Mesoporous MFI zeolite nanosponge supporting cobalt nanoparticles as a Fischer-Tropsch catalyst with high yield of branched hydrocarbons in the gasoline range

Article abstract of DOI:10.1021/cs500784v

A zeolite nanosponge was obtained by a seed-assisted hydrothermal synthesis route using C₂₂H₄₅-N⁺(CH₃)₂-C₆H₁₂-N⁺(CH₃)₂-C₆H₁₃ as the structure-directing agent. The zeolite was composed of disordered network of 2.5-nm-thick MFI zeolite nanolayers having a narrow distribution of mesopore diameters centered at 4 nm. The highly mesoporous texture (mesopore volume = 0.5 cm³ g^-1) was suitable for supporting cobalt nanoparticles with a narrow distribution of particle diameters centered at 4 nm. The Co/MFI zeolite exhibited high stability of the Co nanoparticles against particle growth, and there was accordingly high catalytic conversion of carbon monoxide to hydrocarbons and long catalytic lifetime in the Fischer-Tropsch synthesis. Furthermore, the Co/MFI catalyst exhibited high selectivity for branched hydrocarbons in the gasoline range (C₅-C₁₁), compared to conventional alumina-based catalysts. This high selectivity could be attributed to hydroisomerization in the extremely thin zeolite frameworks that provided short diffusion path lengths for branched hydrocarbons.

Full text of DOI:10.1021/cs500784v

Research Article
pubs.acs.org/acscatalysis
Mesoporous MFI Zeolite Nanosponge Supporting Cobalt
Nanoparticles as a Fischer−Tropsch Catalyst with High Yield of
Branched Hydrocarbons in the Gasoline Range
Jeong-Chul Kim,†,‡ Seungyeop Lee,†,‡ Kanghee Cho,† Kyungsu Na,† Changq Lee,§,† and Ryong Ryoo*,†,§
†Center for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS), Daejeon 305-701, Republic of Korea
‡Graduate School of Nanoscience and Technology, KAIST, Daejeon 305-701, Republic of Korea
§Department of Chemistry, KAIST, Daejeon 305-701, Republic of Korea
S
* Supporting Information
ABSTRACT: A zeolite nanosponge was obtained by a seed-
assisted hydrothermal synthesis route using C22H45−
N+(CH3)2−C6H12−N+(CH3)2−C6H13 as the structure-direct-
ing agent. The zeolite was composed of disordered network of
2.5-nm-thick MFI zeolite nanolayers having a narrow
distribution of mesopore diameters centered at 4 nm. The
highly mesoporous texture (mesopore volume = 0.5 cm3 g−1)
was suitable for supporting cobalt nanoparticles with a narrow
distribution of particle diameters centered at 4 nm. The Co/
MFI zeolite exhibited high stability of the Co nanoparticles
against particle growth, and there was accordingly high
catalytic conversion of carbon monoxide to hydrocarbons
and long catalytic lifetime in the Fischer−Tropsch synthesis.
Furthermore, the Co/MFI catalyst exhibited high selectivity for branched hydrocarbons in the gasoline range (C5−C11),
compared to conventional alumina-based catalysts. This high selectivity could be attributed to hydroisomerization in the
extremely thin zeolite frameworks that provided short diffusion path lengths for branched hydrocarbons.
KEYWORDS: Fischer−Tropsch synthesis, bifunctional catalyst, hierarchical zeolite, uniform mesopore diameter, high cobalt dispersion,
high gasoline yield
and, therefore, activate the dissociation of CO for consecutive
hydrogenation into hydrocarbons. Among such metal catalysts,
cobalt is the most widely used because of its low cost, high CO
conversion activity, and high selectivity of long-chain linear
hydrocarbons (i.e., liquid fuels).5 FT synthesis is a structure-
sensitive reaction, exhibiting maximum catalytic activity in the
range of 4−6 nm cobalt particle diameters.8,9 The catalytic
conversion and selectivity for long-chain hydrocarbons
decreases drastically as the particle size decreases below this
range. On the other hand, if the particle diameter increases
beyond 6 nm, the metal dispersion decreases, and con-
sequently, the weight-specific activity of the cobalt decreases.
To obtain the optimum particle size, cobalt is often supported
on γ-Al2O3, SiO2, and TiO2 with high specific surface areas.10
Among these oxide supports, γ-Al2O3 has been the material
most commonly adopted to date, since it has the advantage of
low production cost, large external surface area, and strong
metal−support interaction.4 High-surface γ-Al2O3 samples
supporting cobalt nanoparticles of optimum diameters showed
1. INTRODUCTION
Fischer−Tropsch (FT) synthesis is a catalytic process that
produces hydrocarbons from a mixture of H2 and CO, which is
referred to as “synthesis gas” or “syngas”.1 Syngas can be readily
obtained by steam reforming of natural gas, coal, and
biomass.2,3 The FT process was industrialized early in Germany
as a method of transforming abundant coal into a hydrocarbon
source, which addresses its lack of domestic petroleum
resources.4 Germany built nine FT plants by the end of
World War II, but since then, almost all FT plants closed as
crude oil became available at a much lower cost than
hydrocarbons produced via FT synthesis. In recent years,
however, the price of oil increased dramatically. Besides, syngas
production from shale gas is anticipated to be cost competitive
in the near future. These factors have led to renewed interest in
the FT process.5 SASOL has been implementing a FT-based
process over the past several decades, and is currently planning
to increase its operational capacity to 34 000 barrels per day.6
Shell has also been operating an FT plant in Malaysia with a
daily capacity of 14 700 barrels.6
In the FT synthesis process, late transition metals such as
iron, ruthenium, and cobalt are used as catalysts.7 These metals
strongly interact with carbon monoxide (CO) on their surfaces
Received: March 2, 2014
Revised: September 22, 2014
© XXXX American Chemical Society
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high catalytic activity in FT synthesis. However, Co/γ-Al2O3
catalysts exhibited a nonselective distribution of product
hydrocarbon chain lengths, according to the Anderson−
Schulz−Flory (ASF) model.6 Recently, Tao et al. reported
that the product selectivity could be enhanced to a desired
range of chain lengths when zeolites (a family of crystalline
microporous aluminosilicates) were used as supports for cobalt
nanoparticles.11−13 This result was explained by hydrocracking
of the hydrocarbon intermediates to desirable chain lengths in
zeolite micropores having strong acid properties. However, the
zeolite-based catalyst exhibited much lower CO conversion
compared to the conventional alumina-based catalyst. This low
activity was due to low metal dispersion (i.e., exceedingly large
metal particles) on the limited area of zeolite external
surfaces.14
In order to resolve the disadvantage of conventional zeolites
as the metal−supporting material, Sartipi et al.15,16 generated
mesopores in an MFI zeolite through an alkali treatment. The
resultant zeolite exhibited improved dispersion of cobalt,
because of the large surface area of the mesopore walls.
Hence, using a mesoporous zeolite to support cobalt
nanoparticles led to high catalytic activity in the FT synthesis.
In addition, the mesoporous Co/MFI catalyst had the
advantage of low production of short-chain hydrocarbons
(<C4), compared with bulk Co/MFI. This result was explained
by the rapidly escaping diffusion of hydrocarbon products
before overcracking. Recently, Kang et al.17,18 reported that
mesoporous MFI and beta zeolites could support ruthenium
nanoparticles with high metal dispersion, as an FT catalyst for
the high yield of gasoline-range hydrocarbons.
In 2009, our group reported the direct synthesis of
mesoporous zeolites using multiammonium surfactants as a
structure-directing agent (SDA), which generated mesopores
and micropores simultaneously.19 Using the synthesis strategy,
we obtained an MFI zeolite exhibiting a morphology of 2.5-nm-
thick nanosheets. The MFI nanosheets were stacked regularly
to form multilayers supported by surfactants, or they were
assembled irregularly into a loose stacking of separate layers,
depending on the synthesis conditions.20 The former (multi-
lamellar assembly) lost most of its interlayer spacing due to
collapse when the surfactant was removed by calcination. On
the other hand, the latter (unilamellar assembly) maintained
the mesoporosity between neighboring nanosheets; however,
the mesopore diameters were widely distributed within a range
from 4 nm to 30 nm. Recently, Jo et al.21 added MFI zeolite
crystals into a synthesis composition for MFI zeolite nano-
sheets. The bulk crystal seeding reduced the zeolite
crystallization time remarkably. More importantly, the crystal
seeding gave rise to the formation of nanosheets exhibiting a
nanosponge-like morphology, which had a very narrow
distribution of pore diameters centered at 4 nm.
In this work, we noted the potential of the MFI zeolite
nanosponge as a catalyst support. In particular, we expected
that MFI zeolite frameworks with uniform mesopore diameters
would have a remarkable merit as a catalyst support in
bifunctional catalytic applications requiring both metal nano-
particles about the diameter of the MFI mesopores and strong
acidity of the MFI zeolite frameworks. For this reason, we
investigated the MFI nanosponge as a supporting material of
cobalt nanoparticles for FT synthesis reaction. The dispersion
of cobalt nanoparticles supported on the MFI nanosponge was
measured by high-resolution transmission electron microscopy
(TEM). The FT synthesis reaction was performed using the
Co/MFI nanosponge as a catalyst, in comparison with bulk
Co/MFI and alumina-based conventional FT catalyst. The
catalytic performances were evaluated, focusing on the total CO
conversion and the product selectivity for branched hydro-
carbons in the gasoline range.
2. EXPERIMENTAL SECTION
2.1. Catalyst Preparation. The MFI zeolite nanosponge
was hydrothermally synthesized, using [C22H45−N+(CH3)2−
C6H12−N+(CH3)2−C6H13(Br−)2] (abbreviated hereafter as
“C22‑6‑6”) as the zeolite SDA, and calcined bulk MFI zeolite
as crystal seeds. The concept of the zeolite synthesis was the
same as that of the previous method reported by Jo et al.21
However, the details of synthesis procedure was somewhat
modified. Water glass (29 wt % SiO2, Si/Na = 1.75, Shinheung
Chemical) was used as silica source instead of tetraethylortho-
silicate (TEOS). The order of mixing synthesis reagents was
also changed. In detail, C22‑6‑6 was dissolved in distilled water.
This solution was added into another solution dissolving
aluminum sulfate [Al2(SO4)3·18H2O, 98%, Sigma−Aldrich].
This mixture was stirred and the water glass was added into this
mixture dropwise. The resultant gel was heated to 333 K and
stirred for 2 h, and then the pH of this gel was adjusted to ∼10
via the addition of 10 wt % sulfuric acid solution. This gel had a
molar composition of 95 SiO2, 0.95 Al2O3, 7.5 C22‑6‑6, 30 Na2O,
21 H2SO4, 5000 H2O. It was stirred for 6 h at 333 K and,
subsequently, a commercial ZSM-5 zeolite (Zeolyst, CBV 8014,
Si/Al = 40) amounting to 5 wt % of the total silica source was
added as a seed into this gel. The composition of the final
synthetic gel was 100 SiO2, 1 Al2O3, 7.5 C22‑6‑6, 30 Na2O, 21
H2SO4, 5000 H2O. This synthetic gel was stirred for 6 h further
at 333 K. The synthesis gel was then heated in a Teflon-lined
stainless autoclave at 423 K with tumbling for 2.5 d. The zeolite
product was filtered, washed by distilled water, and dried in an
oven at 373 K.
Bulk MFI zeolite was synthesized using tetrapropylammo-
nium hydroxide (TPAOH, 10 wt %) as the zeolite SDA,
following a procedure described elsewhere.22 Aluminum sulfate
and TPAOH were dissolved in distilled water, and
subsequently, TEOS was added to this solution under magnetic
stirring. The resultant mixture had a molar composition of 100
SiO2, 1 Al2O3, 30 TPAOH, 3 H2SO4, 6000 H2O. This mixture
was heated in a Teflon-lined stainless autoclave at 443 K with
tumbling for 3 d. The zeolite product was filtered, washed by
distilled water, and dried in an oven at 373 K.
All the zeolite samples (both nanosponge and bulk) were
calcined in air at 823 K. After calcination, the zeolites were
slurried in a 1 M NH4NO3 aqueous solution a total of three
+
+
times for the ion exchange to NH4 . The NH4 -exchanged
zeolites were calcined again in air at 823 K for conversion to the
H+-ionic form. In addition to the zeolites, a γ-Al2O3 sample was
purchased from Sasol (PURALOX, 98%, SBET = 170 m2 g−1),
and supported with Co without further treatments. The Co
supporting on γ-Al2O3, bulk MFI and nanosponge MFI zeolites
was carried out by incipient wetness impregnation using an
aqueous solution of cobalt nitrate [Co(NO3)2·6H2O, Fluka].
Typically, 0.273 g of Co(NO3)2·6H2O was impregnated in 0.5 g
supporting material, to provide 10 wt % Co content in the final
catalyst. All Co-containing samples were dried in a convection
oven at 373 K for 12 h and calcined by O2 (99.9%, flow rate =
400 cm3 min−1 g−1) at 573 K for 4 h.
2.2. Characterization. Powder X-ray diffraction (XRD)
patterns were measured with a Rigaku Multiflex diffractometer
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equipped with Cu Kα radiation (30 kV, 40 mA). The Ar
sorption isotherms were measured at liquid Ar temperature (87
K) with a volumetric Micromeritics Model ASAP-2020
instrument. Si/Al ratios were determined by inductively
coupled plasma−atomic emission spectroscopy (ICP/AES),
using an OPTIMA 4300 DV instrument (Perkin−Elmer).
Scanning electron microscopy (SEM) micrographs were
obtained, using a Verios SEM system operating at 1 kV
(decelerating voltage of 3.0 kV) without a metal coating.
Transmission electron microscopy (TEM) micrographs were
obtained using an aberration-corrected Titan ETEM G2 system
at an operating voltage of 300 kV.
The concentration of Bronsted acid sites was analyzed with
̈
respect to the acid strength, following a 31P NMR spectroscopic
method using trimethylphosphine oxide as a probe mole-
cule.23,24 The 31P NMR chemical shift was used as an index for
acid strength while the peak intensity was measured for
quantification of acid sites. The NMR spectra were acquired in
a solid state with 10-kHz magic angle spinning (MAS) using a
Bruker Model AVANCE 400WB spectrometer at room
temperature. H2-temperature-programmed reduction (TPR)
profiles were obtained using a Micromeritics AutoChem II
2920 instrument equipped with a thermal conductivity detector
(TCD). For the measurement, 50 mg of each sample was
loaded in a quartz U-tube. The sample was degassed at 373 K
for 2 h under helium gas flow (flow rate = 50 cm3 min−1). The
gas flow then was switched to a H2-argon mixture (H2:Ar = 1:9
in moles) at the flow rate of 50 cm3 min−1. The amount of H2
consumption by reduction was measured by TCD, while the
temperature increased from 373 K to 1173 K with the ramping
rate of 10 K min−1.
2.3. Catalytic Measurements. FT synthesis was carried
out in a stainless steel fixed-bed reactor (7 mm inside
diameter), using 0.5 g of cobalt-loaded catalysts. Prior to the
FT reaction, the catalyst was reduced by high-purity H2
(99.999%, flow rate = 50 cm3 min−1) at 673 K for 12 h. The
temperature was decreased to room temperature under the H2
flow. The gas flow then was switched to a syngas−argon
mixture (H2:CO:Ar = 6:3:1 in moles). Argon also was mixed in
the reactant stream, as an internal standard for product analysis
by gas chromatography (GC). The pressure of the reactant gas
mixture was increased to 20 bar, then the flow rate was
maintained at 20 cm3 min−1. The reaction temperature was
increased to 493 K under this flow. During the reaction, gas-
phase products were analyzed using an online gas chromato-
graph equipped with a flame ionization detector and a thermal
conductivity detector. The gas products were separated using a
Gaspro (Agilent) column and a Porapak Q (Supelco) column
in parallel. At the same time, the liquid-phase products were
collected in a cold trap (278 K) for 100 h of the reaction, and
analyzed using a gas chromatograph equipped with an HP-1
column (Agilent).
Figure 1. MFI zeolite nanosponge synthesized using C22‑6‑6 surfactant
as zeolite-structure directing agent and bulk MFI seed: (a) TEM
image, (b) SEM image, (c) XRD pattern, (d) Ar sorption isotherm
obtained at 87 K, and (e) BJH pore size distribution corresponding to
the adsorption branch.
somewhat preferred orientation in parallel. These zeolite
nanosheets were interconnected into a three-dimensional
disordered network with very uniform interlayer spacing
(∼6.3 nm), as judged from the TEM image and a low-intensity
XRD peak appearing at 1.4° 2θ. Despite the uniform thickness,
uniform spacing, and preferred orientation, there were no
distinct long-range orders between the nanosheets. This zeolite
sample is designated as NS-MFI, meaning “nanosponge of MFI
zeolite”. In contrast to this NS-MFI sample, a conventional
zeolite sample that was synthesized using tetrapropyl
ammonium as an SDA exhibited bulk crystal-like particle
morphologies with smooth facets (see Figure S1 in the
Supporting Information). The diameters of the particles ranged
from 500 nm to 1 μm. TEM images and selected-area electron
diffraction patterns indicated that the particles were mostly
single crystals of MFI zeolite. This latter MFI zeolite sample is
designated as B-MFI, where “B” stands for “bulk”. The Si/Al
ratio of the two synthesized zeolites and their Bronsted acidic
̈
properties (obtained by 31P NMR analysis after trimethylphos-
phine oxide adsorption) are summarized in Table 1. The results
indicate that B-MFI and NS-MFI have similar Al contents (Si/
Al = 46 and 48 for B-MFI and NS-MFI, respectively), and also
similar Bronsted acid concentrations and strengths (see Figure
̈
S2 in the Supporting Information provides details of the 31P
NMR analysis after trimethylphosphine adsorption).23,24
Argon adsorption isotherms of B-MFI and NS-MFI at 87 K
are shown in Figure 1. The adsorption isotherm of NS-MFI
exhibits a very sharp increase in the low-pressure region of P/P0
< 0.1, and a second jump in the medium-pressure region of 0.4
< P/P0 < 0.5. The first increase can be interpreted as argon
filling in the zeolite micropores, while the second jump is
attributed to the capillary condensation in mesopores between
zeolite nanosheets. The adsorption isotherm in the region of P/
P0 < 0.1 was analyzed using nonlocal density functional theory.
3. RESULTS AND DISCUSSION
3.1. MFI Zeolite Nanosponge as a Support for Cobalt
Nanoparticles. Figure 1 shows a representative SEM image,
TEM image and XRD pattern of the MFI zeolite nanosponge
sample, which was synthesized using C22‑6‑6 and zeolite seeds.
The zeolite exhibited a nanosponge-like overall morphology.
The individual framework of the nanosponge had a short and
narrow nanosheet-like morphology, composed of the crystalline
MFI zeolite structure. The zeolitic nanosheets had a very
uniform thickness of 2.5 nm along the crystal b-axis, with
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Table 1. Physicochemical Properties of NS-MFI, B-MFI, and γ-Al2O3 Samples
a
b
c
d
e
f
catalyst
Si/Al
SBET (m2 g−1
)
Sext (m2 g−1
)
Vmicro (cm3 g−1
)
Vmeso (cm3 g−1
)
BAtot (μmol g−1
)
NS-MFI
B-MFI
46
48
630
320
170
460
40
0.04
0.12
0.51
0.06
0.45
167
185
g
h
h
γ-Al2O3
n/a
170
n/d
n/d
a
b
Si/Al mole ratio obtained from ICP/AES analysis. SBET is the BET surface area obtained from Ar adsorption in relative pressure range (P/P0) of
c
d
0.05−0.20. Sext is the external surface area, determined according to the t-plot method. Vmicro is the micropore volume calculated from t-plot
e
f
method. Vmeso is the mesopore volume, which is calculated by subtracting Vmicro from the total pore volume. BAtot is the concentration of Bronsted
̈
g
h
acid sites measured by 31P NMR analysis after trimethylphosphine oxide adsorption. Not applicable. Not determined.
This analysis showed a sharp distribution of pore diameters
centered at 0.55 nm, which is in good agreement with the
micropore diameter of the MFI zeolite (0.53 × 0.56 nm and
0.51 × 0.55 nm). The adsorption isotherm in the region of 0.4
< P/P0 < 0.9 was analyzed using the Barrett−Joyner−Halenda
(BJH) algorithm, which resulted in a narrow distribution of
mesopore diameters that peaked at 4 nm. The mesopore
volume of the NS-MFI zeolite was 0.5 cm3 g−1 (Table 1). This
is comparable to the mesopore volume (0.6 cm3 g−1) of
ordered mesoporous MCM-41 silica with similar pore
diameters (∼4.1 nm).25 The NS-MFI zeolite had a high
specific BET surface area (SBET = 630 m2 g−1, Table 1), and an
external surface area of 460 m2 g−1 (determined by the t-plot
method). This result was in good agreement with the large area
of mesopore walls in the highly mesoporous texture. Compared
to the mesoporous NS-MFI zeolite, B-MFI had a very small
volume of mesopores (0.06 cm3 g−1). The pore size distribution
Figure 2. Powder XRD patterns of the Co/NS-MFI, Co/B-MFI, and
Co/γ-Al2O3 catalysts.
analysis confirmed the sole presence of micropores with a very
uniform diameter of 0.55 nm (see Figure S1 in the Supporting
Information). The BET area for B-MFI was much smaller (320
m2 g−1) than that for NS-MFI, and the external surface area was
almost negligible (40 m2 g−1).
diameters over 10−20 nm. The particles were located on the
external surfaces (Figure 3). This result indicates that the
mesopores in NS-MFI were preferred locations of Co
nanoparticles. The locations may be attributed to the large
external surfaces of the zeolite nanosheets that are terminated
by numerous silanol groups. The polarity of the silanol groups
may induce interactions to retain the cobalt species.
In order to evaluate the catalytic performance in the FT
synthesis reaction, the NS-MFI zeolite was supported with 10
wt % cobalt. The cobalt supporting process consisted of
incipient-wetness impregnation of Co(NO3)2 aqueous solution,
and the subsequent calcination to convert Co(NO3)2 to a
cobalt oxide. The NS-MFI zeolite supported with Co is
designated as “Co/NS-MFI”. For comparison, B-MFI was
supported with 10 wt % Co in the same manner. This sample is
denoted as “Co/B-MFI”. A commercially available γ-alumina
sample with high specific surface area (SBET = 170 m2 g−1) was
also supported with 10% wt Co and is denoted by Co/γ-Al2O3.
Figure 2 shows the XRD patterns of the three samples
supporting 10 wt % Co species after calcination. The XRD
patterns exhibited diffraction peaks centered at 2θ = 30°, 37°,
45°, and 59°, which correspond to Co3O4 of the spinel
structure.26 No reflection peaks for other cobalt species were
detected by XRD. Thus, the XRD indicated that the cobalt
nitrate was completely converted to the spinel Co3O4 by
calcination in O2. Figure 3 shows representative TEM images of
the Co/NS-MFI, Co/B-MFI, and Co/γ-Al2O3 samples. In the
case of Co/NS-MFI, the cobalt was supported as tiny
nanoparticles (black spots). The nanoparticle diameters were
estimated using Digital Micrograph software distributed by
Gatan, using several TEM images showing more than 20 zeolite
particles in total. The distribution of the particle diameters
obtained in this manner was quite narrowly peaked at ∼4 nm.
The mode value of the particle diameters (4 nm) was the same
as the mesopore diameters in the NS-MFI zeolite. Compared to
the uniform Co nanoparticles supported on NS-MFI, the Co/
B-MFI sample exhibited a wide distribution of Co particle
A TPR analysis was performed for Co/NS-MFI, in order to
investigate the interactions between the support and the cobalt
species. This result is compared with the TPR profiles of Co/γ-
Al2O3 and Co/B-MFI in Figure 4. All of the samples exhibited
several TPR peaks over the range of 373−1173 K. Over the
TPR range, temperatures below 700 K correspond to the
reduction of Co oxide without significant interactions with
support, while the higher temperature region is attributed to
strong metal−support interactions such as electrostatic binding
and covalent bonding.27 In particular, the location of a peak
appearing at a temperature of 900 K or higher can be used as an
index for strong metal−support interactions. Such a peak is
centered at 915 K for the case of Co/B-MFI, 1000 K for Co/
NS-MFI, and 1070 K for Co/γ-Al2O3. As judged by the peak
temperature, the metal−support interactions could be assessed
to increase in the order of Co/B-MFI < Co/NS-MFI < Co/γ-
Al2O3. From this order, it was expected that the diameters of
cobalt particles would decrease in the order of Co/B-MFI >
Co/NS-MFI > Co/γ-Al2O3. However, the actual result changed
to Co/B-MFI > Co/NS-MFI ≈ Co/γ-Al2O3. That is, the
average Co particle diameters in Co/NS-MFI and Co/γ-Al2O3
were very similar, despite a marked difference in the TPR
profiles. Moreover, as mentioned above, the NS-MFI zeolite
could support Co nanoparticles with quite similar diameters to
the mesopores in the zeolite. Hence, the formation of the Co
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that of Co/B-MFI and Co/γ-Al2O3. In particular, the catalytic
performance is evaluated by focusing on the total conversion of
CO and the product selectivity for branched hydrocarbons in
the gasoline range at 493 K. The CO conversion is plotted as a
function of reaction time in Figure 5. This plot shows a distinct
Figure 5. CO conversion over Co/NS-MFI, Co/B-MFI, and Co/γ-
Al2O3, plotted as a function of time on stream. (Reaction conditions:
GHSV = 2.4 L h−1 g−1, reaction temperature = 493 K, reaction
pressure = 20 bar, and H2/CO ratio = 2.)
increase in the CO conversion at an early period, and
subsequently, a gradual decrease after reaching a maximum
point. The initial period of increase is called an “induction
period”, and its presence is typical for cobalt-based FT
catalysts.28,29 During the induction period, it is known that
cobalt metal nanoparticles generate a surface carbide species
that is catalytically more active than Co3O4 and Co(0) metal.30
Therefore, the catalyst becomes progressively more active with
increasing time. After this, the initial activation is followed by a
gradual decrease in catalytic activity, which is normally due to
the sintering of cobalt particles. As a result, the conversion plot
shows a maximum CO conversion at a certain point. Figure 5
shows that the conversion at the maximum point was 23% in
the case of Co/B-MFI. On the other hand, the cobalt catalyst
supported on Co/NS-MFI exhibited ∼4 times higher
conversion (82%), which is similar to that on Co/γ-Al2O3
shown in Figure 5 (89%). The high CO conversion over the
Co/NS-MFI catalyst means that the Co nanoparticles were
supported with optimum diameters, and were stably retained in
the mesopores of the hierarchical zeolite. So far, many studies
on FT synthesis used zeolites as catalyst supports.13−16
However, to the best of our knowledge, there have been no
other reports of high catalytic conversions that are comparable
to the γ-Al2O3-based catalysts. Compared with the Co/γ-Al2O3,
the present Co/NS-MFI catalyst exhibited a slightly lower
conversion of CO during the early period of reaction time, but
the Co/NS-MFI was deactivated more slowly (Figure 5). As a
result, the Co/NS-MFI catalyst became more active than Co/γ-
Al2O3 when used longer than 50 h. After 200 h of reaction time,
the CO conversion for Co/NS-MFI and Co/γ-Al2O3 are 74%
and 68%, respectively. The slow deactivation of Co/NS-MFI
suggested that the cobalt nanoparticles supported on the zeolite
mesopore walls were more resistant to agglomeration than the
cobalt particles located on an open surface of γ-Al2O3. To
confirm this hypothesis, the diameters of the cobalt particles in
the two catalyst samples were analyzed by high-resolution TEM
before and after the catalytic reactions. In this analysis, the
Figure 3. TEM images of (a, b) Co/NS-MFI, (c, d) Co/B-MFI, and
(e, f) Co/γ-Al2O3 catalysts. Insets of TEM images in right column are
the size distribution of cobalt nanoparticles supported on NS-MFI, B-
MFI, and γ-Al2O3, which were derived from TEM images.
Figure 4. TPR profiles of the Co/NS-MFI, Co/B-MFI, and Co/γ-
Al2O3 catalysts.
nanoparticles with uniform diameters in NS-MFI could be
attributed to the confining effect of uniform mesopores.
3.2. Fischer−Tropsch Synthesis Reaction over Co/MFI
Nanosponge. Conversion of CO. In this section, the catalytic
performance of Co/NS-MFI is presented and, compared to
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cobalt nanoparticles (4−6 nm in diameter) supported on the
NS-MFI zeolite did not show a notable change after 200 h of
reaction at 493 K (Figure S3 in the Supporting Information),
and also after 100 h of reaction 573 K (Figure S4 in the
Supporting Information). On the other hand, the Co particle
size distribution on γ-Al2O3 shifted to a larger size, even after
the reaction at 493 K.
Product Selectivity. All of the products generated from CO
by the zeolite- and alumina-based catalysts were analyzed using
GC and mass spectrometry (MS). The analysis showed that the
products consisted of CO2, oxygenate compounds, and
hydrocarbons with different carbon numbers. The gas products
were analyzed online at various reaction times. This analysis
gave the product selectivity plotted as a function of the reaction
time-on-stream (see Figure S5 in the Supporting Information).
To obtain an average value during the entire reaction period,
the selectivity was integrated over 100 h. On the other hand,
the liquid products were collected in a bottle over 100 h, and
analyzed by off-line GC to determine the average selectivity.
The product selectivity and conversion, which were averaged
over 100 h, are presented in Table 2 and the product selectivity
Figure 6. Product selectivity of Co/NS-MFI (0.5 g), Co/B-MFI (1.5
g), and Co/γ-Al2O3 (0.5 g) catalysts, which were averaged over 100 h
of the FT reaction time. (Reaction conditions: flow rate of reactant
mixture (H2:CO:Ar = 6:3:1 in moles) = 20 mL min−1, reaction
temperature = 493 K, and reaction pressure = 20 bar.)
Table 2. CO Conversion over Co/NS-MFI, Co/B-MFI, and
Co/γ-Al2O3 Samples and Resultant Product Selectivity,
Which Were Averaged over a Fischer−Tropsch (FT)
Reaction Time of 100 h
reactions. In the present work, the product selectivity of the
Co/NS-MFI was analyzed at various points of the reaction
time-on-stream. The result showed that the catalytic selectivity
did not change significantly (see Table S2 in the Supporting
Information). From the selectivity data, it is believed that the
acidity of the catalyst support did not change significantly
during the reaction period.
Co/NS-
a
Co/γ-
Co/B-
a
Co/B-
d
a
MFI
Al2O3
MFI
MFI
average CO conversion
(mmol h−1
11.2
11.3
2.6
10.5
)
When Co/NS-MFI and Co/B-MFI were compared, the Co/
NS-MFI catalyst exhibited markedly higher gasoline selectivity.
Since the Co/B-MFI catalyst exhibited a very low conversion of
CO, compared to the same amount of Co/NS-MFI, the
product selectivity of Co/B-MFI was measured using three
times more catalyst than Co/NS-MFI. This adjustment allowed
us to compare the product selectivity of the two catalysts at
similar CO conversions (i.e., 77% with Co/B-MFI, and 82%
with Co/NS-MFI). The results of this selectivity analysis
performed in this manner indicated that the gasoline selectivity
was much higher in the case of Co/NS-MFI (73.8%) than of
Co/B-MFI (40.3%). Another notable point was that Co/NS-
MFI exhibited lower selectivity to methane (7.9% with Co/NS-
MFI, 16.3% with Co/B-MFI) as well as other low-molecular-
weight hydrocarbons in the range of C2−C4 (5.4% with Co/
NS-MFI, 12.1% with Co/B-MFI). The low selectivity to
methane and short hydrocarbons of the zeolite nanosheet-
supported catalyst is desirable for gasoline production. The low
selectivity to light hydrocarbons seems to be related to the very
small crystal thickness. In the case of the NS-MFI catalyst,
b
selectivity (C%)
CO2
CH4
4.6
7.9
2.2
3.2
35.6
28.4
9.8
7.2
1.1
6.8
8.1
1.2
1.8
6.2
5.1
21.5
45.7
3.6
1.0
1.3
17.1
3.5
16.3
2.4
olefin (C2−C4)
n-paraffin (C2−C4)
olefin (C5−C11)
i-paraffin (C5−C11)
n-paraffin (C5−C11)
olefin + paraffin (C12+
8.7
9.7
14.2
6.7
16.1
11.3
12.9
27.7
2.3
20.8
20.6
7.4
)
c
others
a
Reaction conditions: 0.5 g of catalyst; gas hourly space velocity,
GHSV = 2.4 L h−1 g−1; temperature, T = 493 K; pressure, P = 20 bar;
H2/CO ratio = 2; time-on-stream, 100 h. Selectivity (C%) of
b
individual component in product mixture, which were averaged over
c
100 h of reaction time. Oxygenates and aromatic compounds, which
d
were included in the product mixture. Reaction conditions: 1.5 g of
catalyst, GHSV = 0.8 L h−1 g−1, temperature = 493 K, pressure = 20
bar, H2/CO ratio = 2, time-on-stream, 100 h.
is plotted in Figure 6. As Table 2 shows, the Co/NS-MFI and
Co/γ-Al2O3 catalysts exhibited very similar CO conversion.
Nevertheless, the product distributions were conspicuously
different. Most hydrocarbons generated over Co/NS-MFI were
in the gasoline range (C5−C11), while the hydrocarbons from
Co/γ-Al2O3 were mostly in the diesel or higher range (C12+).
The high selectivity to C5−C11 was checked by repeating the
analysis at a separate laboratory (see Table S1 and Figure S6;
experimental details are provided in the Supporting Informa-
tion). The high selectivity of the Co/NS-MFI catalyst to
gasoline-range hydrocarbons can be attributed to the presence
Bronsted acid sites are located at the external surfaces and on
̈
the micropore walls that are very close to the external surfaces.
It is therefore reasonable that the hydrocarbon intermediates
generated at these sites rapidly diffuse out before cracking
occurs excessively to light hydrocarbons. Similar phenomena
were reported for hydrocarbon reactions in MFI zeolites.22 We
propose that this explains why the cobalt catalyst supported on
the ultrathin framework of the NS-MFI zeolite could result in
such high product selectivity to the gasoline-ranged hydro-
carbons.
Regarding the product selectivity within the gasoline range, i-
paraffin selectivity increased in the order of Co/γ-Al2O3 < Co/
B-MFI < Co/NS-MFI (see Figure 6 and Table 2). High
selectivity for i-paraffins in the zeolite-supported catalysts
of strong Bronsted acid sites in the zeolite support, whereas
̈
these strong Bronsted acid sites are known to tailor long-chain
̈
hydrocarbons to shorter hydrocarbons through hydrocracking
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compared to the alumina-supported catalyst can be attributed
to the synergistic binary catalytic functions of the supported
cobalt species and the zeolite acid sites. The acid sites in zeolite
can convert linear hydrocarbon intermediates to branched
compounds through hydroisomerization reactions during the
FT synthesis reaction on the cobalt surface.31 Of the two
zeolite-based catalysts, the Co/NS-MFI exhibited higher
selectivity to i-paraffins. Recently, Kim et al.22 investigated n-
heptane hydroisomerization using MFI zeolite nanosheets
supporting 1 wt % Pt nanoparticles. They reported that the
selectivity for i-heptane increased as the framework thickness of
the MFI zeolite decreased. The selectivity increase was
attributed to the short diffusion path lengths in the zeolite
nanosheet, so that branched products could easily escape before
cracking. We checked the zeolite thickness effect of Co/NS-
MFI by performing hydroisomerization of n-octane at 493 K
(the same temperature as the FT synthesis). The result of the
hydroisomerization reaction is summarized in Table S3 in the
Supporting Information, and it indicates that the thin
nanosheet catalyst exhibited only a slightly higher conversion
of n-octane compared to the bulk zeolite (7.2% n-octane
conversion over Co/NS-MFI and 5.8% over Co/B-MFI).
However, there was a remarkable difference in the selectivity for
branched octanes (81.0% with Co/NS-MFI, and 55.1% with
Co/B-MFI). Furthermore, we checked the catalytic activity of
the Co/NS-MFI for hydrocracking and hydroisomerization of
n-hexadecane at 493 K. The result indicated that hydro-
isomerization and hydrocracking of the long-chain hydro-
carbons could happen under the reaction conditions (see Table
S4 in the Supporting Information).16
According to the ASF rule, the maximum C5−C11 fraction is
predicted to 50% when the chain growth probability is
optimized. The product selectivity of Co/NS-MFI seemed to
deviate from the ASF rule, but this can be interpreted as a result
of the aforementioned secondary reactions, i.e., hydroisomeri-
zation and hydrocracking.16,17,32 The high selectivity for
gasoline and branched hydrocarbons in Co/NS-MFI was
confirmed under various reaction conditions (temperatures
and H2/CO ratios). The results of the catalytic measurement
under these conditions are summarized in Table S5 in the
Supporting Information. As the results show, the Co/NS-MFI
catalyst exhibited a large increase in CO conversion, from 16%
to 93%, when the reaction temperature was changed from 473
K to 513 K with H2/CO = 2. The CO conversion over Co/γ-
Al2O3 also increased similarly, from 19% to 95%. However,
even at such a high conversion rate, the Co/NS-MFI catalyst
could exhibit much higher selectivity to branched hydrocarbons
in the gasoline range. When the H2/CO ratio changed from 2
to 1 at 493 K, both catalyst samples exhibited a sharp decrease
in the CO conversion (from 82% to 16% in Co/NS-MFI and
from 89% to 11% in Co/γ-Al2O3). Nevertheless, the Co/NS-
MFI catalyst still exhibited much higher selectivity (17.4%) to
the branched hydrocarbons, compared to Co/γ-Al2O3 catalyst
(8.1%).
were prepared through post-synthetic desilication of bulk
zeolite. The resultant zeolites after the generation of mesopores
were supported with ruthenium or cobalt nanoparticles. The
metal-supporting mesoporous zeolites were reported to show
high conversion of CO as well as selectivity of branched
hydrocarbons in the gasoline range, compared to the use of
bulk MFI zeolite as the metal support. However, due to the
difference in the FT reaction conditions, it was difficult to
directly compare these previous results with the Co/NS-MFI
catalyst prepared in the present study. For a direct comparison,
we performed the same desilication treatment on our bulk MFI
zeolite sample (see Supporting Information for the details of
the desilication procedure). The desilicated zeolite prepared in
this manner was denoted as “DS-MFI”. The DS-MFI zeolite
contained a fairly large volume of mesopores (0.18 cm3 g−1; see
Table S6 in the Supporting Information), but the pore size
distribution was much broader than that of NS-MFI (see Figure
S7 in the Supporting Information). Cobalt nanoparticles could
be supported on the DS-MFI zeolite with a fairly narrow
distribution of particle diameters ∼5−10 nm in size (see Figure
S8 in the Supporting Information). Initially, the CO conversion
of Co/DS-MFI catalyst increased to 83%, which was
comparable to that of Co/NS-MFI. However, after 100 h of
reaction time, the cobalt nanoparticles on DS-MFI were easily
agglomerated into particles with a wide distribution of
diameters of ∼5−20 nm. Consequently, the CO conversion
decreased to 59% (see Figure S9 in the Supporting
Information). Moreover, the DS-MFI zeolite frameworks
(∼20 nm, as judged by TEM) were much thicker than the
2.5 nm nanosheet. The Co/DS-MFI catalyst exhibited 14%
product selectivity to branched hydrocarbons in the gasoline
range. The low selectivity seemed to be due to the framework
thickness.
Recently, other types (e.g., MTW and MRE) of zeolite were
synthesized with a nanosponge morphology by the synthesis
strategy using multiammonium surfactants as SDAs.33 Such
MTW and MRE zeolite nanosponges were obtained in the
present study, following the same synthesis procedure (see the
Supporting Information). These zeolites were supported with
10% wt cobalt, for comparison with Co/NS-MFI zeolite as a
catalyst in the FT synthesis reaction. Characterization of the
synthesized zeolite samples using XRD, TEM, and Ar sorption
analysis indicated that the samples were built by a 3D
disordered assembly of 5-nm-thick zeolite frameworks (see
the TEM images in Figures S10 and S11 in the Supporting
Information). The mesoporous textures of the synthesized
MTW and MRE zeolites were very similar to that of NS-MFI.
The mesopore volumes of MTW and MRE were 0.66 cm3 g−1
and 0.51 cm3 g−1, respectively. The pore size distributions were
sharply peaked at 4.5 nm, as in the case of the MFI
nanosponge. The result from the cobalt-supporting experiment
indicated that highly mesoporous structures with uniform pore
diameters had the advantage of dispersing the cobalt nano-
particles with uniform diameters within the mesopores, similar
to the case of Co/NS-MFI (compare Figure 3 and Figure S7 in
the Supporting Information). The Co/MTW and Co/MRE
catalyst samples exhibited high average CO conversions (72.2%
and 70.5% over MTW and MRE, respectively; see Table 3),
which were comparable to the result obtained from Co/NS-
MFI. Both of the catalysts were deactivated slowly (Figure S8 in
the Supporting Information). In addition, the nanosponge
catalysts exhibited high selectivity to branched hydrocarbons in
Comparison with Other Zeolites. As shown in the previous
section, the alumina-based catalyst exhibited high CO
conversion but poor product selectivity in the gasoline range.
In contrast, the bulk zeolite-based catalyst exhibited high
gasoline selectivity but poor CO conversion. The Co/NS-MFI
catalyst had the dual advantages of both high conversion and
high selectivity. In recent years, a few other reports used
mesoporous MFI zeolites as metal catalyst supports for FT
synthesis.15−18 In other studies, the mesoporous MFI zeolites
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Company have been provided. This material is available free of
charge via the Internet at http://pubs.acs.org.
Table 3. Average CO Conversion and Product Distributions
for 100 h over Co/DS-MFI, Co/MTW, and Co/MRE
Samples
a
AUTHOR INFORMATION
■
Co/DS-
MFI
Co/
Co/
MTW
MRE
Corresponding Author
*Tel.: +82 42 350 2830. Fax: +82 42 350 8130. E-mail: rryoo@
kaist.ac.kr.
average CO conversion (mmol h−1
)
9.1
10.3
10.6
b
product distributions (C%)
CO2
1.1
3.2
1.5
Notes
CH4
12.2
6.6
13.5
7.1
11.9
8.3
The authors declare no competing financial interest.
olefin (C2−C4)
n-paraffin (C2−C4)
olefin (C5−C11)
i-paraffin (C5−C11)
n-paraffin (C5−C11)
6.1
7.5
7.3
ACKNOWLEDGMENTS
■
34.8
14.0
11.5
13.7
0.3
28.5
22.0
7.9
31.6
22.0
9.5
This work was supported by Grant No. IBS-R004-D1. The
authors are grateful to SK Innovation, for providing access to
catalysis test facilities for independent checking.
olefin + paraffin (C12+
)
9.0
7.1
c
others
1.3
0.8
a
Reaction conditions: 0.5 g of catalyst; GHSV = 2.4 L h−1 g−1;
REFERENCES
■
temperature, T = 493 K; pressure, P = 20 bar; H2/CO ratio = 2; time-
on-stream = 100 h. Selectivity (C%) of individual component in
(1) Dry, M. In Handbook of Heterogeneous Catalysis, Vol. 6; Ertl, G.,
b
Knozinger, H., Schuth, F., Weitkamp, J., Eds.; Wiley−VCH:
̈
̈
product mixture, which were averaged over 100 h of reaction time.
Weinheim, Germany, 2008; pp 2965−2994.
c
Oxygenates and aromatic compounds, which were included in the
(2) Dry, M. Catal. Today 2002, 71, 227−241.
product mixture.
(3) van Steen, E.; Claeys, M. Chem. Eng. Technol. 2008, 31, 655−666.
(4) Leckel, D. Energy Fuels 2009, 23, 2342−2358.
(5) Khodakov, A. Y.; Chu, W.; Fongarland, P. Chem. Rev. 2007, 107,
1692−1744.
the gasoline range (22% for both Co/MTW and Co/MRE; see
Table 3).
(6) Vandeloosdrecht, J.; Balzhinimaev, B.; Dalmon, J.;
Niemantsverdriet, J.; Tsybulya, S.; Saib, a; Vanberge, P.; Visagie, J.
Catal. Today 2007, 123, 293−302.
4. CONCLUSIONS
́ ́
(7) Henrici-Olive, G.; Olive, S. Angew. Chem., Int. Ed. 1976, 15, 136−
We were able to synthesize an MFI zeolite nanosponge,
following a recently developed zeolite synthesis strategy that
uses hierarchical structure-directing surfactants and seeding for
the zeolite crystallization. The zeolite nanosponge was
composed of ultrathin zeolite walls that were irregularly
interconnected into a three-dimensional mesoporous network.
The mesopore diameters were quite uniform, despite the
disordered pore arrangement. This zeolite nanosponge
exhibited the remarkable advantage of supporting cobalt
nanoparticles with uniformly controlled particle sizes by the
mesopore diameters. With optimum particle diameters, the
cobalt-supporting zeolite nanosponges could have high catalytic
performance in an FT synthesis reaction. The confined cobalt
particles exhibited high resistance to sintering. This was why
the catalyst exhibited high conversion of CO and long catalytic
lifetime. In addition, the thin zeolitic walls provided the
advantage of high selectivity to branched hydrocarbons in the
gasoline range (probably due to the diffusion effect). Recent
studies show that the present synthesis strategy can be
extended to other zeolites, including MTW and MRE. The
mesopore diameters of the zeolites can be tailored to a desired
size by choosing a surfactant with a different tail length, and
also by adding a pore-expanding agent. Such zeolite nano-
sponges may provide new opportunities as advanced catalysts
for various bifunctional catalytic applications that require both
high dispersion of metal/metal oxide nanoparticles and strong
acidity of zeolite frameworks.
141.
(8) Bezemer, G. L.; Bitter, J. H.; Kuipers, H. P. C. E.; Oosterbeek, H.;
Holewijn, J. E.; Xu, X.; Kapteijn, F.; van Dillen, A. J.; de Jong, K. P. J.
Am. Chem. Soc. 2006, 128, 3956−3964.
(9) den Breejen, J. P.; Radstake, P. B.; Bezemer, G. L.; Bitter, J. H.;
Frøseth, V.; Holmen, A.; de Jong, K. P. J. Am. Chem. Soc. 2009, 131,
7197−7203.
(10) Storsater, S.; Totdal, B.; Walmsley, J.; Tanem, B. J. Catal. 2005,
236, 139−152.
(11) Sun, B.; Qiao, M.; Fan, K.; Ulrich, J.; Tao, F. F. ChemCatChem.
2011, 3, 542−550.
(12) Zhang, Q.; Kang, J.; Wang, Y. ChemCatChem. 2010, 2, 1030−
1058.
(13) Zhang, Q.; Cheng, K.; Kang, J.; Deng, W.; Wang, Y.
ChemSusChem 2014, 7, 1251−1264.
(14) Bessell, S. Appl. Catal., A 1993, 96, 253−268.
(15) Sartipi, S.; Parashar, K.; Makkee, M.; Gascon, J.; Kapteijn, F.
Catal. Sci. Technol. 2013, 3, 572−575.
(16) Sartipi, S.; Parashar, K.; Valero-Romero, M. J.; Santos, V. P.; van
der Linden, B.; Makkee, M.; Kapteijn, F.; Gascon, J. J. Catal. 2013,
305, 179−190.
(17) Kang, J.; Cheng, K.; Zhang, L.; Zhang, Q.; Ding, J.; Hua, W.;
Lou, Y.; Zhai, Q.; Wang, Y. Angew. Chem., Int. Ed. 2011, 50, 5200−
5203.
(18) Cheng, K.; Kang, J.; Huang, S.; You, Z.; Zhang, Q.; Ding, J.;
Hua, W.; Lou, Y.; Deng, W.; Wang, Y. ACS Catal. 2012, 2, 441−449.
(19) Choi, M.; Na, K.; Kim, J.; Sakamoto, Y.; Terasaki, O.; Ryoo, R.
Nature 2009, 461, 246−249.
(20) Na, K.; Park, W.; Seo, Y.; Ryoo, R. Chem. Mater. 2011, 23,
1273−1279.
(21) Jo, C.; Cho, K.; Kim, J.; Ryoo, R. Chem. Commun. 2014, 50,
4175−4177.
ASSOCIATED CONTENT
* Supporting Information
■
S
(22) Kim, J.; Kim, W.; Seo, Y.; Kim, J.-C.; Ryoo, R. J. Catal. 2013,
301, 187−197.
Detailed procedures for post-synthetic desilication of MFI, and
the synthesis of MTW and MRE zeolite nanosponges have
been provided. Additional results from the characterization of
the FT catalysts and the investigation of FT synthesis reaction
have been provided. The catalytic results by SK Innovation
(23) Seo, Y.; Cho, K.; Jung, Y.; Ryoo, R. ACS Catal. 2013, 3, 713−
720.
(24) Lunsford, J. H.; Rothwell, W. P.; Shen, W. J. Am. Chem. Soc.
1985, 107, 1540−1547.
3926
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ACS Catalysis
Research Article
(25) Kruk, M.; Jaroniec, M.; Kim, J. M.; Ryoo, R. Langmuir 1999, 15,
5279−5284.
(26) Li, X.; He, J.; Meng, M.; Yoneyama, Y.; Tsubaki, N. J. Catal.
2009, 265, 26−34.
(27) Arnoldy, P.; Moulijn, J. A. J. Catal. 1985, 93, 38−54.
(28) Iglesia, E.; Soled, S. L.; Fiato, R. A. J. Catal. 1992, 137, 212−224.
(29) Song, D.; Li, J. J. Mol. Catal. A: Chem. 2006, 247, 206−212.
(30) Davis, B. H. Fuel Process. Technol. 2001, 157−166.
(31) Bessell, S. Appl. Catal., A 1995, 126, 235−244.
(32) Li, X.-G.; Liu, C.; Sun, J.; Xian, H.; Tan, Y.-S.; Jiang, Z.; Taguchi,
A.; Inoue, M.; Yoneyama, Y.; Abe, T.; Tsubaki, N. Sci. Rep. 2013, 3,
2813−2818.
(33) Kim, W.; Kim, J.-C.; Kim, J.; Seo, Y.; Ryoo, R. ACS Catal. 2013,
3, 192−195.
3927
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