Synthesis and characterization of mesoporous molybdenum catalysts for hydrocracking of atmospheric residual oil

Article abstract of DOI:10.1166/jnn.2013.7753

In this study, performances of mesoporous Mo/Al₂O₃ catalysts prepared by sol-gel and posthydrolysis methods in hydrocracking of atmospheric residual oil were compared. In addition, different methods: (i) the single step and (ii) conventional impregnation method to incorporate active metal over the mesoporous support were also investigated. For single step method, Mo/Al₂O₃ catalysts were synthesized directly by sol-gel and post-hydrolysis method. On the other hand, the impregnation method was a two step procedure which involved the production of alumina via sol-gel or posthydrolysis method and followed by respective Mo impregnation. In general, mesoporous Mo/Al₂O₃ catalysts prepared by sol-gel method resulted in relatively higher surface area (>400 m2/g) and large pore volume (0.8 cm3/g). Mo/Al₂O₃ catalysts prepared by sol-gel method exhibited higher hydrocracking activity as well. The Mo crystal size was found to relate directly with the hydrocracking result. Copyright

Full text of DOI:10.1166/jnn.2013.7753

Copyright © 2013 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 13, 6988–6995, 2013
Synthesis and Characterization of
Mesoporous Molybdenum Catalysts for
Hydrocracking of Atmospheric Residual Oil
P. Y. Looi, A. R. Mohamed, and C. T. Tye∗
School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia,
14300 Nibong Tebal, S.P.S. Pulau Pinang, Malaysia
In this study, performances of mesoporous Mo/Al2O3 catalysts prepared by sol–gel and post-
hydrolysis methods in hydrocracking of atmospheric residual oil were compared. In addition, different
methods: (i) the single step and (ii) conventional impregnation method to incorporate active metal
over the mesoporous support were also investigated. For single step method, Mo/Al2O3 catalysts
were synthesized directly by sol–gel and post-hydrolysis method. On the other hand, the impregna-
tion method was a two step procedure which involved the production of alumina via sol–gel or post-
hydrolysis method and followed by respective Mo impregnation. In general, mesoporous Mo/Al2O3
catalysts prepared by sol–gel method resulted in relatively higher surface area (> 400 m2/g) and
large pore volume (∼ 0.8 cm3/g). Mo/Al2O3 catalysts prepared by sol–gel method exhibited higher
hydrocracking activity as well. The Mo crystal size was found to relate directly with the hydrocracking
result.
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Keywords: Hydrocracking, Mesoporous Alumina, Post-Hydrolysis, Sol–Gel, Single Step.
IP: 192.174.3.200 On: Wed, 04 Nov 2015 18:45:04
Copyright: American Scientific Publishers
1. INTRODUCTION
properties, moderate acid capacity,12 and variable point
of zero charge, which makes it easier to load different
metals.13 Extensive research has been devoted on the pos-
sibility of tailoring physical properties of alumina for
different applications.9ꢀ14–19 Molybdenum supported over
alumina is a catalyst widely used in petroleum residue
hydrocracking.20 In order to further improve the molyb-
denum base catalyst activity, different method to prepare
alumina as well as different metal incorporation method
on the catalyst support could be tested. There are vari-
ous preparation procedure for mesoporous alumina. Meso-
porous alumina has been synthesized by using different
surfactants or template, such as anionic,16ꢀ21 cationic,22ꢀ23
non-ionic15ꢀ24 surfactants that based on sol–gel routes, as
well as pre- and post-hydrolysis methods.14ꢀ25ꢀ26 In gen-
eral, active metal on hydrocracking catalyst was incor-
porated onto the support by conventional impregnation
method which is incipient wetness impregnation. Mean-
while, there are variety of alternative methods available
for metal incorporation such as precipitation,27 solvent-
assisted spreading,28 sonochemical vapor deposition29 and
single step sol–gel30ꢀ31 methods which were used for
assorted applications.
Hydrocracking is one of a promising upgrading process
to convert high molecular weight hydrocarbons such as
residual oil into valuable light molecular weight hydro-
carbons (naphtha and diesel). Hydrocracking is normally
conducted over a bifunctional catalyst that has a cracking
function and hydrogenation–dehydrogenation function.1
To enhance the performance of catalyst in hydrocrack-
ing process and maximize the yields of lighter distillates
from upgrading of residual oil, hydrocracking catalysts
with mesopores are highly desirable.2–4 The use of zeolites
as hydrocracking catalyst has been reported.4–6 However,
the application of zeolites for hydrocracking of residual
oil is limited owing to its small pore size (micropores).
Though there were several studies focused on the modi-
fied zeolites with pore size within the mesoporous range
(2–50 nm), yet the modified zeolites were normally with
mesopore size less than 5 nm.4ꢀ6ꢀ7
Among the mesoporous materials, alumina with meso-
porous structure has been widely employed in catalysis
as a catalyst support for active metals in chemical and
petrochemical industries.8–11 due to its adjustable physical
This study aims to investigate the catalyst prepara-
tion method on catalyst properties and its activity in
∗Author to whom correspondence should be addressed.
6988
J. Nanosci. Nanotechnol. 2013, Vol. 13, No. 10
1533-4880/2013/13/6988/008
doi:10.1166/jnn.2013.7753

Looi et al.
Synthesis and Characterization of Mesoporous Molybdenum Catalysts for Hydrocracking of Atmospheric Residual Oil
hydrocracking reaction. In the present study, mesoporous
alumina was synthesized by post-hydrolysis method and
compared with that prepared from sol–gel method.
These methods were reported to produce alumina with
large surface area (∼ 400 m2/g), mesoporous range pore
size14ꢀ21 and well-organized pore structure.27 In addition,
the resulted mesoporous alumina was incorporated with
molybdenum by using single step method which has never
been reported. This method is an efficient and simple way
for the catalyst synthesis. Activity of prepared Mo/Al2O3
catalysts were tested in the hydrocracking of atmospheric
residual oil and the performance were evaluated in terms
of atmospheric residual oil conversion and product liquid
oil fractions.
the molybdenum precursor. An appropriate amount of
ammonium molybdate (VI) tetrahydrate aqueous solution
was then mixed with alumina powder and stirred. After
that, ꢀthe Mo impregnated material was dried in an oven at
120 C for 16 h andꢀfollowed by calcination in a muffle
furnace in air at 500 C for 3 h.
In order to prepare MoS2/Al2O3 catalyst, ex-situ pre-
sulfidation was carried out in a batch reactor (Parr 4570).
The oxide catalyst was soaked in hexadecane (Sigma,
≥ 99%) with 1 wt% of dimethyl disulfide (Aldrich, 99%).
The reactor was pressurized with H2 gas to 400 psig. Sul-
fidation of catalyst was carried out in a two-stage tem-
perature manner. The reactor temperature was first raisꢀed
ꢀ
to 250 C for 2 h, and then further increased to 320 C
for another 3 h. After the presulfiding process, the catalyst
ꢀ
was filtered and dried at 120 C for 16 h under vacuum.32
2. EXPERIMENTAL DETAILS
Finally, the sulfided catalyst was again loaded into the
batch reactor with the atmospheric residual oil to undergo
hydrocracking reaction.
Name of prepared material is based on the prepara-
tion method. For instance, sample SG-MoMA-1 is meso-
porous alumina (MA) prepared by sol–gel method (SG),
with molybdenum (Mo) impregnated through single step
method (1) or conventional impregnation method (i). PH
represents catalyst prepared with post-hydrolysis method,
while the sulfide catalyst is denoted as S.
2.1. Mo/Al2O3 Catalyst Preparation
Two methods were employed to prepare alumina: (i) sol–
gel and (ii) post-hydrolysis. The sol–gel method used
was based on Ref. [21]. For catalyst prepared by single
step sol–gel method, aluminum tri-ethylate (Merck, 97%)
was first dissolved in ethanol (System, 95 v/v%). Then,
a proper aqueous solution of ammonium molybdate (VI)
tetrahydrate (Acros) was added into the ethanol mixture
solution and stirred. Water was then slowly dropped into
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ꢀ
the mixture at 70 C under constant stirring for 30 min.
IP: 192.174.3.200 On: Wed, 04 Nov 2015 18:45:04
ꢀ
After gel formed, the sample was dried in oven at 120 C
2.2. Characterization of Catalysts
Copyright: American Scientific Publishers
for 24 h. Then, the alumina was calcined in a muffle fur-
nace in air at 500 ꢀC for 3 h. The alumina was prepared by
following the molar composition of aluminum tri-ethylate,
ethanol and water to a ratio of 1:10:4 respectively.
2.2.1. Nitrogen Adsorption–Desorption Isotherm
Specific surface area of sample was measured by nitrogen
adsorption/desorption analysis using Micromeritics ASAP
2020 at 77 K. Prioꢀr to analysis, the alumina sample
was degassed at 350 C for 8 h. Barret–Joyner–Hallender
(BJH) model on desorption branch was employed to cal-
culate the pore size distributions.
Preparation of alumina via post-hydrolysis was based
on Ref. [14]. For catalyst prepared by single step post-
hydrolysis method, stearic acid (Acros, 97%) was used
as the anionic surfactant and aluminum sec-butoxide
(Acros, 97%) was employed as the aluminum precur-
sor. The mesoporous alumina was prepared by follow-
ing the molar composition of aluminum sec-butoxide,
stearic acid, sodium hydroxide, sec-butanol and water to a
ratio of 1:0.20:0.04:5:4 respectively. First, aluminum sec-
butoxide and stearic acid were dissolved in sec-butanol
separately. In order to enhance the solubility of stearic acid
in sec-butanol, small amount of sodium hydroxide was
added. Then, two solutions were mixed. The solution with
desired amount of ammonium molybdate tetrahydrate was
added subsequently. Small amounts of water were slowly
dropped into the mixture until white suspension appeared.
After that, the resulting suspension was further stirred for
24 h with pH regulated at 7. Subsequently, it was dried
at room temperature for 48 h. Finally, the material was
2.2.2. X-Ray Diffraction (XRD)
XRD patterns of catalyst was obtained by using a Philips
diffractometer with Cu target Kꢁ-ray. The powder diffrac-
tion patterns were recorded in the 2ꢂ range from 20–80ꢀ.
2.2.3. Ammonia Temperature-Programmed
Desorption (NH3-TPD)
The acid capacity of catalyst was analyzed by NH3-TPD
conducted using an AutoChem II 2920. The sample was
first degassed at 120 C for 60 min in flowing helium
gas to remove water vapour. After pretreatment, the sam-
ple was cooled down to ambient temperature under helium
gas (20 ml/min). Then, the sample was exposed to 15 %
ꢀ
ꢀ
calcined in a muffle furnace in air at 450 C for 3 h.
For impregnation method synthesis, the alumina sup-
port was first prepared by conventional sol–gel or post-
hydrolysis method as described above without adding
ꢀ
NH3 in He for adsorption at 100 C for 60 min to saturate
acid sites of the catalyst. Then, the sample was swept with
J. Nanosci. Nanotechnol. 13, 6988–6995, 2013
6989

Synthesis and Characterization of Mesoporous Molybdenum Catalysts for Hydrocracking of Atmospheric Residual Oil
Looi et al.
helium at 100 ꢀC for 30 min to remove physisorbed ammo-
700
0.5
SG-MA
SG-MA
nia. After cooling down the sample, furnace temperature
600
SG-MoMA-1
SG-MoMA-1
SG-MoMA-i
ꢀ
0.4
was increased from 50 to 500 C at a ramping rate of
500
SG-MoMA-i
ꢀ
10 C/min and 20 ml/min of helium total flow rate. The
0.3
0.2
0.1
0.0
400
300
200
100
0
amount of desorbed ammonia from sample was detected
by a TCD as desorption peak area. The area under the
peak represents quantitative estimation of acid capacity.
(a)
(b)
2.3. Reaction Studies
0
0.2
0.4
0.6
0.8
1
0
10
20
30
The mesoporous Mo/Al2O3 catalyst activity in hydroc-
racking reaction was carried out in a high-pressure batch
reactor (Parr 4570). The feedstock used in the study was
atmospheric residual oil which contained 1.611 of H/C
atomic ratio, 10.22 wt% of asphathenes and 81.47 vol%
P/P0
Pore size (nm)
Fig. 1. N2 adsorption–desorption isotherms and (b) corresponding BJH
pore size distributions for mesoporous alumina and MoO3/Al2O3 catalysts
prepared with sol–gel method.
ꢀ
of residue with the boiling point higher than 340 C.
size distributions, respectively for different oxide cata-
lysts synthesized by sol–gel and post-hydrolysis meth-
ods. All these catalysts gave a type IV isotherms, which
demonstrates the existence of structural mesoporosity. The
adsorption–desorption isotherms of all samples could also
be attributed to H2 hysteresis loops.33 This suggests that
prepared materials exhibited narrow necks with wide bod-
ies of pores made up within alumina,34 which is common
in many inorganic gels. It is clearly seen that all materi-
als prepared in this work had narrow pore size distribution
centered at around 5 nm. The average pore size was found
First, 70 g of atmospheric residual oil was loaded into
the reactor with 0.5 wt% of catalysts. The batch reactor
was then pressurized with H2 gas to 500 psig at ambi-
ent temperature. This followed by heating up the reactor
ꢀ
to 400 C and maintained for 60 min. There is around
ꢀ
55 min required to reach reaction temperature (400 C)
from room temperature. After the hydrocracking reaction,
the reactor was quenched to room temperature by pass-
ing cooling water through the cooling coil in the reactor.
The reactor was depressurized before unloaded. The liquid
product was then recovered. The weight of gas produced
after reaction was determined by the yield mass balance
before and after a reaction.
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reduced following the incorporation of Mo into SG-MA
IP: 192.174.3.200 On: Wed, 04 Nov 2015 18:45:04
with either single step method or impregnation method
Copyright: American Scientific Publishers
(Fig. 1). Meanwhile, by using post-hydrolysis method,
similar pore size and pore volume were obtained when the
single step method were used to incorporate the molyb-
denum (PH-MoMA-1). On the other hand, PH-MoMA-i
catalyst, which prepared through impregnation method,
exhibited a relatively small peak of pore size distribution
reducing to ∼ 4 nm, implying that this catalyst possessed
relatively smaller pore size with smaller pore volume. This
can also be told by the smaller hysteresis loop and much
lower adsorbed volume for PH-MoMA-i catalyst as shown
in Figure 2.
The liquid products were analyzed for their boiling point
(b.p.) range according to ASTM D86 to determine the
yield of the lighter products after hydrocracking reaction.
The atmospheric residual oil conversion is defined as ratio
of weight percentage of converted liquid fraction with b.p.
ꢀ
> 340 C after hydrocracking reaction to the feed. The
liquid oil fraction is defined as volume percentage of a
distillate fraction in total volume of converted oil. Theꢀliq-
uid product was categorized into naphtha (b.p. <ꢀ250 C),
ꢀ
diesel (b.p. 250–340 C) and residue (b.p. >340 C). The
experimental errors associated with the atmospheric resid-
ual oil conversion was 0.5%, while for products yield
and liquid oil fractions data were 1.5%.
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
700
600
500
400
300
200
100
0
PH -MA
PH -MA
PH -MoMA-1
PH -MoMA-i
PH -MoMA-1
PH -MoMA-i
3. RESULTS AND DISCUSSION
The main purpose of this work is to compare the hydro-
cracking activity of Mo/Al2O3 catalysts prepared by dif-
ferent methods. The difference in catalyst properties due
to different alumina preparation and molybdenum incorpo-
ration methods was analyzed for oxide catalyst assuming
that the effects are similar in sulfide catalyst.
(a)
(b)
0.0 0.2 0.4 0.6 0.8 1.0
P/P0
0
20
40
60
80
Pore size (nm)
3.1. Physical Properties of Synthesized Catalysts
Fig. 2. (a) N2 adsorption–desorption isotherms and (b) corresponding
BJH pore size distributions for mesoporous alumina and MoO3/Al2O3
catalysts prepared with post-hydrolysis method.
Figures 1 and 2 shows the (a) nitrogen adsorption–
desorption isotherms and (b) the corresponding BJH pore
6990
J. Nanosci. Nanotechnol. 13, 6988–6995, 2013

Looi et al.
Synthesis and Characterization of Mesoporous Molybdenum Catalysts for Hydrocracking of Atmospheric Residual Oil
Table I. Physical properties of alumina supports and MoO3/Al2O3
catalysts.
Physical properties
BET surface
area (m2/g)
BJH pore
diameter (nm)
BJH pore
volume (cm3/g)
Sample ID
SG-MA
333
429
404
418
445
327
8ꢃ2
5ꢃ3
5ꢃ7
5ꢃ0
4ꢃ8
3ꢃ9
0ꢃ99
0ꢃ83
0ꢃ80
0ꢃ76
0ꢃ77
0ꢃ27
SG-MoMA-1
SG-MoMA-i
PH-MA
PH-MoMA-1
PH-MoMA-i
The summary of physical properties of catalysts pre-
pared is given in Table I. All prepared catalysts were
in mesoporous range. It is observed that the BET sur-
face areas of SG-MoMA-1 and SG-MoMA-i were larger
than unloaded alumina (SG-MA). SG-MoMA-1 possesses
larger surface area (429 m2/g) with smaller pore size
(5.3 nm) as opposed to SG-MoMA-i (404 m2/g and
5.7 nm). Both SG-MoMA-1 and SG-MoMA-i exhib-
ited similar pore volume (∼ 0.8 cm3/g). Meantime,
PH-MoMA-1 exhibited larger surface area than PH-MA,
however both PH-MoMA-1 and PH-MA had similar pore
size (∼ 5 nm) and pore volume (∼ 0.77 cm3/g). On the
contrary, PH-MoMA-i had lower surface area, pore size
and pore volume than PH-MA which without molybde-
num loading. Comparing the alumina and loaded catalyst
Fig. 3. XRD patterns of MoO3/Al2O3 catalysts (ꢅ ꢆ-Al2O3; • MoO3ꢄ.
was not very strong causing only part of Mo species in
the solution be adsorbed during the impregnation onto the
support surface.28
3.2. X-Ray Diffraction Pattern
XRD patterns of oxide catalysts are shown in Figure 3.
ꢆ-alumina and molybdite (MoO3) phases were observed
in XRD patterns. In this study, two obvious diffraction
peaks that appeared at 2ꢂ of 46ꢀ and 67ꢀ for all cata-
lysts are assigned to ꢆ-Al2O3.14ꢀ21ꢀ27 Another diffraction
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peak at 2ꢂ of 37 that oserved for both PH-MoMA-i
15ꢀ27
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and SG-MoMA-1 catalysts is also by ꢆ-Al2O3.
Sev-
prepared by post-hydrolysis method, Mo/Al O catalysts
prepared by sol–gel method, regardless single step or con-
ventional impregnation method, exhibited rigid structure
as both SG-MoMA-1 and SG-MoMA-i catalysts had large
surface area (> 400 m2/g) with pore size in the range of
5.3–5.7 nm and 0.80–0.83 cm3/g of pore volume.
Copyri2gh3t: American Scientific Publishers
eral prominent diffraction peaks for MoO3 at 2ꢂ of 25.5ꢀ,
33ꢀ, 39ꢀ and 49.2ꢀ 27ꢀ35 were appeared in PH-MoMA-1
catalyst. From XRD patterns, molybdite phase in sol–gel
prepared catalysts were more amorphous than that from
post-hydrolysis method. PH-MoMA-1 catalyst especially
showed sharp and intense peaks for MoO3 phase. This
indicates that a high crystallinity of MoO3 was found in
PH-MoMA-1 catalyst. The dispersion of MoO3 on PH-
MoMA-1 catalyst surface was poor. The crystal sizes of
MoO3 were estimated by using Scherrer Eq. (1):
Basically, catalysts prepared via single step method
(SG-MoMA-1 and PH-MoMA-1) had larger surface area,
pore size and pore volume than the catalysts prepared
by using conventional impregnation method (SG-MoMA-
i and PH-MoMA-iꢄ. It is likely that such differences in
porosity between two Mo/Al2O3 catalysts were closely
related to the synthesis condition.
Dc = Kꢇ/ꢈꢉcosꢂꢄ
(1)
The catalysts prepared by conventional impregnation
method showed lower physical properties than those pre-
pared by single step method because of pore blocking by
metal after impregnation. Asforementioned, the Mo load-
ing employed in this study was 18 wt%, a relatively large
amount of molybdenum. When molybdenum is impreg-
nated on alumina, pore plugging by metal is unavoidable,
particularly for support with larger pore size. In addi-
tion, the pore walls of alumina might be partly destroyed
owing to the aluminum dissolution in Mo solution dur-
ing the impregnation step.30 Besides, the increase of pH
of impregnation solution was reported to reduce the dis-
persion of Mo species on alumina surface30 as the natu-
ral pH of impregnation solution is close to point of zero
charge of alumina (pH 6–8). As a result, the adsorption
where Dc is the average crystal size, K is the Scherrer con-
stant (0.89), ꢇ is the X-ray wavelength (0.154 nm), ꢉ is
full width at half-maximum (in radian) and ꢂ is the diffrac-
tion angle. The catalysts prepared via single step method,
which were SG-MoMA-1 (12.33 nm) and PH-MoMA-1
(36.84 nm) exhibited larger MoO3 crystal sizes compared
to SG-MoMA-i (1.87 nm) and PH-MoMA-i (5.03 nm)
which prepared by conventional impregnation method.
3.3. Acid Capacity of Prepared Mo/Al2O3 Catalysts
NH3-TPD measurements were carried out to examine the
acid capacity of mesoporous molybdenum catalysts pre-
pared by different methods. Figure 4 shows the NH3-TPD
J. Nanosci. Nanotechnol. 13, 6988–6995, 2013
6991

Synthesis and Characterization of Mesoporous Molybdenum Catalysts for Hydrocracking of Atmospheric Residual Oil
Looi et al.
PH-MoMA-1 showed the largest desorption peak for
weak acidity as compared to PH-MoMA-i. In addition to
that, there might be due to the chemical reaction between
molybdenum species and stearic acid during preparation of
alumina in post-hydrolysis through single step procedure
and resulted in more acid sites to appear on PH-MoMA-1
surface.
3.4. Hydrocracking of Atmospheric Residual
Oil Over Mo/Al2O3 Catalyst
Table II reports the results of hydrocracking of the atmo-
spheric residual oil.ꢀThermal hydrocracking in the absence
of catalyst at 400 C achieved only 14.08 wt% of con-
version, with 7.53 vol% of naphtha and 35.12 vol% of
diesel in the liquid product. The presence of mesoporous
oxide or sulfided Mo/Al2O3 catalyst was found to increase
the conversion. For hydrocracking reaction with meso-
porous MoO3/Al2O3, the highest conversion (44.66 wt%)
was achieved by using catalyst prepared via single step
sol–gel method (SG-MoMA-1), while the lowest conver-
sions (40.25 wt%) was obtained in the reaction using PH-
MoMA-1 which prepared via single step post-hydrolysis
method. For hydrocracking reaction with mesoporous
MoS2/Al2O3, higher conversion was observed as expected.
The trend results for conversion was found to be simi-
lar to which that using MoO3/Al2O3. SG-MoMAS-1 gave
Fig. 4. NH3-TPD profile for MoO3/Al2O3 catalysts.
profile of MoO3/Al2O3 catalysts and there are three dif-
ferent desorꢀption peaks presented. The desorption peaks
before 100 C was attributed to the physically adsorbed
ammonia.36 Generally, the acid sites were attributed to
the weak, moderate and strong acid sites correspond-
ing to the NH3 desorption within 150–250, 250–400 and
400–500 ꢀC, respectively.37 Amongst the MoO3/Al2O3 cat-
alysts synthesized, PH-MoMA-1 catalyst displayed signif-
icant desorption peaks for weak acid sites, as shown in
Figure 4.
From TPD analysis, the total acid capacities of Mo/
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the highest conversion (51.39 wt%) while PH-MoMAS-1
Al2O3 catalysts were also calculated. The acid capac-
ity of catalyst increased in the order: PH-MoMA-
(0.017 mmol/g) < SG-MoMA-i (0.019 mmol/g)
< SG-MoMA-1 (0.020 mmol/g) < PH-MoMA-1
IP: 192.174.3.200 On: Wed, 04 Nov 2015 18:45:04
gave the lowest conversion, 47.02 wt%. Meanwhile, SG-
Copyright: American Scientific Publishers
MoMAS-i and PH-MoMAS-i catalysts obtained 49.41
wt% and 49.56 wt% of conversion, respectively. For oxide
catalyst, the highest liquid product (97.94 wt%) with the
least gas product (2.06 wt%) was obtained by using SG-
MoMA-i catalyst, whilst SG-MoMAS-i and PH-MoMAS-
i catalysts gave high liquid product yield (92.54 wt% and
92.27 wt%, respectively) as compared to the rest of sul-
fided catalysts did in the present study.
i
(0.022 mmol/g). As expected, catalyst with alumina as
support was catalyst with weak acid capacity if no special
treatment was caried out. Besides that, the acid capacity of
catalysts prepared by conventional impregnation method
were lower as compared to catalysts synthesized via single
step method. One of the reasons could be those catalysts
prepared via single step method, especially PH-MoMA-1
catalyst possessed high surface area, which had more
concentration of active sites on surface. In Figure 4,
Hydrocracking of atmospheric residual oil over meso-
porous MoO3/Al2O3 catalysts produced naphtha (b.p.
< 250 ꢀC), diesel (b.p. 250–340 ꢀC) and atmospheric
Table II. Residual oil hydrocracking over MoO3/Al2O3 and MoS2/Al2O3 catalysts.
Conversion,
(wt%)
Liquid product
yield (wt%)
Gas product
yield (wt%)
Coke
(wt%)
Diesel
(vol%)
Naphtha
(vol%)
Catalyst
Thermal hydrocracking
None
14ꢃ08
98ꢃ44
1ꢃ56
–
35ꢃ12
7ꢃ53
MoO3/Al2O3
SG-MoMA-1
SG-MoMA-i
PH-MoMA-1
PH-MoMA-i
MoS2/Al2O3
44ꢃ66
41ꢃ00
40ꢃ25
41ꢃ22
97ꢃ14
97ꢃ94
96ꢃ67
97ꢃ20
2ꢃ86
2ꢃ06
3ꢃ33
2ꢃ80
–
–
–
–
42ꢃ46
33ꢃ78
42ꢃ51
38ꢃ89
7ꢃ82
13ꢃ51
7ꢃ19
11ꢃ11
SG-MoMAS-1
SG-MoMAS-i
PH-MoMAS-1
PH-MoMAS-i
51ꢃ39
49ꢃ41
47ꢃ02
49ꢃ56
90ꢃ16
92ꢃ54
90ꢃ48
92ꢃ27
8ꢃ87
6ꢃ75
8ꢃ81
6ꢃ92
0ꢃ97
0ꢃ71
0ꢃ71
0ꢃ81
38ꢃ47
34ꢃ55
38ꢃ22
35ꢃ22
19ꢃ23
18ꢃ29
18ꢃ53
18ꢃ65
6992
J. Nanosci. Nanotechnol. 13, 6988–6995, 2013

Looi et al.
Synthesis and Characterization of Mesoporous Molybdenum Catalysts for Hydrocracking of Atmospheric Residual Oil
residue (b.p. >340 ꢀC). The diesel yield produced by
SG-MoMA-1 (42.46 wt%) and PH-MoMA-1 (42.51 wt%)
catalysts were higher than that by SG-MoMA-i and PH-
MoMA-i, which are 33.78 vol% and 38.89 vol%, respec-
tively. Similarly, both MoS2/Al2O3 catalysts prepared
via conventional impregnation method (SG-MoMAS-iand
PH-MoMAS-iꢄ gave 34.55 vol% and 35.22 vol% of
diesel, which were lower than that produced by reac-
tions with SG-MoMAS-1 (38.47 vol%) and PH-MoMAS-
1 (38.22 vol%). Correspondingly, the catalysts prepared
with conventional impregnation method (SG-MoMA-i and
PH-MoMA-iꢄ showed higher naphtha yield (13.51 vol%
and 11.11 vol%, respectively). On the contrary, both SG-
MoMA-1 and PH-MoMA-1 catalysts produced 7.19–7.82
vol% yield of naphtha. After sulfidation, naphtha yield
increased generally in all the catalyst used. SG-MoMAS-1
produced the highest yield of naphtha, which is 19.23
vol%, while the rest of sulfided catalysts gave 18.29–18.65
vol% of naphtha (Table II). Obviously, MoS2/Al2O3 cat-
alysts produced more naphtha. It also gave higher gas
product with lower liquid product yield as compared to
MoO3/Al2O3 catalyst did. This indicated that MoS2/Al2O3
catalyst was good in promoting secondary cracking into
lighter distillates.
between Mo species with alumina owing to the presence
of stearic acid. Mo species could not uniformly disperse on
alumina surface. Hence, poor metal dispersion or higher
crystallinity was obtained in the post-hydrolysis prepared
catalysts.
The surface acidity was reported as one of the proper-
ties of catalysts responsible for hydrocracking processes.7
In general, conversion is increased with the increasing of
catalyst acid capacity. However the catalyst synthesized
via single step post-hydrolysis method (PH-MoMA-1)
gave the lowest hydrocracking conversion in the present
study, although it had the highest total acid capacity
(0.022 mmol/g). Aside from conversion, PH-MoMA-1 cat-
alyst produced the least of liquid product. This observation
suggests that high acid capcity are not required in produc-
ing liquid product. It rather caused excess cracking leading
to more gaseous products. It is in agreement with the trend
result of liquid and gas product yields produced by using
sulfided catalyst.
Interestingly, the MoO3 crystal sizes on alumina sur-
face was found to gave significant impact on hyrocrack-
ing reaction products. As shown in Figure 5, there is an
optimum crystal size of MoO3 for conversion. The liquid
product and naphtha yields were observed to decrease with
increasing MoO3 crystal size of catalysts. On the contrary,
gas product and diesel yields were found to increase with
increasing MoO crystal size of catalysts (Figs. 6 and 7).
Negligible amount of coke was formed during reactions
with MoO3/Al2O3 catalyst. This could be due to the slight
acid capacity of alumina employed and its moderate C
C
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bonds splitting capacity38 at the reaction temperature. High
IP: 192.174.3.200 On: Wed, 04 Nov 2015 18:45:04
A high crystallinity of MoO3 was found in PH-MoMA-1
Copyrigh7t: American Scientific Publishers
catalyst (Fig. 3). PH-MoMA-1 showed 37 nm of large
acid capacity of catalyst tend to cause coking. However,
small amount of coke (0.7–1.0 wt%) was generated in
hydrocracking reactions with MoS2/Al2O3 catalysts.
MoO3 crystal size, which is triple size of that SG-MoMA-1
possessed (∼12 nm). This could be resulted from poor
dispersion of Mo on alumina surface prepared via sin-
gle step post-hydrolysis method. Both SG-MoMA-i and
PH-MoMA-i prepared via impregnation method exhib-
ited small MoO3 crystal size (< 6 nm). High naphtha
These results showed that mesoporous Mo/Al2O3 cata-
lysts prepared through conventional sol–gel method, espe-
cially catalyst prepared with single step method, offered
a better performance for hydrocracking, in terms of con-
version. The catalysts prepared through single step sol–
gel method (SG-MoMA-1 and SG-MoMAS-1) gave the
highest conversion in the present study. This could be
explained by SG-MoMA-1 possessed larger surface area
(429 m2/g) that had more concentration of acid sites
(0.02 mmol/g) and efficient dispersion of active metals
in the pores.39 Besides that, high surface area with larger
pore volume of mesoporous catalyst assisted in reduc-
ing the mass transfer resistance of heavy hydrocarbons in
the hydrocracking reaction,9 therefore the accessibility of
larger molecules in atmospheric residual oil to acid sites
of catalyst is increased and enhance the cracking activ-
ity. On the contrary, both PH-MoMA-1 and PH-MoMAS-
1 catalysts showed relatively poor conversion. This could
be owing to the presence of stearic acid as hinder during
preparation of catalyst in post-hydrolysis method.31 Alu-
minum source was hydrolyzed in the presence of solution
consisting of molybdenum species and stearic acid during
preparation of alumina in post-hydrolysis through single
step procedure. This phenomenon might limit the contact
45
44
43
42
41
40
0
10
20
30
40
MoO3 crystal size (nm)
Fig. 5. Effect of MoO3 crystal sizes on conversion.
J. Nanosci. Nanotechnol. 13, 6988–6995, 2013
6993

Synthesis and Characterization of Mesoporous Molybdenum Catalysts for Hydrocracking of Atmospheric Residual Oil
Looi et al.
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
98.5
98.3
98.1
97.9
97.7
97.5
97.3
97.1
96.9
96.7
96.5
method as well as molybdenum loading through single
step or conventional impregnation method were inves-
tigated. Catalysts prepared by sol–gel method exhibited
preferable physical properties (> 400 m2/g large surface
area, ∼ 5 nm narrow pore size and ∼ 0.8 cm3/g of
pore volume) in regardless conventional impregnation or
single step method employed. Similar result trend was
obtained in residual oil hydrocracking over MoO3/Al2O3
and MoS2/Al2O3 catalysts. We observed that a much more
stable catalytic performance was attained with catalysts
prepared by conventional sol–gel method. Catalysts with
small MoO3 crystal size would promote higher liquid prod-
uct yield and lighter secondary cracked product yield.
Both MoO3/Al2O3 and MoS2/Al2O3 catalysts prepared via
single step sol–gel method showed highest atmospheric
conversion in the hydrocracking reaction due to its large
porosity and moderate acid capacity that can crack more
residual oil into lighter oil. Meanwhile, catalysts which
attained lower conversion but with higher naphtha yield
could be considered a better hydrogenation catalyst that
slightly depressed the radical reactions and resulted a
lower gas yield and coke yield.
Liquid product
Gas product
0
20
40
MoO3 crystal size (nm)
Fig. 6. Effect of MoO3 crystal sizes on liquid and gas products.
45
40
35
30
25
20
15
10
5
16
14
12
10
8
Acknowledgments: The authors acknowledge financial
support from Universiti Sains Malaysia Short Term Grant,
RU-PRGS and RU grant.
Delivered by Publishing Technology to: University of Waterloo
6
IP: 192.174.3.200 On: Wed, 04 Nov 2015 18:45:04
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Copyr4ight: American Scientific Publishers
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Received: 22 March 2012. Accepted: 4 November 2012.
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Copyright: American Scientific Publishers
J. Nanosci. Nanotechnol. 13, 6988–6995, 2013
6995