Catalytic hydrotreatment using NiMo/MAS catalysts synthesized from ZSM-5 nano-clusters

Article abstract of DOI:10.1016/j.apcata.2011.12.015

Mesostructured alumino-silcate (MAS) materials were synthesized from ZSM-5 nano-clusters and used as catalysts supports for the hydrotreatment of a model compound and real feed stock. Supports and catalysts were thoroughly characterized by using XRD, N₂ adsorption analysis, FT-IR, ²⁷Al MAS NMR, Raman, EXAFS and HRTEM techniques. The alumino-silicate materials exhibited different acid strength and textural properties depending on the duration of hydrothermal treatment of the zeolite seeds. Materials synthesized with low seeding time of 4 h showed properties similar to Al-SBA-15 prepared using the direct synthesis route, whereas material with high seeding time (t_seed = 24 h) resembled ZSM-5. The EXAFS study of the sulfided catalysts revealed that sulfidation was highest in the NiMo catalyst supported on mesoporous alumino-silicate synthesized from ZSM-5 seeds with 16 h of hydrothermal treatment (MAS-16). Hydrotreating experiments were conducted using model compound (DBT) at 325 °C and 600 psi as well as real feed stock (Coker light gas oil) at industrial conditions. Catalytic activity in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) was found to be maximum for this particular catalyst (MAS-16). The same catalyst also gave higher hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) conversion than NiMo/γ Al₂O₃ in the hydrotreating of Light Gas Oil.

Full text of DOI:10.1016/j.apcata.2011.12.015

Applied Catalysis A: General 419–420 (2012) 1–12
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Catalytic hydrotreatment using NiMo/MAS catalysts synthesized from ZSM-5
nano-clusters
S. Mohantya, K. Chandra Moulia, K.Sonia, J. Adjayeb, A.K. Dalaia,∗
a Catalysis and Chemical Reaction Engineering Laboratories, Department of Chemical Engineering, University of Saskatchewan, Saskatoon, SK S7N 5A9, Canada
b Syncrude Edmonton Research Centre, Edmonton AB, T6N 1H4, Canada
a r t i c l e i n f o
a b s t r a c t
Article history:
Mesostructured alumino-silcate (MAS) materials were synthesized from ZSM-5 nano-clusters and used
as catalysts supports for the hydrotreatment of a model compound and real feed stock. Supports and cat-
alysts were thoroughly characterized by using XRD, N2 adsorption analysis, FT-IR, 27Al MAS NMR, Raman,
EXAFS and HRTEM techniques. The alumino-silicate materials exhibited different acid strength and tex-
tural properties depending on the duration of hydrothermal treatment of the zeolite seeds. Materials
synthesized with low seeding time of 4 h showed properties similar to Al-SBA-15 prepared using the direct
synthesis route, whereas material with high seeding time (tseed = 24 h) resembled ZSM-5. The EXAFS study
of the sulfided catalysts revealed that sulfidation was highest in the NiMo catalyst supported on meso-
porous alumino-silicate synthesized from ZSM-5 seeds with 16 h of hydrothermal treatment (MAS-16).
Hydrotreating experiments were conducted using model compound (DBT) at 325 ◦C and 600 psi as well as
real feed stock (Coker light gas oil) at industrial conditions. Catalytic activity in the hydrodesulfurization
(HDS) of dibenzothiophene (DBT) was found to be maximum for this particular catalyst (MAS-16). The
same catalyst also gave higher hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) conversion
than NiMo/␥ Al2O3 in the hydrotreating of Light Gas Oil.
Received 19 September 2011
Accepted 10 December 2011
Available online 20 December 2011
Keywords:
Hydrothermal treatment
ZSM-5 nano-seeds
Acidity
EXAFS
Dibenzothiophene
Hydrotreatment
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
but also promotes alternate pathways to the removal of sulfur atom
from the aromatic molecule. This effect is especially pronounced
Catalytic hydrotreating for the reduction of sulfur content in
gasoline and diesel fuels has been an area of intensive research
recently. Stringent environment legislations have meant that sul-
fur content in gasoline and diesel fuel be lowered to 10–50 ppm
in most countries [1,2]. Consequently, hydrodesulfurization (HDS)
catalysts with improved activity, product selectivity and longevity
are needed to meet the stricter sulfur specifications of transporta-
tion fuels. Past studies have shown that the removal of refractory
molecules like DBT and 4,6 DMDBT poses the greatest challenge for
achieving ultra-low levels of sulfur [3]. One of the most promising
approaches towards improving the performances of hydrotreat-
ing catalyst is the replacement of the conventionally used alumina
by zeolites and other related acidic materials as supports for the
CoMo and NiMo sulfide phases. These acidic materials have high
surface areas for metal dispersion and a higher concentration of
Bronsted and Lewis acid sites compared to alumina. A synergetic
effect arising from the presence of both hydrogenating and strong
acid sites not only accelerates the direct cleavage of the C S bond
in the HDS of 4,6 DMDBT, where isomerization of 4,6 DMDBT to
3,6 DMDBT improves the rate of C S bond scission [4,5]. Regard-
less of their favorable acidic properties, zeolites are essentially
microporous systems (pore size <2 nm) which severely limits their
applications in the field of hydrotreating bulky molecules [6,7]. As a
result, there is a continuous interest in synthesizing materials that
not only possesses the high surface area and strong Bronsted acid
sites of zeolites but also have a more open porous system preferably
with a narrow pore size distribution in the mesoporous range.
Mesoporous silica materials such as MCM-41, HMS, SBA-15 and
KIT-6 with open porous channels are ideal catalyst supports for
the catalytic conversions of large molecules as they can overcome
the diffusion barrier for reactants and products [3,8–10]. In spite of
their excellent textural properties the applications of these mate-
rials in catalytic reactions where acidity plays an important role
is very limited. This restriction stems from the absence of strong
Bronsted acid sites as their surface is predominantly made of silanol
groups [11]. In order to overcome the disadvantages of both zeolites
and siliceous mesoporous materials, various teams have synthe-
sized materials with strong acidity in open porosity through the
surfactant based assembly of zeolite nano-clusters present in the
precursors that nucleate to form the final crystalline zeolite. This
∗
Corresponding author. Tel.: +1 306 966 4771; fax: +1 306 966 4777.
E-mail address: ajay.dalai@usask.ca (A.K. Dalai).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.12.015

2
S. Mohanty et al. / Applied Catalysis A: General 419–420 (2012) 1–12
approach has been demonstrated by the successful assembly of
ZSM-5 (MFI), Beta (BEA), Y (FAU) zeolite nano-clusters resulting
in a mesoporous structure with strong acid sites [12–16]. The main
advantage of this type of approach is the complete or nearly com-
plete incorporation of aluminum atoms into the silica framework
in a tetrahedral coordination similar to that observed in zeolites.
In comparison post synthesis and direct synthesis methods for Al
incorporation into silica framework of various mesoporous mate-
rials have resulted in octahedral aluminum being present as extra
framework atoms.
The fine characterization and the study of the mechanistic
assembly of the zeolite nano-clusters present in the precursor solu-
tion have led to the conclusion that the duration of hydrothermal
treatment of the zeolite precursor solution containing the zeolite
nano-clusters is a key parameter to adjust the final properties of
the resulting material [17]. Zeng et al. reported the transition of
MCM-41 type material synthesized from ␤ zeolite seeds from an
amorphous phase to a crystalline one for hydrothermal treatment
durations between 6 and 16 h [18]. Similarly Frunz et al. have also
studied the effect of hydrothermal treatment on the assembly of
ZSM-5 seeds into a mesoporous structure using CTAB as a tem-
plate. They reported first reflections of the ZSM-5 phase after 48 h
of hydrothermal treatment. Interestingly all works conclude an
enhanced catalytic activity for such materials in acid catalyzed reac-
tions. The cumene cracking activity was found to be comparable to
ZSM-5 and higher than ZSM-5 for the cracking of Tri iso propyl
benzene (TIPB) [19]. Similarly favorable results were obtained in
hydrocracking reactions and HDS of 4,6 DMDBT when these mate-
rials were used as supports for the NiW sulfide phase [20]. Based
on the previous works it appeared interesting to us to evaluate
the catalytic activity of these materials synthesized using differ-
ent hydrothermal treatment durations in the HDS of both model
compounds and real feed stock.
durations. In all three precursor solution with the same chemical
composition (Si/Al ratio 25) but different seeding times of 4, 16 and
24 h were prepared. Another precursor solution was prepared with-
out any heating, but was aged for 2 h after stirring. The organization
of the polymerizing silica present in the precursor solution was
done using the ampiphilic triblock copolymer P123 as described
by Zhao et al. [22]. 10 g of EO20PO70EO20 (Pluronic P123) was dis-
solved in 265 mL of H2O with 98 mL of HCl (10 M/L), followed by
the addition of the precursor solution (containing 8 mmol of SiO2)
obtained in step one. The mixture was stirred at 40 ◦C for 24 h and
then transferred into an autoclave for additional reaction at 100 ◦C
for 36 h. The product was collected by filtration, dried in air, and
calcined at 550 ◦C for 5 h to remove the organic template. The final
samples were labeled as MAS-4, MAS-16 and MAS-24 in accordance
with the heating times of the precursor solution.
Al-SBA-15 and ␥ Al2O3 were used as the reference materials
in this study. Al-SBA-15 was prepared using the direct synthesis
route as described by Yue et al. [23]. The same Si/Al ratio of 25
was maintained for Al-SBA-15 as well. Aluminum nitrate was used
at the Al source in the preparation method. The ␥ Al2O3 support
was procured from La Roche Chemicals and was used without any
further modification.
2.2. Preparation of NiMo catalysts
Supported NiMo catalysts were prepared by the incipient
wetness co-impregnation method using aqueous solutions of
Ammoniumheptamolybdate (AHM) and nickel nitrate hexahydrate
as a Mo and Ni source respectively. The nominal composition of all
these catalysts was 4 wt.% Ni and 15 wt.% Mo. The impregnated cat-
alysts were dried overnight at 100 ◦C and subsequently calcined at
500 ◦C for 4 h to get the final oxide catalyst.
In our current study, Mesostructured alumino-silcate (MAS)
materials were synthesized from the assembly of ZSM-5 nano-
clusters using P123 as the surfactant. The synthesized materials
are then used as supports for NiMo catalysts in the HDS of DBT
and hydrotreating of light gas oil (LGO) obtained from Syncrude,
Canada. To our knowledge, no published work has been found
whereby this type of hydrotreating catalysts was screened using
real feedstock. The aim of this work is to study the effect of
hydrothermal treatment on the synthesis of MAS to develop highly
active hydrotreating catalysts. The activities of these catalysts were
then compared to NiMo catalyst supported on Al-SBA-15 and Al2O3.
2.3. Characterization
2.3.1. ICP-MS
Quantitative estimation of Si/Al ratio was performed using
inductively coupled plasma-mass spectrometer (ICP-MS). A cata-
lyst sample (0.1 g) was dissolved in concentrated hydrofluoric acid
(48–51%) at a temperature of 100–150 ◦C for 3 days. After cooling,
samples were further dissolved in concentrated HNO3 to ensure the
complete dissolution of the metals. The final solution was prepared
using 0.2 N HNO3 and analyzed with a mass spectrometer.
2.3.2. X-ray diffraction (XRD) analysis
The low-angle X-ray diffraction patterns of the samples were
measured using Bruker D8 Advance Powder diffractometer with a
Ge monochromator, producing a monochromatic Cu K␣ (ꢀ = 1.54 A)
2. Experimental
˚
2.1. Synthesis of mesoporous alumino silicates from ZSM-5
radiation. The scanning was made from 1.5◦ to 10◦ for the small
angle measurements and 15–60◦ for the high angle measurements
with a 2ꢁ step size of 0.02 and a step time of 2 s. In all cases, the
generator was operated at 40 kV and 30 mA. To avoid the problem of
illuminated areas at low 2ꢁ angles, all the samples were measured
using the same sample holder.
The mesoporous alumino silicate material was synthesized
using the method proposed by Han et al. [21]. A typical synthe-
sis procedure consisted of two steps: (a) preparation of the ZSM-5
nano-seed solution and (b) assembling the synthesized nano-seeds
in a surfactant based approach to form the final mesoporous
alumino silicate material. The chemicals used for the syntheses
were tetraethoxy silane (TEOS) (>98%, Aldrich), tetrapropylam-
monium hydroxide (TPAOH) (1.0 M in water, Aldrich), a triblock
copolymer based surfactant P123 (EO20PO70EO20) and sodium
aluminate (BDH) as the aluminum source. The zeolite precursor
solution was prepared mixing 14 mL of tetrapropylammonium
hydroxide (TPAOH) aqueous solution, 0.35 g of NaAlO2, and
24 mL of tetraethyl orthosilicate (TEOS) with 68 mL of H2O
under stirring (Al2O3/SiO2/Na2O/(TPA)2O/H2O with molar ratios of
1.0/50/1.0/7/1800). The clear solution thus obtained was subjected
to hydrothermal treatment at 100 ◦C in an autoclave for various
2.3.3. Measurement of N2 adsorption–desorption isotherms
The BET surface area, pore volume, and pore size distribu-
tion of the samples were measured with a Micromeritics ASAP
2000 instrument using low temperature N2 adsorption–desorption
isotherms. Before the measurement, each sample was degassed
in vacuum at 200 ◦C. The surface area was computed from these
isotherms using the multi-point Brunauer–Emmett–Teller (BET)
method based on the adsorption data in the partial pressure P/P0
range from 0.01 to 0.2. The mesopore volume was determined from
the N2 adsorbed at a P/P0 = 0.4. The total pore volume was calcu-
lated from the amount of nitrogen adsorbed at P/P0 = 0.95, assuming

S. Mohanty et al. / Applied Catalysis A: General 419–420 (2012) 1–12
3
that adsorption on the external surface was negligible compared
with adsorption in pores. The pore diameter and pore volume were
determined using the BJH method. In all cases, correlation coeffi-
cients above 0.999 were obtained.
standard procedures for energy calibration, averaging of multiple
scans, background subtraction as well as per atom normalization.
Ab initio theoretical phase shifts and amplitude functions for the
Mo O, Mo S and Mo Mo contributions were calculated using the
program FEFF version 8. Multiple shell fitting of the Mo K edge
EXAFS data was done in R-space using the program Artemis. The
fitting was done over a k range of 3.5–13.98 (Å)−1 range. The fit-
2.3.4. FT-IR spectroscopy
The Fourier transform infra red (FT-IR) spectra were recorded
in the range 400–900 cm−1 wave numbers using 64 scans and a
resolution of 4 cm−1 with a JASCO FT-IR 4100 using pellets with
spectroscopic grade potassium bromide (KBr).
The pyridine adsorption experiments were performed using
a Perkin-Elmer Spectrum GX instrument. Prior to the pyridine
adsorption, the samples were dried at 500 ◦C and maintained under
vacuum (10−7 bar) for 3 h. Pyridine was then injected into the sam-
ple by saturating the He carrier gas for 30 min at room temperature
followed by degassing and evacuation at 250 ◦C. Molar extinction
coefficients of 1.67 cm/␮mol and 2.22 cm/␮mol were used to deter-
mine the absolute amount of Bronsted and Lewis acid sites [24].
˚
ting in R space ranged from 1 to 4 A. This data and modeled regions
contain approximately 18 independent points. This model is a well-
constrained model as the number of independent parameters was
roughly twice more than the number of parameters determined in
the fit. The estimated accuracies of the EXAFS fit parameters were
˚
20% for the coordination number (N), 0.04 A for the coordina-
tion distance (R), 20% for the Debye–Waller factor ꢂs2 and 10%
for the inner-potential correction ꢃE0.
2.4. Catalytic activity
2.4.1. Catalytic hydrodesulfurization of DBT
2.3.5. Transmission electron microscopy (TEM)
Catalytic hydrodesulfurization of model compound DBT was
performed in a 500 mL autoclave type Parr reactor at a reaction
condition of 325 ◦C temperature and 600 psi pressure.
The morphologies of the materials were characterized by trans-
mission electron microscopy (TEM). Sample specimens for TEM
studies were prepared by ultrasonic dispersion of the catalysts in
ethanol, and the suspensions were dropped onto a carbon-coated
copper grid. TEM investigations were carried out using a Philips
CM20 (100 kV) transmission electron microscope equipped with a
NARON energy-dispersive spectrometer with a germanium detec-
tor.
Before starting the reaction, the pelletized oxidic catalysts were
sulfided exsitu by injecting sulfidation solution containing 2.9 vol.%
of butanthiol in straight run atmospheric gas oil at a pressure and
temperature of 8.8 MPa and 325 ◦C, respectively, for 24 h. The flow
rate of the sulfiding solution was 5 mL/h. The H2 flow rate was kept
at a rate corresponding to H2 sulfiding solution ratio of 600 mL/mL.
1 g of the sulfided catalyst (sieved between 0.3 and 0.5 mm) was
transferred into the batch reactor containing the feed in an inert
atmosphere at 25 ◦C.
The feed was prepared by diluting the DBT using a mixture of cis
(55%) and trans decalin (45%) and dodecane (0.05 mol/L) as an inter-
nal reference. The concentration of DBT in the resulting mixture
was kept 0.2 mol/L using 150 mL of decalin mixture. Reaction mass
balances were found to be more than 95% in all experiments, for
each reactant using dodecane as the internal reference. In a typical
experiment, about 6 liquid samples of approximately 0.5 mL each
were withdrawn, so that the volume feed could be considered con-
stant throughout the experiment. The liquid product samples were
diluted in ethanol (500 mL) and analyzed by GC for cyclohexyl ben-
zene (CHB) and biphenyl (BP) using an FID detector and a DB wax
capillary column at a temperature programmed from 50 to 230 ◦C
(15 ◦C/min). DBT in the product was analyzed in the same GC but
using a different Varian CP-Sil 8CB column using an FID detector at
a temperature programmed from 80 to 280 ◦C (15 ◦C/min). Conver-
sions were calculated according to the disappearance of reactant
or the formation of products. The conversions for DBT are reported
here for 6 h of reaction-on-time.
2.3.6. 27Al MAS NMR spectroscopy
27Al MAS NMR experiments were performed on a Bruker AMX-
400 FT NMR spectrometer operated at 104.2 MHz. All spectra were
acquired using single-pulse excitation and spinning speeds rang-
ing from 14 to 15 kHz. The spectra were typically obtained with a
pulse width of 1.5 ␮s, and recycle delay of 1 s. Baselines were cor-
rected and smoothed using the Bruker baseline correction routine.
All spectra were externally referenced to aluminum nitrate solution
(ı = 0 ppm).
2.3.7. Raman spectroscopy
The Raman spectra were obtained using a Renishaw Micro-
Raman System 2000 Spectrometer (Spectra-Physics model 127)
equipped with a He/Ne laser, operated at the argon laser wave-
length of 514.5 nm. The laser spot size was approximately 1 mm
with a power of 10 mW. The wavenumber accuracy was 2 cm−1
.
2.3.8. EXAFS data collection and analysis
Mo K-edge XAS data were collected for three sulfided catalyst
samples sat the Hard X-ray Microanalysis beamline (HXMA, 06ID-
1) at the Canadian Light Source. The synchrotron source at the
HXMA beamline is a superconducting wiggler and the beamline is
equipped with a double-crystal Si(2 2 0) monochromator and Rh-
coated, upstream collimating and downstream focusing mirrors.
The operational current in the storage ring of CLS is 200–250 mA at
2.9 GeV. The harmonic rejection was accomplished by detuning the
second monochromator crystal to 50% of the maximum intensity.
XAS data for the sulfided samples were collected in fluorescence
mode using a 32 element solid state germanium detector. The XAS
data for the catalyst samples were collected at ambient temper-
ature and pressure with the simultaneous measurement of a Mo
reference foil spectra for energy calibration. Approximately 200 mg
of the sample was pressed into the 10 mm ID quartz sample holder.
The weight of the sample was calculated to have a total absorption
length of about 2.0 for optimal signal to noise ratio.
2.4.2. Catalytic hydrotreating of LGO
Catalytic hydrotreating of light gas oil (LGO) feed was performed
in the same 500 mL Parr reactor at reaction temperature of 350 ◦C
and pressure of 1000 psi. The LGO feed had a sulfur and nitro-
gen content of 14,000 ppm and 1450 ppm respectively. A catalyst
to feed ratio of 1:80 (wt/wt) was used in case of LGO. The reac-
tor was flushed by nitrogen to avoid air contact with feed and
sulfided catalysts before injecting H2. After flushing by N2 the
reactor was pressurized with H2 at reactor pressure of 1000 psi.
The batch reactor was kept at a constant stirring of 1000 rpm to
avoid mass transfer limitations. Products were collected after 6 h
of reaction time. The total nitrogen content of the liquid product
was measured by combustion/chemiluminence technique follow-
ing ASTM D4629 method, and the sulfur content was measured
using combustion/fluorescence technique following ASTM 5463
method. Both sulfur and nitrogen were analyzed in an Antek 9000
The XAS spectral data collected were analyzed using Athena
[25]. The data reduction of the XAS spectra included the

4
S. Mohanty et al. / Applied Catalysis A: General 419–420 (2012) 1–12
[100]
800
700
600
500
400
300
200
100
Al-SBA-15
MAS-4
[110]
[200]
[100]
MAS-16
Al-SBA-15
MAS-4
MAS-24
0.8
MAS-16
MAS-24
0.2
0.4
0.6
1.0
Relative Pressure (P/P)
o
0
2
4
6
8
10
12
2θ, degree
Fig. 1. N2 adsorption-desorption isotherms of (a) Al-SBA-15, (b) MAS-4, (c) MAS-16
and (d) MAS-24.
Fig. 2. XRD pattern of (a) Al-SBA-15, (b), MAS-4, (c) MAS-16 and (d) MAS-24 in small
angle range plotted in cascading format.
NS analyzer. The instrumental error in N and S analysis was 3%.
Simulated distillation was performed using ASTM D6352 method
in order to study the boiling range distribution of different product
samples at different temperatures using a Varian model CP3800 gas
chromatograph coupled to a Varian CP 8400 auto sampler.
hydrothermal gel. The alumino silicate framework after 24 h of
hydrothermal treatment is nearly completely connected. The large
connected alumino silicate network in MAS-24 is able to resist
the capillary stress of evaporative drying and calcination. As a
result the micropores are retained by the final material. In contrast,
hydrothermal gel with low seeding durations (tseed = 4 h) possesses
a very high content of silanols, which corresponds to interruption
of the alumino-silicate framework. The presence of weaker silanol
groups instead of a stronger alumino-silicate network allows the
micropores to grow into mesopores [26].
3. Results and discussion
3.1. N2 adsorption–desorption analysis
The N2 adsorption and desorption isotherms of Al-SBA-15, MAS-
4, MAS-16 and MAS-24 are shown in Fig. 1. Also, the various textural
properties for these materials along with ␥-Al2O3 are tabulated in
Table 1. MAS-4 and Al-SBA-15 exhibit a typical Type IV with a hys-
teresis loop which is characteristic of regular mesoporous channels
structure. The initial increase in volume of adsorption at low pres-
sure is due to monolayer adsorption in micropores and mesopores,
and the upward deviation in the 0.6–0.8 P/Po range is associated
with capillary condensation inside the mesopores. An alteration in
type of isotherm and relative shift in the point of inflection with
increasing hydrothermal treatment duration can be observed due
to a change in nature or pores. The surface area as well as the pore
volume decreased continuously with increase in seeding time. The
contribution of mesopores to the total surface area of the material
decreases with seeding time. This effect is particularly visible in
the reduction of surface area of MAS-24 as compared to MAS-16.
In MAS-16 mesopores constitute almost 70% of the total surface
area whereas the mesoporous area in MAS-24 is as low as 50% of
the total surface area. The decline in mesopores is accompanied
with a rapid growth of micropores in the materials especially in
MAS-24. The increase in microporosity in MAS-24 can be ascribed
to the degree of connection of the alumino-silicate network of the
Table 2 shows the surface area and other textural properties
of the Al-SBA-15, MAS-4, MAS-16 and MAS-24 supported NiMo
catalysts. The metal composition is very close to the targeted values,
indicating that the support is able to hold maximum metal content
on its surface which was prepared by using wetness impregna-
tion procedure. As the seeding time increases the textual properties
(SBET, VP, DP) continuously decrease due to a possible blockage of
micropores which are significant in the case of MAS-24. A non-
uniform dispersion of the metal phase may also be a probable
reason for the reduction in surface area and pore volume in MAS-24.
3.2. XRD analysis
The structural arrangement of MAS and Al-SBA-15 materials
were examined using XRD at low and high angles. The low angle
XRD pattern of Al-SBA-15, MAS-4, MAS-16 and MAS-24 are given
in Fig. 2. The reference Al-SBA-15 exhibited an intense peak at
2ꢁ = 0.81◦ and two small humps at 2ꢁ = 1.42◦ and 1.65◦. The peaks
are typical of ordered SBA-15 like material with p6mm symmetry
[22]. In comparison with Al-SBA-15, the synthesized MAS fam-
ily of materials have one broad peak around 2ꢁ = 1.4◦. The poor
Table 1
Textural properties of the supports and reference materials.
Sample
Stot (m2/g)a
dBJH (nm)b
PV (cc/g)
Smicro (m2/g)
Smeso (m2/g)
Smicro/Stot
Si/Alc
Al-SBA-15
MAS-4
MAS-16
MAS-24
Al2O3
887
759
683
478
267
7.1
6.5
5.4
3.3
9.2
1.58
1.36
1.03
0.53
0.72
71
68
128
245
–
816
691
455
223
–
0.08
0.09
0.18
0.51
–
24.8
24.7
24.4
24.6
–
a
Calculated by the BET method.
Calculated by BJH method.
Determined using ICP-MS.
b
c

S. Mohanty et al. / Applied Catalysis A: General 419–420 (2012) 1–12
5
Table 2
Textural properties and concentration of acid sites of the supported catalysts systems.
Sample
Stot (m2/g)
dBJH (nm)
Amount of acid sites (␮mol/gm)
Lewis
Bronsted
Lewis + Bronsted
NiMo/Al-SBA-15
NiMo/MAS-4
NiMo/MAS-16
NiMo/MAS-24
NiMo/Al2O3
465
398
373
202
189
6.9
6.2
5.2
3.4
8.6
385
453
476
513
396
2
5
29
43
–
387
455
505
556
396
resolution of the 110 and 200 planes and a relative broadening
of the peak width in MAS materials as compared to Al-SBA-15
may indicate that the long range ordered hexagonal symmetry is
absent in materials assembled from zeolite nano-clusters. In addi-
tion, a very small peak at 2ꢁ = 8◦ can be observed only for MAS-24
which is a characteristic peak of ZSM-5. From these results it can
be concluded that the duration of hydrothermal treatment of the
zeolite seed solution is a very important factor in deciding the
nature of the final material. At low seeding times of tseed = 4 h, the
final material is essentially similar to mesoporous Al-SBA-15 with
Fig. 3. TEM images of (a) Al-SBA-15, (b), MAS-4, (c) MAS-16 and (d) MAS-24.

6
S. Mohanty et al. / Applied Catalysis A: General 419–420 (2012) 1–12
-1
550 cm
MAS-24
MAS16
MAS-24
MAS-16
MAS-4
MAS-4
Al-SBA-15
Al-SBA-15
10
15
20
25
30
35
40
2θ, degree
Fig. 4. XRD pattern of (a) MAS-24, (b) MAS-16, (c) MAS-4 and (d) Al-SBA-15 in high
angle domain.
400
500
600
700
800
900
-1
associated long range ordered structure exhibiting p6 mm sym-
metry as observed from XRD at low angles. Further, no peaks
associated with crystalline structure was observed for materials
with tseed = 16 h. In contrast MAS-24 exhibited sharp XRD peaks
similar to ZSM-5. The results from the low angle XRD are well
supported by the TEM images of the MAS materials (Fig. 3). In
contrast to the well-ordered 2D hexagonal arrays of mesopores in
Al-SBA-15, MAS materials have very low areas of ordered structure.
Hexagonal arrays are visible only but sporadically. The ill formed
hexagonal mesoporous arrays to be due to the modification in the
structure.
The findings of the XRD at low angles are further confirmed
by the diffraction pattern observed at higher angles (Fig. 4). MAS-
24 showed intense peaks similar to ZSM-5 at 2ꢁ = 22.2◦ [27].
However, this peak is absent for the materials synthesized with
seeding times less than 24 h. A broad peak typical of amorphous
material is observed in MAS-4, indicating very little or no crys-
talline phase formation in the material after 4 h of hydrothermal
treatment.
Wavenumber (cm )
Fig. 5. FTIR spectra of (a) MAS-24, (b) MAS-16, (c) MAS-4 and (d) Al-SBA-15 in
400–900 cm−1
.
1640 cm−1 are assigned to Bronsted acid sites present in the mate-
rial. Further, pyridine co-adsorbed on both Bronsted and Lewis
acid sites gives rise to a band at 1495 cm−1 [30]. Fig. 6 clearly
shows the presence of Bronsted acid sites in NiMo/MAS-24 and
NiMo/MAS-16. In contrast NiMo/MAS-4 exhibits only a weak band
at 1640 cm−1 which corresponds to a very low concentration of
Bronsted acid sites in MAS-4. The reference Al-SBA-15 however
shows no peaks at 1640 or 1540 cm−1, possibly due to the absence
of Bronsted acid sites. Nevertheless Lewis acid sites are present in
all the four catalysts. A peak at 1490 cm−1 corresponding to pres-
ence of both Bronsted and Lewis acid sites is observed for all the
catalysts. Table 2 lists the acid sites distribution in the four catalysts.
The results are calculated after degassing of the adsorbed pyridine
at 300 ◦C. NiMo/MAS-24 possesses more Bronsted acid sites than
NiMo/MAS-16. Presence of Bronsted acid sites is fairly minimal in
NiMo/MAS-4 and almost absent in NiMo/Al-SBA-15. The presence
of Bronsted acid sites may be linked to the distinctive Al chemical
3.3. FT-IR analysis
environment present in the framework in a zeolite like Si
O Al
The FTIR spectra of Al-SBA-15, MAS-4, MAS-16 and MAS-24
samples plotted in transmittance mode are shown in Fig. 5. All the
MAS materials showed a band at 550 cm−1 which is assigned to
the double five ring (D5R) stretching present in MFI type zeolites
[28]. This shows that the nano-crystal segments or nano-crystals
of ZSM-5 were embedded into the framework of the mesoporous
matrix. The intensity of this band is increases with seeding time and
is highest for MAS-24, indicating that the alumino silicate network
network. In agreement with the 27Al MAS NMR results, the FTIR-Py
technique demonstrates that with increase in hydrothermal treat-
ment duration, the extent of Al incorporation into the framework
through tetrahedral AlO4 units increases. Indeed, the number of
AlO4 tetrahedron sharing an oxygen with the SiO4 tetrahedron
involved in the Bronsted acid site determines the Si O(H) Al angle
deprotoantion energy and hence the acid strength [31].
is predominantly present as five membered rings of Si
ilar to those present in ZSM-5. The results are in good agreement
O Al sim-
3.4. 27Al MAS NMR analysis
with the findings of Han et al. who also reported Si
the 550 cm−1 region for similar materials [12].
O Al band in
The 27Al NMR spectra of provides evidence of the framework
connectivity of the alumino-silicate network. 27Al MAS NMR spec-
tra of Al-SBA-15, MAS-4, MAS-16 and MAS-24 materials are shown
in Fig. 7. The sharp peak at ∼58 ppm is generally assigned to tetra-
hedral Al species present in zeolite frameworks, whereas the peak
at 0 ppm is indicative of the extra framework aluminum present
The acid strength of the supported catalyst systems was studied
using the Pyridine FTIR method. Py-FTIR spectra of the protonated
samples were measured in the region of 1700–1400 cm−1. Accord-
ing to literature, pyridine adsorbed on Lewis acid sites exhibits
signals at 1450, 1596 and 1615 cm−1 [29]. Bands at 1540 and

S. Mohanty et al. / Applied Catalysis A: General 419–420 (2012) 1–12
7
L
L
L
B+L
B
B
MAS-24
NiMo/MAS-24
MAS-16
NiMo/MAS-16
NiMo/MAS-4
MAS-4
Al-SBA-15
NiMo/Al-SBA-15
1700
1650
1600
1550
1500
-1
1450
1400
200
400
600
800
1000
Wavenumber (cm )
-1
Wavenumber (cm )
Fig. 6. FTIR spectra of pyridine adsorbed spectra of (a) MAS-24, (b) MAS-16, (c)
Fig. 8. Raman spectra of NiMo loaded on (a) MAS-24, (b) MAS-16, (c) MAS-4 and (d)
Al-SBA-15.
MAS-4 and (d) Al-SBA-15 after degassing at 250 ◦C.
in an octahedral coordination. The extra framework Al peaks are
only observed for Al-SBA-15 and MAS-4. In addition to the 0 ppm
peak, Al-SBA-15 also gave a shoulder at ∼10 ppm. This peak can be
assigned to a hexa coordinated aluminum species with SiO groups
around the AlO6 structural units [32]. These results show the exis-
3.5. Raman spectra analysis
The Raman spectra for the NiMo catalysts are presented in Fig. 8.
Low frequency bands at 220 cm−1 characteristic of Mo
deformation is also observed in all the catalysts. The Mo
O
O
Mo
Mo
tence of extra framework Al
O Si species in Al-SBA-15 and MAS-4
linkages can be attributed to the presence of polymolybdates with
similar linkages. The results are in confirmation with Mestl et
al. who concluded that Mo exists as polymolybdates at inter-
mediate loadings of 15–20 wt% on alumina silica based supports
[33]. A Raman band at ∼958 cm−1 appeared in NiMo/MAS-16 and
NiMo/MAS-24. This band is attributed to the vibration of Mo=O
bond of the Mo species interacting with the MAS support. Another
interesting feature is the appearance of bands at 820 cm−1 and
996 cm−1 for NiMo/MAS-4, NiMo/MAS-24 and Al-SBA-15. These
bands are however not observed for NiMo/MAS-16. These bands are
materials, probably generated by the dealumination of the pre-
cursor in an acidic media during the surfactant based assembly
procedure. Another interesting aspect of the 27Al MAS NMR spec-
tra is the gradual shift in the position of the tetrahedral aluminum
peak. The tetrahedral peak signal for Al is present in Al-SBA-15 is
observed at a chemical shift ı = 53 ppm, whereas in MAS-16 and
MAS-24 the peak shifts to ı = 57 and 58 ppm respectively. The shift
in the peak position is reported in literature to be due to the differ-
ence in the locating environment of Al [12]. The 4 coordinated Al
atoms in MAS materials are present as five membered ring struc-
tures similar to the pentasil unit present in ZSM-5.
assigned to Mo O stretching (820 cm−1) and Mo
O Mo asymmet-
rical stretching (996 cm−1) in crystalline MoO3. A relatively weak
interaction between MoOx and the supports MAS-4 and MAS-24
appears to be the reason for the formation of bulk MoO3. Thus the
duration of hydrothermal treatment which directs the Al incorpo-
ration into the mesoporous framework seems to be a controlling
factor for the dispersion of the MoOx species on the surface of the
support.
3.6. EXAFS analysis
MAS-24
MAS-16
The Mo K edge EXAFS spectra and fits from the sulfided cata-
lysts are shown in Fig. 9. The Fourier transformed Mo spectra of
the samples and the fits are presented in Fig. 10. The real part of
the Fourier Transformed spectra and the corresponding fits are also
shown for consideration in Fig. 11. The EXAFS best fit values for all
the catalysts are summarized in Table 3.
MAS-4
The low noise levels at high K values illustrate the high data qual-
ity of the spectral acquisitions. The Fourier Transformation of these
samples revealed mainly 2 shells due to the Mo S and Mo Mo
Al-SBA-15
˚
˚
contributions. The corresponding peaks occur at 1.96 A and 2.79 A,
both phase incorrected. Crystalline MoS2 is well known to have a
hexagonal structure with each Mo atom surrounded by 6 S atoms
100
80
60
40
20
0
-20
-40
Chemical Shift ( )
δ
˚
˚
at 2.4 A and each S atom surrounded by 6 Mo atoms at 3.16 A [34].
From Table 3, it is evident that the S and Mo coordination in the
sulfided samples is less than crystalline MoS2. The reduction in the
Fig. 7. 27Al MAS NMR spectra of (a) MAS-24, (b) MAS-16, (c) MAS-4 and (d) Al-SBA-
15.

8
S. Mohanty et al. / Applied Catalysis A: General 419–420 (2012) 1–12
Table 3
Mo K edge fit parameters of the sulfided NiMo/ZAS(X) catalysts.
NiMo/MAS-24
Scatterer
N
R (Å)
ꢃꢂ2 (Å)2
ꢃEo (eV)
NiMo/MAS-4
O
S
Mo
0.77
5.37
3.67
1.98
2.4
3.16
0.002136
0.004238
0.004396
−3.92
4.32
3.03
NiMo/MAS-16
NiMo/MAS-4
NiMo/MAS-16
O
S
Mo
0.78
5.43
3.77
1.96
2.4
3.16
0.007902
0.004228
0.004565
−8.99
4.85
3.63
NiMo/MAS-24
O
S
Mo
0.72
5.07
3.79
1.99
2.41
3.16
0.009163
0.003724
0.004702
−6.48
3.43
2.89
Mo Mo coordination in the sulfided samples is due to the small
particles size of the supported MoS2 that are formed upon sulfida-
tion. Further, a decrease in the Mo S contribution in the catalysts
with respect to MoS2 is generally due to incomplete sulfidation or
the presence of a Mo O contribution in the EXAFS spectra. Indeed,
the coordination parameters obtained from the fitting procedure
0
2
4
6
8
10
12
14
16
k (1/Ao)
Fig. 9. EXAFS spectra of sulfided catalysts (line) and corresponding fits (symbols).
˚
revealed the presence of Mo O shell at a distance of 1.96 A. Such
a Mo-O contribution has also been previously observed by Leliveld
˚
et al., who reported the presence of O shell at 1.97 A for sulfided
Mo-S +
Mo-O
NiMo/Al2O3 catalysts [35]. Previous results have reported that the
Mo O contribution at 1.97 A is typical of the first coordination shell
˚
Mo-Mo
in MoO3. The occurrence of the Mo O bond may be attributed to the
presence of unsulfided Mo species possibly from MoO3. The Mo
O
NiMo/MAS-24
NiMo/MAS-16
NiMo/MAS-4
coordination is highest for NiMo/MAS-24 indicating low sulfidation
caused due to the presence of bulk MoO3. This is further corrobo-
rated by the low Mo S coordination in NiMo/MAS-24 followed by
NiMo/MAS-4. Thus it is clear from the Mo K edge EXAFS best fit
values that the sulfidation is highest in NiMo/MAS-16 followed by
NiMo/MAS-4 and NiMo/MAS-24. The results are in agreement with
the Raman results of the oxide phase. The presence of bulk MoO3,
due to the poor dispersion of the MoOx species in NiMo/MAS-4 and
NiMo/MAS-24 does indeed hampers the complete sulfidation of the
catalysts.
1
2
3
4
5
R(Ao)
3.7. HRTEM analysis
Fig. 10. Magnitude of the Fourier transform of sulfided catalysts (line) and corre-
˚
sponding fits (symbols). The fit range for the spectra is 1–4 A.
The HRTEM images of the sulfided catalysts are presented in
Fig. 12. The formation of MoS2 stacks are clearly shown in the
pictures with different stack heights and lengths. MoS2 crystal-
˚
lites with lengths between 20 and 80 A and stacking from two to
six layers are formed on the supports. The results were obtained
through a statistical analysis and are presented in Table 4. Sul-
fided NiMo/MAS-16 shows a very well dispersed MoS2 phase with
mostly single or double-layered slabs of the MoS2 phase. This is
in confirmation with the results obtained from the EXAFS fits, that
sulfidation in catalysts supported on MAS-16 results in the forma-
tion of a well-dispersed sulfide phase. Further, sulfided NiMo on
MAS-24 also yields small MoS2 crystallites mostly present as sin-
gle layered slabs. On the contrary, multiple stacked layers of MoS2
are observed in catalysts supported on Al-SBA-15 and MAS-4. The
stacking of MoS2 layers in Al-SBA-15 and MAS-4 is primarily due to
NiMo/MAS-24
NiMo/MAS-16
NiMo/MAS-4
Table 4
Average MoS2 stack length and height on the surface of the supports from HRTEM
analysis.
0
1
2
3
4
5
Catalyst
Slab density
Avg. length (Å)
Avg. stack height
o
R(A )
NiMo/Al-SBA-15
NiMo/MAS-4
NiMo/MAS-16
NiMo/MAS-24
39
53
65
19
45
41
51
34
4.5
3.6
1.8
2.3
Fig. 11. Real part of the Fourier transform of sulfided catalysts (line) and corre-
sponding fits (symbols). The fit range for the spectra is 1–4 A.
˚

S. Mohanty et al. / Applied Catalysis A: General 419–420 (2012) 1–12
9
Fig. 12. HRTEM images of sulfided (a) NiMo/Al-SBA-15, (b) NiMo/MAS-4, (c) NiMo/MAS-16 and (d) NiMo/MAS-24. The arrows indicate the MoS2 slabs.
the weak interactions between molybdenum and the support. The
MAS-24 despite of MAS-24 having the maximum growth of the zeo-
linkage of the Mo atom to the support through Mo
(silanol groups) instead of the relatively stronger Mo
could be a possible reason for this weakened interaction. As a result
stacked layers of MoS2 are formed upon sulfidation in NiMo/MAS-4
and NiMo/Al-SBA-15.
Silica based materials like SBA-15, KIT-6, MCM-41 are known to
favor multiple stacked layers of MoS2 due to the low metal support
interactions [36]. Single slabs of MoS2 dispersed over the MAS-16
support suggest an improvement in the metal support interac-
tion similar to those present in alumina supports. The extensive
O
O
Si bonds
Al bonds
lite like phase. This is probably due to the small pore size and pore
volume observed in MAS-24. In addition, structural collapse of the
mesophase due to the rapid growth of crystals on the walls of MAS-
24 as observed from the N2 adsorption and desorption isotherms
could be another possible reason for the low DBT conversion. A
good dispersion of the active phase combined with excellent tex-
tural properties and presence of strong Bronsted acid sites resulted
in NiMo supported on MAS-16 exhibiting the highest conversion
among all 4 catalysts. The product distribution analysis was done
bonding of Mo with the framework Al atoms results in Mo
O Al
linkage instead of the weaker Mo Si linkages. Thus, preparation
O
70
NiMo/MAS-16
of mesoporous alumino-silicates from ZSM-5 nano-seeds seems to
have a positive impact on the metal support interaction and hence
the dispersion of the MoOx phase on the support. A well-dispersed
MoOx phase like the one in NiMo/MAS-16, upon sulfidation resulted
in single slabs of MoS2 uniformly spread throughout the surface of
the support.
NiMo/MAS-24
60
NiMo/MAS-4
NiMo/Al-SBA-15
50
40
30
20
10
0
3.8. Catalytic activity measurements
3.8.1. Catalytic activity in the hydrotreating of the DBT
Hydrotreating activity of AlSBA-15, MAS-4, MAS-16 and MAS-
24 supported catalysts is shown in Fig. 13. The MAS-16 supported
NiMo catalyst showed the highest DBT conversion at all times, with
DBT conversion being 30% higher than Al-SBA-15 and MAS-4 sup-
ported catalyst. DBT conversion in Al-SBA-15 and MAS-4 supported
catalyst were similar. This is probably due to similar properties
of Al-SBA-15 and MAS-4 since at lower durations of hydrother-
mal treatment; the nano-clusters do not fully exhibit zeolite like
connectivity and thus have properties similar to Al-SBA-15. In con-
trast, the conversion of DBT over MAS-4 was higher than that of
0
1
2
3
4
5
6
Time (hrs)
Fig. 13. DBT conversions of sulfided NiMo catalysts at various times over different
supports.

10
S. Mohanty et al. / Applied Catalysis A: General 419–420 (2012) 1–12
100
80
60
40
20
0
100
NiMo/Al-SBA-15
NiMo/MAS-24
NiMo/MAS-16
NiMo/MAS-4
80
60
BP
BP
CHB
BP
40
20
CHB
CHB
1
2
3
4
5
6
0
Time (hrs)
0
1
2
3
4
5
6
7
Time (hrs)
Fig. 14. Product distribution of BP and CHB in the HDS of DBT over NiMo/Al-SBA-15
and NiMo/MAS-4.
Fig. 15. Product distribution of BP and CHB in the HDS of DBT over NiMo/MAS-24
and NiMo/MAS-16.
only for cyclohexyl benzene (CHB) and biphenyl (BP) using a GC.
Biphenyl is known to be a product of the direct desulfurization
(DDS) pathway whereas CHB is formed in the hydrogenation (HYD)
pathway. The simplified reaction scheme for the HDS of DBT is
given in Fig. 16. The selectivity for BP over CHB is highest for
catalyst supported on MAS-24. This indicates that NiMo/MAS-24
favors the DDS pathway for the HDS of DBT. The acceleration of
the DDS pathway may be attributed to the presence of Bronsted
acid sites which act as proton donors to the metal sulfide particles
and lead to a direct C S bond cleavage. NiMo/MAS-16 with simi-
lar acid sites also yields more BP as compared to NiMo/MAS-4 and
NiMo/Al-SBA-15. The product analysis for CHB, however gives dif-
ferent results. NiMo/MAS-4 and NiMo/Al-SBA-15 show comparable
concentrations of CHB and BP in the products as compared to cata-
lysts supported on MAS materials with higher seeding times. CHB is
formed by the hydrogenation of cyclohexen-1-yl-benzene (CHEB)
which is a product of direct desulfurization of THDBT [35]. The
THDBT occurs as an intermediate when the HDS of DBT follows the
hydrogenation route. The lower selectivity of CHB in NiMo/MAS-16
and NiMo/MAS-24 can be explained in two ways: (1) the hydro-
genation pathway is less favored as compared to the DDS pathway,
or (2) in presence of strong acid sites and high reaction tempera-
tures of 320 ◦C, CHEB may have undergone further hydrogenation
to form Iso DM decalin and alkyl-CH [37]. The strong Bronsted acid
sites in NiMo/MAS-16 and NiMo/MAS-24 appear to have promoted
the further hydrogenation of CHEB at 320 ◦C. The former seems
unlikely as the presence of acid sites is known to enhance hydro-
genating properties as well which are ascribed to electronic effects
of the acidity on metal sulfide phase [38] (Figs. 14 and 15).
Fig. 16. Simplified reaction schematic of HDS of DBT [42].
distribution comparison of catalyst supported on MAS(X) and ␥-
Al2O3 is given in Fig. 18. The volume fraction of lighter naptha
products (boiling point 90–170 ◦C) in NiMo/MAS-16 is more than
NiMo/␥-Al2O3. The Bronsted acid sites in MAS-16 may have pro-
moted the cracking of large hydrocarbon molecules in LGO into
HDS
HDN
100
80
60
40
20
0
In either case the DDS pathway is accelerated more than the
HYD pathway over catalysts supports with longer durations of
hydrothermal treatment. The presence of acidic protons in MAS-
16 and MAS-24 catalysts arising from the Bronsted acid sites help
in the faster scission of the C S bond.
3.8.2. Catalytic activity in the hydrotreating of the LGO
The HDS and HDN activities of MAS supported catalysts are pre-
sented relative to a ␥-Al2O3 supported catalyst. The conversion
for HDS and HDN of ␥-Al2O3 is standardized to 100% due to low
conversions in a batch type reactor. The HDS and HDN activity
of NiMo/MAS-16 is higher than NiMo supported on commercial
␥-Al2O3 (Fig. 17). However NiMo/␥-Al2O3 showed better conver-
sion than both NiMo/MAS-4 and NiMo/MAS-24. A boiling point
NiMo/MAS-4
NiMo/MAS-16
NiMo/MAS-24
Fig. 17. Hydrotreating activity of MAS supported NiMo catalysts relative to NiMo/␥
Al2O3 after 6 h of reaction time.

S. Mohanty et al. / Applied Catalysis A: General 419–420 (2012) 1–12
11
is equally favored, due to the low concentration of Bronsted acid
sites. The low activity of NiMo/MAS-4 is also reflected in the HDS
and HDN performance of LGO feedstock. Both the HDS and HDN
conversions of NiMo/MAS-4 was found to be less as compared to
NiMo/␥-Al2O3.
Additionally, the EXAFS fits of the Mo K edge spectra for
the sulfided catalysts revealed that sulfidation was highest for
NiMo/MAS-16. The formation of a dispersed MoOx phase due to
optimum metal support interaction in MAS-16 results in proper
sulfidation of NiMo/MAS-16. On the contrary, the lower sulfida-
tion in NiMo supported on MAS-4 and MAS-24 was largely due
to the presence of strong Mo O bonds, either due to the for-
LGO
NiMo/MAS-4
NiMo/MAS-16
NiMo/MAS-24
NiMo/Al2O3
40
30
20
10
0
mation of bulk MoO3 or strong Mo
O Al bonds. The latter may
explain the presence of high Mo O coordination in case of sulfided
NiMo/MAS-16.
Consistent with the characterization results, sulfided NiMo cat-
alyst supported on MAS-16 was found to be most active in the
hydrotreating of both model compound and real feed stock. The
high activity of the NiMo/MAS-16 can be ascribed to the following
reasons: (1) excellent textural properties, (2) Optimum concentra-
tion of strong Bronsted and Lewis acid sites, and (3) formation of a
well-dispersed active phase.
IBP-173
173-273
Boiling Point (Co)
273-FBP
Fig. 18. Boiling point distribution of the product of LGO hydrotreating after 6 h of
reaction over different catalysts.
lighter products. On the other hand ␥-Al2O3 is known to possess
Lewis acid sites which do not favor cracking reactions.
4. Conclusions
From the catalytic study of HDS of DBT and hydrotreatment of
LGO, it is clear that NiMo/MAS-16 is most active for hydrotreat-
ment reactions. Large pores and a narrow pore size distribution can
eliminate diffusion limitations and provides greater accessibility
to the active sites for the reactant and product molecules. Previ-
ous works on HDS of bulky molecules with microporous zeolites
have yielded low conversions [39]. MAS-16 with an average pore
size of 5.2 nm and a surface area of 650 m2/g is 40% more active
than NiMo supported on MAS-24 in the HDS of DBT. NiMo/MAS-
24 which showed the highest concentration of Bronsted acid sites
suffers from low surface areas and small porous channels due to
the rapid zeolite phase formation on the walls after 24 h of seed-
ing time. This leads to a lower activity in hydrotreating tests. The
low surface area (predominantly microporous) causes agglomera-
tion of the MoOx particles leading to the formation of bulk MoO3
which is known to be difficult to sulfide. Further the low HDS and
HDN activity in case of LGO may also be attributed to the rapid
deactivation of the catalyst caused due to unwanted cracking of
the feedstock leading to coke deposition on the catalysts surface
[40]. Nonetheless, the low hydrotreating activity of NiMo/MAS-4
relative to NiMo/MAS-16 may be due to the difference in the chem-
ical nature of the two supports. Indeed, MAS-4 which was found
to be similar to Al-SBA-15 prepared through the direct synthesis
method showed similar conversions in HDS of DBT and HDT of
LGO. The deficiency of strong Bronsted sites in MAS-4 and Al-SBA-
15 as indicated by the absence of the 1540 cm−1 peak in FTIR-Py
spectra, might have resulted in the low catalytic activity of the
sulfided NiMo catalysts system. Proper distribution of acid sites in
supported catalysts is known to improve the conversion in HDS of
DBT and 4,6 DMDBT and the role of acidity in improving catalytic
activity of hydrotreating catalyst is well cited [4,38,39]. Acidic sup-
ports facilitate an alternate hydrogenation route through spillover
hydrogen atoms from the metal particles to the aromatic sulfur
containing molecules [41]. Furthermore, the activity of the DDS
pathway in NiMo/MAS-16 was found to be higher than NiMo/MAS-
4 which was evident from the preferential selectivity towards BP
in the HDS of DBT in NiMo/MAS-16. The Bronsted acid sites in
MAS-16 provide protons in the close vicinity of the metal sul-
fide particles, leading to an accelerated C S bond cleavage. This
effect is less prominent in NiMo/MAS-4 wherein the HYD pathway
Catalytic performance of sulfided NiMo catalysts supported on
mesoporous alumino silicates synthesized using the assembly of
ZSM-5 seeds was evaluated in this study. The acidity of the final
material could be tuned depending on the duration of hydrother-
mal treatment of the zeolite seed solution. The material exhibited
characteristics of ZSM-5 for longer duration of hydrothermal treat-
ment while the nature of the material was found to be similar to
Al-SBA-15 for shorter periods of seeding. However the sulfided
catalyst with maximum hydrotreating activity was the one with
intermediate (tseed = 16 h) heat treatment duration. The high activ-
ity of this catalyst was ascribed to the combination of good textural
properties and strong acid sites arising from Al in a tetrahedral coor-
dination in ZSM-5 like environment. The metal support interaction
improved in the materials synthesized with longer seeding times.
As a result a well dispersed NiMoS phase with single or double lay-
ered slabs of MoS2 were formed upon sulfidation of NiMo/MAS-16.
This was different from sulfided NiMo/MAS-4 where an average
MoS2 stack height of 3.8 was observed. Raman results indi-
cated that owing to low metal support interaction in MAS-4,
bulk MoO3 is formed at 15% Mo loading. Further, EXAFS stud-
ies revealed a high Mo O shell coordination in NiMo/MAS-4 and
NiMo/MAS-24 signifying that sulfidation is low for these particular
systems.
Catalytic tests showed that NiMo/MAS-16 had the highest activ-
ity in the HDS of DBT. Presence of Bronsted acid sites in the
support favored the DDS pathway over the HYD pathway in the
desulfurization of DBT. Availability of the acidic proton in the vicin-
ity of the metal sulfide accelerated the direct C-S bond scission.
However NiMo/MAS-24 showed low conversions due to a partial
collapse in the mesoporous structure after 24 h of hydrothermal
treatment of the zeolite nano-clusters. NiMo/MAS-16 was found to
have superior activity over NiMo catalyst supported on commer-
cial ␥-Al2O3 in the hydrotreatment of LGO. Further, lighter products
were obtained with NiMo/MAS-16 obviously due to the presence of
stronger acid sites in MAS-16. It would be very interesting to evalu-
ate the catalytic performance of these materials especially MAS-16
which combines the good properties of zeolites and SBA-15 in the
hydrotreatment studies in a continuous flow reactor with real feed
stock.

12
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