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Effect of Fe-Mo promoters on HZSM-5 zeolite catalyst for 1-hexene aromatization


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The promotional effect of Fe-Mo species introduced into HZSM-5 (Zeolyst Int., SiO2/Al2O3 = 30) zeolite catalyst by the wetness impregnation method for the 1-hexene aromatization was investigated. The structure and catalytic performance for the aromatization of 1-hexene over xFeyMo-ZSM-5 catalysts in comparison with unmodified HZSM-5 catalysts were studied. The xFeyMo-ZSM-5 catalysts contain fixed loading (5 wt%) and variable Fe/Mo ratio. The catalysts were characterized by BET, ICP-AES, HRSEM-EDS, HRTEM, XRD, FTIR, H 2-TPR, NH 3-TPD, and pyridine DRIFT spectroscopy. The characterization data confirmed the existence of Fe and Mo species in the zeolite matrix. With Fe and Mo species implementation to HZSM-5 zeolite, the amount of the acid sites decreased, but the selectivities to C 9+ aromatics increased. The catalyst evaluation was performed at 350 °C for 6 h on-stream at atmospheric pressure using a fixed-bed quartz tube reactor. The selectivity to products of different carbon number was affected by the Fe/Mo ratio within the zeolite. It was found the product distribution of grouped fractions of C 1-C 17+ from the liquid product. The results indicate that the optimum ratio of Fe/Mo is 1-1.5. The highest selectivity for gasoline and distillate ranges was obtained for the 2.5wt%Fe2.5wt% Mo-and 3wt%Fe2wt%Mo-ZSM-5 samples, which was higher than that for parent HZSM-5 catalyst.
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Effect of Fe-Mo promoters on HZSM-5 zeolite
catalyst for 1-hexene aromatization
Andrii Kostyniuk
, David Key
, Masikana Mdleleni
Department of Catalysis and Chemical Reaction Engineering, National Institute of Chemistry, Hajdrihova 19, Ljubljana
1001, Slovenia
PetroSA Synthetic Fuels Innovation Centre, South African Institute for Advanced Materials Chemistry, University of the Western
Cape, Cape Town, Private Bag X17, Bellville, 7535, South Africa
Received 23 May 2018; revised 9 October 2018; accepted 7 November 2018
Available online 15 November 2018
Fe-Mo species;
Liquid Fuels
Abstract The promotional effect of Fe-Mo species introduced into HZSM-5 (Zeolyst Int.,
30) zeolite catalyst by the wetness impregnation method for the 1-hexene aromatiza-
tion was investigated. The structure and catalytic performance for the aromatization of 1-hexene
over xFeyMo-ZSM-5 catalysts in comparison with unmodified HZSM-5 catalysts were studied.
The xFeyMo-ZSM-5 catalysts contain fixed loading (5 wt%) and variable Fe/Mo ratio. The cata-
lysts were characterized by BET, ICP-AES, HRSEM-EDS, HRTEM, XRD, FTIR, H
-TPD, and pyridine DRIFT spectroscopy. The characterization data confirmed the existence
of Fe and Mo species in the zeolite matrix. With Fe and Mo species implementation to HZSM-5
zeolite, the amount of the acid sites decreased, but the selectivities to C
aromatics increased.
The catalyst evaluation was performed at 350 °C for 6 h on-stream at atmospheric pressure using
a fixed-bed quartz tube reactor. The selectivity to products of different carbon number was affected
by the Fe/Mo ratio within the zeolite. It was found the product distribution of grouped fractions of
from the liquid product. The results indicate that the optimum ratio of Fe/Mo is 1–1.5.
The highest selectivity for gasoline and distillate ranges was obtained for the 2.5wt%Fe2.5wt%
Mo- and 3wt%Fe2wt%Mo-ZSM-5 samples, which was higher than that for parent HZSM-5 cata-
Ó2018 King Saud University. Production and hosting by Elsevier B.V. This is an open access article under
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1. Introduction
An important industrial way for the olefins upgrading is the
aromatization and skeletal hydroisomerization of olefins over
acid catalyst [1–6]. It is well-known that the aromatization of
olefins has great significance in the chemical industrial fields
for synthetic resin, rubber, solvent, detergent, clean gasoline
and other chemical intermediates [5]. The most investigated
olefins are propene and butene using phosphoric impregnated
*Corresponding author.
E-mail addresses: (A. Kostyniuk),
za (D. Key), (M. Mdleleni).
Peer review under responsibility of King Saud University.
Production and hosting by Elsevier
Journal of Saudi Chemical Society (2019) 23, 612–626
King Saud University
Journal of Saudi Chemical Society
1319-6103 Ó2018 King Saud University. Production and hosting by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (
silica–clay acid and zeolite type of catalysts [7–11], but studies
dealing with 1-hexene transformation are consequently limited
[12]. The products of this process are mixtures of olefins,
straight chain paraffins, cycloalkanes, and aromatics which
are contained in gasoline (C
) and diesel (C
[10,11]. 1-hexene aromatization can undergo many reactions
over the zeolites, such as cracking, oligomerization, isomeriza-
tion, cyclization, as well as hydrogen transfer over the
Brønsted and Lewis acid sites of the zeolite [5,6]. In general,
low temperatures (250 °C) favored the double bond shift reac-
tion but for the cracking is the major reaction at temperatures
above 450 °C[6]. The balanced aromatization and hydroiso-
merization reactions at moderate temperatures among 300–
400 °C appear to be attractive for achieving the desired
RON (research octane number) and gasoline yield simultane-
ously in the olefins upgrading [1].
Zeolite catalysts are widely uses for aromatization of olefins
[8,10,13]. ZSM-5 zeolite is one of the best solid acid catalysts
and has been widely applied in petrochemical industry, due
to its unique structures, thermal stability, acidity and shape
selectivity [1,2,14]. Many researchers studied the aromatization
process over ZSM-5 modified by Pt, Ga, and Zn, with the goal
of reducing coke formation, which leads to rapid catalyst deac-
tivation and poor stability [3–6]. In addition, the strength of
acid sites in promoted zeolite catalysts, which can catalyze
the aromatization of olefins, is still unclear. Nevertheless, the
results of these investigations suggest that the development
of a more active catalyst for aromatization of 1-hexene is
needed and still remains a major problem [3,15].
In this paper, the aim of this study was to prepare and
investigate Fe-Mo bimetal zeolite catalysts and study the effect
of adding metal species for the 1-hexene aromatization, which
has never been reported before. For such a purpose, Fe-Mo
species were incorporated into HZSM-5 zeolite by the wetness
impregnation method and can be used to enhance zeolite activ-
ity during the 1-hexene aromatization. The effects of Fe/Mo
ratio on the catalysts activity and product distribution will
be evaluated.
2. Experimental
2.1. Chemicals used
Reagents that have been used in the preparation of the catalyst
and the catalytic reaction: NH
-ZSM-5 zeolite (Zeolyst Int.,
CBV 3024E), iron(III) nitrate nonahydrate (Sigma-Aldrich,
98%), ammonium heptamolybdate tetrahydrate (Sigma-
Aldrich, 99.98%), 1-hexene (Sigma-Aldrich, 97%).
2.2. Catalyst synthesis
The preparation of the xFeyMo-ZSM-5 catalysts has involved
the impregnation of the commercial NH
-ZSM-5 zeolite (SiO
30) using the incipient wetness impregnation method
with solutions of ammonium heptamolybdate (NH
O and iron(III) nitrate Fe(NO
O. At first, the
-ZSM-5 zeolite was calcined at 550 °C in static air for
6 h to convert the ammonium form to its protonated form
(H-ZSM-5). Samples containing both molybdenum and iron
were prepared by a two-step impregnation procedure, in which
the molybdenum phase with a concentration of 0.001 M was
introduced first to the H-ZSM-5 and mixed for 2 h at 80 °C.
After that, the iron salt with a concentration of 0.01 M was
added to the prepared solution with vigorous stirring. The
temperature was kept at 80 °C. Stirring continued until suspen-
sion turned into a slurry. Drying was carried out at 120 °Cin
the ventilated dryer overnight. Thereafter calcination in the
static air was carried out for 6 h at 550 °C. 10 different cata-
lysts based on H-ZSM-5 were prepared in this way with the
following amounts of metals: 5wt%Mo, 1wt%Fe4wt%Mo,
1.25wt%Fe3.75wt%Mo, 1.43wt%Fe3.57wt%Mo, 1.67wt%
Fe3.33wt%Mo, 2wt%Fe3wt%Mo, 2.5wt%Fe2.5wt%Mo,
3wt%Fe2wt%Mo, 4wt%Fe1wt%Mo and 5wt%Mo. All per-
centages associated with metal amount are expressed as weight
2.3. Catalyst characterization
2.3.1. Fourier transform infrared (FT-IR) spectroscopy analysis
The FTIR framework spectra were obtained using Perkin
Elmer UATR FTIR spectrometer. Typically 20 mg of sample
was placed on the ATR diamond crystal and the force gauge
set to 50 (arb. units) to obtain good contact between sample
and crystal. The samples were recorded in the region 400 to
4000 cm
2.3.2. Surface area and micropore analysis (BET)
Brunauer–Emmett–Teller (BET) specific surface area was
determined using a Micrometrics 3300, TriStar surface area
and porosity analyzer. About 0.3 g of sample was degassed
at 400 °C for 4 h. After the degassing process, the samples were
then loaded on the analysis station for determination of the
isotherms at 196 °C. The pore size distributions were calcu-
lated using the Barrett–Joyner–Halenda (BJH) model applied
to the adsorption branch of the isotherm, assuming cylindrical
pore geometry.
2.3.3. ICP-AES analysis
The chemical analysis of elements’ (Fe and Mo) amount in cat-
alysts was determined by inductively coupled plasma atomic
emission spectroscopy (ICP-AES) on Varian model 715-ES.
Prior to the ICP-AES measurements, the zeolite samples were
dissolved in a mixture of HF/HNO
O (1:1:1).
2.3.4. HRSEM-EDS analysis
Scanning electron microscopy (SEM) micrographs were
obtained using a high-resolution SEM EHT 5.00 kV. All sam-
ples were carbon coated before imaging. The HRSEM (AUR-
IGA) was also equipped with an EDS spectrometer with the
INCA EDS system by Oxford Instruments for elemental anal-
ysis of zeolites.
2.3.5. HRTEM analysis
Transmission electron microscopy images were obtained using
the aid of HRTEM techniques using a FEI Tecnai TF20
(200 kV) equipped with a STEM unit, high-angle annular
dark-field (HAADF) detector and X-Twin lenses.
2.3.6. Powder X-ray diffraction analysis
Powder X-ray diffraction data were collected using a Brucker
AXS D8 diffractometer equipped with a primary beam Gobel
Effect of Fe-Mo promoters on HZSM-5 zeolite catalyst 613
mirror, a radial Soller slit, a Vantec-1 detector and using
Cu-Karadiation (40 kV, 40 mA, kKa1 = 1.5406 A
˚). Data
were collected in the 2hrange 5 to 70°and 90°in 0.021°steps,
using a scan speed resulting in an equivalent counting time of
14.7 s/step.
2.3.7. H
-TPR analysis
Temperature programmed reduction (TPR) characteristics of
the catalysts were obtained using a Micrometrics Autochem
2920 II system. Sample (0.1 g) was loaded in a U-shaped
quartz tubular reactor. When performing the TPR analysis,
the sample was exposed to a gas mixture (10% H
, balance
Ar) at a flow rate of 50 mL/min and heated to 900 °Cat
10 °C/min heating rate. The H
consumption was monitored
with a thermal conductivity detector (TCD). A cooling trap
(ice + isopropanol) placed between the sample and the TCD
was used to retain the water produced during the reduction
2.3.8. NH
-TPD analysis
The acid properties of the catalysts were determined by
temperature-programmed desorption of ammonia (NH
TPD) on a Micrometrics Autochem 2920 II system using He
as a carrier gas. All samples (0.1 g) were first heated to
500 °C and then cooled down to 120 °C in He atmosphere.
Afterward, 5 vol% NH
in He (20 mL/min) was adsorbed at
120 °C for 30 min followed by He purging at the same temper-
ature for 1 h. Desorption of NH
was monitored in the range
of 120–700 °Cata10°C/min heating rate. The NH
tion profile was observed using a thermal conductivity
2.3.9. Pyridine-DRIFT analysis
Thermogravimetric method of pyridine adsorption was used
for quantification of acid sites on investigated materials using
Pyris 1 TGA apparatus from PerkinElmer. Prior to analysis,
the samples were degassed in-situ in N
stream (30 mL/min)
at 500 °C for 1 h. Afterward, the sample was cooled to
125 °C and saturated with pyridine vapors by passing the N
stream through a saturator filled with liquid pyridine. Satura-
tion was followed by desorption of weakly bound pyridine by
degassing the sample in N
at 125 °C for an additional 2 h until
achieving a stable sample weight. The total number of acid
sites was calculated based on the weight difference before
and after sample saturation.
Differentiation between Brønsted (BAS) and Lewis (LAS)
acid sites was done for pure HZSM-5 and 2.5Fe2.5Mo-
HZSM-5 materials by DRIFTS analysis using Frontier IR
spectrometer (Perkin Elmer), DiffusIRÒaccessory from Pike
Scientific and pyridine as the probe molecule. The powdered
samples (10 mg) were positioned in the sample cup and pre-
treated in N
(50 mL/min) at 500 °C for 30 min. After cool-
ing to 125 °C, the samples were saturated with pyridine
vapors for 10 min, followed by degassing in a vacuum
(2 10
mbar) for 30 min. Spectra were recorded with 8
accumulations and spectral resolution of 4 nm between 800
and 4000 cm
. For characterization of LAS and BAS,
absorption bands at 1445 cm
and 1545 cm
2.4. Catalytic evaluation
The performances of the zeolite catalysts were tested in the
conversion of 1-hexene in a fixed bed quartz tube reactor at
a weight hourly space velocity (WHSV) of 4 h
and the reac-
tion temperature was kept at 350 °C under atmospheric pres-
sure. The reactor tube was charged with 1 g of a catalyst
then heated from room temperature up to 350 °C. 1-hexene
was introduced by New era syringe pump at a flow rate of
0.098 mL/min with the syringe of 29 mm diameter continu-
ously for 6 h. All products were analyzed on an offline Bruker
450 GC equipped with a BR-Alumina/Na
column (C
), BR-1 column (C
) and a flame ionization (FID)
detector. 1-hexene conversion and selectivity were defined as:
¼ð1-hexene moles in the feedÞ-ð1-hexene moles in the productsÞ
ð1-hexene moles in the feedÞ
SCxHyðmol%Þ¼ CxHy moles in the products
PCxHy moles in the products 100
3. Results and discussion
3.1. Catalyst characterization
3.1.1. Surface area and micropore analysis (BET)
Table 1 summarizes the nominal composition of samples with
different Mo/Fe ratio and fixed loading (5wt%). The BET sur-
face area (S
), microporous surface area (S
), external
surface area (S
), microporous volume (V
), total pore
volume (V
), average pore diameters and hierarchy factor
(HF) of the studied catalysts are listed in Table 2 [16].
Correspondingly, the micropore volume of promoted
HZSM-5 zeolite was reduced from 0.105 to 0.094 cm
/g, as
revealed in Table 2. After loading 5wt% of Mo on HZSM-5,
the S
decreased from 378 to 314 cm
/g due to strong Mo
interaction with HZSM-5 and indicating that Mo mostly
deposited on the external surfaces and could have blocked
some of the micropores of HZSM-5 [16–18]. Upon addition
Table 1 Nominal composition for prepared samples of
xFeyMo-ZSM-5 catalysts.
Sample xFe
(wt %)
Total load
Fixed loading and variable Mo/Fe ratio
5Mo 0 5 15
1Fe4Mo 1 4 4 5
1.25Fe3.75Mo 1.25 3.75 3 5
1.43Fe3.57Mo 1.43 3.57 2.5 5
1.67Fe3.33Mo 1.67 3.33 2 5
2Fe3Mo 2 3 3/2 5
2.5Fe2.5Mo 2.5 2.5 1 5
3Fe2Mo 3 2 2/3 5
4Fe1Mo 4 1 1/4 5
5Fe 5 0 0 5
614 A. Kostyniuk et al.
of 5wt% of Fe the S
decreased to 346, but not so dramat-
ically comparing with 5wt%Mo.
The xFeyMo-ZSM-5 samples noticed a different behavior
with variable Mo/Fe ratio. The xFeyMo-ZSM-5 samples exhi-
bit a greater surface area than 5Mo-ZSM-5 suggesting a better
dispersion when Fe and Mo metals are both present [16,18].
Fig. 1(a, b, c) provides the N
adsorption-desorption iso-
therms for samples with different Mo/Fe ratio. The character-
istic of the xFeyMo-ZSM-5 samples tending to agglomerate
into microsized agglomerates is also featured by its N
tion and desorption isotherms, which could also be supported
by the XRD and SEM results [17]. As shown in Fig. 1 all cat-
alysts exhibit typical type I isotherms with a small hysteresis
loop in the range of p/p
= 0.5–0.9, which indicate that the
HZSM-5 and xFeyMo-ZSM-5 samples have high microporos-
ity and inter-crystal mesoporosity possibly related to the
aggregation of the crystals [3,17,19–22].
Compared with the isotherm of the HZSM-5, for the
xFeyMo-ZSM-5 samples, the N
adsorption decreased. A little
difference in the shape of N
adsorption/desorption isotherms
for xFeyMo-ZSM-5 samples was observed, but the presence of
both Fe and Mo on the external surfaces of zeolite crystals has
little influence on their agglomeration behaviors [17].
The hierarchy factor (HF) can be applied to any material,
to classify the porous characteristic [23,24]. The hierarchy fac-
tors were calculated according to Eq. (1).
HF ¼Sexter=SBET
ðÞ ð1Þ
Well-known conventional zeolites display moderate HF
value (0.1) and hierarchical zeolites display relatively high
HF value (>0.1) due to the introduction of mesopores. The
HF value of the metals promoted and parent ZSM-5 is
0.158–0.178 (>0.1), that is, displaying high relative meso-
porosity, in good agreement with the TEM images [23].
The pore size distribution was obtained by applying the
Barrett–Joyner–Halenda (BJH) method from the adsorption
branches of nitrogen isotherms [25].Fig. 1d shows the meso-
pores with sizes in a range of 12.5–21.0 nm [3]. The majority
of these pores concentrated at about 14 nm. Compared with
HZSM-5 catalyst, there was a notable increase in the pore size
distribution for the 2.5Fe2.5Mo-ZSM-5 (14.5 nm), 3Fe2Mo-
ZSM-5 (14.5 nm), 4Fe1Mo-ZSM-5 (12.5 nm) and 5Fe-ZSM-5
(21.0 nm) samples, exhibiting that the increase in incorpora-
tion of Fe-Mo species in the framework made the pore
diameter larger. Thus, impregnation does not change the
Table 2 Characterization data of the zeolite samples.
Catalyst Fe
BJH Adsorption
average pore
BJH Desorption
average pore
HZSM-5 378 228 150 0.105 0.235 5.92 5.75 0.178
5Mo 4.74 314 207 107 0.096 0.208 6.13 5.81 0.158
1Fe4Mo 0.92 3.82 326 203 123 0.094 0.215 6.24 5.95 0.165
1.25Fe3.75Mo 1.13 3.65 330 205 125 0.095 0.218 5.73 5.50 0.165
1.43Fe3.57Mo 1.40 3.46 324 204 120 0.095 0.211 5.56 5.31 0.167
1.67Fe3.33Mo 1.61 3.10 339 207 132 0.096 0.223 5.67 5.48 0.168
2Fe3Mo 1.94 2.85 316 203 113 0.094 0.210 6.83 4.41 0.161
2.5Fe2.5Mo 2.47 2.36 331 204 127 0.094 0.221 6.01 5.75 0.164
3Fe2Mo 2.91 1.89 339 217 122 0.100 0.222 5.82 5.60 0.162
4Fe1Mo 3.88 0.89 348 212 136 0.098 0.230 5.82 5.62 0.167
5Fe 4.78 – 346 209 137 0.097 0.228 5.89 5.68 0.168
BET method.
t-Plot method.
BJH method.
Fig. 1 N
-adsorption and desorption isotherms (a, b, c) and BJH pore size distribution (d) of the H-ZSM-5 and xFeyMo-ZSM-5
Effect of Fe-Mo promoters on HZSM-5 zeolite catalyst 615
texture of catalysts which agrees with XRD, FTIR, SEM and
TEM results [26].
3.1.2. Electron microscopy and X-ray microanalysis
The HRSEM-EDS images of the HZSM-5 and xFeyMo-ZSM-
5 zeolite catalysts are shown in Fig. 2.
The SEM images showed aggregates of particles. No major
morphological differences were observed between zeolite cata-
lysts. Fig. 2 shows two typical SEM images obtained. It is clear
from the images that the zeolite catalysts have a cube or elon-
gated prismatic shapes [16,17,19,20].
The element mapping of the HZSM-5, 5Fe-ZSM-5, 5Mo-
ZSM-5 and 2.5Fe2.5Mo-ZSM-5 samples by HRSEM is shown
in Fig. 3.
From Fig. 3 we can see that the distribution of the element
Fe and Mo the same as Si and Al is homogeneous. The element
analysis shows that the O–K, Al–K, Si–K, Fe–K, Fe–L, Mo–K
and Mo–L signals display the elements are uniformly dis-
tributed. In other words, the iron and molybdenum species
Fig. 1 (continued)
616 A. Kostyniuk et al.
are well dispersed on the external surface of the HZSM-5 crys-
tals [27].
3.1.3. The high-resolution transmission electron microscopy
HRTEM and Energy Dispersive Spectroscopy (EDS) were
performed for the HZSM-5 and xFeyMo-ZSM-5 samples to
confirm the presence of iron and molybdenum species in
HZSM-5 and study the composition of the metallic phase in
the catalysts. Fig. 4 shows brightfield TEM images. The pres-
ence of Fe and Mo particles in these objects is also evidenced
by EDS analysis, as it is shown in Fig. 5, where the peaks cor-
responding to O–K, Al–K, Si–K, Fe–K, Fe–L, Mo–K and
Mo–L emissions are clearly outlined together with other peaks
that arise from the carbon and the copper grid [28,29].Asitis
seen from EDS spot area the Fe and Mo were always detected
together and involved in the formation of iron and molybde-
num species in the HZSM-5 zeolite catalyst [17].
3.1.4. Fourier transform infrared (FT-IR) measurements
The FT-IR spectra of the HZSM-5 and xFeyMo-ZSM-5 sam-
ples were recorded in the range of 4000–400 cm
and shown
in Fig. 6. The absorption bands at 1220, 1075, 797, 542,
433 cm
are considered as the characteristic signals for the
framework vibration of the HZSM-5 zeolite catalyst [30].It
was found that the band 433 cm
belongs to the T–O bending
vibration of internal tetrahedral (where T = Si or Al),
542 cm
(double ring), 797 cm
(external symmetric stretch),
1075 cm
(internal asymmetric stretch) and 1220 cm
nal asymmetric stretch), respectively [26,30–32].
According to the IR spectra recorded from the xFeyMo-
ZSM-5 samples, all the structure-sensitive bands are similar
Fig. 2 SEM images of the HZSM-5 and xFeyMo-ZSM-5 samples with fixed loading and variable Mo/Fe ratio (A – HZSM-5, B – 5Mo,
C – 1Fe4Mo, D – 1.25Fe3.75Mo, E – 1.43Fe3.57Mo, F – 1.67Fe3.33Mo, G – 2Fe3Mo, H – 2.5Fe2.5Mo, I – 3Fe2Mo, J – 4Fe1Mo, K – 5Fe).
Effect of Fe-Mo promoters on HZSM-5 zeolite catalyst 617
to those of HZSM-5, but for the 5Mo-ZSM-5 catalyst, a new
band was found.
The spectrum of xFeyMo-ZSM-5 catalysts shows major
changes in the region of 750–1000 cm
, weakening of strong
absorption of the band at 797 cm
. A new broad band was
found at 901 cm
, which corresponds to the overlap between
Mo-O-Mo bond vibrations in MoO
. The band at 1075 cm
is sensitive to the ratio of framework Si/Al. By the loading
of Fe and Mo species, the band at 1075 cm
shifted to
1081 cm
(Fig. 6). Thus, the FTIR spectra of HZSM-5 were
not significantly affected after loading the Fe and Mo species,
which means the introduction of these species did not change
the HZSM-5 basic framework [33].
3.1.5. X-ray diffraction (XRD) analysis
Figs. 7-8 shows the XRD patterns of samples with different
Fe/Mo ratios. The similarity between the XRD patterns of
the HZSM-5 and xFeyMo-ZSM-5 samples indicates that the
HZSM-5 framework was preserved after impregnation
[16,27,34,35]. In contrast, the samples impregnated with pure
Fe, Mo, and Fe-Mo species do not exhibit any reflections
related to the iron and molybdenum species indicating very
small particles size [30]. As shown in Figs. 7, 8 the Fe-Mo addi-
tives cause a decrease in the HZSM-5 crystallinity since a
reduction of the HZSM-5 characteristic peaks are observed.
Once all the samples compared with HZSM-5 exhibited a
decrease in the peaks between 2h= 7.6°–9.2°and 2h=22°
29°, it is reasonable to suppose that the dispersion of iron
and molybdenum species takes place on the HZSM-5 surface
as well as inside the channels.
3.1.6. H
–TPR analysis
–TPR experiments were conducted to investigate the
reducibility of the metals modified H-ZSM-5 catalysts. In
Fig. 2 (continued)
618 A. Kostyniuk et al.
Fig. 9, the temperature programmed reduction profiles for Fe,
Mo and Fe-Mo loaded catalysts are shown. The catalysts exhi-
bit different temperature-programmed reduction profiles indi-
cating the different interaction between active phases [36].
-TPR of unmodified H-ZSM-5 did not show hydrogen con-
sumption in the investigated temperature range [37]. The main
reduction peaks corresponding to the metal phase reduction
were located between 305 °C and 731 °C. The addition of
Mo species in the supported Fe oxide catalyst system shifted
the H
-TPR peaks to higher reduction temperatures, showing the
-TPR peak at 426 °C for the 2.5Fe2.5Mo-ZSM-5 sample [38].
In Fig. 9, three reduction peaks arising from the
2.5Fe2.5Mo-ZSM-5 catalyst can be distinct, the one at
426 °C shows a reduction of Fe
to Fe
, and the others
at 523 and 731 °C reduction of Fe
to FeO and Fe and inter-
action with Mo specious [37,39,40].
For the 5Mo-ZSM-5, the H
consumption curve deviates
from the baseline at approximately 300 °C, and the H
peak occurred at above 429, 485 and 668 °C[38]. The peak
at 429 and 485 °C is attributed to the reduction of the species
to Mo
, from the MoO
polymeric species. The peak
at 668 °C is assigned to the reduction of the Mo
phase to
[28]. The H
-TPR curve for the 5Fe-ZSM-5 sample also
showing three peaks at 305, 475 and 598 °C with involving
the reduction of the iron oxide in a three-step reduction pro-
cess: Fe
?FeO ?Fe, respectively.
3.1.7. NH
-TPD analysis
The concentration and strength of acid sites in HZSM-5 and
2.5Fe2.5Mo-ZSM-5 are determined by NH
-TPD, as pre-
sented in Fig. 10 and the quantitative result is listed in Table 3.
Fig. 3 Element mapping of the HZSM-5 (A), 5Fe-ZSM-5 (B), 5Mo-ZSM-5 (C), 2.5Fe2.5Mo-ZSM-5 (D).
Effect of Fe-Mo promoters on HZSM-5 zeolite catalyst 619
Two desorption peaks were observed for the parent HZSM-5
at 191 and 389 °C. The peak at 191 °C has been assigned to
desorption of the absorbed NH
on a weak acid (mostly
Lewis-acid) sites, whereas, the peak at 389 °C was assigned
to medium strong acid (mostly Bronsted-acid) sites
[16,27,41]. With the Fe and Mo species were implemented,
the area of weak and strong acidic sites decreased [42]. The
strong acid sites change more than the weak ones. At the same
time, the 2.5Fe2.5Mo-ZSM-5 sample showed NH
-TPD peaks
with lower desorption temperatures in comparison with that of
the parent HZSM-5 zeolite. The 2.5Fe2.5Mo-ZSM-5 exhibits
obviously weaker acidity than the HZSM-5 catalyst.
The decrease in the amount of strong acid sites results in a
decrease in the selectivities to benzene and toluene and an
increase in the selectivity to C
aromatics [42]. The surface
acid sites, especially strong acid sites, facilitated the second
Fig. 4 HRTEM images of the xFeyMo-ZSM-5 catalysts with fixed loading and variable Mo/Fe ratio (A – HZSM-5, B – 5Mo, C –
1Fe4Mo, D – 1.25Fe3.75Mo, E – 1.43Fe3.57Mo, F – 1.67Fe3.33Mo, G – 2Fe3Mo, H – 2.5Fe2.5Mo, I – 3Fe2Mo, J – 4Fe1Mo, K – 5Fe).
620 A. Kostyniuk et al.
reaction of products and coke formation. Therefore, the
distinct surface acid strength and acid site density may lead
to different catalytic activities of the 2.5Fe2.5Mo-ZSM-5 cata-
lyst for the 1-hexene aromatization reaction [38,43].
3.1.8. Pyridine-DRIFT analysis
For characterization of LAS and BAS, absorption bands at
1445 cm
and 1545 cm
were considered. The first band
originates from pyridine coordinative adsorbed on LAS, while
the second arises from pyridinium ion bound to BAS. The
BAS/LAS ratio was calculated as:
In this equation, I
and I
represent the intensity of
absorption bands at 1545 and 1445 cm
, and 1.73 and 1.23
are relevant extinction coefficients, as reported by Tamura
et al. [44]. When Fe-Mo species were deposited over HZSM-
5, the amount of acid sites decreases slightly, from 0.63 to
0.58 mmol/g
. This could be connected either to pore block-
age and inaccessibility of acid sites to the pyridine probe mole-
cule what was verified by N
physisorption. On a side note, the
total amount of acid sites assuming all framework Al
1.08 mmol/g. Notably less was measured, suggesting inaccessi-
bility of all acid sites for the probe molecule.
Pyridine DRIFT analysis showed that pure HZSM-5 con-
tains mainly BAS (BAS/LAS = 4). A notable fraction (20%)
of aluminum appears as LAS, which suggests their extra-
framework location. After Fe-Mo species deposition, a notable
increase in LAS is observed (BAS/LAS = 2.7, Table 4). Based
on this, the addition of Mo species enhanced the surface weak
acid strength in the 2.5Fe2.5Mo-ZSM-5 catalyst [38]. This is
anticipated since coordinatively unsaturated Mo
in MoO
clusters can exhibit Lewis acidic character.
3.2. Catalyst evaluation
The effect of Fe/Mo ratio on the catalytic conversion of 1-
hexene was studied at a reaction temperature of 350 °C for
6 h on-stream. The reaction was performed at atmospheric
pressure. The conversion of 1-hexene was observed 99% over
Fig. 5 A typical Energy Dispersive Spectrum (EDS) of the
2.5Fe2.5Mo-ZSM-5 sample.
Fig. 6 FT-IR spectra of the HZSM-5 and xFeyMo-ZSM-5 catalysts.
Effect of Fe-Mo promoters on HZSM-5 zeolite catalyst 621
Fig. 7 XRD patterns of the HZSM-5 and 5Fe-, 5Mo-, 1Fe4Mo- and 2.5Fe2.5Mo-ZSM-5 catalysts.
Fig. 8 XRD patterns of the HZSM-5, 1.25Fe3.75Mo-, 1.67Fe3.33Mo-, 2Fe3Mo-, 3Fe2Mo- and 4Fe1Mo-ZSM-5 catalysts.
622 A. Kostyniuk et al.
xFeyMo-ZSM-5 and HZSM-5 catalysts, showing that 1-
hexene is a very active feed.
Fig. 11 shows that a high gasoline selectivity (>40%) was
observed for the 2.5Fe2.5Mo-ZSM-5 and 3Fe2Mo-ZSM-5
The parent HZSM-5 with other promoted catalysts being
kept at 40% and less. The best selectivity for C
obtained over 3Fe2Mo-ZSM-5 catalyst, but C
over 2.5Fe2.5Mo-ZSM-5 and being higher (9wt%) than parent
HZSM-5 catalyst after TOS = 6 h.
Fig. 12 shows the product distribution of grouped fractions
of C
from the liquid product for the HZSM-5,
2.5Fe2.5Mo-ZSM-5 and 3Fe2Mo-ZSM-5 catalysts.
The product distribution of C
and C
was 15.1%,
20.5% and 11.9% respectively for the HZSM-5 catalyst. Upon
addition of Fe-Mo to the parent H-ZSM-5 catalyst the product
distribution of C
and C
increased to 11.3%, 31.2%,
23.0% for the 2.5Fe2.5Mo-ZSM-5 and 18.9%, 30.4%,
18.2% for the 3Fe2Mo-ZSM-5, respectively.
The strong interaction between the Fe and Mo species in
the 2.5Fe2.5Mo-ZSM-5 and 3Fe2Mo-ZSM-5 catalysts was
estimated, which resulted in a high chemical value of
formed in Fe–Mo bimetal oxide system [38]. Moreover,
the catalytic performance of xFeyMo-ZSM-5 catalysts is
affected by Fe/Mo molar ratio. This molar ratio has a
significant influence on the surface acid site density. The main
reason for the enhanced activity of the 2.5Fe2.5Mo-ZSM-5
and 3Fe2Mo-ZSM-5 catalysts is related to the modification
Fig. 10 NH
-TPD profiles of the HZSM-5 and 2.5Fe2.5Mo-
ZSM-5 catalysts.
Table 3 NH
-TPD results for the HZSM-5 and 2.5Fe2.5Mo-ZSM-5.
Catalyst Desorption Temperature (
C) Acidity by strength (mmol/g) Strong/weak
Weak Strong
H-ZSM-5 191 389 0.481 0.218 0.453
2.5Fe2.5Mo-ZSM-5 171 340 0.468 0.038 0.081
Fig. 11 Effect of Fe/Mo ratio with TOS = 6 h on the selectivity
of C
Fig. 9 H
-TPR profiles of the 5Fe-ZSM-5, 5Mo-ZSM-5 and
2.5Fe2.5Mo-ZSM-5 catalysts.
Table 4 Total acidity expressed as mmol pyridine chemi-
sorbed per gram of catalyst.
Sample Total acidity, mmol/g
HZSM-5 0.63 4.0
2.5Fe2.5Mo-HZSM-5 0.58 2.7
Effect of Fe-Mo promoters on HZSM-5 zeolite catalyst 623
of the acidity H-ZSM-5 resulting in an increase in the Lewis
acid sites and a decrease in the BAS/LAS ratio, thus is
increased of the selectivity to C
aromatics what is sup-
ported by pyridine-DRIFTS, NH
-TPD and catalyst evalua-
tion results [18].
The Fe species are important for incorporation to
Mo catalyst not only because of their promotional effects
and stability but because they are abundant, cheap and envi-
ronmentally friendly and can have industrial applications
[45]. We speculate that the electron transfer (strong interac-
tion) occurred between Fe and Mo species for 2.5Fe2.5Mo-
ZSM-5 and 3Fe2Mo-ZSM-5 catalysts and confirmed it by
-TPR. Unfortunately, until now no definitive conclusion
has been established regarding the effect of Fe additive on
Mo catalysts [45], but it can be concluded that the synergetic
effect between Fe and Mo species exists and to improve the
catalytic performance of 1-hexene aromatization reaction
4. Conclusions
The 1-hexene aromatization was studied on metal modified
HZSM-5 and compared with unmodified HZSM-5 (Zeolyst
Int., SiO
30). Modifying of the HZSM-5 catalyst
with Fe and Mo species could enhance the rate of aromatics
production in the 1-hexene aromatization reaction. At
350 °C, a variety of products were detected, where the C
and C
were the major products in the gasoline range and
was the major product in the distillate range. The
Fe-Mo modified H-ZSM-5 zeolites were prepared using the
incipient wetness impregnation method in a varying ratio. A
combination of catalytic testing and detailed catalyst charac-
terization resulted in the identification of effects on the activity
depending on the varying ratio of metals in the zeolite
catalysts. Adding of the Fe-Mo species to HZSM-5 has been
shown to be positive for the high selectivity of gasoline and dis-
tillate production both at standard experimental conditions
with using atmospheric pressure. The decrease in the amount
of strong acid sites results in an increase in the selectivity to
aromatics. The 2.5Fe2.5Mo-ZSM-5 and 3Fe2Mo-ZSM-5
catalysts showed higher selectivity in gasoline and distillate
range than parent HZSM-5 and others promoted catalysts.
Thus, the synergetic effect of Fe and Mo species exists for
2.5Fe2.5Mo-ZSM-5 and 3Fe2Mo-ZSM-5 catalysts, which has
improved the catalytic performance of 1-hexene aromatization
5. Declarations of interest
The authors declare no competing interests.
We are grateful to PetroSA for financial support. We are also
indebted to Dr. Petar Djinovic
ˇ(National Institute of Chem-
istry) for obtaining and description the pyridine-DRIFT spec-
tra of the H-ZSM-5 and 2.5Fe2.5Mo-ZSM-5 samples.
[1] Y. Li, S. Liu, Z. Zhang, S. Xie, X. Zhu, L. Xu, Aromatization
and isomerization of 1-hexene over alkali-treated HZSM-5
zeolites: Improved reaction stability, Appl. Catal. A Gen. 338
(2008) 100–113,
[2] L. Zhang, H. Liu, X. Li, S. Xie, Y. Wang, W. Xin, S. Liu, L. Xu,
Differences between ZSM-5 and ZSM-11 zeolite catalysts in 1-
hexene aromatization and isomerization, Fuel Process. Technol.
91 (2010) 449–455,
[3] Y. Li, S. Liu, S. Xie, L. Xu, Promoted metal utilization capacity
of alkali-treated zeolite: preparation of Zn/ZSM-5 and its
application in 1-hexene aromatization, Appl. Catal. A Gen.
360 (2009) 8–16,
[4] R.J. Nash, M.E. Dry, C.T. O’Connor, Aromatization of 1-
hexene and 1-octene by gallium/H-ZSM-5 catalysts, Appl.
Catal. A Gen. 134 (1996) 285–297.
[5] G. Wang, W. Wu, W. Zan, X. Bai, W. Wang, X. Qi, O.V.
Kikhtyanin, Preparation of Zn-modified nano-ZSM-5 zeolite
and its catalytic performance in aromatization of 1-hexene,
Trans. Nonferrous Met. Soc. China 25 (2015) 1580–1586,
[6] I. Coleto, M.I. Lo
´pez, R. Rolda
´n, J.P. Go
´mez, C. Jime
´n, F.J. Romero-Salguero, Transformation of 1-
hexene on Pt supported ZSM-5 zeolite modified with tin,
copper or chromium, React. Kinet. Mech. Catal. (2015),
[7] G. Bellussi, F. Mizia, V. Calemma, P. Pollesel, R. Millini,
Oligomerization of olefins from Light Cracking Naphtha over
zeolite-based catalyst for the production of high quality diesel
fuel, Microp. Mesopor. Mater. 164 (2012) 127–134, https://doi.
[8] R. Van Grieken, J.M. Escola, J. Moreno, R. Rodrı
´guez, Liquid
phase oligomerization of 1-hexene over different mesoporous
aluminosilicates (Al-MTS, Al-MCM-41 and Al-SBA-15) and
micrometer/nanometer HZSM-5 zeolites, Appl. Catal. A Gen.
305 (2006) 176–188,
[9] J.P.G. Pater, P.A. Jacobs, J.A. Martens, Oligomerization of hex-
1-ene over acidic aluminosilicate zeolites, MCM-41, and silica-
alumina co-gel catalysts: a comparative study, J. Catal. 184
(1999) 262–267,
Fig. 12 Product distribution of fuel range hydrocarbons over
HZSM-5, 2.5Fe2.5Mo-ZSM-5 and 3Fe2Mo-ZSM-5 samples
(TOS = 6 h, T = 350 °C, FR = 0.098 mL/min, WHSV = 4 h
624 A. Kostyniuk et al.
[10] R. Quann, L. Green, S.A. Tabak, F.J. Krambeck, Chemistry of
olefin oligomerization over ZSM-5 catalyst, Ind. Eng. Chem.
Res. (1988) 565–570,
[11] A. Corma, C. Martı
´nez, E. Doskocil, Designing MFI-based
catalysts with improved catalyst life for C 3 = and C 5 =
oligomerization to high-quality liquid fuels, J. Catal. 300 (2013)
[12] A. De Klerk, Oligomerization of 1-hexene and 1-octene over
solid acid catalysts, Ind. Eng. Chem. Res. 44 (2005) 3887–3893,
[13] R. van Grieken, J.M. Escola, J. Moreno, R. Rodrı
´guez, Direct
synthesis of mesoporous M-SBA-15 (M = Al, Fe, B, Cr) and
application to 1-hexene oligomerization, Chem. Eng. J. 155
(2009) 442–450,
[14] E. Kriva
´n, S. Tomasek, J. Hancso
´k, Application Possibilities of
Zeolite Catalysts in Oligomerization of Light Olefins, Period.
Polytech. Chem. Eng. 58 (2014) 149–156,
10.3311/PPch. 7204.
[15] X.B. Li, X.Y. Jiang, Propylene oligomerization to produce diesel
fuel on Zr-ZSM-5 catalyst, Chem. Technol. Fuels Oils 49 (2013)
[16] V. Abdelsayed, D. Shekhawat, M.W. Smith, Effect of Fe and Zn
promoters on Mo/HZSM-5 catalyst for methane
dehydroaromatization, Fuel 139 (2015) 401–410, https://doi.
[17] Y. Xu, Y. Suzuki, Z.G. Zhang, Comparison of the activity
stabilities of nanosized and microsized zeolites based Fe-Mo/
HZSM-5 catalysts in the non-oxidative CH4
dehydroaromatization under periodic CH4-H2 switching
operation at 1073 K, Appl. Catal. A Gen. 452 (2013) 105–116,
[18] S.S. Masiero, N.R. Marcilio, O.W. Perez-Lopez, Aromatization
of methane over Mo-Fe/ZSM-5 catalysts, Catal. Lett. 131 (2009)
[19] Y. Xu, J. Wang, Y. Suzuki, Z.G. Zhang, Effect of transition
metal additives on the catalytic stability of Mo/HZSM-5 in the
methane dehydroaromatization under periodic CH 4–H2 switch
operation at 1073 K, Appl. Catal. A Gen. 409–410 (2011) 181–
[20] A.J.J. Koekkoek, H. Xin, Q. Yang, C. Li, E.J.M. Hensen,
Hierarchically structured Fe/ZSM-5 as catalysts for the
oxidation of benzene to phenol, Microp. Mesop. Mater. 145
(2011) 172–181,
[21] Y. Yan, S. Jiang, H. Zhang, Efficient catalytic wet peroxide
oxidation of phenol over Fe-ZSM-5 catalyst in a fixed bed
reactor, Sep. Purif. Technol. 133 (2014) 365–374,
[22] Y. Wei, P.E. de Jongh, M.L.M. Bonati, D.J. Law, G.J. Sunley,
K.P. de Jong, Enhanced catalytic performance of zeolite ZSM-5
for conversion of methanol to dimethyl ether by combining
alkaline treatment and partial activation, Appl. Catal. A Gen.
504 (2015) 211–219,
[23] L. Huang, F. Qin, Z. Huang, Y. Zhuang, J. Ma, H. Xu, W.
Shen, Hierarchical ZSM-5 zeolite synthesized by an ultrasound-
assisted method as a long-life catalyst for dehydration of
glycerol to acrolein, Ind. Eng. Chem. Res. 55 (2016) 7318–
[24] J. Pere
´rez, D. Verboekend, A. Bonilla, S. Abello
´, Zeolite
catalysts with tunable hierarchy factor by pore-growth
moderators, Adv. Funct. Mater. 19 (2009) 3972–3979, https://
[25] H. Liu, S. Yang, J. Hu, F. Shang, Z. Li, C. Xu, J. Guan, Q. Kan,
A comparison study of mesoporous Mo/H-ZSM-5 and
conventional Mo/H-ZSM-5 catalysts in methane non-oxidative
aromatization, Fuel Process. Technol. 96 (2012) 195–202,
[26] M. Rostamizadeh, A. Taeb, Highly selective Me-ZSM-5 catalyst
for methanol to propylene (MTP), J. Ind. Eng. Chem. 27 (2015)
[27] B. Li, S. Li, N. Li, H. Chen, W. Zhang, X. Bao, B. Lin, Structure
and acidity of Mo/ZSM-5 synthesized by solid state reaction for
methane dehydrogenation and aromatization, Microp. Mesop.
Mater. 88 (2006) 244–253,
[28] G. Espinosa, J.M. Dominguez, L. Diaz, C. Angeles, Catalytic
behavior of CoMo/ZSM5 catalysts for CS2 conversion, Catal.
Today. 148 (2010) 153–159,
[29] K. Velebna
´, M. Horn
ˇek, V. Jorı
´k, P. Hudec, M. C
L. C
ˇ, The influence of molybdenum loading on activity of
ZSM-5 zeolite in dehydroaromatization of methane, Microp.
Mesop. Mater. 212 (2015) 146–155,
[30] F. Lai, X. Liu, W. Li, F. Shen, Macrolactonization of methyl 15-
hydroxypentadecanoate to cyclopentadecanolide over Mo-Fe/
HZSM-5 catalyst, React. Kinet. Mech. Catal. 100 (2010) 407–
[31] M. Hosseinpour, H. Amiri, S.J. Ahmadi, M.A. Mousavian, The
role of supercritical water on the rapid formation of ZSM-5
nanocatalyst, J. Supercrit. Fluids. (2015),
[32] X. Zhao, L. Wei, S. Cheng, Y. Huang, Y. Yu, J. Julson,
Catalytic cracking of camelina oil for hydrocarbon biofuel over
ZSM-5-Zn catalyst, Fuel Process. Technol. 139 (2015) 117–126,
[33] X. Cheng, P. Yan, X. Zhang, F. Yang, C. Dai, D. Li, X.X. Ma,
Enhanced methane dehydroaromatization in the presence of
CO2over Fe- and Mg-modified Mo/ZSM-5, Mol. Catal. 437
(2017) 114–120,
[34] Q. Dong, X. Zhao, J. Wang, M. Ichikawa, Studies on Mo/
HZSM-5 Complex Catalyst for Methane Aromatization, J. Nat.
Gas Chem. 13 (2004) 36–40.
[35] Z. Li, K.C. Xie, W. Huang, W. Reschetilowski, Molybdenum
loaded on HZSM- 50: a catalyst for selective catalytic reduction
of nitrogen oxides 158 (2005) 1741–1748.
[36] H.Y. Wang, T.T. Jiao, Z.X. Li, C.S. Li, S.J. Zhang, J.L. Zhang,
Study on palm oil hydrogenation for clean fuel over Ni-Mo-W/
??-Al2O3-ZSM-5 catalyst, Fuel Process. Technol. 139 (2014) 91–
[37] K. Van der Borght, V.V. Galvita, G.B. Marin, Ethanol to higher
hydrocarbons over Ni, Ga, Fe-modified ZSM-5: Effect of metal
content, Appl. Catal. A Gen. 492 (2015) 117–126, https://doi.
[38] H. Lan, X. Xiao, S. Yuan, B. Zhang, G. Zhou, Y. Jiang,
Synergistic Effect of Mo–Fe Bimetal Oxides Promoting
Catalytic Conversion of Glycerol to Allyl Alcohol, Catal. Lett.
147 (2017) 2187–2199,
[39] Q. Zhang, K. Qiu, B. Li, T. Jiang, X. Zhang, L. Ma, T. Wang,
Isoparaffin production by aqueous phase processing of sorbitol
over the Ni/HZSM-5 catalysts: effect of the calcination
temperature of the catalyst, Fuel. 90 (2011) 3468–3472, https://
[40] T.E. Tshabalala, N.J. Coville, J.A. Anderson, M.S. Scurrell,
Dehydroaromatization of methane over Sn–Pt modified Mo/H-
ZSM-5 zeolite catalysts: Effect of preparation method, Appl.
Catal. A Gen. 503 (2015) 218–226,
[41] X. Li, D. Han, H. Wang, G. Liu, B. Wang, Z. Li, J. Wu,
Propene oligomerization to high-quality liquid fuels over Ni/
HZSM-5, Fuel 144 (2015) 9–14,
Effect of Fe-Mo promoters on HZSM-5 zeolite catalyst 625
[42] H. Long, X. Wang, W. Sun, G. Xiong, K. Wang, Effect of
acidity on n-octene reaction over potassium modified nanoscale
HZSM-5, Fuel 87 (2008) 3660–3663,
[43] J. Li, P. Miao, Z. Li, T. He, D. Han, J. Wu, Z. Wang, J. Wu,
Hydrothermal synthesis of nanocrystalline H[Fe, Al]ZSM-5
zeolites for conversion of methanol to gasoline, Energy Convers.
Manag. 93 (2015) 259–266,
[44] M. Tamura, K. Shimizu, A. Satsuma, Applied Catalysis A :
General Comprehensive IR study on acid / base properties of
metal oxides, Applied Catal. A Gen. 433–434 (2012) 135–145,
[45] A. Sridhar, M. Rahman, S.J. Khatib, Enhancement of
Molybdenum/ZSM-5 Catalysts in Methane Aromatization by
the Addition of Iron Promoters and by Reduction/
Carburization Pretreatment, ChemCatChem. 10 (2018) 2571–
[46] Z. Li, K. Xie, W. Huang, W. Reschetilowski, Selective Catalytic
Reduction of NOxwith Ammonia over Fe-Mo/ZSM-5
Catalysts, Chem. Eng. Technol. 28 (2005) 797–801, https://doi.
626 A. Kostyniuk et al.
... In addition, the aromatic compounds are produced by the presence of the Lewis acid site. It was reported that the Lewis acid site has a high affinity to dehydrogenation and aromatization reactions [42,44]. ...
... This fact confirms that the Mo impregnation to the ZSM-5 catalyst increases the cyclization and aromatization reactions. Some researchers reported that the MoO x center site has a high affinity to the aromatization reaction [10,44]. However, by incorporating Mo with Co, it is found that it decreases the aromatization reaction, as the Co-Mo/ZSM-5 catalyst gives the lowest aromatic compounds, as well as the lowest ratio of naphthenes-to-olefins+paraffins and aromatics-to-olefins+paraffins. ...
Full-text available
The purposes of this study are to investigate the effect of metal (Co and Mo) impregnation to ZSM-5 catalysts on the Brønsted to Lewis (B/L) ratio as the active sites of cracking reaction, and the catalysts’ performance testing for palm oil cracking to produce hydrocarbon-rich biofuels. Both metals were impregnated on the ZSM-5 catalyst using a wet-impregnation method. The catalysts were characterized using X-ray diffraction (XRD), X-ray Fluorescence (XRF), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET), and Pyridine-probed Fourier-Transform Infrared (Py-FTIR) spectroscopy methods. The catalysts were tested on the cracking process of palm oil to biofuels in a continuous fixed-bed catalytic reactor. In order to determine the composition of the organic liquid product (OLP, biofuels), the product was analyzed using a gas chromatography-mass spectrometry (GC-MS) method. The results showed that the co-impregnation of Co and Mo to ZSM-5 highly increased the Brønsted to Lewis acid site (B/L) ratio, although the total number of acid sites decreased. However, the impregnation of Co and Mo on the ZSM-5 decreased the surface area of catalysts due to pore blocking by metals, while the B/L ratio of the catalysts increased. It was obtained that by utilizing Co- and Mo-impregnated ZSM-5 catalysts, the hydrocarbons product selectivity increased from 84.32% to 95.26%; however, the yield of biofuels decreased from 67.57% to 41.35%. The increase in hydrocarbons product selectivity was caused by the improvement of the Brønsted to Lewis (B/L) acid sites ratio.
... The absorption bands at 1225, 1088, 810, and 540 cm −1 are considered as the characteristic signals for the framework vibration of the H-ZSM-5 zeolite catalyst. It was found that the band 540 cm −1 belongs to the T-O (T=Si or Al) vibration of the internal tetrahedral, 540 cm −1 to the double ring, 810 cm −1 to the external symmetric stretch, 1088 cm −1 to the internal asymmetric stretch, and 1225 cm −1 to the external asymmetric stretch, respectively [26,27]. The internal vibrations of SiO 4 and AlO 4 are represented by the absorption bands at 1088 and 810 cm −1 , respectively [28]. ...
... Reactions 2022, 3, 5 of 17 stretch, 1088 cm −1 to the internal asymmetric stretch, and 1225 cm −1 to the external asymmetric stretch, respectively [26,27]. The internal vibrations of SiO4 and AlO4 are represented by the absorption bands at 1088 and 810 cm −1 , respectively [28]. ...
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This study aimed to valorize microcrystalline cellulose (MCC) using protonated zeolite catalysts such as (H-ZSM-5) and Cr/H-ZSM-5 (5%) in ionic liquid. The catalytic effect in synergy with 1-butyl-3-methylimidazolium Chloride ([BMIM] Cl) ionic liquid was studied in detail. The total reducing sugar (TRS) was determined using the 3, 5-dinitrisalcylic acid (DNS) array method. The catalysts were characterized using techniques such as Fourier transform infrared (FT-IR), X-ray diffraction analysis (XRD), temperature-programmed desorption of ammonia (NH3-TPD), and BET-surface area analyzer. H-ZSM-5 effectively depolymerized cellulose with a maximum yield of 70% total reducing sugar (34% glucose, 8% fructose, and 4.5% 5-HMF). Cr/H-ZSM-5 catalyst dehydrated fructose to 5-HMF with a yield of 53%. The use of ionic liquid significantly reduced the activation energy of formation and decomposition. The activation energy determined in cellulose hydrolysis was 85.83 KJ mol−1 for a reaction time of 180 min while the decomposition energy was found to be 42.5 kJ mol−1.
... The peak at 544°C is due to tetrahedral molybdenum species reduction MoO 2+ → Mo 0 [43,44]. The peak at 658°C is assigned to the reduction of the Mo 2+ phase to Mo 0 [45]. Another reduction peak (688 and 814°C) might be due to the reduction of molybdenum oxide (Mo 4+ ) to metallic molybdenum (Mo 0 ) [46]. ...
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Mesoporous aluminosilicate (MAS) and bifunctional catalysts based on it were synthesized. The MAS synthesis is based on the method of copolycondensation of silicon and aluminum sources in the presence of alcohol. Hexadecylamine was used as a template for the formation of a porous structure. The catalysts were characterized by X-ray diffraction, Brunauer–Emmett–Teller, temperature-programmed desorption of ammonia, hydrogen-temperature programmed reduction, Fourier transform infra-red spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopic methods. The catalytic activity of Ni/MAS-H-bentonite and Mo/MAS-H-bentonite was investigated during the hydroconversion of n -hexadecane. It has been shown that a sample promoted with molybdenum and nickel based on MAS has the high activity and selectivity in the process of n -hexadecane hydroisomerization under optimal conditions (320°C, atm pressure).
... The former mainly refers to the introduction of Fe species before or during the formation of zeolite frameworks, including the hydrothermal synthesis [101,102] dry-gel conversion method (DGC) [6], etc. The post-treatment method means that Fe was introduced into the well crystallized zeolite via impregnation method [103], ion exchange method [104], chemical vapor deposition method [48,105], etc. The dispersion of Fe on the zeolite support or into the specific position of the zeolite channel could be realized by controlling the conditions of the treatment process. ...
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Fe-zeolites are widely applied in petrochemical, fine chemical, environmental protection, and other catalytic fields because of the zeolitic properties as well as the redox properties endowed by the introduction of Fe species. After being introduced into the zeolitic framework, the poor properties of traditional aluminosilicate zeolites, i.e., lack of active sites, low catalytic activity, poor anti-coking performance, etc., could be effectively improved. The state of Fe species in zeolite, which significantly affects the properties (stability, acidity, redox properties, etc.) of Fe-zeolite, was determined by both the introduction methods/conditions and the properties (porosity / acidity, etc.) of zeolite. From this point of view, a clear understanding of the structure-activity relationship of Fe-zeolite is an important prerequisite for designing functional materials as necessary. Therefore, in this review, recent developments on the synthesis, properties as well as the application of Fe-based zeolites were briefly summarized. In detail, the factors affecting the recognition of types as well as the distribution of Fe species in Fe-zeolites and the effects of the introduction of Fe on the physicochemical properties & catalytic performance of zeolites are systematically clarified. Then, the applications of Fe-zeolite in chemical industry and environmental engineering were reviewed and outlooked. This review is expected to provide theoretical reference for the structural design and application of Fe-based zeolites in the future.
The study reports the conversion of crude oil to basic chemicals over a template-free green synthesis of ZSM-5(40) zeolite using halloysite (HAL) and bolus alpha (BA) as silica and alumina precursors. The Z(40)HAL and Z(40)BA exhibited hierarchical pores with high surface area of 248 m2/g and 257 m2/g, respectively. The addition of soft template during the synthesis of Z(40)BA forms a Z(40)BAT zeolite with lower surface area. The synthesized zeolites were impregnated with 2wt%Mn and tested for the steam catalytic cracking of crude oil to light olefins and aromatics catalysts at 675 °C in a fixed-bed reactor. Maximum light olefins (C2=-C4=) yield (47 wt%) and total aromatics (14.7 wt%) were attained over 2Mn/Z(40)HAL catalyst. The conversion of crude oil (68.4%) is attributed to hierarchical pores and the presence of large weak and strong acid sites in the 2Mn/Z(40)HAL zeolite. Moreover, due to the high reaction temperature, some effects of thermal cracking such as protolytic cracking reactions with high ethylene yield (22%) were introduced. The addition of 1% phosphorus and 1%Mn to Z(40)HAL resulted in lower catalytic cracking activity. Similarly, the 2Mn/Z(40)BAT performed slightly lower than the template-free 2Mn/Z(40)BA additive. The experimental results demonstrate the technical feasibility of template-free green synthesis of ZSM-5 zeolite in the conversion of crude oil to basic chemicals.
The increasing demand for plastics has resulted in significant plastic waste accumulation and environmental pollution. Catalytic pyrolysis is an attractive treatment method to mitigate the plastic waste management problems and recover high-value oil products. In our study, waste polyethylene (PE) was pyrolyzed to produce benzene, toluene, ethylbenzene and xylene (BTEX)-enriched oil a using dielectric barrier discharge plasma catalytic pyrolysis reactor. Ga-modified Hydro-Zeolite Socony Mobile-Five (HZSM-5) was used as a pyrolysis catalyst. The effects of the PE to Ga/HZSM-5 ratio and discharge power on BTEX enhancement and carbon deposition are discussed. The greatest BTEX selectivity (77.04%) and relatively low coke yield (1.37%) were achieved when the PE/(Ga/HZSM-5) ratio was 2:1 with a non-thermal plasma (NTP) discharge power of 20 W. The regeneration effects of conventional thermal oxidation and NTP on the zeolite catalyst were compared. NTP regeneration at a low temperature (150 °C) achieved the same coke removal rate as that of thermal regeneration at high temperatures (500 °C). Ga/HZSM-5 subjected to NTP regeneration showed higher activity for BTEX formation (BTEX selectivity was 42.10%) as compared to that shown by Ga/HZSM-5 subjected to thermal regeneration (BTEX selectivity was 40.59%). The NTP synergistic catalytic pyrolysis of plastics over Ga/HZSM-5 was found to be a promising strategy for mitigating the plastic waste management problems and upgrading the quality of oil products.
The reduction of olefin content in FCC gasoline is challenging for clean gasoline production, owing to the tightened regulations at 15% (vol.%) olefin content of clean vehicle fuels with China VI standard. The best route for olefin reduction has been proposed by selective converting olefins to aromatics or iso-alkanes with a high-octane number. Here, ZSM-5 zeolite supported metal catalysts have been developed for hydro-upgrading FCC gasoline. ZSM-5 zeolite blended with alumina was firstly treated by hydrothermal treatment at 450 oC, 500 oC and 550 oC, respectively, and the effect of Zn, Ni-Zn and La-Ni-Zn deposition on hydro-upgrading was also investigated. The hydrothermal modification effectively reduced acidity of ZSM-5 zeolite with the increase of B/L ratio and the decrease of L acid sites. The introduction of Zn, Ni and La to the zeolite supports increases the proportion of medium-strong acid from 42% to 48%, and the resulting catalyst shows excellent olefin reduction performance in FCC gasoline hydro-upgrading. The content of aromatics increases 5% (1.2 vol%); iso-alkane content increases 16% (5.5 vol%) and the research octane number (RON) increases 4.6. These findings show the ZSM-5 supported Zn-Ni-La catalyst can be served as a potential industrial catalyst for FCC gasoline hydro-upgrading.
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In this study, KIT-6 silica with well-ordered 3-D mesoporosity was developed as support to prepare Fe/KIT-6, Mo/KIT-6, and MoFe-x/KIT-6 (x = 0.25, 0.3, and 0.35) oxide catalysts for catalytic conversion of gas-glycerol into allyl alcohol. The catalysts were also characterized by XRD, BET, XPS, H2-TPR, and NH3-TPD. The catalytic conversion of glycerol showed a positive correlation with the surface moderate acid density of catalysts, following the order of Fe/KIT-6 < MoFe0.25/KIT-6 < MoFe0.35/KIT-6 < MoFe0.3/KIT-6 < Mo/KIT-6. Differently, the production of allyl alcohol was closely related with the moderate redox sites following a hydrogen transfer mechanism. The MoFe-x/KIT-6 showed much higher selectivity than the Fe/KIT-6 and Mo/KIT-6, which resulted from the strong synergistic effect between Fe2O3 and MoO3 altering the surface moderate acid strength, surface acid amounts, and reducibility of catalysts. The MoFe-0.3/KIT-6 exhibited a remarkable yield of 26.8% of allyl alcohol at 94.0% conversion of glycerol without external hydrogen donors supplied to the system, which benefits from the good balance between moderate acidity and weak reducibility of catalysts. The developed cubic Ia3d meso-structure was also benefit for improving the catalytic stability of MoFe0.3/KIT-6. Graphical Abstract Allyl alcohol can produce from gas–solid catalytic conversion of glycerol over the weekly acidic Fe2O3 and MoO3 supported on SiO2. The yield of allyl alcohol can be significantly improved over the MoO3–Fe2O3/SiO2 composite oxide catalysts, because of the strong interaction between MoO3 and Fe2O3. The catalytic conversion of glycerol was positively related with the surface weak acid site density of catalysts, while the allyl alcohol seems to form over the redox sites. Comparing with the single component Fe2O3/SiO2and MoO3/SiO2 catalysts, the strong synergistic effect of MoO3 with Fe2O3 guarantee the MoO3–Fe2O3/SiO2 having relatively high surface week acid site density and certain reducibility, which showed a good balance between weak acidity and reducibility thus obviously increasing the allyl alcohol yield from 26.8 to 94% catalytic conversion of glycerol through gas–solid catalytic reaction without any additives. Open image in new window
The influence of Fe additive and different types of pretreatment were studied on HZSM-5 supported Mo-oxide (MoOx) catalysts for methane aromatization. The catalytic behavior of catalysts consisting of 6 wt% Mo/ZSM-5 with 0, 0.2 and 1wt% Fe was tested with two types of pretreatment: 1) heating under He flow, 2) reducing in H2/CH4 and carburizing in CH4. Under He pretreatment, adding 0.2 wt% Fe improved the benzene yield, but 1 % Fe slightly decreased it. Precarburizing the catalysts resulted in enhanced catalytic properties for all Fe loadings, and furthermore, improved the catalyst stability. The precarburized 6wt% Mo-0.2wt%Fe catalyst presented the highest benzene yield (6.9%), which was almost stable in the subsequent 10-hour test. The fresh and spent catalysts were characterized by XRD, N2 adsorption, TPR, SEM, TPO and TGA. The results show that precarburized catalysts are more stable due to the formation of smaller amounts of carbon deposits, and consequently lower pore blockage. Addition of Fe causes the carbon deposits to be more reactive and easier to burn off. Higher Fe loadings are linked to the formation of carbon nanotubes.
A series of metal-modified (i.e., Fe or Mg) Mo/ZSM-5 were prepared by the impregnation method and subsequently tested in the aromatization of CH4-CO2 mixtures in a continuous flow fluidized-bed quartz reactor. Mg modification improved both the catalytic activity (9.7 vs. 12.3% conversion) and the selectivity to benzene (65.7 vs. 68.4%) while inhibiting carbon deposition (13.9 vs 10.1% carbon deposited, as determined by thermogravimetry, TG) during the dehydroaromatization of methane in the presence of CO2. SEM confirmed that the carbon species deposited over Mo/HZSM-5 and Fe-Mo/HZSM-5 catalysts were mainly carbon nanotubes. In contrast, carbon nanotubes were not detected over Mg-Mo/HZSM-5. The TG profiles and the XPS spectra revealed that the introduction of Mg likely favored the generation of Mo2C species which are considered active sites for methane dehydroaromatization. The present work provides a strategy for greatly improving the catalytic performance in the methane dehydroaromatization in the presence of CO2.
This paper presents a facile and economical route to synthesize hierarchical porous ZSM-5 zeolite (HP-ZSM-5) by ultrasound-assisted method as along-life catalyst for glycerol dehydration reaction, which is an important reaction for the sustainable production of acrolein from bio-based glycerol. The systematic characterizations indicate that the HP-ZSM-5 catalyst possesses large intracrystal mesopores and abundant accessible acid sites. The ultrasonic treatment and violent stirring play a critical role in the synthesis process. Compared with commercial ZSM-5 zeolite (C-ZSM-5), the TOF value at time zero of the HP-ZSM-5 catalyst increased nearly one times, the lifetime of the HP-ZSM-5 catalyst was prolonged nine times.The HP-ZSM-5 catalyst exhibits a slower coking rate with higher coke tolerance, the cokes preferentially form inside the intracrystal mesopores and the ratio of hardly removed graphitic carbonis lower than that of the C-ZSM-5. HP-ZSM-5 catalyst exhibits prominent stability of nearly 50 hand high acrolein selectivity of 82%.
Cracking of camelina oil over non-catalyst and ZSM-5 catalyst doped with different Zn concentrations (0, 10, 20 and 30 wt.%) in a fixed-bed reactor was investigated. The fresh and used catalysts were characterized using XRD, FT-IR, BET and TEM. Characterizations of the produced hydrocarbon biofuel, distillation residual and non-condensable gas were carried out. The effect of non-catalyst and catalyst on the physicochemical properties and yield of products was discussed. The results showed that the introduction of Zn did not change the zeolite crystalline structure and ZnO might deposit on the external surface and/or inside the pores of the support ZSM-5. After upgrading, hydrocarbon biofuel had a lower viscosity, lower density, higher heating value (HHV) and higher water content than raw camelina oil. The optimum Zn concentration to ZSM-5 was 20 wt.%, at which the highest hydrocarbon biofuel yield and comprehensively the best quality were obtained. Compared to non-catalytic cracking of camelina oil, the loading of Zn to ZSM-5 could improve some physicochemical properties of the hydrocarbon biofuel. In addition, the loading of Zn to ZSM-5 could facilitate the chemical reactions such as decarbonylation and dehydrogenation.
Zeolite ZSM-5 (MFI) due to its excellent hydrothermal stability and high catalytic activity for methanol dehydration to dimethyl ether (MTD) has been considered for use in combination with a methanol synthesis catalyst, such as Cu/ZnO/Al2O3, in the conversion of syngas to dimethyl ether. However, the decline of dimethyl ether selectivity and catalytic activity over ZSM-5 by the formation of hydrocarbons and coke at optimum operation temperature of Cu/ZnO/Al2O3 catalyst impedes industrial application. In this work, for the first time the effects of alkaline treatment combined with partial activation on the catalytic performance of ZSM-5 catalysts with different Si/Al ratio have been studied for MTD reaction. The relationship between the physicochemical properties and catalytic performance has been assessed from the combined results of XRD, SEM, N2 physisorption, NH3-TPD, elemental analysis, online-GC and other characterization techniques. The results show that at a reaction temperature of 300 °C and WHSV of 13 g g−1 h−1, all the parent and alkaline-treated ZSM-5 after full activation at 500 °C exhibited a decline of dimethyl ether selectivity and methanol conversion over time. Alkaline treatment improved DME selectivity over ZSM-5 with an Si/Al ratio of 25, which could be ascribed to the formation of extra mesoporosity enhancing the diffusion capability and decreasing the probability of secondary reactions of DME to hydrocarbons. A decrease of the activation temperature led to a significantly improved DME selectivity for all parent and alkaline-treated ZSM-5 because ammonium cations were selectively retained in the structure and blocked the strong acid sites that brought about side-reactions. ZSM-5 with Si/Al ratio of 25 modified by combining alkaline treatment and partial activation, due to the synergy effect of moderated acidity and enhanced diffusion capability, exhibited improved catalytic performance with almost 100% DME selectivity, near 84% methanol conversion and excellent stability during 4 days of reaction.
The effect of different catalyst preparation methods to make tin–platinum modified Mo/H-ZSM-5 zeolite catalysts for methane dehydroaromatization at 700 °C was investigated. The catalysts were prepared by both incipient wetness co-impregnation and sequential impregnation and calcined at 500 °C for 6 h. Catalysts prepared by the co-impregnation method showed a good platinum dispersion (10.8%), higher than found for the Pt/Sn and Sn/Pt sequentially impregnated catalysts (5.6% and 1.4%, respectively). Successive calcination treatments influenced the location of both tin and platinum in the catalyst and a decrease in platinum dispersion after reduction was evident from CO chemisorption studies. The order of sequentially loading platinum before or after tin had an effect on the electronic and structural properties of platinum as shown by XPS and FTIR studies. Different catalytic activities and aromatic selectivities were observed for the Pt/Sn and Sn/Pt catalysts. The co-impregnated Sn–Pt and the sequentially impregnated Pt/Sn catalysts showed high aromatic selectivity (>70%) and low coke selectivity (<20%). The decrease in coke selectivity is mainly dependent on the availability of platinum sites for hydrogenation of carbonaceous species.
ZSM-5 zeolite samples containing Pt and a second metal (Sn, Cu or Cr) were prepared by different impregnation procedures. All these catalysts were highly active in the transformation of 1-hexene. A great variety of hydrocarbons were obtained, whose proportion depended on the particular catalyst and the reaction conditions. In general, low temperatures (250 °C) favored the double bond shift reaction, whereas medium temperatures (350 °C) predominantly led to cracking and skeletal isomerization. However, cracking was the major reaction at temperatures above 450 °C. The addition of the second metal decreased the hydrogenating activity of Pt and so olefins constituted a considerable fraction in the product. The use of nitrogen as a carrier gas instead of hydrogen favored the formation of both internal and branched olefins while reducing cracking. The reaction products are interesting for their use in gasoline blending.
The promoting effect of introducing Zn into nano-ZSM-5 zeolites by conventional impregnation method and isomorphous substitution on the performance of 1-hexene aromatization was investigated. The nano-ZSM-5 zeolite was synthesized by a seed-induced method without organic templates. The Zn-modified nano-ZSM-5 zeolite catalysts, xZn/HNZ5 and yZn/Al-HNZ5, were prepared by the conventional impregnation method and isomorphous substitution, respectively. The structure, chemical composition and acidity of the catalysts were characterized by XRD, XRF, N2 adsorption, SEM, NH3-TPD and Py-IR, while the catalytic properties were evaluated at 480 °C and a weight hourly space velocity (WHSV) of 2.0 h-1 in the aromatization procedure of 1-hexene. Compared with xZn/HNZ5, yZn/Al-HNZ5 exhibited smaller particles and higher dispersion of Zn species, which led to greater intergranular mesopore and homogeneous acidity distribution. Experimental results indicated that the synergy effect between the Brønsted and Lewis acid sites of the isomorphously substituted nano-ZSM-5 zeolites could significantly increase aromatics yield and improve catalytic stability in the 1-hexene aromatization.