Influence of HZSM-5 content on behavior of CoMo/HZSM5-HMS composite catalysts in hydrodesulphurization of dibenzothiophene

Article abstract of DOI:10.1007/s13738-017-1089-x

CoMo-supported micro/mesoporous catalysts (CoMo/HZSM5(x)-HMS) were synthesized by varying the weight percent of zeolite (10, 20, 30 and 40 wt%). Catalytic functionalities were investigated for hydrodesulphurization reaction of dibenzothiophene over a wide temperature range of 250–400?°C. Characterization methods as XRD, XRF, FT-IR, UV–Vis DRS, NH₃-TPD, H₂-chemisorption, nitrogen adsorption–desorption and TGA confirmed the obtained results from these catalysts. A significant enhancement of the catalytic activity was observed for the catalysts supported on CoMo/HZSM5(20)-HMS at T?=?350?°C (>97%).

Full text of DOI:10.1007/s13738-017-1089-x

J IRAN CHEM SOC
DOI 10.1007/s13738-017-1089-x
ORIGINAL PAPER
Influence of HZSM‑5 content on behavior of CoMo/HZSM5‑HMS
composite catalysts in hydrodesulphurization of dibenzothiophene
N. Parsafard1 · M. H. Peyrovi2 · Ni. Parsafard2
Received: 9 September 2016 / Accepted: 28 February 2017
© Iranian Chemical Society 2017
Abstract CoMo-supported micro/mesoporous catalysts
(CoMo/HZSM5(x)-HMS) were synthesized by varying
the weight percent of zeolite (10, 20, 30 and 40 wt%).
Catalytic functionalities were investigated for hydrodesul-
phurization reaction of dibenzothiophene over a wide tem-
perature range of 250–400 °C. Characterization methods
as XRD, XRF, FT-IR, UV–Vis DRS, NH3-TPD, H2-chem-
isorption, nitrogen adsorption–desorption and TGA con-
firmed the obtained results from these catalysts. A signifi-
cant enhancement of the catalytic activity was observed
for the catalysts supported on CoMo/HZSM5(20)-HMS at
T = 350 °C (>97%).
for this process, it needs to know its properties and rela-
tionship to the nature of the support, composition, prepa-
ration method, promoters, additives and other variables. It
has been demonstrated that a support can affect the disper-
sion of active phase, interactions between metal-support
and metal-promoter and thus can alter the catalytic proper-
ties. For this process, molybdenum or tungsten is usually
used as an active phase and cobalt or nickel is added as a
promoter [6]. Since supports have a large influence on the
catalytic activity, many studies have been done on various
supports to achieve the best result in the removal of sulfur
using the HDS reaction [7–9].
During the past decades, mesoporous materials with
ordered pore structures, large pore diameters and high sur-
face areas like FSM-16 [6], HMS [10–12], KIT-6 [3, 4, 15],
SBA-15 [13–17], MCM-41 [18] and so on, and their sub-
stituted analogs attracted widespread attention as potential
support materials [19, 20]. These materials have controlla-
ble pore size, but they involve poor hydrothermal stability
and low reactivity as compared to employed zeolites for
this reaction [12].
So in recent years, there has been great interest in com-
posite supports due to their high ability in the catalytic
applications. These micro/mesoporous composite materials
have developed significant advances in the improvement of
acidity and stability [21]. Many micro/mesoporous mate-
rials, such as MSU/S [22], Beta/MCM-41 [23] and Beta/
SBA-15 [24] were synthesized and used for various cata-
lytic reactions [25, 26]. According to our knowledge, there
are no focused reports on combining the particular advan-
tages of HZSM-5 and HMS in this process and especially
investigating the effects of HZSM-5 contents on the char-
acteristics and the catalytic activities of these composite
HDS catalysts. Hence, in the present research, CoMo cata-
lysts were prepared using the micro/mesoporous supports
Keywords Micro/mesoporous catalysts ·
Hydrodesulphurization · Dibenzothiophene · Catalytic
activity
Introduction
Due to strict environmental legislations to reduce sulfur
from natural gas and refined petroleum products, hydrodes-
ulphurization (HDS) is widely used as a catalytic chemical
process to remove sulfur [1–3]. For this reason, the produc-
tion of more active HDS catalysts is one of the main targets
in the refining industry [4, 5]. To generate an active catalyst
* N. Parsafard
n_dastmoozeh@sbu.ac.ir
1
Department of Applied Chemistry, Kosar University
of Bojnord, Bojnord, North Khorasan, Iran
2
Department of Petroleum Chemistry and Catalysis, Faculty
of Chemistry Science and Petroleum, University of Shahid
Beheshti, Tehran 1983963113, Iran
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J IRAN CHEM SOC
(HZSM-5/HMS) with different amounts of zeolite and were
applied in desulfurization reaction of dibenzothiophene.
Scanning electron microscopy (SEM) analyzes were
conducted on a HITACHI S-4160 instrument operating at
an accelerating voltage of 30 kV over the coated samples
with gold prior to SEM measurements.
Experimental
The amounts of coke laid down on the surfaces of the
spent composites were measured by thermogravimetric
analysis TGA/STA503 M instrument. In this analysis, the
weight changes in the coked samples during oxidation
were measured. The coke was calcined by heating rate of
10 °C min−1 to a final temperature of 800 °C in flowing air.
Synthesis and preparation of materials
A
series of micro/mesoporous composite supports
(HZSM5/HMS) with various amounts of HZSM-5 were
prepared by a method similar to our published procedure
[26]. The molybdenum- and cobalt-promoted catalysts
were prepared by successive impregnation method using
these supports and appropriate amounts (3 wt% Co and 10
wt% Mo) of ammonium heptamolybdate tetrahydrate (as a
molybdenum source) and cobalt nitrate hexahydrate (as a
cobalt source). The impregnated catalysts were dried in an
oven at 110 °C overnight followed by calcination at 300 °C
for 4 h. Prior each reactor test, the calcined catalysts were
pretreated and sulfurized at 400 °C for 2 h in a CS2/H2 flow
(40 mL min−1).
Catalytic performance evaluation
Hydrodesulphurization of dibenzothiophene was carried
out at a temperature range of 250–400 °C and 1 atm pres-
sure in a continuous fixed-bed microreactor packed with
1.0 g of each sulfurized composite. The liquid reactant
(dibenzothiophene/n-heptane mixture with 5% by volume
dibenzothiophene) was fed into the reactor with a space
velocity (LHSV) 1.0 h−1. Hydrogen was also introduced
in a best H2/HC molar ratio for our samples to get the
best selectivity of desired products (H2/HC = 7). The
reaction products were analyzed by online gas chroma-
tography (Agilent Technologies 7890A) equipped with an
FID detector.
Hereafter, the above micro/mesoporous samples would
be denoted as CoMo/ZH-x that x is HZSM-5 weight per-
cent and is equal to 10, 20, 30 and 40 versus wt%.
Characterization of the samples
For measuring the metal contents, the synthesized samples
were characterized by XRF (XRF-8410 Rh 60 kV).
X-ray diffraction patterns (XRD) were recorded by
X-PERT diffractometer Cu–Kα radiation (45 kV and
50 mA).
Results and discussions
X‑ray diffraction (XRD) patterns
A BOMEM FT-IR spectrophotometer model Arid-Zone
TM, MB Series, was used to obtain the FT-IR spectra, sur-
face characterization for the dehydroxylation and removal
of the residual surfactants from the dried samples. This
analysis was performed in the wave numbers range from
To reveal whether or not the structures of HMS and
HZSM-5 were preserved after impregnation of metal
CoMo/ZH-10
CoMo/ZH-20
CoMo/ZH-30
CoMo/ZH-40
CoMo/HMS
4000 to 400 cm−1
.
The UV–Visible diffuse reflectance spectra were
recorded by a Shimadzu UV-2100 spectrophotometer
equipped with a diffuse reflectance attachment. The spectra
were collected in the 200–800 nm range at room tempera-
ture with BaSO4 as a reference.
CoMo/HZSM-5
The specific surface area, pore volume and pore size
distributions were measured by N2 physisorption (BET)
at −196 °C by High-Speed Gas Sorption Analyzer
(NOVA2200) version 7.11 using a standard procedure.
To evaluate the acidity, these samples were analyzed by
a TPD/TPR analyzer (2900 micromeritics) equipped with
a TCD sensor. The obtained profiles of NH3 desorption
were recorded from 25 to 800 °C under a heating rate of
10 °C min−1. Also, hydrogen pulse chemisorption was per-
formed to measure the metal dispersion on the supports.
0
20
40
60
80
2θ (degree)
Fig. 1 XRD patterns for calcined CoMo-supported samples. (calci-
nation: 300 °C for 4 h)
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J IRAN CHEM SOC
oxide precursors, the XRD analysis was performed
(Fig. 1). In all XRD patterns, it can be seen the peaks
for HMS structure (2θ = 2.3° [27]) and HZSM-5 phases
(6–11° and 22–25° [28]). The amorphous part of the
substrate also is observed between 20° and 30°. Com-
pared with pure supports, the XRD patterns reveal that
the diffraction peaks become less intense, broader and
shift to higher angles. These data indicate a partial lat-
tice collapse upon metals (Co and Mo) incorporation
[29]. Table 1 shows the d-spacing (d100), unit cell param-
eter (a0) and wall thickness (wt) values that have been
calculated from XRD data. These values decrease with
increasing HZSM-5 content and after incorporating Co
and Mo species. It should be noted the metal or metal
alloy in these XRD patterns does not show any peak that
it shows their good dispersion.
CoMo/HMS
CoMo/ZH-10
CoMo/ZH-20
CoMo/ZH-30
CoMo/ZH-40
CoMo/HZSM5
3400
2400
1400
400
Wavenumbers (cm-1)
Fig. 2 FT-IR spectra of the framework vibration for the calcined
powder samples. (calcination: 300 °C for 4 h)
Fourier transform infrared (FT‑IR) spectroscopy
results
spectra, the characterization bands for HMS and HZSM-5
as the pure supports were observed [26].
The FT-IR spectra of the CoMo samples were shown in the
4000–400 cm−1 range (Fig. 2). These spectra were com-
pared with the pure supports spectra which were given
in our previous work [26] and so not shown here. In all
The region of ~1085–500 cm−1 is important for char-
acterization of molybdates. The bonds in ~1050–900
and ~850–700 cm−1 ranges represent terminal Mo = O
and asymmetric Mo–O–Mo and O–Mo–O stretching
Table 1 Physicochemical
properties of CoMo-supported
Samples
HMS
HZSM5
ZH-10
ZH-20
ZH-30
ZH-40
samples. (calcination: 300 °C
for 4 h)
Surface properties
SBET (m2 g−1
Vap (cm3 g−1
Smicro (m2 g−1
)
714
0.72
–
256
712
711
619
524
)
0.17
188
0.84
24
0.79
48
0.71
74
0.67
94
)
Vmicro (cm3 g−1
dp (nm)
NSbBET
Mdc
Si/Ald
)
–
0.10
2.66
0.65
16.3
13.03
0.09
4.72
0.90
15.5
65.51
0.15
4.44
0.90
22.1
60.09
0.20
4.59
0.87
20.9
54.13
0.25
5.11
0.83
14.8
49.11
4.03
0.90
17.8
∞
Strength of acid sites (mmol NH3/gcat
)
Weak acid (100–300 °C)
Strong acid (300–600 °C)
Total acid
1.15
1.30
0.95
2.25
1.17
0.60
1.77
1.23
0.63
1.86
1.27
0.79
2.06
1.32
0.83
2.15
–
1.15
Lattice properties
de100 (nm)
ae0 (nm)
4.51
5.21
1.95
3.24
4.26
4.92
2.58
4.23
4.89
2.57
4.16
4.80
2.51
3.51
4.05
1.77
3.74
wte (nm)
~2.24
a0 calculated by equation a0 = d100 × 2/√3 and wt was evaluated by subtracting pore diameter (dp) from
the unit cell parameter [29]
a
Using BJH method
b
NSBET is normalized SBET and calculated from equation [29, 30]: NSBET = SBET of catalyst/
[(1−y) × SBET of support]; y is the weight fraction of the guest phases
c
Metal dispersion using H2-chemisorption method
d
Using XRF method
e
d100 as calculated from the XRD patterns
1 3

J IRAN CHEM SOC
vibrations, respectively. The tetrahedral, octahedral and
other poly molybdates and crystalline MoO3 create some
features around ~930, 980 and 580 cm−1. Also the octa-
hedral and tetrahedral molybdenum species make the
bands between ~1085 and ~800 cm−1. The vibrations of
Mo tetrahedral, octahedral and other polyhedral species
appear at ~930–830, 990–930 and 860–800 cm−1, respec-
tively. These characteristic bands normally overlap with
the characteristic bands of HMS and HZSM-5. Therefore,
it is difficult to ascertain the bands [4].
CoMo/HZSM-5
CoMo/HMS
CoMo/ZH-10
CoMo/ZH-20
CoMo/ZH-30
CoMo/ZH-40
UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS)
200
400
600
800
UV–Vis DRS was used to find the symmetry of the CoMo
species and information about the distribution of oxide
species or their dispersion over the supports (Fig. 3). The
CoMo/HMS spectrum shows the bands in the ranges of
200–400 and 450–700 nm. These bands in the spectrum
of CoMo/HZSM-5 have low intensity. The bands in the
220–270 and 300–330 nm ranges, which are observed
in all spectra, are assigned to O2−–Mo6+ ligand to metal
charge transfer transition in isolated tetrahedral coordina-
Wavelength (nm)
Fig. 3 UV–Vis DRS of CoMo samples supported on HMS, HZSM-5
and ZH-x. (calcination: 300 °C for 4 h)
CoMo/ZH-10
CoMo/ZH-20
CoMo/ZH-30
CoMo/ZH-40
CoMo/HMS
2−
tion MoO4 and octahedral Mo6+ species, respectively
[29]. A second peak at around 230 nm is related to both
tetrahedral and octahedral Mo6+ species. The mixtures of
both tetrahedral and octahedral Mo6+ species are present
in all spectra. It seems that the contribution of octahedral
Mo6+ species increases in intensity and becomes almost
distinguishable shoulder of the tetrahedral Mo6+ species
absorption [29]. It can be concluded that tetrahedral Mo6+
species are better dispersed over these samples. Besides,
the absorption spectra of CoMo/HMS and CoMo/ZH
composite catalysts in UV region are more symmetrical
than the CoMo/HZSM-5 catalyst. It shows the disper-
sion of Mo in the presence of HMS phase is much higher
than the ZSM-5 pure phase. All samples present a band in
the ~480–720 nm range of the visible region, which are
related to Co species. This broad peak is characterized as
the tetrahedrally and octahedrally coordinated Co2+ [12].
CoMoO4 species are as an octahedral component and the
Co2+ species interacting with the support are as a tetrahe-
dral component. According to the literature [29], the UV–
Vis DRS bands at about 400–450 and 700–750 nm, could
be ascribed as the Co3O4 phase with octahedral Co (III).
These bands were not observed in any of spectra that it
shows a higher dispersion of the Co species. The effect
of cobalt promoter addition was reported as a blue shift
of the Mo absorption and an increase in the dispersion of
octahedral Mo species or the change in the coordination
of the Mo oxide species from octahedral to tetrahedral
[12, 31, 32].
CoMo/HZSM-5
0
0.25
0.5
0.75
1
Relative pressure (P/P0)
Fig. 4 Nitrogen adsorption–desorption isotherms for CoMo-sup-
ported samples. (calcination: 300 °C for 4 h)
Textural properties
The nitrogen physisorption isotherms of the samples are
showed in Fig. 4 and listed in Table 1. N2 adsorption–des-
orption isotherms of the CoMo/supports indicate surface
areas that changed between 524 and 712 m2 g−1 indicating
that the incorporations of Co and Mo display a significant
effect into the frameworks of composites (Table 1). When
molybdenum co-impregnates with cobalt, the lower surface
areas were obtained as compared with the surface areas of
HZSM5(x)/HMS supports [26]. According to the results, it
seems that the incorporations of Co and Mo metals block
the micropores of the supports and so surface areas and
pore volumes decrease. These incorporations are also due
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J IRAN CHEM SOC
to partial loss of structural ordering of the channels. In
Table 1, the NSBET values were also calculated for the pre-
pared samples. These amounts suggest a very good disper-
sion of the supported species.
NH3‑TPD results
NH3-TPD method was used to measure the acidity of sam-
ples. The effects of zeolite content and metal oxides on the
acidity of samples were exhibited in Fig. 5 and listed in
Table 1. As expected, the acidity increased with increasing
HZSM-5 content. On the other hand, the overall acidity of
modified composites, in compared with pure supports [26],
increased with an addition of cobalt and molybdenum met-
als. According to the literature [33], it has been reported
that due to the complex formation by Co2+ ions and the
generation of acid sites with the cobalt–molybdenum
oxide, the acidity increases.
CoMo/ZH-10
CoMo/ZH-20
CoMo/ZH-30
CoMo/ZH-40
Scanning electron microscopy (SEM)
Figure 6 shows SEMs of the CoMo composites. As
observed, the primary structures that were seen in the pure
composites [26], undergo decomposition during the incor-
poration of Co and Mo metals.
80
280
480
680
Catalytic activity in the HDS of dibenzothiophene
Temperature (oC)
Table 2 shows the data of conversion of dibenzothiophene
(DBT) over CoMo/HMS, CoMo/HZSM-5, CoMo/ZH-10,
CoMo/ZH-20, CoMo/ZH-30 and CoMo/ZH-40 samples
Fig. 5 NH3-TPD profiles of the calcined CoMo samples supported
on the ZH-10, ZH-20, ZH-30 and ZH-40 materials. (calcination:
300 °C for 4 h)
Fig. 6 Scanning electron micrographs of CoMo/ZH samples. (calcination: 300 °C for 4 h; scale bars are 5, 10 and 20 μm for (a), (b) and (c)
images, respectively)
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J IRAN CHEM SOC
Table 2 Conversion and BP and CHB yields for various samples at
different temperatures. (calcination: 300 °C for 4 h; time on stream in
reactor test: 1 h)
Table 3 Conversion, BP and CHB yields and coke amounts at
350 °C for various times
Samples
Time (h) Conversion
(%)
Yield (%)
Coke amounts
(wt%)
Samples
Temperature (oC) Conversion (%) Yield (%)
BP CHB
BP
CHB
CoMo/HMS
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
71.1
70.7
70.1
69.5
63.1
50.9
45.7
44.6
63.8
60.2
59.4
57.8
90.6
84.3
81.5
79.8
88.3
80.3
76.5
74.9
60.5
53.3
51.2
50.3
68.5 2.6
68.2 2.5
67.1 3.0
65.7 3.8
60.8 2.3
49.1 1.8
43.7 2.0
42.2 2.4
61.4 2.4
58.0 2.2
56.8 2.6
54.6 3.2
87.2 3.4
81.3 3.0
78.0 3.5
75.4 4.4
85.0 3.3
77.4 2.9
73.2 3.3
70.8 4.1
58.3 2.2
51.4 1.9
49.0 2.2
47.6 2.7
0.9
12.5
2.1
CoMo/HMS
250
300
350
400
56.3
61.2
75.8
71.2
54.1
60.1
71.4
69.8
45.8
52.7
66.3
59.9
63.4
74.3
97.1
80.1
56.3
62.9
92.6
78.2
42.9
45.6
65.9
58.9
54.2 2.1
59.0 2.2
72.5 3.3
67.3 3.9
52.1 2.0
57.9 2.2
68.3 3.1
66.0 3.8
44.1 1.7
50.8 1.9
63.4 2.9
56.6 3.3
61.0 2.4
71.6 2.7
92.9 4.2
75.7 4.4
54.2 2.1
60.6 2.3
88.6 4.0
73.9 4.3
41.3 1.6
44.0 1.6
63.0 2.9
55.7 3.2
CoMo/
HZSM-5
CoMo/HZSM-5 250
300
350
400
CoMo/
ZH-10
CoMo/ZH-10
CoMo/ZH-20
CoMo/ZH-30
CoMo/ZH-40
250
300
350
400
250
300
350
400
250
300
350
400
250
300
350
400
CoMo/
ZH-20
3.2
CoMo/
ZH-30
3.4
CoMo/
ZH-40
5.3
for 1 h on stream at each temperature in the range of
250–400 °C. Under our experimental conditions, the only
detectable products for hydrodesulphurization of diben-
zothiophene were biphenyl (BP) and very low amounts of
cyclohexylbenzene (CHB). Obtaining BP as a main prod-
uct shows the direct hydrogenolysis or direct desulfuriza-
tion (DDS) pathway [33]. CHB product is achieved from
a hydrogenation of the rings prior the desulfurization
(HYD) pathway through to tetra-hydro-dibenzothiophene
(THDBT) intermediate [33].
effect of MoS2 phase on the catalytic activity and its subse-
quent migration from the surface to the bulk [1].
In order to study the stability of the composites as a
function of the time on stream, the catalytic HDS test over
these materials was performed at 350 °C during 8 h. In
accordance with the results summarized in Table 3, signifi-
cant deactivation and coke formation (by TG/DTA) were
observed for CoMo/HZSM-5 and then CoMo/ZH-40. As
deduced from these results, the coking amount increases
with increasing the catalytic acidity.
As seen in Table 2, the CoMo samples at 350 °C show
the highest catalytic activity and then this high catalytic
activity decreases. This decline in activity is probably
due to the loss of sulfur by the over-reduction [2] and the
increase in severe side reactions such as cracking and
reforming up to 350 °C. The most active of the prepared
composite for the dibenzothiophene hydrodesulphurization
is CoMo/ZH-20 at 350 °C; whereas, the lowest conversion
is observed for CoMo/ZH-40 at 250 °C. The results show
that the activity of the samples does not follow their acidic
properties (Table 1). This may be related to the sintering
Conclusion
CoMo/ZH composites were prepared by co-impregnation
method. The characterization results showed that ZH com-
posites were successfully synthesized. The textural and
acidity properties of these composites improved HDS reac-
tion compared with those of HZSM-5 and HMS. The influ-
ence of temperature and time on stream was investigated in
the HDS of dibenzothiophene. The catalytic performance
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J IRAN CHEM SOC
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