Synthesis and characterization of mesoporous alumina for use as a catalyst support in the hydrodechlorination of 1,2-dichloropropane: Effect of preparation condition of mesoporous alumina

Article abstract of DOI:10.1016/j.molcata.2004.04.038

Samples of mesoporous γ-aluminas were synthesized by a post-hydrolysis method which contained different mole ratios of stearic acid (surfactant)/Al(sec-OBu)₃ (aluminum precursor). The Ni catalysts supported on aluminas were then prepared by an impregnation method used as catalysts in the hydrodechlorination of 1,2-dichloropropane. The effect of the mole ratio of surfactant/aluminum precursor on the properties of aluminas and supported Ni catalysts was investigated. The dissolution of aluminum occurred during the impregnation step, and the amounts of aluminum dissolved were correlated with the mole ratio of surfactant/aluminum precursor. As the mole ratio of surfactant/aluminum precursor increased, large amounts of aluminum ions were dissolved in the nickel nitrate solution, leading to the formation of large amounts of nickel aluminate species in the supported catalyst. A supported catalyst that contained a large portion of nickel aluminate species was resistant to being reduced to active nickel metal efficient for the hydrodechlorination. When the nickel was impregnated on an alumina, which was prepared with low mole ratio of surfactant/aluminum precursor, the supported catalyst exhibited the enhanced catalytic activity in the hydrodechlorination of 1,2-dichloropropane.

Full text of DOI:10.1016/j.molcata.2004.04.038

Journal of Molecular Catalysis A: Chemical 219 (2004) 87–95
Synthesis and characterization of mesoporous alumina for use as a
catalyst support in the hydrodechlorination of 1,2-dichloropropane:
effect of preparation condition of mesoporous alumina
∗
Pil Kim, Younghun Kim, Heesoo Kim, In Kyu Song, Jongheop Yi
School of Chemical Engineering, Colleage of Engineering, Seoul National University, Shinlim-dong, Kwanak-ku, Seoul 151 742, South Korea
Received 14 May 2003; accepted 12 April 2004
Available online 15 June 2004
Abstract
Samples of mesoporous ␥-aluminas were synthesized by a post-hydrolysis method which contained different mole ratios of stearic acid
surfactant)/Al(sec-OBu) (aluminum precursor). The Ni catalysts supported on aluminas were then prepared by an impregnation method used
(
3
as catalysts in the hydrodechlorination of 1,2-dichloropropane. The effect of the mole ratio of surfactant/aluminum precursor on the properties
of aluminas and supported Ni catalysts was investigated. The dissolution of aluminum occurred during the impregnation step, and the amounts
of aluminum dissolved were correlated with the mole ratio of surfactant/aluminum precursor. As the mole ratio of surfactant/aluminum
precursor increased, large amounts of aluminum ions were dissolved in the nickel nitrate solution, leading to the formation of large amounts
of nickel aluminate species in the supported catalyst. A supported catalyst that contained a large portion of nickel aluminate species was
resistant to being reduced to active nickel metal efficient for the hydrodechlorination. When the nickel was impregnated on an alumina, which
was prepared with low mole ratio of surfactant/aluminum precursor, the supported catalyst exhibited the enhanced catalytic activity in the
hydrodechlorination of 1,2-dichloropropane.
©
2004 Elsevier B.V. All rights reserved.
Keywords: Mesoporous alumina; Surfactant; Aluminum precursor; Hydrodechlorination; Supported Ni catalyst
1
. Introduction
a post-hydrolysis method, where small amounts of water
were used as a catalyst after micelle formation [3,4]. It
has also been reported that pure mesophase aluminas could
be synthesized by the reaction of aluminum alkoxides and
carboxylic acids in the presence of the controlled amounts
of water [5]. After calcination of the synthesized mate-
rials, thermally stable and randomly ordered mesoporous
aluminas with a high surface area and a narrow pore size
distribution were obtained. Another report demonstrated
that a mesoporous alumina with a well-ordered pore struc-
ture could be synthesized by a nonionic templating method
[9].
Nickel catalysts supported on alumina have been utilized
in heterogeneous catalytic reactions such as hydrogenation
[10], hydrogenolysis [11], and partial oxidation of methane
[12]. When a nickel catalyst is supported on alumina by
an impregnation method, one of most critical problems en-
countered in using the resulting nickel/alumina catalyst is
the formation of nickel aluminate-like species caused by the
Transition aluminas such as ␥-Al2O3 or ␩-Al2O3 have
been widely used in the field of catalysis and adsorption
technology [1]. Numerous attempts have been made to
synthesize stable and high-quality transition aluminas, be-
cause of their potential importance in petroleum industries.
Since the discovery of M41S by mobil researchers [2], a
number of research groups have also attempted to produce
mesoporous aluminas with a high surface area and a nar-
row pore size distribution [3–8]. In the early stage of the
synthesis of mesoporous alumina, difficulty in controlling
the hydrolysis rate of aluminum precursors was found to
be the crucial problem prior to establishing a systematic
strategy for preparing mesoporous silica materials. How-
ever, this problem was solved successfully by introducing
∗
Corresponding author. Tel.: +82 2 880 7438; fax: +82 2 888 7295.
E-mail address: jyi@snu.ac.kr (J. Yi).
1
381-1169/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2004.04.038

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P. Kim et al. / Journal of Molecular Catalysis A: Chemical 219 (2004) 87–95
diffusion of Ni2 ions into the alumina lattice. It is known
that nickel aluminate species exhibits a poor activity for sev-
eral hydrogen-involving reactions because of their difficulty
in reduction into active metals [13]. It has been reported that
the dissolution of aluminum ions during the impregnation
step accelerates the formation of nickel aluminate species
on the catalyst surface [14].
+
sor was varied for this purpose. The effect of parameters
used in preparation of mesoporous ␥-alumina on the char-
acteristics and catalytic activities of supported nickel cata-
lysts was investigated extensively. The hydrodechlorination
of 1,2-dichloropropane was carried out as a model reaction
in this study.
In a previous study [15] investigating the nickel catalyst
supported on a mesoporous ␥-alumina by an impregnation
method, it was shown that mesoporous ␥-alumina could
serve as an efficient support for the nickel catalyst for hy-
drodechlorination reaction. Furthermore, we also found that
considerable amounts of surface aluminum species were dis-
solved during the impregnation step, resulting in the for-
mation of nickel aluminate species. In the preparation of a
nickel catalyst supported on mesoporous ␥-alumina, there-
fore, the stability of ␥-alumina is an important consider-
ation and needs to be improved. In order to improve the
stability of mesoporous ␥-alumina as a support for nickel
catalyst in the impregnation step, mesoporous ␥-aluminas
were synthesized under a variety of conditions. The mole
ratio of surfactant with respect to the aluminum precur-
2. Experimental
2.1. Preparation of mesoporous alumina and
supported Ni catalyst
Mesoporous ␥-aluminas were prepared by a post-hydro-
lysis method, as described previously [3,4]. All prepara-
tion procedures were conducted at room temperature and at
atmospheric pressure. In a typical procedure, the required
amounts of Al(sec-BuO)3 (aluminum source) and stearic
acid (surfactant) were dissolved separately in sec-butyl al-
cohol, and the two solutions were then mixed. Water was
then added to the mixture at a rate of 1 ml/min, until a white
precipitate was formed. The mole ratio of surfactant with
Fig. 1. N2 adsorption–desorption isotherms of mesoporous aluminas as a function of mole ratio of surfactant/aluminum precursor.

P. Kim et al. / Journal of Molecular Catalysis A: Chemical 219 (2004) 87–95
89
respect to the aluminum precursor was varied within the
range of 0.1–0.25, while other preparation conditions were
fixed. The resulting slurry was further stirred for 24 h, and
subsequently, dried in a stream of air. The crude product
(micromeritics) apparatus. Pore size distributions were de-
termined by the BJH method applied to the desorption
branch of the N2 isotherm. The metallic states of the Ni
species were confirmed by ultra violet diffuse reflectance
spectroscopy (UV-DRS, Perkin-Elmer, Ramda-20 spec-
trometer) within the range of 200–800 nm. X-ray photoelec-
tron spectra (XPS) were obtained on a AXIS-HS equipment.
Temperature-programmed reduction (TPR) measurements
were carried out in a conventional flow system with a mois-
ture trap connected to a TCD at temperatures ranging from
◦
was thermally treated at 500 C for 3 h to yield the final
form. The prepared alumina samples were denoted as Al-X,
where X represents 10 times the mole ratio of the surfac-
tant/aluminum precursor.
Nickel catalysts supported on alumina were prepared by
an impregnation method using nickel nitrate as a nickel
source. The prepared catalysts were dried overnight at
◦
◦
room temperature to 900 C (heating rate = 10 C/min). A
mixed stream of H2 (2 ml/min) and N2 (20 ml/min) was
used as a reducing gas for 0.1 g of catalyst. The amounts
of aluminum dissolved [14] in the nickel nitrate solution
◦
◦
1
20 C, and then calcined at 500 C for 5 h in a stream
of air. The nickel loading of the supported catalysts was
1
0 wt.%. The prepared catalysts were denoted as Ni/Al-X.
.2. Characterization
(10 wt.%) were determined by ICP-AES.
2
2.3. Hydrodechlorination of 1,2-dichloropropane
Small angle X-ray scattering (SAXS) patterns were
recorded on a GADDS (Bruker) instrument using Cu K␣
radiation to analyze the periodicity. Adsorption-desorption
isotherms of nitrogen were obtained with an ASAP 2010
The selective hydrodechlorination of 1,2-dichloropropane
(DCPA) into propylene was carried out in a continuous
flow fixed-bed reactor at atmospheric pressure. Each cata-
Fig. 2. Pore size distributions of mesoporous aluminas as a function of mole ratio of surfactant/aluminum precursor.

9
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P. Kim et al. / Journal of Molecular Catalysis A: Chemical 219 (2004) 87–95
lyst (0.1 g) was charged into a tubular quartz reactor, and
activated with a mixed stream of H2 (20 ml/min) and N2
uptake at low partial pressures is due to the monolayer ad-
sorption of probe molecules in the mesopores, and the ad-
sorbed volume up to the relative pressures of ca. 0.4 results
from the filling of the mesopores with N2 [5]. All alumina
samples showed IV-type isotherms irrespective of the vari-
ation of mole ratio of surfactant/aluminum precursor. The
pore size distributions of these alumina samples are shown
in Fig. 2. All alumina samples were found to have a rela-
tively narrow pore size distribution centered at around 4 nm.
Fig. 3 and Fig. 4 show the N2 isotherms and the pore
size distributions of the supported Ni catalysts, respectively.
Compared to the isotherms of bare alumina supports (Fig. 1),
Fig. 3 clearly shows the different shapes for the isotherms.
Furthermore, Fig. 4 shows that the supported Ni catalysts
exhibited different pore size distributions from those of bare
alumina supports (Fig. 2). It is inferred that these results
arose from the following two factors; (i) incorporation Ni
particles, and (ii) restructuring of catalyst framework caused
by aluminum dissolution during the impregnation step. It is
likely that the latter is the major factor.
◦
−3
(
20 ml/min) at 500 C for 2 h. DCPA (5.13 × 10 mol/h)
was sufficiently vaporized and fed into the reactor. The cat-
alytic reaction was carried out at 300 C. The products were
◦
periodically sampled and analyzed with a GC–MS and a GC
(HP 5890 II, FID). The catalytic reactions were carried out
several times for each catalyst under the same conditions. In
each run, DCPA conversion and propylene selectivity were
within the error range of ± 2%.
3
. Results and discussion
3
.1. Physical properties of alumina and the
supported Ni catalyst
Fig. 1 shows the N2 adsorption–desorption isotherms of
mesoporous aluminas prepared with a variation of mole ra-
tio of surfactant/aluminum precursor. It is known that N2
2
40
20
00
80
60
40
20
00
220
Ni/Al-1.0
Ni/Al-2.0
2
00
80
60
40
20
2
1
2
1
1
1
1
1
1
100
80
1
60
1
40
80
2
0
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
3
00
80
60
40
20
00
80
60
40
20
Relative Pressure (P/Po)
Relative Pressure (P/Po)
1
80
60
40
20
00
2
1
Ni/Al-1.5
Ni/Al-2.5
2
1
2
1
2
1
2
8
0
1
6
0
1
4
0
1
20
0
1
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/Po)
Relative Pressure (P/Po)
Fig. 3. N2 adsorption–desorption isotherms of Ni/Al-X catalysts.

P. Kim et al. / Journal of Molecular Catalysis A: Chemical 219 (2004) 87–95
91
0.12
0
.14
.12
.10
.08
.06
.04
.02
.00
0.02
0
.10
Ni/Al-2.0
0
Ni/Al-1.0
0
0.08
0
0.06
0
0.04
0
0
0.02
0
0.00
-
0
10
20
30
40
50
0
10
20
30
40
50
0
.16
.14
.12
.10
.08
.06
.04
.02
.00
0.02
0.10
Pore Size (nm)
Pore Size (nm)
0
0.08
0
Ni/Al-2.5
0
Ni/Al-1.5
0.06
0
0.04
0
0
0.02
0
0
0.00
-
0
10
20
30
40
50
0
10
20
30
40
50
Pore Size (nm)
Pore Size (nm)
Fig. 4. Pore size distributions of Ni/Al-X catalysts.
The surface area and pore volume of mesoporous alumina
and supported Ni catalyst are listed in Table 1. The meso-
porous aluminas employed in this work have a relatively
high surface area and pore volume as well. The surface
area and pore volume of the supported Ni catalyst are lower
than those of the corresponding alumina support. Table 2
shows the amounts of aluminum dissolution in a nickel ni-
trate solution. As listed in Table 2, the amount of aluminum
dissolved becomes significant with increasing mole ratio of
surfactant/aluminum precursor. Furthermore, Fig. 4 clearly
shows an evolution of a second peak in the pore size distri-
bution with increasing the mole ratio of surfactant/aluminum
precursor, as the result of the partial destruction of the pore
structure of the alumina. These results are in good agreement
with a previous study reporting that significant amounts
of aluminum ions are dissolved from the alumina surface
during the impregnation of nickel nitrate precursor onto alu-
mina, resulting in the restructuring of the textural properties
of the supported nickel catalyst [13]. Therefore, it is reason-
able to conclude that the supported Ni catalyst experiencing
serious aluminum dissolution during the impregnation step
exhibited large deviations of N2 isotherm and pore size
distribution from those of the bare alumina support.
Table 1
Surface area and pore volume of alumina and supported Ni catalyst
Al-1.0
Al-1.5
Al-2.0
Al-2.5
2
Table 2
Surface area (m /g)
316
376
0.60
380
0.44
340
0.39
3
Amounts of aluminum dissolved in a nickel nitrate solution (10 wt.%)
Pore volume (cm /g) 0.53
Al-1.0
31
Al-1.5
38.9
Al-2.0
52.6
Al-2.5
64.2
Ni/Al-1.0 Ni/Al-1.5 Ni/Al-2.0 Ni/Al-2.5
2
Surface area (m /g)
229
230
254
234
Amounts of aluminum
dissolved (ppm)
3
Pore volume (cm /g) 0.27
0.30
0.30
0.27

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P. Kim et al. / Journal of Molecular Catalysis A: Chemical 219 (2004) 87–95
Al-2.0
Al-1.5
Al-1.0
Al-2.5
Ni/Al-1.5
Ni/Al-1.0
Ni/Al-2.0
Ni/Al-2.5
0
2
4
6
8
10
0
2
4
6
8
10
2
Theta
2 Theta
Fig. 5. SAXS patterns of mesoporous aluminas and calcined Ni catalysts.
3
.2. SAXS and TEM analyses
of the alumina support have a wormhole or sponge-like ap-
pearance indicative of a highly inter-connected pore system.
This result is consistent with the SAXS result. The TEM
image of the reduced Ni catalyst showed finely dispersed
Ni particles, although some agglomerations larger than the
pore size were observed. The sizes of the nickel particles
were nearly the same in all catalysts.
The SAXS patterns of mesoporous aluminas and sup-
◦
ported Ni catalysts calcined at 500 C are shown in Fig. 5. It
should be noted that SAXS patterns of mesoporous alumina
and supported Ni catalyst show a continuous decay with no
peaks, indicating a randomly connected pore structure [16].
The SAXS intensity of the supported Ni catalyst was weaker
than that of the alumina support. According to the literature
3.3. TPR analyses
[17], the generation of X-ray peaks results from a differ-
ence in the scattering power (or scattering contrast) between
two building blocks (amorphous wall and channel) of meso-
porous materials. Therefore, it is likely that the introduction
of Ni particles onto an alumina support would give rise to a
weak peak intensity of X-rays.
Fig. 7 shows the TPR profiles of the supported Ni cata-
lysts. The reduction profiles of the supported Ni catalysts
could be divided into two zones (T1 and T2), when the re-
duction profiles were deconvoluted using a Gaussian model.
◦
The peak at around 630 C can be assigned to the typi-
cal reduction peak of Ni2 which interacts strongly with
+
Fig. 6 shows the TEM images of the calcined mesoporous
◦
◦
alumina and the reduced Ni catalyst at 500 C. The pores
␥-Al2O3 [14,18]. The second peak at around 780 C can
◦
Fig. 6. TEM images of (a) mesoporous alumina (Al-1.5) and (b) Ni catalyst (Ni/Al-1.5) reduced at 500 C.

P. Kim et al. / Journal of Molecular Catalysis A: Chemical 219 (2004) 87–95
93
T2
T1
Ni/Al-2.5
T1/T2 = 1.44
T1/T2 = 1.74
T1/T2 = 2.12
Ni/Al-2.0
Ni/Al-1.5
T1/T2 = 2.28
Ni/Al-1.0
500
600
700
800
900
o
Temperature ( C)
Fig. 7. TPR profiles and peak area ratios of supported Ni catalysts.
solution, it is known that some parts of Al3 that are located
on the surface are dissolved in the solution by hydrogen
ions, and the resulting aluminum ions are subsequently
readsorbed along with nickel ions [13,14]. This mixed ad-
sorption may yield the formation of some nickel aluminate
species on the oxide surface. As listed in Table 2 earlier, the
amounts of aluminum dissolution increased with increasing
mole ratio of surfactant/aluminum precursor. From these
data, we conclude that large amounts of nickel aluminate
species are formed when the nickel precursor is impreg-
+
be assigned to the reduction peak of nickel aluminate-like
species [14,18]. Interestingly, as the mole ratio of surfac-
tant/aluminum precursor increased, the reduction peaks
shifted to the higher temperature. It is also noteworthy
that the peak areas of Ni2 (T1) relative to the nickel
aluminate-like species (T2) decreased with increasing mole
ratio of surfactant/aluminum precursor; the portion of nickel
aluminate-like species (T2) increased with an increase in
the mole ratio of surfactant/aluminum precursor. Upon the
impregnation of nickel on alumina from the nickel nitrate
+
NiO NiAl O4
2
Ni/Al-1.0
8
8
8
8
50
50
50
50
855
855
855
855
860
860
860
865
865
865
865
870
870
870
870
Ni/Al-1.5
Ni/Al-2.0
Ni/Al-2.5
860
Binding Energy ( eV )
Fig. 8. XPS profiles of supported Ni catalysts.

9
4
P. Kim et al. / Journal of Molecular Catalysis A: Chemical 219 (2004) 87–95
nated on a mesoporous alumina experiencing large amounts
of aluminum dissolution during the impregnation step.
Ni/Al-1.5
Ni/Al-2.0
Ni/Al-1.0
Ni/Al-2.5
3
.4. XPS and UV-DRS analyses
In order to investigate the metallic state of the nickel
species, XPS measurements were carried out on the bind-
ing energy of the Ni 2p3/2 level. It is known that the bind-
ing energies of Ni in NiO and in nickel aluminate are 855
and 857 eV, respectively [19,20]. As shown in Fig. 8, broad
peaks were observed for all the supported catalysts. Impor-
tantly, the contribution of binding energy from the nickel
aluminate species became strong with increasing mole ra-
tio of surfactant/aluminum precursor. This indicates that
Ni catalyst supported on an alumina, which was prepared
with a high mole ratio of surfactant/aluminum precursor,
retained large amounts of nickel aluminate species in its
structure.
400
500
600
700
800
Wave Length ( nm )
Fig. 9. UV-DRS profiles of supported Ni catalysts after calcination at
◦
5
00 C.
In order to confirm the identity of the nickel species and
the formation of nickel aluminate, UV-DRS measurements
for the supported Ni catalysts were taken. Bands at 715, 377,
the range of 600–645 nm became strong, in good agreement
with the TPR (Fig. 7) and XPS results (Fig. 8).
and/or 410 nm represent the octahedrally coordinated Ni2
+
species, while the bands in the range of 600–645 nm corre-
spond to the tetrahedrally coordinated Ni2 species [21]. In
+
3.5. Hydrodechlorination of 1,2-dichloropropane (DCPA)
the nickel aluminate spinel structure, it is well known that
2
+
the ratio of octahedrally coordinated Ni relative to tetra-
Fig. 10 shows the catalytic activities of the supported Ni
catalysts in the hydrodechlorination of 1,2-dichloropropane.
In the catalytic reaction, propylene and chloropropylene
were the major products, while trace amounts of ethylene
and chloroethylene were detected by GC–MS. However, no
saturated hydrocarbons such as propane or chloropropane
were formed. This can be attributed to the activation energy
for the hydrogenationn of unsaturated hydrocarbons, which
is higher than that for the cleavage of C–Cl bonds [23].
Another possible reason for this observation is the rapid
hedrally coordinated Ni2 is dependent on the calcination
temperature, the calcination time, and the ramping rate [22].
From this point of view, UV-DRS measurement can be a
useful characterization tool for investigating the interaction
between nickel and the alumina support. Fig. 9 shows the
UV-DRS spectra of the supported Ni catalysts as a func-
tion of the molar ratio of surfactant/aluminum precursor. As
the molar ratio of surfactant/aluminum precursor increased,
the characteristic bands of nickel aluminate appearing in
+
80
100
Ni/Al-1.0
Ni/Al-1.5
Ni/Al-2.0
Ni/Al-2.5
Ni/Al-1.0
Ni/Al-1.5
Ni/Al-2.0
7
0
Ni/Al-2.5
60
90
50
4
0
80
70
30
20
0
2
4
6
8
10
0
2
4
6
8
10
Time ( h )
Time ( h )
◦
Fig. 10. DCPA conversions and propylene selectivities over supported Ni catalysts at 300 C with time on stream.

P. Kim et al. / Journal of Molecular Catalysis A: Chemical 219 (2004) 87–95
95
deactivation of available active sites for the hydrogenation,
which is caused by the adsorption of HCl on the catalyst
surface [24]. It was observed that propylene selectivities
over all supported catalysts were nearly the same during
the reaction. However, the catalytic activities (DCPA con-
version) were roughly decreased with increasing mole ratio
of surfactant/aluminum precursor.
tant/aluminum precursor. In other words, the catalyst show-
ing a high reducibility at the pretreatment conditions had an
enhanced catalytic activity. We conclude that a supported
catalyst containing a large portion of nickel aluminate in its
structure was difficult to be reduced into active nickel metal.
We conclude that the different catalytic activities in the
model hydrodechlorination reaction resulted from differ-
ences in the reducibility of Ni particles. It is well known
that the catalytic activity in hydrodechlorination reaction de-
pends on the metal particle size, the interactions between
the metal and the support, and the reducibility of the metal
oxide [24–28]. In this work, aluminas having almost the
same surface area were used as catalyst supports. Therefore,
it is likely that the effect of metal particle size on the cat-
alytic activity would be minor compared to the other fac-
tors. For the efficient initiation of hydrodechlorination, the
chlorinated reactant, along with hydrogen must be adsorbed
on metallic nickel (neither nickel oxide nor nickel alumi-
nate). That is, the catalyst having low reducibility shows a
poor catalytic activity. Nickel aluminate species could not
be easily reduced into active metallic nickel at the condi-
tions used for catalyst pretreatment. Therefore, Ni/Al-2.5
and Ni/Ai-2.0 containing large amounts of nickel aluminate
species showed suppressed catalytic activities compared to
Ni/Al-1.5 and Ni/Al-1.0. A Ni catalyst supported on meso-
porous alumina had a low reducibility, when the alumina
was prepared with a high mole ratio of surfactant/aluminum
precursor.
Acknowledgements
This work was supported by National Research Labora-
tory (NRL) program of the Korea Science and Engineering
Foundation (KOSEF).
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