Metal substituted pyrochlore phase LixLa2-xCe1.8Ru0.2O7-δ (x = 0.0-0.6) as an effective catalyst for oxidative and auto-thermal steam reforming of ethanol

Article abstract of DOI:10.1039/c8cy01992d

Pyrochlore phase Li_xLa_2-xCe_1.8Ru_0.2O_7-δ (x = 0.0-0.6) [LLCRO] substituted by Li and Ru in A and B sites was synthesized and studied for performance in oxidative steam and auto-thermal reforming of ethanol (OSRE, ATR). The samples were characterized by powder X-ray diffraction (PXRD), X-ray absorption spectroscopy (XAS), and X-ray photoelectron spectroscopy (XPS) to examine the effect of substituted Li⁺ and Ruⁿ⁺ on OSRE performance. The results indicated that the substituted Li ions modified the oxidation states of Ru and Ce in LLCRO, which led to oxygen vacancies/mobility and played an important role in the catalytic performance of OSRE. Using LLCRO as the catalyst and supported by Al₂O₃, La₂Zr₂O₇ (LZO) was investigated for its hydrogen production performance. The catalytic stability of the LLCRO (x = 0.6)/LZO catalysts was tested at 350 °C under oxidative steam conditions (OSRE) and showed a stable ethanol conversion and hydrogen production (X_EtOH = 98(3)%; S_H2 = 95(3)%). Under autothermal conditions (ATR), the LLCRO (x = 0.6) catalyst supported by LZO exhibited a stable catalytic performance with an average ethanol conversion and hydrogen selectivity of 90(3)% and 71(4)%, respectively. Carbon deposition was significantly suppressed during the OSRE and ATR processes on LLCRO (x = 0.6) catalysts supported by LZO, whereas, a significant carbon deposition was observed for LLCRO (x = 0.6)/Al₂O₃ as the catalyst. These results indicate that LLCRO (x = 0.6) supported by LZO is an effective catalyst for hydrogen production. The enhanced activity was attributed to the effectively suppressed carbon deposition and the sintering of highly dispersed Ru ions in the LLCRO catalyst, which may be due to the strong binding between the catalyst and LZO.

Full text of DOI:10.1039/c8cy01992d

Catalysis
Science &
Technology
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PAPER
Metal substituted pyrochlore phase
Li La Ce Ru O (x = 0.0–0.6) as an effective
catalyst for oxidative and auto-thermal steam
x
2−x
1.8
0.2 7−δ
Cite this: DOI: 10.1039/c8cy01992d
reforming of ethanol†
ab
a
a
a
Ho-Chen Hsieh, Yuan-Chia Chang, Ping-Wen Tsai, Yen-Yu Lin,
c
bc
ad
Yu-Chun Chuang, Hwo-Shuenn Sheu and Chi-Shen Lee
*
x
Pyrochlore phase Li La2−xCe1.8Ru0.2O7−δ (x = 0.0–0.6) [LLCRO] substituted by Li and Ru in A and B sites
was synthesized and studied for performance in oxidative steam and auto-thermal reforming of ethanol
(
OSRE, ATR). The samples were characterized by powder X-ray diffraction (PXRD), X-ray absorption
+
spectroscopy (XAS), and X-ray photoelectron spectroscopy (XPS) to examine the effect of substituted Li
n+
and Ru on OSRE performance. The results indicated that the substituted Li ions modified the oxidation
states of Ru and Ce in LLCRO, which led to oxygen vacancies/mobility and played an important role in
2 3 2 2 7
the catalytic performance of OSRE. Using LLCRO as the catalyst and supported by Al O , La Zr O (LZO)
was investigated for its hydrogen production performance. The catalytic stability of the LLCRO (x = 0.6)/
LZO catalysts was tested at 350 °C under oxidative steam conditions (OSRE) and showed a stable etha-
nol conversion and hydrogen production (XEtOH = 98(3)%; SH2 = 95(3)%). Under autothermal conditions
(ATR), the LLCRO (x = 0.6) catalyst supported by LZO exhibited a stable catalytic performance with an
average ethanol conversion and hydrogen selectivity of 90(3)% and 71(4)%, respectively. Carbon deposi-
tion was significantly suppressed during the OSRE and ATR processes on LLCRO (x = 0.6) catalysts
supported by LZO, whereas, a significant carbon deposition was observed for LLCRO (x = 0.6)/Al O as
Received 25th September 2018,
Accepted 7th February 2019
2
3
the catalyst. These results indicate that LLCRO (x = 0.6) supported by LZO is an effective catalyst for hy-
drogen production. The enhanced activity was attributed to the effectively suppressed carbon deposition
and the sintering of highly dispersed Ru ions in the LLCRO catalyst, which may be due to the strong
binding between the catalyst and LZO.
DOI: 10.1039/c8cy01992d
rsc.li/catalysis
lems, and transport problems make it difficult to use as a
source of energy. Hydrogen can be produced via various pro-
1
. Introduction
The energy crisis caused by the overconsumption of fossil
cesses, such as methane steam reforming, from biomass-
derived liquid fuels (such as methanol, ethanol, and biodie-
1
–4
fuels is an important issue for today's society.
To reduce
7–10
our dependence on fossil fuel energy, it is necessary to de-
sel), and photocatalytic water splitting.
Energy production
5
,6
velop renewable energy technologies. Hydrogen is a clean
from the conversion of biomass-derived hydrocarbons has
attracted increasing attention in recent years because these
can be considered a renewable energy resource obtained from
−
1
energy source owing to its high energy density (142 MJ kg ),
and it is also a zero-emission fuel when reacted with oxygen.
However, disadvantages like a gaseous state, storage prob-
processing agricultural products where the emitted CO can be
2
1
1–16
reutilized through the photosynthetic process of plants.
a
Department of Applied Chemistry, National Chiao Tung University, 1001
Other advantages of ethanol include a high hydrogen content,
ease of transport, biodegradability, and low toxicity.
University Rd., Hsinchu 30010, Taiwan. E-mail: chishen@mail.nctu.edu.tw
b
Graduate Degree Program of Science and Technology of Accelerator Light Source,
Ethanol conversion to hydrogen is an active research field,
which includes steam reforming of ethanol (SRE) (eqn (1)),
National Chiao Tung University, Hsinchu 30010, Taiwan
c
National Synchrotron Radiation Research Center, Hsinchu, 300, Taiwan
d
Center for Emergent Functional Matter Science, National Chiao Tung University,
partial oxidation of ethanol (POE) (eqn (2)), and oxidative
Hsinchu 30010, Taiwan
17–22
steam reforming of ethanol (OSRE) (eqn (3)).
Among
†
Electronic supplementary information (ESI) available: Detailed information
these hydrocarbon conversion techniques, OSRE combines
endothermic SRE and exothermic POE reactions, and the re-
action can be controlled to reduce the exothermic enthalpy
can be found in the ESI, including X-ray powder diffraction and Rietveld refine-
ment data, spectra, SEM images, the catalytic activity test, and TGA and XPS
analysis data. See DOI: 10.1039/c8cy01992d
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by adjusting the relative oxygen concentration. The reaction
may produce carbon monoxide, which can be further
converted into hydrogen with water through a water–gas shift
reaction (WGS) (eqn (4)). The external energy input can be
minimized to reach the condition of autothermal steam
reforming of ethanol (ATRE). The lifetime of the catalyst may
be increased due to gasification of carbon deposition with
oxygen. These features are of great interest for hydrogen pro-
the ATR of ethanol, which showed an optimized hydrogen se-
lectivity of ∼108.71% at 600 °C. The enhanced activity may be
due to the modified surface electronic properties induced by
4
0
the iron-substituted spinel phase. S. M. de Lima et al. stud-
ied the reduced perovskite-type oxide La1 Ce NiO as a cata-
−x
x
3
lyst for OSRE. The catalyst contained a mixture of Ni/CeO
2
/
La O nanoparticles that exhibits high oxygen vacancies and
2
3
oxygen mobility and showed high activity and suppressed car-
2
3
41
duction and they can be applied to fuel cell devices.
bon deposition on OSRE. Wang et al. reported a study on
catalysts of perovskite-type La1 Ca Fe Co O oxides. The
−x
x
1−x
x 3
C H OH(g) + 3H O(g)
authors proposed that the reduced metallic cobalt nano-
particles are active during the OSRE process. Nano-Co parti-
cles could be oxidized back to cobalt ions in the OSRE pro-
2
5
2
0
−1
→
2CO
2
(g) + 6H
2
(g)ΔH298K = 173.3 kJ mol
(1)
4
2
cess that promoted their anti-sintering ability.
3
0
1
C H OH

g

+
O

g

 3H2

g

2CO2

g

H
 552 kJ mol
2
5
298K
Pyrochlore-related oxides have been investigated for their
catalytic activity, electro-optic and magnetic properties, the-
ory calculation, structural spectroscopy, and fuel cell
2
(
2)
4
3–47
C
2
H
→
5
OH(l) + (3 − 2x)H
2CO
2
O(l) + xO
2
(g)ΔH298K
2
(g)
applications.
The general formula of pyrochlore can be
0
2
(g) + (6 − 2x)H
formulated as A B O with a cubic structure type (with a
2
2 7
−
1
=
(173.3 − 483.6x) kJ mol
(3)
space group of Fd ¯3 m, No. 227). Some researchers investigated
the pyrochlore phases as catalysts in various reactions.
Bespalko et al. reported Rh decorated trimetallic oxides RhM/
2 2 7
La Zr O with M = Co, Ni in their structure in SRE. The re-
(g)ΔH298K = −48.4 kJ mol−1 (4)
0
CO(g) + H
2
O(g) → H
2
(g) + 2CO
2
Conventional catalysts for OSRE are made up of well-
dispersed active metal nanoparticles supported with metal ox-
duced deactivation rate of the catalysts was attributed to the
higher reducibility and gasification of carbon deposits for
SRE by the oxycarbonate species formed. Spivey et al. stud-
24–26
48
ides, such as Al O , SiO , TiO , ZrO , MgO, and La O .
2
3
2
2
2
2 3
The active metals can be first row transition metals (Fe, Co,
ied partially substituted 1–2 wt% Ru, Rh, and Pt at the B-site
2
7–29
and Ni) or noble metals (Rh, Ru, Pt, and Ir).
The major
in La Zr O and found an enhanced catalytic ability and anti-
2
2 7
4
9,50
concern is the activity degradation of catalysts during long-
term processing that is mostly due to the aggregation of active
metal, carbon deposition, or poisoning by organosulfur com-
carbon deposition for dry methane reforming reaction.
The pyrochlore phases have also been utilized as a support in
the catalyst. Tada et al. found that the active metal, Ni,
supported on the pyrochlore structured Ce Zr O as a catalyst
30,31
pounds.
Another way to promote the activity of an OSRE
2
2 7
catalyst is to include a promoter with active metal as a sup-
port. Ceria and related fluorite-type compounds are promoters
which exhibit a unique oxygen storage capacity and redox and
oxygen mobility properties, which improve the reactivity of cat-
provided stable activity due to the oxygen storage/release ca-
5
1
pacity of Ce Zr O . Ma et al. used La Zr O and La Sn O as
2
2
7
2
2
7
2
2 7
supports for methane steam reforming and they exhibited su-
perior coke resistance. The results indicated the formation of
32–35
52
alysts and reduce carbon deposition.
Deluga et al. investi-
La O CO species on catalyst suppressed carbon deposition.
2
2
3
gated 5 wt% Rh/CeO /Al O and Pt/CeO2 as catalysts in a
x 7−δ
Our previous study on Ni-substituted La Ce Ni O in
2
2
3
2
2−x
double-bed reactor which integrated POE and WGS reactions.
pyrochlore indicated that the reduced nickel atom may dif-
fuse to the surface to form nickel clusters in a reduction envi-
ronment. If the catalyst contains nickel oxide particles, the
reduced nickel metal was severely sintered, and the catalyst
The ethanol–water mixtures can be converted into hydrogen
3
6
with a selectivity of ∼117% at C/O ∼0.7. Pirez et al. reported
the use of the catalyst nano-oxyhydride CeNiH in OSRE
studies. They reported that the catalyst split the C–C bond ef-
fectively and produced H from the hydride species at a low
z y
O
5
3
decayed quickly in the OSRE process. Another work on Ru-
substituted pyrochlore oxides La Ce Ru O (x = 0–0.35)
2
2
2−x
x 7
3
7
n+
3+/4+
temperature. Our previous work on the effect of ceria and
metal-doped ceria nanoparticles with controlled morphologies
showed that the 5 wt% (Rh or Ru)/ceria NP catalysts exhibited
enhanced performance, but the performance gradually
decayed during the time-on-stream test due to the loss of dis-
tinct shapes and particle aggregations. These results show the
positive effect of metal oxides for OSRE to produce hydrogen,
acting either as active components or as supporting materials
exhibited a synergetic effect between the Ru and Ce
ions that allowed the structure to remain stable during the
OSRE process. The OSRE performance test on
La Ce1.8Ru0.2O /Al O catalyst showed a degraded hydrogen
a
2
7
2 3
selectivity of 5–10% after a 48 h time-on-stream test. That
was due to the interaction between La Ce1.8Ru0.2O and the
2
7
Al O supporting material. The results suggest that new
2
3
supporting materials should be developed to suppress the
interaction between the pyrochlore catalyst and the
38,39
for active catalysts.
Multinary oxides with structures simi-
5
4
lar to spinel and perovskite have been used as OSRE and ATR
catalysts in previous studies. Huang et al. utilized iron-
substituted spinel-type oxides NiAl O –FeAl O as catalysts for
supporting material.
To date, studies on the dual substituted pyrochlore phases
on A and B sites for OSRE catalysts are relatively rare. Dual
2
4
2 4
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substituted metal oxides have been studied in oxide systems
in perovskite, double perovskites, garnet, and Ruddlesden–
Popper oxides to enhance the electrochemical properties of
mixed-metal oxide was sintered at 800 °C for 5 h to form
LZO powder. The as-prepared LZO powders were mixed with
10 wt% PVB as a binder, and wet grinding was utilized to
make them well-blended. The well-mixed powders were
pressed into disc-shaped pellets (31 mm in diameter) and
then heated to 1400 °C for 1 h. The pellets were pounded
into pieces of different sizes. The sieved pieces in a 16–18
mesh were used as the supporting material in this study.
Catalysts were prepared using the conventional impregna-
5
5–57
SOFC electrode materials.
the dual substituted pyrochlore oxide Li La Ce Ru0.2O
7−δ
In this study, we investigated
x
2−x 1.8
5
8
(LLCRO) material with A = Li/La and B = Ru/Ce. The site
composition of Ru/Ce in the B site was fixed at 0.2/1.8, which
corresponds to the optimized catalyst La Ce1.8Ru0.2O [LCRO]
2
7
+
in a previous study. It is anticipated that the substituted Li
ions in the A-site of the pyrochlore structure would modify
the crystal structure, the oxidation states of Ru in the B site
tion process. In a general procedure, the as-prepared
n+
pyrochlore oxides (0.1 g) were dispersed well in about 3 mL
ethanol in appropriate proportions with an ultrasonic treat-
ment (MICROSONTM XL 2000). Supporting materials of alu-
and the oxygen vacancy to maintain the charge balance in
the lattice. We combined different characterization tech-
niques to understand the correlation between the structure
and activity of the catalyst in OSRE. The lanthanum zirconate
pyrochlore LZO was prepared and utilized as the supporting
material to compare with a catalyst supported by Al O . The
2
−1
mina (corundum; 18 mesh; 1 g; S
> 200 m g ) or lab-
BET
2
−1
made LZO (SBET = 15.9 m g ) were then immersed in the
solution, which was dried at 80 °C. The entire procedure
was repeated at least five times to yield well-dispersed metal
2
3
as-prepared powder catalysts were characterized by induc-
tively coupled plasma-mass spectrometry (ICP-MS), powder
X-ray diffraction (PXRD), temperature programmed reduction
2 3
oxides on the Al O and LZO support. The as-prepared cata-
lysts were used to perform the OSRE reaction at atmospheric
pressure.
(TPR), X-ray photoelectron spectroscopy (XPS), and X-ray ab-
sorption spectroscopy (XAS). The carbon deposition was mea-
sured by Raman spectroscopy and thermogravimetric analysis
2.2 Characterization
(
TGA) after the OSRE reaction.
The purity and crystallinity of the as-prepared samples were
characterized by powder X-ray diffraction (XRD) on a Bruker
D8 Advance diffractometer with Cu Kα radiation (λ = 1.5418
Å). Powder X-ray spectra were collected in the two theta
range of 10–80°, while the voltage and electric current were
held at 40 kV and 40 mA, respectively. To understand the
oxidation states of each element, XPS measurements were
recorded on a PHI Quantera SXM instrument and an X-ray
source using an aluminum anode (Al Kα, hv = 1486.6 eV).
The pressure in the chamber was kept at less than 6.7 ×
2
. Experimental
2
.1 Synthesis
All reagents were of analytical grade and were used without
further purification: LaIJNO ·6H (99.9%, Alfa Aesar),
CeIJNO ) ·6H O (99.99%, Sigma-Aldrich), RuCl ·xH O
99.98%, Sigma-Aldrich), LiCl (99%, Alfa Aesar), and
ZrOIJNO (99.8%, Alfa Aesar). Metal-substituted pyrochlore
3
)
3
2
O
3
3
2
3
2
(
3 2
)
−
7
oxides were synthesized with the sol–gel method. In a typical
experiment, polyIJethandiol)-block-polyIJpropandiol)-block-poly-
IJethandiol) copolymer, HOIJCH
CH O) H (designated EO PO EO ; Pluronic 123; Aldrich,
0
Metal ion sources, such as metal nitrate and metal chloride
were added in stoichiometric amounts and fixed to 5 mmol in
total. After stirring for at least 1 h, the resulting sol solution
was gelled at 40 °C in air for 3 d, during which the surfactant
P123 polymerized and a metal oxide was formed in a network.
The resulting surfactant was then removed upon burning the
gel at 250 °C. The as-prepared product was further calcined at
10 Pa. The spectra of C1s, Ru3d, O1s, Ce3d, and La3d core
levels were measured. The samples were calibrated by using
the binding energy of the C1s peak at 284.8 eV, and the
2 2 2 3 2
CH O)20IJCH CHIJCH )O)70IJCH -
5
9
spectra were fitted with the XPSPEAK 4.1 software package.
The spectra were decomposed using the ratio of 20% Gauss-
ian/Lorentzian and Shirley-type background was
2
20
20
70
20
.5 g), was dissolved in ethanol and served as a surfactant.
a
subtracted. The contents of the oxidation state were esti-
mated from the peak area. TPR analysis was performed at a
−
1
heating rate of 10 °C min in a quartz microreactor (China
Chromatography 660 instrument, thermal-conductivity detec-
tor, TCD). Approximately 0.08 g of sample were loaded into
a silica tube and each sample was sealed with silica wool.
900 °C for 5 h so that the products of metal-substituted
The H O formed was trapped using a molecular sieve during
2
pyrochlore powder samples of Li La Ce1.8Ru0.2 (x = 0.0–
O
7−δ
the time that the temperature was ramped to 900 °C in a re-
x
2−x
0.7) could be obtained.
2 2
ducing atmosphere (10% H in flowing Ar). The H con-
The lab-made supporting material LZO was synthesized
by the Pechini method. Metal nitrates, as precursors, were
diluted in DI water. Citrate acid (CA) and ethylene glycol
sumption was estimated by using the weighted CuO reduc-
tion process as the calibration standard. N2 adsorption–
desorption measurements were performed at 77 K using a
Micrometrics sorptometer Tri Star 3000. Prior to the sorp-
tion measurement, the samples were degassed at 200 °C
overnight. The specific surface areas of the as-prepared ma-
terials were measured and estimated using the Barrett–
Emmett–Teller method. Thermogravimetric measurements
(
EG) at a molar ratio of metal : CA : EG = 1 : 3 : 4 were added
into the solution. The resulting sol solution was stirred at
00 °C to become a gel when ethylene glycol started poly-es-
terification. The gel was re-calcined at 350 °C to remove or-
1
−
1
ganic compounds at a ramp rate of 1.7 °C min , and the
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were performed with a thermal analyzer (NETZSCH STA
2.3 Measurement of catalytic performance
4
09PC). The experiments were carried out with about 50–100
An experimental set-up to study the OSRE was carried out in
a fixed-bed quartz reactor with an inner diameter of 4 mm
and a length of 12 cm. Catalysts within 1.5 cm in length were
loaded, and the gas hourly space velocities (GHSV) were
maintained at 1.6 × 10 h . A high-performance liquid chro-
matography (HPLC) pump was equipped to feed fuels
−
1
mg catalysts with a ramping rate of 10 °C min from 50 to
−
1
8
00 °C in an oxygen flow of 60 ml min . The morphologies
of the products were examined with a scanning electron
microscope (JEOL JSM-7401F FE-SEM). The images were ac-
quired with an accelerating voltage of 10 kV with several
magnifications. Semi-quantitative microprobe analysis was
performed with an energy-dispersive spectral detector (Ox-
ford INCA Energy 350) on the SEM. Raman spectroscopy was
conducted using a Thorlabs HRR170 instrument with 633
nm radiation from He–Ne. Sample powders were dispersed
on the holder and a counting time of 60 s per step with a la-
ser power of 5 mW was used. The spectra were recorded at
room temperature under the same conditions.
5
−1
containing a water/ethanol mixture of a known composition
−1
(
molar ratio of H O : C H OH = 3 : 1, 0.263–0.702 mL min )
2
2
5
−1
in the reactor. The air flow rate was fixed at 0.5 L min . Un-
der these conditions, the ethanol and air mixture was mea-
sured in terms of the carbon-to-oxygen ratio (C/O). A three-
zone heating furnace was used to maintain the temperature
of the water/ethanol mixture and the preheating temperature
of the catalysts. The fuels and air stream were pumped into
the steel chamber and mixed well at 220 °C in the first
heating zone. The second heating zone was maintained at
A synchrotron light source at the National Synchrotron
Radiation Research Center (NSRRC, Hsinchu, Taiwan) was
utilized for the XRD and XAS experiments. The electron stor-
age ring was operated at 1.5 GeV with a stored current of
240 °C to prevent condensation of the evaporating gas mix-
tures. The third heating zone containing the catalyst bed was
evaluated to the starting temperature. Furthermore, the redox
properties of the catalyst were activated, which triggered an
exothermic reaction under the catalytic reforming of oxygen.
The output energy of the third heating zone was initially
turned off and then the reaction temperatures were moni-
tored for the time-on-stream test during the stream test using
type-K thermocouples placed on the reaction tube.
The outlet gases passed through a cold water trap to con-
dense the excess water, unreacted ethanol, and other possible
high molecular weight species during the reaction. The re-
sults were analyzed using a gas chromatograph (Agilent GC
3
60 mA. For SXRD (Beam Line 01C2), all patterns were mea-
sured on an image plate detector (Mar345) at room tempera-
ture. The powder samples were packed in capillaries with a
diameter of 0.5 mm. Data were collected in the X-ray wave-
length of 0.6888 Å, and LaB
correct the environmental instrument. Powder rings were
integrated using GSAS-II software. The unit cell was re-
fined with the CelRef program. The structure was refined
using the Rietveld method with the program GSAS. The
XAS was recorded on BL 01C1 and 17C1. The double crys-
tals, Si (111) crystals, were used as a monochromator for en-
ergy selection. Powder samples were uniformly spread onto
6
was used as the standard to
6
0
6
1
6
2
7890A). Two six-port valves were used to inject the sample of
3
M and Kapton tapes to get the desired thickness. The spec-
the produced effluents into the injection port of the GC
equipped with a molecular sieve column (30 m·0.32 mm ID,
MOL SIV 5A, carrier gas = Ar) on an FID and a micro-packed
tra of target element foil was concomitantly recorded for
internal energy calibration using the first inflection point.
The Ru K-edge spectra were scanned over the energy 21.867–
column on a TCD. All products were quantified, and the N
2
2
2.86 keV in fluorescence mode using a Lytle detector, with
gas served as an internal standard. The fractions of the feed
carbon were detected in the effluent gas, and the carbon bal-
ance was noted for all products. The analysis showed that a
negligible amount of carbon had been deposited on the cata-
lyst. The ethanol conversion, hydrogen production and the
carbon production are defined below:
a step size in the near-edge region of 0.4 eV. Data were col-
lected from 22.077 keV below the Ru K-edge to 22.187 keV
above the edge. The XANES data were processed by standard
procedures, including background subtraction and normali-
zation with respect to the edge jump. The spectra were
corrected for background and normalized according to χ(k) =
Ethanolconversion
 
%
[
μ(k) − μ0IJk)]/Δμ0 using the AUTOBK algorithm in Athena,
where μ(k) was the measured absorption coefficient, μ0IJk)
was the background, and Δμ0 was the edge jump.
wavenumber was defined as k = [2m(E − E )/ℏ] , where E is
0
the photo energy, E is the threshold energy, ℏ is the Planck


molesC

CO  CO  CH  C H  CH COH

in reformate

2
4
2
4
3

63,64

100
The

molesC

C H OH
in feed


2
5

1
/2
0
constant, and m is the electron mass. The extended X-ray ab-
sorption fine structure (EXAFS) data analysis was done by
plane wave single scattering approximation, where FjIJk) was
Moleof ProductSpecies
Selectivity


% 
nMoleof Fuel XEtOH
n 1for C -species; 2forC -species; n  3forhydrogen
2
1
j
the backscattering amplitude from each of the N atoms in
the shell at a distance R (relative to the absorbing atom),
j
2
2
expIJ−2k σ
j
) was the Debye–Waller factor with a mean-
2
j 0
squared displacement σ , S was the amplitude reduction

moles of H in reformate

2
factor, δ IJk) was the total phase shift, and λ(k) was the photo-
electron mean free path.
Hydrogen yield

%


100
j
6
5

maximum theoretical moles of H
2

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3
. Results
ments of the solution phases with mixed occupied Li/La, and
Ce was replaced by Ru on the A and B sites. The P-type struc-
ture belonged to a space group of Fd ¯3 m (NO. 227). A profile
that fit the synchrotron powder data was obtained for all
samples, and the refined data are presented in Fig. S1 and
Table S1.† The refined cell parameters for the LLCRO sam-
3
.1 Physiochemical properties of Li
x
La2−xCe1.8Ru0.2O7−δ solid
solution
x
The as-synthesized solid solution phases of Li La2−xCe1.8Ru0.2-
O7 (LLCRO) were examined by PXRD, and the results are
−δ
shown in Fig. 1(a). LLCRO shows the single phase of the
pyrochlore-type structure for x = 0.0–0.6 and impurity phases
for La O (ICSD 96196) start to appear when x = 0.7. The re-
flections of LLCRO patterns are shifted to a high angle com-
pared to the diffraction peaks of La Ce (ICSD 187612), in-
dicative of a reduced unit cell dimension. The diffraction
data were fitted by the Rietveld method to observe detailed
structural information. The pyrochlore structure, La
ples were gradually reduced from 11.1339(1) to 11.0680(4) Å
3+
(
(
Fig. 1(b)), which essentially obeys Vegard's law with the La
+
2
3
1.16 Å) substitution for the smaller Li (0.59 Å) cations. The
results indicate that the solid solution limit of LLCRO is
close to x = 0.6. The as-prepared compositions of La and Ru
are consistent with the chemical analyses of ICP-MS, and the
results are summarized in Table 1 together with the results
of specific surface areas and crystal sizes of the materials.
The morphology was investigated with SEM (Fig. S3†) and
showed irregular shapes and particle sizes in the range of
2
2 7
O
2 2 7
Ce O
(ICSD 187612), was used as a starting model for the refine-
2
−1
2
0–28 nm, reflecting small SBET values (2 to 7 m g ) for
samples sintered under high temperature.
The refined thermal parameters are within a reasonable
range. The site occupancy of site A was fixed according to the
as-prepared Li/La composition for LLCRO (x = 0–0.7). The oc-
cupation and thermal factors of O (8b)/O (48f), Ru/Ce (16c),
and Li/La (16d) were constrained to avoid correlations in the
refinements. The structure of LLCRO contained two cation
and two anion sites. Site A, 16d (1/2, 1/2, 1/2), is an eight co-
ordination with a distorted cube shape that is occupied with
+
3+
a Li /La cation; site B, 16c (0, 0, 0), is a distorted octahedral
3
,4+
4–6+
coordination for a Ce /Ru
metal cation. There are two
2
−
anion sites, 48f (x, 1/8, 1/8) and 8b (3/8, 3/8, 3/8) sites, for O
ions, and one vacant site 8a (1/8, 1/8, 1/8). The Li/La atoms
are coordinated to eight oxygen atoms with two axial oxygen
atoms at site 8b and six oxygen atoms in site 48f. The Ce/Ru
cations are coordinated to six oxygen atoms with the 48f oxy-
gen atoms. The O (48f) atoms are located at (x, 1/8, 1/8) in the
structure and are correlated with two Li/La and two Ru/Ce
atoms. The 8b oxygen atoms are correlated with four Li/La.
As the cubic unit cell gradually contracted, the variable pa-
rameter x in the O (48f) ion increased from 0.374(2) to
0.391(1) over the series of LLCRO (x = 0.0–0.7) as seen in Fig.
S2.† The shift in the O (48f) position affected the inter-
atomic distances and bond angles, and these data are
shown in Table S1.† The results show that as the lithium
content increased, dIJB-O48f) increased from 2.40 to 2.51 Å,
and dIJA-O48f) decreased from 2.41 to 2.30 Å, whereas dIJA-
O8b) was essentially not changed, as shown in Fig. 1(c). The
bond angles for A-O48f-A increased from 109 to 117°, and
B-O48f-B decreased from 109.8 to 102.7°, respectively. The
results indicated that the coordination environments of A
and B were distorted during the lithium substitution on site
A. The reduced dIJLi/La–O8b) reflected the effect of Li-substi-
tution, and the increased Ce/Ru–O48f distance may be af-
fected by the oxidation state of Ce/Ru ions and oxygen va-
cancies. During the Li-substitution process, the average
oxidation state of site A decreased, which affected the
charge of site B and the oxygen composition needed to
maintain the charge balance. The oxidation states of cerium
Fig. 1 Phase identification of LLCRO (x = 0–0.7): (a) powder X-ray dif-
fraction; (b) phase identification of LLCRO (x = 0–0.7) cell refinement
and (c) variation of the A-O8b, A-O48f and B-O48f bond distances
with the Li content in LLCRO (x = 0.0–0.7).
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Table 1 Unit cell parameter, crystal size, La molar content, Ru molar content, and BET surface area of the solid solution LLCRO (x = 0–0.7)
x
0
0.1
0.2
0.3
Cell parameter/Å
11.1339(1)
22.5
2.02
0.22
5.11
11.1292(1)
20.8
1.88
0.19
4.16
11.1275(1)
22.5
1.83
0.21
6.30
11.1145(2)
20.5
1.70
0.21
6.53
a
Crystal size/nm
b
La content
b
Ru content
2
−1
Surface area/m g
x
0.4
0.5
0.6
0.7
Cell parameter/Åa
Particle size/nm
11.1003(2)
28.2
1.62
0.21
3.79
11.0937(3)
18.7
1.52
0.22
6.77
11.0819(3)
20.5
1.43
0.19
2.90
11.0680(4)
25.7
1.30
0.19
6.90
b
La content
Ru content
b
2
−1
Surface area/m g
a
b
The particle size was measured from the SEM image. Calculated from ICP-MS results (the Ce content was fixed at 1.8).
+
and ruthenium will be discussed in the section on XPS and
XAS analysis.
849 eV, which is indicative of the effect of Li substitution on
6
6
site A on the distorted coordination environment. The spec-
tra of Ce3d are shown in Fig. 2(b) in which eight peaks could
be assigned resulting in the mixed oxidation states of Ce
ions. Peak areas U′ and V′, centered at 884.0 and 903.0 eV, ap-
pear to be typical Ce ions and are absent for Ce ions
which had been used to integrate the peak area of Ce . The
3
.2 X-Ray photoelectron spectra (XPS)
3
+
4+
The XPS of LLCRO were fitted by Gaussian and Lorentzian
functions and are shown in Fig. 2. The La3d spectra of the
as-prepared samples are shown in Fig. 2(a). The characteristic
spectrum of La3d exhibited two asymmetric lines at 839
3
+
3
+
4+
contributions of the Ce and Ce ions to the ratio were eval-
uated by integrating the area in the Ce3d spectra of the mate-
3
+
4+
(La3d5/2) and 856 eV (La3d3/2) with their satellites at the
rials. The calculated values of Ce and Ce are listed in Ta-
smaller BE side as a shoulder; these were assigned to the BE
of the La ions. There are weak XPS lines centered at 836
and 853 eV with their satellites at lower energies of 833 and
ble S2.† For the series of LLCRO, the calculated values were
3
+
+
correlated with the amounts of Li in the materials. The re-
4
+
sults indicated that the relative amount of Ce increased as
Fig. 2 X-ray photoelectron spectra of LLCRO (x = 0–0.7): (a) La3d; (b) Ce3d; (c) Ru3d and (d) O1s.
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+
the content of doped Li increased until x = 0.7. The relative
4+
3+
compositions of Ce /Ce were analyzed using the proce-
dures described in Fig. 3. The one with the binding energy of
5
31.3 eV could be assigned to 48f (surrounded with 2 Li/La
and 2 Ru/Ce) in the series of LLCRO structures. It was
expected that Li substitution on site A would affect the aver-
age oxidation state on site B and possibly create oxygen va-
cancies. The spectra of Ru3d are shown in Fig. 2(c) with the
binding energies of Ru3d5/2 in the range of 281.5–283.5 eV
(
Table S3†). According to the literature, the Ru3d signal of
5/2
4
+
Ru was located in the range 280.7–281.0 eV, and the signals
Fig. 4 The normalized Ru K-edge XANES spectra of references and
LLCRO (x = 0.6).
of the highly oxidized RuO
3
and RuO
4
were assigned at
6
7,68
2
82.5–282.6 eV and 283.3 eV, respectively.
The results in-
dicate that the Ru ion in site B contains oxidation states
higher than +4. The XPS of O1s for LLCRO samples are
presented in Fig. 2(d), exhibiting a broad asymmetry peak.
The O1s spectra could be deconvoluted into two peaks for ox-
ygen ions in different coordination environments. The
binding energy of the oxygen ion in site O48f is higher than
that of O8b, which may be due to the higher average electro-
negativity of 2A(Li/La) + 2B(Ru/Ce) compared to that of 4A(Li/
La). The interatomic distance dIJA-O8b) was greater than that
of d(B-O48f). Thus, the peak with the lower binding energy of
5
+
and Ru ions, and the results are consistent with XPS analy-
ses. From the EXAFS data analyses, the χ(k) in the EXAFS re-
gion was 2.8 ≤ k ≤ 10.35 Å and was further weighted by k
6
9
−1
3
3
and Fourier-transformed into the R-space as FT [k χ(k)], as
shown in Fig. S4(b).† For the series of LLCRO (x = 0.0–0.7),
the first shell was the contribution of the bonding of Ru–O
atoms and the coordination number which was set at 6.0, as
shown in Table 2. The refined bond distance of Ru–O fluctu-
ated and the average distance was 1.959(6), which is within a
5
28.7 eV in the O1s spectrum could be assigned to oxygen
7
0
ions at 8b (surrounded with 4 Li/La). The charge distribution
of sites A and B in the LLCRO solid solutions leads to charge-
compensating and oxygen vacancies, which may play an im-
portant role in the catalytic activity of LLCRO during the
OSRE process.
reasonable range, as shown in Fig. S4(c).†
3
.4 Analyses of TPR profiles and H reduction ability
2
The reduction behaviour of LLCRO (x = 0–0.7) as prepared
was examined with a TPR system and the TPR profiles are
shown in Fig. 5(a). The reduction of Ru ions contributed to
the temperature region at 130 °C and 190 °C. The profile also
showed a broad peak corresponding to the reduction features
of Ce ions that were observed on the surface of the bulk
structure when the temperature went above 300 °C. For Li -
substituted samples, two reduction peaks were observed for
the reduction of ruthenium ions. In addition, the reduction
temperature of Ru ions gradually shifted to a lower tempera-
3
.3 X-Ray absorption spectroscopy (XAS)
Ru K-edge XANE spectra were collected for LLCRO (x = 0.6)
and reference samples, and they are shown in Fig. 4. The Ru
K-edge XANES spectra of all the samples are shown in Fig.
S4(a).†
4
+
+
Looking into the main absorption edge near 22.13 keV, it
was found that all samples had an absorption energy higher
n+
ture, which correlated with the shift of BE values for Ru
4
+
than that of the reference sample Ru ions from the rising
ions with oxidation states n ≧ 4 (Table S3†). As the propor-
tion of Li increased to x = 0.6 and 0.7, only one broad reduc-
tion line centered below 130 °C was observed. The catalyst of
+
edge profile. As a Li ion was incorporated into the structure,
the absorption edge of Ru was gradually shifted to a higher
4
+
energy corresponding to the oxidation states of mixed Ru
−
1
hydrogen consumed was 1.5(1) mmol g for LLCRO (x = 0–
.7). The average hydrogen consumption was 0.9(1) mmol
0
−
1
mmol Ru, which indicates that each H
2
molecule (two
electrons) consumed will reduce the oxidation state of one
n+
(n−2)+
Ru ion to Ru
, as shown in Fig. 5(b). The powder sam-
ples after TPR experiments were checked with PXRD and they
showed no sign of an impurity phase (Fig. S5†). The results
indicate that the Li-substituted LLCRO (x = 0–0.7) affected
the oxidation states of Ru and Ce ions and the pyrochlore
structure did not collapse during the reduction process.
3.5 Catalytic performance
3.5.1 Effect of carbon-to-oxygen ratio. The carbon-to-
Fig. 3 Ce3d X-ray photoelectron spectroscopy of LLCRO (x = 0–0.7).
oxygen ratio (C/O) was changed from 0.4 to 0.8 to evaluate
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Table 2 EXAFS fitting results and bond length (Å) in the LLCRO (x = 0–0.7)
x
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Ru–O (Å) a
N/number
1.969(7)
6
0.0067(3)
0.1
1.957(4)
6
0.0065(1)
0.03
1.972(4)
6
0.0063(4)
0.2
1.947(3)
6
0.0061(1)
0.02
1.964(8)
6
0.0062(3)
0.1
1.955(5)
6
0.0062(2)
0.05
1.957(5)
6
0.0067(2)
0.04
1.958(5)
6
0.0061(2)
0.04
2
−2 b
σ
(Å
)
c
R-Factor (%)
E
0
(eV)
−1.0
−2.9
−0.8
−2.9
−1.7
−3.2
−2.4
−2.3
a
b
2
c
N/number: coordination number. σ : Debye–Waller factor. R-Factor: the goodness of the fit.
the effect of the oxygen composition on the contribution of
the total oxidation and partial oxidation during the OSRE
process. The performances are shown in Fig. 6 (x = 0.6) and
of CO and H O and the release of heat. The CO composition
2 2
was generally determined through the combustion reactions
and WGS reaction, which allowed the conversion of CO into
Fig. S6† (x = 0–0.7), including the ethanol conversion (XEtOH
)
CO . The maximum selectivity to hydrogen was found at C/O
2
and the selectivity to hydrogen (SH2), C1 species (SCO, SCO2
and SCH4), and C2 species (SC2H4). Other than the products of
,
= 0.6. The combustion reaction helped to reduce carbon for-
mation on the surface under a low C/O ratio. When the C/O
ratio exceeded 0.6, partial oxidation became predominant at
gaseous H , CO, CO , CH , CH CHO, and C H , no other CH
x
2
2
4
3
2
4
species was detected. The composition of the products was
affected by the inlet concentration of oxygen that induced the
exothermic reaction, and the measured temperature on the
catalyst was in the range of 530–650 °C during the OSRE reac-
tion. For all catalysts, SH2 and SCO increased with the increase
in the C/O ratio, whereas SCO2 showed the opposite trend.
These results indicate that total oxidation was favored at a
2 2
a high C/O ratio (low O partial pressure) producing H and
CO, and the selectivity to CO decreased as the C/O ratio in-
2
creased. When the C/O ratio was greater than 0.6, the conver-
sion of ethanol was less than 100%, and the composition of
the coke precursor (C H ) increased.
2
4
2 3
3.5.2 Time on stream test on the LLCRO (x = 0.6)/Al O
catalyst. The catalyst with the highest content of lithium,
LLCRO (x = 0.6), was used for the time-on-stream test at C/O
low C/O ratio (high O partial pressure) with the production
2
=
2 3
0.6 under OSRE and ATR processes using Al O as the
supporting material. The ratios of water/ethanol and C/O
were fixed at 3 : 1 and 0.6, respectively. Air was used as the
5
−1
carrier gas at GHSV = 1.6 × 10 h . For the OSRE reaction,
the oven temperature was fixed at 350 °C. The results are
shown in Fig. 7(a). The activities of the catalysts remained
stable for ∼120 h with a nearly full conversion of ethanol
(
XEtOH = 98(2)%) and stable selectivities to all products. The
average selectivity to H , CO and CO was 102(1)%, 41(1)%,
2
2
and 57(1)%, respectively. The undesired products CH
4
and
2 4
C H
were kept in low selectivities of 2.7(5)% and 0.05(1)%
during the OSRE process. The used catalyst was studied by
powder X-ray diffraction after the long-term stability test (Fig.
S7(a)†). The diffraction peaks can be indexed to defect
pyrochlore phases with a reduced peak width, indicative of
increased crystallite sizes. The supporting material was
2 3
decomposed to γ-Al O and α-, δ-, and κ-phase alumina. In
Fig. 5 (a) Temperature programmed reduction profile and (b) H
consumption of LLCRO (x = 0–0.7).
2
2
Fig. 6 Performance in OSRE with LLCRO (x = 0.6, H O/ethanol = 3,
5
−1
GHSV = 1.6 × 10
h , T = 260 °C).
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and CO of 93(2)%, 69(4)%, 63(3)%, and 31(3)%, respectively.
2
The selectivities to CH , C H , and CH CHO were less than
4
2
4
3
5%, indicative of an efficient ethanol conversion and a low
carbon deposition rate. After 65 h of the time-on-stream test,
the ethanol conversion, selectivity to products, and tempera-
ture on the catalyst fluctuated (Fig. 7(b) and S9†). The stan-
dard deviation of the products' selectivity and temperatures
after 65 h during an ATRE reaction increased. The average se-
lectivity to C
2(2)% and 34(2)% from 65–100 h, respectively.
The used LLCRO (x = 0.6) supported by Al O was studied
2 5 2 2
H OH, H , CO, and CO was 88(2)%, 68(1)%,
6
2
3
by powder X-ray diffraction after the long-term stability test
Fig. S10(a)†). The diffraction peaks can be indexed to defect
pyrochlore phases, the supporting materials γ-Al O and α-, δ-
(
2
3
3
and κ-phase alumina. In addition, a new phase of LaAlO was
formed. The results indicate that the as-prepared LLCRO col-
lapsed during the time-on-stream test due to the interaction
between the catalyst and the support. The particles were
gradually sintered and carbon deposition may have built up,
leading to reduced OSRE activity.
3.5.3 Time-on-stream test on the LLCRO (x = 0.6)/La
2 2 7
Zr O
catalyst. The study on the LLCRO/Al O catalyst for OSRE and
2
3
ATR clearly indicates that the performance degradation dur-
ing the time-on-stream test was due to the interaction be-
tween LLCRO and the supporting material, Al O . Therefore,
2
3
Fig. 7 Stability test on catalysts (a) OSRE, LLCRO (x = 0.6)/Al
2
O
3
, T =
a new supporting material that is stable and won't interact
with the LLCRO is desired for a stable OSRE/ATR process. To
understand the effect of supporting materials for the OSRE
3
2 3 2
50 °C and (b) ATR, LLCRO (x = 0.6)/Al O . H O/ethanol = 3 and GHSV
5
−1
=
1.6 × 10
h
conditions.
2 2 7
reaction, a new supporting material La Zr O (LZO), with the
same pyrochlore type structure as LLCRO, was synthesized
and used as a supporting material. LZO was very stable under
redox conditions and stable when mixed with the LLCRO cat-
alyst and calcined at elevated temperatures. However, the
drawback for the as-prepared support is a low specific surface
addition, a new phase of LaAlO (ICSD-180175) was indexed.
3
The results clearly indicate that the LLCRO catalyst was
decomposed during the time on stream test due to the inter-
action between LLCRO and the Al O support. During the
2
3
3
+
2
−1
OSRE process, the La ions may diffuse to the supporting
material, which advances the solid state reaction and affects
the catalytic activity and stability during an OSRE reaction.
Although the performance remained stable over the 100 h
stability test, the structure of LLCRO (x = 0.6) gradually col-
lapsed during the OSRE process. A controlled experiment
area (6.12 m g ). The catalyst LLCRO (x = 0.6)/LZO was pre-
pared using the same procedures as the LLCRO (x = 0.6)/
Al O catalyst and used for OSRE and ATR experiments. The
2
3
reaction conditions were the same as the study for the
LLCRO (x = 0.6)/Al catalyst. As shown in Fig. 8(a), the cata-
2 3
O
lytic activity remained stable for nearly 120 h in OSRE. The
results showed a performance with a nearly complete
C H OH conversion of 98(3)%. The H selectivity gradually
2 5 2
decreased from 98.8(7) to 88(1)%, and the selectivity to CO
increased from 36(2) to 54(1)%. The selectivity to the undesir-
using a catalyst made up of (RuO
Al was tested for the OSRE reaction. The stoichiometries
of Ru, Ce, and Li were kept at the same weight percentage as
LLCRO (x = 0.6)/Al (Fig. S8†). The overall performance
2 2 2 3
+ CeO + Li O + LaAlO )/
O
2 3
2 3
O
shows XEtOH = 89(3)% and SH2 = 70.8(8)%, which was inferior
to the solid solution catalyst. The results indicate that the
catalytic activity contributed to better dispersion of active
metals in a solid solution than in a mixture of active oxides.
Time-on-stream tests under the ATR of ethanol with the
4 2 4
able products, CH and C H , was kept at a low value of
3.2(8) and 0.031(9)%, respectively. The powder X-ray diffrac-
tion study on the used catalyst showed no sign of decomposi-
tion, indicating that the stable LZO support suppressed the
decomposition of the LLCRO catalyst, as shown in Fig.
S7(b).† However, the particle size of the LLCRO crystallite
may be gradually increased due to the high reaction tempera-
2 3
LLCRO (x = 0.6)/Al O catalyst were performed, and the re-
sults are shown in Fig. 7(b). The reaction was initially acti-
vated at 260 °C and the oven was turned off after the ethanol
conversion process started. The results show that the ethanol
conversion was initially at a high value of 98(2)% and gradu-
ally reduced to 88(2)% during the 10 h experiment. The cata-
7
1
ture and affect the conversion of ethanol. The results are
shown in Fig. 8(b) for autothermal conditions. The ethanol
conversion remained constant between 98(2) and 94(3)% for
50 h before slowly declining to 86(1)% after 50 h of time-on-
lyst was stable for 65 h with averages for C
2 5
H OH, H
2
, CO,
stream. The hydrogen and CO/CO
2
selectivities were stable
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2 3
Fig. 9 TGA and DSC profiles of LLCRO (x = 0.6) on the Al O and LZO
catalyst after long-term reaction of ATRE.
shown in Fig. 9. On the other hand, the used LLCRO/LZO cat-
alyst showed no sign of weight loss nor DSC signal, which in-
dicates significantly suppressed carbon deposition for the
catalyst with the LZO support.
Raman spectroscopy of the used catalysts was carried out
to find the characteristic bands for coke, and the spectra of
the fresh/used catalysts are shown in Fig. 10. In general, the
carbon deposition for both catalysts was not significant dur-
ing the OSRE processes, as shown in Fig. S11.† In the case of
the LLCRO/Al O catalyst, two groups of bands were observed
2
3
−
1
−1
Fig. 8 Stability test on catalysts (a) OSRE, LLCRO (x = 0.6)/LZO, T =
at 1370 and 1400 cm and 1600–1900 cm which were char-
3
=
2
50 °C and (b) ATR, LLCRO (x = 0.6)/LZO. H O/ethanol = 3 and GHSV
acteristic of the disordered carbonaceous and ordered gra-
phitic species. The intensity from 1300 cm was significantly
5
−1
1.6 × 10
h
conditions.
−1
for 100 h on stream. The total selectivity for the CH , C H ,
4
2
4
3
and CH CHO products remained below 5% during the entire
process. The used LLCRO (x = 0.6)/LZO catalyst was checked
by PXRD and the results are shown in Fig. S10(b).† The dif-
fraction patterns from fresh and used catalysts were essen-
tially the same and showed no signs of decomposition, indic-
ative of a stable catalyst for the time-on-stream test. The
results obtained from the different supporting materials,
Al O and LZO, suggest that the compatibility of the catalyst
2 3
and support played an important role in the stability of the
OSRE catalyst, as seen in Table S4.†
LLCRO (x = 0.6)/LZO showed stable catalytic activity under
vigorous exothermic reactions, indicating thermal stability.
Although the as-prepared LZO support exhibited a low spe-
cific surface area, the active sites on the surface of LLCRO
were numerous and active in converting ethanol and produc-
ing a high yield of hydrogen.
3
.5.4 Characterization of used catalysts. The used catalysts
after the time-on-stream test were investigated by PXRD,
TGA, DSC, and Raman spectroscopy. The PXRD results were
mentioned in the previous section, and the results of TGA-
DSC and Raman spectroscopy will be discussed. For the used
2 3
LLCRO/Al O catalyst in the OSRE and ATR process, the TGA
shows a ∼5% weight loss and the DSC measurement shows a
strong exothermic peak starting at ∼490 °C, indicative of sig-
nificant carbon deposition during the time-on-stream test, as
Fig. 10 The Raman spectrum of (a) LLCRO (x = 0.6)/Al
LLCRO (x = 0.6)/LZO fresh and long-termed used catalysts.
2 3
O and (b)
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−
1
higher than the band at 1600–1900 cm , indicating that
temperature of OSRE may be due to the increased number of
n+
4+
amorphous carbon was the dominant form on the used
high oxidation state Ru and Ce ions that effectively inter-
+
LLCRO/Al O
2 3
catalyst. This could be attributed to the forma-
act with ethanol molecules. The amount of substituted Li in
tion of deposits of polymeric carbon via the precursor ethyl-
ene, which are formed by the ethanol dehydration reaction.
The coke formation may be due to the decomposition of
LLCRO in the Al O supported catalyst and aggregation of ac-
tive particles under the OSRE processes, shown in Fig. S12.†
The Raman spectrum obtained for the used LLCRO/LZO cata-
lyst shows no sign of signals from carbonaceous species. The
results obtained for the Raman spectra indicate that the
the pyrochlore structure induced structural defects, which
could result in metal/oxygen vacancies in the structure.
According to the results from XPS, XAS, and TPR experi-
+
ments, the Li substitution on site A of LLCRO affected the
2
3
4
+
3+
n+
4+
relative composition of the Ce /Ce and Ru /Ru ions, and
7
2
the more active ions stay in high oxidation states. The ac-
tive metal ions at a high oxidation state reduced the initial
temperature and affected the catalytic activity for the OSRE
reaction. A controlled experiment was performed using a cat-
2 3
amount of carbon on the LLCRO/Al O catalyst is significantly
+
greater than that on the LLCRO/LZO catalyst after the time-
on-stream test. The results clearly show that the catalyst
supported by LZO effectively suppresses carbon deposition
during the OSRE process. The high performance of the
LLCRO/LZO catalyst is probably because of the basic property
of LZO that suppresses the dehydration reaction of ethanol
and reduces the carbon deposition rate. The distribution of
metal ions after the OSRE reaction was measured using SEM
element-mapping analysis, as shown in Fig. S13.† From the
images from the SEM element-mapping analysis, it can be
seen that the metal ions were still well-dispersed on the cata-
lyst for used samples after a long-term stability reaction. The
results indicate that the solid solution catalyst suppressed
the aggregation of active metals.
alyst with the same metal molar percentage of Li ions in
LLCRO (x = 0.6), but it was pre-calcined with Al O to form
2
3
LiOH–Al O
2 3
and subsequently impregnated the catalyst
LCRO. The mixture of LCRO and LiOH on Al O showed infe-
2
3
rior activity compared to that of LLCRO (x = 0.6) with an in-
complete ethanol conversion (90(3)%) and a low SH2 value
(81(1)%), as shown in Fig. S15.† Therefore, the catalyst
LLCRO (x = 0.6) showed better catalytic activity than the cata-
+
lyst with Li ions outside the pyrochlore structure. The solid
solution structure that spreads the active metal ions evenly
on the surface plays an important role for the high OSRE ac-
tivity of LLCRO (x = 0.6).
The Rietveld refinements on the LLCRO phases showed
distorted coordination environments on the A(Li/La) and
B(Ce/Ru) sites. The Ru/Ce–O (48f) bonds increased when the
3
+
+
A-site La ions were substituted with Li ions. The charge
distribution of LLCRO could be compensated for by the for-
4
. Discussion
7
3,74
The effect of lithium substitution on the initial activation
temperature of OSRE was observed over LLCRO (x = 0–0.6).
During the experiment, the oven temperature was increased
gradually until the OSRE process started. The results are
shown in Fig. S14.† In general, the ethanol conversion and
mation of cation and oxygen vacancies.
The results from
XPS, XAS, and TPR show that the relative amounts of high ox-
5
+
4+
75,76
idation state ions, Ru
and Ce , were increased.
According to the H -TPR and XPS analyses, the initial reduc-
2
tion profile was reduced from 136 °C to 127 °C with an in-
+
H selectivity were within 90–100%, and the lowest activation
creased Li concentration because of the increased number
2
n≧4
temperature required to start OSRE decreased as the lithium
content increased. For the series of LLCRO (x = 0–0.6), the
OSRE reaction started at T = 300 °C (x = 0), and the mini-
mum temperature to initiate the reaction gradually decreased
of high oxidation state Ru
ions. The hydrogen consump-
tion rate suggests that the oxidation state of Ru was reduced
from n+ to (n − 2)+. These results also suggest that the Ru
ions in LLCRO are more active than in LCRO, which agrees
well with the reduced OSRE's starting temperature. During
the OSRE process, reductive adsorption, which leads to dehy-
to T = 260 °C (x = 0.6). The H selectivity gradually increased
2
+
as the amount of substituted Li ions increased. The results
are shown in Table 3. The optimized catalyst in OSRE was
2 5
drogenation of C H OH and the oxidation of CO molecules,
LLCRO (x = 0.6) with the highest hydrogen selectivity SH2
=
is enhanced because of the high oxidation state cations of
Ru /Ce , as shown in Fig. S14.†
Oxidative (OSR) and autothermal steam reforming (ATR)
of ethanol provide an ethanol conversion route that contains
an endothermic steam reforming (ESR) reaction and
n+
4+
1
03.92IJ7)%, and the conversion of ethanol was 99.4(1)%. The
+
results indicate that the Li ions substituted into LLCRO led
to decrease in the ethanol activation temperature.
According to XPS and TPR studies, the decreased activation
a
Table 3 Activated temperatures, carbon-to-oxygen ratios, ethanol conversion, hydrogen selectivity and yield of the solid solution LLCRO/Al
2 3
O
(x = 0–0.7)
x
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Activated temperature/°C
Carbon-to-oxygen ratio
EtOH conversion/%
300
0.6
91(1)
92(1)
2.50
290
0.6
92(1)
92.3(2)
2.57
290
0.6
91(3)
91.2(8)
2.53
280
0.6
87.0(7)
89(1)
2.32
280
0.6
93.5(8)
94(1)
2.65
270
0.6
96(3)
96(3)
2.78
260
0.6
99.4(1)
103.92(7)
3.10
260
0.6
93.03(4)
91.4(8)
2.55
H
2
selectivity/%
Yield of H /mol
2
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exothermic partial oxidation. Under controlled conditions,
OSRE/ATR does not need a large supply of energy and may be
operated at much lower temperatures than ESR. The appro-
priate oxygen input affected the product composition and
lifetime of the catalyst and reduced the yield of C H and
conditions with supporting materials, Al O and LZO. In gen-
2
3
eral, the processes retained a high ethanol conversion rate
and yield of hydrogen gas. The activity was gradually reduced
due to the sintering effect of the catalysts. There was signifi-
cant carbon deposition from the used LLCRO catalyst (x =
2
4
coke. LLCRO contains mixed-oxidation states of Ru and Ce
2 3
0.6) supported by Al O in the OSRE/ATR processes, whereas
ions that contribute to both C–C bond cleavage and redox re-
the LLCRO catalyst (x = 0.6) supported by LZO showed no
sign of carbon deposition. This study indicates that LZO is a
stable supporting material in this study. The LLCRO (x = 0.6)/
LZO catalyst shows high activity in the OSRE and ATR pro-
cesses and a low carbon deposition rate, making it a promis-
ing catalyst for hydrogen production.
7
7
+
actions. The substituted Li in LLCRO promotes the reduc-
3+
4+
tion and oxidation of Ce /Ce and a high valence state of
n+
Ru ions. These active sites were reduced and re-oxidized dy-
7
8
namically during the ethanol conversion process. Although
the surface area of the used LLCRO (x = 0.6)/LZO catalyst
2
−1
(
1.27 m g ) is less than that of LLCRO (x = 0.6)/Al O (58.71
2 3
2
−1
m g ), the evenly distributed Ru and Ce ions in LLCRO pro- Conflicts of interest
vide enough active sites for ethanol conversion. Therefore,
The authors declare no competing financial interests.
LZO is a better supporting material than Al O for the OSRE/
2
3
ATR process using LLCRO as the catalyst, which prohibits
interaction between the LLCRO and supports under exother-
mic conditions. Overall, the LLCRO/LZO catalyst has a posi-
tive effect on the regeneration of catalysts as they facilitated
the redox of active sites under OSRE/ATR processes.
Acknowledgements
We are grateful to Prof. Hiro-o Hamaguchi and Mr. Chun-Hao
Cho for their help in Raman experiments provided by the Ul-
timate Spectroscopy and Imaging Laboratory (USIL). We
thank Dr. H. S. Sheu, Dr. Yu-Chun Chuang, Dr. Jyh-Fu Lee
and Dr. Ting-Shan Chan of the National Synchrotron Radia-
tion Research Center for the XRD and XAS experiments, and
Prof. S. T. Chiu and Dr. Chia-Kan Hao for the BET measure-
ments. This work was financially supported by the Ministry of
Science and Technology (107-2113-M-009-006 and 107-3017-
F009-003) and the Ministry of Education, Taiwan (SPROUT
Project-Center for Emergent Functional Matter Science of Na-
tional Chiao Tung University).
Table S5† shows recent reports on OSRE/SRE catalysts
performed under various conditions. The total conversion of
ethanol can take place in different temperatures when the re-
action system is performed in a fixed content of ethanol, oxy-
gen and water. The noble elements Ru/Rh/Ir have been stud-
2
7,36,39,79,80
ied as an effective catalyst for OSRE/SRE processes.
It has been reported that the Rh/CeO /Al O catalyst is an effi-
2
2 3
cient catalyst for OSRE to produce a high yield of hydrogen.
The yield of H production by metal/metal oxide catalysts is
around 55–69%. Metal oxides like perovskite and spinel type
2
3
7,40–42,53,54,81
oxides were reported for the OSRE process.
The
Notes and references
reaction temperatures and yield of hydrogen are 280–650 °C
and 45–68%, respectively. In this study, Ru was used as the
active component because it shows comparable catalytic ac-
tivity with Rh in the OSRE process. The dual metal-
substituted pyrochlore contains mixed-oxidation states of ac-
tive metals that contributed to both C–C and C–H bond cleav-
age when these active sites were reduced and re-oxidized dur-
ing the OSRE process. The as-prepared catalysts supported
on LZO are very stable under the time-on-stream test. Com-
pared to other systems, it can be seen that the LLCRO (x =
1 R. Alkama and A. Cescatti, Science, 2016, 351, 600–604.
2 P. Agre, M. Molina and S. Chu, Nature, 2017, 550, S62.
3 C. M. Friend and B. Xu, Acc. Chem. Res., 2017, 50, 517–521.
4 ExxonMobil., Outlook for Energy: A View to 2040, 2018, pp. 1–
63.
5 H. Arakawa, M. Aresta, J. N. Armor, M. A. Barteau, E. J.
Beckman, A. T. Bell, J. E. Bercaw, C. Creutz, E. Dinjus, D. A.
Dixon, K. Domen, D. L. DuBois, J. Eckert, E. Fujita, D. H.
Gibson, W. A. Goddard, D. W. Goodman, J. Keller, G. J.
Kubas, H. H. Kung, J. E. Lyons, L. E. Manzer, T. J. Marks, K.
Morokuma, K. M. Nicholas, R. Periana, L. Que, J. Rostrup-
Nielson, W. M. H. Sachtler, L. D. Schmidt, A. Sen, G. A.
Somorjai, P. C. Stair, B. R. Stults and W. Tumas, Chem. Rev.,
0
.6) catalyst displays superior catalytic activity with a low re-
action temperature and a high yield of hydrogen.
5
. Conclusions
2
001, 101, 953–996.
LLCRO (x = 0–0.7) solid solutions were synthesized by a sol–
6 S. R. Foit, I. C. Vinke, L. G. J. de Haart and R.-A. Eichel,
Angew. Chem., Int. Ed., 2017, 56, 5402–5411.
7 D. Li, X. Li and J. Gong, Chem. Rev., 2016, 116, 11529–11653.
8 J. J. Spivey and A. Egbebi, Chem. Soc. Rev., 2007, 36,
1514–1528.
9 D. R. Palo, R. A. Dagle and J. D. Holladay, Chem. Rev.,
2007, 107, 3992–4021.
10 J. Chen, J. Sun and Y. Wang, Ind. Eng. Chem. Res., 2017, 56,
4627–4637.
gel method and their activities in OSRE and ATR processes
3
+
+
were studied. Substitution of La by Li metal cations altered
n+
4+
the relative compositions of active metal ions Ru /Ru and
4+
3+
Ce /Ce in LLCRO, which led to the formation of vacancies.
The starting temperature for an ethanol conversion reaction
is reduced and is correlated with the amount of substituted
+
Li ions in LLCRO (x = 0–0.6). Time-on-stream tests were car-
ried out on LLCRO (x = 0.6) catalysts under OSRE and ATR
Catal. Sci. Technol.
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Paper
1
1
1
1 A. E. Farrell, R. J. Plevin, B. T. Turner, A. D. Jones, M. O'Hare
and D. M. Kammen, Science, 2006, 311, 506–508.
2 R. M. Navarro, M. A. Peña and J. L. G. Fierro, Chem. Rev.,
38 W.-T. Chen, K.-B. Chen, M.-F. Wang, S.-F. Weng, C.-S. Lee
and M. C. Lin, Chem. Commun., 2010, 46, 3286–3288.
39 W.-I. Hsiao, Y.-S. Lin, Y.-C. Chen and C.-S. Lee, Chem. Phys.
Lett., 2007, 441, 294–299.
40 L. Huang, J. Xie, W. Chu, R. Chen, D. Chu and A. T. Hsu,
Catal. Commun., 2009, 10, 502–508.
41 S. M. de Lima, A. M. da Silva, L. O. O. da Costa, J. M. Assaf,
L. V. Mattos, R. Sarkari, A. Venugopal and F. B. Noronha,
Appl. Catal., B, 2012, 121–122, 1–9.
42 Z. Wang, H. Wang and Y. Liu, RSC Adv., 2013, 3,
10027–10036.
2
007, 107, 3952–3991.
3 M. Czaun, J. Kothandaraman, A. Goeppert, B. Yang, S.
Greenberg, R. B. May, G. A. Olah and G. K. S. Prakash, ACS
Catal., 2016, 6, 7475–7484.
1
1
1
4 D. M. Alonso, J. Q. Bond and J. A. Dumesic, Green Chem.,
2
010, 12, 1493–1513.
5 Y. Shen, D. Ma and X. Ge, Sustainable Energy Fuels, 2017, 1,
700–1729.
1
6 X. Zhao, H. Zhou, V. S. Sikarwar, M. Zhao, A.-H. A. Park,
43 D. E. P. Vanpoucke, P. Bultinck, S. Cottenier, V. Van
Speybroeck and I. Van Driessche, Phys. Rev. B: Condens.
Matter Mater. Phys., 2011, 84, 054110.
P. S. Fennell, L. Shen and L.-S. Fan, Energy Environ. Sci.,
2
017, 10, 1885–1910.
1
1
1
2
2
2
2
7 E. Kraleva, M.-M. Pohl, A. Jürgensen and H. Ehrich, Appl.
Catal., B, 2015, 179, 509–520.
8 J. P. Breen, R. Burch and H. M. Coleman, Appl. Catal., B,
44 H. Kumar, R. S. Dhaka and A. K. Pramanik, Phys. Rev. B,
2017, 95, 054415.
45 B. J. Nyman, M. E. Björketun and G. Wahnström, Solid State
Ionics, 2011, 189, 19–28.
46 K. Sardar, E. Petrucco, C. I. Hiley, J. D. B. Sharman, P. P.
Wells, A. E. Russell, R. J. Kashtiban, J. Sloan and R. I.
Walton, Angew. Chem., 2014, 126, 11140–11144.
47 F. Brisse and O. Knop, Can. J. Chem., 1968, 46, 859–873.
48 N. Bespalko, A.-C. Roger and J. Bussi, Appl. Catal., A,
2011, 407, 204–210.
49 D. Pakhare, C. Shaw, D. Haynes, D. Shekhawat and J. Spivey,
J. CO2 Util., 2013, 1, 37–42.
50 D. Pakhare, H. Wu, S. Narendra, V. Abdelsayed, D. Haynes,
D. Shekhawat, D. Berry and J. Spivey, Appl. Petrochem. Res.,
2013, 3, 117–129.
2
002, 39, 65–74.
9 S. Velu, N. Satoh, C. S. Gopinath and K. Suzuki, Catal. Lett.,
002, 82, 145–152.
2
0 L. V. Mattos, G. Jacobs, B. H. Davis and F. B. Noronha,
Chem. Rev., 2012, 112, 4094–4123.
1 G. Rabenstein and V. Hacker, J. Power Sources, 2008, 185,
1
293–1304.
2 D. K. Liguras, K. Goundani and X. E. Verykios, Int. J.
Hydrogen Energy, 2004, 29, 419–427.
3 J. L. Silveira, L. B. Braga, A. C. C. de Souza, J. S. Antunes and
R. Zanzi, Renewable Sustainable Energy Rev., 2009, 13,
2
525–2534.
2
2
2
2
2
2
3
3
4 M. H. Youn, J. G. Seo, H. Lee, Y. Bang, J. S. Chung and I. K.
Song, Appl. Catal., B, 2010, 98, 57–64.
5 T. Mondal, K. K. Pant and A. K. Dalai, Int. J. Hydrogen
Energy, 2015, 40, 2529–2544.
6 K. Sato, K. Kawano, A. Ito, Y. Takita and K. Nagaoka,
ChemSusChem, 2010, 3, 1364–1366.
7 W. Cai, F. Wang, E. Zhan, A. C. Van Veen, C. Mirodatos and
W. Shen, J. Catal., 2008, 257, 96–107.
8 S. Cavallaro, V. Chiodo, A. Vita and S. Freni, J. Power
Sources, 2003, 123, 10–16.
9 T. Y. Kim, S. M. Kim, W. S. Lee and S. I. Woo, Int. J.
Hydrogen Energy, 2013, 38, 6027–6032.
0 D. Zanchet, J. B. O. Santos, S. Damyanova, J. M. R. Gallo and
J. M. C. Bueno, ACS Catal., 2015, 5, 3841–3863.
1 J. A. Moulijn, A. E. van Diepen and F. Kapteijn, Appl. Catal.,
A, 2001, 212, 3–16.
51 M. Tada, S. Zhang, S. Malwadkar, N. Ishiguro, J.-i. Soga, Y.
Nagai, K. Tezuka, H. Imoto, S. Otsuka-Yao-Matsuo, S.-i.
Ohkoshi and Y. Iwasawa, Angew. Chem., Int. Ed., 2012, 51,
9361–9365.
52 Y. Ma, X. Wang, X. You, J. Liu, J. Tian, X. Xu, H. Peng, W.
Liu, C. Li, W. Zhou, P. Yuan and X. Chen, ChemCatChem,
2014, 6, 3366–3376.
53 S.-F. Weng, H.-C. Hsieh and C.-S. Lee, Int. J. Hydrogen
Energy, 2017, 42, 2849–2860.
54 S.-F. Weng, Y.-H. Wang and C.-S. Lee, Appl. Catal., B,
2013, 134–135, 359–366.
55 M. A. Peña and J. L. G. Fierro, Chem. Rev., 2001, 101,
1981–2018.
56 M. Morales and M. Segarra, Appl. Catal., A, 2015, 502,
305–311.
57 Q. Yang, G. Liu and Y. Liu, Ind. Eng. Chem. Res., 2018, 57,
1–17.
58 K. E. Sickafus, L. Minervini, R. W. Grimes, J. A. Valdez, M.
Ishimaru, F. Li, K. J. McClellan and T. Hartmann, Science,
2000, 289, 748–751.
3
3
2 A. Trovarelli and J. Llorca, ACS Catal., 2017, 7, 4716–4735.
3 J. A. Rodriguez, D. C. Grinter, Z. Liu, R. M. Palomino and
S. D. Senanayake, Chem. Soc. Rev., 2017, 46, 1824–1841.
4 T. Montini, M. Melchionna, M. Monai and P. Fornasiero,
Chem. Rev., 2016, 116, 5987–6041.
3
3
3
3
59 E. Talik, A. Novosselov, M. Kulpa and A. Pajaczkowska,
J. Alloys Compd., 2001, 321, 24–26.
60 B. H. Toby and R. B. Von Dreele, J. Appl. Crystallogr.,
2013, 46, 544–549.
61 I. E. Grey, L. M. D. Cranswick, C. Li, L. A. Bursill and J. L.
Peng, J. Solid State Chem., 1998, 138, 74–86.
62 B. Toby, J. Appl. Crystallogr., 2001, 34, 210–213.
5 X. Han, Y. Yu, H. He, J. Zhao and Y. Wang, J. Power Sources,
2
013, 238, 57–64.
6 G. A. Deluga, J. R. Salge, L. D. Schmidt and X. E. Verykios,
Science, 2004, 303, 993–997.
7 C. Pirez, M. Capron, H. Jobic, F. Dumeignil and L. Jalowiecki-
Duhamel, Angew. Chem., Int. Ed., 2011, 50, 10193–10197.
This journal is © The Royal Society of Chemistry 2019
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
6
3 S. I. Zabinsky, J. J. Rehr, A. Ankudinov, R. C. Albers and
73 B. D. Mukri, U. V. Waghmare and M. S. Hegde, Chem.
Mater., 2013, 25, 3822–3833.
M. J. Eller, Phys. Rev. B: Condens. Matter Mater. Phys.,
1
995, 52, 2995–3009.
74 B. M. Reddy, L. Katta and G. Thrimurthulu, Chem. Mater.,
2010, 22, 467–475.
75 J. S. Lee, Y. S. Lee, T. W. Noh, S. Nakatsuji, H. Fukazawa,
R. S. Perry, Y. Maeno, Y. Yoshida, S. I. Ikeda, J. Yu and C. B.
Eom, Phys. Rev. B: Condens. Matter Mater. Phys., 2004, 70,
085103.
6
6
4 A. L. Ankudinov and J. J. Rehr, Phys. Rev. B: Condens. Matter
Mater. Phys., 1997, 56, R1712–R1716.
5 M. Newville, P. Līviņš, Y. Yacoby, J. J. Rehr and E. A. Stern,
Phys. Rev. B: Condens. Matter Mater. Phys., 1993, 47,
1
4126–14131.
6
6
6 B. Vijaya Kumar, R. Velchuri, V. Rama Devi, B. Sreedhar, G.
Prasad, D. Jaya Prakash, M. Kanagaraj, S. Arumugam and M.
Vithal, J. Solid State Chem., 2011, 184, 264–272.
7 I. A. Carbajal-Ramos, M. F. Gomez, A. M. Condó, S. Bengió,
J. J. Andrade-Gamboa, M. C. Abello and F. C. Gennari, Appl.
Catal., B, 2016, 181, 58–70.
76 T. Munenaka and H. Sato, J. Phys. Soc. Jpn., 2006, 75,
103801.
77 H. Tian, X. Li, L. Zeng and J. Gong, ACS Catal., 2015, 5,
4959–4977.
78 S. Alayoglu, K. An, G. Melaet, S. Chen, F. Bernardi, L. W.
Wang, A. E. Lindeman, N. Musselwhite, J. Guo, Z. Liu, M. A.
Marcus and G. A. Somorjai, J. Phys. Chem. C, 2013, 117,
26608–26616.
79 F. Wang, W. Cai, H. Provendier, Y. Schuurman, C.
Descorme, C. Mirodatos and W. Shen, Int. J. Hydrogen
Energy, 2011, 36, 13566–13574.
80 W.-T. Chen, K.-B. Chen, M.-F. Wang, S.-F. Weng, C.-S. Lee
and M. C. Lin, Chem. Commun., 2010, 46, 3286–3288.
81 S. M. de Lima, A. M. da Silva, L. O. O. da Costa, J. M. Assaf,
G. Jacobs, B. H. Davis, L. V. Mattos and F. B. Noronha, Appl.
Catal., A, 2010, 377, 181–190.
6
6
7
7
7
8 L. Ji, J. Lin and H. C. Zeng, Chem. Mater., 2001, 13,
2
403–2412.
9 P. Anithakumari, V. Grover, C. Nandi, K. Bhattacharyya and
A. K. Tyagi, RSC Adv., 2016, 6, 97566–97579.
0 A. A. Bolzan, C. Fong, B. J. Kennedy and C. J. Howard, Acta
Crystallogr., Sect. B: Struct. Sci., 1997, 53, 373–380.
1 I. I. Soykal, H. Sohn and U. S. Ozkan, ACS Catal., 2012, 2,
2
335–2348.
2 G. Giampaoli, J. Li, A. P. Ramirez, A. W. Sleight and M. A.
Subramanian, Inorg. Chem., 2017, 56, 4706–4715.
Catal. Sci. Technol.
This journal is © The Royal Society of Chemistry 2019