Isopropylation of biphenyl over ZSM-12 zeolites

Article abstract of DOI:10.1016/j.molcata.2012.10.018

ZSM-12 zeolites, ZSM-12L and ZSM-12S, with MTW topology were synthesized by using methyltriethylammonium bromide (MTEABr) and tetraethylammnoium bromide (TEABr) as structure directing agents (SDA), respectively, for the isopropylation of biphenyl (BP) usi

Full text of DOI:10.1016/j.molcata.2012.10.018

Journal of Molecular Catalysis A: Chemical 367 (2013) 23–30
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Isopropylation of biphenyl over ZSM-12 zeolites
a
b
b
b
b
Anand Chokkalingam , Hiroaki Kawagoe , Seiji Watanabe , Yasuhiro Moriyama , Kenichi Komura ,
b,c
d
d
a,∗
a,b,∗∗
Yoshihiro Kubota , Jong-Ho Kim , Gon Seo , Ajayan Vinu , Yoshihiro Sugi
Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld 4072, Australia
Department of Materials Science and Technology, Faculty of Engineering, Gifu University, Gifu 501-1193, Japan
Department of Materials Science and Engineering, Graduate School of Engineering, Yokohama National University, Yokohama 240-8501, Japan
School of Applied Chemical Engineering, Chonnam National University, Gwangju 500-757, Republic of Korea
a
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
ZSM-12 zeolites, ZSM-12L and ZSM-12S, with MTW topology were synthesized by using methyltriethy-
lammonium bromide (MTEABr) and tetraethylammnoium bromide (TEABr) as structure directing agents
Received 19 September 2012
Received in revised form 16 October 2012
Accepted 17 October 2012
Available online 30 October 2012
(SDA), respectively, for the isopropylation of biphenyl (BP) using propene as an alkylating agent. The par-
ticle sizes of the ZSM-12L and ZSM-12S were in the range of 5–10 ␮m and less than 0.5 ␮m, respectively.
ꢀ
ꢀ
The selectivities for 4,4 -diisopropylbiphenyl (4,4 -DIPB) were 60–70% for ZSM-12L and 40–50% for ZSM-
◦
1
2S at lower temperatures below 275 C, and rapidly decreased with further increase in temperatures to
less than 20% at 350 C over both zeolites. The kinetic controlled catalyses on external acid sites at lower
temperatures were resulted in the formation of bulkier isomers, 2,x -DIPB (x:2,3,4). The decreases in the
selectivity for 4,4 -DIPB occurred by the isomerization of 4,4 -DIPB to stable isomers, 3,4 - and 3,3 -DIPB
on external acid sites at higher temperatures. These catalyses were decreased remarkably over ZSM-12LD
prepared by the dealumination of ZSM-12L with EDTA-3Na, because of effective removal of external acid
sites.
Keywords:
ZSM-12
Particle size
Biphenyl
Isopropylation
Shape-selective catalysis
◦
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
The isopropylation of BP over ZSM-12 zeolites was moderately shape-selective for the formation of
ꢀ
ꢀ
4
,4 -DIPB at appropriate temperatures, particularly over ZSM-12L and ZSM-12LD. The formation of 4,4 -
DIPB occurred primarily near pore-entrances but not deep in the channels. ZSM-12 channels are less
ꢀ
effective for the selective formation of 4,4 -DIPB than MOR channels.
©
2012 Elsevier B.V. All rights reserved.
1
. Introduction
selectivities of the least bulky products because confined circum-
stances in the materials highly influence shape-selective catalysis.
Recently, we have studied the alkylation of BP over zeolites with
one-dimensional 12- and 14-MR pore-entrances and over three-
dimensional zeolites with 12-MR pore-entrances, and proposed
that shape-selective catalysis occurs by the differences of steric
restriction with channels at the transition states of the product iso-
mers [4–18]. We have been interested in the zeolites which have
smaller channels than MOR to elucidate what are optimal struc-
Zeolites are the most promising microporous crystals for achiev-
ing highly shape-selective catalysis because of their uniform
distribution of pores and channels. They have dimensions that
allow both organic reactants and products to enter, to be accommo-
dated, and to leave [1–8]. Large-pore molecular sieves (LPMS) with
1
2- and 14-membered ring (12- and 14-MR) entrances have been
extensively used as the catalysts for the alkylation of bulky polynu-
clear aromatics [4–25]. In particular, 4,4 -diisopropylbiphenyl
ꢀ
ꢀ
tures for the shape-selective formation of 4,4 -DIPB.
ꢀ
(
4,4 -DIPB) and 2,6-diisopropylnaphthalene (2,6-DIPN) have been
ZSM-12 zeolites with MTW topology have the smallest pore-
entrances (0.56 nm × 0.6 nm) among 12-MR zeolites with straight
channels. The channels are smaller than those of MOR and SSZ-
24 with AFI topology, but larger than those of ZSM-5 with MFI
topology of 10-MR entrances [26]. We expected that ZSM-12 chan-
nels should offer higher shape-selective natures than MOR and
SSZ-24 channels in the alkylation of BP and NP because ZSM-
selectively produced over dealuminated H-mordenite (MOR) from
biphenyl (BP) and naphthalene (NP), respectively [6–10,20–25].
It has been of great interest to elucidate the catalytic features
of the LPMS with different type of pores and channels from the
1
2 channels are expected to have severer steric restriction than
∗
∗
Corresponding author. Tel.: +61 7 334 64122.
Corresponding author at: Department of Materials Science and Technology, Fac-
MOR channels. In this paper, we examined the isopropylation of
BP over ZSM-12 with different particle sizes, and discussed the
differences in shape-selective catalyses by the different type of
zeolites.
∗
ulty of Engineering, Gifu University, Gifu 501-1193, Japan. Tel.: +81 47 343 3539;
fax: +81 47 343 3539.
E-mail addresses: a.vinu@uq.edu.au (A. Vinu), ysugi@gifu-u.ac.jp (Y. Sugi).
1
381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.10.018

2
4
A. Chokkalingam et al. / Journal of Molecular Catalysis A: Chemical 367 (2013) 23–30
2
2
2
. Experimental
capillary column (25 m × 0.2 mm; film thickness: 25 ␮m; Agilent
Technologies Co. Ltd., MA, U.S.A.).
.1. Preparation of ZSM-12 zeolites
The yield of each product was calculated according to the
amount of BP used in the isopropylation of BP, where the sensi-
tivities were normalized by carbon number of each product. The
selectivity for isopropylbiphenyl (IPBP) and diisopropylbiphenyl
(DIPB) isomers was expressed as a percentage of each IPBP and
DIPB isomer among the total possible IPBP and DIPB isomers.
The analysis of encapsulated products in the catalyst used for
the reaction was carried out as follows. The catalyst was filtered
.1.1. ZSM-12 with tetraethylammonium bromide (ZSM-12L)
ZSM-12L was synthesized using tetraethylammonium bro-
mide (TEABr) as a structure-directing agent (SDA) according
to previous literature [27]. The molar gel composition was
+
1
SiO :0.18[TEA] :0.18NaOH:0.008Al O :7.8H O. The typical pro-
2
2
3
2
cedures are as follows: NaAlO2 0.98 g, TEABr, 20 g, H O 60 g, and
SiO (Ludox HS-40) 75 g were added to the solution of NaOH 3.5 g
2
◦
off, washed well with 200 mL of acetone, and dried at 110 C for
2
in water 25 g in 500 mL PP bottle. Subsequently, the resulting solu-
tion was sonically agitated for 40 min, and kept the gel at 100 C
for 90 days. A small quantity of water was added in the gel dur-
ing heating to keep the water level constant. The resultant solid
products were filtered, washed several times with water, and dried
12 h. 50 mg of the resulting catalyst was dissolved carefully using
1 mL of aqueous hydrofluoric acid (47%) at room temperature. This
solution was basified with solid potassium carbonate, and organic
layer was extracted three times with 20 mL of dichloromethane.
After removal of the solvent in vacuo, the residue was dissolved
in 1 mL of toluene. GC analysis was done according to the same
procedure as for bulk products. The products are classified as BP,
IPBP, DIPB, and triisopropylbiphenyls (TriIPB) isomers.
◦
◦
at 110 C. Then, the solid was heated in a flow of air (50 mL/min)
◦
◦
with a temperature-programmed rate of 2 C/min up to 550 C, and
calcined for 7 h. Calcined samples were converted to H-form by
using 20 mL of 1 M solution of ammonium nitrate per gram of a
◦
ꢀ
sample for 12 h at 80 C. This procedure was repeated three times,
2.3. The stability of 4,4 -DIPB
and the zeolites were heated in a flow of air (50 mL/min) with a
temperature-programmed rate of 2 C/min up to 550 C, and cal-
cined for 7 h.
◦
◦
ꢀ
◦
The stability of 4,4 -DIPB was examined at 300 C under propene
pressure following the procedures of the isopropylation of BP. The
products analyses were carried out by the same procedures as in
ꢀ
the isopropylation of BP. The products were classified as 4,4 -DIPB,
isomerized DIPB, IPBP, and TriIPB isomers.
2.1.2. ZSM-12 with methytriethylammonium bromide (ZSM-12S)
ZSM-12S was synthesized using methytriethylammonium bro-
mide (MTEABr) as a structure-directing agent (SDA) according
2
.4. Characterization of catalysts
to previous literature [28]. The molar gel composition was
+
1
SiO :0.17[MTEA] :0.25NaOH:0.01Al O :25H O. The typical pro-
2
2
3
2
Phase purity and crystallinity of the zeolites were determined by
cedures are as follows: Ludox S-40, 4.187 g (SiO : 28.9%) was added
2
using a powder X-ray diffractometer (Shimadzu XRD-6000) with Cu
K␣ radiation (ꢀ = 0.15418 nm). Elemental analysis was performed
using inductively coupled plasma spectroscopy (JICP-PS-1000UV,
Leeman Labs Inc., NH, U.S.A.). The crystal size and the morphology of
the sample were observed by scanning electron microscopy using
a Philips XL30 apparatus (Philips Electronics Japan, Tokyo, Japan).
Nitrogen adsorption measurements were carried out on a BELSORP
to the solution of MTEABr, 1.686 g and Al(NO ) ·6H O, 0.1502 g
3
3
2
with a continuous stirring. pH of the mixture was adjusted to 10
by adding H SO (97%) and stirred for 1 h. Resulting gel was heated
2
4
◦
in Teflon autoclave at 150 C for 10 days. The solid products were
filtered, washed several times with water, and dried at 110 C. Post
◦
synthesis treatments were done by the same way as ZSM-12L.
2
8SA (BEL Japan Inc., Osaka, Japan). Acidity measurements were
performed by temperature programmed desorption of ammonia
NH -TPD) on a BEL TPD-66 apparatus (BEL Japan). The amounts of
acid sites were calculated from desorbed NH3 from the sample to
gas phase based on calibrated amounts of NH3.
2.1.3. The dealumination of ZSM-12L
Calcined ZSM-12L (1.0 g) was heated in 20 mL of 0.1 M aque-
ous solution of trisodium hydrogen ethylenediaminetetraacetate
(
3
◦
hydrate (EDTA-3Na) with stirring at 80 C for 12 h [29]. The result-
◦
ing zeolite was heated to 550 C in air-stream of 50 mL/min with a
◦
◦
programmed rate of 2.5 C/min, and calcined at 550 C for 7 h. The
calcined ZSM-12L was heated with the equal weight of ammonium
sulfate in water during 3 h under reflux. Finally, dealuminated H-
3. Results and discussion
3.1. Properties of the ZSM-12 zeolites
◦
ZSM-12L (ZSM-12LD) was obtained by the calcination at 550 C for
7
h.
Typical properties of ZSM-12 zeolites used in this study are
shown in Table 1. SiO /Al O ratios are 75.5 for ZSM-12L and 65.3
2
2
3
2
.2. Isopropylation of BP
for ZSM-12S, respectively. Fig. 1 shows the XRD patterns of the
ZSM-12 zeolites synthesized by the two procedures. Amorphous
phases were not observed for both ZSM-12 zeolites; however, the
crystallinity of the ZSM-12L is much higher than that of ZSM-12S.
SEM images of the samples are shown in Fig. 2. Particle size of
the ZSM-12L (5–10 ␮m) is much larger than that of ZSM-12S (less
than 0.5 ␮m).
The isopropylation of BP was carried out in a 100 mL SUS-
16 autoclave under propene pressure. The reaction conditions
3
were as follows: BP: 3.86 g (25 mmol); catalyst: 125 mg; propene
pressure: 0.8 MPa; operating time: 4 h; and reaction temperature:
2
◦
00–350 C. The autoclave was purged with nitrogen, and heated to
the reaction temperature. Subsequently, the reaction was started
with agitation by introduction of propene to the autoclave, and the
temperature and pressure were maintained throughout the reac-
tion. After cooling the autoclave, the products were separated from
the catalysts by filtration, and washed well with toluene. The fil-
trates and washings were combined, and an approximately 1.5 mL
portion of the solution was diluted with toluene (1.5–6.0 mL). The
products were analyzed on a gas chromatograph (GC-14C and/or
GC-18A; Shimadzu Corp., Kyoto, Japan) equipped with an Ultra-1
Textural parameters of the ZSM-12S and ZSM-12L are given in
Table 1. Specific surface area of ZSM-12S was much higher than
that of ZSM-12L. In addition, the external surface area, and pore
volume of ZSM-12S calculated by t-plot method were also higher
as compared to those of ZSM-12L. These results also support the fact
that ZSM-12L has much higher crystallinity than ZSM-12S. These
differences in particle size and crystallinity are highly influenced
in surface and channel structures, resulting in different features in
catalytic properties in this work.

A. Chokkalingam et al. / Journal of Molecular Catalysis A: Chemical 367 (2013) 23–30
25
Table 1
Textual properties of ZSM-12 zeolites.a
SiO2/Al2O3
Surface area
Surface area
External surface
Pore volume
Peak temperature
(NH3-TPD) ( C)
Acid amount
2
−1
b
2
−1
c
2
−1
c
3
−1
c
◦
−1
(
m
g
)
(m
g
)
area (m
g
)
(mm
g
)
(mmol g
)
ZSM-12L
ZSM-12S
ZSM-12LD
75.5
65.3
78.6
173.8
220.9
166.8
236.3
299.0
224.9
6.0
34.4
9.3
65.8
83.9
61.0
332
324
338
0.29
0.29
0.30
a
Sample: H-form.
BET method.
t-Plot method.
b
c
dealumination removes almost only the acid sites at the external
surface because EDTA-3Na cannot enter the pores of ZSM-12L.
3.2. Isopropylation of BP over ZSM-12 zeolites
Fig. 3 shows the effects of reaction temperatures on the iso-
propylation of BP over ZSM-12L. The conversion of BP increased
with increasing reaction temperatures, and reached around 80%
◦
at around 250–275 C as shown in Fig. 3a. The yields of IPBP and
DIPB isomer also increased with an increase in temperatures. IPBP
isomers were the principal products at low and moderate temper-
◦
atures below 250 C. The yield of DIPB isomers increased with a
concomitant decrease of the yield of IPBP isomers with increas-
ing the temperature. The yield of IPBP increased again with the
decrease in the yield of DIPB isomers at further high temperatures
◦
as 350 C. The formation of TriIPB isomers was gradually increased
◦
with the increase in the temperatures up to 10–15% at 300–350 C.
Fig. 3b shows the effects of the temperature on the yield of IPBP
isomers. 4-IPBP was a predominant isomer at the lower temper-
Fig. 1. XRD patterns of ZSM-12. (a) ZSM-12S; (b) ZSM-12L; and (c) ZSM-12LD.
◦
atures below 275 C. However, the yield of 4-IPBP was decreased
◦
◦
from around 30% at 200 C to 10% at 325 C. On the other hand,
the yields of 3-IPBP remained almost constant with the increase
◦
in the temperature up to 300 C. These results indicate that 4-IPBP
Temperature programmed desorption of NH (NH -TPD) of both
was predominantly formed from BP and preferentially consumed
3
3
ꢀ
the ZSM-12 zeolites displays two peaks, l-peak and h-peak, where
h-peak is correlated to Brønsted acid sites from tetrahedral alu-
minum cations. Peak temperatures of h-peak indexed to acidity
were at almost the same temperatures for both the samples as
shown in Table 1. The amounts of acid sites calculated from area of
by the formation of 4,4 -DIPB without significant isomerization to
ꢀ
3-IPBP. The rate of the formation of DIPB isomers, such as 3,4 -DIPB,
from 3-IPBP was much slower as compared to that of the forma-
ꢀ
tion of 4,4 -DIPB from 4-IPBP. A further increase in the temperature
◦
from 300 to 350 C makes a significant increase in the yield of 3-
−1
h-peak is 0.29 mmol g for both the ZSM-12L and ZSM-12S. How-
ever, the acid strength of the ZSM-12 zeolites is much weaker than
that of MOR zeolites [29].
IPBP; however, the yield of 4-IPBP remained almost constant. These
results mean that the increase of the yield of 3-IPBP is due to the
de-alkylation of DIPB isomers to IPBP isomers in addition to the
isomerization of 4-IPBP to 3-IPBP. The yield of 2-IPBP was less than
7%, and gradually decreased with the increased temperatures.
The effects of the temperature on the yield of DIPB isomers
◦
ZSM-12L was dealuminated by EDTA-3Na at 80 C for the deac-
tivation of external acid sites. No changes in the XRD pattern were
observed after the dealumination as shown in Fig. 1. Textual and
acidic properties also remained those of original ZSM-12L by the
dealumination as shown in Table 1. These results indicate that the
ꢀ
are shown in Fig. 3c. The yield of 4,4 -DIPB was rapidly increased
◦
with increased temperatures, and reached a maximum at 275 C.
Fig. 2. SEM images of as-synthesized ZSM-12.

2
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A. Chokkalingam et al. / Journal of Molecular Catalysis A: Chemical 367 (2013) 23–30
Fig. 3. Effects of reaction temperature on the isopropylation of BP over ZSM-12L. (a) Yield of isopropylates. (b) Yield of IPBP isomers. (c) Yield of DIPB isomers. (d) Selectivity
for DIPB isomers. Reaction conditions: BP: 3.86 g (25 mmol); catalyst: ZSM-12L, 125 mg; propene pressure: 0.8 MPa, period: 4 h. Legends: (a) ( ) IPBP; ( ) DIPB; ( ) TriIPB;
ꢀ
ꢀ
ꢀ
ꢀ
and ( ) conversion. (b) ( ) 4-IPBP; ( ) 3-IPBP; and ( ) 2-IPBP. (c) and (d) ( ) 4,4 -DIPB; ( ) 3,4 -DIPB; ( ) 3,3 -DIPB; and ( ) 2,x -DIPB.
◦
These increases suggest that 4-IPBP preferentially participates in
with increasing the temperatures from 300 C, although they were
less than 10%.
ꢀ
ꢀ
the formation of 4,4 -DIPB because the increase in 4,4 -DIPB cor-
responds well to the decrease the formation of 4-IPBP. However,
a further increase in temperature caused a decrease in the yield
These features over ZSM-12L suggest that moderately shape-
selective formation of 4,4 -DIPB occurred at low and moderate
temperatures, although some kinetic controlled reactions, proba-
bly at the external sites, were accompanied at lower temperatures
as 200 C, leading to the formation of 2,x -DIPB. However, ther-
ꢀ
ꢀ
ꢀ
of 4,4 -DIPB with a concomitant increase in the yield of 3,4 -
ꢀ
◦
DIPB. The yield of 3,4 -DIPB was then saturated at 325–350 C.
The yield of 2,x -DIPB (sum of 2,2 -, 2,3 - and 2,4 -DIPB) was
ꢀ
ꢀ
ꢀ
ꢀ
◦
ꢀ
gradually increased with increasing the reaction temperature and
modynamic controlled catalyses occurred at higher temperatures,
resulting in the isomerization of 4,4 -DIPB to 3,4 -DIPB.
◦
ꢀ
ꢀ
reached a maximum at 275–300 C, whereas remained almost
ꢀ
constant at further higher temperatures. The yields of 3,3 -DIPB
Fig. 4 shows the effects of reaction temperatures on the iso-
propylation of BP over ZSM-12LD which was prepared by the
dealumination of ZSM-12L to reduce the catalysis at external
acid sites. The catalytic activity was decreased by the dealumina-
were increased at high temperatures although they were less than
5
%.
Fig. 3d shows the effects of the temperature on the selec-
ꢀ
◦
tivity for DIPB isomers. The selectivity for 4,4 -DIPB was 60% at
tion, particularly at the lower temperatures from 200 to 275 C
◦
◦
2
00 C, increased up to 70% at 225–250 C; however, then rapidly
decreased with a threshold of 275 C by the increase in the
temperature, accompanying the increase in the selectivity for 3,4 -
DIPB. Gradual decrease in the selectivities for 2,x -DIPB occurred
with the increased temperatures from 20% at 200 C to 10% at
50–350 C. Further, the selectivities for 3,3 -DIPB were increased
(Fig. 4a). The yield of IPBP isomers was increased with increas-
ing the temperatures. Among IPBP isomers, the yield of 4-IPBP
◦
ꢀ
◦
was maximized at around 250 C, and then, decreased with the
ꢀ
increase in the temperatures, whereas the yield of 3-IPBP was spon-
taneously increased with the increase in temperature (Fig. 4b). The
yield of DIPB isomers was increased to 30% with increasing the
◦
◦
ꢀ
2

A. Chokkalingam et al. / Journal of Molecular Catalysis A: Chemical 367 (2013) 23–30
27
Fig. 4. Effects of reaction temperature on the isopropylation of BP over ZSM-12LD. (a) Yield of isopropylates. (b) Yield of IPBP isomers. (c) Yield of DIPB isomers. (d) Selectivity
for DIPB isomers. Reaction conditions and legends: see Fig. 3.
◦
ꢀ
temperature to 300 C (Fig. 4a). The yield of 4,4 -DIPB was maxi-
EDTA-3Na, resulting in the occurrence of some non-selective
reactions.
◦
◦
mized at 325 C, and then decreased at 350 C, whereas, the yield
of 3,4 -DIPB was increased spontaneously with the increase in the
temperature (Fig. 4c). The formation of TriIPB isomers was grad-
ually increased to 10% with the increase in the temperature to
50 C. ZSM-12LD gave the similar results to ZSM-12L although the
catalytic activities were slightly decreased, particularly at lower
temperatures.
Fig. 4d shows the effects of reaction temperature on the selectiv-
ity for DIPB isomers over ZSM-12LD. The selectivity for DIPB was
significantly improved by the dealumination, particularly at high
ꢀ
The isopropylation of BP over ZSM-12S were examined to know
the effects of external acid sites because ZSM-12S has larger exter-
nal surface than ZSM-12L due to smaller particle size as shown
in Table 1. Fig. 5 shows the influences of reaction temperature
on the isopropylation of BP over ZSM-12S. Catalytic activity of
ZSM-12S was increased with the increased temperatures, and the
◦
3
◦
conversion was reached 80% at 275 C although ZSM-12S was less
active than ZSM-12L at lower temperatures (Fig. 5a). 4-IPBP was a
principal product at lower temperatures; however, decreased with
the increased temperatures. The yield of 3-IPBP was spontaneously
increased with the increase in temperature; however, the yield
of 2-IPBP was decreased with the temperature (Fig. 5b). The yield
ꢀ
temperatures. The selectivity for 4,4 -DIPB was increased 55% at
◦
◦
2
3
00 C to 70% at 275 C, and then, gradually decreased to 56% at
◦
ꢀ
50 C. These results show that the selectivities for 4,4 -DIPB were
improved particularly at 250–350 C by the dealumination of ZSM-
◦
◦
of DIPB increased with increasing the temperatures up to 300 C,
1
2L, and that ZSM-12 channels had the moderately shape-selective
accompanying the decrease in the yield of IPBP isomers, and
further increase in temperature resulted in the saturation of the
ꢀ
natures for the formation of 4,4 -DIPB even at high temperatures.
ꢀ
The formation of bulky isomers and the isomerization of
yield of DIPB isomers. The yield of 4,4 -DIPB was maximized at
ꢀ
◦
4
,4 -DIPB at the external acid sites were effectively decreased
300 C, and further increase in temperature decreased the yield of
ꢀ
ꢀ
by the dealumination. However, the external acid sites
were not completely deactivated by the dealumination with
4,4 -DIPB with the increase in those of 3,4 -DIPB (Fig. 5c). The yield
of TriIPB isomers increased spontaneously up to 20% at 350 C.
◦

2
8
A. Chokkalingam et al. / Journal of Molecular Catalysis A: Chemical 367 (2013) 23–30
Fig. 5. Effects of reaction temperature on the isopropylation of BP over ZSM-12S. (a) Yield of isopropylates. (b) Yield of IPBP isomers. (c) Yield of DIPB isomers. (d) Selectivity
for DIPB isomers. Reaction conditions and legends: see Fig. 3.
These catalytic behaviors of ZSM-12S were fundamentally similar
to those of ZSM-12L although the catalytic activities were lower
than ZSM-12L, particularly at lower temperatures.
extensive for ZSM-12S compared to ZSM-12L. These catalytic prop-
erties are due to their active acid sites at the external surfaces.
Actually, these acid sites were decreased by the dealumination of
ZSM-12L, although, unfortunately, we could not deactivate com-
pletely them.
Fig. 5d shows the effects of the temperature on the selectivity
ꢀ
for DIPB isomers. ZSM-12S had lower selectivity for 4,4 -DIPB than
ZSM-12L. The selectivity was gradually increased with tempera-
tures; reached a maximum, 55% at 300 C; and then, decreased to
Fig. 6 shows the effects of reaction temperature on the stability
◦
ꢀ
◦
of 4,4 -DIPB over ZSM-12 zeolites at 300 and 350 C under 0.8 MPa
◦
ꢀ
around 20% with a threshold of 300 C by the increase in the tem-
of propene pressure. The consumption of 4,4 -DIPB over ZSM-12S
ꢀ
ꢀ
perature. The selectivities for 3,4 - and 3,3 -DIPB remained almost
constant from 200 C to 300 C; however, rapidly increased with
compensation of the selectivity for 4,4 -DIPB at further higher tem-
peratures. The selectivity for 2,x -DIPB was decreased with the
increase in the temperature from 35% at 200 C to 5% at 350 C.
The increase in the selectivity for 4,4 -DIPB corresponded to the
decrease in the selectivity for 2,x -DIPB formed by the kinetic con-
was much more significant than that over ZSM-12L, and increased
with increasing the temperature. The decrease in the selectivity
◦
◦
ꢀ
ꢀ
for 4,4 -DIPB at high temperatures is due to the isomerization to
ꢀ
ꢀ
stable isomers. The differences in stability for 4,4 -DIPB by the
◦
◦
contact with ZSM-12L and ZSM-12S are due to the availability of
the external acid site by the difference of particle sizes. However,
the isomerization to DIPB isomers was remarkably decreased over
ZSM-12LD because of the deactivation of external acid sites. These
results suggest that the similar decrease in the yield and selectivity
ꢀ
ꢀ
trolled reaction at the external acid sites.
ꢀ
◦
The yield of 4,4 -DIPB was maximized at 300 C, and the increase
ꢀ
ꢀ
in temperature decreased the yield of 4,4 -DIPB with concomitant
for 4,4 -DIPB occurred during the isopropylation of BP.
ꢀ
increase in those of 3,4 -DIPB. These trends in DIPB isomers resem-
Fig. 7 shows the effects of reaction temperature on the prod-
ucts composition of encapsulated products contained in ZSM-12L,
ꢀ
bled the results over ZSM-12L. The formation of 2,x -DIPB was more

A. Chokkalingam et al. / Journal of Molecular Catalysis A: Chemical 367 (2013) 23–30
29
dynamically stable isomers, if zeolite channels are wide enough
to allow the accommodation of the bulky isomers. The features
suggest that the confined structures of zeolite channels are impor-
tant for shape-selective catalysis. We have considered that a little
bit narrow channels of ZSM-12 compared to MOR can achieve the
highly shape-selective catalysis.
The isopropylation of BP over a ZSM-12 zeolite consecutively
occurred in two steps as shown in Figs. 3–5: BP to IPBP iso-
mers, and IPBP to DIPB isomers. The formation of 4-IPBP occurred
predominantly from BP, and 4-IPBP was consumed preferen-
ꢀ
tially to 4,4 -DIPB in the second step at moderate temperatures.
These results indicate that the moderately shape-selective catalysis
occurs in ZSM-12 channels.
ꢀ
The selectivities for 4,4 -DIPB was 60–70% for ZSM-12L and
3
3
5–50% for ZSM-12S at the reaction temperatures between 200 and
00 C. Further, the dealumination of ZSM-12L improved the selec-
◦
tivities particularly at high temperatures. These results indicate
that ZSM-12 channels have high potential for the shape-selective
formation of 4,4 -DIPB: the restriction by the channels can differ-
ꢀ
Fig. 6. The stability of 4,4 -DIPB over ZSM-12L, ZSM-12S, and ZSM-12LD under
ꢀ
propene pressure. Reaction conditions: 4,4 -DIPB: 2.95 g (12.5 mmol); catalyst:
25 mg; temperature: 300 and 350 C; propene pressure: 0.8 MPa, period: 4 h. Leg-
ends: ( ) 4,4 -DIPB; ( ) isomerized DIPB; ( ) IPBP; and ( ) TriIPB.
ꢀ
◦
1
ꢀ
ꢀ
entiate 4,4 -DIPB from other bulky isomers at the transitions states.
ꢀ
However, the selectivities for 4,4 -DIPB were rapidly decreased
to around 20% at 350 C for ZSM-12L and ZSM-12S by the ther-
modynamic controlled isomerization of 4,4 -DIPB, once formed
in ZSM-12 channels, to 3,4 -DIPB at the external acid sites. The
formation of bulky DIPB isomers, 2,x -DIPB also occurred at low
temperatures. The formation of bulky 2,x -DIPB indicates the par-
◦
ꢀ
ZSM-12S, and ZSM-12LD used for the isopropylation of BP at 250
and 300 C. BP was principal component of the encapsulated prod-
ucts in both ZSM-12 zeolites, although the conversions of BP were
0–90% over these zeolites. IPBP and DIPB were only less than 40%,
and afforded almost the same composition irrespective of the tem-
peratures. DIPB isomers were only 10–15% for ZSM-12L, 20% for
ZSM-12S, and around 10% for ZSM-12LD. These results of encapsu-
lated products of ZSM-12 zeolites were quite different from those
of MOR: DIPB isomers contain high amounts in the encapsulated
products of MOR in the isopropylation of BP [10]. We can suggest
that the different features between ZSM-12 and MOR are due to
less availability of ZSM-12 channels for the isopropylation of BP,
and that principal catalytic sites are near pore-entrances.
ꢀ
◦
ꢀ
ꢀ
7
ticipation of kinetic controls. The latter two reactions occurred at
the external acidic ites, because these isomers were preferentially
formed for ZSM-12S compared to ZSM-12L. The increased forma-
ꢀ
ꢀ
tion of 4,4 -DIPB over ZSM-12LD supports the formation of 2,x - and
ꢀ
3
,4 -DIPB occurred at the external acidic sites.
The selectivities for 4,4 -DIPB were highly influenced by the
ꢀ
particle sizes. The differences are ascribed to external acid sites,
because ZSM-12S has higher external surfaces (Table 1). The
external acid sites enhanced kinetic controlled catalysis at lower
ꢀ
temperatures, and the isomerization of 4,4 -DIPB at higher tem-
ꢀ
peratures, resulting in the decrease in the selectivity for 4,4 -DIPB,
3
.3. Mechanistic aspects of the Isopropylation of BP over ZSM-12
particularly over ZSM-12S. These reactions were decreased over
ZSM-12LD after the dealumination of ZSM-12L with preferential
removal of external acid sites without changes of textural proper-
ties.
zeolites
ꢀ
We have studied the relation between the selectivity for 4,4 -
DIPB and pore structure of zeolites, and found that the steric
restriction of zeolite at the transition state of the product iso-
mers, resulting in the formation of the least bulky products [4–7].
The catalysis is kinetic and thermodynamic controlled, resulting in
the predominant formation of bulky products and/or of thermo-
The encapsulated products over ZSM-12S and ZSM-12L show
that a large amount of BP remained unchanged in ZSM-12 chan-
◦
nels although the conversions of BP were 70–90% at 300 C (Fig. 7).
These are quite different results compared to the isopropylation
◦
over MOR: most of BP disappeared over MOR even at 250 C, result-
ꢀ
ing preferential formation of DIPB isomers, particularly 4,4 -DIPB
[
10]. These results indicate that large differences in the availability
of the channels between ZSM-12 (S and L) and MOR: ZSM-12 chan-
nels, particularly deep from pore-entrances, cannot work fully as
active sites, probably due to deficient supply of propene in addition
to narrow channels, and that the channels are not enough wide to
diffuse out/out BP, IPBP, and DIPB isomers, either. We can conclude
that the shape-catalysis occurred at the acidic sites in the channels
near from pore-entrances, although further studies are necessary
on these aspects.
It is interesting to compare the roles of channels of SSZ-24,
MOR, and ZSM-12, with 12-MR straight channels in the isopropy-
lation of BP. Their widths of channels decrease in the order:
SSZ-24 > MOR > ZSM-12 [26]. MOR gave higher selectivities than
SSZ-24 because MOR channels have more effective steric interac-
ꢀ
tion at the transition state of 4,4 -DIPB. However, MOR channels
ꢀ
still allow the formation of bulkier isomer, 3,4 -DIPB, because the
ꢀ
highest selectivities for 4,4 -DIPB are as high as 85–90% [10–12].
Fig. 7. Effects of reaction temperature on the distribution of encapsulated products
in the isopropylation of BP over ZSM-12. Reaction conditions: see Figs. 3–5. Legends:
We expected that the ZSM-12 zeolites can differentiate more
severely 4,4 -DIPB from the other bulkier isomers, particularly,
ꢀ
(
) BP; ( ) IPBP; ( ) DIPB; and ( ) TriIPB.

3
0
A. Chokkalingam et al. / Journal of Molecular Catalysis A: Chemical 367 (2013) 23–30
ꢀ
3
,4 -DIPB, at their transition states than MOR, because ZSM-12
Acknowledgements
has the smallest channels among 12-MR zeolites. However, unex-
ꢀ
pectedly, the selectivities for 4,4 -DIPB over ZSM-12 zeolites were
A part of this work was financially supported by Grant-in-
Aids for Scientific Research ((B) 16310056, (B) 19061107, and (C)
21510098), the Japan Society for the Promotin of Science (JSPS). A.
Vinu thanks the Australian Research Council for the future fellow-
ship and the University of Queensland for the start-up grant.
lower than those of MOR. The results of ZSM-12 zeolites indi-
cate that the channels afford moderately shape-selective formation
of 4,4 -DIPB although the non-selective catalysis, particularly the
formation of 2,x -DIPB, occurred at the external acid sites. The
formation of 4,4 -DIPB occurred primarily in the channels, prob-
ꢀ
ꢀ
ꢀ
ably near the pore-entrances, not so deep in the channels as
discussed above. We consider that ZSM-12 channels are mod-
erately shape-selective to fit transition states to 4,4 -DIPB for a
highly shape-selective catalysis. However, the channels are a lit-
tle bit narrow for the isopropylation of BP to occur only inside
them, and to exclude them at the external acid sites. It is impor-
tant that the appropriate steric restriction at the transition states
of the bulky isomers by the zeolite channels excludes bulky
products for the selective formation of the least bulky products
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