co–␥Al2O3
9 wt% Co–C
CoB
CoMnB on Ni foam
Ru supported on anion exchange resin
Ru nanoclusters
Ru nanoclusters
Ru nanoclusters
3 wt% Ru–C
3 wt% Ru–C
PtPd–Carbon nanotubes
1–10
5–5 in wt%
5–5 in wt%
20–5
5–5
20–10 in wt%
0.15 mol L−1–0
0.15 mol L−1–0
0.15 mol L−1–10 wt%
1.32 mol kg−1–5 wt%
0.015 M–pH 13

62
U.B. Demirci, F. Garin / Journal of Molecular Catalysis A: Chemical 279 (2008) 57–62
been determined in identical experimental conditions. As this
difference is quite important, one can deplore that the authors
did not discuss that in Ref. [26]. These authors showed, besides,
that NaOH did not affect the apparent activation energy: 41 and
43 kJ mol−1 without NaOH and with NaOH, respectively [26].
concerning the reaction order for the catalyst, a few papers hav-
ing determined this datum report a positive order. In fact, the
kinetic studies are at their early stages and that explains the
discrepancies in the kinetic data.
References
3.6. Summary
[1] Official web site of the Nobel foundation, http://www.nobelprize.org.
[2] Prof. Herbert C. Brown’s biography available, http://www.chem.purdue.
edu/hcbrown.
[3] H.I. Schlesinger, H.C. Brown, collaborators, J. Am. Chem. Soc. 75 (1953)
(a) 186–190, (b) 199–204, (c) 205–209, (d) 215–129.
The established HGR can be given following a power
law, namely r = k[NaBH4]0.23[NaOH]−0.35[Ru]1.27 with
k = A exp(−76.103/RT).
It is besides interesting to compare the efficiency of our cat-
alysts to that of other catalysts reported in the literature and a
good “tool” is the HGR given in L(H2) min−1 g−1(catalyst) or
in L(H2) min−1 g−1(Ru). In a previous paper, we have listed
most of them [32]. Note that the best HGR ever published
is 3.1 L(H2) min−1 g−1(catalyst) or 206.5 L(H2) min−1 g−1(Pt)
for 1.5 wt% Pt–LiCoO2 at 22 ◦C [15]: this catalyst is
outstanding. In the present study, the best result was
0.36 L(H2) min−1 g−1(catalyst) or 9.1 L(H2) min−1 g−1(Ru) for
4 wt% Ru–SZ at 24 ◦C (Table 1, line 20) and this HGR is sim-
ilar to those of most catalysts [32]. Indeed, our catalyst can
be directly compared to two Ru-based catalysts. Amendola
et al. [20] reported HGRs of 0.2 L(H2) min−1 g−1(catalyst) or
4.1 L(H2) min−1 g−1(Ru) for 5 wt% Ru dispersed on anionic
resin at 25 ◦C (20 wt% NaBH4, 10 wt% NaOH); their experi-
mental conditions are less favourable on account of the high
concentration of NaOH. Zhang et al. [28] reported HGRs of
0.7 L(H2) min−1 g−1(catalyst) or 12.9 L(H2) min−1 g−1(Ru) for
5 wt% Ru–C at 25 ◦C (1 wt% NaBH4, 4 wt % NaOH). These data
suggest that the performances of these three Ru-based catalysts
are quite similar even if the proportion of Ru in our catalyst
4 wt% Ru–SZ is smaller. Our HGR results are promising and
improvement ways are going to be explored.
[4] Web site of the Energy Information Administration, Official Energy Statis-
tics from the U.S. Government, http://www.eia.doe.gov.
[5] L. Schlapbach, A. Zu¨ttel, Nature 414 (2001) 353–358.
[6] A. Zu¨ttel, A. Borgschulte, S.I. Orimo, Scripta Mater. 56 (2007) 823–828.
[7] S.C. Amendola, S.L. Sharp-Goldman, M.S. Janjua, N.C. Spencer, M.T.
Kelly, P.J. Petillo, M. Binder, Int. J. Hydrogen Energy 25 (2000) 969–975.
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for the hydrogen generation reaction is 76 kJ mol−1
.
A short survey of the kinetic studies available in the open lit-
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