Rational design of ethanol steam reforming catalyst based on analysis of Ni/La2O3 metal-support interactions

Article abstract of DOI:10.1039/c5cy00410a

Understanding the metal-support interactions between Ni ansd La₂O₃ has helped us design an improved catalyst for the ethanol steam reforming (ESR) reaction. Information from in situ X-ray absorption spectra (XAS) and high-resolution transmission electron microscopy (HRTEM) has helped us to prepare a Ni-based catalyst, in which strong metal-support interactions (SMSI) maximize the hydrogen yield by suppressing undesired reaction pathways. It was found that the Ni, formed as nanoparticles, was well dispersed both in and on the La₂O₃. The Ni/La₂O₃ catalyst, when compared to a Ni/SiO₂ catalyst, yielded twice as much H₂ (3.7 mol H₂ per mol EtOH) at 395 °C by both inhibiting methanation (CO + 3H₂ → CH₄ + H₂O) and promoting the water gas shift reaction (CO + H₂O → CO₂ + H₂). It is expected that our enhanced understanding of Ni/La₂O₃ physical/chemical interactions will help us design new catalysts for various catalytic applications.

Full text of DOI:10.1039/c5cy00410a

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Rational design of ethanol steam reforming
catalyst based on analysis of Ni/La2O3 metal–
support interactions†
Cite this: DOI: 10.1039/c5cy00410a
Jyong-Yue Liu,a Wei-Nien Su,b John Rick,a Sheng-Chiang Yang,a Chun-Jern Pan,a
c
c
ac
*
Jyh-Fu Lee, Jin-Ming Chen and Bing-Joe Hwang
Understanding the metal–support interactions between Ni ansd La2O3 has helped us design an improved
catalyst for the ethanol steam reforming (ESR) reaction. Information from in situ X-ray absorption spectra
(XAS) and high-resolution transmission electron microscopy (HRTEM) has helped us to prepare a Ni-based
catalyst, in which strong metal–support interactions (SMSI) maximize the hydrogen yield by suppressing
undesired reaction pathways. It was found that the Ni, formed as nanoparticles, was well dispersed both in
and on the La2O3. The Ni/La2O3 catalyst, when compared to a Ni/SiO2 catalyst, yielded twice as much H2
(3.7 mol H2 per mol EtOH) at 395 °C by both inhibiting methanation (CO + 3H2 → CH4 + H2O) and pro-
moting the water gas shift reaction (CO + H2O → CO2 + H2). It is expected that our enhanced understand-
ing of Ni/La2O3 physical/chemical interactions will help us design new catalysts for various catalytic
applications.
Received 18th March 2015,
Accepted 8th December 2015
DOI: 10.1039/c5cy00410a
www.rsc.org/catalysis
catalysts still face issues related to their high working tem-
perature window (>500 °C), sintering and coke deposition.
Introduction
With increasingly rapid industrialization the need to satisfy
growing energy demands has been thrown into sharp focus.1
Fossil fuels, due to their cost and ease of extraction, are still
the main global energy source; however, the ongoing con-
sumption of fossil fuels is creating serious environmental
problems. How to address these problems is an important
unresolved issue.
Among the renewable energy technologies, e.g. solar en-
ergy, wind power, marine energy etc., hydrogen fuel cells that
use hydrogen, sourced from hydrocarbons or ethanol, offer
conversion efficiency and environmental benefits.2 Of the
means used to generate hydrogen, ethanol steam
reforming3–5 [ESR (C2H5OH + 3H2O → 6H2 + 2CO2)] is com-
monly preferred due to its minimal environmental impact.6,7
Transition metals such as Rh, Pt, Ru, Pd Ir, Co, Ni, Cu
and Fe (ref. 8) show significant activity and selectivity for
ESR. Of these, Rh shows a particularly impressive activity;
however, its high cost limits its more widespread application.
Apart from the noble metals, Ni shows promise due to its
C–C and OH bond breaking activity.9 However, Ni-based
Many authors have proposed strategies to prevent coke depo-
sition and agglomeration on Ni-based catalysts, e.g. Nichele
et al.10 used CaO-doped Ni/ZrO2 to improve coking resis-
tance, while Carrero et al.11 used Cu–Ni, supported on high
surface area SBA-15a, to prevent sintering at high
temperatures.
The pathways for hydrogen production in a generalized
ESR scheme9 are shown below:
Dehydrogenation: C2H5OH → C2H4O + H2
Acetaldehyde decomposition: C2H4O → CH4 + CO
Acetaldehyde steam reforming: C2H4O + H2O → 3H2 + 2CO
In addition to the main reaction pathways, some impor-
tant side reactions may occur:
Water gas shift reaction (WGSR): CO + H2O → CO2 + H2
Methanation: CO + 3H2 → CH4 + H2O
a Department of Chemical Engineering, National Taiwan University of Science and
Technology, Taipei 10617, Taiwan. E-mail: bjh@mail.ntust.edu.tw
b Graduate Institute of Applied Science and Technology, National Taiwan
University of Science and Technology, Taipei 10617, Taiwan
c National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c5cy00410a
Ni is a well-known methanation catalyst:12 during low-
temperature ESR (<500 °C), methanation may occur, con-
suming large volumes of H2 and CO. Generally, catalytic
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methanation on supported nickel catalysts is dependent on
the active phase's particle or crystal size13 and the interac-
tions between the active metal and its support (SMSI).14 If
this side reaction can be suppressed we can potentially maxi-
mize hydrogen yield, reduce energy loss, and minimize cata-
lytic sintering.
synchrotron light source (to record in situ XRD) at the
beamline 01C of the National Synchrotron Radiation Re-
search Center (NSRRC), Hsinchu, Taiwan. The electron stor-
age ring was operated at 1.5 GeV with a beam current of 100–
200 mA. The XRD pattern was recorded using a wavelength of
0.5167 Å for limited angular regions at room temperature.
The wavelength was changed to 1.5418 Å as the energy of
CuKα1. The crystallite size of the nickel was estimated using
the Scherrer equation. In situ X-ray absorption spectra (XAS)
were obtained using the beamlines 17C and 20A at the
NSRRC as above. The electron storage ring was operated at
1.5 GeV with a beam current of 300 mA. Hard XAS were
recorded at beamline 17C, with a double Si (111) crystal
monochromator being used for energy selection. One colli-
mating mirror and one refocusing mirror, both coated with
Rh, were respectively located upstream and downstream of
the monochromator. These two mirrors also served to reject
high harmonics. The focused beam size at the sample posi-
tion was 4 × 2 mm2. Soft XAS, made in fluorescence mode for
the oxygen K-edge, using an ultrahigh-vacuum (UHV) cham-
ber with a base pressure of 1 × 10−10 torr, were recorded at
the beamline 20A. A 6 m high energy spherical grating mono-
chromator (6 m-HSGM) was used to perform the energy scan.
High-resolution transmission electron microscopy (HRTEM)
was conducted using a Philips Tecnai F30 FEI-TEM at an ac-
celeration voltage of 200 kV. The powder samples for the
HRTEM were prepared (in ethanol) by ultrasonic dispersion
prior to deposition and drying on carbon-coated copper grids.
The reduction behaviour of the samples was measured by
temperature programmed reduction (H2-TPR) controlled by
an AutoChem II analyzer. Samples (50 mg) were heated in
10% H2 at a flow rate of 30 ml min−1, with the temperature
being increased from room temperature to 600 °C. Prior to
the H2 uptake experiment, all catalysts were reduced in situ
in 10% H2/N2 at various temperatures (1 h) and then cooled
to room temperature using high purity N2.
Recently, SMSI have been widely discussed15–17 and inter-
preted in terms of how electron transfer can lead to tailored
catalytic properties.18 The catalysts derived from ABO3 perov-
skite have many features that encourage their use in dry
reforming of methane (DRM),19,20 ESR21,22 and oxidative eth-
anol steam reforming (OESR).23–25 LaNiO3 is an easily reduc-
ible perovskite structure that was first used by de Lima
et al.21 in a partially reduced form to enhance ESR activity
and stability. However, the current literature focus remains
on how carbon formation can be inhibited on the dispersed
metal particles during ESR.26,27 At the time of writing, little
experimental evidence has been offered to substantiate the
existence of SMSI and how they affect reaction paths. To ad-
dress this issue and explore the underlying catalytic mecha-
nism we prepared two catalysts with supports shown to be in-
ert towards ESR: (i) Ni/La2O3, derived from perovskite, and
(ii) Ni/SiO2, prepared by a sol–gel method with a similar Ni
loading/size.
Experimental
Catalyst preparation
LaNiO3, was prepared using a co-precipitation method. Ini-
tially, 100 mL of 0.6 M solutions of both aqueous lanthanum
nitrate hexahydrate (98% ACROS) and nickel nitrate hexahy-
drate (99% ACROS) were mixed (1 : 1 molar ratio) and stirred
while NaOHaq (3.2 M, 400 mL) was added dropwise (for 1 h)
to produce precipitation. The suspension was filtered and re-
peatedly washed with DI water and the product dried at 110
°C overnight. Finally, the sample was calcined at 400 °C for 2
h and then at 700 °C for 6 h (ramp rate 5 °C min−1). The cata-
lyst derived from LaNiO3 is denoted as Ni/La2O3. The sol–gel
method28 was used to synthesize Ni/SiO2. Nickel nitrate hexa-
hydrate (0.01 mol, 99% ACROS) and citric acid (0.015 mol)
were dissolved into 100 mL of absolute ethanol and stirred at
60 °C for 4 h. Then, a solution of deionized water and abso-
lute ethanol (molar ratio, 3 : 1) was added. Tetraethyl ortho-
silicate (5.62 g, TEOS) was added dropwise into the solution.
After drying at 80 °C overnight, the precursor was calcined at
450 °C under air for 3 h. All catalysts were reduced in situ in
hydrogen at various temperatures. For the Ni/La2O3 catalyst,
the reduction was performed at 550 °C for 1 h (heating rate 7
°C min−1); while for Ni/SiO2 the reduction was performed at
600 °C for 1 h. The Ni loading for both samples was 26.5
wt%.
Catalytic activity measurement
The samples' catalytic activities with respect to the ESR reac-
tion were evaluated at atmospheric pressure in a fixed-bed
reactpr. Catalyst (50 mg) was placed in a quartz tubular reac-
tor allowing activity to be evaluated using stepwise tempera-
ture changes from 325 to 500 °C (ramp rate 1 °C min−1) with
30 minutes waiting time for reaction equilibrium at each
analysis reaction temperature with measurements taken for
each 35 °C reaction temperature increase. A liquid reactant
mixture of H2O/EtOH = 6 molar ratio was introduced at a
flow rate of 0.005 mL min−1 and further eluted by He (15 mL
min−1). The weight hourly space velocity (WHSV = 1.74 h−1)
was defined as the ratio between the inlet feed (ethanol)
mass flow rate and the mass of catalyst. It should be noted
that a higher steam/ethanol ratio was meant for evaluation of
catalyst but the condition is also associated with higher en-
ergy penalty. Prior to the reaction, samples were activated by
reduction with 10% hydrogen (at a temperature determined
Characterization
Specimens were characterized using X-ray powder diffraction
(XRD) with either a Bruker D2 Phaser X-ray powder diffrac-
tion spectrophotometer (in-house) or by using the
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by temperature programmed reduction (H2-TPR) measure-
ments) for 1 hour to ensure that the nickel species (NiO or
LaNiO3) was reduced to metallic Ni. The gaseous products
were characterized by gas chromatography (GC) on an Acme
6100 instrument equipped with a pulsed discharge helium
ionization detector (PDHID). Three factors were selected to
evaluate the ESR reaction of the samples: (i) the conversion
of ethanol [XEthanolIJ%)], (ii) the product distribution [PiIJ%)]
and (iii) the hydrogen yield (YH ) which was calculated using
2
the mole ratios of MEthanol and products (Mi), as defined by
eqn (1), (2) and (3), respectively:
(1)
(2)
Fig. 2 In situ XRD patterns of LaNiO3 sample with different reduction
temperature.
reduction of bulk perovskite. The as-prepared Ni/SiO2 shows
three main reduction peaks. The first two at 329 and 402 °C
represent the reduction of NiO to Ni, while the broad reduc-
tion peak at 534 °C is associated with Ni release from the
SiO2 matrix.
(3)
The TEM image of LaNiO3 perovskite (particle diameters
∼50–100 nm) is shown in Fig. 3(a). The Ni/La2O3 catalyst is
shown in Fig. 3(b)–(d). Comparing Fig. 3(a) LaNiO3 and
Fig. 3(b), i.e. after pretreatment with 10% H2 at 550 °C for 1
h, it is apparent that the perovskite phase is transformed –
this observation is in good agreement with the in situ XRD
(Fig. 2). Notable are the well-dispersed Ni nanoparticles (NPs)
on the La2O3 support (average diameter 5.9 nm; see TEM re-
sults and XRD, Fig. S1†). Interestingly, Fig. 3(c) and the en-
larged section of Fig. 3(d) show one Ni NP with a clear Ni
(111) lattice on La2O3 surrounded by the lanthanum oxide
support. This indicates that Ni NPs can be partially
Results and discussion
H2-TPR and morphology analysis
Profiles (a) and (b) in Fig. 1 represent H2-TPR measurements
of the LaNiO3 (perovskite type) and the as-prepared Ni/SiO2
samples, respectively. LaNiO3 shows three reduction peaks at
305 °C, 339 °C and 489 °C, with the first two slightly
overlapping. By referring to the results of in situ XRD in
Fig. 2, the first reduction peak at 305 °C was identified as
originating from the partial reduction of LaNiO3, i.e. with the
perovskite phase retained. The second reduction peak at 339
°C was identified as Ni metal, reduced from NiO, which indi-
cates that not all the Ni participates in the perovskite phase.
Finally, the third peak at 489 °C is associated with the complete
Fig. 3 TEM images of (a) LaNiO3 sample, (b–d) Ni/La2O3 catalyst
Fig. 1 H2-TPR of (a) LaNiO3 and (b) as-prepared Ni/SiO2 samples.
(derived from LaNiO3).
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embedded into the La2O3 support after reduction. For the Ni/
SiO2 catalyst shown in Fig. 4, the Ni NPs are well dispersed
(average diameter of 6 nm; see TEM results and XRD, Fig.
S2†). From the above results, the Ni/La2O3 and Ni/SiO2 cata-
lysts have similar Ni particle sizes.
Analysis of the strong interaction between Ni and La2O3
In situ XAS was used to study the electronic structures of the
Ni/La2O3 and Ni/SiO2 catalysts. Fig. 5 shows the Ni K-edge
XANES of the Ni/La2O3 and Ni/SiO2 catalysts (metallic Ni foil
is also included as a reference). The dominant XANES peak
(white line, denoted as WL) at the Ni K-edge is an absorption
threshold resonance, which is assigned to the allowed orbital
transition from 1s to 4p.29 As shown in this figure, the Ni/
La2O3, Ni/SiO2 and metallic Ni foil had the same resonance,
thereby indicating that the oxidation state of Ni in the Ni/
La2O3 and Ni/SiO2 catalysts was that of metallic Ni. However,
a white line of slightly higher intensity was obtained for Ni/
La2O3, suggesting that the Ni atoms' orbital electron density
was modified by interaction between the Ni NPs and the
La2O3 support.30 The interaction between the Ni NPs and the
La2O3 support was examined using O K-edge XAS on Ni/La2O3
and Ni/SiO2, as shown in Fig. 6 and 7, respectively. To facili-
tate comparison, La2O3, SiO2 and LaNiO3 samples are also in-
cluded as references. The spectra reveal excitations from the
O 1s orbital to unoccupied states.31 The O K-edge spectrum
of the Ni/La2O3 catalyst in Fig. 6(a) has two major excitation
peaks: O 1s to Ni 3d–O 2p from 530 to 531.7 eV and O 1s to
La 5d–O 2p from 533 to 537 eV. The small shoulder from 530
to 531.7 eV is due to the transitions of the O 1s electron to
the antibonding O 2p state hybridized with the 3d metal
states.32 In contrast to Ni/La2O3 catalyst, there is no peak be-
tween 530 and 531.7 eV for Ni/SiO2, see Fig. 7(a), which indi-
cates that there is no strong interaction between Ni and the
SiO2 support. This result can be explained by the chemical
environment of the Ni NPs in Ni/La2O3 in which most Ni NPs
Fig. 5 XANES spectra of the Ni K-edge of (a) Ni/La2O3 catalyst, (b) Ni/
SiO2 catalyst and (c) metallic Ni foil sample.
formed by reduction migrate from the lattice to the surface,33
while others become partially embedded in the lanthanum
oxide, producing multiple interfaces between the Ni and its
support.
Evaluation of catalytic activity
Fig. 8 shows ESR reaction conversion profiles as a function of
reaction temperature (°C) from 325 to 500 °C. At 325 °C the
Ni/SiO2 catalyst shows a maximal conversion of ethanol
(100%), whereas the Ni/La2O3 catalyst showed only 32% con-
version; however, as the reaction temperature increased from
325 to 395 °C, the conversion approached 100%. Generally,
ESR depends on the catalyst's ‘active surface area’ which may
be the case with Ni/La2O3 and Ni/SiO2, as the Ni NP sizes were
similar [see XRD (Fig. S1 and S2†) and TEM (Fig. 3 and 4)].
H2 uptake data were obtained to determine the active areas;
Fig. 6 XANES spectra of the O K-edge of (a) Ni/La2O3 catalyst, (b)
Fig. 4 TEM image of Ni/SiO2 catalyst.
La2O3 and (c) LaNiO3 samples.
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Fig. 7 XANES spectra of the O K-edge of (a) Ni/SiO2 catalyst and (b)
SiO2 sample.
Fig. 9 ESR reaction of (a) Ni/SiO2 and (b) Ni/La2O3 catalysts with
WHSV = 1.74 h−1 and H2O/EtOH = 6. The conversion of ethanol for all
catalysts at the reaction temperature range between 395 and 500 °C
was 100%, and the temperature rate was 1 °C min−1, with 30 min
waiting time for the reaction equilibrium at each analysis temperature
that was taken every 35 °C increase in the reaction temperature.
Fig. 8 ESR reaction of ethanol conversion of (a) Ni/SiO2 and (b) Ni/
La2O3 catalysts with WHSV = 1.74 h−1 and H2O/EtOH = 6.
(20.2%), CO2 (8.2%) and CH4 (6.1%) were the main gaseous
products with a small amount of CO (3.3%). At 395 °C, the
concentration of CH4 was ∼8.3% with the CO being only
∼1.6%. Within a reaction temperature window between 360
and 500 °C, the Ni/La2O3 catalyst gave the greatest H2 yield
(3.7 mol H2 per mol EtOH at 395 °C), with lower concentra-
tions of methane, but higher CO.
The Ni/SiO2 catalyst, having the largest surface area, gave
the highest hydrogen yield below 360 °C (1.64 mol H2 per
mol EtOH), cf. Ni/La2O3 (0.51 mol H2 per mol EtOH). How-
ever, within the reaction temperature set between 360 and
500 °C, the situation was reversed with the Ni/La2O3 catalyst
giving a greater H2 yield. This may be explained as follows.
After the dehydrogenation of ethanol, the acetaldehyde gener-
ated can undergo two competing reaction paths,36 (i) decom-
position into CH4 and CO (CH3CHO → CO + CH4, or (ii) acet-
aldehyde steam reforming (CH3CHO + H2O → 2CO + 3H2).
From either of these reaction paths, the water gas shift reac-
tion (WGSR) can take place (CO + H2O → CO2 + H2).37 In
see Table S1.† The H2 uptakes for Ni/SiO2 and Ni/La2O3 were
552.8 and 54.4 μmol per g respectively, indicating that the
main effect of SMSI is the suppression of H2 adsorption34 or
metallic Ni partial embedding into the support to reduce the
exposed Ni surface area.
Fig. 9 shows ESR product distribution profiles, as a func-
tion of reaction temperature (°C), from 325 to 500 °C, for Ni/
SiO2 and Ni/La2O3. For the Ni/SiO2 catalyst at 325 °C, H2
(46.6%), CO (18.9%) and CH4 (25.3%) were the main gaseous
products, with a small amount of CO2 (9.2%). With the reac-
tion temperature raised to 360 °C, in addition to the main
gaseous products H2 (50.14%) and CH4 (26.37%), the concen-
tration of CO decreased to 0.34%, while the concentration of
CO2 increased to 23.14%. The CO concentration remained
low for temperatures between 395 and 465 °C. At relatively
high CH4 concentrations our results agree with the existing
catalytic Ni methanation literature.35 The Ni/La2O3 catalyst
was tested for comparison. At 325 °C, H2 (62.2%), CH3CHO
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contrast to Ni/La2O3, the Ni/SiO2 catalyst produces less CO
(0.3%) and more CH4 (23.01%) at 395 °C, implying that the
Ni/SiO2 catalyst also promotes methanation, producing meth-
ane and water by consuming CO and H2.
carbon later diffuses and nucleates into a carbon fiber.45 The
comparative morphologies of used Ni/La2O3 and used Ni/
SiO2 catalysts after the ESR reaction at 395 °C for 14 h are
shown in Fig. 10. The sizes of the nickel NPs were ∼8.3 nm
for used Ni/La2O3 and 13 nm for used Ni/SiO2. In addition,
most carbon fibers, or carbon nanotubes, grew from metallic
nickel.
In order to confirm this hypothesis, mixed gases compris-
ing CO (29.5 torr), H2 (295 torr) and H2O (334 torr) were used
as reactants (at 395 °C) with the two catalysts, as seen in Fig.
S3.† For Ni/SiO2 [Fig. S3(a)†], H2 (89%) and CH4 (8.2%) were
the main gaseous products plus CO2 (2.8%), with most CO
being consumed by methanation. In contrast, in the case
with Ni/La2O3, the concentrations of H2, CH4, and CO2 were
92%, 1.1% and ∼6.9% respectively. With this catalyst, the CO
produced was more likely to go through the WGSR. In addi-
tion, the CH4/CO species in the given ESR with Ni/La2O3 were
significantly suppressed. The SMSI significantly affects the re-
action pathways by promoting the water gas shift reaction.
The water dissociation provides the required oxygen source
to remove CH4/CO and this could be attributed to the La2O3
support and the SMSI between Ni and the support, as
discussed in the literature,38,39 where the interaction signifi-
cantly enhances the ability of the admetal to dissociate the
O–H bond in the adsorbed water molecule to produce a high
Fatsikostas et al.46 proposed that the La2O3 support can re-
act with CO2 to form a lanthanum oxy-carbonate species that
reacts with surface carbon, thereby removing carbon deposits
by the reaction La2O2CO3 + C–Ni → La2O3 + 2CO + Ni. Thus,
the La2O2CO3 species is believed to function as a scavenger
able to clean the deposited carbon from the Ni surface. As
shown in Fig. S4,† the used Ni/La2O3 indeed exhibits similar
XRD patterns to La2O2CO3. Additionally, SMSI also inhibits
coke deposition in close proximity to metallic Ni; however,
the accumulation of carbon deposits may move particulate Ni
away from the support.47,48
Coke deposition for Ni/SiO2 and Ni/La2O3 was quantified
using TGA measurements; see Fig. S5.† The TGA of used Ni/
SiO2 [Fig. S5(a)†] exhibited a weight loss (D1) at around 400–
600 °C that was the oxidation of carbon filaments,49 while, in
contrast, the used Ni/La2O3 showed distinct weight losses in
various temperature ranges, i.e. 200–400 °C (D1), 400–600 °C
(D2), 620–656 °C (D3) and 656–718 °C (D4) (ref. 22 and 49),
suggesting that the ranges D2 and D3 were the oxidation of
carbon filaments and graphitic carbon, respectively, and D4
was thought to result mainly from the lanthanum decomposi-
tion, i.e.: La2O2CO3 → La2O3 + CO2.50 In addition, the weight
gain D1 was the oxidation of nickel to nickel oxide. Further-
more, the total wt% of carbon was estimated to be about
18.5% for Ni/La2O3 and 57.8% for Ni/SiO2. In addition to the
support as a scavenger to remove the coke deposition, the
less carbon deposits on Ni/La2O3 catalyst could be also due to
the less exposed Ni particles, which are the active sites for
carbon deposition. Furthermore, SMSI not only favours the
dissociation of O–H bond to improve catalytic activity but
also makes the cleavage of C–O bonds more difficult to pre-
vent coke deposition by inhibiting the Boudouard reaction
(2CO → C + CO2) during the ESR.51–53 Therefore, as seen in
the case of Ni/La2O3, the strong interaction not only inhibits
the particles from growing during the reaction at high tem-
peratures but also contributes to the decreased amount of
hydrogen yield (YH ).38 At 395 °C, the Ni/La2O3 catalyst
2
showed the highest hydrogen yield (3.7 mol H2 per mol
EtOH), which clearly indicated its high ESR activity at mild
temperatures, especially when compared with Ni/SiO2 cata-
lyst. Table 1 gives a comparative summary of the various Ni-
based catalysts for ESR.40–43 Despite differences in the steam/
ethanol ratio, the Ni/La2O3 catalyst shows the highest hydro-
gen yield. From the observations and experiments above, we
conclude that SMSI plays an important role in catalysis. We
have demonstrated that the interactions can be effectively
used to suppress methanation while generating higher hydro-
gen yields, thus helping us to design a superior catalyst for
ethanol steam reforming.
Morphology and TGA analysis for used catalysts
The carbon balance for ESR reaction on Ni/La2O3 catalyst is
shown in Table S2.† Carbon deposition has been frequently
mentioned in the literature as a problem associated with Ni-
based catalysts. Whisker carbon44 or carbon nanotubes result
from adsorbed carbon atoms on Ni particles, this adsorbed
Table 1 Comparison of SRE performance of various Ni-based catalysts
Catalysts
Reaction temp (°C)
H2O/EtOH (molar ratio)
H2 yield (mol H2 per mol EtOH)
Ref.
Ni/La2O3
Ni/SiO2
CuNi/SiO2
CuNi/CeZrOx
CuNi/La20-SBA
Ni0.5Cu0.1Mg2.4Al
395
395
400
400
600
450
6
6
3.7
8
3.7
3
3.7
1.8
1.1a
2.4
3.8
3
This study
This study
40
41
42
43
a
Derived from hydrogen selectivity, calculated according to the following equation:
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Fig. 10 TEM images of used (a) Ni/La2O3 and (b) Ni/SiO2 catalysts.
carbon deposition. This physical/chemical phenomenon is
not found with Ni/SiO2.
Conclusions
In summary, using LaNiO3 as the catalyst precursor; we
observed, using X-ray absorption spectroscopy and HR-TEM
analysis, nanosized Ni particles both supported on and em-
bedded within the La2O3 support. SMSI was shown to inhibit
methanation and enhance the stability of the nanocatalyst
while promoting the WGSR during ESR. In comparison, coke
formation on Ni/La2O3 was also significantly reduced. It was
found that the Ni/La2O3 nanocatalyst showed a much higher
hydrogen yield at 395 °C compared to the data reported in
the literature. Moreover, the work not only discusses the cata-
lytic role of supports but also shows that the interaction
between metal and support can significantly influence the
reaction pathways. In addition to these effects, the SMSI
prevented Ni NPs from agglomerating at high temperatures,
while also suppressing coke deposition. We also demonstrate
approaches of preparing nanocatalyst with desirable SMSI
properties which can hold promise for the design and prepa-
ration of nanocatalysts for various heterogeneous reactions
in the future.
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Acknowledgements
The authors gratefully acknowledge the financial support
from the Top Universities Project by the Ministry of Education
(102H451401), National Science Council of Taiwan (NSC-99-
2120-M-011-001), and National Taiwan University of Science
and Technology (NTUST) as well as the facility support from
National Synchrotron Radiation Research Center (NSRRC).
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