Preparation of [Fe]-SSZ-24 through the isomorphous substitution of [B]-SSZ-24 with iron, and its catalytic properties in the isopropylation of biphenyl

Article abstract of DOI:10.1016/j.molcata.2011.08.027

[Fe]-SSZ-24, a ferrosilicate with AFI topology, was prepared through an isomorphous substitution of [B]-SSZ-24 with iron, and applied for the isopropylation of biphenyl (BP) to understand the mechanism of shape-selective catalysis. The substitution of [B]-SSZ-24 with an aqueous solution of a limited amount of Fe(NO₃)₃·6H₂O effectively gave [Fe]-SSZ-24, and its XRD gave clear patterns of AFI topology without the peaks assigned to Fe₂O₃. [Fe]-SSZ-24 exhibited enhanced catalytic activity for the isopropylation of BP. Shape-selective formation of 4,4′-diisopropylbiphenyl (4,4′-DIPB) occurred at moderate temperatures (250-300 °C); however, the decreases of the selectivity for 4,4′-DIPB occurred at high temperatures (325-350 °C). On the other hand, the selectivities for 4,4′-DIPB in encapsulated products remained almost constant (ca 75%), irrespective of the reaction temperature and the SiO₂/Fe₂O₃ ratios. The differences in the selectivities for 4,4′-DIPB between bulk and encapsulated products indicate that shape-selective formation of 4,4′-DIPB occurs in the [Fe]-SSZ-24 channels, and these channels prevent the isomerization of 4,4′-DIPB, even at 350 °C. These results suggest that the channels of SSZ-24 can discriminate 4,4′-DIPB from other possible DIPB isomers at their transition states although high reaction temperatures cause isomerization at external acid sites. Large pore molecular sieves of AFI topology, [Fe]-SSZ-24, [Al]-SSZ-24, MgAPO-5, ZnAPO-5, and SAPO-5, gave similar levels of selectivities for 4,4′-DIPB in the isopropylation of BP. These results indicate that the framework of AFI topology primarily controls shape-selective formation of 4,4′-DIPB, although catalytic activities of the materials were dependent on acidic properties.

Full text of DOI:10.1016/j.molcata.2011.08.027

Journal of Molecular Catalysis A: Chemical 350 (2011) 1–8
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Editor’s choice paper
Preparation of [Fe]-SSZ-24 through the isomorphous substitution of [B]-SSZ-24
with iron, and its catalytic properties in the isopropylation of biphenyl
Hiroaki Kawagoea, Kenichi Komuraa, Jong-Ho Kimb, Gon Seob, Yoshihiro Sugia,∗
a Department of Material Science and Technology, Faculty of Engineering, Gifu University, Gifu 501-1193, Japan
b School of Applied Chemical Engineering, Chonnam National University, Gwangju 500-757, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 July 2011
Received in revised form 30 August 2011
Accepted 30 August 2011
Available online 7 September 2011
[Fe]-SSZ-24, a ferrosilicate with AFI topology, was prepared through an isomorphous substitution of [B]-
SSZ-24 with iron, and applied for the isopropylation of biphenyl (BP) to understand the mechanism of
shape-selective catalysis. The substitution of [B]-SSZ-24 with an aqueous solution of a limited amount
of Fe(NO3)3·6H2O effectively gave [Fe]-SSZ-24, and its XRD gave clear patterns of AFI topology without
the peaks assigned to Fe2O3. [Fe]-SSZ-24 exhibited enhanced catalytic activity for the isopropylation
of BP. Shape-selective formation of 4,4ꢀ-diisopropylbiphenyl (4,4ꢀ-DIPB) occurred at moderate tempera-
tures (250–300 ◦C); however, the decreases of the selectivity for 4,4ꢀ-DIPB occurred at high temperatures
(325–350 ◦C). On the other hand, the selectivities for 4,4ꢀ-DIPB in encapsulated products remained almost
constant (ca 75%), irrespective of the reaction temperature and the SiO2/Fe2O3 ratios. The differences in
the selectivities for 4,4ꢀ-DIPB between bulk and encapsulated products indicate that shape-selective for-
mation of 4,4ꢀ-DIPB occurs in the [Fe]-SSZ-24 channels, and these channels prevent the isomerization of
4,4ꢀ-DIPB, even at 350 ◦C. These results suggest that the channels of SSZ-24 can discriminate 4,4ꢀ-DIPB
from other possible DIPB isomers at their transition states although high reaction temperatures cause
isomerization at external acid sites.
Keywords:
SSZ-24
Isomorphous substitution
Isopropylation
Biphenyl
Shape-selective catalysis
Large pore molecular sieves of AFI topology, [Fe]-SSZ-24, [Al]-SSZ-24, MgAPO-5, ZnAPO-5, and SAPO-5,
gave similar levels of selectivities for 4,4ꢀ-DIPB in the isopropylation of BP. These results indicate that the
framework of AFI topology primarily controls shape-selective formation of 4,4ꢀ-DIPB, although catalytic
activities of the materials were dependent on acidic properties.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
and over three-dimensional zeolites with 12-MR pore entrances
from the aspects of steric restriction at the transition states of the
Large pore molecular sieves (LPMS) including zeolites, met-
allosilicates, and metallophosphates are the most promising
microporous crystals for achieving highly shape-selective catalysis
because their pores are uniformly distributed and because they
have dimensions that allow both organic reactants and products
to enter, to be accommodated, and to leave [1–5]. Among them,
LPMS with 12- and 14-membered ring (12- and 14-MR) entrances
are expected for the catalysts of the alkylation of polynuclear
aromatics [3–20]. For example, dealuminated H-mordenite (MOR)
selectively gave 4,4ꢀ-diisopropylbiphenyl (4,4ꢀ-DIPB) in the iso-
propylation of biphenyl (BP) [3,5–8]. It has been of great interest to
elucidate the catalytic features of the LPMS pores because confined
circumstances of the materials highly influence shape-selective
catalysis. Recently, we studied the alkylation of BP over various
zeolites with one-dimensional 12-MR and 14-MR pore entrances
product isomers in the channels [9–17].
SSZ-24 is a high-silica LPMS isostructural with AlPO4-5 (AFI
topology) with 12-membered ring cylindrical channels and pore
entrances of 0.72 nm radii [21]. Zones et al. first synthesized SSZ-
24 in its pure-silica form using 1-trimethylammonioadamantane
as a structure-directing agent (SDA) [22]. The borosilicate version
([B]-SSZ-24) was subsequently synthesized using a calcined form
of boron-substituted zeolite ␤ ([B]-BEA) as the boron and silicon
sources [23]. Lobo and Davis also reported the synthesis of [B]-
SSZ-24 using N(16)-methylasparteinium bromide [MeSPA]+Br− as
the SDA and sodium borate as the source of boron, and they
converted to [Al]-SSZ-24 by an isomorphous substitution with alu-
minum nitrate [24]. More recently, we developed a new method of
[Al]-SSZ-24 by phase transformation of zeolite ␤ ([Al]-BEA) using
[MeSPA]+OH− as the SDA [25].
It is important to understand how the zeolite properties, such as
structure of channels and acidity, influences shape-selective cataly-
sis. In particular, we have been interested in the catalytic properties
of isostructural LPMS with AFI topology in the isopropylation of BP,
∗
Corresponding author.
E-mail address: ysugi@gifu-u.ac.jp (Y. Sugi).
1381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.08.027

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H. Kawagoe et al. / Journal of Molecular Catalysis A: Chemical 350 (2011) 1–8
Table 1
because they have slightly bigger pore entrances and channels com-
pared to MOR. We have studied the isopropylation of BP over LPMS
with AFI topology, [Al]-SSZ-24, MgAPO-5, ZnAPO-5, and SAPO-5,
and discussed that the topology is a key factor in shape-selective
formation of 4,4ꢀ-DIPB [18–20]. It is also important to elucidate the
influences of acidic properties of zeolites on shape-selective catal-
ysis. We consider that [Fe]-SSZ-24 is an appropriate candidate to
study the influences of acidity on shape-selective catalysis in AFI
channels, because [Fe]-SSZ-24 has AFI topology with weak acidity.
In this paper, we studied the preparation of [Fe]-SSZ-24 by an
isomorphous substitution of [B]-SSZ-24 with iron, and applied it for
the isopropylation of BP to elucidate the relation between the acidic
and catalytic properties and to determine the role of topology and
acidity in shape-selective catalysis through comparison to other
isostructural LPMS with AFI topology.
Textural properties of [Fe]-SSZ-24 zeolites.
SiO2/B2O3
SiO2/Fe2O3
Surface area
(m2/g)
Pore volume
(cm3/g)
Calcined
Deboronated
53
361
–
–
379
343
0.16
0.14
F1
F3
F5
–
–
–
53
38
28
421
261
191
0.21
0.10
0.067
C3
C5
–
–
6.5
3.1
380
327
0.15
0.14
containing BP and the catalyst was purged with nitrogen before
heating. After reaching the reaction temperature, propene was
introduced to the autoclave, and the reaction was started by agita-
tion. The pressure was kept constant throughout the reaction. After
cooling the autoclave and release of excess propene, the catalysts
were filtered off, and the bulk products were diluted with toluene.
The products were analyzed by a Gas Chromatograph (GC-14C or
GC-18A, Shimadzu Corporation, Kyoto, Japan) equipped with an
Ultra-1 capillary column (25 m × 0.2 mm, 0.25 ␮m thickness, Agi-
lent Technologies, MA, U.S.A.) and confirmed by a Shimadzu Gas
Chromatograph-Mass Spectrometer (GC-MS-5000) using the same
type column.
The yield of each product was calculated on the basis of the
amount of starting BP, and the selectivities for each isopropy-
lbiphenyl (IPBP) and diisopropylbiphenyl (DIPB) isomers were
expressed according to the total amounts of each IPBP and DIPB
isomers, respectively.
The analysis of the encapsulated products in the catalyst used
for the reaction was carried out as follows. The catalyst was fil-
tered off, washed with 200 ml of acetone, and dried at 110 ◦C for
12 h. Then, 50 mg of the resultant catalyst was carefully dissolved
in 3 ml of aqueous hydrofluoric acid (47%) at room temperature.
This solution was basified with solid potassium carbonate, and was
extracted three times with 20 ml of dichloromethane. After remov-
ing the solvent in vacuo from the collected organic phases, the
residue was dissolved in 5 ml of toluene and was subjected to a
GC analysis following the same procedure as for the bulk products.
2. Experimental
2.1. Synthesis of [Fe]-SSZ-24
[B]-SSZ-24 was synthesized by hydrothermal condi-
tions using [MeSPA]+OH− according to
a
procedure in the
literature [23]. The typical gel composition is as follows
SiO2:[MeSPA]+OH−:NaOH:B2O3:H2O = 1:0.2:0.1:0.04:50.
SiO2
(Carb-O-Sil M5) 0.608 g, [MeSPA]+OH− 2.9125 g, Na2B4O7·10H2O
0.0766 g, 32 wt.% NaOH solution 0.0791 g, water 6.5474 g, and
[B]-BEA (SiO2/B2O3 = 50) 0.0125 g as seeds were placed in Teflon
container, and resultant gel was stirred during 3 h. Then, the
gel was transferred to Teflon-lined autoclave, heated at 175 ◦C
during 6 d. After the crystallization was completed, the autoclave
was cooled to room temperature. The obtained BEA zeolite was
collected, washed thoroughly with water, and dried overnight at
room temperature. The resultant zeolites were heated in a flow of
air (50 ml/min) with temperature programmed rate of 2 ◦C/min up
to 650 ◦C, and calcined for 6 h under an air stream (50 ml/min). [B]-
SSZ24 with 53.0 of SiO2/B2O3 was obtained. [B]-SSZ-24 (1.0 g) was
then deboronated by stirring with 100 ml of 0.01N hydrochloric
acid for 1 d. Then, resulting [B]-SSZ-24 after calcination at 650 ◦C
was converted to [Fe]-SSZ-24 according to analogous method for
the transformation of [B]-SSZ-24 to [Al]-SSZ-24 [24]. [B]-SSZ-24
was heated at 80 ◦C with an aqueous Fe(NO3)3 solution (1:0.5:50
(weight ratio) [B]-SSZ-24:Fe(NO3)3·9H2O:H2O) for 18 h with stir-
ring. After cooling the mixture, the solid was filtered and washed
two times with 0.5 mol/l hydrochloric acid. Then, the resultant
sample was dried at 40 ◦C overnight and calcined at 550 ◦C for
6 h. The samples with n times repetitions of the substitution with
Fe(NO3)3/[B]-SSZ-24 = 0.5 were abbreviated Fn (n = 1–5). Thus, F1,
F3, and F5 were used as catalysts. The SiO2/Fe2O3 ratios of F1, F3,
and F5 were 55, 38, and 28, respectively.
2.3. Characterization of the zeolites
Crystal structures of the zeolite were determined by powder X-
ray diffraction using a Shimadzu XRD-6000 with Cu K␣ radiation
Isomorphous substitution of [B]-SSZ-24 with the ratio of [B]-
SSZ-24:Fe(NO3)3·9H2O:H2O (1:2.0:50 weight) was also examined
to know the influence of the co-precipitation of ferric hydroxide on
the zeolite. The obtained solid was filtered and washed two times
with water. Then, the resultant sample was dried at 40 ◦C overnight
and was calcined at 550 ◦C for 6 h. The samples of the zeolites with
Fe(NO3)3/[B]-SSZ-24 = 2.0 were abbreviated Cn (n = 1–5).
˚
(ꢀ = 1.5418 A). An elemental analysis was performed by inductive
coupled plasma atomic emission spectroscopy on a JICP-PS-1000
UV (Leeman Labs Inc., CA, USA). Scanning electron microscopy
(SEM) was recorded by using an S-4300 FE-SEM microscope
(Hitachi Corporation, Tokyo, Japan). N2 adsorption measurements
were performed on a Belsorp 28SA (Bel Japan, Osaka, Japan).
Ammonia-temperature programmed desorption (NH3-TPD) was
measured using a TPD-66 apparatus (Bell Japan). Here, the cata-
lyst was evacuated at 400 ◦C for 1 h, and ammonia was adsorbed
at 100 ◦C, followed by further evacuation for 1 h. Then, the sample
was heated from 100 to 710 ◦C at a rate of 10 ◦C/min under a helium
stream. A TG analysis was performed using a Shimadzu TG-DTG-50
analyzer with a temperature-programmed rate of 10 ◦C/min in an
air stream. The adsorption of o-xylene was measured by a gravimet-
ric method using a microbalance at 25 ◦C and after the evacuation
of the sample at 500 ◦C.
The textual properties of [Fe]-SSZ-24 prepared by isomorphous
substitution of [B]-SSZ-24 are summarized in Table 1.
2.2. Isopropylation of BP
The isopropylation of BP was carried out in a 100-ml SUS-
316 autoclave under propene pressure. Typical reaction conditions
were 3.9 g of biphenyl (25 mmol) and 0.125 g of the catalyst with
0.8 MPa propene pressure at 250–350 ◦C for 4 h. An autoclave

H. Kawagoe et al. / Journal of Molecular Catalysis A: Chemical 350 (2011) 1–8
3
Fig. 1. Isomorphous substitution of [B]-SSZ-24 to [Fe]-SSZ-24. Substitution condi-
tions: [B]-SSZ-24:Fe(NO3)3·9H2O:H2O = 1:0.5:50 (weight ratio); temperature, 80 ◦C;
and period, 18 h. Legends: S: starting gel; A: as-synthesized [B]-SSZ-24; B: calcined
[B]-SSZ-24; C: deboronated [B]-SSZ-24; F1, F3, F5: sample of repetition times of
substitution.
3. Results and discussion
Fig. 2. XRD pattern of as-synthesized and calcined [B]-SSZ-24 and [Fe]-SSZ-24.
Substitution conditions: F1, F3, and F5: [B]-SSZ-24:Fe(NO3)3·9H2O:H2O = 1:0.5:50
(weight ratio). C3 and C5: [B]-SSZ-24:Fe(NO3)3·9H2O:H2O = 1:2.0:50 (weight ratio).
Temperature: 80 ◦C; period: 18 h.
3.1. Preparation and properties of [Fe]-SSZ-24
[B]-SSZ-24 (SiO2/B2O3 = 53; B2O3/SiO2 = 0.0377) was prepared
under hydrothermal conditions by using [MeSPA]+OH− as the SDA
according to the methods in the literature [24]. [Fe]-SSZ-24 was
then prepared from deboronated [B]-SSZ-24 by isomorphous sub-
stitution with ferric nitrate by the similar methods for [Al]-SSZ-24
[24].
of the original [B]-SSZ-24, and a new diffraction at around 36◦
appeared for C3 and C5. This weak diffraction is due to Fe2O3 with
poor crystallinity [27], which results in no observation of the other
peaks. These results also mean that an efficient substitution of B to
Fe occurred by the substitution when the ratio of Fe(NO3)3/[B]-SSZ-
24 was 0.5; however, severe precipitation of ferric hydroxide due to
the hydrolysis of Fe3+ occurred at a ratio of 2.0 for Fe(NO3)3/SSZ-24.
We must note that the deposition of ferric hydroxide and the result-
ing Fe2O3 formation probably occurred even for the substitution
using small amounts of ferric nitrate by our method.
SEM images of [Fe]-SSZ-24 prepared by isomorphous substitu-
tion of [B]-SSZ-24 shown in Fig. 3 support the results discussed
above. Clear crystal images were observed for F1 and F3; however,
the crystals were accompanied by small particles in F5. Moreover,
Fe2O3 particles were observed for C3; however, these Fe2O3 parti-
cles are almost amorphous judging from their XRD patterns.
Fig. 4 shows the N2 adsorption isotherms of [Fe]-SSZ-24. F1 and
F3 adsorbed large amounts of N2 compared with the original [B]-
SSZ-24; however, the further substitution in F5 was accompanied
by a decrease in N2 adsorption. On the other hand, N2 adsorption
on C3 and C5 decreased much more than that on [B]-SSZ-24. These
results suggest that the site due to B species in F1 and F3 were
substituted with ferric-cation without significant choking from the
Fe2O3 particles. Unfortunately, the formation of the precipitate by
repetitive substitution procedure eventually caused a choke of the
channels of the zeolite. This result was clearly seen in C3 and C5
after the calcination. Thus, the substitution with the least formation
of ferric hydroxide can be achieved by using an appropriate amount
of the Fe(NO3)3 solution.
It is important to choose the appropriate amount of aque-
ous solution of Fe(NO3)3·9H2O for effective substitution on the
framework of [B]-SSZ-24 to form [Fe]-SSZ-24 because the Fe3+
cations in the nitrate could be easily hydrolyzed to an ferric clus-
ter, and precipitated as ferric hydroxide [26]. Fig. 1 shows the
influence of the boron and iron contents on the substitution with
Fe(NO3)3·9H2O/[B]-SSZ-24 = 0.5 (weight ratio). The boron content
of [B]-SSZ-24 decreased rapidly by deboronation and substitution,
and the SiO2/Fe2O3 ratios for [Fe]-SSZ-24 were 55, 38, and 28
for F1, F3, and F5 samples, respectively. The color of these sam-
ples was pale off-white to yellow after calcination at 550 ◦C for
6 h. These results suggest that the substitution was accompanied
by the precipitation of ferric hydroxide during the treatment of
the ferric nitrate solution with [B]-SSZ-24. In other words, the
incorporation of the Fe species with frameworks accompanies the
formation of ferric hydroxide, independently from the substitu-
tion with zeolites. Actually, a large amount of Fe2O3 particles were
found by SEM observation for calcined C3 samples substituted with
Fe(NO3)3·9H2O/[B]-SSZ-24 = 2. Resultant C3 and C5 samples had
much lower SiO2/Fe2O3 ratios than F3 and F5 samples, as shown in
Fig. S1 in Supporting Information. However, particle sizes of Fe2O3
cannot be estimated because the peaks due to them are too weak.
These results mean that the precipitation of the ferric hydroxide,
leading to Fe2O3 by calcination, occurred simultaneously during the
substitution of [B]-SSZ-24 or the Fe incorporation into the voids of
the frameworks formed by deboronation. These materials, C3 and
C5, are brown in color after the calcination. The textural proper-
ties of the [Fe]-SSZ-24 prepared by isomorphous substitution are
shown in Table 1.
Fig. 5 shows the adsorption of o-xylene on [B]-SSZ-24 and [Fe]-
SSZ-24 (F1 and F3). [B]-SSZ-24 and F3 rapidly adsorbed o-xylene,
which is indicative of LPMS. The results mean that o-xylene can
adsorb rapidly into the channels of F3 and [B]-SSZ-24, and that the
channels of F3 are not choked severely by Fe2O3 due to cluster for-
mation. On the other hands, the adsorption on C3 was less than
that of F3 and [B]-SSZ-24. This decrease means that some of the
pore entrances of C3 were choked or narrowed by Fe2O3 formation.
Fig. 2 shows the XRD pattern of the calcined [Fe]-SSZ-24
samples. F1, F3, and F5 have almost the same patterns as the
as-synthesized and calcined [B]-SSZ-24; however, the peaks of [Fe]-
SSZ-24 for C3 and C5 were relatively small compared with those

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H. Kawagoe et al. / Journal of Molecular Catalysis A: Chemical 350 (2011) 1–8
Fig. 3. SEM image of [Fe]-SSZ-24.
These results mean that the substitution of B to Fe is not a rapid pro-
cess compared with the precipitation of ferric hydroxide at the sur-
face of the extra-framework by the hydrolysis of the ferric cations.
NH3-TPD was measured to know the acidity of [Fe]-SSZ-24. F3
only gave a peak at 200 ◦C (Fig. 6). The peak is so-called l-peak due
to the physically adsorbed NH3, probably on Fe2O3, which has no
acidic properties [28]. This result indicates that [Fe]-SSZ-24 does
not have acidity which can be estimated by NH3-TPD. That is, Fe3+
incorporated in the framework of [Fe]-SSZ-24 has much weaker
acidity than Al3+ of [Al]-SSZ-24 previously reported [10,25].
The overall results for the preparation of [Fe]-SSZ-24 by iso-
morphous substitution can summarized as follows: [B]-SSZ-24
afforded [Fe]-SSZ-24 by isomorphous substitution with ferric
nitrate. However, the hydrolysis of ferric cation inevitably accom-
panies the formation of ferric hydroxide, which gave Fe2O3 after
Fig. 4. N2 adsorption isotherm of [Fe]-SSZ-24.
Fig. 5. o-Xylene adsorption of [Fe]-SSZ-24.

H. Kawagoe et al. / Journal of Molecular Catalysis A: Chemical 350 (2011) 1–8
5
from the precipitated ferric hydroxide by the calcination at 550 ◦C
had no activities for the isopropylation of BP at 250 ◦C. On the other
hands, [Fe]-SSZ-24 enhanced effectively the catalytic activity for
the isopropylation of BP. F1, F3, and F5 had high activities and gave
IPBP, DIPB, and triisopropylbiphenyl (TriIPB) isomers, although the
catalytic activities were much less than those of [Al-SSZ-24 previ-
ously reported [10,15]. Furthermore, the activities of [Fe]-SSZ-24
increased with decreasing the SiO2/Fe2O3 ratio, which means that
acid mounts increase by the substitution. These activities also show
that [Fe]-SSZ-24 works as an acid catalyst even though its acidity
was not observed by NH3-TPD and that the weak acid sites, due to
Fe3+ incorporated to the SSZ-24 frameworks, work for the catalyst
in the isopropylation of BP. These results mean that the isopropyla-
tion of BP occurred solely on [Fe]-SSZ-24, and not on iron species at
the extra-framework. However, the activities of F1, F3, and F5 are
much lower than those of the [Al]-SSZ-24 catalysts described pre-
viously [10,15]: these results are due to the differences in acidity
for Al and Fe in the frameworks.
The effects of the reaction temperature and of the SiO2/Fe2O3
ratio of [Fe]-SSZ-24 on the selectivities for DIPB isomers are shown
in Fig. 8. The selectivities for 4,4ꢀ-DIPB were maintained around
75% at moderate temperatures (250–300 ◦C) for all [Fe]-SSZ-24;
however, they decreased at higher temperatures (325–350 ◦C),
accompanying an increase in the selectivities for 3,4ꢀ-DIPB. The
decrease in the selectivity for 4,4ꢀ-DIPB started at low tempera-
tures for the [Fe]-SSZ-24 sample with a low SiO2/Fe2O3 ratio. Thus,
the increase in acid sites on the catalyst enhanced the isomeriza-
tion of 4,4ꢀ-DIPB to 3,4ꢀ-DIPB. On the other hands, the selectivities
for 4,4ꢀ-DIPB in encapsulated products were almost constant at
75%, irrespective of the SiO2/Fe2O3 ratio. These results mean that
the acid sites in the channels of [Fe]-SSZ-24 were not active for
the isomerization of 4,4ꢀ-DIPB and that the isomerization occurred
probably on the external acid sites on the [Fe]-SSZ-24 catalyst, as
proposed in previous papers for MOR [3,5,8,10].
Fig. 6. NH3-TPD profile of [Fe]-SSZ-24 (F3). Temperature-programmed rate:
10 ◦C/min.
calcination during the isomorphous substitution. The formation
of the hydroxide occurs independently from the zeolites or at the
extra-framework site on the internal and external surfaces of the
zeolites. Actually, Fe2O3/SiO2 ratios of [Fe]-SSZ-24 shown in Fig. 1
are in the higher levels as B2O3/SiO2 ratio of [B]-SSZ-24. These
results suggest that ferric hydroxide is formed during the substitu-
tion. The optimization of the ratio of Fe(NO3)3·9H2O to [B]-SSZ-24
is important for minimization of the formation of ferric hydroxide
and for maximization of Fe3+ species in the framework. However,
it is difficult to evaluate the amount of Fe3+ in the framework in
all of the iron species of [Fe]-SSZ-24. From these consideration,
the isomorphous substitution in this study was carried out at
0.5 of Fe(NO3)3·9H2O/[B]-SSZ-24 ratio although some of Fe2O3
was accompanied. We examine the isopropylation of BP over
[Fe]-SSZ-24 to confirm the formation of Fe3+ in the framework of
[Fe]-SSZ-24 and to evaluate the acid properties and effectiveness
for shape-selective catalysis in the channels of the [Fe]-SSZ-24.
Fig. 9 shows the amount of coke formation on [Fe]-SSZ-24 during
in the isopropylation of BP. It was found to be at a level of 5–9 wt.%,
irrespective of the SiO2/Fe2O3 ratio. Coke formation occurred on
the internal and external acid sites of [Fe]-SSZ-24.
Highly selective formation of 4,4ꢀ-DIPB shows that catalysis
occurred in the [Fe]-SSZ-24 channels because of their shape-
selective nature and that the isomorphous substitution with ferric
nitrate incorporated the formation of a framework Fe3+ species of
the [Fe]-SSZ-24.
3.2. Isopropylation of BP over [Fe]-SSZ-24
Fig. 10 shows the effects of the SiO2/Fe2O3 ratio on the selec-
tivities for DIPB isomers in the isopropylation of BP at 250 ◦C and
300 ◦C. Here, the selectivities for 4,4ꢀ-DIPB were around 80% for all
Fig. 7 shows the influence of reaction temperature on the yield of
the isopropylated products in the isopropylation of BP over F1, F3,
and F5 (SiO2/Fe2O3 = 55, 38, and 28). [B]-SSZ-24 and Fe2O3 prepared
Fig. 7. Effects of reaction temperature on the isopropylation of BP over [Fe]-SSZ-24. Reaction conditions: BP, 3.9 g (25 mmol); catalyst, 0.125 g; temperature, 200–350 ◦C;
propene pressure, 0.8 MPa; period, 4 h. Legends: (ꢀ) conversion (BP); (ꢁ) IPBP; (᭹) DIPB; (ꢂ) triIPB.

6
H. Kawagoe et al. / Journal of Molecular Catalysis A: Chemical 350 (2011) 1–8
Fig. 8. Effects of reaction temperature on the selectivity for DIPB isomers in the isopropylation of BP over [Fe]-SSZ-24. Reaction conditions: see Fig. 7. Legends: (ꢁ) 4,4ꢀ-DIPB
in bulk products; (ꢃ) 4,4ꢀ-DIPB in encapsulated products; (᭹) 3,4ꢀ-DIPB; (ꢁ) 3,3ꢀ-DIPB.
[Fe]-SSZ-24 catalysts (F1, F2 and F3); however, the selectivities for
4,4ꢀ-DIPB at 300 ◦C decreased with the decrease in the ratio. The
increase in acidity by the isomorphous substitution resulted in the
decrease in the selectivity for 4,4ꢀ-DIPB.
Catalytic features of [Fe]-SSZ-24 in the isopropylation of BP
clearly indicate that the catalysis occurred on the acid sites
appeared on Fe3+ incorporated in the frameworks of [Fe]-SSZ-24,
where iron species at the extra-frameworks formed from ferric
hydroxide during the substitution with ferric nitrate have no influ-
ences on the catalytic activities of [Fe]-SSZ-24, and that the weak
acid sites of [Fe]-SSZ-24 worked as a catalyst for the isopropyla-
tion of BP although the NH3-TPD indicate no strong acidities on
[Fe]-SSZ-24.
3.3. Shape-selective catalysis over LPMS with AFI topology
Catalytic performances of LPMS for shape-selective catalysis are
generally varied with many factors. Some typical factors are pore
Fig. 9. Effects of reaction temperature on coke formation on [Fe]-SSZ-24 during the
isopropylation of BP. Reaction conditions: see Fig. 6.
structure, physical properties, such as crystal size, morphology, and
acidity, type of components, and the distribution of active species,
which are also influenced by preparation and post-synthesis meth-
ods. Reaction conditions, such as temperature, pressure, period, and
catalyst amount, can also influence catalytic performances. How-
ever, pore structure is the most important factor in controlling
the shape-selectivity of the catalysis. Particularly, the differences
in selectivity for 4,4ꢀ-DIPB reflect the pore structures of the corre-
sponding zeolites.
Shape-selective catalysis is highly dependent on the confined
structure of the zeolites, including the size and shape of the
pore entrances and channels. We previously proposed that shape-
selective alkylation of BP over MOR occurred inside straight
channels [3,5,8]. These results mean that the least bulky isomers
with the transition states, that could fit in the MOR channels, only
appeared as products. In other words, isopropylation of BP allows
for the formation of 4-IPBP from BP and 4,4ꢀ-DIPB from 4-IPBP by
the steric restriction of the transition states in the MOR channels.
These features suggest that shape-selective catalysis selectively
occurs to yield the least bulky molecule if pore environments
exclude the transition sates of bulky isomers. However, the forma-
tion of other bulky isomers can also allow inside the zeolite if the
pore environment is large enough for the formation of the transi-
tion state to bulky DIPB isomers. Thus, the steric interactions of the
isomers with the channels differentiate the transition states dur-
ing the formation of DIPB isomers in the isopropylation of BP over
Fig. 10. Effects of the SiO2/Fe2O3 ratio of [Fe]-SSZ-24 on the selectivities for DIPB
isomers at 250 and 300 ◦C in the isopropylation of BP. Reaction conditions: see Fig. 7.
Legends: ( ) conversion. ( ) 4,4ꢀDIPB; (ꢃ) 3,4-DIPB; ( ) 3,3ꢀ-DIPB; ( ) 2,x-DIPB.
(For interpretation of the references to color in this figure legend, the reader is
referred to the web version of the article.)

H. Kawagoe et al. / Journal of Molecular Catalysis A: Chemical 350 (2011) 1–8
7
of 4,4ꢀ-diisopropylbiphenyl (4,4ꢀ-DIPB) occurred at moderate tem-
peratures (250–300 ◦C); however, the decrease in the selectivity
for 4,4ꢀ-DIPB was observed at high temperatures (325–350 ◦C).
The selectivity for 4,4ꢀ-DIPB in the encapsulated DIPB isomers was
almost constant at all temperatures, irrespective of the SiO2/Fe2O3
ratio. These results mean that the AFI channels have a high potential
for discrimination of 4,4ꢀ-DIPB from the other possible DIPB iso-
mers at their transition states, and that the channels of [Fe]-SSZ-24
prevent the isomerization of 4,4ꢀ-DIPB, although the isomerization
occurred at external acids sites at higher temperatures.
LPMS with AFI topology, [Fe]-SSZ-24, [Al]-SSZ-24, MgAPO-5,
ZnAPO-5, and SAPO-5, gave similar levels of the selectivity for
4,4ꢀ-DIPB in the isopropylation of BP. These results indicate that
the framework of the materials primarily governs shape-selective
catalysis in the isopropylation of BP; however, their activities are
due to their Fe3+ incorporated acidic sites.
The results discussed in the paper proved that the isomorphous
substitution of [B]-SSZ-24 with iron successfully incorporated with
the frameworks of [Fe]-SSZ-24; however, the formation of Fe2O3
cannot be prevented completely on the internal and external
surfaces of the zeolites or independently from the zeolites. The cat-
alytic features of [Fe]-SSZ-24 in the isopropylation of BP clearly
show that the catalysis occurred on acid sites appeared from Fe3+
incorporated to the framework, where iron species at the extra-
frameworks formed from ferric hydroxide during the substitution
with ferric nitrate have no influences on catalytic properties of [Fe]-
SSZ-24. Furthermore, investigations are now underway to establish
an effective isomorphous substitution of boron to Fe3+ species in
the framework of the zeolites for the development of catalysts with
high performance.
Fig. 11. Selectivities for 4,4ꢀ-DIPB in the isopropylation of BP over LPMS with AFI
topology. Reaction conditions: see Refs. [15,18–20]. Legend: see Fig. 10.
MOR, which results in the enhancement of selective formation of
the slimmest 4,4ꢀ-DIPB.
Fig. 11 summarizes the selectivities for the DIPB isomers in the
isopropylation of BP over LPMS with AFI topology, where the val-
ues of the selectivities were the highest selectivities for 4,4ꢀ-DIPB
[10,15,18–20,25]. As shown in Fig. 11, the selectivities for 4,4ꢀ-
DIPB were almost at the same level as 65–75% for all the LPMS,
[Fe]-SSZ-24, [Al]-SSZ-24 [10,15,25], MgAPO-5 [18], ZnAPO-5 [19],
and SAPO-5 [20] with AFI topology, which commonly have straight
channels with 0.72 × 0.72-nm pore entrances. These results of the
selectivity for 4,4ꢀ-DIPB of the LPMS indicate that their confined
structures control the catalysis by their steric restriction of the
transition states to form the least bulky 4,4ꢀ-DIPB from the other
isomers. The results shown in Fig. 11 suggest that the acidities of
the LPMS are not principal factors for controlling shape-selective
catalysis because these materials had quite different acid strengths
and amounts.
Acknowledgements
A part of this work was financially supported by Grant-in-
Aids for Scientific Research ((B) 16310056, (B) 19310060, and (C)
21510098)), the Japan Society for the Promotion of Science (JSPS).
Y.S. would also like to thank Dr. Ajayan Vinu of the National Insti-
tute of Materials Science (NIMS) for his helpful discussion and the
Department of Research, Nagoya Industrial Science Research Insti-
tute for their continuing cooperation.
The selectivities for 4,4ꢀ-DIPB over LPMS with AFI topology were
slightly lower than that over MOR (65–75% for AFI and 80–90% for
MOR). The differences of the selectivities are due to the difference of
their pore structures. MOR channels strictly differentiate the tran-
sition state of bulkier 3,4ꢀ-DIPB from that of 4,4ꢀ-DIPB because MOR
has a slightly bigger channels than LPMS with AFI topology.
As discussed above, the decreases in the selectivities for 4,4ꢀ-
DIPB were observed in the isopropylation of BP over [Fe]-SSZ-24 at
high temperatures (325–350 ◦C). However, the selectivities for 4,4ꢀ-
DIPB in encapsulated products remained constant even at 350 ◦C
for all of the [Fe]-SSZ-24. These results mean that the [Fe]-SSZ-24
channels can prevent the isomerization of 4,4ꢀ-DIPB and that the
isomerization of 4,4ꢀ-DIPB occurs at external acid sites. Similar pre-
vention of isomerization of 4,4ꢀ-DIPB was observed for MOR [3,5,8].
However, we also previously described that the isomerization of
4,4ꢀ-DIPB occurred at both the acid sites in internal and exter-
nal sites in the isopropylation of BP over [Al]-SSZ-24 and SAPO-5
[8,10,20]. The main differences are the acidic properties of these
LPMS with AFI topology because [Fe]-SSZ-24 has only weak acid
sites in their channels compared to the others.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molcata.2011.08.027.
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