Vapor-phase catalytic dehydration of terminal diols

Article abstract of DOI:10.1016/j.cattod.2010.10.026

Vapor-phase catalytic reactions of several terminal diols were investigated over several rare earth oxides, such as Sc₂O₃, Y ₂O₃, CeO₂, Yb₂O₃, and Lu₂O₃. Sc₂O₃ showed selective catalytic activity in the dehydration of terminal diols with long carbon chain, such as 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and 1,12-dodecanediol, to produce the corresponding unsaturated alcohols. In the dehydration of 1,6-hexanediol, 5-hexen-1-ol was produced with selectivity over 60 mol%, together with by-products such as ε-caprolactone and oxacycloheptane. In the dehydration of 1,10-decanediol, 9-decen-1-ol was produced with selectivity higher than 70 mol%. In addition to Sc ₂O₃, heavy rare earth oxides such as Lu₂O ₃ as well as monoclinic ZrO₂ showed moderate selectivity in the dehydration of the terminal diols.

Full text of DOI:10.1016/j.cattod.2010.10.026

Catalysis Today 164 (2011) 419–424
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Vapor-phase catalytic dehydration of terminal diols
Katsutoshi Abe, Yusuke Ohishi, Takuto Okada, Yasuhiro Yamada, Satoshi Sato∗
Graduate School of Engineering, Chiba University, Yayoi, Inage, Chiba 263-8522, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 4 November 2010
Vapor-phase catalytic reactions of several terminal diols were investigated over several rare earth oxides,
such as Sc2O3, Y2O3, CeO2, Yb2O3, and Lu2O3. Sc2O3 showed selective catalytic activity in the dehydration
of terminal diols with long carbon chain, such as 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-
nonanediol, 1,10-decanediol, and 1,12-dodecanediol, to produce the corresponding unsaturated alcohols.
In the dehydration of 1,6-hexanediol, 5-hexen-1-ol was produced with selectivity over 60 mol%, together
with by-products such as ␧-caprolactone and oxacycloheptane. In the dehydration of 1,10-decanediol,
9-decen-1-ol was produced with selectivity higher than 70 mol%. In addition to Sc2O3, heavy rare earth
oxides such as Lu2O3 as well as monoclinic ZrO2 showed moderate selectivity in the dehydration of the
terminal diols.
Keywords:
Dehydration
1,6-Hexanediol
Unsaturated alcohols
5-Hexen-1-ol
Sc2O3
Rare earth oxides
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
We have also found that Yb2O3 shows different catalytic activ-
ities depending on its crystal structure [7], which varies from
More than four decades ago, it was discovered that rare earth
oxides (REOs) promote the Hofmann elimination reaction in the
dehydration of 2-alcohols such as 4-methyl-2-pentanol [1]. An ␣-
olefin, such as 1-butene, is formed with selectivity higher than
80% in the dehydration of 2-butanol over REOs, except La2O3 and
CeO2 [2]. We have previously investigated the catalytic perfor-
mance of REOs [3–11], and reported that several REOs, such as
CeO2, Tb4O7, Er2O3, and Yb2O3, are effective for the dehydration of
diols, such as 1,3-, 1,4, and 1,5-diols, to produce unsaturated alco-
hols. CeO2 catalyzes the dehydration of 1,3-diols into unsaturated
alcohols [3–5]: 3-buten-2-ol and trans-2-buten-1-ol are produced
from 1,3-buanediol at 325 ◦C. CeO2 is the most active catalyst for
the formation of the unsaturated alcohols from 1,3-buanediol [11].
In the dehydration of 1,4-butanediol over CeO2 at 400 ◦C, 3-
buten-1-ol is produced with maximum selectivity of 68 mol%,
together with the formation of tetrahydrofuran (THF) [6]. Heavy
REO catalysts, such as Tb4O7, Er2O3, and Yb2O3, are also selec-
tive for the production of 3-buten-1-ol from 1,4-butanediol [7]:
the selectivity to 3-buten-1-ol exceeds 80 mol% over cubic Yb2O3.
The surface character of REOs is basic rather than acidic [8,10].
In the reaction of 1,4-butanediol, the catalytic function of REOs is
related to the basic properties of REO originated in lanthanide con-
traction [8]. Yb2O3 is more active than CeO2 in the dehydration of
1,4-butanediol.
monoclinic to cubic at temperatures around 800 ◦C. Yb2O3 with the
cubic bixbyite structure shows higher selectivity to 3-buten-1-ol
than the monoclinic one. Yb2O3 also works as an effective catalyst
in the dehydration of 1,5-pentanediol to produce 4-penten-1-ol [9].
In addition to REOs, monoclinic ZrO2 [12,13] and In2O3 [14] also
show the catalytic activity for the formation of 3-buten-1-ol in the
dehydration of 1,4-butanediol.
-
H2O
OH
HO
OH
It is known that scandium trifluoromethanesulfonate is used
for a reusable Lewis acid catalyst in organic synthesis such as
Diels–Alder reaction [15]. On the other hand, there are a few stud-
ies on the catalytic property of Sc2O3. In heterogeneous catalysis, it
is reported that pure Sc2O3 as well as Sm2O3 is selective for C2 for-
mation in the oxidative coupling of methane [16]. Sc2O3 and Y2O3
are active for the reduction of nitric oxide with methane [17]. Scan-
dium is an expensive metal, so that catalytic performance of Sc2O3
has rarely been investigated.
9-Decen-1-ol is synthesized in the decomposition of monoesters
of 1,10-decanediol and carboxylic acids, such as palmitic acid and
stearic acid, at temperatures of 330-345 ◦C [18]. In the dehydration
of terminal diols, there is no research report on the direct synthesis
of long-chain unsaturated alcohols, such as 5-hexen-1-ol and 9-
decen-1-ol. We preliminarily found that Sc2O3 was active for the
formation of unsaturated alcohols from terminal diols with long
carbon chain. In this paper, we investigated catalytic activity of pure
Sc2O3 as well as several REOs for the reactions of diols with carbon
chains of 6–12 and of cyclohexanol as a reference of monoalcohol.
Then, we discussed the catalytic properties of Sc2O3 in connection
with the radius of cation in the REOs.
-
H2O
HO
OH
OH
∗
Corresponding author. Tel.: +81 43 290 3376; fax: +81 43 290 3401.
E-mail address: satoshi@faculty.chiba-u.jp (S. Sato).
0920-5861/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2010.10.026

420
K. Abe et al. / Catalysis Today 164 (2011) 419–424
-
3. Results and discussion
H2O
HO
OH
OH
3.1. Reaction of diols over several oxide catalysts
Table 1 shows catalytic activity of several REOs in the dehydra-
tion of 1,6-hexanediol. The REO samples were calcined at either 800
or 1000 ◦C. Among the catalysts compared in Table 1, Sc2O3 showed
the highest selectivity in the dehydration of 1,6-hexanediol into 5-
hexen-1-ol, and the conversion over Sc2O3 was higher than those
over the other REOs. Although Yb2O3 and Y2O3 show high selec-
tivity to 3-buten-1-ol in the dehydration of 1,4-butanediol in our
previous work [7,10], they were less selective than Sc2O3 in the
formation of 5-hexen-1-ol from 1,6-hexanediol. In addition, CeO2,
which is an excellent catalyst for the formation of 2-propen-1-ol
from 1,3-propnediol [3], was also less selective to 5-hexen-1-ol
than the other REOs, and CeO2 produced cyclohexanone and 1-
hexanol as by-products. Over the catalysts we tested, several cyclic
compounds such as oxacycloheptane, cyclopentanone, cyclopen-
tanemethanol were observed. During the reactions in the initial 5 h,
the conversion of 1,6-hexanediol was decreased by 10–20% with
time on stream, while the selectivity to 5-hexen-1-ol was hardly
changed. As a reference catalyst, monoclinic ZrO2 showed the con-
version higher than Sc2O3, whereas the selectivity to 5-hexen-1-ol
is low. Al2O3 was also active but not selective in the dehydration of
1,6-hexanediol: a lot of by-products were observed.
2. Experimental
2.1. Samples
REO samples, such as Sc2O3, Y2O3, Yb2O3, CeO2, and Lu2O3, were
purchased from Kanto Kagaku Co. Ltd., Japan. The commercial REO
samples were prepared by decomposing the corresponding chlo-
rides at temperatures >2000 ◦C for ca. 2 s in the vapor phase, and
their physical properties used in this study are listed in tables of Ref.
[19]. Monoclinic ZrO2 (RSC-HP) was supplied by Daiichi Kigenso
Kagaku Kogyo Co. Ltd. Al2O3 was supplied by Dia Catalyst, DC-
2282. The samples used for the catalytic reactions were calcined
at an appropriate temperature between 500 and 1000 ◦C for 3 h
[10]. The specific surface area of the catalysts, SA, was calculated
with the BET method using N2 isotherm at −196 ◦C.
1,6-Hexanediol, cyclohexanol, and ethanol were purchased
from Wako Pure Chemical Industries, Japan. The other diols, such as
1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol,
and 1,12-dodecanediol, were purchased from Tokyo Kasei Kogyo
Ltd., Japan. The alcohols were used for the catalytic reaction without
further purification.
Table 2 shows catalytic performance of REOs on the dehydration
of several terminal diols at 350 ◦C, except 1,12-dodecanediol. The
dehydration of 1,12-dodecanediol was conducted at a high tem-
perature of 400 ◦C, and so the conversion of 1,12-dodecanediol was
higher than those of the other terminal diols. In a similar way to
the dehydration of 1,6-hexanediol, Sc2O3 showed high conversion
and selectivity to the corresponding unsaturated alcohols from the
terminal diols we tested. The other REOs such as Yb2O3 and Y2O3
showed lower selectivity to unsaturated alcohols than Sc2O3. Cyclic
ketones such as cyclohexanone and cyclopentanone were produced
from 1,7-heptanediol and 1,8-octanediol. Fig. 1 summarizes selec-
tivity to the corresponding unsaturated alcohol in the dehydration
of terminal diols over REOs. Although the selectivity was obtained
at different conversions, it is meaningful: the highest selectivity
was obtained at high conversion over Sc2O3, while the low selec-
tivity was at low conversion over CeO2. The terminal diols with
carbon chains between 6 and 10 had a similar reactivity over the
REO catalysts. The conversion and selectivity in Table 2 is strongly
dependent on the catalysts. Because the interaction between the
two OH groups in the long chain diols is weak, the conversion and
selectivity would be similar in the reaction of various long diols
over the same catalyst.
2.2. Catalytic reaction
The catalytic reactions were performed in a fixed-bed down-
flow reactor. Prior to the reactions, a catalyst sample (weight,
W = 0.50 g) was preheated in the flow reactor in N2 flow at 500 ◦C
for 1 h. After the temperature of catalyst bed was set at a prescribed
temperature between 325 and 425 ◦C, a reactant solution was fed
through the reactor top at a liquid feed rate, F, of 1.80 cm3 h−1
together with N2 flow of 27 cm3 min−1. The reactant diol dissolved
in ethanol at 20 wt.% was used as a reactant solution. The efflu-
ent collected every hour was analyzed by gas chromatography
(GC-8A, Shimadzu, Japan) with a flame ionization detector and a
30-m capillary column (TC-WAX, GL Science Inc., Japan) and by
gas chromatography with a mass spectrometer (GCMS-QP-5050A,
Shimadzu, Japan) and a 30-m capillary column (DB-WAX, Agilent
Technologies, USA).
In this paper, the catalytic activity was evaluated by averaging
the conversion data in the initial 5 h. The conversion of alcohol is
defined as the amount of alcohol consumed in the reaction. The
selectivity to each product is defined as molar selectivity.
Table 1
Catalytic conversion of 1,6-hexanediol over several oxides at 350 ◦C.a
Catalyst (calcination/◦C)
SAb (m2 g−1
)
Conversion (%)
Selectivity (mol%)
5Hx1ol
HxOH
OCH
CHN
Dienes
CPNs
Sc2O3
CeO2
Y2O3
(800)
(800)
(1000)
(1000)
(1000)
(800)
51.5
34.3
21.8
15.7
14.1
29.0
205.0
47.8
45.2
20.0
29.8
32.9
52.9
99.9
60.9
4.8
0
4.4
4.3
8.4
11.7
9.9
22.4
14.3
0
0
0
3.7
11.0
8.8
6.9
7.0
9.4
0
9.4
0.3
0.3
0.3
0.5
0
25.2
2.4
2.5
2.8
1.9
0
26.3
17.6
32.2
32.6
2.1
1.9
0.1
0.1
1.2
21.0
Yb2O3
Lu2O3
c
ZrO2
d
Al2O3
(600)
a
Conversion and selectivity were averaged in the initial 5 h. W/F = 1.39 g h cm−3 where W and F are catalyst weight and feed rate of reactant diol, respectively. 1,6-Hexanediol
dissolved in ethanol at 20 wt.% was fed through the reactor top. N2 carrier flow rate = 27 cm3 min−1
.
5Hx1ol, 5-hexen-1-ol; HxOH, 1-hexanol; OCH, oxacycloheptane; CHN, cyclohexanone; Dienes, 1,5-hexadiene + 1,4-hexadiene; CPNs, cyclopentanone + cyclopentanol. Other
by-products are 4-hexen-1-ol, ␧-caprolactone, cyclohexanol, cyclopentylmethanol, 2-cyclopentenylmethanol, cyclohexene, cyclohexane, and several unidentified products.
b
Specific surface area.
c
Monoclinic ZrO2.
Reacted at 300 ◦C.
d

K. Abe et al. / Catalysis Today 164 (2011) 419–424
421
Table 2
Catalytic conversion of diols over several oxides at 350 ◦C.a
Catalyst(calcination/◦C)
1,7-Hexanediol
1,8-Octanediol
1,9-Nonanediol
1,10-Decanediol
1,12-Dodecanediol
Conv.
Selec.b
Conv.
Selec.c
Conv.
Selec.d
Conv.
Selec.e
Conv.f
Selec.f
Sc2O3
CeO2
Y2O3
(800)
(800)
(1000)
(1000)
(1000)
(800)
42.3
25.5
26.4
37.2
28.9
44.2
59.6
2.6
19.0
18.0
38.7
37.2
55.8
27.0
33.5
29.2
35.0
27.5
65.0
7.7
22.6
40.0
59.0
46.7
55.9
26.8
26.0
20.7
25.2
26.3
57.6
5.2
29.4
34.0
56.6
55.2
59.7
24.1
26.0
26.8
33.8
32.1
74.0
6.6
16.9
29.4
49.7
51.1
93.4
73.6
70.2
70.8
76.1
96.2
60.1
13.1
37.4
42.1
56.2
36.5
Yb2O3
Lu2O3
g
ZrO2
a
Diol dissolved in ethanol at 20 wt.% was fed through the reactor top. Conversion (%) and selectivity (mol%) were averaged in the initial 5 h. Reaction conditions are the
same as those in Table 1.
b
Selectivity to 6-hepten-1-ol.
Selectivity to 7-octen-1-ol.
Selectivity to 8-nonen-1-ol.
c
d
e
Selectivity to 9-decen-1-ol.
f
Reacted at 400 ◦C. Selectivity to 11-dodecen-1-ol.
g
Monoclinic ZrO2.
100
80
60
40
20
0
100
80
60
40
20
0
Sc2O3
Lu2O3
b
Yb2O3
a
Y2O3
Ce2O3
300
350
400
450
Reaction temperature / ºC
6
7
8
9
10
Carbon number of diol
Fig. 2. Changes in conversion and selectivity in the dehydration of 1,6-hexanediol
over Sc2O3 calcined at 800 ◦C with reaction temperature. (a) Solid circle, conversion
of 1,6-hexanediol; (b) open triangle, selectivity to 5-hexen-1-ol. 1,6-Hexanediol dis-
solved in ethanol at 20 wt.% was fed through the reactor top. Reaction temperature,
Fig. 1. Changes in the selectivity to unsaturated alcohols in the dehydration of ter-
minal diols over several oxide catalysts, such as Sc2O3, CeO2, Y2O3, Yb2O3, and Lu2O3.
The data are cited from Tables 1 and 2.
400 ◦C; W/F = 1.39 g h cm−3
.
3.2. Reaction of 1,6-hexanediol over Sc2O3
tivity to 5-hexen-1-ol was decreased because of the increase in
␧-caprolactone as a dehydrogenated product.
Calcination temperatures of REO greatly affect the catalytic per-
formance, especially product selectivity [4,5,10,11]. Table 3 shows
effects of calcination temperature of Sc2O3 on the dehydration of
1,6-hexanediol at 400 ◦C. The conversion of 1,6-hexanediol was
slightly decreased with the decrease in SA of Sc2O3. The selectiv-
ity to 5-hexen-1-ol was maximized at a calcination temperature of
800 ◦C. At higher calcination temperatures than 800 ◦C, the selec-
Fig. 2 shows a change in the catalytic activity with reaction tem-
perature in the dehydration of 1,6-hexanediol over Sc2O3 calcined
at 800 ◦C. The conversion of 1,6-hexanediol was increased with
increasing reaction temperature. The selectivity to 5-hexen-1-ol
was maximized at reaction temperatures between 375 and 400 ◦C.
A main by-product at low reaction temperature was oxacyclohep-
tane, which is decreased at high temperature, while dienes, cyclic
Table 3
Dehydration of 1,6-hexanediol over Sc2O3 calcined at different temperatures.a
Calcination (◦C)
SAb (m2 g−1
)
Conversion (%)
Selectivity (mol%)c
5-Hexen-1-ol
OCH
␧-Caprolactone
Dienes
CPMs
CPNs
As-obtained
500
600
700
800
98.4
81.8
72.1
64.6
51.5
45.4
30.9
93.3
95.6
94.6
93.1
94.6
87.6
82.2
38.4
41.4
41.9
53.7
62.0
57.6
49.8
2.1
2.2
1.6
2.0
2.1
2.1
3.0
0.5
0.5
0.5
0.6
0.8
1.5
4.7
7.0
3.8
6.1
6.5
5.2
7.2
7.5
8.2
10.3
8.0
4.1
3.2
4.0
4.2
4.1
2.9
2.2
1.9
1.9
900
1000
2.5
2.3
a
Conversion and selectivity at 400 ◦C were averaged in the initial 5 h. Reaction conditions are the same as those in Table 1.
Specific surface area.
OCH, oxacycloheptane; CPMs, cyclopentylmethanol + 2-cyclopentenylmethanol; CPNs, cyclopentanone + cyclopentanol; other by-products are 4-hexen-1-ol, 1-hexanol,
b
c
cyclohexanone, cyclohexanol, cyclohexene, and several unidentified products.

422
K. Abe et al. / Catalysis Today 164 (2011) 419–424
100
80
60
40
20
0
ketones, and cyclic alcohols such as cyclopentanone and cyclopen-
tanemethanol were increased at high reaction temperatures. In the
reactions over Sc2O3, cyclohexanol and cyclohexene were observed
as very minor by-products. Thus, we tested the catalytic reaction of
cyclohexanolas areferencemonoalcoholoverREOs inthe following
section.
A
B
C
1,6-hexanediol
1,7-heptanediol
1,8-octanediol
1,9-nonanediol
1,10-decanediol
3.3. Reactivity of cyclohexanol over the REO catalysts
Sc
Y
Table 4 shows catalytic performance of REOs on cyclohexanol
at 350 ◦C in order to compare with the reactivity of diols. Cyclo-
hexanone and cyclohexene were detected in the reaction through
dehydrogenation and dehydration, respectively. Sc2O3 and Lu2O3
showed a comparable product ratio of cyclohexanone to cyclohex-
ene. Over the other REOs such as Yb2O3 and Y2O3, cyclohexanone
was produced more than cyclohexene.
Product selectivity in the reaction of cyclohexanol over REOs
would be an indicator to evaluate the dehydration ability of REO,
and to differentiate the reactivity between the diol and monoal-
cohol in the dehydration (Table 4). In other words, the abilities for
the dehydration and for the dehydrogenation can be determined by
product ratio in such a way that cyclohexene is hydration product
and cyclohexanone is hydrogenation product. The results in Table 4
indicate that Sc2O3 has higher ability of dehydration and lower
dehydrogenation ability than the other REOs. Namely, dehydration
ability of Sc2O3 is superior to that of other REOs.
Lu
Ce
Yb
0.07
0.08
0.09
0.1
Ionic radius / nm
2
1.5
1
Sc
Lu
Yb
At 350 ◦C, the dehydration product was only cyclohexene over
Sc2O3, while the conversion was low. The reactivity of cyclohexanol
was lower than those of terminal diols over Sc2O3 by comparison
of the conversion at the same temperature (Tables 1 and 4). In the
present reactions, ethanol is used as a solvent for the reactants.
Ethanol is hardly reacted over REOs at 350 ◦C. Thus, it also indicates
that monoalcohol is much less reactive than diols and cyclohexanol.
0.5
0
Y
Ce
0.07
0.08
0.09
0.1
Ionic radius / nm
3.4. Catalytic activities of Sc2O3 compared to the other REOs
Lu
0.06
0.04
0.02
0
Ionic radii of rare earth metals are reported to be 0.0745 nm
(Sc3+), 0.0900 nm (Y3+), 0.0970 nm (Ce4+), 0.0868 nm (Yb3+), and
0.0861 nm (Lu3+), where the trivalent ions have 6 coordination
number except for Ce4+ with 8 coordination number [20]. In2O3
with cubic bixbyite crystal structure is reported to be active in the
dehydration of diols [14]: the formation of unsaturated alcohols is
considered to proceed via tridentate coordination of diol on the sur-
face of In2O3. It is also speculated that the tridentate adsorption of
diolsonthe surface of cubicbixbyiteSc2O3 couldbean intermediate
during catalysis.
The dehydration ability of REOs would be related to the ionic
radius of metal cations in REOs. Therefore, the selectivity to unsat-
urated alcohol and the formation rate of unsaturated alcohols in
the dehydration of various diols with the number of carbon atom
from 6 to 10 were plotted in the relation with ionic radius of rare
earth cations in Fig. 3A and B, respectively. Both the selectivity and
the formation rate decreases with increasing the ionic radius. The
terminal diols have the same tendency of increasing the selectivity
and the formation rate as the ionic radius decreases. In other words,
REO with small ionic diameter of rare earth metal cation is effective
in the formation of unsaturated alcohol.
In Table 4, the selectivity to cyclohexene in the dehydration of
cyclohexanol is in the order of Sc > Lu > Ce > Y > Yb. The order in
the selectivity is not always the same as the order in the selec-
tivity to 5-hexen-1-ol in the dehydration of 1,6-hexanediol (Fig. 1),
Sc > Lu > Yb > Y > Ce. Table 4 also lists the formation rate of cyclohex-
ene, which is in the order of Lu > Sc > Yb > Y > Ce. The order is quite
the same as the order in the formation rate of 5-hexen-1-ol per
unit surface area shown in Fig. 3C. Since the formation rate based
on unit surface area means the intrinsic activity, it can be estimated
Yb
Y
Sc
Ce
0.07
0.08
0.09
0.1
Ionic radius / nm
Fig. 3. Changes in the selectivity to unsaturated alcohol (A) and the formation
rate of unsaturated alcohol (B and C) in the dehydration of several terminal diols,
such as 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-
decanediol, over oxide catalysts at 350 ◦C with ionic radius of rare earth cation.
the ability of dehydration. Comparing the values of formation rate
in Fig. 3C with those in Table 4, diols are much more reactive than
monoalcohol such as cyclohexanol.
3.5. Probable reaction route over REOs
1,6-Hexanediol produces various by-products, whereas 1,4-
butanediol produces only several by-products [12,13]. One of
the most important factors of this difference is the stability of
cyclic compounds. Two cyclic compounds with 5-membered ring,

K. Abe et al. / Catalysis Today 164 (2011) 419–424
423
Table 4
Catalytic conversion of cyclohexanol at 350 ◦C.a
Catalyst (calcination/◦C)
Conversion (%)
Selectivity (mol%)b
Cyclohexene
Cyclohexanone
Sc2O3
CeO2
Y2O3
Yb2O3
Lu2O3
(800)
(800)
(1000)
(1000)
(1000)
14.7
14.8
12.7
16.5
13.0
33.1 (0.0071)
13.0 (0.0041)
10.7 (0.0046)
8.4 (0.0065)
16.8 (0.0113)
31.0 (0.0066)
23.6 (0.0075)
27.4 (0.0117)
40.8 (0.0315)
31.7 (0.0215)
a
Reaction conditions are the same as those in Table 1. Cyclohexanol dissolved in ethanol at 20 wt.% was fed through the reactor top.
Data in the parentheses mean the formation rate (mmol h−1 m−2).
b
tetrahydrofuran and ␥-butyrolactone, can be produced from 1,4-
Taking into account the by-products listed in Table 3, Fig. 4
suggests possible reaction routes from 1,6-hexanediol. There
are possibly four main reaction routes. The first route pro-
duces 5-hexen-1-ol via dehydration, in which reaction route
involves production of 4-hexen-1-ol by isomerization, or produc-
tion of by-products such as 1-hexanol or dienes by hydrogenation
butanediol, while no 4-membered ring compounds were observed
due to the low stability of 4-membered ring. 1,6-Hexanediol, on
the other hands, produces various cyclic products such as 5- and
6-membered rings, and 7-membered ring including oxygen within
the ring (Tables 1 and 3).
OH
OH
OH
O
4-Hexen-1-ol
1-Hexanol
+H2
Oxacycloheptane
5-Hexen-1-ol
-H2O
1,5-Hexadiene
-H2O
-H2O
(2)
(1)
OH
HO
1,4-Hexadiene
1,6-Hexanediol
-H2
-H2
-H2O
O
O
-H2
(3)
HO
O
Over
CeO2
(6-Hydroxyhexanal)
-H2
(1,6-Hexanedial)
Aldol
O
-H2O
(4)
addition
O
O
+H2
OH
-H2O, +H2
Cyclohexanone
CHO
ε-Caprolactone
OH
OH
-CO2, H2
O
Cyclohexanol
Cyclohexene
Cyclopentylmethanol
Cyclopentanone
-H2
+H2
OH
OH
Cyclopentanol
2-Cyclopentenylmethanol
Fig. 4. Proposed reaction pathway of 1,6-hexanediol over REOs.

424
K. Abe et al. / Catalysis Today 164 (2011) 419–424
or excessive dehydration, respectively. The second route pro-
duces oxacycloheptane via intramolecular etherification. Over
Sc2O3, however, a little amount of oxacycloheptane is produced
from 1,6-hexanediol, whereas 1,4-butanediol mainly produces
tetrahydrofuran in the dehydration. The third route produces
cyclopentanol and cyclopentanone in the dehydrogenation of 1,6-
hexanediol to 6-hydroxyhexanal and to 1,5-hexanedial followed
by the formation of cyclic intermediate via aldol addition. Since
the ratio of cyclopentanone in the cyclic compounds is large, this
reaction preferably proceeds over Sc2O3. The last route is similar to
the third route: ␧-caprolactone is produced via 6-hydroxyhexanal
with the selectivity higher than 70 mol%. Heavy REOs such as Lu2O3
as well as monoclinic ZrO2 show moderate catalytic activity in
the dehydration of the terminal diols, while their selectivity was
lower than Sc2O3. CeO2, which is an excellent catalyst in the for-
mation of 2-propen-1-ol from 1,3-propnediol, was less selective
in the dehydration of terminal diols than the other REOs. In the
reaction of cyclohexanol, Sc2O3 was the most selective catalyst
for the dehydration to produce cyclohexene, while the other REOs
predominantly catalyzed the dehydrogenation to produce cyclo-
hexanone.
as an intermediate. Since
a little amount of ␧-caprolactone
References
is produced, this route does not proceed favorably over
Sc2O3.
[1] A.J. Lundeen, R.V. Hoozer, J. Org. Chem. 32 (1967) 3386–3389.
[2] J.M. Trillo, S. Bernal, J. Catal. 66 (1980) 184–190.
[3] S. Sato, R. Takahashi, T. Sodesawa, N. Honda, H. Shimizu, Catal. Commun. 4
(2003) 77–81.
[4] A. Igarashi, N. Ichikawa, S. Sato, R. Takahashi, T. Sodesawa, Appl. Catal. A 300
(2006) 50–57.
[5] M. Kobune, S. Sato, R. Takahashi, J. Mol. Catal. A 279 (2008) 10–19.
[6] S. Sato, R. Takahashi, T. Sodesawa, N. Yamamoto, Catal. Commun. 5 (2004)
397–400.
[7] A. Igarashi, S. Sato, R. Takahashi, T. Sodesawa, M. Kobune, Catal. Commun. 8
(2007) 807–810.
[8] S. Sato, R. Takahashi, T. Sodesawa, A. Igarashi, H. Inoue, Appl. Catal. A 328 (2007)
109–116.
[9] S. Sato, R. Takahashi, N. Yamamoto, E. Kaneko, H. Inoue, Appl. Catal. A 334
(2008) 84–91.
[10] S. Sato, R. Takahashi, M. Kobune, H. Inoue, Y. Izawa, H. Ohno, K. Takahashi, Appl.
Catal. A 356 (2009) 64–71.
Over CeO2, cyclohexanone and cyclohexanol are observed. They
would be produced from 6-hydroxyhexanal, but the mechanism is
unclear. However, cyclopentanone is a major product over CeO2
in the reaction using aqueous 1,6-hexanediol as a feed solution
instead of ethanol solution [21]. Although pure ethanol dose not
react over REOs at 350 ◦C, ethanol solvent used in the feed solution
may affect the catalytic dehydration. We need further investigation
on the dehydration of terminal diols using direct feed of terminal
diols melted.
4. Conclusions
[11] H. Gotoh, Y. Yamada, S. Sato, Appl. Catal. A 377 (2010) 92–98.
[12] N. Yamamoto, S. Sato, R. Takahashi, K. Inui, Catal. Commun. 6 (2005) 480–484.
[13] N. Yamamoto, S. Sato, R. Takahashi, K. Inui, J. Mol. Catal. A 243 (2006) 52–59.
[14] M. Segawa, S. Sato, M. Kobune, T. Sodesawa, T. Kojima, S. Nishiyama, N.
Ishizawa, J. Mol. Catal. A 310 (2009) 166–173.
The catalytic activity of several REOs such as Sc2O3, CeO2,
Y2O3, Yb2O3, and Lu2O3 was investigated in the vapor-phase
catalytic reactions of terminal diols with carbon numbers from
6 to 12, such as 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol,
1,9-nonanediol, 1,10-decanediol, and 1,12-dodecanediol. Sc2O3
showed the highest selectivity to the corresponding unsaturated
alcohols in the dehydration of the terminal diols. For instance,
5-hexen-1-ol was produced as a dehydration product of 1,6-
hexanediol with the selectivity over 60 mol%, together with
by-products of ␧-caprolactone and oxacycloheptane. In the dehy-
dration of 1,10-decanediol over Sc2O3, 9-decen-1-ol was produced
[15] S. Kobayashi, I. Hachiya, M. Araki, H. Ishitani, Tetrahedron Lett. 34 (1993)
3755–3758.
[16] K. Otsuka, K. Jinno, A. Morikawa, Chem. Lett. (1985) 499–500.
[17] M.D. Fokema, J.Y. Ying, Appl. Catal. B 18 (1998) 71–77.
[18] T. Yamanaka, T. Imai, Bull. Chem. Soc. Jpn. 54 (1981) 1585–1586.
[19] S. Sato, R. Takahashi, M. Kobune, H. Gotoh, Appl. Catal. A 356 (2009) 57–63.
[20] R.D. Shanon, Acta Crystallogr. A32 (1976) 751–767.
[21] T. Akashi, S. Sato, R. Takahashi, T. Sodesawa, K. Inui, Catal. Commun. 4 (2003)
411–416.