Lanthanoid exchanged mordenites as catalysts for the isopropylation of biphenyl

Article abstract of DOI:10.1246/bcsj.20110022

Liquid-phase isopropylation of biphenyl (BP) with propene was studied to understand the acidities resulting from lanthanoid exchanged sodium mordenite (Ln,NaMOR; Ln: La, Ce, Pr, Sm, Dy, and Yb). The acidities of La³⁺ exchanged sodium mordenite (La,NaMOR) appeared at around 0.60-.8 exchange calculated from La/3Al molar ratio. Similar acidities appeared with all Ln,NaMORs. The resultant zeolites have Bronsted acidic sites appearing near unsaturated lanthanoid cations. The isopropylation of BP predominantly afforded 4,4'-diisopropylbiphenyl (4,4'-DIPB) among DIPB isomers over all Ln,NaMORs. These catalyses occur on the acidic sites in the channels. The exchanged catalysts had high selectivities for 4,4'-DIPB even at temperatures as high as 300 °C although the selectivities decreased by the isomerization of 4,4'-DIPB over H-mordenite (HMOR) with similar SiO₂/Al ₂O₃ ratio. These results indicate the external acid sites are lowly active for the isopropylation of BP and the isomerization of 4,4'-DIPB. The combustion of coke-deposits on Ln,NaMORs, particularly Ce,NaMOR, used for the isopropylation occurred at lower temperatures than that on HMOR because the lanthanoids dispersed in MOR channels work as an oxidation catalyst.

Full text of DOI:10.1246/bcsj.20110022

6
60
Bull. Chem. Soc. Jpn. Vol. 84, No. 6, 660–666 (2011)
© 2011 The Chemical Society of Japan
Lanthanoid Exchanged Mordenites as Catalysts
for the Isopropylation of Biphenyl
³
Yoshihiro Sugi,* Seiji Watanabe, Hiroaki Naiki, Ken-ichi Komura, and Yoshihiro Kubota
Department of Materials Science and Technology, Faculty of Engineering, Gifu University, Gifu 501-1193
Received January 21, 2011; E-mail: ysugi@gifu-u.ac.jp
Liquid-phase isopropylation of biphenyl (BP) with propene was studied to understand the acidities resulting from
lanthanoid exchanged sodium mordenite (Ln,NaMOR; Ln: La, Ce, Pr, Sm, Dy, and Yb). The acidities of La3 exchanged
sodium mordenite (La,NaMOR) appeared at around 0.6­0.8 exchange calculated from La/3Al molar ratio. Similar
acidities appeared with all Ln,NaMORs. The resultant zeolites have Brønsted acidic sites appearing near unsaturated
lanthanoid cations. The isopropylation of BP predominantly afforded 4,4¤-diisopropylbiphenyl (4,4¤-DIPB) among DIPB
isomers over all Ln,NaMORs. These catalyses occur on the acidic sites in the channels. The exchanged catalysts had high
selectivities for 4,4¤-DIPB even at temperatures as high as 300 °C although the selectivities decreased by the isomerization
of 4,4¤-DIPB over H-mordenite (HMOR) with similar SiO2/Al2O3 ratio. These results indicate the external acid sites are
lowly active for the isopropylation of BP and the isomerization of 4,4¤-DIPB. The combustion of coke-deposits on
Ln,NaMORs, particularly Ce,NaMOR, used for the isopropylation occurred at lower temperatures than that on HMOR
because the lanthanoids dispersed in MOR channels work as an oxidation catalyst.
+
Lanthanoid exchanges of zeolites are well-known to improve
isopropylation of BP and discuss the mechanism of the
catalysis by the MOR channels.
catalytic properties such as activity and life span of zeolite
catalysts. Particularly, they are devoted to the improvement
of catalysts for cracking heavy hydrocarbons in FCC and
reduction of NOx in flue exhaust.1 Lanthanum exchanged
zeolites are also applied to the alkylation of isobutane with
alkenes to replace hazardous hydrofluoric acid with environ-
mental benign solid catalysts.4 They enhance thermal and
hydrothermal stabilities with acidity different from the conven-
tional protic acidity of H-type zeolite.6 They are also
Experimental
­3
Catalyst Preparation.
H-Mordenite (HMOR, SiO2/
Al O = 18.7) was obtained from Tosoh Corporation, Tokyo,
2
3
Japan. Sodium mordenite (NaMOR) was prepared from HMOR
by treatment with aqueous sodium hydroxide solution, thor-
oughly washed with water, dried at 110 °C, and calcined at
500 °C for 6 h.
,5
­9
important solid acid catalysts in organic synthesis because the
Lanthanum exchange of NaMOR was carried out with
lanthanum nitrate hexahydrates (La(NO ) ¢6H O; Nacalai
acidities can be designed by cation exchange.1
0­15
There have
3
3
2
been however no systematic studies on the lanthanoid exchange
of zeolites for organic synthesis.
H-Mordenite (HMOR) has been found to be the most potent
Tesque, Kyoto, Japan) in aqueous solution at 90 °C. The
amounts of La were 0.1 to 10 (mmol-La/mmol-Al in NaMOR).
The resulting zeolites were dried at 110 °C and calcined at
500 °C. Other lanthanoid exchanged sodium mordenites were
also cation-exchanged at the Ln/NaMOR = 5.0 mmol-Ln/
mmol-Al in NaMOR similarly to lanthanum cation. All
exchanged mordenites were calcined at 500 °C for 6 h just
before using.
catalysts for the alkylation of polynuclear aromatics such as
biphenyl (BP) and naphthalene (NP).1
6­29
The catalysis occurs
shape-selectively at acidic sites inside the channels by steric
restriction through a restricted transition state mechanism. To
clarify how their channels work in the catalysis, we have been
much interested in the nature of lanthanoid exchanged sodium
mordenite, where new acidities appear by the exchange of
sodium mordenite (NaMOR) with lanthanoid cations. We have
already published preliminary results in the isopropylation of
BP over cerium exchanged mordenites.15
Lanthanoid to aluminum ratios (Ln/Al) of the zeolite were
determined by inductively coupled plasma atomic emission
spectroscopy on a JICP-PS-1000 UV spectrometer (Teledyne
Leeman Labs Inc., NH, USA). The details of the procedure are
as follows: K CO powder (100 mg) was taken and mixed with
2
3
In this paper, we describe the acidic properties and
the catalysis of lanthanoid exchanged sodium mordenite
20 mg of the sample. This mixture was then heated in a
platinum crucible using a natural gas­oxygen torch. After the
sample melted completely, the entire platinum crucible was
placed in 80 mL of water and agitated until the flux was freed
from the crucible. The resulting solution with the flux was
(
Ln,NaMOR; Ln: La, Ce, Pr, Sm, Dy, and Yb) exchanged
3+
3+
3+
3+
3+
3+
with La , Ce , Pr , Sm , Dy , and Yb cations in the
³
Present address: Department of Materials Science and Engineer-
ing, Graduate School of Engineering, Yokohama National
University, Yokohama, Kanagawa 240-8501
acidified with ca. 20 mL of ca. 3­4 M HNO with stirring,
diluted to 100 mL, and subjected to ICP analysis to quantify
sodium, silicon, aluminum, and lanthanoid.
3
Published on the web June 4, 2011; doi:10.1246/bcsj.20110022

Y. Sugi et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011)
661
Table 1. Properties of Ln,NaMORsa)
100
80
NH3-TPD peak
temperature
Acid
amount
/mmol g
SiO2/ Na/ Ln/
Mordenite
b)
Al2O3
Al 3Al
¹1
/°C
HMOR 18.7
NaMOR 17.6
La,NaMOR 17.87 0.34 0.71
®
1.00
®
®
435
®
0.512
®
6
4
2
0
0
0
0
396
386
403
408
418
406
0.519
0.448
0.387
0.532
0.595
0.633
Ce,NaMOR 20.25 0.35 0.76
c)
Pr,NaMOR n.d.
n.d.
n.d.
Sm,NaMOR 19.32 0.10 0.63
Dy,NaMOR 18.43 0.07 0.89
Yb,NaMOR 18.58 0.03 0.80
a) Ln: La, Ce, Pr, Sm, Dy, and Yb. b) Calculated on the basis
of 3Al exchanged to a lanthanoid. c) Not determined.
0
2
4
6
8
10
Textural and acidic properties of lanthanoid exchanged
sodium mordenites (Ln,NaMOR) are summarized in Table 1.
The degree of lanthanoid exchange was calculated based on a
Ln/3Al ratio (mol/mol), and complete exchange was assumed
to be Ln/3Al ratio = 1.
-1
La/Al /mmol mmol
Figure 1. Effects of cation exchange on the lanthanum
amounts against Al content of La,NaMOR.
Characterization of Catalysts. XRD was measured using
a Shimadzu XRD-6000 apparatus with Cu K¡ radiation (­ =
each IPBP and DIPB isomer among total IPBP and DIPB
isomers.
1
.5418 ¡). NH -TPD was measured with a BEL-TPD-66
3
apparatus (Bell Japan, Osaka, Japan) in a helium stream at
00 °C after evacuation at 500 °C. TG analysis was performed
on a Shimadzu DTG-50 analyzer with temperature-program-
Results and Discussion
1
Properties of Lanthanoid Exchanged Sodium Morden-
ites. Figure 1 shows the changes of acidity by lanthanum
exchange of sodium mordenite (NaMOR), where the degree
of lanthanum exchange was calculated based on a La/3Al
ratio (mol/mol). Thus, complete exchange corresponds to
¹
1
med rate of 10 °C min in an air stream.
Cracking of 1,3,5-Triisopropylbenzene (1,3,5-TIPB) and
Cumene (IPB). Cracking of 1,3,5-TIPB and IPB was carried
out using a conventional pulse reactor under N2 flow (catalyst
amount: 20 mg; pulse size: 0.02 ¯L for IPB and 1,3,5-TIPB;
3
+
La/3Al = 1 because La can be exchanged with 3NaOAl
moieties. The cation exchange occurred very rapidly up to
temperature: 400 °C; N pressure: 0.2 MPa). The products were
2
analyzed with a Shimadzu GC-4C gas chromatograph directly
connected to the reactor: column: 10 wt.% Carbowax 6000
on Celite 545 with 2 m length (GL Science, Tokyo, Japan);
temperature: 80 °C.
around 60­70% with an increase in the amount of La(NO )¢
3
6H O relative to aluminum content of NaMOR, however large
2
lanthanum amounts were necessary for further exchange. No
changes of XRD patterns were observed after the exchange.
This means there is no significant change of zeolite structure
and formation of agglomerates of lanthanoid oxide in the
resulting mordenites.
Figure 2 shows the changes of acidity of lanthanum
exchanged sodium mordenite (La,NaMOR) with the degree
of lanthanum exchange, where the acidities and acid amounts
were calculated from peak temperatures and peak area of
Isopropylation of BP.
The isopropylation of BP was
carried out in a 100 mL SUS-316 autoclave using propene as an
alkylating reagent. Standard conditions were: 50 mmol (7.7 g)
of BP, 250 mg of catalyst, 0.8 MPa of propene pressure, and 4 h
time at 200­300 °C. The autoclave was purged with nitrogen
before heating, and heated to reaction temperature. Then,
propene was supplied to the autoclave, and temperature was
maintained under constant propene pressure throughout the
reaction. After cooling the autoclave, the products were
separated from catalysts by filtration. The solution (ca.
NH -TPD profiles. The acidities appeared at around 60%, and
3
they were enhanced rapidly to around 80% exchange. How-
ever, they were saturated by further exchange. The acid
strength remained almost constant by the exchange, because
the peak temperatures were around 400 °C for all samples. The
acidities did not appear at lower exchange because of the
formation of saturated triexchanged (La-3Al) species with
only low acidity. However, the diexchanged (La-2Al) and/or
monoexchanged (La-Al) species appear at higher lanthanum
1
.5 mL) taken from the combined filtrate and washings was
diluted with toluene (1.5­6.0 mL), and an aliquot was subjected
to analysis by gas chromatography (Shimadzu GC-14C or
GC-18A; FID detector) equipped with an Ultra-1 capillary
column (25 m © 0.2 mm; film thickness: 0.25 ¯m; Agilent
Technologies Co., Ltd., MA, USA). The products were also
confirmed by using a Shimadzu GC-MS-5000 Gas Chromato-
graph-Mass Spectrometer using the same type of column.
The yield of every product in the isopropylation of BP was
calculated on the basis of BP used for the reaction; i.e., the
selectivity for each isomer of isopropylbiphenyls (IPBP) and
diisopropylbiphenyls (DIPB) is expressed as a percentage of
1
,9
exchange, resulting in the appearance of Brønsted acidity.
Table 1 summarizes properties of lanthanoid exchanged
sodium mordenites (Ln,NaMOR; Ln: La, Ce, Pr, Sm, Dy, and
3+
3+
3+
3+
3+
3+
Yb) with La , Ce , Pr , Sm , Dy , and Yb cations at
around 0.7 of Ln/3Al ratio. The cation exchanges were carried
out in a similar manner to lanthanum. The XRD patterns show

6
62
Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011)
Isopropylation of BP over Ln,NaMOR
2
1
1
0
0
.0
600
Ln(OH)3-m]m+
H+
O
Na+
O
[
O
O
O
Al-
Si
Al-
Si
Si
Al-
5
00
00
.5
.0
.5
.0
4
Scheme 1. Suggested Brønsted acidic sites on Ln,NaMORs.
Ln: lanthanoid cation; m = 1, 2, 3.
300
Table 2. Catalytic Cracking of 1,3,5-TIPB and IPB over
a)
Ln,NaMOR
2
1
0
00
Conversion/%
Mordenite
1
,3,5-TIPB
IPB
00
HMOR
NaMOR
93.1
0.0
18.3
8.7
29.1
14.9
15.7
15.5
99.4
0.0
La,NaMOR
Ce,NaMOR
Pr,NaMOR
Sm,NaMOR
Dy,NaMOR
Yb,NaMOR
64.6
27.0
67.5
38.7
43.1
48.1
0
.0
0.2
0.4
0.6
0.8
1.0
Degree of La exchange
Figure 2. Effects of acid amounts and peak temperature of
NH3-TPD on La,NaMOR.
a) Reaction conditions: catalyst, 20 mg; 1,3,5-TIPB or IPB,
.02 ¯L; temperature, 450 °C; carrier gas, N2, 0.2 MPa.
0
HMOR
NaMOR
La,NaMOR
Ce,NaMOR
Pr,NaMOR
Sm,NaMOR
Dy,NaMOR
Yb,NaMOR
It is well known that new acidity appears by the cation
exchange of sodium zeolites with multivalent cations.
1,9,15,30,31
These acidities are due to protons formed from hydrated
multivalent cations. The acidities also appear in the case of
lanthanoid exchange of NaMOR. The saturated species,
triexchanged (Ln-3Al), have only low acidity because of
valence saturation with Al species. However, stronger acidities
appear through the formation of unsaturated lanthanoid cation
(
diexchanged (Ln-2Al) and/or monoexchanged (Ln-Al)) as
shown in Scheme 1. From the scheme, the acidity highly
resembles all the lanthanoids. These acidities of Ln,NaMOR
are sufficient strength and amount for solid acid catalysis.
Cracking of 1,3,5-TIPB and IPB over Lanthanoid
Exchanged Sodium Mordenites. Table 2 summarizes the
cracking of 1,3,5-TIPB and IPB over Ln,NaMOR (Ln: La, Ce,
Pr, Sm, Dy, and Yb) by pulse method. All Ln,NaMORs had
low activities for the cracking of 1,3,5-TIPB, although NaMOR
was inactive. However, HMOR had high activity for cracking
1
00
300
500
700
o
Temperature/ C
Figure 3. NH3-TPD profiles of Ln,NaMORs.
1
5­20
the structures of NaMOR remained after the exchange and
following calcination at 500 °C. Aluminum leaching was not
significant during the exchange beccause SiO /Al O ratio
remained in the range of 18­20 after the exchange.
Figure 3 shows the NH3-TPD profiles of Ln,NaMORs.
NaMOR has only an l-peak at around 150 °C, due to
as discussed previous papers.
Because the cracking of
1,3,5-TIPB occurs at the external acid sites because the
molecule cannot enter the MOR channels, these results indicate
that external acid sites of these mordenites are less active for
the cracking of 1,3,5-TIPB than internal sites, and that they
are lowly active for acid catalysis. On the other hand, all
Ln,NaMORs were highly active for cracking of IPB although
their activities are much lower than HMOR. The cracking of
IPB occurs principally at the internal acid sites because IPB can
enter the MOR channels. From these differences of catalytic
properties toward cracking of 1,3,5-TIPB and IPB, the internal
acid sites of Ln,NaMORs are active enough for the solid acid
catalysis, however the external acid sites are lowly active for
the catalysis.
2
2
3
physisorption of NH on basic and neutral sites. However,
3
two types of peaks, l and h, appeared after lanthanoid exchange
of NaMOR. The l-peaks became larger by the exchange. The
h-peaks, which are assigned to Brønsted acid sites, have almost
the same peak-temperatures at around 400 °C, where unmodi-
fied HMOR has a peak at around 470 °C. These results mean
that acidities of Ln,NaMORs are almost the same strength
irresective of types of lanthanoid although they are weaker than
that of HMOR. Ln,NaMORs also have almost the same
amounts of acidic sites although they are slightly lower than the
unmodified HMOR.
Isopropylation of BP.
Figure 4 shows the effects of
lanthanum exchange on catalytic activities and selectivities
for 4,4-DIPB in the isopropylation of BP. Catalytic activities

Y. Sugi et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011)
663
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
100
100
80
100
80
60
40
20
0
Conversion
8
6
4
2
0
0
0
0
0
60
4
0
0
0
IPBP
DIPB
2
0
0.67
0.73
0.82
Degree of La exchange
Figure 5. Effects of the isomerization of 4,4¤-DIPB on
degree of cation exchange of La,NaMOR. Reaction
conditions: 4,4¤-DIPB, 50 mmol; catalyst, 0.5 g; propene,
0
0.2
0.4
0.6
0.8
1
Degree of La exchange
0
4
.8 MPa; temperature, 300 °C; period, 4 h. Legend:
,4¤-DIPB; : 3,4¤DIPB; : TriIPB; : IPBP.
:
Figure 4. Effects of degree of La,NaMOR on the isopro-
pylation of BP. Reaction conditions: BP, 100 mmol;
catalyst, 0.5 g; propene, 0.8 MPa; temperature, 300 °C;
period, 4 h.
temperature, and these MORs have catalytic activities at a
similar level as unmodified HMOR. The principal products
were IPBP isomers at lower temperatures, however the yields
of DIPB increased with increasing temperature, and the
formation of triisopropylbiphenyl (TriIPB) isomers accompa-
nied in small amounts at higher temperatures (Figures S1 and
S2 in Supporting Information). The selectivities for 4,4¤-DIPB
remained at 70­80% in the temperature range of 200 to 300 °C
although the selectivity significantly decreased at 300 °C
for HMOR. The selectivities for 4,4¤-DIPB in encapsulated
products remained at 70­80% at temperatures for all MORs
(results not shown). Figure 7 shows the BP conversion
and selectivities for 4,4¤-DIPB at 250 and 300 °C over
Ln,NaMORs. The selectivities for 4,4¤-DIPB were as high as
75­80% for all mordenites including HMOR at 250 °C. The
selectivities still remained at 70­75% for all Ln,NaMORs at
300 °C, although the selectivities decreased to 50% for HMOR.
The decrease in selectivity for 4,4¤-DIPB over HMOR is due to
the isomerization of 4,4¤-DIPB to thermodynamically stable
DIPB isomers, particularly 3,4¤-DIPB. However, the external
acid sites are likely deactivated, probably because of the
saturation of Ln cations on aluminum moieties, resulting in
prevention of the isomerization for 4,4¤-DIPB.
Figure 8 shows the isomerization of 4,4¤-DIPB under
propene pressure at 300 °C, The isomerization extensively
occurred over unmodified HMOR as in the isopropylation of
BP, however it was effectively prevented by lanthanoid
exchange. The isomerization does not occur at the acid sites
gradually appeared at around 20%, increased with an increase
in the degree of exchange, and then rapidly enhanced at around
0­70% of the exchange with the increase in acid amounts,
6
however they were saturated at around 80% exchange, and then
decreased slightly after further exchange. The catalytic activ-
ities appearing at low exchange states are due to the acidities of
Ln-3Al species, which have weaker acidities than Ln-2Al and
Ln-1Al species.
Principal products were IPBP isomers at lower exchanges.
The formation of DIPB isomers started at around 60%
exchange, saturated at around 80%, and decreased with further
exchange. These features of the catalysis, particularly the
formation of DIPB isomers, reflect the appearance and
characteristics of Brønsted acidity of Ln-2Al and Ln-1Al
species as shown in Scheme 1.
The selectivities for 4,4¤-DIPB were almost constant at about
0% irrespective of the degree of lanthanum exchange. The
3
2
8
catalysis occurs at the acidic sites in the MOR channels, and the
selectivities appeared due to the shape-selective nature of the
channels of La,NaMOR. These results indicate that the channels
of La,NaMOR work as the sites of shape-selective catalysis as
previously reported for HMOR and Ce,NaMORs.1
5­18,20­25
As shown in Figure 5, the isomerization of 4,4¤-DIPB was not
particularly significant over La,NaMORs with 70­80% ex-
change under propene pressure at 300 °C, although 4,4¤-DIPB
was extensively isomerized to thermodynamically stable
1
7,18,20,24
in the MOR channels, but on the external surface.
3
,4¤- and 3,3¤-DIPB32 over unmodified HMOR. The results
These results also correspond to the results of the cracking of
1,3,5-TIPB over Ln,NaMORs, and mean that internal Brønsted
acid sites only work for the isopropylation of BP, resulting in
shape-selective formation of 4,4¤-DIPB.
From these results, we can summarize that the isopropylation
of BP over Ln,NaMOR occurs in the channels by shape-
selective catalysis, resulting in the selective formation of the
least bulky 4,4¤-DIPB, and that the isomerization of 4,4¤-DIPB
did not occur significantly because external acid sites by Ln
cation exchange are inactive.
correspond to the low activities of La,NaMOR in the cracking
of 1,3,5-TIPB, and indicate that the external acid sites of
La,NaMOR are lowly active for the isomerization of 4,4¤-DIPB,
resulting in the highly selective formation of 4,4¤-DIPB in the
isopropylation of BP even at temperatures as high as 300 °C.
Figure 6 shows the effects of reaction temperature on the BP
conversion and the selectivity for 4,4¤-DIPB over Ln,NaMORs
exchanged with La3 , Ce , Pr , Sm , Dy , and Yb
cations. The catalytic activities increased with the increase in
+
3+
3+
3+
3+
3+

6
64
Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011)
Isopropylation of BP over Ln,NaMOR
1
00
100
80
60
40
20
0
(
a)
(b)
8
6
4
2
0
0
0
0
0
HMOR
La,NaMOR
Ce,NaMOR
Pr,NaMOR
Sm,NaMOR
Dy,NaMOR
Yb,NaMOR
2
00
225
250
275
300
200
225
250
275
300
o
o
Reaction temperature/ C
Reaction temperature/ C
Figure 6. Effects of temperature on the isopropylation of BP over Ln,NaMORs. (a) The activities, (b) the selectivities of 4,4¤-DIPB.
Reaction conditions: BP, 100 mmol; catalyst, 0.5 g; propene, 0.8 MPa; temperature, 200­300 °C; period, 4 h.
1
00
100
80
60
40
20
0
Mechanistic Aspects of the Catalysis over Lanthanoid
Exchanged Sodium Mordenites. The characteristic acidity
shown in previous chapters indicates that a new type of
acid sites appears on NaMOR by lanthanoid exchange. The
Brønsted acidic sites appeared by the unsaturated lanthanoid
cation (mono- and/or diexchanged lanthanoid cation) near the
aluminum sites. The acid sites assigned to Brønsted acidities
have the quite common features of Ln,NaMOR as suggested in
Scheme 1. It is well known that the appearance of acid sites
shares common features of multivalent cation exchange of
o
3
2
00 C
80
60
40
20
0
o
50 C
1
,9,15,30,31
zeolites.
The results indicate the Ln,NaMORs have
H
La
Ce
Pr
Sm
Dy
Yb
active acid sites in their channels strong enough for acid
catalysis.
Lanthanoid
These Ln,NaMORs have high activities for the cracking
of IPB at 410 °C by pulse reaction, however they are only
lowly active for the cracking of 1,3,5-TIPB. The differences are
due to the bulkiness of reactant molecules. External acid sites
are lowly active for the cracking of IPB and 1,3,5-TIPB.
Internal acid sites are only active for cracking of IPB because
Figure 7. Effects of temperature on the isopropylation of
BP over Ln,NaMORs. Reaction conditions: BP, 100 mmol;
catalyst, 0.5 g; temperature, 250 and 300 °C; propene
pressure, 0.8 MPa; period, 4 h. Legend: : 250 °C;
00 °C.
:
3
1
,3,5-TIPB cannot enter the MOR channels. This indicate that
1
00
100
80
60
40
20
0
internal Brønsted acid sites only work for acid catalysis, and
that the external acid sites are lowly active for the crackings,
probably due to Ln satuation of aluminum moieties at the
external surface.
Ln,NaMORs were active catalysts for the isopropylation
of BP. BP predominantly yields 4-IPBP among the isomers in
the first step, and 4-IPBP selectively forms 4,4¤-DIPB. BP
conversions were not dependent on types of lanthanoid cations,
and increased with the increase in reaction temperature. These
results suggest that acid sites appearing by the exchange are
very similar to Brøntsted acid sites in Scheme 1 for all
lanthanoids. The selectivities for 4,4¤-DIPB were also around
80
60
40
20
0
H
La
Ce
Pr
Sm
Dy
Yb
Lanthanoid
8
0% for all Ln,NaMORs in the range from 200 to 300 °C;
which show that the channels of Ln,NaMORs work as shape-
selective catalytic sites similarly to those of unmodified
HMOR. The channels can exclude the transition states of
bulky DIPB isomers, resulting in the selective formation of
Figure 8. The
Ln,NaMORs. Reaction conditions: 4,4¤-DIPB, 50 mmol;
catalyst, 0.5 g; temperature, 300 °C; propene pressure,
isomerization of
4,4¤-DIPB
over
0.8 MPa; period, 4 h. Legend: the same as in Figure 5.

Y. Sugi et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 6 (2011)
Conclusion
665
4
,4¤-DIPB by product selectivity and restricted transition
state mechanisms, as proposed for the catalysis over
1
7,18,20,24
HMOR.
The lanthanoid exchange was applied to sodium mordenite
(NaMOR) using aqueous lanthanoid nitrate solution. The
acidities of La,NaMOR appear gradually at 60­70% exchange
based on La/3Al ratio. Similar acidities were also observed for
other lanthanoid exchanged sodium mordenites, Ln,NaMOR
(Ln: Ce, Pr, Sm, Dy, and Yb). The acidic properties have
features in common with Brønsted acidities, which appear due
to unsaturated lanthanoid cations on aluminum moieties.
The liquid-phase isopropylation of BP with propene was
studied to elucidate the acidic properties appearing by
lanthanoid exchange of NaMOR. Shape-selective formation
of 4,4¤-diisopropylbiphenyl (4,4¤-DIPB) occurred over
Ln,NaMORs. Ln,NaMORs afforded almost the same level of
selectivities for HMOR with similar SiO /Al O ratios. These
No significant decreases in the selectivity for 4,4¤-DIPB
were observed in the isopropylation of BP over Ln,NaMOR
even at 300 °C although the extensive decrease occurred for
unmodified HMOR. The differences indicate that the external
acid sites of Ln,NaMOR are lowly active for the isomerization
of 4,4¤-DIPB, probably due to the low acidity of Ln saturation
of aluminum moieties at the external surface. These results also
corresponds to low activities of Ln,NaMORs in the cracking of
1
,3,5-TIPB because internal Brønsted acid sites only work for
the catalysis.
There are no significant differences in catalytic properties in
the channels of Ln,NaMOR discussed in the isopropylation of
BP and the cracking of IPB and 1,3,5-TIPB. This means that
both the unmodified and lanthanoid exchanged channels work
as similar reaction sites, and that there are no significant steric
differences from the cationic exchange of sodium to lantha-
noids.
Combustion of Coke Deposit in MOR Channels.
Figure 9 summarizes TG profiles of Ln,NaMORs after using
for catalysis. A peak appeared at around 600 °C for unmodified
HMOR. The peak from coke combustion for Ln,NaMORs
appeared at lower temperatures more than 100 °C. Thus, the
peak appeared at around 380 °C for Ce,NaMOR, and at around
2
2
3
results indicate that the catalyses occurred inside the channels
on the Brønsted acidic sites appearing from unsaturated
lanthanoid species on aluminum sites. Ln,NaMORs remained
highly selective for 4,4¤-DIPB at temperatures as high as
300 °C although the selectivities decreased over HMOR with
the isomerization of 4,4¤-DIPB. The results in this paper show
that the shape-selective catalysis arises from MOR channels,
and not from the acidities of the zeolites.
The combustion of coke-deposits of used catalysts for the
catalysis occurred at lower temperatures over Ln,NaMORs
because the lanthanoids work as oxidation catalysts. This is
ascribed to the fact that finely dispersed lanthanoid species
work for the catalysis of combustion of coke inside the
channels. It should be noted that the low temperature coke-
combustion can prevent the collapse of zeolite structure during
the regeneration of the spent catalysts.
4
30 °C for the other lanthanoids. These results indicate that
lanthanoid species, formed by the exchange, work as oxidation
catalysts for coke combustion. Particularly, cerium species,
dispersed in MOR channels work as effective catalysts for
combustion of coke-deposit inside the channels. Hashimoto
et al. also found cerium oxide dispersed in MOR channels was
active for the oxidation of p-xylene.33 The coke combustion
at low temperatures below 400 °C indicates the advantages to
prevent the collapse of zeolite structure during the regeneration
of the spent catalysts.
A part of this work was financially supported by Grant-in-
Aid for Scientific Research (B) Nos. 16310056 and 19061107,
the Japan Society for the Promotion of Science (JSPS). YS also
appreciates Dr. Ajayan Vinu of National Institute of Materials
Science (NIMS) for helpful discussion, and the Department of
Research, Nagoya Industrial Science Research Institute for
their continuing cooperation.
HMOR
La,NaMOR
Ce,NaMOR
Pr,NaMOR
Sm,NaMOR
Dy,NaMOR
Yb,NaMOR
Supporting Information
Figure S1: The isopropylation of BP over HMOR.
Figure S2: The isopropylation of BP over Ln,NaMOR (Ln:
La, Ce, Pr, Sm, Dy, and Yb). These materials are available free
of charge on the Web at: http://www.csj.jp/journals/bcsj/.
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