Enhanced catalytic activity of monodispersed porous Al2O3 colloidal spheres with NiMo for simultaneous hydrodesulfurization and hydrogenation

Article abstract of DOI:10.1039/c8ra01866a

Novel composites made from monodispersed porous Al-glycolate spheres (NiMo/Al-SP) were synthesized through alcoholysis or hydrolysis treatments. The obtained samples were characterized by a complementary combination of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), N₂ physisorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), hydrogen temperature-programmed reduction (H₂-TPR), and pyridine Fourier transform infrared spectroscopy (Py FT-IR). In addition, the catalytic performances of the resultant catalysts were evaluated in the simultaneous HDS of dibenzothiophene (DBT) and HYD of naphthalene (DBT and naphthalene represent the sulfur-containing compounds and polycyoalkanes, respectively). The experimental results showed that, 71.22% DBT and 88.28% naphthalene were converted by NiMo/Al-SP(H) under the conditions of 270 °C temperature, 5 MPa H₂ (initial pressure at room temperature) and 10 h reaction time. The design and preparation of NiMo/Al-SP provide an effective and novel pathway for the development of high-performance catalysts and production processes.

Full text of DOI:10.1039/c8ra01866a

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Enhanced catalytic activity of monodispersed
porous Al O colloidal spheres with NiMo for
2
3
Cite this: RSC Adv., 2018, 8, 18059
simultaneous hydrodesulfurization and
hydrogenation
Kaihong Xie, Yanxiong Fang, Baoyu Liu * and Chengchao Li*
Novel composites made from monodispersed porous Al-glycolate spheres (NiMo/Al-SP) were synthesized
through alcoholysis or hydrolysis treatments. The obtained samples were characterized by
a complementary combination of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-
IR), N
2
physisorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM),
-TPR), and pyridine Fourier transform infrared
hydrogen temperature-programmed reduction (H
2
spectroscopy (Py FT-IR). In addition, the catalytic performances of the resultant catalysts were evaluated
in the simultaneous HDS of dibenzothiophene (DBT) and HYD of naphthalene (DBT and naphthalene
represent the sulfur-containing compounds and polycyoalkanes, respectively). The experimental results
Received 3rd March 2018
Accepted 11th May 2018
showed that, 71.22% DBT and 88.28% naphthalene were converted by NiMo/Al-SP(H) under the
ꢀ
conditions of 270 C temperature, 5 MPa H
2
(initial pressure at room temperature) and 10 h reaction
DOI: 10.1039/c8ra01866a
time. The design and preparation of NiMo/Al-SP provide an effective and novel pathway for the
rsc.li/rsc-advances
development of high-performance catalysts and production processes.
active phase, but also inuences the properties of active
1
Introduction
9–11
components.
In recent years, due to the decline of crude oil's quality, envi- to developing novel materials that could be used as support
ronmental issues resulting from the combustion of sulfur and materials. Some examples include metal oxides (Al , TiO
ordered mesoporous materials (MCM-41, SBA-15,
Until now, remarkable attention has been paid
O
3
,
2
2
12–14
polycyclic aromatic containing fossil fuels have been the cause ZrO ),
2
of greater concern. Therefore, in many countries, more and KIT-6)
1,2
15,16
10,17,18
and carbon materials.
Although these mate-
more stringent environmental legislation has been enforced for rials showed excellent properties for hydrotreament processes,
the transportation of fuels to limit the amount of polycyclic their further application is restricted owing to their low specic
aromatic compounds and heteroatoms, such as sulfur, oxygen area, low hydrothermal stability, weaker acidity, and lower
3–5
and nitrogen in fossil fuels. The hydrogenation process (HYD) metal–support interaction for carbon materials.
is one of the most efficient and conventional industrial
Al is the most widely used support material in the
methods to remove sulfur-containing and polycyclic aromatic petroleum industries due to its adjustable pore structure and
2 3
O
2,19
compounds from fossil fuels, so that they would meet the new good mechanical strength. However, conventional Al O has
2 3
emission specications for exhaust gases. The activities of some obvious disadvantages, such as low surface area, and
catalysts for hydrogenation play a very important role in broad pore size distribution, which restricts its commercial
obtaining ultra-clean products. Therefore, it is important to application. Therefore, many efforts have been devoted to
design and develop new catalysts with high HDS and HYD developing new methods to prepare Al
activity to produce clean diesel.
2
O
3
having excellent
properties. Rashidi et al. prepared nanostructured alumina,
It is well known that traditional hydrotreating catalysts are and used it as a support in ultra-deep hydrodesulphurization of
composed of supported active components, such as MoS
or diesel fuels. The surface area of as-prepared alumina was 403
WS
particles promoted with either nickel (Ni) or cobalt (Co) on m g , while the pore size was 10 nm. Furthermore, the cor-
the support material. The support plays a key role in the responding catalysts exhibited high HDS activity. Badoga et al.
11
2
2
ꢁ1
2
6–8
14
hydrotreating process, and not only helps the dispersion of the have synthesized a series of mesoporous alumina with different
pore sizes, and the resulting NiMo catalysts were used for
hydrotreating heavy gas oil. They found that the NiMo/Meso-Al-
Faculty of Chemical Engineering and Light Industry, Guangdong University of 0.6 showed the highest activity among various alumina-based
Technology, Guangzhou, China 510009. E-mail: baoyu.liu@gdut.edu.cn; licc@gdut.
edu.cn
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support materials due to its special physicochemical properties, Kemiou Chemical Reagent Co., China. Nano-Al
2
O
3
was
highest metal dispersion and weak acidic sites. purchased from Aladdin, China. All reagents were used as
It is well known that the morphology and composition of received without any further purication.
catalysts are important to inuence the activity and selectivity of
2
0,21
the catalyst.
The morphology and pore size of supports are
2
.2 Preparation of materials
Synthesis of Al-glycolate spheres. The Al-glycolate spheres
were prepared following the method reported in a previous
important for the diffusion of reactant and product molecules
and for the dispersion of active phase, which are vital for the
catalytic activity.
nanorods as an efficient catalyst for HDS, and the correspond-
ing catalysts exhibited higher activities compared to the
conventional NiMo/Al O . The results showed that the nano-
22,23
24
J. N. D. de Le ´o n et al. prepared 1D-Al
2 3
O
26
study. In a typical synthesis process, 4 mmol of aluminum
isopropoxide was dissolved in 20 ml ethylene glycol under
stirring, followed by the addition of 8 ml of nitric acid (65–68%),
and kept under continuous stirring for 30 min until the mixture
became homogenous. Then, 80 ml of acetone was added to the
above solution, and stirred for another 30 min. Finally, the
resultant mixture was transferred to a 200 ml Teon-lined
stainless steel autoclave, and heated to 100 C for 6 h. The
yellow products were harvested, washed with 95% ethanol
thrice, and dried at 70 C. Finally Al-glycolate spheres were
obtained as the product, which were calcined at 550 C for 8 h.
2
3
rods with plane (110) were favorable for WS slabs, and allowed
2
25
the formation of W–S–Al bonds. Gao et al. compared different
morphologies of SBA-15 with spheres, rods and hexagonal
prisms, and the corresponding catalysts were tested for the
hydrodesulphurization of DBT. The results showed that the
spherical catalyst exhibited highest activities because of the
suitable meso-channels and high dispersion of active phase.
Generally speaking, the metal–support interaction and the
dispersion of active phase are inuenced by the physicochem-
ical properties and the shape of support, which dramatically
enhance the activity of a catalyst. Besides, the textural and
acidic properties of a support also play an important role in the
activity of the hydrotreating catalysts. However, studies focusing
on the adjustment of physicochemical properties and acidic
sites of catalysts during the preparation of porous Al O with
ꢀ
ꢀ
ꢀ
Herein, the nal product is denoted as Al-SP (T).
2 3
Preparation of porous Al O spheres by hydrolysis of Al-
glycolate spheres. In a typical synthesis process, the as-
prepared Al-glycolate spheres were rst ultrasonically sus-
pended in 160 ml ethanol–water solution (ethanol to water
volumetric ratio was 1 : 1, respectively), which was followed by
the addition of 4 mmol urea (CO(NH ) ). Then, the mixture was
2
2
2
3
stirred for 60 min. The resultant mixture was placed in a 200 ml
Teon-lined stainless-steel autoclave and heated to 120 C for
controllable morphology are still scarce in literature.
ꢀ
In this work, two kinds of novel porous Al-glycolate spheres
with tuneable acidity and texture properties were prepared for
the simultaneous HDS of dibenzothiophene (DBT) and HYD of
naphthalene to investigate the effect of acidity and texture on
catalytic properties. The results showed that the acidity
exhibited a strong effect on the hydrogenation of naphthalene.
Interestingly, the hydrolysis and alcoholysis played key roles in
the preparation of monodispersed porous colloidal spheres.
The physicochemical properties and the surface acidity of Al-
glycolate spheres (Al-PS) can be tuned using different treat-
ment pathways of Al-glycolate spheres. Additionally, the corre-
sponding NiMo catalysts were tested in hydrodesulphurization
and hydrogenation reaction using dibenzothiophene and
naphthalene as the probe compounds. The effect of reaction
time on the DBT and naphthalene were investigated over these
catalysts.
1
2 h. The product was collected, washed with 95% ethanol, and
ꢀ
ꢀ
dried at 70 C. It was then calcined at 550 C for 8 h. The ob-
tained product without calcination was denoted as Al-glycolate
spheres (H), while the calcined product was denoted as Al-SP
(H).
Preparation of porous Al O spheres by alcoholysis of Al-
2
3
glycolate spheres. In a typical synthesis process, the as-
prepared Al-glycolate spheres were rst ultrasonically sus-
pended in 160 ml absolute ethanol, followed by the addition of
1
4
.6 g PVP and 0.8 g NH Cl. The mixture was stirred for 60 min.
The resultant mixture was transferred to a 200 ml Teon-lined
stainless steel autoclave, and heated to 180 C for 12 h. The
product was collected, washed with 95% ethanol, dried at 70 C,
and then, calcined at 550 C for 8 h. The obtained product
without calcination was denoted as Al-glycolate spheres (A),
while the calcinated product was denoted as Al-SP (A).
ꢀ
ꢀ
ꢀ
Synthesis of the NiMo supported catalysts. The corre-
sponding NiMo supported catalysts having 4 wt% NiO and
2
Experimental
3
10 wt% MoO were prepared by impregnation with aqueous
2
.1 Materials
Aluminum isopropoxide (Al(OPri)
PVP; molecular weight (MW) ¼ 58 000 g mol ) were purchased
from Aladdin, China. Nitric acid (HNO ; 65–68 wt%), ethylene
glycol (EG) and acetone (C O) were purchased from
Guangzhou Chemical Reagent Factory, China. Ethanol
OH), urea (CO(NH ), nickel nitrate (Ni(NO $6H O),
naphthalene (C H ) and heptane (C H ) were purchased
solutions of heptamolybdate tetrahydrate, nickel nitrate and
3
) and polyvinylpyrrolidone
ꢀ
citric acid. The impregnation sample was dried at 80 C for 12 h,
ꢁ
1
(
ꢀ
ꢀ
ꢁ1
and calcined at 550 C for 6 h at the rate of 2 C min . The
corresponding catalysts were denoted as NiMo/Al-SP (T), NiMo/
Al-SP (H), and NiMo/Al-SP (A), respectively.
3
2
H
5
(C
2
H
5
2
)
2
3
)
2
2
2
.3 Characterization
from Damao Chemical Reagent Factory, China. Dibenzothio- X-ray powder diffraction (XRD) was carried out on Bruker DS
phene (C12 S) was purchased from J&K, China. Ammonium advance unit with Cu Ka radiation. Fourier transform infrared
molybdate ((NH Mo 24$4H O) was purchased from Tianjin spectroscopy (FT-IR) was carried out using a Bruker Fourier
1
2
10
7
16
H
8
4
)
6
7
O
2
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transform infrared spectrometer, which used potassium where c
S
(%) is the conversion of dibenzothiophene, CS0 is the
bromide (KBr) pellet technique within the range of 500– concentration of feedstock, and C is the concentration of the
S
ꢁ
1
4
000 cm . The nitrogen adsorption–desorption measurements product.
of the materials were performed on a Micromeritics ASAP2450
analyzer at ꢁ196 C. Scanning electron microscopy (SEM) and
ꢀ
N
cN (%) ¼ [(CN0 ꢁ C )/CN0] ꢂ 100,
(2)
transmission electron microscopy (TEM) were used to investi-
gate the morphology and microstructure of Al-glycolate spheres,
respectively. Scanning electron microscopy (SEM) images of the
as-synthesized materials were obtained using a Hitachi S3400N
instrument. Transmission electron microscopy (TEM) micro-
graphs of as-prepared materials were obtained using a Hitachi
HT7700 instrument. Hydrogen temperature-programmed
where c
N
(%) is the conversion of naphthalene, CN0 is the
concentration of feedstock, and CN is the concentration of the
product.
3
Results and discussion
2
reduction (H -TPR) was used to investigate the reducibility of 3.1 Characterizations
as-prepared catalysts, while the oxide samples were pretreated
in argon atmosphere at 300 C for 1 h. As the temperature
Fig. 1(A) and (B) showed the FT-IR spectra of Al-glycolate
spheres, Al-glycolate spheres (H) and Al-glycolate spheres (A).
ꢀ
ꢀ
decreased to 80 C, the argon ow was switched to a H
2
/Ar (5/95;
ꢁ1
The bands centered at 1698 cm
were attributed to the
ꢁ1
ꢀ
v/v) ow (50 ml min ). The samples were then heated to 800 C
27
ꢁ1
stretching vibration of O–C]O. The bands at 1068 cm were
attributed to the stretching vibration of Al–OH. The bands at
ꢀ
ꢁ1
at the heating rate of 20 C min . Fourier transform infrared
spectroscopy (FT-IR) of adsorbed pyridine was used to deter-
mine the type and strength of acidic sites of catalysts. Before the
22
ꢁ1
9
10, 813, and 628 cm were attributed to the chelation of
26
carboxylate oxygen to central metal. These results showed that
the Al-glycolate spheres were coordination compounds,
ꢀ
tests, the samples were degassed under vacuum at 400 C for
2
h, and then, cooled and exposed to pyridine atmosphere. Aer
26
composed of carboxylate group and Al ion. Besides, it can be
ꢀ
adsorption, the infrared spectrum was recorded at 200 C and
3
noticed that the chelating carboxylate oxygen decreased in
intensity aer the hydrolysis or alcoholysis treatment of Al-
glycolate spheres, while the intensity of Al–OH increased. The
intensity of Al–OH exhibited the following ascending order: Al-
ꢀ
50 C. The amount of L acidic sites and B acidic sites were
calculated as follows.
C (pyridine on L acidic sites) ¼ 1.42 IA (L) R /W, where C ¼
2
ꢁ
1
concentration (mmol g ), IA (L) ¼ integrated area of L band
ꢁ
2
(
cm ), R ¼ radius of sample disk (cm), W ¼ weight of disk (mg).
2
C (pyridine on B acidic sites) ¼ 1.88 IA (B) R /W, where C ¼
ꢁ1
concentration (mmol g ), IA (B) ¼ integrated area of L band
ꢁ2
(
cm ), R ¼ radius of sample disk (cm), W ¼ weight of disk (mg).
The X-ray photoelectron spectra (XPS) of the sulded cata-
lysts were acquired on a Thermo Scientic spectrometer. The
sulded catalysts were prepared under the same conditions as
the catalytic activity evaluation in the following section.
2.4 Performance of catalysts
The activities of the as-prepared catalysts for dibenzothio-
phene's HDS and the hydrogenation of naphthalene were
assessed in a batch reactor using dibenzothiophene (1268 ppm
of S) and 10 wt% naphthalene in heptane as the model
compounds. Prior to testing the performance of catalysts, 60 mg
of catalysts' precursor was placed inside the batch reactor
ꢀ
containing sulde at 250 C and 3 MPa H
2
(initial pressure at
room temperature) for 6 h using a heptane solution of CS
3 wt%). Aer pre-sulfurization, the catalyst's performance was
2
(
ꢀ
determined in a 100 ml stainless steel autoclave at 270 C and
MPa H (initial pressure at room temperature) for 8 h using
a heptane solution of DBT (1268 ppm of S) and naphthalene
10 wt%). Additionally, the reactant and liquid product were
5
2
(
analyzed using an Agilent 7820A gas chromatograph, which was
Fig. 1 (A and B) FT-IR patterns of Al-glycolate spheres, Al-glycolate
spheres (H) and Al-glycolate spheres (A); (C and D) XRD patterns of Al-
glycolate spheres' supports prepared using different methods: (C)
equipped with a DB-624 capillary column (30 m ꢂ 0.25 mm) and

ame ionization detector (FID). The activity of the catalysts was
determined according to the following equation.
before calcinations; (D) after calcinations; (E and F) the N adsorption/
2
desorption isotherm and BJH pore size distribution of Al-glycolate
c
S
(%) ¼ [(CS0 ꢁ C )/CS0] ꢂ 100,
S
(1) spheres' supports prepared using different methods.
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Table 1 Textural properties of the Al-glycolate spheres
The nitrogen adsorption–desorption isotherms and the cor-
responding pore size distributions for the as synthesized
samples are shown in Fig. 1(E) and (F), respectively. For the
sample of Al-SP (T), the hysteresis loop could not be observed in
the isotherms, which indicated that the Al-glycolate spheres (T)
did not possess any mesoporous structure. In addition, the
results also conrmed that the Al-glycolate spheres without
alcoholysis or hydrolysis treatment could not produce any
mesoporous structure. For the sample of Al-SP (A) and Al-SP (H),
the isotherms exhibited Type IV curves with an H3 hysteresis
a
2
ꢁ1
b
p
3
ꢁ1
c
Sample
S
g
(m g
)
V
(cm g
)
p
D (nm)
Al-SP (A)
Al-SP (H)
Al-SP (T)
267
243
8.5
0.49
0.84
0.023
5.8
10
18
a
b
c
BET surface area. Pore volume. Pore sizes were calculated from the
desorption branches using BJH method.
31
glycolate spheres (H) > Al-glycolate spheres (A) > Al-glycolate loop indicative of a mesoporous structure. These results were
spheres. On the contrary, the intensity of chelating carbox- different from the Al-SP (T), indicating that the Al-glycolate
ylate oxygen followed the following descending order: Al- spheres treated with ethanol or water could produce meso-
glycolate sphere (H) < Al-glycolate sphere (A) < Al-glycolate porous structure. The surface area showed the following order:
sphere. These results showed that, for Al-glycolate spheres Al-SP (T) (8.5 m g ) < Al-SP (H) (243 m g ) < Al-SP (A) (267 m
treated with either water or ethanol, the carboxylate groups were
2
ꢁ1
2
ꢁ1
2
ꢁ1
g
). However, the pore sizes were found to be in the following
gradually replaced by the hydroxyl groups (Table 1).
order: Al-SP (T) (18 nm) > Al-SP (H) (10 nm) > Al-SP (A) (5.8 nm).
The XRD patterns are displayed in Fig. 1(C) and (D). The as- And the pore volume showed the following order: Al-SP (H) (0.84
3
ꢁ1
3
ꢁ1
3
ꢁ1
prepared Al-glycolate spheres (X) (X ¼ A, H and T) are shown in cm g ) > Al-SP (A) (0.49 cm g ) > Al-SP (T) (0.023 cm g ).
Fig. 1(C). It can be clearly seen that Al-glycolate spheres did not
The SEM and TEM micrographs of the as-prepared materials
exhibit any diffraction peaks that can be attributed to the are presented in Fig. 2. As can be seen in Fig. 2(A–C), all the
amorphous nature of Al-glycolate spheres. The XRD pattern of samples exhibited monodispersed sphere-like morphologies,
Al-glycolate spheres (H) exhibited ve diffraction peaks at indicating that the colloidal spheres treated with water or
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1
(
4.06 , 28.32 , 38.42 , 49.24 and 64.74 corresponding to (020), ethanol did not change their shape. Compared with the Al-
120), (031), (200) and (171), which were ascribed to the typical glycolate spheres, the colloidal spheres treated with water or
28
peak of boehmite phase. Compared with the Al-glycolate ethanol exhibited spherical shape with coarse surface. Different
spheres (H), the XRD pattern of Al-glycolate spheres (A) from the Al-glycolate spheres, the Al-glycolate spheres (A)
ꢀ
ꢀ
ꢀ
ꢀ
showed four peaks at 28.78 , 38.1 , 49.9 and 64.88 , which were exhibited wrinkled surfaces.
assigned to the diffraction peak of boehmite. However, the
The TEM analysis was used to further investigate the detailed
intensity of diffraction peaks of Al-glycolate spheres (H) were morphology and structure of the as-prepared colloidal spheres.
stronger than Al-glycolate spheres (A) owing to the difference in As shown in Fig. 2(D–F), all the as-prepared samples exhibited
decomposition of Al-glycolate spheres coordination compound. mono-disperse spherical shape. For the sample of Al-glycolate
Fig. 1(D) shows the XRD pattern of the calcined material at spheres (shown in Fig. 5(D)), it is clearly observed that the
ꢀ
5
50 C. It can be seen that the Al-SP (T) displayed two very broad colloidal spheres were solid spheres with smooth surface. The
diffraction peaks, which conrmed the amorphous nature of Al- TEM images of Al-glycolate spheres (A) (shown in Fig. 5(E))
glycolate spheres treated without hydrolysis or alcoholysis. This clearly show that the uniform porous acanthosphere is
phenomenon can be explained that the additional carboxylate composed of nanoakes. Compared with the Al-glycolate
29,30
groups inhibit the crystallization of Al
2
O
3
.
The as- spheres (A), the Al-glycolate spheres (H) (shown in Fig. 5(F))
synthesized sample treated with ethanol showed XRD peaks at
ꢀ
ꢀ
4
5.9 and 66.8 , which corresponded to (440) and (400), and
were attributed to the g-Al O (JCPDS card no. 10-0425). The
2
3
ꢀ
XRD of hydrolysis sample displayed diffraction peaks at 37.09 ,
ꢀ
ꢀ
ꢀ
3
(
9.44 , 45.9 and 66.8 , corresponding to (311), (322), (400) and
440), and were attributed to the typical diffraction peaks of g-
Al . While, the intensity of diffraction peaks of g-Al
2
O
3
2 3
O
derived from hydrolysis of Al-glycolate spheres was stronger
than the alcoholysis of Al-glycolate.
Table 2 Textural properties of the as-prepared catalysts
a
g
2
ꢁ1
b
p
3
ꢁ1
c
Catalysts
S
(m g
)
V
(cm g
)
p
D (nm)
NiMo/Al-SP (A)
NiMo/Al-SP (H)
NiMo/Al-SP (T)
218
211
9.2
0.41
0.64
0.063
5.9
9.3
30
Fig. 2 SEM images of the as-synthesized samples: (A): Al-glycolate
spheres; (B): Al-glycolate (A); (C) Al-glycolate (H); TEM images of the
a
b
c
BET surface area. Pore volume. Pore sizes were calculated from the as-synthesized samples: (D): Al-glycolate spheres; (E): Al-glycolate
spheres (A); (F): Al-glycolate spheres (H).
desorption branches using BJH method.
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Fig. 5 Temperature-programmed reduction profiles of NiMo/Al-SP
Fig. 3 XRD pattern of NiMo/Al-SP (A), NiMo/Al-SP (H) and NiMo/Al-SP
(A), NiMo/Al-SP (H) and NiMo/Al-SP (T) catalysts.
(
T) catalysts.
2
The H -TPR was used to study the reducibility of the as-
exhibited non-uniformity in shape, and consisted of porous
spheres, core–shell uff ball structure and hollow spheres.
As shown Fig. 3, the characteristic peak positions of NiMo/Al-
prepared NiMo/Al-SP (X) (X ¼ A, H and T) catalysts, and the
results are shown in Fig. 5. As can be seen from Fig. 5, the NiMo/
Al-SP (T) showed two reduction peaks. The low temperature
ꢀ
ꢀ
ꢀ
SP (A) and NiMo/Al-SP (H) at 2q ¼ 66.8 , 45.9 and 37.09 were
ꢀ
peak at 475 C was assigned to the polymeric Mo species (from
attributed to g-Al (JCPDS card no. 10-0425). Meanwhile, the
2 3
O
6
+
4+ 14,34
35
Mo to Mo )
and the reduction of Ni species, while the
NiMo/Al-SP (A) and NiMo/Al-SP (H) did not show the presence of
any diffraction peaks related to Ni and Mo species, which
indicated that the active phase was well dispersed in the
ꢀ
high temperature peak at 677 C was attributed to the deep
4
+
0
reduction of Mo to Mo . For NiMo/Al-SP (A) and NiMo/Al-SP
H), the TPR proles displayed two main reduction peaks and
one shoulder peak. The rst temperature peak, lower than
1
9,32
(
support.
In comparison, for the sample of Al-SP (T), the
ꢀ
ꢀ
ꢀ
ꢀ
diffraction peaks appeared at 23.32 , 26.67 , 32.15 , 33.70 ,
ꢀ ꢀ ꢀ
0.60 , 43.89 , and 47.76 , which belonged to the b-NiMoO
4
phase (JCPDS card no. 45-0142). These results can be attrib-
uted to the overloading of Ni and Mo species, indicating that
most of the Ni and Mo species were agglomerated on the
support.
ꢀ
2
0
32
4
00 C, was assigned to Ni to Ni , while the high temperature
4
ꢀ
33
peak (in the range 700–800 C) was assigned to deep reduction
of tetrahedrally coordinate monomeric Mo species (from Mo
to Mo ). Furthermore, the shoulder peak (in the range of 500–
00 C) was attributed to the octahedral coordination of Mo
species. Compared with NiMo/Al-SP (A) and NiMo/Al-SP (H),
the lower reduction temperature of NiMo/Al-SP (T) had higher
4
+
19
0
34
ꢀ
6
36
2
The N adsorption–desorption isotherm and BJH pore size
distributionof NiMo/Al-SP (X) (X ¼ A, H and T) are shown in
Fig. 4. As can be seen from Fig. 4, all the three NiMo/Al-SP (X)
catalysts exhibited Type IV curves with an H3 hysteresis loop.
Comparing with the Al-SP (T) support, the NiMo/Al-SP (T)
catalyst exhibited hysteresis loop at relatively high pressure and
showed relatively broader pore size distribution. Besides, the
pore size distributions of NiMo/Al-SP (T) were relatively broad
2
H consumption, which can be caused by the larger number of
36
poorly dispersed Mo species. This has been conrmed
through aforementioned XRD results. In addition, in the low
ꢀ
temperature region between 500–600 C, compared with the
NiMo/Al-SP (H), NiMo/Al-SP (A) exhibited a lower reduction
temperature, which indicated the weaker metal–support inter-
action, leading to higher reducibility. This phenomenon can be
explained that the Al-SP (A) was more easy to interact with Mo
species than Al-SP (H) owing to the lower number of Al–OH on
34
due to the disordering of the pore size structure. Compared
with the support, the surface area, pore volume and pore sizes
of NiMo/Al-SP (A) and NiMo/Al-SP (H) decreased due to the
introduction of active phase.
34
Al-SP (A) compared with Al-SP (H).
To identify the type and strength of acidic sites in NiMo/Al-
SP (A), NiMo/Al-SP (H), NiMo/Al-SP (T), pyridine-IR was con-
ꢀ
ꢀ
ducted at 200 C and 350 C within the wavelength of 1700–
ꢁ
1
1
400 cm . The corresponding results are shown in Fig. 6.
There were three bands positioned at about 1450 cm
577 cm , and 1612 cm , which were assigned to the pyridine
adsorbed onto L acidic sites.
541 cm was attributed to pyridine adsorbed onto B acidic
sites, while that position at 1492 cm was ascribed to the
pyridine adsorbed on both L and B acidic sites. According to
ꢁ1
,
ꢁ
1
ꢁ1
1
1,37
The band positioned at
ꢁ
1
1
ꢁ1
38
39
Fig. 4 Texture properties of NiMo/Al-SP (A), NiMo/Al-SP (H) and a previous study, the number of L and B acidic sites for the
NiMo/Al-SP (T) catalysts.
three catalysts can be calculated from the spectra of pyridine
adsorption, the corresponding results are shown in the Table 3.
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2
ꢁ
2
26.5 eV is belonged to the S . The suldation degree of Mo is
4
+
4+
5+
6+
calculated by that Mo /(Mo + Mo + Mo ) and the results are
shown in the Table 4. As shown in the Table 4, the suldation
degree of NiMo catalysts are followed the order: NiMo/Al-SP (T)
(54.13%) > NiMo/Al-SP (H) (39.89%) > NiMo/Al-SP (A) (33.09%).
The NiMo/Al-SP (T) exhibited the highest suldation degree,
which could be assigned to the lowest interaction between
active phases and Al-SP (T), which is in consistent with the H
TPR results.
2
-
Fig. 6 FTIR spectra of pyridine adsorbed on different catalysts after
degassing at (A) 200 C and (B) 350 C.
ꢀ
ꢀ
3.2 Evaluation of the catalysts
The DBT and naphthalene were used as the probe compounds,
Table 3 Amounts of L and B acidic sites determined by pyridine-FTIR and the HDS and hydrogenation results over NiMo/Al-SP (T),
for different catalysts
2 3
NiMo/Al-SP (A), NiMo/Al-SP (H) and NiMo/C-Al O at different
reaction times within 4–10 hours are shown in the Fig. 7(A) and
B). As can be seen from Fig. 7(A) and (B), for all catalysts, the
ꢁ
1
Amount of acid sites (mmol g
)
(
ꢀ
ꢀ
2
00 C
350 C
conversion of DBT and naphthalene signicantly increased with
increasing the reaction time. In HDS of DBT, there are two
parallel reaction routes: one is the direct desulfurization (DDS),
and biphenyl (BP) is the main product. The other one is the
hydrogenation (HYD) to yield cyclohexylbenzene (CHB). The
selectivity (BP/CHB) of the HDS of DBT for all the catalysts was
decreased with increasing reaction time. And BP is the main
products in the HDS reaction, which indicated that the DDS
Catalysts
L
B
L + B
L
B
L + B
NiMo/Al-SP (A)
NiMo/Al-SP (H)
NiMo/Al-SP (T)
108.1
139.2
0
3.2
12.3
0
111.3
151.5
0
39.9
68.8
—
0.4
1.7
—
40.3
70.5
—
The intensity of the spectra showed the following order: NiMo/ route is the main reaction route. Besides, the main products of
ꢁ
ꢁ
1
ꢁ1
Al-SP (H) (151.5 mmol g ) > NiMo/Al-SP (A) (111.3 mmol g ) > hydrogenation of naphthalene are tetralin and no cracking
1
NiMo/Al-SP (T) (0 mmol g ). As can be seen from Fig. 6(A), there products are detected. In addition, for the four catalysts, the
are no peaks for the NiMo/Al-SP (T). Compared with NiMo/Al-SP efficiencies of hydrogenation of naphthalene were higher than
(T), both the NiMo/Al-SP (A) and NiMo/Al-SP (H) exhibited L that of HDS. The HDS efficiency over all the catalysts and the
acidic sites and B acidic sites. Besides, the intensity of B acidic hydrogenation of efficiency followed the order of: NiMo/Al-SP
sites of NiMo/Al-SP(H) was stronger than that for the NiMo/Al- (H) > NiMo/C–Al O > NiMo/Al-SP (A) > NiMo/Al-SP (T). The
2
3
SP (A), which may have been caused by the difference in DBT and naphthalene conversion of the NiMo/Al-SP (H) catalyst
degree of dissociation of Al-glycolate spheres. It means that the reached 71.22% and 88.28%, respectively.
number of bridging hydroxyl groups was different from both the
Al-SP (A) and Al-SP (H). These results are also conrmed by the desulfurization of DBT and hydrogenation of naphthalene.
previous FT-IR results, as shown in Fig. 1(B).
Large surface area is benecial for the dispersion of active phase
The textural properties play a key role in the hydro-
The Mo 3d XPS spectra of sulde catalysts were tested and and large pore size and pore volume has great inuence on the
the results were shown in the Fig. 7. The related parameters are diffusion of reactant and product molecules. The pore volume
1
9,34
3
ꢁ1
ꢁ1
summarized in Table 4. According to the previous research,
of catalyst followed the order: NiMo/Al-SP (H) (0.64 cm g ) >
3
ꢁ1
3
the peak at 228.7 ꢃ 0.2 eV and 231.9 ꢃ 0.2 eV are assigned to the NiMo/Al-SP (A) (0.41 cm g ) > NiMo/Al-SP (T) (0.063 cm g ),
4
+
3d
and 3d of Mo with x intensity ratio of 3 : 2. The peak which is well in line with the activity of catalyst. Compared with
/2 3/2
5
5
+
at 230.4 ꢃ 0.4 eV and 233.6 ꢃ 0.4 eV are related to the Mo in the pore size of NiMo/Al-SP (A) (5.9 nm), NiMo/Al-SP (H) (9.3
the MoS
x
O
y
, The peak at 232.5 ꢃ 0.3 eV and 235.7 ꢃ 0.3 eV nm) exhibited larger pore size. Large pore volume and pore size
6+
corresponds to the Mo oxides species. Finally, the peak at can not only enhance the interaction between the reactant and
Fig. 7 Mo 3d XPS spectra of sunfided catalysts: (A) NiMo/Al-SP (A), (B) NiMo/Al-SP (H), (C) NiMo/Al-SP (T).
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Table 4 XPS fitting results of Mo 3d spectra of the sulfided catalysts
4+
5+
6+
Mo
Mo
Mo
a
b
Catalysts
Ar% (d5/2
)
Ar% (d3/2
)
Ar% (d5/2
)
Ar% (d3/2
)
Ar% (d5/2
)
Ar% (d3/2
)
S
Mo
NiMo/Al-SP (A)
NiMo/Al-SP (H)
NiMo/Al-SP (T)
19.85
23.93
32.48
13.24
15.96
21.65
9.08
6.97
12.32
6.06
4.65
8.22
31.06
29.09
15.20
20.71
19.40
10.13
33.09
39.89
54.13
a
b
4+
4+
5+
6+
Ar% means the area percent of the XPS peak.
S
Mo ¼ Mosuldation ¼ Mo /(Mo + Mo + Mo ).
acidity is benecial for the scission of C–S bond and can
promote the migration of hydrogen. Besides, compared with the
suldation degree of catalyst: NiMo/Al-SP (T) (54.13%) > NiMo/
Al-SP (H) (39.89%) > NiMo/Al-SP (A) (33.09%). Higher sulda-
tion degree of catalysts is benecial for the reaction. However,
the activity of NiMo/Al-SP (T) is not coincided with the sulda-
tion degree. The lowest pore volume is responded to this
phenomenon (Table 2) (Fig. 8).
Above all, the NiMo/Al-SP (H) has the best performance of
hydrodesulfurization and hydrogenation was due to the synergistic
effects of textural property, appropriate acidity and suldity.
Besides, the pore volume and the pore size is the most important
factor to inuence the activity of catalyst in this research.
4
Conclusions
In this work, Al-glycolate spheres having porous acanthosphere,
porous spheres and core–shell spheres morphologies were
prepared through alcoholysis or hydrolysis treatments. The
characterization results showed that the Al-glycolate spheres
were coordination compound, composed of carboxylate groups
and Al ion. The carboxylate groups in Al-glycolate spheres were
replaced by the hydroxyl groups during alcoholysis or hydrolysis
treatment. The Al-glycolate sphere is a solid sphere without
a mesoporous structure. Aer alcoholysis or hydrolysis treat-
ment, the porous sphere can be produced. Additionally, the
Fig. 8 Conversions and selectivity of DBT and naphthalene in the
reaction over NiMo/Al-SP (A), NiMo/Al-SP (H) NiMo/Al-SP (T) and
2 3
NiMo/C–Al O
catalysts at different reaction times: (A) conversions amorphous nature is transformed into boehmite phase. The
and selectivity of DBT over NiMo/Al-SP (A), NiMo/Al-SP (H) NiMo/Al-SP corresponding NiMo catalysts were prepared by the incipient
(
T) and NiMo/C–Al
NiMo/Al-SP (A), NiMo/Al-SP (H) NiMo/Al-SP (T) and NiMo/C–Al
catalysts; (C)–(F): selectivity of naphthalene over NiMo/Al-SP (A),
NiMo/Al-SP (H) NiMo/Al-SP (T) and NiMo/C–Al catalysts.
2 3
O catalysts; (B) conversions of naphthalene over
wetness method, and the catalytic properties were tested in
simultaneous hydrodesulfurization and hydrogenation using
dibenzothiophene and naphthalene as the probe compounds,
respectively. The activity of hydrodesulfurization of DBT and the
hydrogenation of naphthalene followed the order: NiMo/Al-SP
2
O
3
2 3
O
(
H) > NiMo/Al-SP (A) > NiMo/Al-SP (T). The NiMo/Al-SP (H)
active phase but also eliminate the diffusion resistant mole-
cules. Besides, the lowest surface area of NiMo/Al-SP (T) leads to
the agglomeration of active phase, which conrm in XRD
results, also responding to the lowest catalyst activity. Appro-
priate acidity of catalyst is another factor to inuence on the
hydrodesulfurization of DBT and hydrogenation of naphtha-
possessed the largest catalytic activity due to the synergistic
effects of textural property, appropriate acidity and suldity.
Conflicts of interest
There are no conicts to declare.
34,38,40
lene.
In this research, the intensity of the B acid site and
and L acid site are followed the order: NiMo/Al-SP(H) (3.2 mmol
ꢁ1
ꢁ1
ꢁ1
Acknowledgements
g
, 108.1 mmol g ) > NiMo/Al-SP (A) (12.3 mmol g , 139.2
ꢁ1
ꢁ1
ꢁ1
mmol g ) >NiMo/Al-SP (T) (0 mmol g , 0 mmol g ), which is in
The authors acknowledge the support from Startup R&D fund-
ing of One-Hundred Young Talents of Guangdong University of
Technology (No. 220413141), the Science and Technology
accord with the activity of catalyst. Although the L acidity is
41
harmful for the saturated hydrogenation of naphthalene,
B
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