Zeolite-graphene composite as support for molybdenum-based catalysts and their hydrodesulfurization performance

Article abstract of DOI:10.1016/j.apcata.2020.117542

A composite of zeolite Y type -graphene as a support doped with molybdenum-cobalt and molybdenum-nickel (active phase and promoter) was synthesized and evaluated as hydrodesulfurization (HDS) catalysts. The ZGMoCo was found to have the ability to reduce the sulfur content by ≈98 % after a 5 h reaction time which is higher compared to the ZMoCo or ZMoNi. This activity can be ascribed to the improved surface area and better distribution of the active phases (molybdenum and cobalt or nickel) on the zeolite Y type -graphene surface. SEM images showed enhanced dispersion of the active phases on the support surface. As per the BET measurements, the surface area was improved due to the introduction of graphene to be 323.6 m²/g ZGMoCo compared to 257.3 m²/g ZMoCo; and 312.5 m²/g for ZGMoNi compared to 245.7 m²/g for ZMoNi. The work offers a convenient approach to prepare an effective HDS catalyst.

Full text of DOI:10.1016/j.apcata.2020.117542

Journal Pre-proof
Zeolite-Graphene composite as support for Molybdenum-based catalysts
and their Hydrodesulfurization performance
Islam Ali, Tawfik A. Saleh
PII:
S0926-860X(20)30135-6
DOI:
https://doi.org/10.1016/j.apcata.2020.117542
APCATA 117542
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Applied Catalysis A, General
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23 November 2019
21 March 2020
24 March 2020
Please cite this article as: Ali I, Saleh TA, Zeolite-Graphene composite as support for
Molybdenum-based catalysts and their Hydrodesulfurization performance, Applied Catalysis
A, General (2020), doi: https://doi.org/10.1016/j.apcata.2020.117542
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Zeolite-Graphene composite as support for Molybdenum-based
catalysts and their Hydrodesulfurization performance
Islam Ali & Tawfik A. Saleh *
Department of Chemistry, King Fahd University of Petroleum & Minerals, Dhahran 31261,
Saudi Arabia
*Corresponding author
E-mail address: tawfik@kfupm.edu.sa ; tawfikas@hotmail.com
Home Page: http://faculty.kfupm.edu.sa/CHEM/tawfik/publications.html
Graphical Abstract
1

Highlights
 A composite of zeolite-graphene as a support decorated with molybdenum-cobalt and
molybdenum-nickel were synthesized
 The ZGMC was found to reduce the sulfur content by around 98.7% after 6 h reaction time
and it showed higher catalytic activity compared to the ZMC or ZMI.
 The present work is offering a convenient approach to prepare an effective HDS catalyst.
Abstract
A composite of zeolite Y type -graphene as a support doped with molybdenum-cobalt and
molybdenum-nickel (active phase and promoter) was synthesized and evaluated as
hydrodesulfurization (HDS) catalysts. The ZGMoCo was found to have the ability to reduce
the sulfur content by ≈98 % after a 5 h reaction time which is higher compared to the ZMoCo
or ZMoNi. This activity can be ascribed to the improved surface area and better distribution
of the active phases (molybdenum and cobalt or nickel) on the zeolite Y type -graphene
surface. SEM images showed enhanced dispersion of the active phases on the support surface.
As per the BET measurements, the surface area was improved due to the introduction of
graphene to be 323.6 m2/g ZGMoCo compared to 257.3 m2/g ZMoCo; and 312.5 m2/g for
ZGMoNi compared to 245.7 m2/g for ZMoNi. The work offers a convenient approach to
prepare an effective HDS catalyst.
Keywords: Zeolite; Graphene; Dibenzothiophene; Distribution; Hydrodesulfurization.
1. Introduction
Environmental concerns related to the fuel specifications with ultra-low sulfur content became
an important approach to prevent air pollution caused by sulfur dioxide emission. Nowadays,
the demand for deep desulfurization has become a requirement to meet the regulations for
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sulfur in petroleum products [1-4]. Recently, sulfur content reduction in diesel fuel and
gasoline by using catalytic hydrotreating has become a very intensive research area.
Environmental regulation suggested that the sulfur contents in diesel and gasoline should be
lowered to be 10-15 ppm [5-7]. In the refinery processes, hydrodesulfurization (HDS) has
been used extensively to reduce sulfur-containing contents in petroleum. The use of
hydrodesulfurization catalysts has attracted researchers owing to their good catalytic
activities, product longevity, and selectivity. As a result, HDS catalysts are required to meet
the specifications of sulfur during fuel transportation. Previous studies demonstrated the
removal of refractory molecules like 4,6 dimethyl dibenzothiophene (4,6 DMDBT) and
dibenzothiophene (DBT) which present the greatest challenge to get sulfur at ultra-low levels
[8]. A highly efficient HDS catalyst with excellent properties towards desulfurization is a
challenge [9-11].
The catalyst support is an important factor due to its catalytic performance [12]. To improve
the hydrotreating performance of the catalyst, researchers tested zeolite and alumina. This
showed that these acidic materials that contain alumina and silica mixture have a better surface
area for the dispersion of metals and high concentrations of Lewis and Bronsted acid sites
compared to alumina. As a result, zeolites were used extensively as a support for CoMo and
NiMo [13]. The presence of a hydrogenating strong acid site has a synergetic effect, not only
for accelerating the C-S bond cleavage but also for enhancing different ways of sulfur atom
removal from the aromatic molecules. The microporous natural system of zeolites has a role,
which limits its applications in the bulky molecules' hydrotreating field. Subsequently, the
need to obtain a synthesized material with Bronsted acid sites and more surface area became
of great interest [14].
Zeolite as a catalyst support is promising in the petroleum refining industry [15] because of
its hierarchical structure, micro-mesoporous nature, and acid-base properties that can be
3

changed using synthesis methods. Zeolite was used as an adsorbent due to its capacity for
ionic exchange besides its role in catalysis as a support for the dispersal of the catalyst
nanoparticles [16]. Zeolite also has a role to provide acidity to the catalyst structure while the
finely dispersed metal nanoparticles are used to exert hydrogenation-dehydrogenation
activity. A large variety of applications are present for noble metals supported by zeolite such
as the production of high-octane gasoline throughout the hydroisomerization of C5-C6 n-
paraffins [17-18] Also, these types of catalysts can be used in the hydrocracking process
depending on the obtained product, the partial pressure of the sulphurated contaminants and
the feedstock types [19]. Many types of zeolite were also included as subjects to be studied
like zeolite beta (BEA) and Y zeolite-based catalyst due to their good properties as a surface
for catalyst dispersion [20-23]. Supports modified with carbon such as monocarboxylic acid
and citric acid have been reported to synthesize supported active metal catalysts [24-25].
These types of surface modification used to be an effective alternative way, besides the used
ones [26]. For example, the intrinsic role of citric acid includes its ability to partly change to
carbonaceous deposits during the sulfidation, decreasing the WS2 slab length. It may also
react with basic and neutral hydroxyl groups to moderate the interactions between the active
phase and the support. The stability and catalytic performance of catalysts can be enhanced
through the incorporation of nanocatalysts within suitable conductive materials. It avoids the
agglomeration of the nanoparticles and accelerates charge transfer. Nickel and cobalt-based
catalysts have been implemented in various applications such as HER and OER and it was
used extensively as a promoter in desulfurization processes. Those materials are low cost with
facile fabrication processes [27-29].
Graphene has a two-dimensional single sheet of carbon atoms distributed in a hexagonal
network. It has a plate-like structure with a one-atom-thick material [30]. Due to its properties,
such as a high surface area and excellent mechanical properties, it has been used in different
4

applications like batteries, solar cells, and composite materials, as well as catalysts [31]. One
of the most characteristic features of graphene is its large specific surface area. Other
properties such as mechanical, thermal and electronic features have made graphene an
attractive substrate for the dispersion and deposition of nanoparticles to obtain a composite
catalyst [32-33]. Recently, catalysts that use graphene as a support have become a hot area of
interest [34]. Both graphene and zeolite have been implemented in various applications such
as their good ability towards the molecular dye adsorption from aqueous solution. The
composite fabrication for effective separation should be with a hierarchical porous structure
based on zeolite or graphene. It became a promising approach for hazardous substances
removal [33-38]. Also, the combination between zeolite and graphene was used extensively
for the electrochemical detection of various compounds like dopamine and ascorbic acid [39]
and as invitro drug carrier for anticancer drug [40].
Catalyst structure, surface atomic arrangement, and coordination are very sensitive
parameters involved in catalytic reactions. Control of these parameters occurred by tuning the
morphology, composition and catalyst size. The catalytically active components are bonded
to support with a large surface area like alumina, zeolite, and others to confirm its dispersion
on the support surface [41-44]. Different alternative supports have been used for HDS
reactions such as MgO [5], SiO2 [8], ZrO2 [12], Al2O3 [4], and mixed oxides [5]. The role of
supports to disperse the active phases on its surface has still not been thoroughly investigated
[6].
Here, zeolite Y type - molybdenum- nickel (cobalt) (ZMoNi or ZMoCo) and Zeolite Y type -
graphene/ molybdenum- nickel (cobalt) (ZGMoNi or ZGMoCo) were synthesized to illustrate
the effective role of graphene for enhancing the catalyst activity. The performance of the
synthesized catalyst has been investigated in catalytic reactions using desulfurization of
dibenzothiophene. The structural and morphological properties of the prepared catalyst and
5

the role of graphene for improving the catalyst activity were characterized by different
techniques.
2. Experimental
2.1. Chemicals
Commercial zeolite Y type, polyvinylpyrrolidone (C6H9NO)n, decalin (>99 % purity),
dibenzothiophene (DBT) (98%), ammonium molybdate tetrahydrate (98 %), cobalt nitrate
hexahydrate (98%), nickel acetate tetrahydrate (98%), and ethanol (99%) were purchased
from Sigma Aldrich, Eschenstrasse, Taufkirchen, Germany. De-ionized water with high
purity distilled with a Labstrong FiSTREEM™ II 2S Glass Still distiller, USA and acquired
in-house using Thermo-Scientific Barnstead Nanopure.
2.2. Preparation of the catalyst
Composite support of zeolite Y type -graphene (ZG) was obtained by mixing graphene
dispersed in water and commercial zeolite (Y type). The sol-gel method has been used to mix
around 20 mg of graphene dispersed in water with 6.4g of zeolite. During this process, 100
ml of deionized water and 0.2 g of polyvinylpyrrolidone were added to enhance the interaction
between the two supports beside its role for dispersing the active phase and 10 ml ethanol was
added to ZG. The stirring of the composite support was for 1 h and refluxing 5 h at 110 °C.
After cooling, the filtration was performed and the product was then dried at 90 °C.
The incipient wetness impregnation procedure was used for adding the active phases of
molybdenum (Mo) and cobalt (Co) or nickel (Ni) nanoparticles to the support with ratios of
15 % Mo and 5 % Co (Ni), respectively. The selection of these percentages for the active
phases was decided after a literature survey and it was found that Co (Ni) was from 1-5 %
and the catalyst was from 8-15 % [7]. A solution of cobalt nitrate (1.97g) and ammonium
molybdate (2.43g) was prepared. Also, around 5.53 g of ZG support dispersed in 0.1 L of
deionized water was kept under stirring at 90°C for 30 min. This is followed by mixing the
6

catalysts solutions with ZG support under stirring at 100°C for 5 h. Then, the catalyst was
filtered and dried at 100 °C. Catalyst calcination in a pure nitrogen medium occurred at 350
°C for 3 h. When synthesizing the reference catalysts ZMoCo or ZMoNi, the same steps were
used without the incorporation of graphene for comparison. Here, we should mention an
important process during catalyst work which is the sulfidation process. It occurred within the
reactor where molybdenum sulfidation happened after the temperature reached to optimum
300 °C that took around 3h.
2.3 Characterization techniques used for catalysts.
Several techniques were used for structural and morphology characterization. The textural
properties of the catalysts including surface area, pore size distribution and pore volumes were
measured by Micromeritics TriStar II PLUS surface area. Sample degassing before
measurement at 150 °C for 3 h was performed to remove moistures and gasses. Then, the
isotherm curves N2 adsorption-desorption at -196 °C were obtained. The surface area was
calculated from BET method while total pore volume was obtained by nitrogen adsorption
and the pore size was attained from BJH method and its adsorption isotherm. Function groups
of the catalysts were characterized by Nicolet 6700 spectrometer (Thermo Scientific) fourier
transform infrared (FTIR) with a deuterated triglycine sulfate detector. A very small quantity
of the material was mixed with KBr powder to prepare a thin translucent disc for
measurement. The background noises correction was done using16 scans with resolution 2
cm -1. Crystallinity was recorded using Rigaku Mini-flex II x-ray diffraction (XRD). The
radiation of Cu-Kα was used in the 2θ range (5-80o) and detector angular speed of 2o /min and
step size of 0.02o. The surface morphology was recorded using a scanning electron
microscopy (SEM) with mode name JEOL e JSM6610LV. A backscattered electron (BSE)
and a secondary electron (SE) mode at an accelerating voltage of 20 kV were used. The
elemental composition and sample mapping were measured with the attached Energy
7

dispersive X-ray spectrometer (EDX, Oxford Inc.) detector. Catalysts' thermal stability at high
temperature was investigated through thermogravimetric analysis (TGA) with a model name
of Q600 Thermal Analyzer Instrument. The sample heating started from ambient temperature
up to 900 °C using Platinum/ Platinum Rhodium (Type R) thermocouples. The binding
energies and chemical states were measured by x-ray photoelectron spectroscopy (XPS) with
a model name PHI 5000 Versa Probe II, ULVAC-PHI Inc. spectroscope. A high vacuum for
the disc pelletized form of the catalyst was applied before the XPS analysis start. The sample
components were defined through gas chromatography-mass spectrometric technique (GC-
MS) with model name Shimadzu GC17A/GC14C using quadrupole ion-trap analyzer, ions
with m/z values orbits around the cavity.
2.4 Assessment of the catalysts
A batch reactor (model 4848B) from Parr instruments co. Moline, Illinois USA, was used to
assess the catalyst activity (ZMoNi, ZMoCo, ZGMoNi, and ZGMoCo) towards the
hydrodesulfurization of dibenzothiophene. Decalin acted as a solvent model fuel for
dissolving DBT to make a feedstock solution for HDS of DBT that has 0.5 % of sulfur. The
catalytic reaction conditions were 55 bars for hydrogen partial pressure and 300 °C as a
reaction temperature. About 0.6 g of the synthesized catalysts interacted with 0.1L decalin
and 550 ppm-S DBT. The reaction started when inserting the mixture into the vessel of the
reactor. A collection of six samples and a zero point (first sample) was taken after the
temperature of the reaction reached 300 °C. Reaction monitoring during 5 h was mandatory
with collecting a sample every hour by a manual valve. The determination of the sulfur
concentration for the collected samples was carried out by a gas-chromatography sulfur
chemiluminescence detector (GC-SCD), (column: J&W 123-1033 - DB-1, 30m, 0.32mm,
1.00um). Agilent Stevens Creek Blvd. Santa Clara, United States. GC-MS technique was
implemented to illustrate the components of the synthesized catalysts.
8

3. Results and discussion
3.1. Physico-chemical properties
The N2 sorption isotherms and distribution of pore size of the catalysts were conducted, Fig.
S1. The textural properties of the catalysts are illustrated in Table 1. Incorporation of
graphene within zeolite Y type to form composite support increased the surface area from
245.7 m2·g-1 (ZMoNi) to 312.5 m2·g-1 (ZGMoNi) and from 257.3 m2·g-1 (ZMoCo) to 323.6
m2·g-1 (ZGMoCo) and. This improvement in the surface area enhances the activity of the
catalysts. Also, the improvement was attributed to the quantity of graphene after parameter
optimization for commercialization purposes. The isotherm curves are like type IV. At a high
value of relative pressure, there is a hysteresis loop which clarifies the mesoporous nature of
the material, while the nitrogen uptake at low pressures indicated the microporous existence
within the catalysts. Therefore, graphene improved the textural properties of the catalysts that
lead to an enhanced activity towards the hydrodesulfurization of benzothiophenes. It was
found the slight change in the textural properties of the catalyst ZGMoCo after HDS reaction
that prove the stability of the catalyst.
The hierarchy factor (HF) was also calculated to illustrate the role of graphene on the textural
properties of the catalysts as:
HF = (Vmicro/Vtotal) ∗ (Smeso/SBET
)
(1)
By replacing these parameters in Eq. (1), the HF was obtained. It was shown that the HF
values for ZGMoNi and ZGMoCo are higher than the reference sample ZMoNi and ZMoCo
which clarifies their higher adsorption efficiency [8]. The quantity adsorbed-desorbed for
catalysts was always higher than the reference one at any relative pressure value, which
supports our results regarding HF.
9

The incorporation of graphene into the catalyst component has a crucial effect on its stability.
TGA curves, Fig. S2, indicated that in the temperature range 0-900 °C and inert gas medium,
it is obvious that the weight loss for the ZMoNi reference sample was 17 % at 400 °C and 27
% at 800 °C, while for ZGMoNi, it was 13 % at 400 °C and was reduced by only 4 % up to
800 °C. In addition, the weight loss for ZMoCo was 14.6 % at 400 °C and 23 % up to 800 °C,
compared to ZGMoCo which was 11 % and 18 % for the same temperature scale. The total
decomposition rate of ZGMoNi and ZGMoCo after 800 °C was 18.9 % and 17 %, which is
better than the reference ones (ZMoNi and ZMoCo) that were 22.5 % and 27 %. These results
reflected the enhanced thermal stability of the synthesized catalyst after graphene
incorporation into the zeolite Y type.
The XRD patterns for the synthesized catalysts, Fig. S3, indicated that the characteristic peak
at 2θ =27.3◦ (100) was attributed to MoO3 according to JCPDS card no. 05-0508. Peaks at 2θ
= 6.3° (002), 19.2° (006), 21.3° (101), 24.6° (104), 32.7° (108), 35.6° (112) can be assigned
to zeolite material that appeared in the four catalysts. No clear peaks for the active phases
Mo and Co (Ni) could be due to their enhanced dispersion on the composite support surface
which is consistent with the nitrogen adsorption-desorption results. In the modified catalyst,
no diffraction peak for graphene appeared in the curve, which may be due to the low
diffraction intensity of graphene and its low amount [9].
In the FTIR patterns, Fig. S4, reveal a slightly small peak at 3600 cm-1 was ascribed to the
≈
bridging OH group in Al-OH-Si [8, 10]. The observed peaks at 486 and 1086 cm-1 were related
to the Mo=O central vibrational mode [13]. Bands in the range of 450-1000 cm-1 indicated
good dispersion of the active phases on the composite support surface [11]. The band at 1566
cm-1 maybe for the OH bending mode.
The catalysts’ surface morphologies and their elemental compositions were examined by a
scanning electron microscope (SEM) and energy-dispersive x-ray spectroscopy (EDX). Fig.
10

1 illustrates the SEM images for the four catalysts. The surface modification by graphene
doping enhanced the dispersion of the active phases Mo and Co (Ni) on the composite support
surface. Images of ZGMoCo and ZGMoNi (5e-h) show a better distribution of the catalyst and
promoter on the catalyst support surface and the role of graphene sheets for enhancing the
surface area. From these images, graphene sheets are present beside the zeolite support. In
comparison to the reference samples, it was noticed in the ZMoNi and ZMoCo images (5 a-d),
that the dispersion of the active phase is poor and not homogenous [18]. The catalyst SEM
image was presented in (5 ) and it does not show a big difference from the catalyst before
i-j
HDS reactions. EDX spectra were used to confirm the presence of elements introduced into
the catalysts’ composition. The existence of all the elements Al, Si, Co, Mo, and nickel were
confirmed in the reference samples, Fig. 1, while the carbon element attributed to the
graphene incorporation. Consequently, we successfully introduced support and active phases
into the four catalysts. HRSEM and mapping were utilized to evaluate the distribution and
introduction of the components in the ZGMoCo catalyst, Fig. 2. It was shown that all the
components have been induced within the catalyst with a homogenous dispersion.
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Fig. 1. SEM Images and EDX spectra of ZMoNi (a), ZMoCo (b), ZGMoNi (c), and ZGMoCo
(d)
12

Fig. 2. HRSEM and illustration iof the structure and Mapping of the ZGMoCo catalyst
The surface study regarding chemical states and binding energies of the catalyst components was
discussed using XPS in Fig. 3, and Table (2). The fully scanned spectrum proved the presence of
many elements in the synthesized catalyst. Some insights and identification for the degree of Mo
species sulfidation [39]. The characteristic binding energies of Mo oxide species were illustrated
as per deconvoluted XPS spectra. The spectra confirmed the presence of MoO2 (Mo4+ (3d5/2)) and
MoO3 (Mo6+(3d5/2) and Mo6+(3d3/2) at 230.3 eV, 232.7 eV and 235.8 eV respectively. The peaks
in the range 775-786 eV was related to Co2p [41-42]. The characteristic peak for C1s which is
located at 284.7 eV reflected the graphitized structure [43]. The peak at 529 eV was attributed to
O1s that contribute to Mo-O and O of MoO3 exists in the form of O-2 [44].
13

Fig. 3. XPS spectra of Mo3d, Co2p, C1s and O1s for the catalyst ZGMoCo.
14

3.2. Catalysts activity towards HDS
Fig. 4 and 5 show the sulfur conversion in ppm for 5 h reaction time and the percent of this
value for the mentioned four catalysts. The reaction parameters used for DBT desulfurization
were 300 ◦C temperature, H2 partial pressure of 55 bar, rotation of 190 rpm, catalyst amount
(0.6 g), and 0.1 L model fuel. It was noted that after 5 h, the sulfur concentration for the
reference samples ZMoNi and ZMoCo were 66.3 and 55.8 ppm, respectively, while the
modified catalyst showed enhanced sulfur removal to be 16.7 and 11.2 ppm for ZGMoNi and
ZGMoCo respectively. The conversion percentage for the catalysts is illustrated in Fig. 5. It
was 89.8 %, 91.4 %, 97.5 and 98.3 % for ZMoNi, ZMoCo, ZGMoNi and ZGMoCo,
respectively, Table S1,2. The improvement in the surface area of the catalyst after the
incorporation of graphene has a crucial role in increasing the catalytic activity. Also, the HF
calculation and adsorption-desorption isotherm supported our conclusion regarding the
activity. All the textural properties like pore volume and surface area with average pore
diameter were enhanced with graphene doping which leads to a better distribution of the active
phases on the composite support surface.
Fig. 4. Catalytic activity of the prepared catalysts in ppm sulfur
15

Fig. 5. Percentage of conversion using the prepared catalysts
3.3. Proposed reaction mechanism for hydrodesulfurization
There are two routes for sulfur removal from DBT, namely, hydrogenation (HYD) and
hydrogenolysis or direct desulfurization (DDS), as in Fig. 6. In the case of hydrogenation,
tetrahydro and hexahydro DBT were obtained as intermediate products for DBT. Then,
desulfurization occurred to form cyclohexyl benzene and finally bicyclohexyl, while, in the
DDS route, no intermediate products are formed as DBT was desulfurized directly to form
biphenyl. The reaction pathway of DBT hydrodesulfurization over the synthesized catalysts
is proposed in Fig. 7. Product analysis in GC-MS was used to illustrate the proposed pathway.
It was expected to be hydrogenolysis as DBT was desulfurized by C-S bond breaking to obtain
biphenyl (BP). The presence of a hydrogen source leads to the hydrogenation of biphenyl to
get cyclohexyl benzene (CHB). The large number of peaks in GC-MS may be attributed to
the high number of products that were separated for each analysis, Fig. S5. The characteristic
peak at 154 m/z is related to biphenyl, while the peak at 166 m/z was attributed to
bicyclohexyl. As a conclusion from these results, the direct desulfurization pathway can be a
dominant path for DBT over the ZGMoCo catalyst. The percent distribution of the compounds
16

biphenyl, cyclohexyl benzene, tetrahydro dibenzothiophene and hexahydro dibenzothiophene
were listed in Table S3, it was shown that the contribution of the intermediate products
THDBT and HDDBT is very low while the ratio of CHB and BP is high to confirm the
conclusion regarding the dominance of DDS pathway as the main one for
hydrodesulfurization of DBT [45-47].
In Fig. 7, structural interactions are proposed between graphene and zeolite, in addition to the
combination of the active phases and the composite support surface. As a final step, C-S bond
breaking and releasing of biphenyl from DBT. The existence of hydrogen during HDS lead
to the formation of bicyclohexyl. A comparison of our catalyst with literature was made and
presented in Table 3.
17

Fig. 6: A proposed route for DBT hydrodesulfurization
Fig. 7. Proposed mechanism for the interaction between the composite support and active
phases.
Conclusion
The results in this work showed the higher activity of zeolite Y type -graphene/ molybdenum
- cobalt (nickel) compared to zeolite Y type / molybdenum-cobalt (nickel) for dibenzo
thiophene hydrodesulfurization reactions. Data obtained for the synthesized catalyst showed
18

an improvement in the textural properties like surface area and pore size after doping graphene
as a co-support with zeolite Y type. The SEM images illustrated the enhanced dispersion of
the active phases on the support surface in the presence of graphene. TGA indicated the
improved thermal stability of the synthesized catalyst, as the percentage weight loss for the
four catalysts has been reduced after graphene incorporation within the support. The EDX
results confirmed the successful introduction of the nanoparticles' active phase on the support
surface. The novel catalysts ZGMoCo and ZGMoNi evaluation for the desulfurization of DBT
was found to be superior when compared to the reference samples ZMoCo and ZMoNi. The
catalyst activity was ≈98 % (ZGMoCo) removal of sulfur compared to 91.4% (ZMoCo) and
97.5% (ZGMoNi) to 89.8% (ZMoNi). Regarding the mechanism pathway involved during
the HDS reaction, it was found to be direct desulfurization as per the obtained data from GC-
MS. In conclusion, we confirmed the effective role of graphene doping within the catalyst to
form composite support. The superior activity for sulfur removal with enhanced properties
was also obtained.
Author contribution
Islam Ali performed the experiments and results. Tawfik A. Saleh reviewed the paper and
checked the manuscript.
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22

Table 1: Textural properties of the prepared catalysts
ZGMoCo
after HDS
Items
ZMoNi
ZMoCo
ZGMoNi
ZGMoCo
BET surface area (m2·g-1)
245.7
193.8
51.9
257.3
198.6
58.7
312.5
251.3
61.2
323.6
248.8
74.8
72423
253.6
71.1
Microporous surface area
(m2·g-1)
External surface area (m2·g-1)
Microporous pore volume
(m3·g-1)
0.0078
3.5
0.0091
3.8
0.0096
3.2
0.0095
3.6
0.0093
723
Average pore size (nm)
Total Pore volume (m3·g-1)
Hierarchy factor (HF)
0.23
0.24
0.18
0.21
2222
0.016
0.019
0.025
0.027
22220
23

Table 2: XPS data for the catalyst ZGMoCo
Elements
Mo3d (Mo4+ (3d5/2)
Mo3d (Mo6+(3d5/2)
Mo3d (Mo6+(3d3/2)
Co2p
BE (ev)
230.3
232.7
235.8
785.2
531
FWHM
2.5
2.3
2.1
3.4
O1s
1.7
C1s
284.7
1.3
24

Table 3: Comparison between the catalytic activity of ZGMoCo and other reported catalysts.
Sulfur concentration
Catalysts
Sulfur removal (%)
References
(ppm)
ZGMoCo
550 ppm
740 ppm
4000 ppm
340 ppm
≈98 %
90 %
67 %
97 %
Current work
[48]
NiMo/Al2O3
Co-Mo/Al2O3
CoMoS and NiMoS
[49]
[50]
P and Ni-Al2O3 supported Mo
oxycarbide
520 ppm
50 %
[51]
CoMo/SBA-15
FeMoS/Carbon
MoCo/CNT
2160 ppm
1000 ppm
1300 ppm
300 ppm
77 %
30 %
[28]
[29]
[1]
73.5 %
60.5 %
CoMo/TiO2
[2]
25