Activity and kinetics of ruthenium supported catalysts for sodium borohydride hydrolysis to hydrogen

Article abstract of DOI:10.1039/C6RA00747C

Ru–RuO₂/C prepared by galvanic replacement has high catalytic activity for sodium borohydride hydrolysis. In the present study, a series of Ru–RuO₂/C catalysts, Ru–RuO₂/C reduced, RuO₂/C and Ru supported on Ni foam (Ru/Ni foam) are prepared and characterized. Results show that RuO₂ on Ru–RuO₂/C is formed from both the consumption of the parent Ni and NiO nanoparticles and the disproportionation of RuCl₃ with epitaxial growth of Ru species. The quantity of RuO₂ with oxygen vacancies in Ru–RuO₂/C determines the hydrolysis activity for sodium borohydride. In contrast to Ru–RuO₂/C, Ru/Ni foam without oxygen vacancies has the lower hydrolysis activity. Results of kinetics calculation further confirm that without mass transfer limitation, Ru–RuO₂/C has lower intrinsic activation energy and correspondingly higher catalytic activity due to existence of oxygen vacancies than those from Ru–RuO₂/C reduced, RuO₂/C, Ru/Ni foam and catalysts from the literature.

Full text of DOI:10.1039/C6RA00747C

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PAPER
Activity and kinetics of ruthenium supported
catalysts for sodium borohydride hydrolysis to
Cite this: RSC Adv., 2016, 6, 29371
hydrogen†
Yunhua Li, a Xing Zhang,a Qi Zhang,a JinBao Zheng,a NuoWei Zhang,a Bing H. Chena
*
and K. J. Smithb
Ru–RuO2/C prepared by galvanic replacement has high catalytic activity for sodium borohydride hydrolysis.
In the present study, a series of Ru–RuO2/C catalysts, Ru–RuO2/C reduced, RuO2/C and Ru supported on
Ni foam (Ru/Ni foam) are prepared and characterized. Results show that RuO2 on Ru–RuO2/C is formed
from both the consumption of the parent Ni and NiO nanoparticles and the disproportionation of RuCl3
with epitaxial growth of Ru species. The quantity of RuO2 with oxygen vacancies in Ru–RuO2/C
determines the hydrolysis activity for sodium borohydride. In contrast to Ru–RuO2/C, Ru/Ni foam
without oxygen vacancies has the lower hydrolysis activity. Results of kinetics calculation further confirm
that without mass transfer limitation, Ru–RuO2/C has lower intrinsic activation energy and
correspondingly higher catalytic activity due to existence of oxygen vacancies than those from Ru–
RuO2/C reduced, RuO2/C, Ru/Ni foam and catalysts from the literature.
Received 10th January 2016
Accepted 12th March 2016
DOI: 10.1039/c6ra00747c
www.rsc.org/advances
activation energies over catalysts.13,14 Catalytic activity of cata-
lysts, however, is inuenced by internal and external diffusion
1. Introduction
as well as catalytic capacity of active site. In this case, their
results for NaBH4 hydrolysis may be more reasonable if the
effect of mass transfer limitation in the solution is considered
to determine real catalytic properties of catalysts.
Hydrogen is a clean, available alternative energy. Hydrolysis of
alkaline sodium borohydride (NaBH4) to produce hydrogen has
been proposed for hydrogen delivery in portable applications
due to the theoretically high hydrogen storage capacity (10.8
wt%). Active catalysts for hydride hydrolysis have included Co,
Ni, Co and Ni borides,1,2 Ru,3 Pt,4 CoO and Cu2O.5,6
Recently, a large number of bimetallic catalysts, such as Pd–
Cu/C, Pd–Ni/Ni foam,7 Ag–Pd8 and Au–Ag9 have been prepared by
galvanic replacement, in which a non-noble metal with a lower
potential is replaced by a noble metal to form the bimetallic
material. In addition, the existence of the reduced surface can
induce the generation of oxygen vacancies10 while the presence of
oxygen vacancies in the catalysts can facilitate many redox reac-
tions due to the decrease in work function of the materials.11,12 To
our knowledge little has been reported on the synthesis of
hydrolysis catalyst with oxygen defects using a reductive base
metal as the precursor for galvanic replacement.
In our previous study,15 we reported on the catalytic activity
and stability of a Ru–RuO2/C catalyst with oxygen vacancies for
sodium borohydride hydrolysis. Although the catalyst showed
promising activity, the source of the high catalytic activity and
intrinsic activity capacity of Ru–RuO2/C remained unclear. In
the present study a series of Ru–RuO2/C catalysts were prepared
by galvanic replacement and characterized to investigate the
formation of RuO2 with the oxygen vacancies as well as Ru–
RuO2/C reduced, RuO2/C and Ru supported on Ni foam (Ru/Ni
foam). Under the conditions that the effect of mass transfer was
eliminated, intrinsic activation energies of these catalysts were
also calculated to compare real catalytic activity of Ru supported
catalysts. This work is of great importance for the controllable
preparation and reliable comparison of hydrolysis activity of
heterogeneous catalysts.
Kinetics study on NaBH4 hydrolysis to produce hydrogen has
extensively focused on the calculation and comparison of
2. Material and methods
2.1 Preparation, characterization and evaluation of catalytic
aDepartment of Chemical and Biochemical Engineering, College of Chemistry and
Chemical Engineering, National Engineering Laboratory for Green Chemical
Productions of Alcohols-Ethers-Esters, Xiamen University, Xiamen 361005, PR materials
China. E-mail: yunhuali@xmu.edu.cn
bDepartment of Chemical and Biological Engineering, University of British Columbia,
Ru–RuO2/C was prepared by the method described previously.15
In a typical synthesis, the precursor Ni/C was prepared by
hydrothermal synthesis (see ESI†). The as-prepared sample was
dried in vacuum at 333 K for 5 h. Prior to characterization of the
2360 East Mall, Vancouver, BC, V6T 1Z3 Canada
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra00747c
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Ni/C, the dried sample was calcined at 573 K for 3 h. To obtain to a combination of the Knudsen diffusion coefficient (Dk) and
the RuO2-based catalyst, the uncalcined Ni/C (0.3 g) was the bulk diffusion coefficient (Db,i). As for equimolar counter
impregnated in an aqueous solution of RuCl3 (25 mL, 9.64 diffusion, Dp is dened according to the literature (eqn (3)).22
mmol Lꢀ1) at 323 K, ltered, dried and calcined 653 K for 3 h. If
1
1
1
¼
þ
(3)
no specication is made, Ru–RuO2/C denotes the sample
treated for 18 h by the galvanic replacement reaction. For
comparison, RuO2/C and Ru/Ni foam (Ni foam was from
Changsha Lyrun New Material Co. Ltd.) were also prepared
from directly impregnating carbon and Ni foam support,7
respectively, as well as Ru–RuO2/C reduced in H2 atmosphere.
X-ray diffraction (XRD) of the catalysts was performed on
a Rigaku Ultima-IV diffractometer equipped with a Cu Ka
radiation. X-ray photoelectron spectroscopy (XPS) tests were
measured with the PHI Quantum 2000 Scanning ESCA Micro-
probe equipment. Temperature-programmed reduction (TPR)
was performed using a conventional TPR apparatus. Electron
spin resonance (ESR) was carried out using a Bruker EMX-10/12
Spectrometer at 90 K. Scanning electron microscope (SEM)
images of original Ni foam and Ru/Ni from were acquired with
a Hitachi S-4800 FE-SEM. The elemental analysis of the samples
was conducted on inductive couple plasma (ICP). The surface
area of catalysts was determined via the N2 adsorption–
desorption isotherm method at 77 K using a Micromeritics
TriStar II 3020 and the BET (Brunauer–Emmett–Teller) method.
The pore size was calculated using the BJH (Barrett–Joyner–
Halenda) method. Prior to the analyses, the samples were out-
gassed at 523 K for 3 h to eliminate volatile adsorbates on the
surface.
Dp
Dk Db;i
Among them, Dk can be calculated from eqn (4)
rffiffiffiffiffiffi
T
Dk ¼ 48:5Dp
Mi
(4)
On the other hand, Majumder et al.23 studied mass transport
through carbon nanotube membranes with ꢁ7 nm pore diam-
eter and found that ionic diffusion through the carbon nano-
tube (CNT) membranes is close to bulk diffusion expectations
and electrostatically inuenced by a charged carboxyl func-
tionality at the CNT entrance. In our work, Ru–RuO2/C treated
in RuCl3 solution was functionalized by a large number of
hydrophilic groups. This implied that reactant ion, BH4
ꢀ
,
diffusion in Ru–RuO2/C is similar to that in the literature.
Therefore, the Knudsen diffusion coefficient of NaBH4 in the
pore of Ru–RuO2/C can be obtained with two methods: (1) the
conventional calculation for the gas phase according to eqn (4);
(2) the Knudsen diffusion coefficient was regarded as the bulk
diffusion23 to simplify calculation. Eqn (3) was changed into
eqn (5).
1
2
¼
(5)
In a typical procedure for sodium borohydride hydrolysis,
0.01 g Ru–RuO2/C (0.05 g Ru/Ni foam used because of lower
reaction activity) was added into a 25 mL ask and then 5 mL
alkaline NaBH4 aqueous solution was introduced into this ask.
Hydrogen generated during reaction process was collected into
a gas collecting bottle (1 L), which has a minimum scale of 25
mL and an error of 5.0%.
Dp
Db;i
The bulk diffusion coefficient, Db,i, was 3.63 ꢂ 10ꢀ5 cm2 sꢀ1
estimated from experimental result in alkaline NaBH4 solu-
tion.24 Thus, the diffusion coefficient Dp in the pores of catalysts
can be calculated according to eqn (3) or (5), respectively.
3. Results and discussion
2.2 Mass transfer calculations
3.1 Catalytic hydrolysis reaction of sodium borohydride
Internal diffusion rate might directly affect catalytic perfor-
mances for NaBH4 hydrolysis reaction. Herein, the Wheeler–
Weisz group was used to investigate the inuence of internal
mass transfer and dened as follows.16–19
The catalytic activity of the catalysts prepared by galvanic
replacement was determined for the hydrolysis of NaBH4 and
further was normalized by the metal amount in the catalysts
ꢀ
ꢁ
robsR2 n þ 1
h42 ¼
(1)
Deff;iCs
2
where R is the diameter of pellet catalysts used in hydrolysis
reaction process, which was detected through OMEC LS-908
type Laser Particle Size Analyzer. A general relationship
between the effective diffusivity (Deff,i) and the pore diffusivity
(Dp) is determined by parallel pore model.16,18,20
3
Deff;i
¼
Dp
(2)
s
3 is the porosity, which can be measured by BET method. s is the
tortuosity factors, which is inuenced by temperature, adsor-
bate density and the diffusion mode and so on.21 A tortuosity
factor for typical porous catalysts, 2, was used in this work. The
Fig. 1 Hydrolysis activity of NaBH4 on Ru–RuO2/C at different treat-
diffusion coefficient, Dp, in the pores was calculated according ment time.
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Fig. 2 Hydrolysis activity of NaBH4 on different catalysts.
Fig. 3 XRD patterns of Ni foam and Ru/Ni foam.
(Fig. 1). As shown in Fig. 1, hydrogen generation rates of the
catalysts increased with increased galvanic replacement time,
i.e. in the order of Ni/C precursor < Ru–RuO2/C treated for 2 h <
that treated for 10 h < that treated for 18 h. In comparison with
Ru–RuO2/C, Ru–RuO2/C reduced, RuO2/C and Ru/Ni foam
present the lower hydrolysis activity (Fig. 2). To understand the
change of catalytic activity of catalysts, a series of character-
izations were conducted.
3.2 Characterization of catalysts
Ru/Ni foam. Table 1 demonstrated the textural characteris-
tics of the materials. During impregnating and reducing
process, the pore size and surface area of a series of Ru sup-
ported carbon change slightly except for Ru/Ni foam. Fig. 3
showed XRD patterns of Ni foam and Ru supported on Ni foam.
Only diffraction peaks of Ni metal were found on Ni foam. Aer
impregnating ruthenium precursor solution, NiO (101) is
generated because of the dissolution of partial Ni foam and re-
deposition. At the same time, a distinct peak was observed
between Ru (002) and Ni (111) during the impregnation process,
indicating the formation of a composite composed of metal Ru
and Ni. XPS results (Fig. 4 and S1†) showed that Ru/Ni foam has
the lower binding energy of Ru 3p than Ru–RuO2/C catalysts.
This further indicated that more Ru metal exists over Ru/Ni
foam. In addition, H2-TPR result showed that a few Ru oxide
species are reduced as well as a large amount of Ni oxide species
over Ru/Ni foam. And the addition of Ru contributes to the
reduction of NiO over Ru/Ni foam compared with Ni foam
(Fig. 5). Combining with SEM micrographs and EDX analysis of
Fig. 4 XPS spectra of Ru 3p for different catalysts.
Fig. 5 H2-TPR of Ni foam and Ru/Ni foam.
Table 1 The physiochemical structure of the materials
BET surface area
(m2 gꢀ1
Pore size
(nm)
Catalyst
)
Ni foam and Ru/Ni foam (Fig. 6), we believe that most of surface
Ni and Ru oxide species interact with a composite consisting of
Ru and Ni and exist in the form of a large number of nanoplates
on Ni foam support.
Ru–RuO2/C catalysts. Ni species in the form of Ni and NiO
were highly dispersed over Ni/C (Fig. 7 and S1†). During the
subsequent galvanic replacement process, the adsorbed precursor
RuCl3, with higher potential than the Ni species, reacts with the
Ru–RuO2/C for 0 h (Ni/C)
Ru–RuO2/C for 2 h
Ru–RuO2/C for 10 h
Ru–RuO2/C for 18 h
Ru–RuO2/C reduced
RuO2/C
1315.02
1442.80
1476.14
1155.69
1182.82
1429.32
13.79
4.25
3.94
3.90
4.28
3.84
4.11
23.09
Ru/Ni foam
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Fig. 8 H2-TPR profiles of Ru–RuO2/C at different galvanic replace-
ment time.
Fig. 6 SEM micrograph and EDX analysis of Ni foam and Ru/Ni foam.
(a) Ni foam, (b) Ru/Ni foam and (c) EDX of Ru/Ni foam.
different galvanic replacement time. As shown in Fig. 8, Ru–
RuO2/C has no obvious reduction peak for Ni oxide species aer
galvanic replacement for 2 h. These results indicate that the
formation of RuO2 is at the expense of both Ni metal and NiO in
the initial stage of galvanic replacement. Since the standard
reduction potential of Ni2+/Ni pair (ꢀ0.25 V, vs. standard
hydrogen electrode, SHE) is lower than that of the RuCl3/Ru pair
(0.68 V, vs. SHE), RuCl3 can be reduced to Ru by Ni under certain
conditions. The produced Ru might be further oxidized in the
solution.25 We also impregnated commercial NiO powder with
the RuCl3 solution at 323 K. RuO2 was observed by XRD (data not
shown) and by XPS (Fig. S2†). Therefore, we conclude that Ru and
RuO2 on the Ru–RuO2/C catalyst come from the reactions of Ni
and NiO with RuCl3 in the initial stage of galvanic replacement.
ICP analysis shows that the Ru loadings in Ru–RuO2/C are
4.40, 5.23 and 6.13 wt% aer treatment for 2, 10 and 18 h,
respectively. H2-TPR (Fig. 8) results demonstrated that the total
amount of reduced oxygen species in Ru–RuO2/C also increased
gradually for the catalysts treated for 2, 10 and 18 h, respectively.
The ratio of TPR peak area for Ru oxide species is almost equal
and the total Ru loading is proximate for the samples for 2, 10
and 18 h, implying that both ruthenium oxide species and Ru
metal increase simultaneously with increased galvanic replace-
ment time. Since reactions between Ni species and RuCl3 proceed
Fig.
7 XRD patterns of C and Ru–RuO2/C at different galvanic
replacement time.
nano-particle nickel because nickel has a higher reduction ability
than the carbon support. The evolution of the adsorbed RuCl3
into ruthenium oxide with oxygen vacancies was investigated by
changing the galvanic replacement time.
In the XRD patterns of Fig. 7, diffraction peaks at 23.7ꢃ and
43.9ꢃ are attributed to reections from carbon (JCPDS: 46-0945).
The characteristic peaks at 28.0ꢃ, 35.1ꢃ and 54.3ꢃ correspond to
(110), (101) and (211) reections from rutile RuO2 (JCPDS: 40-
1290) while the diffraction peaks at 44.5ꢃ and 44.0ꢃ are attributed
to Ni (111) and Ru (101), respectively. As shown in Fig. 7,
diffraction peak of Ni (111) over Ni/C (0 h for Ru–RuO2/C) is
observed in comparison with carbon by hydrothermal treatment.
XPS spectrum (Fig. S1†) of Ni/C showed that NiO appears in
accompany with Ni metal. The negligible diffraction peak in XRD
pattern is due to the high dispersion of NiO on Ni/C. The nickel
(111) disappears while RuO2 is formed (Fig. 7) aer galvanic
replacement. With increased galvanic replacement time, diffrac-
tion peak of RuO2 over Ru–RuO2/C is also gradually prominent,
indicating the RuO2 increases with increased treatment time.
In comparison with Ni/C, the appearance of a Ru 3p signal
from the XPS spectra (Fig. 4) was accompanied by the disap-
pearance of the Ni 2p spectrum aer galvanic replacement for 2
h. In addition, Fig. 8 showed the H2-TPR results of Ru–RuO2/C at
Fig. 9 Low-temperature ESR spectrum of catalysts in different treat-
ment time.
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within 2 h and the Ru and RuO2 loading further increase with while Ru metal acts as an active phase to dissociate NaBH4.
increased galvanic replacement time, the formation of Ru and Thus, under the conditions that Ru metal and RuO2 cocatalyze
RuO2 results from the disproportionation of RuCl3 adsorbed on NaBH4 hydrolysis, Ru–RuO2/C shows the highest catalytic
catalysts under the conditions of the presence of air.26,27
activity of sodium borohydride hydrolysis.
Fig. 9 showed low-temperature ESR spectra of different
ESR spectrum presented no oxygen defects on Ru/Ni foam.
catalysts. The signals with characteristic g-factor values of 2.002 In other words, Ru and Ni metal composite, rather than Ru and
and 1.997 are identied as oxygen vacancies on RuO2 (ref. 28) at RuO2 with oxygen vacancies, was obtained by Ni foam as a rich
magnetic elds of about 3360 G. There were no the other reductive support impregnated by Ru precursor solution. In
pronounced resonant features in the spectra. As shown in Fig. 9, comparison with Ru–RuO2/C, Ru/Ni foam without oxygen
the catalytic materials treated for 10 and 18 h, especially aer 18 defects has relative low catalytic activity for NaBH4 hydrolysis to
h, had obvious signals for oxygen vacancies.
hydrogen. This is also further discussed in 3.3 section.
In agreement with the content of oxygen vacancies, hydrogen
generation rates of the catalysts increased with increased
galvanic replacement time, i.e. in the order of Ni/C precursor <
Ru–RuO2/C treated for 2 h < that treated for 10 h < that treated
for 18 h (Fig. 1). The consumption of Ni species accompanied
with the formation of oxygen vacancies on RuO2 occurred
within 2 h. However, the highest catalytic activity occurs on Ru–
RuO2/C treated for 18 h. This is mainly because of continued
disproportionation of RuCl3 yielding an increased number of
Ru and RuO2 species with oxygen vacancies epitaxially grown on
the catalyst. RuO2 with oxygen vacancies can facilitate water
decomposition, a rate-determining step for NaBH4 hydrolysis,
3.3 Intrinsic kinetic study
A Ru–RuO2/C catalyst with oxygen vacancies showed the high
catalytic activity in NaBH4 hydrolysis. Herein, intrinsic kinetics
of Ru–RuO2/C was studied and compared with the Ni and Ru
metal composites, Ru–RuO2/C reduced and Ru/Ni foam, and the
results from literatures. Fig. S3† presented the NaBH4 hydro-
lysis reaction results over Ru–RuO2/C at various stirring speed
to check the effect of external diffusion on hydrolysis reaction.
With increased stirring speed, the rate of hydrogen generated
rstly increases29 and then decreases. At the stirring speed
higher than 200 rpm, hydrogen generation rate reached the
Fig. 10 Arrhenius plot obtained from TOF for different catalysts.
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maximal value, indicating that external mass transfer limitation However, considering the pore diffusion limitation, true
is almost completely eliminated in this case. At 300 rpm, the apparent reaction activation energies (Et) are modied by
decreasing in reaction rate might be result from unexpected a diffusion activation energy (Ed) term such that the observed
adhesion of catalysts to the upper wall of the ask at high apparent activation energy is given by Eob ¼ (Et + Ed)/2.30 Thus,
stirring speed.
more sever diffusion limitations might lead to the low apparent
Inuence of internal diffusion on hydrolysis reaction was activation energies from those literatures or difficulty in
further estimated over Ru–RuO2/C. Calculation value of the comparison of catalytic results. Although some catalysts in the
Wheeler–Weisz group, based on the conventional gas phase or literatures reported were used in the form of nanoparticles for
the assumption that the Knudsen diffusion coefficient is equal hydrolysis reaction, the effect of particle aggregation in the
to the bulk diffusion, is 0.0048 or 0.0024, respectively. It is solution on internal mass transfer is still unclear. To reliably
generally accepted that the effect of the internal mass transfer determine catalytic capacity of active site over heterogeneous
on the reaction rate can be neglected when the value of h42 is catalysts, the intrinsic activation energies for hydride hydrolysis
less than 0.1. In this work, the difference of the Wheeler–Weisz to hydrogen should be presented on the basis of elimination of
group on the basis of two methods derives from the Knudsen mass transfer limitation. This was done for the rst time in the
diffusion coefficient. At present, the accurate calculation for present work.
Knudsen diffusion coefficient of uid component is still under
way. However, since the possible calculation values of h42 were
far away from 0.1, the inuence of internal mass transfer on the
4. Conclusions
The present study shows that the formation of a part of Ru and
RuO2 is at the expense of Ni and NiO and the other comes from
the disproportionation of RuCl3. RuO2 with oxygen vacancies in
Ru–RuO2/C determines hydrolysis activity of sodium borohy-
dride. In contrast, Ru/Ni foam without oxygen vacancies
exhibits the low catalytic activity. Under the conditions elimi-
nating internal and external diffusion, intrinsic activation
energy obtained is, 48.36 kJ molꢀ1, lower than that from Ru–
RuO2/C reduced, RuO2/C and Ru/Ni foam. Ru–RuO2/C with
oxygen vacancies has the higher intrinsic catalytic activity than
metal Ru and Ni composite. Since the apparent activation
energies are affected by mass-transfer limitations, the compar-
ison of real activity on hydrolysis catalysts should be conducted
based on intrinsic activation energies.
hydrolysis reaction should be negligible over Ru–RuO2/C. The
porous structure of Ru–RuO2/C reduced and RuO2/C is similar
to that of Ru–RuO2/C (Table 1), so the effect of diffusion on
activity over Ru–RuO2/C reduced and RuO2/C was also not
prominent. With respect to Ru/nickel foam, the pore size is very
large even though aer it was modied by Ru (Table 1). In this
case, the effect of internal diffusion is negligible.
Under the conditions that the reaction process is free from
the external and internal mass transfer limitations, turnover
frequency (TOF) was estimated by dividing the mole amount of
hydrogen produced per second by the mole amount of metal on
catalysts used. Arrhenius plots for TOF as a function of
temperature was given in Fig. 10. The corresponding activation
energy of catalysts was also presented in Fig. 10. As displayed in
Fig. 10, Ru–RuO2/C has the relative lower activation energy than
Ru/Ni foam. When the apparent activation energy is not affected
by mass transfer, the lower activation energy implies the relative
higher catalytic activity of Ru–RuO2/C than Ru/Ni foam. In
contrast, most of activation energies from literatures are
apparent results (Table 2) and they might be inuenced by mass
transfer. In this case, Ru–RuO2/C showed a moderate activity.
Abbreviations
h42 Wheeler–Weisz group, dimensionless
robs Apparent reaction rate, mol Lꢀ1 sꢀ1
R
Thickness of wash-coat or diameter of the pellet and
cylindrical catalysts, m
n
Reaction order
Deff,i Effective diffusion coefficient in the pores of the catalyst,
Table 2 The comparison of activation energies of catalysts from
literatures
m2 sꢀ1
ꢀ
Cs
Dp
Dk
dp
T
BH4 concentration at the surface of catalyst, mol mꢀ3
The diffusion coefficient in the pores, m2 sꢀ1
The Knudsen diffusion coefficient, m2 sꢀ1
Pore diameter of catalyst, m
Catalyst
Temperature (K)
Ea (kJ molꢀ1
)
Ref.
Ni45Au45Co10
Ru/Ti3C2X2
Au20Ni80 BNP
Co–Mo–B
Ni–B
Ru/HMS
303–318
298–313
303–318
293–323
303–333
283–303
303–323
303–333
293–323
298–328
288–348
273–353
303–323
18.8
22.1
30.3
43.7
31
32
33
14
34
35
36
37
38
39
40
41
Temperature, K
ꢀ
M
Molecular weight of BH4 species
Db,i The bulk diffusion coefficient of specie i, m2 sꢀ1
ꢁ45–47
46.7
Co–P
47.0
49.3
51.2
52.1
52.7
66.3–81.7
48.4
NiB/capsule
Co–La–Zr–B
Ni–Co–P/g-Al2O3
Ni–Ru/50WX8
Co–B/IR-120
Ru–RuO2/C
Greek letters
3
Void fraction (porosity) of catalyst bed, dimensionless
Tortuosity factor, dimensionless
s
This work
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21 M. R. Bonilla and S. K. Bhatia, J. Phys. Chem. C, 2013, 117,
3343–3357.
Acknowledgements
22 J.
von
Rickenbach,
F.
Lucci,
C.
Narayanan,
This work was supported by National Natural Science Founda-
tion of China (Grant No. 21476188, 21106118).
P. D. Eggenschwiler and D. Poulikakos, Chem. Eng. J.,
2015, 276, 388–397.
23 M. Majumder, N. Chopra and B. J. Hinds, ACS Nano, 2011, 5,
3867–3877.
Notes and references
1 N. Patel and A. Miotello, Int. J. Hydrogen Energy, 2015, 40,
1429–1464.
2 N. Sahiner and A. O. Yasar, Fuel Process. Technol., 2014, 125,
148–154.
24 M. Chatenet, M. B. Molina-Concha, N. El-Kissi, G. Parrour
and J. P. Diard, Electrochim. Acta, 2009, 54, 4426–4435.
25 G. Chen, S. Desinan, R. Rosei, F. Rosei and D. Ma, Chem.
Commun., 2012, 48, 8009–8011.
3 H. Y. Ma and C. Z. Na, ACS Catal., 2015, 5, 1726–1735.
4 C. Salameh, A. Bruma, S. Malo, U. B. Demirci, P. Miele and
S. Bernard, RSC Adv., 2015, 5, 58943–58951.
5 Y. Yamada, K. Yano and S. Fukuzumi, Energy Environ. Sci.,
2012, 5, 5356–5363.
26 Y. Guo, H. Li and H. Kameyama, Chem. Eng. Sci., 2011, 66,
6287–6296.
27 D. V. Bavykin, A. A. Lapkin, P. K. Plucinski, J. M. Friedrich
and F. C. Walsh, J. Catal., 2005, 235, 10–17.
28 P. A. Osorio-Vargas, C. Pulgarin, A. Sienkiewicz, L. R. Pizzio,
6 H. Zhang, T. Ling and X. W. Du, Chem. Mater., 2015, 27, 352–
357.
7 Y. Li, L. Zhu, K. Yan, J. Zheng, B. H. Chen and W. Wang,
Chem. Eng. J., 2013, 226, 166–170.
´
M. N. Blanco, R. A. Torres-Palma, C. Petrier and J. A. Rengifo-
Herrera, Ultrason. Sonochem., 2012, 19, 383–386.
29 S. F. Lim, Y. M. Zheng, S. W. Zou and J. P. Chen, Chem. Eng.
J., 2009, 152, 509–513.
8 L. Xu, Z. M. Luo, Z. X. Fan, S. J. Yu, J. Z. Chen, Y. S. Liao and
C. Xue, Chem.–Eur. J., 2015, 21, 8691–8695.
30 T. Zhang, J. Li, J. Liu, D. Wang, Z. Zhao, K. Cheng and J. Li,
AIChE J., 2015, 61, 3825–3837.
9 J. Lee, K. Han and D.-J. Jang, Appl. Catal., A, 2014, 469, 380–
386.
31 C. Jiao, Z. Huang, X. Wang, H. Zhang, L. Lu and S. Zhang,
RSC Adv., 2015, 5, 34364–34371.
10 X. Wang, N. M. Perret, J. J. Delgado, G. Blanco, X. Chen,
C. M. Olmos, S. Bernal and M. A. Keane, J. Phys. Chem. C,
2013, 117, 994–1005.
11 M. V. Ganduglia-Pirovano, A. Hofmann and J. Sauer, Surf.
Sci. Rep., 2007, 62, 219–270.
12 M. T. Greiner, L. Chai, M. G. Helander, W. M. Tang and
Z. H. Lu, Adv. Funct. Mater., 2012, 22, 4557–4568.
13 S. G. Peng, X. J. Fan, J. Zhang and F. Y. Wang, Appl. Catal., B,
2013, 140, 115–124.
14 D. D. Ke, Y. Tao, Y. Li, X. Zhao, L. Zhang, J. D. Wang and
S. M. Han, Int. J. Hydrogen Energy, 2015, 40, 7308–7317.
15 Y. Li, Q. Zhang, N. Zhang, L. Zhu, J. Zheng and B. H. Chen,
Int. J. Hydrogen Energy, 2013, 38, 13360–13367.
16 H. R. Yue, Y. J. Zhao, L. Zhao, J. Lv, S. P. Wang, J. L. Gong and
X. B. Ma, AIChE J., 2012, 58, 2798–2809.
32 X. Li, G. Fan and C. Zeng, Int. J. Hydrogen Energy, 2014, 39,
14927–14934.
33 X. Wang, S. Sun, Z. Huang, H. Zhang and S. Zhang, Int. J.
Hydrogen Energy, 2014, 39, 905–916.
34 Z. J. Wu, X. K. Mao, Q. Zi, R. R. Zhang, T. Dou and
A. C. K. Yip, J. Power Sources, 2014, 268, 596–603.
35 S. Peng, B. Pan, H. Hao and J. Zhang, J. Nanomater., 2015,
2015, 1–11.
36 Y. Wang, K. Qi, S. Wu, Z. Cao, K. Zhang, Y. Lu and H. Liu, J.
Power Sources, 2015, 284, 130–137.
37 Y. Chen, Y. Shi and Y. Wang, Int. J. Energy Res., 2015, 39, 634–
642.
38 M. H. Loghmani and A. F. Shojaei, Energy, 2014, 68, 152–159.
39 Z. Li, H. Li, L. Wang, T. Liu, T. Zhang, G. Wang and G. Xie,
Int. J. Hydrogen Energy, 2014, 39, 14935–14941.
40 C.-H. Liu, B.-H. Chen, C.-L. Hsueh, J.-R. Ku, M.-S. Jeng and
F. Tsau, Int. J. Hydrogen Energy, 2009, 34, 2153–2163.
41 Y.-H. Chen and C.-Y. Pan, Int. J. Hydrogen Energy, 2014, 39,
1648–1663.
17 K. Arnby, A. Torncrona, B. Andersson and M. Skoglundh, J.
Catal., 2004, 221, 252–261.
18 L. Ronchin and L. Toniolo, Catal. Today, 1999, 48, 255–264.
19 E. Crezee, B. W. Hoffer, R. J. Berger, M. Makkee, F. Kapteijn
and J. A. Moulijn, Appl. Catal., A, 2003, 251, 1–17.
20 Z. G. Wang, S. L. Chen, J. N. Pei, A. C. Chen, J. H. Zhang,
Z. M. Xu and J. B. Benziger, AIChE J., 2014, 60, 3267–3275.
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