Isomerization of endo-tetrahydrodicyclopentadiene over clay-supported chloroaluminate ionic liquid catalysts

Article abstract of DOI:10.1016/j.molcata.2009.09.002

Various halide salts with different alkyl lengths were allowed to intercalate into the layer structure of sodium montmorillonite clay through an ion exchange reaction. Intercalation of 1-hexadecyl-3-methylimidazolium chloride, hexadecyltrimethylammonium bromide, dihexadecyldimethylammonium bromide, and tributylhexadecylphosphonium bromide could expand the spacing of the silicate layers from 12 to 37-41 ? (measured by X-ray diffraction). The modified clays were pretreated with the pyridine hydrochloride/AlCl₃ mixture and used for suitably supporting a chloroaluminate ionic liquid catalyst for the isomerization of endo-tetrahydrodicyclopentadiene into the corresponding exo-isomer. Nearly quantitative conversion to the desired product and nearly quantitative selectivity were observed for the newly developed clay-supported ionic liquid catalysts, which were proven to be recyclable.

Full text of DOI:10.1016/j.molcata.2009.09.002

Journal of Molecular Catalysis A: Chemical 315 (2010) 69–75
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Isomerization of endo-tetrahydrodicyclopentadiene over clay-supported
chloroaluminate ionic liquid catalysts
Ming-Yu Huanga,b, Jung-Chung Wu , Fuh-Sheng Shieu , Jiang-Jen Lin
a
b,∗
b,c,∗∗
a
Refining & Manufacturing Research Institute, Taiwan CPC Corporation, Chia-Yi 60051, Taiwan
Department of Materials Science and Engineering, National Chung Hsing University, Taichung 40227, Taiwan
Institute of Polymer Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 June 2009
Received in revised form 3 September 2009
Accepted 3 September 2009
Available online 10 September 2009
Various halide salts with different alkyl lengths were allowed to intercalate into the layer structure
of sodium montmorillonite clay through an ion exchange reaction. Intercalation of 1-hexadecyl-3-
methylimidazolium chloride, hexadecyltrimethylammonium bromide, dihexadecyldimethylammonium
bromide, and tributylhexadecylphosphonium bromide could expand the spacing of the silicate layers
from 12 to 37–41 Å (measured by X-ray diffraction). The modified clays were pretreated with the pyri-
dine hydrochloride/AlCl3 mixture and used for suitably supporting a chloroaluminate ionic liquid catalyst
for the isomerization of endo-tetrahydrodicyclopentadiene into the corresponding exo-isomer. Nearly
quantitative conversion to the desired product and nearly quantitative selectivity were observed for the
newly developed clay-supported ionic liquid catalysts, which were proven to be recyclable.
Keywords:
Montmorillonite
Tetrahydrodicyclopentadiene
Chloroaluminate ionic liquids
©
2009 Elsevier B.V. All rights reserved.
1
. Introduction
ble with various polymers, including polyamide [11], polystyrene
11,12], poly(caprolactam) [13], polypropylene [14], poly(ethylene
[
A number of different applications have been reported for
naturally occurring clays. These applications include catalysis
1], adsorbing materials [2,3], nanocomposites [4–7], organic
oxide) [15], and poly(l-lactide) [16]. Ultimately, the blending of
organic silicate clays with polymers affords polymer/layered-
silicate nanocomposites [11–16] with advanced properties.
Ionic liquids (ILs), defined as salts with a melting point below
[
light-emitting diodes [8], and encapsulating agents for biomacro-
molecules [9]. The generic structure of smectite clays such as
montmorillonite (MMT) is a multilayered structure of two sheets
of tetrahedra sandwiching a sheet of edge-sharing octahedra [10].
The inherent ionic character and hydrophilic nature may be altered
when the metal ions are exchanged with cationic surfactants such
as C18 alkyl quaternary ammonium salts [11–16]. Depending on
the intercalated organics, the resulting modified organoclays can
be tailored for their interlayer spacing and compatibility with
hydrophobic polymers. Such organoclays can be made compati-
◦
about 100 C, have been found to have unique chemical and
physical properties [17]. With a low vapor pressure, adjustable
hydrophilic/lipophilic solvating properties, high charge density,
and high conductivity, ILs have been commonly used as catalysts,
adsorbents, electrolytes, liquid supports, acid scavengers, and per-
formance additives [17,18]. Recent developments in the field of
ILs include the uses as supported catalysts for organic and elec-
trochemical reactions [17], and as components of microemulsifiers
for the synthesis of organic polymers [19] and inorganic nanopar-
ticles [20]. The approach of supporting ILs on solid materials is
expected to provide the advantages that heterogeneous liquid and
solid phases offer, both for catalyst performance and for prod-
uct separation. For example, ILs have been impregnated into silica
gel [21,22], diatomic earth [23], molecular sieves [24], and MMT
Abbreviations: ADM, adamantine; BMIC, 1-butyl-3-methylimidazolium chlo-
ride; CEC, cation exchange capacity; DHDDMAB, dihexadecyldimethylammonium
bromide; HDMIC, 1-hexadecyl-3-methylimidazolium chloride; HDTMAB, hexade-
+
cyltrimethylammonium bromide; I , intercalated cation; IL, ionic liquid; MMT,
[
25], and then used for catalyzing hydroformylation [21], the Heck
montmorillonite; OMIC, 1-octyl-3-methylimidazolium chloride; PHC, pyridine
hydrochloride; POP, poly(oxypropylene)diamine; TBHDPB, tributylhexadecylphos-
phonium bromide; TEM, transmission electron microscopy; THDCPD, tetrahydrod-
icyclopentadiene; XRD, X-ray diffraction.
reaction [22], hydroamination [23], and hydrogenation [24,25].
Conventionally, aluminum chloride (AlCl ) is widely used for cat-
3
alyzing many organic reactions, but it has the serious drawbacks of
being non-recyclable and of generating a corrosive waste stream
during post-treatment. The chloroaluminate IL is one type of AlCl3
substitutes, prepared from quaternary ammonium chloride and
∗
Corresponding author. Tel.: +886 4 2285 4563; fax: +886 4 2285 7017.
Corresponding author at: Department of Materials Science and Engineering,
National Chung Hsing University, Taichung 40227, Taiwan. Tel.: +886 2 3366 5312;
fax: +886 2 3366 5237.
E-mail addresses: fsshieu@dragon.nchu.edu.tw (F.-S. Shieu),
jianglin@ntu.edu.tw (J.-J. Lin).
∗
∗
AlCl (Fig. 1), and has shown similar acidity and efficacy for organic
3
synthesis [17]. Furthermore, chloroaluminate ILs are effective for
1
381-1169/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2009.09.002

7
0
M.-Y. Huang et al. / Journal of Molecular Catalysis A: Chemical 315 (2010) 69–75
Fig. 1. Chloroaluminate ILs prepared from quaternary ammonium chloride and
AlCl3.
hydrocarbon cracking and isomerization with various feed sources
of polyethylene [26], alkanes [27], fatty acids [28,29], and fatty acid
methyl esters [29]. The separation of hydrogenation products could
also be facilitated by impregnating chloroaluminate ILs on MMT
[
25].
The
Fig. 2. Structures of various halide salts investigated in this work.
compound,
exo-tetrahydrodicyclopentadiene
(exo-
THDCPD), is valuable for high-energy density fuel, especially
for short-range missiles and aircraft, and other industrial applica-
tions including solvent for paints, diluents for surfactants, waxes
and washing agents [30]. The exo-THDCPD is derived from the
corresponding endo-isomer which is the hydrogenation product
of dicyclopentadiene from C5 fraction of stream cracker. For
using as fuels such as Jet Propellant-10 (JP-10), exo-THDCPD of
purity higher than 98.5% is required. Hence, the process of endo-
THDCPD isomerization with a high conversion and selectivity is
required. In the past, heterogeneous catalysts, zeolites [32,33] or
heteropolyacids [34], were studied for producing exo-THDCPD,
but with a high processing temperature and byproduct formation.
In the present work, we have first modified the natural clay by
intercalation with various chloride salts. The organic-intercalated
clays, with an expanded interlayer spacing and solvating ability,
were further pretreated and impregnated with a chloroaluminate
IL, and employed for the isomerization of endo-THDCPD into its
exo-isomer.
Table 1
+
Basal-plane spacing and dispersion properties for various halide salts embedded Na -MMT.
Intercalation agenta
Molar ratio of I /(CEC of MMT)
+
d spacing XRD (Å)b
Wt fraction of intercalated MMT (org./inorg.)c
Dispersibilityd
Water
+
Toluene
None
PHC
12
−
0.2
16
13
13
9/91
10/90
12/88
+
+
+−
−
−
−
0
.5
.0
1
BMIC
0.2
14
14
14
8/92
14/86
17/83
+
−
−
−
0.5
.0
+−
1
−
OMIC
HDMIC
0.2
13
15
16
12/88
16/84
21/79
+
−
0
1
.5
.0
+−
−
−
+−
0.2
15
16
37
41
15/85
23/77
35/65
43/57
+
−
+−
+
0.5
1.0
2.0
−
−
−
+
HDTMAB
0.2
14
16
18, 25
41
15/85
25/75
35/65
50/50
+
−
0.5
1.0
2.0
+−
+−
+−
+−
−
−
DHDDMAB
0.2
14
28
35
37
21/79
32/68
48/52
63/37
+
−
0.5
1.0
2.0
+−
+−
+−
+−
−
−
TBHDPB
0.2
14
20
25
34
17/83
25/75
39/61
44/56
+
−
−
+
0.5
1.0
2.0
−
−
+−
+
a
Intercalation agents: PHC, pyridine hydrochloride; BMIC, 1-butyl-3-methylimidazolium chloride; OMIC, 1-octyl-3-methylimidazolium chloride; HDMIC, 1-hexadecyl-3-
methylimidazolium chloride; HDTMAB, hexadecyltrimethylammonium bromide; DHDDMAB, dihexadecyldimethylammonium bromide; TBHDPB, tributylhexadecylphos-
phonium bromide.
b
Basal-plane spacing calculated from XRD results according to the Bragg equation (nꢀ = 2d sin ꢁ) with n = 1.
Based on TGA measurements.
c
d
+
, Dispersible; −, aggregated; +−, sedimentation after 5 min settlement.

M.-Y. Huang et al. / Journal of Molecular Catalysis A: Chemical 315 (2010) 69–75
71
Table 2
2
. Experimental
a
Isomerization of endo-THDCPD by PHC/AlCl3 catalyst impregnated into
HDMIC/MMT supports.
2
.1. Materials
Supportb
Nonec
Reaction time (min)
Conversion (%)
Selectivity
+
The sodium montmorillonite (Na -MMT) used was sup-
exo-THDCPD
ADM
plied by Nanocor Co. and had
CEC) of 1.20 mequiv./g and
a
cation exchange capacity
surface area of 750 m /g.
30
61.9
83.2
96.2
100
99.8
99.4
0
0.2
0.6
2
(
a
A
60
+
−
series of halide salts (I X ), namely pyridine hydrochloride
PHC), 1-butyl-3-methylimidazolium chloride (BMIC), 1-octyl-
-methylimidazolium chloride (OMIC), hexadecyltrimethylam-
120
(
3
+
Na -MMT
30
42.5
61.4
82.7
100
100
100
0
0
0
60
monium bromide (HDTMAB), dihexadecyldimethylammonium
bromide (DHDDMAB), and tributylhexadecylphosphonium bro-
mide (TBHDPB), were purchased from Fluka. 1-Hexadecyl-3-
methylimidazolium chloride (HDMIC) and AlCl3 were purchased
from Merck. endo-Tetrahydrodicyclopentadiene was purchased
from Tokyo Kasei Kogyo Co. The structures of these halide salts
are shown in Fig. 2.
120
HDMIC/MMTd
120
0
0
0
e
HDMIC/MMT
0.2
30
60
2.3
4.7
8.5
100
100
100
0
0
0
f
1
1
20
HDMIC/MMT
+
2
.2. Preparation of Na -MMT ionic exchanging with halide salts
f
0
0
1
.2
30
60
20
47.1
69.5
84.6
100
100
100
0
0
0
+
to I /MMT (Step I)
Various halide salts with different equivalent ratios were inter-
.5f
30
92.3
98.3
99.3
100
100
100
0
0
0
+
calated with Na -MMT and results are summarized in Table 1. A
typical experimental procedure, using HDMIC as an example, was
described as follows. Na -MMT (1.0 g, 1.2 mequiv./g) was placed in
60
120
+
.2f
30
93.1
98.8
99.2
100
99.9
99.9
0
0.1
0.1
a 250 mL beaker and 100 mL of deionized water was added. The
mixture was vigorously stirred with a magnetic stirrer and heated
6
120
0
◦
+
to 80 C to become a swollen Na -MMT slurry. In a separate vessel,
the IL (HDMIC, 0.41 g, 1.2 mmol) was dissolved in 20 mL of deion-
.2f,g
1
30
60
120
92.5
98.4
99.1
100
99.9
99.9
0
0.1
0.1
+
ized water and then poured into the vessel containing the Na -MMT
◦
slurry. The mixture was stirred vigorously at 80 C for 5 h and then
a
Reaction conditions: mole ratio of initial amount of PHC used for catalyst prepa-
ration in Fig. 3, Step III/endo-THDCPD = 1/12.8, reaction temperature 50 C.
◦
allowed to cool to room temperature. The solid product was col-
lected and washed thoroughly with deionized water to remove the
b
Pretreatment time 5 min for Step II.
c
◦
PHC/AlCl3 catalyst itself without MMT support.
Control experiment—without impregnating the catalyst.
Control experiment—without the pretreatment step.
Mole ratio of HDMIC to the CEC of the silicate.
excess organic salts. The product, HDMIC/MMT, was dried at 80 C
d
for 24 h before analysis.
e
f
+
2
.3. Pretreatment of I /MMT with PHC/AlCl3 (Step II)
g
Control experiment—reproducibility tests.
+
The pretreatment of I /MMT hybrids before impregnation with
the chloroaluminate catalyst was carried out as follows. The pre-
2.5. Catalytic isomerization of endo-THDCPD
+
◦
pared I /MMT hybrids were first dried at 100 C under 0.06 Torr
vacuum for 2 h. In a glove box filled with dried nitrogen, the pre-
treating reagent was prepared by mixing PHC (3.75 g, 32.5 mmol)
Catalysts prepared in the manner described above were tested
for the isomerization of endo-THDCPD. The supported chloroalumi-
nate catalyst, containing the organic-salt intercalated silicates and
added PHC/AlCl3 (0.529/1.13 g, 4.58/8.50 mmol), was placed in a
glass-flask reactor equipped with a nitrogen line, stirrer, condenser,
with AlCl (7.50 g, 56.2 mmol) in a two-neck round-bottomed flask
3
equipped with a magnetic stirring bar. After a period of agitation
(
5 min), the pretreated reagent became a homogeneous, viscous
+
◦
liquid, and then dichloromethane (20 mL) was added. The I /MMT
and heating oil-bath, and heated to 50 C. Then, the feedstock, endo-
+
(
containing 3.8 g Na -MMT) was pretreated with the PHC/AlCl3
THDCPD (8 g) in cyclohexane at 1/1 weight ratio, was added with a
syringe. At intervals, samples were taken with a syringe for subse-
quent analysis by gas chromatography (GC).
Catalyst reusability of the supported chloroaluminate was per-
formed by the procedures of withdrawing the liquid from the
reaction system by a syringe and recharged a fresh feed for the next
run (Table 4). Identical experimental procedures were applied for
the recyclability and catalyst activity was monitored by sampling
and analysis periodically.
agent by stirring for 5, 30 or 60 min, filtered, and washed with
several portions of dichloromethane. The pretreatment procedure
+
with different time periods was performed for various I /MMT,
as indicated in Tables 2 and 3. The reproducibility tests with
HDMIC/MMT as the example were shown in Table 2.
+
2
.4. Impregnation of PHC/AlCl3 on pretreated I /MMT (Step III)
The chloroaluminate IL was prepared from PHC and AlCl3 by
the following procedures. In a glove box filled with dried nitro-
gen, PHC (0.529 g, 4.58 mmol) and AlCl3 (1.13 g, 8.5 mmol) were
added in sequence to a round-bottomed flask with a magnetic stir-
rer. After dilution with dichloromethane (5 mL), the mixture was
2
.6. Instruments and analysis
X-ray diffraction (XRD) patterns were obtained with a pow-
der diffractometer (Shimadzu SD-D1) using a Cu target at 35 kV
and 30 mA. The d spacing was calculated according to the
Bragg equation (nꢀ = 2d sinꢁ). Thermogravimetric analysis (TGA)
was performed with a thermogravimetric analytical instrument
+
added to the pretreated I /MMT hybrid (containing 3.8 g MMT).
The reaction vessel was then taken out of the glove box and fitted
with a condenser under a nitrogen atmosphere. Dichloromethane
+
was removed from the I /MMT-supported chloroaluminate cata-
(PerkinElmer Pyris 1) over the temperature range from 100 to
lyst under reduced pressure.
◦ ◦
50 C at 10 C/min in air. Transmission electron microscopy (TEM)
8

7
2
M.-Y. Huang et al. / Journal of Molecular Catalysis A: Chemical 315 (2010) 69–75
Table 3
Isomerizationa of endo-THDCPD by PHC/AlCl3 catalyst impregnated on I /MMT.
+
Supportb
Pretreatment time (min)
Reaction time (min)
Conversion (%)
Selectivity
exo-THDCPD
ADM
BMIC/MMT
0
30
1.2
1.9
2.2
100
100
100
0
0
0
60
1
1
1
1
1
1
1
1
1
20
BMIC/MMT
OMIC/MMT
OMIC/MMT
HDMIC/MMT
PHC/MMT
PHC/MMT
PHC/MMT
5
0
30
40.2
62.0
73.0
100
100
100
0
0
0
60
20
30
1.0
1.1
1.2
100
100
100
0
0
0
60
20
5
30
87.9
98.2
98.9
100
99.9
99.9
0
0.1
0.1
60
20
5
30
93.1
98.8
99.2
100
99.9
99.9
0
0.1
0.1
60
20
0
30
3.8
8.7
14.6
100
100
100
0
0
0
60
20
5
30
40.3
52.0
64.2
100
100
100
0
0
0
60
20
30
60
30
61.4
78.6
93.4
100
100
100
0
0
0
60
20
PHC/MMT
30
65.0
81.8
95.3
100
100
100
0
0
0
60
20
a
◦
Reaction conditions: mole ratio of initial amount of PHC used for catalyst preparation in Fig. 3, Step III/endo-THDCPD = 1/12.8; reaction temperature, 50 C.
b
The intercalated cation I+ mole ratio relative to the CEC of the silicate was 1.2.
+
was performed with a Zeiss EM 902A instrument operated at
0 kV. The reaction mixture was analyzed with a gas chromato-
the Na -MMT (d spacing = 12 Å by XRD analysis). The intercalation
was performed through an ion exchange reaction with the example
of HDMIC shown in Fig. 3, Step I. Other examples involving PHC,
BMIC, OMIC, HDMIC, HDTMAB, DHDDMAB, and TBHDPB (struc-
tures shown in Fig. 2), were shown in Table 1. At an equivalent ratio
of one with respect to the CEC of the clay, the resultant silicates
were expanded to basal-plane spacings of 13, 14, 16, 37, 18–25,
8
graph (HP6890) equipped with an automatic injector (HP7683)
and a capillary column (Chrompack CP-Sil 5CB). The GC response
factors (peak area divided by the substance weight) for endo-
THDCPD/exo-THDCPD/ADM was 1.00:1.00:1.06 were assigned for
the calculation.
3
5, and 25 Å, respectively. These results indicated that the embed-
3
. Results and discussion
ment of alkylammonium and alkylphosphonium cations into the
silicate layers enlarged the spacing. In the series of imidazolium
salts, when the length of alkyl groups increased, from butyl to
octyl to hexadecyl, the silicate d spacing expanded to 14, 16, and
3.1. Preparation of the organic-salt intercalated clays as the
supports
3
7 Å, respectively. In addition to the size effect, the type of organic
Various alkylammonium, alkylpyridinium, alkylimidazolium,
and alkylphosphonium halides, were allowed to intercalate into
cations may also contribute to the interlayer expansion. We note
that HDMIC, HDTMAB, and TBHDPB have the same hexadecyl, but
that HDMIC expanded the basal-plane spacing of the clay more
effectively, to over 37 Å at 1.0 CEC equivalent. In contrast, HDTMAB
and TBHDPB required greater than 1.0 CEC equivalent of intercalat-
ing agent to expand the basal-plane spacing to 34 Å. In addition to
the changes in the d spacing, the embedment of the lengthy alkyl
cations could also affect the polar nature of the silicate plates. The
Table 4
Recyclabilitya of PHC/MMTb supported catalyst for isomerization of endo-THDCPD.
Cycle
Reaction time (h)
Conversion (%)
Selectivity (%)
exo-THDCPD
ADM
1
2
3
1
2
81.8
95.3
100
100
0
0
+
pristine Na -MMT is dispersible, or swells in water. With increas-
ing amounts of organics in the galleries, the silicates lost their
hydrophilic properties. In other words, with a significant amount
of alkyl incorporation into the silicate galleries, for example, in the
case of incorporation of HDMIC into MMT at a 37 Å d spacing and a
1
2
82.8
94.5
100
100
0
0
1
2
82.0
94.0
100
100
0
0
3
5 wt% organic composition, the hybrid became hydrophobic and
4
1
2
80.0
93.7
100
100
0
0
dispersible in toluene.
A critical intercalation profile was previously reported for the
intercalation of MMT clay by poly(oxypropylene)diamine (POP)
salts [31]. The incorporation of the POP salts caused the clay inter-
layer spacing to widen from 12 to 20 Å and then sharply to 58 Å in a
a
Reaction conditions: mole ratio of initial amount of PHC used for catalyst prepa-
◦
ration in Fig. 3, Step III/endo-THDCPD = 1/12.8, reaction temperature 50 C.
b
The PHC mole ratio relative to the CEC of the silicate was 1.2. Pretreatment time
1
h.

M.-Y. Huang et al. / Journal of Molecular Catalysis A: Chemical 315 (2010) 69–75
73
+
Fig. 3. Schematic illustration of preparation procedures and catalyst species of clay-supported chloroaluminate IL catalysts—Step I: intercalation of Na -MMT with HDMIC;
Step II: pretreatment with AlCl3 (in PHC) for a required time and solvent washed; Step III: impregnation of chloroaluminate IL catalyst (e.g., PHC/AlCl3).
two-stage manner. It was found in this work that the use of halide
salts as intercalating agents may generate similar critical points
in the expansion of the basal-plane spacing. Similar results were
obtained for various organic salts, including HDMIC, HDTMAB, and
+
DHDDMAB, intercalated into Na -MMT. The intercalation profiles
were generated by using a series of independent experiments that
were performed with different stoichiometric amounts of organic
salts relative to the clay, where the content was varied from 0.2
to 2.0 CEC, as shown in Fig. 4. The intercalation of HDMIC afforded
a basal-plane spacing of 16–20 Å, which was observed throughout
the addition of HDMIC from 0.2 to 0.6 CEC. Continuing addition
of HDMIC beyond 0.6 CEC resulted in a sudden increase in the d
spacing to 37 Å. When HDTMAB and DHDDMAB were intercalated
+
into Na -MMT, they led to a similar sudden increase in d spacing
to 35 Å, at 1.5 and 0.7 CEC, respectively. The critical concentrations
of the hexadecyl group for HDTMAB and DHDDMAB were similar,
at about 1.4–1.5 CEC. The spatial enlargement can be expressed by
plotting the basal-plane spacing against the amount of HDMIC, as
illustrated in Figs. 4 and 5. It was observed that the silicate basal-
plane spacing did not increase in a linear manner. The HDMIC may
accumulate in the silicate galleries up to a critical concentration,
similarly to the behavior of surfactants, which form micelles at a
critical concentration.
Fig. 4. Intercalation profiles for incorporation of three representative halide salts
into Na -MMT.
+

7
4
M.-Y. Huang et al. / Journal of Molecular Catalysis A: Chemical 315 (2010) 69–75
Fig. 5. Schematic illustration of HDMIC accumulation in galleries and generation of a new hydrophobic phase, which expands the basal-plane spacing.
+
+
For preparing the final catalysts, the I /MMT supports were
Results for I /MMT catalysts based on PHC/MMT, BMIC/MMT,
first pretreated with AlCl3 (in mixing with PHC), washed with
dichloromethane to remove the excess AlCl3 and followed by
adding the designated amounts of the chloroaluminate IL catalyst,
as illustrated in Fig. 3, Step II and III. For the pretreatment step, the
OMIC/MMT, and HDMIC/MMT for the conversion of endo-THDCPD
are shown in Table 3. It is noteworthy that the pretreatment
time of the support had an effect on the activity of the cata-
lyst. The conversions for OMIC/MMT and HDMIC/MMT catalysts
at 30 min reaction time were over 87.9% and 93.1%, respectively.
The PHC/MMT and BMIC/MMT catalysts showed lower activities in
comparison; the conversions at 30 and 60 min reaction time were
40% and 62%, respectively. It has been estimated [32] that endo-
THDCPD molecules have dimensions of either 0.67 nm × 0.65 nm
or 0.58 nm × 0.60 nm. The gallery widths of MMT intercalated with
PHC, BMIC, OMIC, and HDMIC were estimated to be 0.3, 0.4, 0.6,
and 2.7 nm by XRD analysis, and the platelet thickness was esti-
mated to be 1 nm. The observed low conversion for the PHC/MMT
and BMIC/MMT catalysts could be due to the difficulty of access for
endo-THDCPD entering the layer structure. For OMIC/MMT (0.6 nm
spacing), its ability to disperse in organic solvents may explain why
its catalytic activity was similar to that of HDMIC/MMT.
PHC/AlCl mixture is conveniently used since it is an easily handled
3
liquid and excess amount washable by dichloromethane.
3.2. Isomerization of endo-THDCPD
The clay-supported ILs, prepared by stepwise MMT intercala-
tion, pretreatment and chloroaluminate IL catalyst impregnation,
were evaluated for the isomerization of endo-THDCPD. The con-
trol experiments showed that an active catalyst required the
+
I /MMT support to be pretreated and impregnated in two separated
steps. As shown in Table 2, HDMIC/MMT without IL impregnation
failed to catalyze the isomerization while the same HDMIC/MMT
without going through the pretreatment step but directly impreg-
nating with IL gave a low catalytic activity. The procedure of
pretreatment described above was required for deactivating the
silanol (≡Si–OH) groups on the silicate plate surface. The repro-
ducibility of catalyst preparations was demonstrated and shown in
Table 2.
When the period of pretreatment for PHC/MMT was increased
from 5 to 30 and then 60 min, the conversion increased from 52.0%
to 78.6% and then to 81.8%, respectively. It is expected that the effect
of the pretreatment was mainly to avoid the presence of silanol
groups on the surface of the MMT.
The HDMIC/MMT hybrids were used as the supports for the
chloroaluminate IL catalyst. Three different clay hybrids, with 0.2,
3.3. Catalyst recyclability
0.5, and 1.2 CEC of organic salt with respect to the MMT, were
selected for performing the isomerization of endo-THDCPD to the
exo-product. As summarized in Table 2, the conversions after
For demonstrating the catalyst recyclability, PHC/MMT was
selected because of its easiness for product separation from the
hybrid catalyst. The PHC/MMT hybrid was pretreated for 1 h,
impregnated with PHC/AlCl3 catalyst and used for recycle stud-
ies. The results are summarized in Table 4. Clearly, the supported
chloroaluminate IL catalyst remained similar activity for four
cycles. At the fourth run, the catalyst showed 98% of the activ-
ity in comparison to the first run. Apparently, the clay-supported
chloroaluminate ILs could be recycled a number of times before
noticeable loss of activity.
3
0 min of reaction for these three different hybrids impregnated
using the same initial amount of chloroaluminate IL were found to
be 47.1%, 92.3%, and 93.1%, respectively. The basal-plane spacings
for 0.2 and 0.5 CEC were very similar, but the reaction conversions
were noticeably different. We observed further that HDMIC/MMT
with 0.5 CEC or higher of the organic salt could be dispersed in
a hydrocarbon solvent; however, the catalyst remained granular
in appearance at 0.2 CEC. When the organic-salt content was over
0.5 CEC, the intercalation expanded the interlayer spacing of the
silicate and caused the silicate to disperse well in the reaction
mixture. The IL-impregnated HDMIC/MMT with 0.5 or 1.2 CEC of
the organic salt demonstrated higher conversions than the values
4. Conclusions
Several
different
halides,
including
1-hexadecyl-3-
+
obtained without any support or with impregnated Na -MMT. It
methylimidazolium chloride (HDMIC), have been intercalated
into the layer structure of Na -MMT by an ion exchange reaction to
generate effective supports for a chloroaluminate IL. The resulting
organic-salt intercalation could expand the silicate interlayer
spacing from 12 to 37–41 Å and rendered the clay hydrophobic
and compatible with a hydrocarbon feedstock. When impreg-
+
appears that the use of HDMIC/MMT as a support can provide an
increased contact area between the catalyst and reactant and also
phase compatibility for reaction feedstock that would otherwise
be immiscible with unsupported catalyst, and that this ultimately
accelerates the rate of the catalytic reaction.

M.-Y. Huang et al. / Journal of Molecular Catalysis A: Chemical 315 (2010) 69–75
75
nated with a chloroaluminate IL, the MMT-supported ILs became
effective catalysts for the isomerization of endo-THDCPD. The
rate was enhanced with the presence of clay supports, perhaps
due to the increase in the gallery spacing of the clay and organic
[12] F.A. Bottino, E. Fabbri, I.L. Fragala, G. Malandrino, A. Orestano, F. Pilati, A. Polli-
cino, Macromol. Rapid Commun. 24 (2003) 1079–1084.
[
13] A. Usuki, A. Koiwai, Y. Kojima, M. Kawasumi, A. Okada, T. Kurauchi, O. Kamigaito,
J. Appl. Polym. Sci. 55 (1995) 119–123.
[14] M. Kawasumi, N. Hasegawa, M. Kato, A. Usuki, A. Okada, Macromolecules 30
(1997) 6333–6338.
+
compatibility. An optimized I /MMT catalyst with 0.5 CEC equiv-
[
[
15] N. Ogata, S. Kawakage, T. Ogihara, Polymer 38 (1997) 5115–5118.
16] N. Ogata, G. Jimenez, H. Kawai, T. Ogihara, J. Polym. Sci. B: Polym. Phys. 35
(1997) 389–396.
alents of HDMIC affected the isomerization of endo-THDCPD with
nearly quantitative conversion and selectivity. More importantly,
the newly developed clay-supported ILs could be recyclable and
practically used for the commercialization of the exo-THDCPD
production.
[17] P. Wassercheid, T. Welton, Ionic Liquids in Synthesis, 2nd ed., Wiley–VCH,
Weinheim, 2008.
[
18] H. Ohno, Electrochemical Aspects of Ionic Liquids, John Wiley & Sons, Hoboken,
NJ, 2005.
[
[
19] F. Yan, J. Texter, Chem. Commun. 25 (2006) 2696–2698.
20] E. Rodil, L. Aldous, C. Hardacre, M.C. Lagunas, Nanotechnology 19 (2008)
Acknowledgment
105603.
[
[
[
[
[
21] A. Riisager, R. Fehrmann, S. Flicker, R. van Hal, M. Haumann, P. Wasserscheid,
Angew. Chem. Int. Ed. 44 (2005) 815–819.
22] H. Hagiwara, Y. Sugawara, K. Isobe, T. Hoshi, T. Suzaki, Org. Lett. 6 (2004)
We acknowledge financial support from the National Science
Council (NSC) of Taiwan and CPC Corporation, Taiwan.
2325–2328.
23] S. Breitenlechner, M. Fleck, T.E. Müller, A. Suppan, J. Mol. Catal. A: Chem. 214
(2004) 175–179.
24] J. Huang, T. Jiang, H.X. Gao, B. Han, Z. Liu, W.Z. Wu, Y.H. Chang, G.T. Zhao, Angew.
Chem. Int. Ed. 43 (2004) 1397–1399.
References
[
[
1] G. Sartori, R. Maggi, Chem. Rev. 106 (2006) 1077–1104.
2] K. Gopal, S.B. Srivastava, S. Shukla, J.L. Bersillon, J. Environ. Biol. 25 (2004)
25] S. Miao, Z. Liu, B. Han, J. Huang, Z. Sun, J. Zhang, T. Jiang, Angew. Chem. Int. Ed.
45 (2006) 266–269.
4
69–475.
3] J.H. Potgieter, S.S. Potgieter-Vermaak, P.D. Kalibantonga, Miner. Eng. 19 (2006)
63–470.
[
[
[
26] C.J. Adams, M.J. Earle, K.R. Seddon, Green Chem. 2 (2000) 21–23.
27] P.N. Barnes, K.A. Grant, K.J. Green, N.D. Lever, WO Pat., 0040673, 2000.
28] G. Roberts, C.M. Lok, C.J. Adams, K.R. Seddon, M.J. Earle, J.T. Hamill, US Pat.
[
4
[
[
[
[
4] M. Alexandre, P. Dubois, Mater. Sci. Eng. 28 (2000) 1–63.
5] D. Porter, E. Metcalfe, M.J.K. Thomas, Fire Mater. 24 (2000) 45–52.
6] X. Fu, S. Qutubuddin, Polymer 42 (2001) 807–813.
6
255504 B1, to Unichema Chemie BV, 2001.
29] G. Roberts, C.M. Lok, C.J. Adams, K.R. Seddon, M.J. Earle, J.T. Hamill, US Pat.
316643 B1, to Unichema Chemie BV, 2001.
30] E. Xing, Z. Mi, C. Xin, L. Wang, X. Zhan, J. Mol. Catal. A: Chem. 231 (2005)
61–167.
31] J.J. Lin, I.-J. Chen, C.C. Chou, Macromol. Rapid Commun. 24 (2003) 492–
95.
[
[
[
6
7] A. Usuki, N. Hasegawa, H. Kasoura, T. Okamoto, Nano Lett. 1 (2001) 271–
2
72.
8] H. Tetsuka, T. Ebina, T. Tsunoda, H. Nanjo, F. Mizukami, Nanotechnology 18
2007) 355701.
9] M. Wei, S. Shi, J. Wang, Y. Li, X. Duan, J. Solid State Chem. 177 (2004) 2534–2541.
1
[
[
(
4
[
[
[
32] E. Xing, X. Zhang, L. Wang, Z. Mi, Catal. Commun. 6 (2005) 737–741.
33] E. Xing, X. Zhang, L. Wang, Z. Mi, Green Chem. 9 (2007) 589–593.
34] B.H. Jeong, J.S. Han, S.W. Ko, J.H. Lee, B.J. Lee, J. Ind. Eng. Chem. 13 (2007)
[
[
10] M. Zanetti, S. Lomakin, G. Camino, Macromol. Mater. Eng. 279 (2000) 1–9.
11] J.W. Gilman, W.H. Awad, R.D. Davis, J. Shields, R.H. Harris, C. Davis, A.B. Mor-
gan, T.E. Sutto, J. Callahan, P.C. Trulove, H.C. Delong, Chem. Mater. 14 (2002)
310–313.
3
776–3785.