3D ordered mesoporous Fe-KIT-6 catalysts for methylcyclopentane (MCP) conversion and carbon dioxide (CO2) hydrogenation for energy and environmental applications

Article abstract of DOI:10.1016/j.apcata.2015.03.032

The direct hydrothermal synthesis of Fe-KIT-6 mesoporous materials with Ia3d symmetry and high iron loadings is reported for the first time. The Fe-KIT-6 mesoporous materials were characterized by XRD, N₂ adsorption/desorption isotherms, SEM, FT-IR, XPS and EPR spectroscopy. The physico-chemical characterization results show that all of the samples have well-ordered cubic mesostructures and that the structural integrity is preserved for n_Si/n_Fe ratios as high as 10. It was found that most of the iron ions exist as isolated framework species, but for Fe-KIT-6 with an n_Si/n_Fe ratio of 10, the presence of extra-framework species/small iron oxide clusters cannot be excluded. The catalytic performances of these materials were tested for carbon dioxide (CO₂) hydrogenation and methylcyclopentane (MCP) conversion. The catalytic results show that their catalytic activity increases significantly with increasing iron content. For the MCP conversion, the ring-opening selectivity can be improved by increasing the density of isolated iron atom sites at low reaction temperatures. For the CO₂ hydrogenation, the methanation selectivity can be improved by increasing the iron active site density and employing a high reaction temperature. Specifically, the high density of iron sites at high catalyst loadings promotes the methanation reaction at the expense of the RWGS (reverse water gas shift) reaction. Thus, the Fe-KIT-6 materials appear to be suitable catalysts for MCP conversion at low temperatures and CO₂ hydrogenation at high temperatures.

Full text of DOI:10.1016/j.apcata.2015.03.032

Accepted Manuscript
Title: 3D ordered mesoporous Fe-KIT-6 catalysts for
methylcyclopentane (MCP) conversion and carbon dioxide
(CO2) hydrogenation for energy and environmental
applications
Author: R. Merkache I. Fechete M. Maamache M. Bernard P.
Turek K. Al-Dalama F. Garin
PII:
S0926-860X(15)00218-5
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2015.03.032
APCATA 15322
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
10-12-2014
23-3-2015
24-3-2015
Please cite this article as: R. Merkache, I. Fechete, M. Maamache, M. Bernard,
P. Turek, K. Al-Dalama, F. Garin, 3D ordered mesoporous Fe-KIT-6 catalysts for
methylcyclopentane (MCP) conversion and carbon dioxide (CO2) hydrogenation
for energy and environmental applications, Applied Catalysis A, General (2015),
http://dx.doi.org/10.1016/j.apcata.2015.03.032
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3D ordered mesoporous Fe-KIT-6 catalysts for methylcyclopentane (MCP)
conversion and carbon dioxide (CO2) hydrogenation for energy and
environmental applications
R. Merkachea, I. Fechetea*, M. Maamacheb, M. Bernardc,d, P. Turekc,d, K. Al-Dalamae, F.
Garina
a Institut de Chimie et Procédés pour l’Energie, l’Environnement et la Santé - ICPEES, UMR
7515 CNRS, Université de Strasbourg, 25 rue Becquerel, 67087 Strasbourg Cedex 2, France
b Laboratoire de Physique Quantique et Systèmes Dynamiques, Département de Physique,
Université Ferhat Abbas Sétif 1, Sétif 19000, Algeria
c Institut de Chimie, UMR 7177 CNRS - Université de Strasbourg, 1 rue Blaise Pascal, 67008
Strasbourg cedex, France
d Fondation IcFRC International Center for Frontier Research in Chemistry, 8 allée Gaspard
Monge, F-67000 Strasbourg, France
e Petroleum Refining Department, Petroleum Research Center, Kuwait Institute for Scientific
Research, P.O. Box 24885, Safat 13109, Kuwait
This article is part of the special issue dedicated to the scientific work of Mr. J.C. Védrine at
his 75th birthday.
Corresponding author. Tel.: +33 (0)3 68852756; fax: +33 (0)368852761.
E-mail address: ifechete@unistra.fr (I. Fechete).
Abstract
The direct hydrothermal synthesis of Fe-KIT-6 mesoporous materials with Ia3d symmetry
and high iron loadings is reported for the first time. The Fe-KIT-6 mesoporous materials were
characterized by XRD, N2 adsorption/desorption isotherms, SEM, FT-IR, XPS and EPR
spectroscopy. The physico-chemical characterization results show that all of the samples have
well-ordered cubic mesostructures and that the structural integrity is preserved for nSi/nFe
ratios as high as 10. It was found that most of the iron ions exist as isolated framework
species, but for Fe-KIT-6 with an nSi/nFe ratio of 10, the presence of extra-framework
species/small iron oxide clusters cannot be excluded. The catalytic performances of these
materials were tested for carbon dioxide (CO2) hydrogenation and methylcyclopentane (MCP)
conversion. The catalytic results show that their catalytic activity increases significantly with
increasing iron content. For the MCP conversion, the ring-opening selectivity can be
improved by increasing the density of isolated iron atom sites at low reaction temperatures.
For the CO2 hydrogenation, the methanation selectivity can be improved by increasing the
iron active site density and employing a high reaction temperature. Specifically, the high
density of iron sites at high catalyst loadings promotes the methanation reaction at the
expense of the RWGS (reverse water gas shift) reaction. Thus, the Fe-KIT-6 materials appear
to be suitable catalysts for MCP conversion at low temperatures and CO2 hydrogenation at
high temperatures.
Keywords: Fe-KIT-6; high iron loading; methylcylopentane; carbon dioxide; methane.
1. Introduction
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Different forms of iron oxides have long been used in environmental engineering due
to their ability to degrade and treat a wide variety of toxic pollutants and hazardous chemicals
in the soil, air, and water [1-4]. A meaningful assessment of the importance of iron oxide
catalysts over time should be performed. Iron oxide solids play an important role in all areas
of catalysis, especially in energy and environmental applications [5, 6]. Iron oxides have been
shown to be very active for oxidation reactions [7-10], water splitting [11,12], the water-gas
shift reaction [13], the Fischer-Tropsch reaction [14, 15], the Prins reaction and aldol
condensation [16, 17], aromatic hydrocarbon conversion [18], the selective oxidation of
benzene to phenol using N2O as the oxidant [19, 20]. In particular, mesoporous iron catalysts
have been widely studied because of their potential to catalyze various reactions efficiently
and selectively [21-25]. However, developing highly active and selective reaction systems is a
significant challenge in all chemistry fields and modern technologies [26-30]. The activity and
selectivity of porous iron catalysts are influenced by the iron loading, location of the iron
species (framework or extra-framework), nature of the iron species, and stoichiometry and
oxidation state of the Fe atoms in the iron oxide [21-25, 31-33]. These active species comprise
different types of catalytic sites, which influence the catalytic activity and selectivity.
Following a careful analysis of previous studies, we ascertained that isolated iron sites in
porous solid frameworks are required for high activity and selectivity. It is very challenging to
prepare uniformly distributed, isolated sites in mesoporous catalysts. Mesoporous catalysts
are of great interest because of their highly ordered pore structure, high specific surface area,
and tailorable pore size, framework, and surface properties [34-37]. Of the various
mesoporous materials available, cubic ordered mesoporous KIT-6 exhibits high hydrothermal
and thermal stability due to its large pore size, which facilitates mass transfer; thick pore
walls; high surface area, which allows for a high concentration of active sites per material
mass; and high hydrothermal stability. This structure has received much attention due to its
potential for application in catalysis, separations and adsorption [38-43]. The cubic network is
thought to provide a highly opened porous structure, which allows guest species to adsorb in
the pores or diffuse through the pore channels without blocking the pores. It is known that the
location and nature of the iron (or other metal) species in porous catalysts depend on the
preparation method and iron loading [16-18, 44]. Several studies have investigated the
incorporation of metal ions into KIT-6 using solely post-synthesis methods. However, these
methods can allow extra-framework iron species to form by aggregation during the
preparation or during heat treatments before and after the catalytic tests. These extra-
framework species are irregularly distributed iron active sites that might block the pore
channels, leading to a decrease in the specific surface area, pore volume, and pore diameter,
which negatively affects the activity and selectivity. Under certain preparation conditions, the
post-synthesis route leads to the destruction of the mesoporous structure, and the iron ions
might undergo some leaching, resulting in a decrease in the catalyst efficiency and a short
catalyst lifetime. Additionally, the iron atoms introduced by post-synthesis methods are often
octahedrally coordinated instead of tetrahedrally coordinated, which is desirable for high
catalyst selectivity.
To overcome these problems, a direct hydrothermal synthesis approach can be used to
prepare tetrahedrally coordinated single-site iron centers. Therefore, Fe-KIT-6 materials with
high iron loadings (nSi/nFe between 60 and 10) were prepared by direct hydrothermal synthesis
to obtain a precise arrangement of isolated, tetrahedrally coordinated iron atoms. Fe-KIT-6
was previously prepared by direct hydrothermal synthesis, but it had a low iron loading
(nSi/nFe of 50) [45, 46]. This result is expected because the difficulties in forming Fe–O–Si
groups under strongly acidic conditions hinders the direct synthesis of mesoporous materials
with high iron loadings via hydrothermal methods. These conditions do not facilitate the
formation of ordered mesostructures because the iron ions do not exist in the oxo form and
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cannot interact with the framework to form Si-O-Fe bonds. Because of this difficulty, the
synthesis of Fe-KIT-6 with a high iron loading and ordered mesostructure is challenging.
To synthesize Fe-KIT-6 with a high iron content and create isolated, ordered active
sites under acidic conditions, the effects of the nSi/nFe ratio, synthesis temperature, and
synthesis time were studied. The calcined Fe-KIT-6 mesoporous samples were characterized
by SEM, XRD, N2 sorption measurements, chemical analysis, XPS, FT-IR spectroscopy, and
EPR spectroscopy. To our knowledge, the use of Fe-KIT-6 with high iron loadings to catalyze
MCP ring opening and CO2 hydrogenation has not been reported in the literature.
MCP ring opening, which is often used as a model reaction to examine the structural
sensitivity of hydrocarbon conversion catalyzed by noble metals, is an important reaction in
the petrochemical industry for improving the cetane number of diesel fuels [47-54]. To
achieve a high cetane number, the desired products of MCP ring opening are n-hexane (n-H),
2-methylpentane (2-MP) and 3-methylpentane (3-MP) [47-54]. The distribution of the ring-
opening products is sensitive to the type of metal, spatial distribution of the metal particles,
nature of the support and experimental conditions. However, several excellent reports have
demonstrated the catalytic efficiency of noble metals in the MCP ring-opening reaction and
other naphthenic molecules [55-59]. Despite the effectiveness of supported noble metals,
which efficiently catalyze MCP conversion with atom efficiency, the high cost and limited
availability of precious metals restrict their wide application. A practical solution is to find a
clean, efficient heterogeneous catalyst to replace noble metal catalysts [6, 36, 60]. It is
cheaper to employ base metal oxide catalysts for environmental and economic reasons, and
they exhibit good catalytic performance and are competitive with noble metal catalysts. The
development of new efficient catalysts is crucial. Mesoporous materials are good candidates
for MCP conversion because they can transform MCP into high-cetane-number products [36,
61, 62].
CO2 hydrogenation is another crucial reaction for energy and environmental reasons
[6]. In our modern society, energy is based on the combustion of carbonaceous fuels, mainly
fossil fuels [48, 55-59, 63]. The emissions of pollutants (NOx, SOx) and greenhouse gases
such as carbon dioxide (CO2) from fossil fuel burning in various stationary and mobile energy
systems have become a major global problem. Although photosynthesis and food production
depends on atmospheric CO2 as a carbon source, concerns about the role of CO2 in global
climate change are increasing, thus stimulating much interest in reducing CO2 emissions
worldwide. Because of increasingly stringent environmental and economic regulations, the
foremost challenge is to develop greener processes that utilize CO2. CO2 hydrogenation into
methane or synthetic natural gas (SNG) is an important way to achieve this goal. The
synthetic fuels produced by CO2 conversion can be used in current hydrocarbon-based
automobiles and transportation systems. A large number of excellent studies on various metal
catalysts have appeared in the literature [63-66], but supported nickel catalysts are the most
widely studied. Their higher activities and selectivities to methane have been attributed to
various factors, including the nature of the support, nature of the metal, amount of metal and
dispersion. However, CO2 is kinetically and thermodynamically stable; thus, CO2 conversion
reactions are endothermic and require the use of efficient catalysts to obtain high yields.
Therefore, developing an appropriate catalyst for carbon dioxide methanation is of great
interest. However, CO2 hydrogenation by iron catalysts has not received much attention [67,
68]. Due to their low cost and high availability, iron catalysts, as namely Fe-KIT-6, were
tested for this reaction. This work aims to elucidate the nature of the isolated active sites to
understand their catalytic activity in CO2 hydrogenation.
2. Experiments
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2.1. Materials
Pluronic P123 [poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) triblock
copolymer, EO20PO70EO20, MW 5800, Sigma-Aldrich] and 1-butanol (BuOH, 99.5%, Fluka)
were used as the structure-directing agents. Tetraethyl orthosilicate (Si(OC2H5)4, TEOS, 98%,
Sigma-Aldrich) and iron (III) acetylacetonate (Fe(acac)3, 99%, Aldrich) were used as the
silicon and iron precursors, respectively. Hydrochloric acid (HCl, 35%, Sigma Aldrich) was
used as the acid source. All chemicals were used as received without further purification.
Millipore water was used in all the experiments. Methylcyclopentane (MCP) was supplied by
Aldrich (purity > 99.99%). Hydrogen, helium, nitrogen, carbon dioxide and air were
purchased from Air Liquide.
2.2. Synthesis of Fe-KIT-6 mesoporous materials
Fe-KIT-6 mesoporous materials with different nSi/nFe ratios were prepared by an adapted
version of a direct hydrothermal synthesis procedure for Si-KIT-6 [62, 69]. The synthesis
procedure involved adding 3 g of the amphiphilic triblock copolymer Pluronic P123 and
108.5 g of distilled water to 5.9 g of conc. HCl (35%). When P123 was completely dissolved,
3 g of butanol were added under stirring at 35°C. After 1 h of stirring, 6.45 g of tetraethyl
orthosilicate and the required amount of Fe(acac)3 in 1.5 ml ethanol were added dropwise to
the clear homogeneous solution. The molar composition of the gel synthesis mixture was: 1.0
TEOS: (0.017-0.10) Fe: 0.017 P123: 1.83 HCl: 195 H2O:1.93 BuOH. The resulting gel was
stirred at 35°C for 24 h and subsequently warmed at 100°C and 130°C for 24-72 h under
static conditions in a closed polypropylene bottle. The products obtained from the
hydrothermal treatment were filtered and dried for 30 h at room temperature. To remove the
template, the dried materials were extracted in an ethanol-HCl mixture and then calcined in a
programmable oven for 5 h in air (25-550°C; heating rate 1°C/min).
2.3. Catalyst characterization
2.3.1. Elemental analysis
The nSi/nFe molar ratios of the solids were determined by inductively coupled plasma atomic
emission spectroscopy (ICP-AES) at the Service Central d’Analyse of CNRS-Solaize.
2.3.2. X-ray diffraction (XRD)
Powder XRD measurements were performed in an ambient atmosphere using a Bruker D8
Advance powder diffractometer operating in the reflection mode with CuKα (λ = 1.5418 Å)
radiation, a 40 kV beam voltage and a 40 mA beam current. The samples were scanned from
0.5° to 4° for the small-angle measurements and from 10° to 90° for the wide-angle
measurements using a step size of 0.02° and step time of 10 s.
2.3.3. N2 adsorption–desorption isotherms
The textural properties, including the BET (Brunauer–Emmett–Teller) specific surface area
(SBET), specific pore volume (Vp) and pore diameter (Dp), were determined from low-
temperature N2 adsorption–desorption measurements collected using an ASAP 2010
Micrometrics apparatus. Prior to the analysis, the samples were degassed under vacuum at
150 °C until the static pressure was less than 6.6×10−4 Pa. The specific surface area was
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calculated from the N2 sorption isotherm using the BET equation and taking into account the
cross-sectional area of a physically adsorbed N2 molecule (0.1620 nm2). The pore diameter
and pore size distributions were calculated from the desorption branch of the isotherms using
the Barrett–Joyner–Halenda (BJH) method. The total pore volume was calculated from the
amount of nitrogen adsorbed at P/P0 = 0.98, assuming that adsorption on the external surface
was negligible compared to adsorption within the pores.
2.3.4. Scanning electron microscopy (SEM)
Scanning electron microscopy (SEM) images were obtained using a Philips XL 30 FEG
electron microscope operating at 200 kV. The sample was dispersed as a thin film on a holly
carbon grid and sputtered with a thin gold film (5 nm thick) to minimize charging effects.
2.3.5. Fourier transform infrared (FT-IR) spectroscopy
The Fourier transform infrared (FT-IR) spectra of the samples were recorded in the mid-
infrared (IR) region (4000–400 cm−1) using a Nicolet Impact 400 spectrometer. The resolution
was 4 cm−1, and 128 scans were collected using the KBr pellet technique. Approximately 100
mg of dry KBr were ground with 10 mg of the sample to obtain a homogeneous mixture,
which was subsequently dried at 100 °C. The fine powder was then pressed into a transparent
thin pellet at 5 tons·cm−2 and used for the IR spectral measurements.
2.3.6. X-ray photoelectron spectroscopy (XPS)
XPS spectra were recorded on a Multilab 2000 spectrometer equipped with Al(Kα) X-ray
radiation (1486.6 eV) at an anode current of 20 mA and 10 keV. The XPS analyses were
performed in a static system, and the base pressure during the analysis was 10-9 Pa. The
binding energies obtained from the Fe, O, and Si photoelectron peaks were corrected for
charging effects by referencing them to the C 1s peak at 284.6 eV. In addition, the Fe and Si
2p peaks of the catalysts were used to quantitatively calculate the atomic ratios of the
elements, assuming that the compositions of the samples were uniform throughout the area
probed by XPS. To calculate the 2p peak areas, the background was subtracted using the
procedure suggested by Shirley.
2.3.7. Electron paramagnetic resonance (EPR) measurements
The electron paramagnetic resonance (EPR) spectra were recorded on a Bruker ESP-300E
spectrometer (microwave frequency of approximately 9.5 GHz). The EPR spectra were
recorded at room temperature and -163°C at the X-band (n ~ 9.33 GHz), and they were
normalized to similar spectrometer settings (microwave attenuation, modulation amplitude,
sensitivity) to allow for relative scaling in the graph. The magnetic field was calibrated with a
proton resonance meter, and tetracyanoethylene (geff = 2.0077) was used as a reference. The
magnetic field was measured with respect to the standard 2,2-diphenyl-1-picrylhydrazyl
hydrate (DPPH).
2.4. Catalytic testing
2.4.1. Methylcyclopentane (MCP) conversion
Methylcyclopentane (MCP) was reacted under atmospheric pressure in the temperature range
of 200-500°C using a pulse method. Prior to the catalytic tests, the catalysts were reduced in
situ under an H2 flow (40 ml/min) for 4 h at 500°C (heating rate 5°C/min). The gas flow used
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for the catalytic tests was fixed at 40 cm3·min-1. The catalyst mass was 200 mg, and the
volume of MCP injected into the reactor was 5 μl. The C1-C6 products were analyzed by on-
line gas chromatography (GC-2010 Plus, Shimadzu) using a capillary column and flame
ionization detector (FID). The experiments were repeated several times to ensure the
reproducibility of the obtained data. It should be noted that the preliminary experiments were
performed at 400 °C to determine the surface catalyst deactivation rate. In this case, the mean
value of pulses 2-4 was considered.
2.4.2 Carbon dioxide (CO2) hydrogenation
The catalytic carbon dioxide methanation tests were conducted in a tubular, continuous-flow,
fixed-bed quartz reactor (6 mm i.d., Vinci Technology) under atmospheric pressure in the
temperature range from 250 to 500°C. The quartz tube reactor, which contained 60 mg of the
catalyst, was placed inside the tubular furnace. The catalyst samples were reduced at 350°C
for 2 h under a hydrogen flow of 50 ml·min-1. The reduced catalysts were then cooled under
an H2 flow to the specified temperature. The temperature was measured using a thermocouple
inserted into the catalyst bed and was monitored by a temperature programmable controller
(Vinci Technology). All gases were controlled by calibrated mass flow controllers (Brooks).
The feed gas mixture, which was flowed over the catalysts, consisted of CO2 (10.0 vol%), H2
(40.0 vol%), and N2 (50.0 vol%). The catalytic CO2 hydrogenation conversion and selectivity
data were obtained from repeated experiments at the specified temperature over 120 min. The
gas products were monitored using an on-line micro-GC (SRA Instruments).
3. Results and discussion
The effects of various parameters on the direct hydrothermal synthesis of mesoporous Fe-
KIT-6 samples with cubic Ia3d symmetry were investigated. In particular, the hydrothermal
synthesis temperature, synthesis time, and nSi/nFe ratio, which can influence the degree of
heteroatom insertion and the structural and textural properties of the material, were studied.
3.1. Effect of the synthesis temperature
The synthesis temperature was varied from 100 to 130°C for 24 h to investigate the textural
and structural properties of the samples. The nSi/nFe molar ratio of the synthesis gel was fixed
at 30.
The structural ordering of the calcined Fe-KIT-6 (nSi/nFe=30) sample was analyzed by
XRD, and the results are shown in Fig. 1 b,f. The XRD reflection peaks are well-defined and
indexed to the (211) and (220) reflections of a 3D cubic mesostructure with Ia3d symmetry.
The small-angle XRD patterns of the Fe-KIT-6 series are somewhat similar to that of Si-KIT-
6 [62, 69], suggesting that the mesostructures have similar ordered arrangements. For the Fe-
KIT-6 sample synthesized at 130°C (Fig. 1f), the XRD reflection peaks are more intense, and
they shift to lower 2θ values, which is attributed to an increase of the unit cell parameter
(Table 1). Clearly, the structural ordering is maintained at this temperature, and the results are
consistent with those for Si-KIT-6 [62, 69], i.e., the unit cell parameter increases when the
synthesis temperature is increased from 100 to 130°C. No typical Fe2O3 XRD peaks were
observed for any of the samples (not shown). The N2 adsorption-desorption isotherms shown
in Fig. 2 (b, f) are type IV and exhibit the characteristic hysteresis loops of the Si-KIT-6
structure [69]. The position of the capillary condensation step for the sample synthesized at
130°C (Fig. 2f) shifts to a higher relative pressure, and the amount of N2 adsorbed also
increases with the synthesis temperature. The textural properties obtained from the nitrogen
isotherms of Fe-KIT-6 prepared at two different temperatures are summarized in Table 1. A
comparison of the data shows that the sample synthesized at 130°C has a slightly higher
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mesopore volume, higher unit cell parameter and larger mesopore diameter than that prepared
at 100°C, whereas the surface area and pore wall thickness of the 130°C sample are smaller
than those of the 100°C sample. This behavior might be attributed to the surfactant properties
because the hydration of the methyl groups in both the hydrophilic PEO and hydrophobic
PPO blocks is temperature dependent [70]. It is expected that the copolymer block size
increases with increasing synthesis temperature because at higher reaction temperatures, the
length of the hydrophobic PPO block increases due to the interactions between these blocks,
and the hydrophilicity of PEO decreases, making it more hydrophobic than PPO [70]. The
nSi/nFe ratio determined by chemical analysis shows that introducing iron into the structure by
direct hydrothermal synthesis is difficult. Moreover, the nSi/nFe ratios of the samples prepared
at 100°C are similar to those of the samples synthesized at 130°C. These results indicate that
the synthesis temperature does not affect the amount of iron species incorporated into the
silica walls.
Fig. 1.
Fig. 2.
Table 1.
3.2. Effect of the synthesis time
The condensation synthesis time was varied from 24 to 72 h under static conditions at 100°C
to investigate its effect on the structural and textural properties of the resulting materials. The
nSi/nFe molar ratio in the synthesis gel was fixed at 30. To monitor the structural and textural
changes, XRD and N2 sorption analyses were performed. As shown in the XRD data in Fig. 1,
all samples exhibit the characteristic peaks of the Ia3d symmetry group, indicating a high
degree of mesoscopic cubic ordering. The peak intensities of the samples synthesized over 24
h (Fig. 1b) are slightly larger than those of the samples synthesized over 48 h (Fig.1d) and 72
h (Fig. 1e). The large peak in the XRD pattern for the Fe-KIT-6 synthesized over 24 h might
result from a highly organized framework with uniformly packed iron ions. The unit cell
parameter increases from 21.06 to 21.81 nm as the hydrothermal treatment time increases
from 24 to 72 h (Table 1). No crystalline or segregated iron phases are observed in any of the
samples by XRD (not shown). Fig. 2 presents the N2 adsorption-desorption isotherms for Fe-
KIT-6 synthesized over 24 (Fig. 2b), 48 (Fig. 2d), and 72 h (Fig. 2e). All the samples have
type IV isotherms with type H1 hysteresis loops according to the IUPAC classification, which
is typical of mesoporous structures. The isotherms of the three samples are very similar, with
a steep increase in the amount of N2 adsorbed at P/P0 = 0.7-0.8 due to capillary condensation
in the mesopores. However, some differences can be observed. The relative pressure at which
capillary condensation is observed increases with an increase in the hydrothermal treatment
time from 24 to 72 h. Consequently, the pore diameter also increases. These results indicate
that the mesopore diameter increases as the hydrothermal treatment time increases, which
leads to concomitant decreases in the mesopore wall thickness and specific surface area.
Accordingly, the results reported in Table 1 show that the surface area decreases gradually
from 734 to 668 m2/g with increasing hydrothermal synthesis time. These results are caused
by variations in the PEO-PPO self-assembly behavior mainly induced by changes in the
intermolecular interactions over time.
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3.3. Effect of the nSi/nFe ratio
Fe-KIT-6 with nSi/nFe molar ratios between 60 and 10 were synthesized at 100°C for 24 h.
These synthesis conditions were chosen to obtain large pores and wall thicknesses to improve
the stability of the catalysts
The morphologies of the Fe-KIT-6 catalysts with different nSi/nFe ratios were analyzed
using SEM (Fig. 3). The SEM images of the Fe-KIT-6 samples with low (nSi/nFe=60) and high
iron (nSi/nFe=10) loadings are similar, suggesting that incorporating a large amount of iron
into the structure does not affect strongly the catalyst morphology. All the catalysts are
composed of dense, rock-like aggregates. The particles are not homogeneously distributed,
which is typical of three-dimensional cubic mesoporous KIT-6. One fraction of the particles
has an undefined morphology, although the edges are apparent, and truncated, rod-like
particles and spherical particles are also observed.
Fig.3.
The nSi/nFe molar ratios of the calcined materials are listed in Table 1 and compared to
the nSi/nFe values of the synthesis gel. The nSi/nFe molar ratios in the calcined materials,
obtained from the ICP and XPS analysis, are higher than those in the synthesis gel. However,
a slight but systematic increase in the Si/Fe ratio, from integral intensities of Si 2p and Fe 2p
photoelectron spectra, was observed compared with the chemical analysis. These results can
be attributed to the solubility of Fe in an acid medium, which results in a lower amount of Fe
being incorporated into the framework.
Small-angle XRD measurements were used to study the pore ordering of the Fe-KIT-6
samples. Fig. 1 shows the small-angle powder X-ray diffractogram of Fe-KIT-6 samples with
different nSi/nFe ratios after calcination. All the samples have two well-resolved reflections,
(211) and (220), which are associated with the Ia3d symmetry of the cubic ordered pore
structure. The small-angle XRD patterns of the Fe-KIT-6 (nSi/nFe=60) samples have strong
first-order reflections, which is characteristics of KIT-6 materials [69], confirming that the
cubic structure is preserved after the addition of iron. However, the first-order d211 peak
intensities of the Fe-KIT-6 (nSi/nFe=30) (Fig. 1b) and Fe-KIT-6 (nSi/nFe=10) (Fig. 1a) samples,
which have higher iron contents, decrease relative to that of Fe-KIT-6 (nSi/nFe=60) (Fig. 1c).
These results indicate that the reflections are not highly ordered and these samples are
structurally distorted due to interactions between the iron and silica species when iron is
incorporated into the framework. X-ray absorption of the iron species might also contribute to
this effect [60]. Increasing the amount of iron in the materials leads to a shift in the reflection
peak position of the Fe-KIT-6 (nSi/nFe=10) catalyst to a lower angle than that of Fe-KIT-6
(nSi/nFe=60). The shift in the d211 peak to a lower angle and its broadening with increasing iron
content reveal that the lattice expands and the d-spacing increases when Fe is incorporated
into the KIT-6 framework. As shown in Table 1, the unit cell parameter increases from 4.07
for Fe-KIT-6 (nSi/nFe=60) to 4.45 for Fe-KIT-6 (nSi/nFe=10) as more iron is introduced into the
KIT-6 framework. The increase in the unit cell parameter with decreasing nSi/nFe ratio is
consistent with tetrahedrally coordinated iron atoms in the KIT-6 silica framework. It is
expected that the unit cell parameter will increase when metal cations are incorporated into
the structure because the ionic radius of Fe is larger than that of Si (rFe3+ = 6.3 nm, rSi4+ = 4.0
nm), resulting in a longer Fe-O bond than Si-O bond. Thus, the larger ionic radius and longer
Fe–O bond lead to an increase in the unit cell parameter (a0) (Table 1). Similar results have
also been reported for metal-substituted mesoporous materials [39,40,45,46]. The crystalline
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iron phases are not detected in the wide-angle X-ray diffraction patterns (not shown) of Fe-
KIT-6 (nSi/nFe=60), Fe-KIT-6 (nSi/nFe=30) and Fe-KIT-6 (nSi/nFe=10) catalysts, suggesting that
either the metal species are homogeneously dispersed on the support or their compositions are
below the X-ray scattering coherence length. Thus, it can be inferred that Fe exists as a
framework species and/or Fe2O3 particles, which are very small (less than 4.5 nm). The N2
adsorption–desorption isotherms of calcined catalysts with different nSi/nFe ratios are shown in
Fig. 2. The catalysts have type IV isotherms, which is characteristic of ordered mesoporous
materials according to the IUPAC classification. The samples exhibit an H1-type hysteresis
loop and a sharp nitrogen capillary condensation step in the P/P0 range of 0.7–0.8, which is
typical for large, uniform mesopores with a narrow pore size distribution. A parallel hysteresis
loop, which is characteristic of large, highly ordered mesopores with a uniform pore size
distribution, is observed for the Fe-KIT-6 (nSi/nFe=60) (Fig. 2c) and Fe-KIT-6 (nSi/nFe=30)
(Fig. 2b) samples. These results clearly indicate that the catalysts have a uniform textural
porosity. However, the height of the Fe-KIT-6 (nSi/nFe=10) (Fig. 2a) hysteresis loop is smaller
due to high metal loading in the mesopores. The inflection point shifts slightly to higher
relative pressures as more metal is incorporated in the structure, indicating that the pore size
increases. The specific surface area (SBET), cumulative pore volume (Vp) and pore diameter
(Dp) of the Fe-KIT-6 catalysts are listed in Table 1. The results in this table indicate that the
porosities of the Fe-KIT-6 materials are comparable with surface areas in the range of 435–
815 m2·g−1, pore diameters between 6.2 and 6.5 nm and pore volumes between 0.83 and 1.13
cm3·g−1. Excepting the pore diameters, a gradual decrease in these parameters is observed
with increasing heteroatom content for the 3D cubic mesoporous KIT-6 samples. The smaller
values for the Fe-KIT-6 (nSi/nFe=10) sample might be due to the decrease in its structural
ordering. However, the reduction in the pore volume with increasing Fe content might be due
to obstruction of some of the Fe-KIT-6 mesoporous channels with iron oxide species during
calcination. It should be noted that these parameters do not vary much with iron content for
the Fe-KIT-6 (nSi/nFe=60) and Fe-KIT-6 (nSi/nFe=30) samples. These parameters only decrease
significantly for the Fe-KIT-6 (nSi/nFe=10) sample, presumably due to the presence of a
significant amount of Fe. These data were combined with the XRD results to estimate the wall
thickness of the Fe-KIT-6 catalysts. The wall thickness of the Fe-KIT-6 catalysts varies
between 4.07 and 4.45 nm and increases with increasing Fe content (Table 1).
The FT-IR absorption spectra of the calcined mesoporous Fe-KIT-6 samples are
shown in Fig. 4 as a function of the iron loading. In the hydroxyl region, all the samples
exhibit a broad absorption band centered at approximately 3450 cm-1 attributable to the O-H
stretching vibrations of water molecules adsorbed on the mesoporous Fe-KIT-6 surfaces. The
weak band at approximately 1640 cm-1 is assigned to the bending vibrations of adsorbed
water molecules. In the framework region, absorption bands are detected at 1100 cm-1, (the
shoulder at 1220 cm-1), 960 cm-1, 810 cm-1, and 460 cm-1 for all the samples. The presence of
these bands confirms that the mesoporous Fe-KIT-6 framework is formed and the structural
properties are unchanged despite the isomorphous substitution of Fe for Si up to an nSi/nFe
ratio of 10. The absorption band at 1100 cm-1, the shoulder at 1220 cm-1, and the band at 810
cm-1 are assigned to the asymmetric and symmetric stretching vibrations of the structural
siloxane (Si-O-Si) group, while the band at 460 cm-1 is attributed to the Si-O-Si and Si-O-Fe
bending vibrations in the mesoporous framework (i.e., the SiO4 tetrahedron vibrations) [71].
The band at 970 cm-1 is usually attributed to silanol (Si-OH) groups in the mesoporous solid
framework or to a stretching mode of a [SiO4] unit bonded to iron atoms [72]. However, for
the Fe-KIT-6 (nSi/nFe=30) and Fe-KIT-6 (nSi/nFe=10) samples, this band can be attributed to
the presence of Si-O-Fe groups and indicates that the iron atoms are incorporated into the
mesoporous Fe-KIT-6 framework. These results show that high iron loadings do not affect the
Fe-KIT-6 framework structure.
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Fig. 4.
To determine the iron environment, EPR analysis was performed at room temperature.
The EPR spectra of calcined Fe-KIT-6 (nSi/nFe=30) are presented in Fig. 5. The two distinct
signals (geff at 4.3 and 2) observed in the spectra are typical of two different Fe3+
environments [62,73]. Bordiga et al. [74] suggested that the EPR signal at g = 4.3 originating
from the middle Kramers doublet could be assigned to tetrahedrally coordinated iron species
(Fe3+) in the framework. The intense higher field signal at geff = 2.0 is ascribed to Fe3+ in a
symmetrical (tetrahedral) environment, whereas the lower field signal at geff = 4.3 or higher is
assigned to trivalent iron in a distorted (tetrahedral) environment. These results show that the
iron atoms in the Fe-KIT-6 (nSi/nFe=30) sample are tetrahedrally coordinated to the silica
walls. It should be noted that a geff value of 2.0 could be attributed to high-spin Fe3+ in a
symmetrical tetrahedral/octahedral geometry. The sample contain a large fraction of
tetrahedrally coordinated iron atoms, but the existence of octahedrally coordinated iron
species cannot be excluded. These findings are also supported by the XRD results and XPS
measurements, which indicate a high surface atomic ratio (Table 1).
Fig. 5.
Fig. 6 presents the X-ray photoelectron spectra for Fe-KIT-6 samples with nSi/nFe
ratios of 60, 30 and 10. The Fe 2p transition splits into two peaks, 2p3/2 and 2p1/2. The Fe 2p1/2
and 2p3/2 peaks are centered at 723.1 eV and 709.4 eV, respectively. These values are
consistent with typical Fe3+ 2p1/2 and 2p3/2 binding energies for tetrahedrally coordinated
atoms [61,62]. The peak at 709.4 eV corresponds to the Fe–O–Si groups. The spin-orbit
separation between the peaks is 13.7 eV for all the samples. The intensities of the Fe 2p peaks
increase with increasing Fe content, and the stability of the Fe3+ tetrahedral environment in
the framework is maintained for all iron loadings [61,62]. The nSi/nFe molar ratios calculated
from the integral intensities of the Si 2p and Fe 2p photoelectron spectra are included in Table
1. The surface nSi/nFe molar ratios are slightly higher than the bulk ratios calculated from the
chemical analysis.
Fig. 6.
3.4. Catalytic activity
3.4.1. CO2 hydrogenation
The catalytic hydrogenation reaction was investigated for Fe-KIT-6 samples, nSi/nFe
ratios of 60, 30 and 10, at a hydrogen:carbon dioxide ratio (H2:CO2) of 4:1 at atmospheric
pressure and different reaction temperatures. The catalytic performances, including the CO2
hydrogenation catalytic activity and selectivity, are shown in Fig. 7A-C. Fig. 7A shows that
the Fe-KIT-6 (nSi/nFe=10) catalyst with the highest iron content has a higher catalytic activity
for CO2 hydrogenation than Fe-KIT-6 (nSi/nFe=30). The Fe-KIT-6 (nSi/nFe=60) sample is not
catalytically active, suggesting that the iron content is too low to activate the CO2 molecule.
Thus, it is clear that the catalyst with the highest Fe content has a high concentration of active
sites on the KIT-6 pore surfaces, which could promote CO2 activation more efficiently. In
addition, the CO2 conversion increases with increasing reaction temperature. For Fe-KIT-6
(nSi/nFe=10), the CO2 conversion increases from 0.7% to 16.0% when the reaction temperature
increases from 400°C to 500°C, while it only increases from 0.2 to 1.7% when the reaction
temperature increases from 450°C to 500°C for FeKIT-6 (nSi/nFe = 30), showing that the CO2
10
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conversion of FeKIT-6 (nSi/nFe=30) is lower than that of Fe-KIT-6 (nSi/nFe =10). These results
indicate that CO2 is only converted to CO through the RWGS reaction during the catalytic
CO2 hydrogenation. The Fe-KIT-6 (nSi/nFe=30) catalyst only promote the RWGS reaction and
produce no methane in the temperature range of 250-500°C at low iron loading (Fig. 7B).
Other catalytic hydrogenation products, including methanol and other C2 compounds, are not
detected. The Fe-KIT-6 (nSi/nFe=10) catalyst also performs the methanation reaction with low
selectivity, but this reaction competes with the RWGS reaction. Clearly, this catalyst exhibits
the best performance in CO2 hydrogenation. As the reaction temperature is increased (500°C),
more reactant molecules (including CO2 and H2) can be induced to participate in the CO2
hydrogenation reaction, leading to high catalytic activity for this reaction at high
temperatures. These results indicate that increasing the temperature and iron loading
suppresses the RWGS reaction. High iron loadings improve the hydrogenation ability of the
catalyst. Thus, the decrease in the CO selectivity and concomitant increase in the CH4
selectivity at high iron loadings and high temperatures might indicate that the Fe species can
catalyze the chemisorption and subsequent conversion of CO to CH4. These results are
consistent with those reported previously [67, 68].
However, this catalytic study demonstrates that Fe-KIT-6 catalysts can catalyze the
hydrogenation of CO2 to CH4, but the main product is CO (Fig. 7C). Increasing the Fe loading
and the temperature could improve the hydrogenation ability of the catalyst by suppressing
the RWGS reaction to form CH4 and change the product distribution. Further studies are
needed to clarify why high iron loadings improve the catalytic performance for CH4
formation.
Fig. 7.
3.4.2. MCP conversion
The MCP conversion of Fe-KIT-6 catalysts with different nSi/nFe ratios is presented as a
function of the reaction temperature in Table 2. The conversions of all the studied catalysts
are temperature dependent. The catalysts are active in the temperature range of 200-500°C
and have similar product distributions. The dominant products are methane and n-H, and Bz is
observed only at high temperatures.
The total conversion increases monotonically with increasing reaction temperature. It
should be noted that at a given temperature, the catalytic activity increases with increasing
iron content. The Fe-KIT-6 (nSi/nFe=10) and Fe-KIT-6 (nSi/nFe=30) catalysts exhibit MCP
conversions of 2.7 % and 0.92 %, respectively, at 200°C. The MCP conversion of these
catalysts reaches a maximum of 53% and 65%, respectively, at 500°C. These results suggest
that the catalytic activity is an inherent property of the Fe-doped mesoporous structure and is
strongly dependent on the active site density in the mesoporous matrix, as previously
observed in other catalytic systems [60-62].
At low temperatures between 200-300°C, the ring-opening selectivity is 100%, and n-
H is the only product for all the catalysts, except for Fe-KIT-6(nSi/nFe=10), which has a ring-
opening selectivity of 84%. Furthermore, the ring-opening selectivity decreases at 350°C, but
ring opening is still the dominant conversion pathway. The selectivity to n-H at this low
temperature and the low conversion observed in the absence of secondary reactions
demonstrates the intrinsic ability of the catalysts to break endocyclic substituted C-C bonds. It
appears that the C-C bond rupture primarily produces n-H. However, n-H formation is
observed between 200 and 500°C, which suggests that the isolated, tetrahedrally coordinated
Fe active sites preferentially induce the rupture of endocyclic substituted C-C bonds in the
11
Page 11 of 27

temperature range studied. At high temperatures and high iron loadings, the ring-opening
selectivity decreases as the cracking selectivity (C1) increases. C1 is formed by the successive
rupture of C-C bonds through the subsequent reactions of intermediate products. At high
temperatures, all the catalysts actively convert MCP, but they are not selective for the ring-
opening reaction. Most likely, the heat of adsorption on the Fe-KIT-6 active sites is large,
favoring multiple C–C bond-breaking reactions.
These results show that at low reaction temperatures, all the catalysts are active and
selective for MCP ring opening to form n-hexane exclusively. As the iron loading increases,
the activity and selectivity of the studied catalysts also decrease in the following order: Fe-
KIT-6(nSi/nFe=10) > Fe-KIT-6(nSi/nFe=30) > Fe-KIT-6(nSi/nFe=60). The formation of large
amounts of n-H might require a high density of isolated tetrahedral Fe active sites for
endocyclic C-C bond rupture.
Table 2.
Conclusions
Highly ordered mesoporous Fe-KIT-6 with a bicontinuous cubic Ia3d structure and high iron
loading of up to an nSi/nFe ratio of 10 was successfully synthesized using a hydrothermal
approach. The physico-chemical characterization shows that the structural integrity is
preserved for iron loadings of up to an nSi/nFe ratio of 10. The FT-IR, XPS and EPR
spectroscopy results show that most of the iron ions exist as isolated framework species, but
for Fe-KIT-6 with a nSi/nFe ratio of 10, the presence of extra-framework species/small iron
oxide clusters cannot be excluded. Thus, it is inferred that in the Fe-KIT-6 sample with a
nSi/nFe ratio of 10, Fe exists as a framework species and/or iron nanoparticles, which are very
small (less than 4.0 nm). These catalysts were tested for CO2 hydrogenation and MCP
conversion. The catalytic activity of the Fe-KIT-6 catalysts increases significantly with
increasing iron content. For MCP conversion, the ring-opening selectivity can be improved by
increasing the density of atomically isolated iron sites. The iron loading governs the iron
coordination environment, i.e., the nature and structure of the Fe species. Low temperatures
favor high selectivity (100%) to n-H by endocyclic C-C bond rupture. For CO2
hydrogenation, the Fe-KIT-6 materials catalyze CO2 hydrogenation to mainly CO. The rate of
carbon hydrogenation on the Fe-KIT-6 catalysts is a function of the iron active site density
and the temperature. The high iron active site density due to a high iron loading promotes the
methanation reaction at the expense of the RWGS reaction. Thus, Fe-KIT-6 appears to be a
suitable catalyst for MCP conversion at low temperatures and CO2 hydrogenation at high
temperatures. However, further studies are needed to support these findings.
Acknowledgments
This work was partly supported by the Kuwait Institute for Scientific Research, Petroleum
Research and Studies Center, Petroleum Refining and by a DEMETER grant from the
National Research Agency (ANR) of France. We would like to thank L. Josien from IS2M for
performing the SEM experiments. For their support during her internship at the ICPEES, R.
Merkache gratefully acknowledges the wonderful technical service team of A. Rach and M.
Wolf. Because this article is part of the special issue dedicated to the scientific work of Mr.
J.C. Vedrine at his 75th birthday, we congratulate Mr. J.C. Vedrine for his important
contributions to the field of oxide catalysis and, in particular, to understanding the nature of
12
Page 12 of 27

oxide active sites and their physico-chemical characterization. Moreover, we would like to
thank him for his friendly attitude and gracious manner in establishing contacts.
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Figures and Tables
Fig. 1. Small-angle XRD patterns of Fe-KIT-6 catalysts synthesized at 100°C for 24 h with
nSi/nFe=10 (a), nSi/nFe=30 (b), nSi/nFe=60 (c), Fe-KIT-6 (nSi/nFe=30) synthesized at 100°C for
48 h (d), 72 h (e), Fe-KIT-6 (nSi/nFe=30) synthesized at 130°C for 24 h (f).
Fig. 2. N2 adsorption-desorption isotherms of Fe-KIT-6 catalysts synthesized at 100°C for 24
h with nSi/nFe=10 (a), nSi/nFe=30 (b), nSi/nFe=60 (c), Fe-KIT-6 (nSi/nFe=30) synthesized at
100°C for 48 h (d), 72 h (e), Fe-KIT-6 (nSi/nFe=30) synthesized at 130°C for 24 h (f).
Fig. 3. SEM images of Fe-KIT-6 catalysts with nSi/nFe=60 (a) and nSi/nFe=10 (b).
Fig. 4. FT-IR spectra of Fe-KIT-6 catalysts synthesized at different nSi/nFe ratios: (a) Fe-KIT-
6 (nSi/nFe=10), (b) Fe-KIT-6 (nSi/nFe=30), and (c) Fe-KIT-6(nSi/nFe=60).
Fig. 5. EPR spectra of Fe-KIT-6 (nSi/nFe=30) catalysts.
Fig. 6. XPS spectra of (a) Fe-KIT-6 (nSi/nFe=60), (b) Fe-KIT-6 (nSi/nFe=30), and (c) Fe-KIT-6
(nSi/nFe=10) catalysts.
Fig. 7. Effect of temperature on the CO2 hydrogenation of a) Fe-KIT-6 (nSi/nFe=60), (b) Fe-
KIT-6 (nSi/nFe=30), and (c) Fe-KIT-6 (nSi/nFe=10) catalysts (H2:CO2 = 4:1 at atmospheric
pressure; mcatalyst = 60 mg; the catalyst samples were reduced at 350°C for 2 h - 50 ml·min-1).
Table 1. Effect of the synthesis temperature, effect of the synthesis time and effect of the
nSi/nFe molar ratios on the structural and textural properties of the calcined Fe-KIT-6 catalysts.
Table 2. Effect of the nSi/nFe ratios and temperature on the conversion of MCP.
15
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Table 1.
Sample
nSi/nFe
T(°C) t (h) a0
(nm)c
SBET
Vp, BJH
(cm3/g)e
Dp, BJH
(nm)f
w
(m2/g)d
(nm)g
gel calcineda XPSb
Fe-KIT-6
(nSi/nFe=60)
Fe-KIT-6
(nSi/nFe=30)
Fe-KIT-6
(nSi/nFe=10)
Fe-KIT-6
(nSi/nFe=30)
Fe-KIT-6
(nSi/nFe=30)
Fe-KIT-6
60
30
10
30
30
30
71
38
14
36
39
39
76
100
100
100
100
100
130
24
24
24
48
72
24
20.58
21.06
21.87
21.35
21.81
21.57
815
734
435
711
668
668
1.13
1.11
0.83
1.18
1.23
1.23
6.2
6.3
6.5
6.6
7.2
7.1
4.07
4.23
4.45
4.07
3.77
3.68
42
21
n.dh
n.d.
n.d.
(nSi/nFe=30)
a: obtained from ICP analysis.
b: obtained from XPS analysis.
c: unit cell parameter calculated based on the XRD results corresponding to the 3D cubic pore structure with a Ia3d space
group, a0 = dhkl
peak.
, where dhkl diffraction values were evaluated using the interplanar spacing of the (211) XRD
d: specific surface area obtained from N2 sorption isotherm studies.
e: pore volume obtained from N2 sorption isotherm studies.
f: mesopre diameter obtained from N2 sorption isotherm studies.
g: pore wall thickness calculated from formula: (a0/2) - Dp.
h : non determined.
16
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Table 2.
Sample
T
TOF ( s-1)· XT (%)
SRO, n- SC, C1 (%)
H (%)
SRE
(%)
,
Bz
(°C) 10-5
Fe-KIT-6
(nSi/nFe=60)
200 2.06
250 4.63
300 13
350 44
400 78
450 113
500 168
0.42
0.94
2.68
9.12
15.8
23.1
34.2
100
100
100
91
68
39
0
0
0
9
32
61
86
0
0
0
0
0
0
0
24
Fe-KIT-6
(nSi/nFe=30)
200 2.25
250 6.12
300 15
350 37
400 66
450 103
500 129
0.92
2.5
6.2
15.4
27.3
42.4
53.0
100
100
100
72
38
17
0
0
0
28
62
83
88.8
0
0
0
0
0
0
4.2
7
Fe-KIT-6
(nSi/nFe=10)
200 1.26
250 3.49
300 9.22
350 20
400 30
450 39
500 48
2.7
4.7
12.4
27
41
53
100
100
84
66
16
3
0
0
0
0
0
0
0
3.9
7.3
16
34
84
96.1
92.7
65
0
XT:total conversion of MCP; SRO:ring opening selectivity; SC:cracking selectivity; SRE:ring enlargement
selectivity. The catalyst samples were reduced under an H2 flow (40 ml/min) for 4 h at 500°C (heating rate
5°C/min); mcatalyst=200 mg; VMCP injected = 5 µl ;The gas flow used for the catalytic tests was fixed at 40
cm3·min-1.
17
Page 17 of 27

(211)
2000000
1500000
1000000
500000
0
(220)
f)
e)
d)
c)
b)
a)
0
1
2
3
4
2 Theta (degree)
Fig. 1.
18
Page 18 of 27

167
147
127
107
87
f)
e)
d)
c)
67
47
27
b)
a)
7
0
0.2
0.4
0.6
0.8
1
Relative pressure (P/P0)
Fig. 2.
19
Page 19 of 27

Fig. 3.
20
Page 20 of 27

200
180
160
140
120
100
80
a)
b)
c)
60
40
20
0
0
1000
2000
3000
4000
Wavenumber (cm-1)
Fig. 4.
21
Page 21 of 27

1000000
500000
0
-500000
-1000000
-1500000
-2000000
0
2000
4000
6000
8000
Magnetic field [G]
Fig. 5.
22
Page 22 of 27

Fe 2p
c)
b)
a)
705
710
715
720
725
730
Binding energy (eV)
Fig. 6.
23
Page 23 of 27

C)
100
80
60
40
20
0
c)
a)
b)
250
300
350
400
450
500
Temperature, °C
3
2.5
2
B)
1.5
1
c)
b)
0.5
0
a)
250
300
350
400
450
500
Temperature, °C
24
Page 24 of 27

16
14
12
10
8
A)
6
c)
4
b)
2
a)
0
250
300
350
400
450
500
Temperature, °C
Fig. 7.
25
Page 25 of 27

Graph_Abst
26
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High
 Fe-KIT-6 mesoporous materials with Ia3d symmetry and high iron loadings were
synthesized.
 Iron ions exist as isolated framework species.
 Fe-KIT-6 materials appear to be adapted catalysts for MCP conversion at low
temperatures.
 Fe-KIT-6 materials appear to be suitable catalysts for CO2 hydrogenation at high
temperatures.
27
Page 27 of 27