Shape-selective alkylation of biphenyl with propylene using zeolite and amorphous silica-alumina catalysts

Article abstract of DOI:10.1016/j.apcata.2012.12.011

The influence of zeolite structure for the alkylation of biphenyl with propylene was studied over various zeolites such as HY, HZSM-5, and dealuminated mordenite (DMOR), as well as amorphous SiO₂/Al₂O ₃, in a stirred tank reactor. Biphenyl conversion was found to increase with reaction time for HZSM-5 and DMOR zeolites and reach a leveling off in 4 h, whereas for HY and amorphous SiO₂/Al₂O ₃ a leveling off was reached within an hour. DMOR displayed the highest selectivity for 4,4′-diisopropylbiphenyl (4,4′-DIPB) even at temperatures as high as 300 °C, whereas for HY, HZSM-5 and amorphous SiO₂/Al₂O₃ selectivities fell in the range of 10-35%; they were significantly lower than observed for DMOR. These differences in selectivity might be due to the structure and pore channels of the zeolites. DMOR was found to be an active catalyst, the selectivity for 4-isopropylbiphenyl (4-IPB) and (4,4′-DIPB) was high among isopropylbiphenyl (IPB) and diisopropylbiphenyl (DIPB) isomers, respectively, indicating DMOR possesses shape-selectivity. The selectivity of 4,4′-DIPB increased with time, while the corresponding selectivity of 4-IPB decreased for DMOR catalyst. Alkylation of biphenyl with propylene occurred with predominant formation of 4-IPB in the first step. 4-IPB is only a source in the second step of alkylation of biphenyl with propylene for the formation of 4,4′-DIPB, while 3-IPB does not participate in the formation of DIPB isomers.

Full text of DOI:10.1016/j.apcata.2012.12.011

Applied Catalysis A: General 453 (2013) 195–203
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Shape-selective alkylation of biphenyl with propylene using zeolite
and amorphous silica–alumina catalysts
Venkat Ramana Rao Pendyala, Gary Jacobs, Wilson D. Shafer, Robert A. Keogh,
Jungshik Kang, Dennis E. Sparks, Burtron H. Davis∗
The University of Kentucky, Center for Applied Energy Research, 2540 Research Park Drive, Lexington, KY 40511, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The influence of zeolite structure for the alkylation of biphenyl with propylene was studied over various
zeolites such as HY, HZSM-5, and dealuminated mordenite (DMOR), as well as amorphous SiO2/Al2O3,
in a stirred tank reactor. Biphenyl conversion was found to increase with reaction time for HZSM-5 and
DMOR zeolites and reach a leveling off in 4 h, whereas for HY and amorphous SiO2/Al2O3 a leveling
off was reached within an hour. DMOR displayed the highest selectivity for 4,4ꢀ-diisopropylbiphenyl
(4,4ꢀ-DIPB) even at temperatures as high as 300 ◦C, whereas for HY, HZSM-5 and amorphous SiO2/Al2O3
selectivities fell in the range of 10–35%; they were significantly lower than observed for DMOR. These
differences in selectivity might be due to the structure and pore channels of the zeolites. DMOR was
found to be an active catalyst, the selectivity for 4-isopropylbiphenyl (4-IPB) and (4,4ꢀ-DIPB) was high
among isopropylbiphenyl (IPB) and diisopropylbiphenyl (DIPB) isomers, respectively, indicating DMOR
possesses shape-selectivity. The selectivity of 4,4ꢀ-DIPB increased with time, while the corresponding
selectivity of 4-IPB decreased for DMOR catalyst. Alkylation of biphenyl with propylene occurred with
predominant formation of 4-IPB in the first step. 4-IPB is only a source in the second step of alkylation of
biphenyl with propylene for the formation of 4,4ꢀ-DIPB, while 3-IPB does not participate in the formation
of DIPB isomers.
Received 8 August 2012
Received in revised form
29 November 2012
Accepted 1 December 2012
Available online xxx
Keywords:
Alkylation
Biphenyl
Propylene
Mordenite
Zeolites
Shape-selectivity
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Alkylation of biphenyl with propylene has been successfully
demonstrated by numerous research groups using a variety of
The alkylation of biphenyl with propylene is
a
reaction
catalysts. Valuable insights into the controlling factors and their
influence on the conversion and selectivity are well documented.
Accordingly, existing catalysts were compared, and a few modi-
fied or new catalysts were developed and tested to further enhance
desired product selectivity. A 98% conversion of biphenyl and 72%
yield of 4,4ꢀ-DIPB have been obtained over highly dealuminated
mordenite at 250 ◦C with SiO2/Al2O3 molar ratio of 2600 by Lee
et al. [11]. Out of Na-mordenite, ZSM-5, HY and dealuminated Y
tested for this reaction, Vergani et al. [12] found that the mordenite
catalyst had the best performance and was most selective toward
4,4ꢀ-DIPB. Matsuda et al. [13] investigated HY, H-beta, H-mordenite,
H-offretite, H-ZSM-8, H-ZSM-5 and silica/alumina catalysts. They
found that mordenite was the most active for the isopropylation of
biphenyl with 40% conversion and 7% yield of 4,4ꢀ-DIPB at 250 ◦C.
Exchange of 55% of Na cations of mordenite with protons was
found to increase the DIPB yield. Low yields of 7% with unmodi-
fied H-mordenite were attributed to the presence of strong acid
sites, especially on the external catalyst surface, which catalyze
the isomerization of 4,4ꢀ-DIPB. Impregnation of mordenite with
phosphoric acid blocks Al sites on the outer surface, thus effec-
tively suppressing isomerization. Loktev and Chekriy [14] studied
this reaction over zeolites Y, Beta, mordenite, ZSM-5 and ZSM-12.
of practical interest since it produces 4,4ꢀ-diisopropylbiphenyl
(4,4ꢀ-DIPB) [1–5]. 4,4ꢀ-DIPB is a promising precursor for biphenyl-
4,4ꢀ-dicarboxylic acid, which is an intermediate for polyester
fibers, engineering plastics, liquid crystalline polymers for elec-
tronic and mechanical devices, and films with high heat resistance
and strength [6,7]. Selective synthesis of 4,4ꢀ-DIPB is not possi-
ble on traditional Friedel–Crafts [8] catalysts such as Lewis acids
or silica/alumina [9], which generally produce large amounts of
undesired products having low para-selectivity. In contrast, zeo-
lites, being microporous and crystalline, shape-selectively yield
the least bulky para-isomers [10]. Zeolite catalysts are attractive
for several reasons: enhanced selectivity of the desired product,
easy separation, and reusability; most importantly, they are envi-
ronmentally benign materials. Shape selectivity characteristics of
zeolites in alkylation of biphenyl can therefore be very useful for
the synthesis of linear 4,4ꢀ-dialkylbiphenyl derivatives.
∗
Corresponding author. Tel.: +1 859 257 0251; fax: +1 859 257 0302.
E-mail address: burtron.davis@uky.edu (B.H. Davis).
0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2012.12.011

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Table 1
Physical properties various zeolites.
Catalyst
SiO2/Al2O3
ratio
BET surface
area (m2/g)
Single point pore
volume (cm3/g)
BJHads pore volume
(cm3/g)
Acidity ratio
(Lewis/Brønsted)
Ammonia
adsorptiona
HY
30.0
20.0
6.1
45.7
5.1
783.8
364.7
449.8
434.2
427.1
0.506
0.200
0.308
0.315
0.701
0.204
0.058
0.143
0.148
0.721
1.743
0.273
16.5
4.7
1.3
1
HZSM-5
HMOR
DMOR
SiO2–Al2O3
1.192
2.375
1.9
a
Ammonia adsorption related to dealuminated mordenite.
They related the activity and selectivity of the catalysts with their
pore structures and concluded that the constraint effects present in
mordenite and ZSM-12 zeolites are needed to obtain a high selec-
tivity to 4,4ꢀ-DIPB. Matsuda et al. [15,16] poisoned external acid
sites of mordenite with tributylphosphite to enhance the yield of
4,4ꢀ-DIPB, thus suppressing the side reactions of propylene. Cerium
has a similar effect and deactivates the external acid sites of H-
mordenite without choking its pores [17]. At 300 ◦C the selectivity
toward 4,4ꢀ-DIPB was enhanced from 40% to 85% by cerium mod-
ification, while the conversion of biphenyl was unaltered at 95%.
Recently Sugi et al. [18–22] reported shape-selective isopropylation
of biphenyl over many types of zeolites. Bandyopadhyay et al. [23]
reported that unmodified SAPO-5 at 300 ◦C converted 98% biphenyl
with 35% selectivity toward DIPB. Modification of SAPO-5 with ceria
blocked the external acid sites preventing non-regioselective reac-
tions on external surfaces. This resulted in an improvement of the
selectivity for 4,4ꢀ-DIPB.
Among zeolite catalysts, mordenite (MOR) type zeolite pos-
sesses particularly good shape selectivity characteristics for the
alkylation of biphenyl with propylene [1,2,11,12,24,25]. In com-
parison with low silica MOR catalysts, highly dealuminated MOR
catalysts displayed high activity and improved selectivity in the
alkylation of biphenyl with propylene. The purpose of the present
work is to systematically examine changes in conversion and selec-
tivity with reaction time using different zeolites, and to achieve
both high activity and high 4,4ꢀ-diisopropylbiphenyl selectivity.
The present study explores the use of propylene as the alkylating
agent in the alkylation of biphenyl over various zeolites such as HY,
HZSM-5, and DMOR as well as amorphous silica alumina as cata-
lysts under liquid phase conditions. From these findings, a plausible
mechanism is proposed for the selective formation 4,4ꢀ-DIPB over
dealuminated mordenite catalyst.
size distributions (PSD) of the catalysts were quantified by the
Barrett, Joyner, Halenda (BJH) desorption model, which provides
a relationship whereby the amount of adsorbate lost during a
desorption step gives the average size of the pore emptied during
that desorption step. Physical properties are presented in Table 1.
The nature of the acid sites (Brønsted or Lewis) was determined
by FT-IR of chemisorbed pyridine. All spectra were recorded on a
Thermo Nicolet Nexus 870 Fourier-transform infrared spectrom-
eter. The samples (∼22 mg) were ground to a fine powder, which
were then placed into an infrared cell and outgassed at 400 ◦C for
3 h as a pretreatment procedure to clean the surface and eliminate
possible impurity prior to adsorption of the base. The sample was
cooled to 150 ◦C, and pyridine was dosed until saturation adsorp-
tion was achieved. After 1 h of adsorption, the excess and weakly
adsorbed pyridine was removed by evacuation at the same tem-
perature for 1.5 h. In order to measure the acid strength, pyridine
absorption was carried out at 150 ◦C, and the corresponding spectra
were recorded.
Catalysts performance for the alkylation of biphenyl with pro-
pylene was evaluated at 300 ◦C using a 1 L stirred tank reactor
equipped with a magnetically driven stirrer with turbine impeller,
a gas-inlet line, and a vapor outlet line with a stainless steel (SS) frit-
ted filter (2 ␮m) placed external to the reactor (Fig. 1). In a typical
run, 2.1 moles of biphenyl and 3.5 g of catalyst were introduced into
the reactor. Prior to heating, the reactor was purged with nitrogen
and heated to attain the desired reaction temperature. After reach-
ing the reaction temperature, propylene gas was introduced to the
reactor and the pressure kept constant (1.0 MPa) during the reac-
tion. The propylene gas entered the reactor below the stirrer, which
was operated at 500 rpm. The reactor temperature was maintained
constant ( 1 ◦C) using a temperature controller. After flowing the
propylene gas, reaction products were periodically sampled and
analyzed off-line, using a HP 5890 gas chromatograph with a flame
ionization detector and a 50 m DB-5 column. Reaction products
were also confirmed with an Agilent 5975N Mass Selective Detector
2. Experimental
H-mordenite (HMOR), having a Si/Al ratio of 6, and the NH4 form
of ZSM-5, were obtained from Clariant Inc., Louisville, and HY zeo-
lite was purchased from Alfa Aesar. For dealumination, H-MOR was
then refluxed with 6 N HNO3 solution for 3 h, using 15 mL of solu-
tion/gram of HMOR. After the acid treatment, the samples were
washed with water to remove residual nitrate, and the washing
procedure was repeated twice. The resulting material was dried
overnight at 383 K and calcined statically under an ambient atmo-
sphere at 823 K for 12 h, and it is denoted as DMOR (dealuminated
mordenite). The NH4 form of ZSM-5 was converted to the hydro-
gen form by calcining the catalyst from room temperature to 823 K
(held for 12 h), at a ramp rate of 5 K/min under air flow.
The surface areas, pore volumes, and average pore radii of the
catalysts were measured by BET using a Micromeritics Tri-Star
3000 gas adsorption analyzer system. Nitrogen was used as
the adsorption gas and sample analysis was performed at 77 K.
Prior to the measurement, the samples were slowly ramped to
433 K and evacuated overnight to approximately 50 mTorr. Pore
Fig. 1. Alkylation of biphenyl reactor setup.

V.R.R. Pendyala et al. / Applied Catalysis A: General 453 (2013) 195–203
197
Fig. 2. Biphenyl conversion of various zeolites.
(MSD) directly connected to a 6890 GC using the same GC condi-
tions and column as the 6890 Agilent GC-FID. Thus, the retention
times and patterns of specific compounds between the two instru-
ments theoretically remain identical.
Fig. 3. Pyridine adsorption FT-IR spectra of zeolite catalysts.
3. Results and discussion
Typical reaction results for the different zeolite catalysts used
in the alkylation of biphenyl with propylene under standard condi-
tions are shown in Fig. 2. HY and amorphous SiO2/Al2O3 catalysts
exhibited high initial activity, 90% conversion of biphenyl for HY
and around 70% for SiO2/Al2O3 within 5 min of reaction, after
which a leveling off was observed within 1 h, as shown in Fig. 2.
The conversion of biphenyl was found to increase with reaction
time for HZSM-5 and DMOR zeolites, leveling off in approximately
4 h. After a leveling off, HZSM-5 zeolite exhibited 33% conversion,
while that of DMOR was much higher at 96%. For comparison
untreated mordenite zeolite (HMOR) was also tested and found
to be less active than the dealuminated mordenite. The behavior
of the zeolites differed somewhat with reaction time. The activ-
ity trend of the different catalysts used was as follows: amorphous
SiO2/Al2O3 > HY > DMOR > HMOR ꢁ HZSM-5.
3.1. Amorphous SiO2/Al2O3 catalyst
Fig. 4A shows the selectivity of isopropylates for the amor-
phous SiO2/Al2O3 catalyst. The selectivity of isopropylbiphenyl
(IPB) isomers decreased with reaction time. However, the selec-
tivity of diisopropylbiphenyl (DIPB) isomers first increased with
time, reached a maximum in 30 min, and then further decreased
with time. The formation of triisopropylbiphenyl (TriIPB), tetraiso-
propylbiphenyl (TetraIPB) and penta isomers were also enhanced
with time. The results of silica–alumina catalyst are caused by the
large reaction spaces inside the channels. The selectivity of mono
and DIPB isomers are shown in Fig. 4B. The initial selectivity of
4-IPB was found to be 37% and it decreased with time, and simi-
lar trends were observed in the cases of the 2- and 3-IPB isomers.
However, the selectivities of 4,4ꢀ-DIPB and 3,4ꢀ-DIPB were almost
identical and less than 10%. The selectivities of IPB and DIPB of
silica–alumina catalyst are shown in Fig. 5A and B, respectively.
The selectivity of IPB isomers changed with reaction time. Among
the IPB isomers, the selectivities for 4-, 3- and 2-IPB were ca. 50,
25, and 25%, while that of 3-IPB increased with time with corre-
sponding decreases in selectivities of 2- and 4-IPB isomers. 3-IPB is
thermodynamically stable among the IPB isomers. These changes
are also considered to be due to the isomerization of 4- and 2-IPB
to 3-IPB. Among the DIPB isomers, the formation of 4,4ꢀ-DIPB and
3,4ꢀ-DIPB isomers were obtained only in low selectivities, and thus
the formation of the other DIPB isomers (2,2ꢀ-, 2,3ꢀ-, 2,4ꢀ-, and 3,3ꢀ-
DIPB) were predominant. The selectivities of all the DIPB isomers
did not change significantly with reaction time. These features of
the catalysis over silica–alumina suggest that their channels have
no shape-selective nature for the alkylation of biphenyl with pro-
pylene because the reaction spaces inside the channels are too large
for the selective formation of 4,4ꢀ-DIPB, while it can allow all DIPB
Fig. 3 shows the FT-IR spectra of pyridine adsorbed on the var-
ious catalysts. In the region 1400–1570 cm−1, three sharp bands
due to the C C stretching vibrations of pyridine were observed. The
band at 1490 cm−1 is due to pyridine adsorbed on both Brønsted
and Lewis acid sites, while the bands at 1546 and 1455 cm−1 are
due to the protonated pyridine molecule adsorbed on Brønsted
acid sites (B) and Lewis acid sites (L), respectively [26]. Gener-
ally, the acidity of a catalyst influences product distribution as
well as catalytic activity. In order to understand the relationship
between catalytic activity and the acidic properties of a cata-
lyst, we measured band intensity ratio for pyridine adsorbed on
Brønsted acid sites and Lewis acid sites respectively, as illustrated
in Table 1. The Brønsted to Lewis acid ratios were determined on
the basis of the integrated absorbances of the bands at 1546 and
1455 cm−1, respectively. The L/B acidity ratio was found to be high
for amorphous SiO2/Al2O3 and low for HZSM-5 zeolite. Biphenyl
conversions for all of the catalysts followed a similar trend as the
Lewis to Brønsted (L/B) acidity ratios.

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Fig. 4. Selectivity of various isopropylates over amorphous SiO2/Al2O3 catalyst.
isomers to form, including bulky isomers such as 2,2ꢀ-, 2,3ꢀ-, 2,4ꢀ-,
3,3ꢀ-, and 3,4ꢀ-DIPB.
results indicate that HY zeolite has no shape-selective nature for
the alkylation of biphenyl with propylene because the channels
allow for the formation of bulky transition states, even those of
bulky DIPB isomers. The alkylation of biphenyl with propylene over
HY was accompanied by significant formation of polyisopropylated
products, such as triisopropylbiphenyls (TriIPB) and tetraisopropy-
lbiphenyls (TetraIPB). The results support the assertion that HY
channels are too large for the selective formation of 4,4ꢀ-DIPB.
3.2. HY zeolite
The HY zeolite framework type code is FAU (Faujasite), and it
has large pores with three-dimensional zeolite channels with cubic
˚
symmetry having 12-m ring openings of 7.4 A in diameter that
˚
provide access to a supercage of diameter 12.4 A [27]. The selec-
tivities of various isopropylates over HY zeolite catalyst are shown
in Fig. 6A and B. Diisopropylbiphenyl isomers are the predominant
products, IPB and DIPB selectivities were found to be ∼22% and 48%
respectively; however, no significant changes in selectivity were
observed with time. The formation of tri, tetra, and penta isomers
was also observed. The selectivity of 4,4ꢀ-DIPB in the products over
HY zeolite was found to be less than 10%. The sum of other DIPB
isomers (2,xꢀ and 3,3ꢀ) was much higher than this. It was found
that, among the mono isopropyl biphenyls, 3-IPB is the dominant
isomer. The selectivities for 4-, 3- and 2-IPB were ca. 40, 55, and
5%, and no significant changes in selectivities were observed with
time (Fig. 7A). The selectivities of 4,4ꢀ-DIPB and 3,4ꢀ-DIPB isomers
were relatively low (10% and 35%, respectively) and thus the forma-
tion other DIPB isomers predominated (Fig. 7B). The selectivities of
DIPB isomers were almost constant throughout the reaction. The
3.3. HZSM-5 zeolite
The HZSM-5 zeolite framework type code is MFI; it has three-
dimensional zeolite channels, with a 10-MR pore entrance [27]. The
selectivities of various isopropylates over HZSM-5 zeolite catalyst
are shown in Fig. 8A and B. IPB isomers are the major products, the
selectivity of isopropylbiphenyl (∼84%) over HZSM-5 zeolite was
found to initially increase and then slightly decrease with time,
whereas the selectivity of DIPB slightly increased with time, reach-
ing a maximum value of 10% (Fig. 8A). Another interesting feature
of the catalyst is that the formation of higher isopropylates was
not observed. The selectivities of individual isomers are shown in
Fig. 8B, the selectivity of 4-IPB isomer being the highest among
the products and 4,4ꢀ-DIPB selectivity being very low (i.e., <5%).
It was found that among the mono isopropyl biphenyls 4-IPB is
Fig. 5. Selectivity of IPB and DIPB isomers over amorphous SiO2/Al2O3 catalyst.

V.R.R. Pendyala et al. / Applied Catalysis A: General 453 (2013) 195–203
199
Fig. 6. Selectivity of various isopropylates over HY zeolite.
Fig. 7. Selectivity of IPB and DIPB isomers over HY zeolite.
the predominant one (Fig. 9A). The selectivities for 4-, 3- and 2-
IPB were ca. 55, 33, and 12%, and the selectivities were constant
throughout the reaction. Among the DIPB isomers, the selectivities
of 4,4ꢀ-DIPB and 3,4ꢀ-DIPB isomers were found to be 34% and 23%,
respectively. The selectivities of all the DIPB isomers remained rel-
atively constant with reaction time. These features of the catalysis
over HZSM-5 suggest that their channels have no shape-selective
nature for the alkylation of biphenyl with propylene, because the
Fig. 8. Selectivity of various isopropylates over HZSM-5 zeolite.

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Fig. 9. Selectivity of IPB and DIPB isomers over HZSM-5 zeolite.
ZSM-5 channels are too small for the selective formation of 4,4ꢀ-
DIPB, they cannot allow the DIPB isomers to form including even
the least bulky isomer, such as 4,4ꢀ-DIPB. Hence, the formation of
mono alkylated biphenyls predominated.
the formation of 4,4ꢀ-DIPB. The yield of 4-IPB reached a maximum
at 60% conversion, and then, decreased at higher conversion.
However, the yield of 3-IPB slightly increased with the conversion,
although its formation leveled off at high conversion (Fig. 11A).
This shows that 4-IPB was much more reactive than 3-IPB for the
formation of DIPB isomers. The yields of 4,4ꢀ-DIPB and 3,4ꢀ-DIPB
increased linearly with increasing total DIPB yield during the
reaction, as shown in Fig. 11B. The yield of DIPB isomers, and
especially 3,4ꢀ- and 4,4ꢀ-DIPB, increased with the consumption of
4-IPB. The formation of 4,4ꢀ-DIPB was highly selective, and the
selectivity was almost constant throughout the course of the reac-
tion. Fig. 12 shows the yields of 3-IPB, 4IPB, 3,4ꢀ-DIPB and 4,4ꢀ-DIPB
of untreated mordenite (HMOR) zeolite. HMOR also followed the
same trends in yields with DMOR, whereas the percentages of
yields are lower relative to dealuminated mordenite.
It was found that among the mono isopropyl biphenyls, 4-IPB
is the predominant one (Fig. 13A). In the early stages of the reac-
tion, the selectivities for 4-, 3- and 2-IPB were ca. 82, 17, and
1%. The selectivity of 4-IPB was found to decrease with reaction
time, and the corresponding 3-IPB selectivity gradually increased.
Finally, after conversion reached a leveling off, both 4-IPB and
3-IPB reached the same selectivity, due to the 3-IPB being the
thermodynamically more stable isomer. The formation of 4,4ꢀ-DIPB
predominates among the DIPB isomers, and it has 90% selectivity,
while 3,4ꢀ-DIPB and other DIPB isomers had very low selectivities
3.4. Dealuminated mordenite (DMOR) zeolite
Mordenite belongs to the category of zeolites having
orthorhombic symmetry, with a pore structure that is effec-
tively one-dimensional. Elliptical straight channels of 12-MR
˚
˚
pore entrances (6.5 A × 7.0 A) run parallel to the [0 0 1] direction
˚
˚
and have small side pockets (2.6 A × 5.7 A) parallel to the [0 1 0]
direction, which connect to the next 12-m channel. Dealumina-
tion is an important method for the enhancement of catalytic
performance of mordenite, because it results in a decrease in
acid sites and an increase in mesoporosity. The selectivities of
IPB isomers decreased with reaction time, whereas the selectivity
of DIPB isomers increased monotonically with reaction time.
Another interesting feature of the catalyst is that the formation of
higher isopropylates was low (i.e., less than 3%), which is shown
in Fig. 10A. Fig. 10B shows a typical profile for the alkylation of
biphenyl with propylene over DMOR under 1 MPa of propylene
pressure. At an early stage of the reaction, biphenyl is converted
into IPB isomers, and especially 4-IPB. At the same time the
selectivity of DIPB isomers increased with time, especially toward
Fig. 10. Selectivity of various isopropylates over DMOR zeolite.

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201
Fig. 11. Effect on IPB yield and DIPB yield over DMOR zeolite.
Fig. 12. Effect on IPB yield and DIPB yield over HMOR zeolite.
(Fig. 13B). The selectivity of 4,4ꢀ-DIPB isomer slightly decreased
with time, while the corresponding 3,4ꢀ-DIPB selectivity slightly
increased. The decrease in the selectivity for 4,4ꢀ-DIPB is due to
the isomerization to thermodynamically stable 3,4ꢀ-DIPB on exter-
nal acid sites of MOR. These results indicate that the dealuminated
mordenite channels are appropriate for shape-selective formation
of 4,4ꢀ-DIPB. The time-on-stream (TOS) analysis against activity for
the alkylation of biphenyl reaction over dealuminated MOR zeo-
lite was carried out for a continuous period of 30 h and the results
are represented in Fig. 14. It is evident that dealuminated MOR
Fig. 13. Selectivity of IPB and DIPB isomers over DMOR zeolite.

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Scheme 1. Alkylation of biphenyl with propylene reaction pathway.
zeolite exhibits better stability with a period of 30 h. However the
selectivity of 4,4ꢀ-diisopropylbiphenyl decreased with time and the
corresponding selectivity increased for of 3,4ꢀ-diisopropylbiphenyl
(not shown), which might be due to the isomerization of 4,4ꢀ-
diisopropylbiphenyl on external acid sites.
even at 300 C. This is because there is not enough space in the
mordenite pores for the transition state of further alkylation of 4,4ꢀ-
DIPB. Selectivity for 4,4ꢀ-DIPB is high with mordenite among all
these zeolite, due to the bulky isomers being prohibited by these
channels, whereas, HY and SiO2/Al2O3 channels are too large for
the elimination of bulkier isomers. HZSM-5 channels are too small
to accommodate such a large product molecules. These findings
for HY, HZSM-5 and DMOR indicate that the geometry of the zeo-
lite channels is very important for the shape-selective formation of
4,4ꢀ-DIPB.
Figs. 10 and 13 reveal that shape-selective alkylation of biphenyl
with propylene occurs to yield, predominantly, the least bulky
4-IPB among IPB isomers and 4,4ꢀ-DIPB among DIPB isomers. 4,4ꢀ-
DIPB is produced by the consumption of 4-IPB, leading to the
accumulation of 2-IPB and 3-IPB. The high selectivity of 4,4ꢀ-DIPB
among the other DIPB isomers suggests that alkylation of biphenyl
with propylene proceeds through a consecutive reaction mecha-
nism via 4-IPB, as shown in Scheme 1; in the first stage of the
reaction biphenyl is predominantly converted to form IPB isomers
as governed by the shape-selectivity of the mordenite pore to yield
4-IPB as the principal isomer (Fig. 10A), which yields 4,4ꢀ-DIPB by
further alkylation of biphenyl with propylene. 3,4ꢀ-DIPB and 3,3ꢀ-
DIPB were also formed by the isomerization of 4,4ꢀ-DIPB as side
products. 4-IPB is a precursor to produce 4,4ꢀ-DIPB, but 3-IPB does
not participate significantly in the formation of 3,4ꢀ-DIPB, except
at a late stage, because it is a bulkier isomer than 4-IPB. No further
alkylation of 4,4ꢀ-DIPB to tri, tetra and penta isomers was observed
4. Conclusions
The reaction of alkylation of biphenyl with propylene has been
studied on HY, HZSM-5, DMOR, HMOR zeolites and amorphous
SiO2/Al2O3 catalyst. The catalytic activity of the reaction follows
the order: amorphous SiO2/Al2O3 > HY > DMOR > HMOR ꢁ HZSM-
5. Lewis to Brønsted (L/B) acidity ratios were found to be high for
amorphous SiO2/Al2O3 and low for HZSM-5 zeolite. A 96% conver-
sion of biphenyl and 90% selectivity of 4,4ꢀ-DIPB was obtained over
dealuminated mordenite zeolite, even at temperatures as high as
300 ◦C. Highly shape-selective alkylation of biphenyl with propyl-
ene was achieved over DMOR zeolite. The selectivity for 4,4ꢀ-DIPB
is high for dealuminated mordenite zeolite, whereas for HY, HZSM-
5 and amorphous SiO2–Al2O3 the selectivity was very low and in
the range of 10–35%. These results show that the shape-selective
catalysis of zeolites in the alkylation of biphenyl with propylene is
governed by the geometry of the channels and pore entrances.
Acknowledgment
This work was supported by the Commonwealth of Kentucky.
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