Synthesis of trans-stilbene through the hydrogenation of diphenylacetylene

Article abstract of DOI:10.1016/j.cattod.2010.10.089

Trans-stilbene (trans-ST) was produced through the hydrogenation of diphenylacetylene (DPA). Pd-based intermetallic compounds (IMCs) supported on silica were applied to the selective hydrogenation of DPA into cis- and trans-ST. Pd₃Bi/SiO₂ showed the highest selectivity to stilbenes without accelerating the deep hydrogenation into diphenylethane (DPE), after DPA was completely converted. Proton-type zeolites were examined for the isomerization of cis-ST, the main product in the hydrogenation of DPA, into trans-ST. H-USY zeolite partially exchanged with Na⁺ ions gave the highest activity owing to the appropriate acid strength and enough space inside the pores for cis-ST to enter. The mixture of Pd₃Bi/SiO₂ and H-USY gave trans-ST yield of 74 mol% through the one-pot reaction of DPA. The isomerization rate was significantly retarded by coexisting DPA and DPE molecules.

Full text of DOI:10.1016/j.cattod.2010.10.089

Catalysis Today 164 (2011) 143–147
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Catalysis Today
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Synthesis of trans-stilbene through the hydrogenation of diphenylacetylene
Takayuki Komatsua,∗, Kaori Takagib, Ken-ichi Ozawaa
a Department of Chemistry and Materials Science, Tokyo Institute of Technology, 2-12-1-E1-10 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
b Department of Chemistry, Tokyo Institute of Technology, 2-12-1-E1-10 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 July 2010
Received in revised form 23 October 2010
Accepted 26 October 2010
Available online 3 December 2010
Trans-stilbene (trans-ST) was produced through the hydrogenation of diphenylacetylene (DPA). Pd-based
intermetallic compounds (IMCs) supported on silica were applied to the selective hydrogenation of DPA
into cis- and trans-ST. Pd3Bi/SiO2 showed the highest selectivity to stilbenes without accelerating the deep
hydrogenation into diphenylethane (DPE), after DPA was completely converted. Proton-type zeolites
were examined for the isomerization of cis-ST, the main product in the hydrogenation of DPA, into trans-
ST. H-USY zeolite partially exchanged with Na+ ions gave the highest activity owing to the appropriate
acid strength and enough space inside the pores for cis-ST to enter. The mixture of Pd3Bi/SiO2 and H-
USY gave trans-ST yield of 74 mol% through the one-pot reaction of DPA. The isomerization rate was
significantly retarded by coexisting DPA and DPE molecules.
Keywords:
Stilbene
Zeolite
Selective hydrogenation
Intermetallic compound
Isomerization
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
genation into DPE, routes (4) and (5) in Scheme 1, for the selective
formation of stilbenes. As shown in Scheme 2, the molecule of trans-
Liquid crystal displays have been widely used for various appli-
cations. Trans-ST is one of the raw materials for the syntheses
of liquid crystal molecules. In addition, trans-ST and its deriva-
tives are used for the production of dyes, pigments, fluorescent
whitener, electro-luminescent display, and so on. Trans-ST is now
produced from benzene derivatives through the coupling reactions,
such as Grignard reaction and Wittig reaction. These reactions usu-
ally give cis-ST predominantly with trans-ST as a by-product. In
this study, we take up a new route for the production of trans-
ST through the hydrogenation of DPA as shown in Scheme 1. In
this process, the catalyst should be selective both for the par-
tial hydrogenation of a carbon–carbon triple bond into a double
bond and the stereo-selective formation of trans-ST instead of
cis-ST.
The purpose of this study is to obtain an effective catalyst for
the formation of trans-ST directly from DPA or through the partial
hydrogenation of DPA into cis-ST followed by the isomerization into
trans-ST. We have studied on the catalytic properties of IMCs for
the selective hydrogenation and found that IMC catalysts, CoGe [1],
Ni3Sn2/SiO2 [2], Ni3Ge/MCM-41 [3], Pd3Bi/SiO2 [4], etc., are highly
selective for the partial hydrogenation of acetylene into ethylene.
The high selectivity of IMCs for the partial hydrogenation of acety-
lene has been reported also for PdGa, Pd3Ga7 [5] and NiZn [6].
Therefore, we applied Pd-based IMCs to retard the deep hydro-
ST has a plane structure, whereas that of cis-ST has a bending one.
Therefore, the second selectivity, the stereo-selective formation of
trans-isomer, could be achieved by the shape selective catalysis
inside the pores of zeolite.
2. Experimental
2.1. Catalyst preparation
Pd(3 wt%)/SiO2 was prepared by a pore-filling impregnation
method using an aqueous solution of PdCl2 and silica gel (CARiACT
G-6, Fuji Silysia). After drying the mixture at 403 K, it was reduced
in flowing hydrogen at 823 K. Supported Pd-based IMC catalysts
were prepared by a successive impregnation method onto Pd/SiO2.
Aqueous solutions of Bi(NO3)3, Fe(NO3)3, TlNO3 were used to pre-
pare Pd3Bi/SiO2, PdFe/SiO2 and Pd3Tl/SiO2, respectively. Toluene
solution of Ga(acac)3 and benzene solution of In(acac)3 were used
to obtain Pd5Ga2/SiO2 and PdIn/SiO2. After the impregnation, they
were reduced at 773 K (PdFe), 873 K (PdIn, Pd3Tl), and 1073 K
(Pd3Bi, Pd5Ga2), respectively, to accelerate the solid-phase reaction
into each IMC. Lindlar catalyst was purchased from Aldrich contain-
ing 5 wt% Pd on calcium carbonate with a small amount of lead.
H-USY(Si/Al = 16) was supplied from Catalysts & Chemicals Ind.
Na-Y (Y-30, Tosoh) was ion-exchanged with an aqueous solution
of NH4Cl and calcined in air at 743 K to obtain H(59%)-Y(2.9). H-
ZSM-5(20), H-beta(12), H-MCM-22(19) and Al-MCM-41(19) were
synthesized hydrothermally followed by the NH4+-exchange and
calcination. H-USY was partially exchanged by Na+ with aqueous
∗
Corresponding author. Tel.: +81 3 5734-3532; fax: +81 3 5734 2758.
E-mail address: komatsu@cms.titech.ac.jp (T. Komatsu).
0920-5861/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2010.10.089

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T. Komatsu et al. / Catalysis Today 164 (2011) 143–147
100
trans-ST
(3)
(4)
(1)
80
60
DPA
DPE
(2)
(5)
40
cis-ST
20
Scheme 1. Reaction paths in the hydrogenation of DPA.
0
0
50
100
150
solutions (2.4–100 mM) of NaCl at 298 or 343 K for 12–24 h to obtain
Na+-exchange levels of 12–74%.
Reaction time / min
Fig. 1. Hydrogenation of DPA on Pd/SiO2 at 298 K. DPA conversion (ꢀ), selectivity
to cis-ST (᭹), trans-ST (ꢀ) and DPE (ꢁ).
2.2. Characterization
The crystal phases of IMC catalysts and zeolites were observed
by powder X-ray diffraction (RINT 2400, Rigaku) with CuK␣ radi-
ation. The bulk composition of prepared catalysts was determined
by ICP (Rigaku, JY38) after dissolving samples with HF solution and
aqua regia. TPD of adsorbed ammonia was measured by a flow
system with a TCD detector. After dehydrating zeolite in flowing
helium at 773 K, ammonia was introduced onto the sample at 423 K
for 10 min. The sample was purged with flowing helium for 10 min
and a TPD pattern was obtained from 298 to 1073 K at a heating
located on the support with relatively large pores. The hydrogena-
tion occurred at 298 K to produce cis- and trans-ST and DPE. As
shown in Table 1, DPA conversion was as high as 96% in 60 min
of reaction. The main product was cis-ST, whereas the selectivity
to trans-ST was only 2 mol%. Fig. 1 shows the change in DPA con-
version and selectivity to each product with reaction time. When
the conversion became closer to 100%, the selectivity to cis-ST
decreased steeply, whereas that to DPE increased. DPA molecules
would be adsorbed on the surface of Pd particles more strongly than
cis-ST. When the residual amount of DPA becomes smaller at higher
conversions, the adsorption of cis-ST would occur to be hydro-
genated into DPE. The selectivity to trans-ST was always lower than
5 mol%. At the reaction time of 120 min, DPE was the only product.
Then we carried out the reaction on Pd/zeolite catalysts, expecting
the shape-selective catalysis in their micropores (Table 1). Though
DPA conversion depended on the kind of zeolites, the selectivity to
trans-ST was always lower than 15 mol%. When we extended the
reaction time to obtain higher conversion, the selectivity to DPE
increased to lower the selectivity to cis- and trans-ST as in the case
of Pd/SiO2 (Fig. 1). The prolonged reaction accelerated the deep
hydrogenation into DPE, routes (4) and (5). Therefore, we concluded
that it is difficult to obtain trans-ST with high selectivity through
the direct hydrogenation with Pd/zeolite catalysts.
rate of 10 K min−1
.
2.3. Catalytic reaction
The hydrogenation of DPA was carried out with a three-neck
flask under atmospheric pressure of flowing H2. The catalyst (0.10
or 0.50 g) was put into the flask and pretreated in situ with flowing
H2 at 673 K. After purging the flask by argon, DPA (1.0 g) dissolved in
5 ml of toluene was injected through a septum. The hydrogenation
was started by flowing H2 into the flask with agitating the reaction
mixture. The isomerization of cis-ST was carried out with the same
reaction system as that used for the hydrogenation. After the in situ
pretreatment of catalyst in flowing argon at 673 K, the isomeriza-
tion was started by injecting cis-ST (0.20 ml) diluted with 5 ml of
toluene. Reaction products in both reactions were analyzed using
an FID gas chromatograph (GC-14B, Shimadzu) with a column of
TC-70 (0.25 mm × 60 m, GL Science).
3.2. Selective hydrogenation of DPA into cis-ST
Next, we studied the formation of trans-ST through cis-ST by
routes (2) and (3). At first, the hydrogenation of DPA into cis-ST,
route (2), was examined on various Pd catalysts. To obtain trans-ST
selectively, it must be important to retard the secondary hydro-
genation of cis-ST into DPE. For this purpose, we used various
Pd-based IMCs supported on SiO2. XRD patterns showed that all
the IMC catalysts gave their specific diffraction, indicating that
they were composed of single-phase IMC particles supported on
SiO2. For example, Pd3Bi/SiO2 gave the main diffraction peaks at
2ꢀ = 38.2◦ and 41.0◦, whereas the main peaks of Pd/SiO2 appeared
at 40.1◦ and 46.7◦. Fig. 2 shows the change in the total selectivity
to cis- and trans-ST with conversion at the reaction temperature of
333 K. The selectivity was almost 100 mol% when the conversion
was low. The selectivity decreased significantly with increasing
the conversion. Some IMC catalysts showed higher selectivity than
Pd/SiO2 and Lindlar catalyst at high DPA conversions. Among them,
Pd3Bi/SiO2 gave the highest selectivity of 98 mol% at around 90%
conversion. We have reported that this catalyst had exhibited the
highest selectivity to ethylene in the hydrogenation of acetylene
among Pd-based IMC catalysts [4].
3. Results and discussion
3.1. Direct hydrogenation of DPA into trans-ST
Direct hydrogenation of DPA into trans-ST, route (1) in Scheme 1,
was examined with Pd-containing catalysts. Pd(0.7 wt%)/SiO2 was
first used to know the catalytic properties of Pd metal particles
The high selectivity of Pd3Bi/SiO2 for the partial hydrogenation
of DPA at higher conversions was further confirmed by the reac-
Scheme 2. Molecular structure of cis-ST (a) and trans-ST (b).

T. Komatsu et al. / Catalysis Today 164 (2011) 143–147
145
Table 1
Hydrogenation of DPAa on Pd-supported catalysts.
Catalysts
Solvent
DPA conversion (%)
Selectivity (mol%)
cis-ST
trans-ST
DPE
Pd/SiO2
Pd/ZSM-5
Pd/USY
Pd/USY
Pd/MCM-22
Toluene
Toluene
Toluene
THF
96
59
39
40
17
75
88
77
81
79
2
2
14
10
14
23
10
9
9
7
THF
a
Reaction temperature: 298 K, reaction time: 60 min, catalyst weight: 0.10 g.
100
100
80
60
40
20
0
90
Pd3Bi/SiO2
PdFe/SiO2
Pd5Ga2/SiO2
Pd3Tl/SiO2
PdIn/SiO2
Pd/SiO2
80
70
60
Lindlar
0
20
40
60
80
100
0
20
40
60
80
100
Reaction time / min
DPA conversion / %
Fig. 4. Isomerization of cis-ST at 333 K on H-USY (ꢂ), H-MCM-22 (ꢃ), H-beta (ꢁ),
H-Y (ꢀ), H-ZSM-5 (᭹) and Al-MCM-41 (×).
Fig. 2. Selectivity to stilbene in the hydrogenation of DPA on Pd-based catalysts at
333 K.
333 K, the same temperature as that in the hydrogenation (Fig. 2),
on various proton-type zeolites. On all the catalysts, only trans-ST
was produced. It is clear that H-USY has the highest activity. The
conversion of cis-ST reached 69% at the reaction time of 90 min. H-
Y, however, gave the very low conversion compared with H-USY,
suggesting that the weaker acid sites in H-Y are not effective for
the isomerization. The very low conversion on Al-MCM-41 also
indicates that the isomerization does not proceed on the weak
acid sites. Though H-ZSM-5 and H-beta have stronger acid sites
than H-USY, they showed lower conversion than H-USY. Their pore
openings would be too small for the bending molecule of cis-ST to
enter. The medium conversion observed on H-MCM-22 may result
from the reaction in the cups on its external surface. Owing to the
large pore diameter and the sufficient acid strength, H-USY would
be the most effective catalyst for the isomerization of bulky cis-ST.
To clarify the role of Brønsted acid sites in H-USY, we prepared
H-USY with various proton concentration by Na+-exchange into H-
USY. Fig. 5 shows the effect of Na+-exchange level on the amount
of acid sites and the conversion of cis-ST in the isomerization.
tion with the larger amount of catalyst (0.50 g) at higher reaction
temperature (353 K). Fig. 3 shows that the conversion reached 100%
at 210 min. However, the selectivity to DPE increased only slightly
even after 210 min to be as low as 3 mol% at 300 min. It is revealed
that Pd3Bi/SiO2 does not accelerate the secondary hydrogenation
of cis- and trans-ST significantly even in the absence of DPA. This
catalyst will be effective for the formation of trans-ST through the
routes (2) and (3).
3.3. Isomerization of cis-ST into trans-ST
The isomerization of cis-ST, route (3), was next studied on acidic
zeolites as catalysts. Though the photosensitized isomerization of
stilbene has been studied using the stabilizing effect of zeolite pores
[7,8], the catalytic isomerization of cis-ST has been reported for H-
Y [9] and Ca-Y [10]. Fig. 4 shows the reaction results obtained at
100
80
60
40
20
0
10
8
100
80
60
40
20
0
6
4
2
0
0
100
200
300
0
20
40
60
80
Reaction time / min
Na+-exchange level / %
Fig. 3. Hydrogenation of DPA on Pd3Bi/SiO2 (0.50 g) at 353 K. Symbols are the same
as those in Fig. 1.
Fig. 5. Effect of Na+-exchange on the amount of acid sites (♦) and cis-ST conversion
in isomerization at 333 K (ꢂ).

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T. Komatsu et al. / Catalysis Today 164 (2011) 143–147
100
100
80
60
40
20
0
80
60
40
20
0
0
100
200
300
400
500
0
50
100
150
200
Reaction time / min
Reaction time / min
Fig. 8. Comparison between trans-ST yields in the isomerization of cis-ST (ꢃ) on
Na(16%), H-USY (0.50 g) and the one-pot reaction of DPA (ꢀ) on the mixture of
Pd3Bi/SiO2 (0.10 g) and Na(16%), H-USY (0.50 g) at 353 K.
Fig. 6. One-pot reaction of DPA on the mixture of Pd-USY (0.10 g) and Na(16%),
H-USY (0.50 g) at 333 K. Symbols are the same as those in Fig. 1.
The parent H-USY contained Na+ with exchange level of 9%. The
acid amount, measured by NH3-TPD, decreased monotonously with
increasing Na+-exchange level and the acid sites which can adsorb
NH3 almost disappeared at 74% exchange level. On the other hand, a
slight Na+-exchange into the parent H-USY resulted in the increase
in cis-ST conversion. The further Na+-exchange decreased the con-
version. The isomerization would be catalyzed by Brønsted acid
sites though a small number of the strong acid sites may accelerate
the oligomerization of ST resulting in the slight deactivation.
100
80
60
40
20
0
3.4. One-pot formation of trans-ST via cis-ST
In the hydrogenation of DPA (Table 1), Pd/USY gave cis-ST as
the main product with selectivity of ca. 80 mol%. Then we added
Na(16%), H-USY (0.50 g), having the highest activity for isomer-
ization (Fig. 5), into Pd/USY (0.1 g) to accelerate the isomerization
of primarily produced cis-ST for the one-pot formation of trans-ST
from DPA. As shown in Fig. 6, the selectivity to cis-ST decreased with
reaction time indicating the secondary reaction of cis-ST. However,
the formation of DPE was mainly accelerated at higher conver-
sion consuming trans-ST as well as cis-ST. The highest selectivity
to trans-ST was only 29 mol%. To retard the secondary hydrogena-
tion into DPE, Pd/USY was replaced by Pd3Bi/SiO2 (0.10 g) because
of its high selectivity for the partial hydrogenation (Figs. 2 and 3).
As shown in Fig. 7, cis-ST was the main product at the initial stage.
With increasing reaction time, the selectivity to cis-ST decreased,
whereas that to trans-ST increased. Though DPE formation was also
observed, the isomerization of cis-ST was effectively accelerated
by Na(16%), H-USY. The selectivity and yield of trans-ST reached
74 mol% through 450 min of one-pot reaction of DPA.
0
20
40
60
80
100
Reaction time / min
Fig. 9. Change in conversion in the isomerization of cis-ST without additive (ꢂ), and
with DPA (♦), DPE (ꢀ) and biphenyl (ꢁ) on Na(16%), H-USY at 333 K. Molar ratio of
additive/cis-ST is 1.0.
Fig. 7 also indicates that the rate of hydrogenation was much
higher than that of isomerization. The rate-determining step will
be the isomerization of cis-ST. Fig. 8 shows the change in trans-
ST yield with reaction time during the one-pot reaction of DPA
(Fig. 7) and the isomerization of cis-ST at the same temperature
of 353 K. Though we used the same amount (0.50 g) of Na(16%), H-
USY for both reactions, the formation rate of trans-ST was much
lower in the one-pot reaction. The co-existing DPA molecules may
hinder the isomerization of cis-ST. We examined the effect of co-
existing molecules on the rate of isomerization of cis-ST (Fig. 9).
The addition of DPA with DPA/cis-ST molar ratio of 1.0 strongly
retard the isomerization. The electronic effect of the triple bond in
DPA molecule could affect the isomerization of cis-ST. However, the
similar effect was observed when DPE or even biphenyl was added
instead of DPA. The diffusion of cis-ST between supercages of USY
may be hindered by these molecules. In the case of the one-pot
reaction, therefore, the formation of DPE should be minimized to
obtain trans-ST with higher reaction rate after DPA is completely
converted into cis-ST.
100
80
60
40
20
0
4. Conclusions
The formation of trans-ST from DPA is achieved through the one-
pot reaction consisting of the partial hydrogenation into cis-ST and
the concomitant isomerization of cis-ST into trans-ST. The partial
hydrogenation of DPA is catalyzed by Pd-based intermetallic com-
pounds, such as Pd3Bi/SiO2, with high selectivity even after DPA
is fully converted into cis- and trans-ST. The isomerization of cis-
ST is effectively catalyzed by Brønsted acid sites of H-USY slightly
0
100
200
300
400
Reaction time / min
Fig. 7. One-pot reaction of DPA on the mixture of Pd3Bi/SiO2 (0.10 g) and Na(16%),
H-USY (0.50 g) at 353 K. Symbols are the same as those in Fig. 1.

T. Komatsu et al. / Catalysis Today 164 (2011) 143–147
147
exchanged with Na+ ions. The acid strength and pore size of the
Na+-exchanged H-USY are appropriate for the isomerization. The
yield of trans-ST exceeds 70 mol% through the one-pot reaction on
the mixture of Pd3Bi/SiO2 and Na(16%), H-USY.
[3] T. Komatsu, T. Kishi, T. Gorai, J. Catal. 259 (2008) 174.
[4] T. Komatsu, T. Gorai, Abst. 14th Intern. Congr. Catal. OB31, Seoul, 2008, p. 69.
[5] J. Osswald, R. Giedigkeit, R.E. Jentoft, M. Armbrüster, F. Girgsdies, K. Kovnir, T.
Ressler, Y. Grin, R. Schlögl, J. Catal. 258 (2008) 210.
[6] F. Studt, F. Abild-Pedersen, T. Bligaard, R.Z. Sørensen, C.H. Christensen, J.K.
Nørskov, Science 320 (2008) 1320.
[7] A. Corma, V. Fornes, H. Garcia, M.A. Miranda, J. Primo, M.-J. Sabater, J. Am. Chem.
Soc. 116 (1994) 2276.
Acknowledgement
[8] P.H. Laksminarasimhan, R.B. Sunoj, S. Karthikeyan, J. Chandrasekhar, L.J. John-
ston, V. Ramamurthy, J. Photochem. Photobiol. A: Chem. 153 (2002) 41.
[9] M. Kojima, H. Takeya, Y. Kuriyama, S. Oishi, Chem. Lett. (1997) 997.
[10] K. Pitchumani, A. Joy, N. Prevost, V. Ramamurthy, Chem. Commun. (1997) 127.
The authors would like to thank Dr. Masukawa for the valuable
information and discussion on the application and analysis of trans-
ST.
References
[1] T. Komatsu, M. Fukui, T. Yashima, Stud. Surf. Sci. Catal. 101 (1996) 1095.
[2] A. Onda, T. Komatsu, T. Yashima, J. Catal. 201 (2001) 13.