Efficient production of 1,3-butadiene in the catalytic dehydration of 2,3-butanediol

Article abstract of DOI:10.1016/j.apcata.2014.12.006

Vapor-phase catalytic dehydration of 2,3-butanediol (2,3-BDO) was investigated over rare earth oxide catalysts and In₂O₃ at around 400 ° C. In the dehydration of 2,3-BDO over Sc₂O₃,1,3-butadiene was mainly produced together with butanone, 2-methyl-propanal, 2-methyl-propanol, 3-buten-2-ol, and butene isomers. Sc₂O₃ calcined at 800°C showed the highest 1,3-butadiene yield of 88.3% at 411 °C in H₂ carrier gas flow. Since 3-buten-2-ol is produced selectively from 2,3-BDO over Sc₂O₃ at a low temperature of 325 °C, 3-buten-2-ol rather than butanone is a probable intermediate from 2,3-BDO to 1,3-butadiene. 3-Buten-2-ol is readily converted into 1,3-butadiene at temperatures lower than 411 °C over Sc₂O₃ and Al₂O₃. In addition, double-bed catalysts composed of an upper catalyst bed of Sc₂O₃ and a lower of Al₂O₃ successfully converted 2,3-BDO directly into 1,3-butadiene with a stable selectivity higher than 94% at 318°C and 100% conversion of 2,3-BDO.

Full text of DOI:10.1016/j.apcata.2014.12.006

Applied Catalysis A: General 491 (2015) 163–169
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Efficient production of 1,3-butadiene in the catalytic dehydration
of 2,3-butanediol
Hailing Duan, Yasuhiro Yamada, Satoshi Sato∗
Graduate School of Engineering, Chiba University, 1-33 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:
Vapor-phase catalytic dehydration of 2,3-butanediol (2,3-BDO) was investigated over rare earth oxide
catalysts and In2O3 at around 400 ◦C. In the dehydration of 2,3-BDO over Sc2O3, 1,3-butadiene was mainly
produced together with butanone, 2-methyl-propanal, 2-methyl-propanol, 3-buten-2-ol, and butene iso-
mers. Sc2O3 calcined at 800 ◦C showed the highest 1,3-butadiene yield of 88.3% at 411 ◦C in H2 carrier
gas flow. Since 3-buten-2-ol is produced selectively from 2,3-BDO over Sc2O3 at a low temperature of
325 ◦C, 3-buten-2-ol rather than butanone is a probable intermediate from 2,3-BDO to 1,3-butadiene.
3-Buten-2-ol is readily converted into 1,3-butadiene at temperatures lower than 411 ◦C over Sc2O3 and
Al2O3. In addition, double-bed catalysts composed of an upper catalyst bed of Sc2O3 and a lower of Al2O3
successfully converted 2,3-BDO directly into 1,3-butadiene with a stable selectivity higher than 94% at
318 ◦C and 100% conversion of 2,3-BDO.
Received 7 October 2014
Received in revised form
28 November 2014
Accepted 2 December 2014
Available online 10 December 2014
Keywords:
Dehydration
2,3-Butanediol
1,3-Butadiene
3-Buten-2-ol
Rare earth oxide
Sc2O3
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
Unfortunately, sufficient catalysts for the ethanol route have not
been developed yet.
1,3-Butadiene (BD) is one of the most important chemicals for
manufacturing polymers such as styrene-butadiene rubber (SBR)
[1–5], polybutadiene rubber (BR) [6,7], acrylonitrile-butadiene-
styrene resins, and adiponitrile [1,8]. The major products such as
SBR and BR are in great demand to produce tires of automobiles.
More than 95% BD is produced in the steam cracking of petroleum
over the global world [8]. However, the supply of BD depends on the
production of ethylene, so that it is not stable under the situation
changing the supply of chemical resources in recent years.
Ethanol [9–11] and 2,3-butanediol (2,3-BDO) [12–18] can be
derived from potential resources of “bio-carbon” such as glucose
and cellulose converted from corn and sugar cane. The bio-based
chemicals have the possibility to take the place of naphtha to
produce BD. Catalytic conversion of ethanol into BD has been con-
sidered as a possible route [19–25]: a high BD selectivity of 72%
has been reported [23]. In either the direct process using pure
ethanol [19] or the two-step process using a mixture of ethanol
and acetaldehyde [25], a complexed reaction sequence of differ-
ent types of reactions such as dehydrogenation, aldol condensation,
hydrogenation, and dehydration is required to produce BD directly.
On the other hand, 2,3-BDO is an alternative resource to produce
BD because of its C4 structure, and the dehydration of 2,3-BDO to
BD has been also investigated since 1940s [26–28]. Great attention
had been paid to the exploitation of renewable resources to pro-
duce BD. Winfield disclosed that BD was obtained with a yield of
62% over ThO2 at 500 ◦C [26]. ThO2 has the catalytic activities to
produce BD from 2,3-BDO. Winfield also described that the dehy-
dration product of 3-buten-2-ol (3B2OL) was obtained with a yield
of 70% at a low temperature of 350 ◦C [26]. It is reasonable that 2,3-
BDO can be dehydrated into 3B2OL and further dehydrated into
BD at a higher temperature. However, it is difficult to use ThO2
as a commercial catalyst for its radioactive properties. Although
several catalysts were proposed in the production of BD from 2,3-
BDO, most of the process resulted in high yields of butanone (MEK)
[28,14,29]. Recently, the probability of the synthesis of BD from bio-
based ethanol and butanediols has been discussed in review papers
[30,31].
In our previous work, we have investigated the dehydration of
2,3-BDO over all the rare earth oxide (REO) catalysts [32]. It has been
found that Sc2O3 calcined at 800 ◦C shows an excellent catalytic
activity with the highest 3B2OL selectivity of 85.0% at a 2,3-BDO
conversion of 99.9% in an average of the initial 5 h at a low reac-
tion temperature of 325 ◦C. In addition, In2O3 calcined at 400 ◦C
also showed the dehydration activity with a 3B2OL selectivity of
∗
Corresponding author. Tel.: +81 43 290 3376; fax: +81 43 290 3401.
E-mail address: satoshi@faculty.chiba-u.jp (S. Sato).
http://dx.doi.org/10.1016/j.apcata.2014.12.006
0926-860X/© 2014 Elsevier B.V. All rights reserved.

164
H. Duan et al. / Applied Catalysis A: General 491 (2015) 163–169
Table 1
Dehydration of 2,3-BDO over REOs calcined at 800 ◦Ca
Catalyst
Rib (nm)
SAc (m2 g−1
)
CPd
Conv. (mol%)
Selectivity (mol%)
BD
3B2OL
MEK
IBA
1.6
IBO
Otherse
Sc2O3
Sc2O3
Sc1.5Yb0.5O3
Sc1.0Yb1.0O3
Sc0.5Yb1.5O3
In2O3
Lu2O3
Yb2O3
Tm2O3
Er2O3
Y2O3
Ho2O3
Dy2O3
Tb4O7
Gd2O3
Eu2O3
Sm2O3
CeO2
Nd2O3
Pr6O11
La2O3
0.0745
0.0745
0.0776
0.0807
0.0837
0.0800
0.0861
0.0868
0.0880
0.0890
0.0900
0.0901
0.0912
0.0923
0.0938
0.0947
0.0958
0.0970
0.0983
0.0990
0.1032
51.5
51.5
53.2
35.9
26.2
13.2
27.8
28.8
27.0
21.5
29.3
23.7
19.1
17.7
20.6
19.8
20.3
53.7
18.2
22.7
18.0
C
C
C
C
C
C
C
C
100.0
100.0
98.8
99.1
99.2
99.0
99.4
97.2
78.4
100.0
99.3
92.3
99.1
83.6
96.1
99.2
99.5
100.0
87.8
95.6
92.5
58.2
88.3
42.6
27.1
9.2
2.5
23.2
0.5
0.8
2.4
0.3
1.7
0.5
0.0
1.9
0.8
10.6
10.9
35.3
0.6
5.0
20.5
6.5
20.0
19.3
24.6
13.0
20.0
20.6
17.5
21.3
0.5
12.8
1.1
1.7
0.3
4.7
6.2
5.9
0.6
0.8
11.2
16.2
7.2
7.0
8.2
9.2
9.9
6.4
3.7
6.2
0.6
6.0
9.3
11.8
23.8
9.4
f
0.1
2.1
2.6
6.3
1.8
1.8
5.4
17.6
7.2
7.0
4.4
5.9
6.1
4.6
6.1
7.1
2.4
4.0
8.6
9.2
f
f
f
14.9
15.3
14.9
22.8
23.1
20.2
34.1
21.1
22.8
23.9
15.7
19.8
18.2
32.9
21.7
39.2
16.9
34.7
23.2
25.1
37.9
28.4
70.7
46.1
42.2
24.8
42.1
43.6
37.2
55.7
44.2
50.2
39.2
42.5
56.8
37.9
37.1
47.2
C
M+C
M+C
M
M
CF
M
M
M
CF
H
0.0
0.6
1.2
0.5
0.0
0.7
0.5
35.2
9.6
8.1
CF
H
BD, 1,3-butadiene; 3B2OL, 3-buten-2-ol; MEK, butanone; IBA, 2-methylpropanal; IBO, 2-methyl-1-propanol.
a
Reaction temperature: 425 ◦C, catalyst weight: 1 g, feed rate: 1.06 g h−1, flow rate of H2: 45 cm3 min−1, conversion and selectivity were averaged in the initial 5 h.
Ionic radius of trivalent rare earth cation with coordination number 6, except Ce4+ with coordination number 8, the data cited from Refs. [33,38].
The data cited from Ref. [33].
CP: crystal phase; H, A-type hexagonal; M, B-type monoclinic; C, C-type cubic bixbyite; CF, cubic fluorite. The data cited from Ref. [33].
Others included 3-hydroxy-2-butanone, 2,3-butanedione, 2-butanol, trans-2-butene, 1-butene, isobutene, propylene, ethylene, etc.
Reaction temperature: 411 ◦C.
b
c
d
e
f
79.6% and a conversion of 51.9% at 305 ◦C [32]. In this work, we
(VZ-7). The catalytic activity was evaluated by averaging the con-
version and selectivity data in the initial 5 h. Both the conversion of
2,3-BDO and the selectivity to each product were defined as mol%.
The above-mentioned description is essentially the same as those
described in the previous work [32,36,37].
investigated the dehydration of 2,3-BDO over Sc2O3 and In2O3 at
high reaction temperatures to produce BD directly from 2,3-BDO,
and also investigated the dehydration of 3B2OL and MEK over Sc2O3
and Al2O3 to establish the direct reaction route.
In Section 3.4, the dehydration of MEK and 3B2OL was also
examined in the same way as the 2,3-BDO dehydration in order to
confirm an intermediate product in the dehydration from 2,3-BDO
to BD. In Section 3.5, the dehydration of 2,3-BDO was also inves-
tigated over two different catalysts packed in the tubular reactor,
which consisted of 1.0 g of Al2O3 placed in a lower bed with 6 mm
height and 1.0 g of Sc2O3 placed in an upper bed with 4 mm height,
to establish the efficient BD formation.
2. Experimental
2.1. Catalyst preparation
All the REO catalysts and In2O3 were purchased from KANTO
CHEMICAL CO., INC., and they were calcined in air at a prescribed
temperature for 3 h, while the samples are the same as the previous
work [32,33] and the physical properties are reported elsewhere
[33]. Al2O3 (JRC-ALO-6) with a specific surface area of 180 m2 g−1
[34] was supplied by the Reference Catalyst Division, the Cataly-
sis Society of Japan. The Al2O3 catalyst was used for the reaction
without further heat treatment. Composite oxide of Sc2−xYbxO3
with x = 0.5, 1.0, and 1.5, namely Sc1.5Yb0.5O3, Sc1.0Yb1.0O3, and
Sc0.5Yb1.5O3, were supplied by Daiichi Kigenso Kagaku Kogyo Co.,
Ltd., Japan [35].
3. Results
3.1. Dehydration of 2,3-BDO catalyzed by REOs calcined at 800 ◦C
Winfield reported that in the dehydration of 2,3-BDO over ThO2:
3B2OL was mainly obtained with a selectivity of 70% at 350 ◦C, and
BD was mainly obtained with a selectivity of about 62% together
with 3B2OL selectivity of only 8% at 500 ◦C [26]. This indicates that
3B2OL and BD can be obtained as stepwise dehydration products
of 2,3-BDO at low and high reaction temperatures, respectively. In
our previous reports, we have synthesized 3B2OL at high yields
from 2,3-BDO over monoclinic ZrO2 modified with alkaline earth
metal oxides [37] as well as monoclinic ZrO2 [36] at 350 ◦C. Nei-
ther monoclinic ZrO2 nor the modified ones showed their activities
to produce BD even at high reaction temperatures. We have also
found that In2O3 and Sc2O3 show excellent catalytic activity to pro-
duce 3B2OL at 325 ◦C [32]. In the REO catalysts, Sc2O3 shows the
highest selectivity to 3B2OL. However, the possibility of the REO
catalysts was not evaluated in the BD formation from 2,3-BDO at
high temperatures.
2.2. Catalytic reaction
The dehydration of 2,3-BDO was carried out in a fixed-bed tubu-
lar flow reactor under atmospheric pressure of H2 with a flow rate
of 45 cm3 min−1 at a prescribed temperature. Prior to the reaction,
a catalyst (1.0 g) was preheated in an H2 flow at the prescribed
temperature for 1 h. After the catalyst bed had been preheated, 2,3-
BDO was fed through the reactor top at a feed rate of 1.06 g h−1
(11.8 mmol h−1). The liquid effluent collected every hour was ana-
lyzed by gas chromatography (GC-8A, Shimadzu, Japan) with a
60-m capillary column (DB-WAX). The products were identified by
gas chromatography with a mass spectrometer (GCMS-QP5050A,
Shimadzu) and a 30-m capillary column (DB-WAX). Gaseous prod-
ucts such as BD and butene isomers were analyzed by on-line gas
chromatography (GC-8A, Shimadzu) with a 6-m packed column
Table 1 summarizes the results in the catalytic reaction of
2,3-BDO over the REO catalysts at 425 ◦C. In the dehydration of

H. Duan et al. / Applied Catalysis A: General 491 (2015) 163–169
165
100
20
15
10
5
100
80
60
40
20
0
2,3-BDO
BD
Conv. of 2,3-BDO
3B2OL
80
60
40
20
BD
PE
BEs
MEK
3B2OL
MEK
0
1
2
3
4
5
250
300
350
400
450
0
Reaction temperature /oC
Time on stream /h
Fig. 2. Changes in conversion and selectivities to BD, 3B2OL and MEK in the dehydra-
tion of 2,3-BDO over Sc2O3 with time on stream. Calcination temperature of Sc2O3,
800 ◦C; Reaction temperature, 411 ◦C; catalyst weight, 1.0 g; feed rate of 2,3-BDO,
Fig. 1. Changes in the dehydration ability of Sc2O3 in the dehydration of 2,3-BDO
into BD, 3B2OL, and MEK with reaction temperature. Calcination temperature of
Sc2O3, 800 ◦C; catalyst, 1.0 g; feed rate of 2,3-BDO, 1.06 g h−1; flow rate of H2 carrier
1.06 g h−1; flow rate of H2, 45 cm3 min−1
.
gas, 45 cm3 min−1
.
rapidly at 425 ◦C. At 425 ◦C, BD dimers such as octenes were also
detected along with MEK. It indicates that the appropriate reaction
temperature is 411 ◦C for a high yield of BD.
Fig. 2 shows the changes in catalytic activity of Sc2O3 calcined at
800 ◦C in the dehydration of 2,3-BDO with time on stream. Stable
catalytic activity was obtained in the initial 5 h: the conversion of
2,3-BDO kept 100% with BD selectivity of 88% in H2 flow at 411 ◦C.
The selectivity to propylene was ca. 3% while the selectivity to
the sum of butene isomers such as trans-2-butene, 1-butene, and
isobutene was ca. 3%. Both the selectivities of 3B2OL and MEK were
as low as 1%.
2,3-BDO, BD was mainly produced only over Sc2O3, together with
by-products such as 3B2OL, MEK, 2-methyl-propanal, 2-methyl-
propanol, and butene isomers. In particular, Sc2O3 calcined at
800 ◦C showed a high BD yield of 88.3% at 411 ◦C. In the com-
posite oxides of Sc 2-xYbxO3 (x = 0.5, 1.0, and 1.5), the selectivity
to BD simply decreased with increasing Yb content. Nd2O3 and
Lu2O3 showed almost the same ability for the formation of BD and
MEK. The other REOs such as Yb2O3, Er2O3, Y2O3, Ho2O3, Dy2O3,
Tb4O7, Gd2O3 and Sm2O3 displayed similar catalytic activities to
form 3B2OL and MEK, but BD was not produced.
3.2. Dehydration of 2,3-BDO over In2O3 and Sc2O3 calcined at
different temperatures
3.3. Effects of carrier gas on the dehydration of 2,3-BDO over
Sc2O3 calcined at 800 ◦C
In2O3 calcined at 800 ◦C (Table 1) shows a quite low selec-
tivity to BD, although it shows a 3B2OL selectivity of 68.5% at a
2,3-BDO conversion of 72.9% at 305 ◦C [32]. In the case of In2O3 cat-
alyst, calcination at 400 ◦C is preferable to obtain a 3B2OL-selective
In2O3 catalyst [32]. Table 2 shows the catalytic activity of In2O3
calcined at 400 and 800 ◦C. The 3B2OL selectivity was 84.1% at
280 ◦C, and it decreased steeply with increasing the reaction tem-
perature. At 425 ◦C, BD and 3B2OL were hardly obtained over In2O3.
It was also found that 2,3-BDO was converted into MEK and some
gaseous by-products such as trans-2-butene, 1-butene, isobutene,
and propylene over In2O3 but not BD at high temperatures.
Table 3 shows the dehydration ability of Sc2O3 calcined at differ-
ent temperatures in the dehydration of 2,3-BDO at 411 ◦C. Under
the conditions, the conversion of 2,3-BDO reached ca. 100%. It is
obvious that Sc2O3 calcined at 800 ◦C showed the highest BD selec-
tivity, which exceeded 88%. The change in the selectivity had no
correlation with the specific surface area, which decreased with
increasing the calcination temperature.
Fig. 3 shows the catalytic activity of Sc2O3 in N2 carrier gas. The
trend in the catalytic activity of Sc2O3 in N2 flow resembled that
in H2 flow (Fig. 1). However, even at the same reaction tempera-
ture, the selectivities to both 3B2OL and BD in N2 flow were lower
than those in H2 flow, as being compared with Fig. 1. In addition,
it was observed that less coke on the catalyst used in H2 flow was
accumulated than in N2 flow, judging from the color of the catalyst
used: gray in H2 in contrast to dark brown in N2.
100
Conv. of 2,3-BDO
80
3B2OL
60
BD
In our previous report, we have already investigated the dehy-
dration activities of Sc2O3 at reaction temperatures up to 350 ◦C
in the formation of 3B2OL from 2,3-BDO. Over Sc2O3 calcined at
800 ◦C, the highest yield of 3B2OL was obtained at 325 ◦C with
a selectivity of 85% and the selectivity declined rapidly at 350 ◦C
with only a little BD detected [32]. In the present work, the dehy-
dration ability of Sc2O3 calcined at 800 ◦C was further investigated
at higher reaction temperatures. Fig. 1 shows the changes in the
catalytic activity of Sc2O3 calcined at 800 ◦C. 3B2OL was mainly
obtained at low reaction temperatures, and the formation of BD
was increased at high temperatures. Sc2O3 showed the maximum
BD yield of 88.3% at 411 ◦C. However, the selectivity to BD declined
40
20
MEK
0
320
340
360
380
400
420
Reaction temperature / oC
Fig. 3. Dehydration ability of Sc2O3 in the dehydration of 2,3-BDO in N2 flow. Cal-
cination temperature of Sc2O3, 800 ◦C; catalyst weight, 1.0 g; feed rate of 2,3-BDO,
1.06 g h−1; flow rate of N2, 45 cm3 min−1
.

166
H. Duan et al. / Applied Catalysis A: General 491 (2015) 163–169
Table 2
Dehydration of 2,3-BDO over In2O3 calcined at different temperatures.a
Reaction temp. (◦C)
Conv. (mol%)
Selectivity (mol%)
BD
3B2OL
MEK
IBA
IBO
BEs
0
1.4
6.9
2.3
6.7
11.0
5.2
16.2
12.2
49.1d
PE
0.1
EE
Others
280b
305b
325b
325c
350b
355c
375b
375c
404c
425c
11.6
51.9
85.4
59.4
89.9
87.4
90.0
97.0
95.1
99.0
0
84.1
79.6
64.8
65.8
58.0
44.3
36.2
32.5
15.9
0.9
2.3
1.5
3.2
4.0
9.0
2.7
0
0.4
0.9
0.1
0.4
0.2
0.3
0.5
0.3
1.1
0.6
0
0
0
0
0
0
0
0
9.4
15.8
19.1
26.4
21.4
36.0
32.1
30.3
35.9
13.1
0.1
4.6
0.3
2.9
1.9
1.3
4.7
0.9
2.5
0.7
0.7
0.5
0.5
1.2
0.3
1.1
1.5
11.0
0.6
0.3
1.3
0.5
2.0
1.3
1.6
1.8
8.8
22.4
13.6
30.8
20.8
0.1
1.3
BD, 1,3-butadiene; 3B2OL, 3-buten-2-ol; MEK, butanone; IBA, 2-methylpropanal; IBO, 2-methyl-1-propanol; BEs included trans-2-butene, 1-butene, and isobutene; PE,
propylene; EE, ethylene; others included 3-hydroxy-2-butanone, 2,3-butanedione, 2-butanol, etc.
a
Catalyst weight: 1 g, feed rate: 1.06 g h−1, flow rate of H2: 45 cm3 min−1, conversion and selectivity were averaged in the initial 5 h.
b
In2O3 calcined at 400 ◦C.
c
In2O3 calcined at 800 ◦C.
BEs included trans-2-butene (20.8%), 1-butene (14.8%), and isobutene (13.5%).
d
Table 3
Dehydration of 2,3-BDO over Sc2O3 calcined at different temperatures.a
Calcination temp.(◦C)
SAb (m2 g−1
)
Conv. (mol%)
Selectivity (mol%)
BD
3B2OL
MEK
IBA
IBO
BEs
PE
EE
Others
As-received
600
700
800
900
98.4
72.1
66.2
51.5
45.4
30.9
99.9
99.9
100.0
100.0
100.0
100.0
50.4
66.5
83.0
88.3
62.4
62.6
4.4
0.8
0.9
0.8
1.9
2.5
11.9
8.3
1.9
1.1
11.8
7.6
1.8
1.2
0.1
0.1
1.7
0.9
4.0
2.0
0.6
0.3
3.1
1.5
3.9
4.6
3.8
2.8
6.2
4.1
6.1
7.5
4.5
2.9
4.8
8.7
2.2
2.2
2.8
1.6
1.5
4.2
15.3
6.9
2.4
2.1
6.6
7.9
1000
Abbreviations are the same as those in Table 2.
a
Reaction temperature: 411 ◦C, catalyst weight: 1 g, feed rate: 1.06 g h−1, flow rate of H2: 45 cm3 min−1, conversion and selectivity were averaged in the initial 5 h.
The data cited from Ref. [33].
b
Fig. 4 shows the changes in the selectivities to BD, 3B2OL, and
Therefore, the proper flow rate of H2 carrier gas can be considered
as 80 cm3 min−1
MEK in the dehydration of 2,3-BDO over Sc2O3 with the flow rate
of H2 carrier gas at 411 ◦C. Under all the conditions at different H2
flow rates, the conversion of 2,3-BDO reached 100%. At a H2 flow
rate of 80 cm3 min−1, a stable BD selectivity over 90% was obtained.
At a H2 flow rate of 100 cm3 min−1, however, by-products such as
butene isomers increased so that they resulted in a decreased BD
selectivity. At a low H2 flow rate of 20 cm3 min−1, 3B2OL and MEK
were observed together with BD. Because the feed rate of 2,3-BDO is
constant in Fig. 4, the low H2 flow rate means a high partial pressure
of 2,3-BDO, at which 3B2OL and MEK are observed as by-products.
.
3.4. Dehydration of MEK and 3B2OL
MEK is one of the products in the dehydration of 2,3-BDO, so that
it could be an intermediate in the BD formation. Table 4 summarizes
the dehydration of MEK over Sc2O3 and Al2O3 catalysts. However,
the reactant MEK was rarely reacted at 325 ◦C over Al2O3 catalyst.
Even at 550 ◦C, the decomposition of MEK proceeded over Al2O3
to produce mainly butene isomers, propylene, and ethylene, while
BD with a selectivity of 8.6% was detected. On the other hand, the
reaction proceeded at 425 ◦C over Sc2O3 but little BD was detected
from MEK. Therefore, MEK would not be the major intermediate in
the BD formation from 2,3-BDO over Sc2O3.
100
Conv. of 2,3-BDO
80
60
3B2OL could also be an intermediate in the BD formation from
2,3-BDO. Fig. 5 shows the dehydration of 3B2OL over Sc2O3 and
Al2O3 catalysts as well as a blank test without using catalysts. It is
obvious that even at 425 ◦C the thermal decomposition of 3B2OL
hardly proceeded without catalysts. Sc2O3 showed the dehydra-
tion ability at temperatures between 300 and 400 ◦C. Over Sc2O3,
both the conversion of 3B2OL and the BD selectivity increased with
increasing the reaction temperature and they reached the highest at
372 ◦C. In addition, the BD selectivity from 3B2OL (91.5%) is higher
than that directly from 2,3-BDO even at the same reaction temper-
ature in comparison with Fig. 1. This indicates that the formation
of BD from 3B2OL is much easier than that from 2,3-BDO.
Fig. 5 also indicates that Al2O3 is more active than Sc2O3 on
the formation from 3B2OL to BD. Although their catalytic activ-
ities showed a similar trend over the reaction temperature, the
highest BD yield was obtained over Al2O3 at 250 ◦C: 3B2OL conver-
sion, 95.4%; BD selectivity, 91.2%. Al2O3 showed the similar trend
BD
40
20
MEK
3B2OL
0
0
20
40
60
80
100
Flow rate of carrier gas /cm3min-1
Fig. 4. Changes in the dehydration of 2,3-BDO at different flow rates of H2 carrier gas
over Sc2O3. Calcination temperature of Sc2O3, 800 ◦C; reaction temperature, 411 ◦C;
catalyst, 1.0 g; feed rate of 2,3-BDO, 1.06 g h−1
.

H. Duan et al. / Applied Catalysis A: General 491 (2015) 163–169
167
Table 4
Dehydration of MEK over Sc2O3 and Al2O3.a
Catalyst (1 g)
Temp. (◦C)
Conv. (mol%)
Selectivity (mol%)
BD
3B2OL
IBA
IBO
BEs
PE
EE
1.6
21.0
4.6
Others
Al2O3
Al2O3
Sc2O3
325
550
425
2.7
39.7
40.2
0
8.6
0
0
0
0
4.2
7.2
2.2
0
0
6.9
22.9
34.3
15.7
23.4
12.5
18.5
47.9
16.4
52.1
b
Abbreviations are the same as those in Table 2.
a
Feed rate: 1.06 g h−1, flow rate of H2: 45 cm3 min−1, conversion and selectivity were averaged in the initial 5 h.
Sc2O3 calcined at 800 ◦C.
b
to Sc2O3 in the catalytic performance at a temperature which is
Therefore, the double-bed catalysts consisted of Sc2O3 and Al2O3
efficiently work to produce BD directly from 2,3-BDO.
127 ◦C lower than Sc2O3 did. It is reasonable that the dehydration
of 3B2OL into BD can be easily catalyzed by solid acid catalyst such
as Al2O3 at a low temperature. Although Al2O3 catalyzes the dehy-
dration of 2,3-BDO into MEK and 2-methylpropanal as well as into
BD [36], it is expected as a catalyst in the dehydration of 3B2OL into
BD.
4. Discussion
4.1. Correlation between ionic radii and catalytic activity of REOs
Relationships between the ionic radii of rare earth cations
[33,38] and the selectivities to unsaturated alcohols similar to
Fig. 7 have also been observed in the dehydration of other
3.5. Efficient formation of BD in the dehydration of 2,3-BDO with
a combination of acid catalyst
100
80
20
15
10
5
Al2O3 catalyzes the dehydration of 3B2OL at 250 ◦C (Fig. 5),
and 3B2OL has been obtained with a yield of 85% from 2,3-BDO
over Sc2O3 at 325 ◦C [32]. Thus, 2,3-BDO could be effectively con-
verted to BD using Al2O3 as a dehydration catalyst for 3B2OL at
a low temperature. In order to obtain BD directly from 2,3-BDO
at a low temperature, the dehydration was investigated over two
catalyst beds packed in the tubular reactor, which composed of
Sc2O3 loaded in the upper bed to convert 2,3-BDO into 3B2OL
and Al2O3 placed in the lower bed to convert 3B2OL into BD.
Fig. 6 shows the catalytic activities at 318 ◦C with time on stream.
The flow rate of H2 carrier gas was 80 cm3 min−1, and all the
other conditions were the same as the dehydration of 2,3-BDO
over the single-bed Sc2O3 catalyst (Fig. 2). The average of the
BD selectivity was 94% with the complete conversion of 2,3-BDO
at 318 ◦C during the initial 5 h. Butene isomers with the total
selectivity less than 5% and propylene with less than 1% were
observed whereas little MEK and 3B2OL were detected. In contrast,
MEK and 3B2OL were observed over the single-bed Sc2O3 cata-
lyst at 411 ◦C (Fig. 2). It is obvious that the double-bed catalysts
had stable catalytic activity, and that the selectivity to BD was
higher than that of the single-bed Sc2O3 catalyst tested at 411 ◦C.
2,3-BDO
BD
60
40
BEs
PE
20
0
1
2
3
4
5
0
Time on stream /h
Fig. 6. Changes in conversion and selectivities to BD, BEs, and PE in the dehydration
of 2,3-BDO at 318 ◦C over the double-bed catalysts of Sc2O3 and Al2O3 with time
on stream. Reaction conditions: catalyst weight: Sc2O3 (calcined at 800 ◦C) placed
in the upper bed, 1.0 g; Al2O3 located in the lower bed, 1.0 g; feed rate of 2,3-BDO,
1.06 g h−1; flow rate of H2 carrier gas, 80 cm3 min−1. BEs included trans-2-butene,
1-butene, and isobutene; PE, propylene.
Sc (411oC)
0.2
100
80
Sc
425 o
C
60
Sc1.5Yb0.5
(411oC)
0.1
Lu
Sc2O3
Sc1.0Yb1.0
(411oC)
Al2O3
40
20
0
Sc0.5Yb1.5
(411oC)
Sm
Nd
Er
Yb Tm
Conv. of 3B2OL
Selec. to BD
Ho
Tb
YDy Eu
Ce
La
Pr
No catalyst
400
Gd
0
0.07
0.08
0.09
Ionic radium /nm
0.1
200
300
Reaction temperature /ºC
Fig. 7. Formation rate of BD at 425 ◦C over REO catalysts with different ionic radii of
rare earth cations. Calcination temperature, 800 ◦C; flow rate of H2, 45 cm3 min−1
Fig. 5. Changes in the dehydration of 3B2OL into BD with reaction temperature over
.
Al2O3 and Sc2O3. Calcination temperature of Sc2O3, 800 ◦C; catalyst weight, 1.0 g;
The formation rate was averaged in the initial 5 h. The reaction temperature over
flow rate of H2 carrier gas, 45 cm3 min−1
.
Sc2−xYbxO3 catalysts was 411 ◦C.

168
H. Duan et al. / Applied Catalysis A: General 491 (2015) 163–169
HO
- H2O
- H2O
Sc2O3
OH
2,3-BDO
OH
BD
3B2OL
- H2O
OH
- H2O
- H2O
HO
O
O
H2
MEK
IBA
IBO
Scheme 1. Probable reaction pathway to various products from 2,3-BDO over REOs.
diols [35,39–43]. Terminal diols such as 1,5-pentanediol [35,42],
1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol,
1,10-decanediol, and 1,12-dodecanediol [41] were converted into
the corresponding unsaturated alcohols with sufficient selectiv-
ity over Sc2O3 catalyst. In the formation of 4-penten-1-ol from
1,5-pentanediol [42], Sc0.5Yb1.5O3 with the average ionic radius of
0.0837 nm shows the highest formation rate, so that there must be
the most proper lattice parameter between that of Sc2O3 and Lu2O3.
As a result, Sc0.5Yb1.5O3 was confirmed to be more active than Sc2O3
and Lu2O3. Except CeO2, Lu2O3 is the most active in the dehydra-
tion of 1,3-butanediol, and 1,4-butanediol [43]. In the dehydration
of 1,3-butanediol, CeO2 is exceptionally the most active catalyst
[40].
adsorption of 1,4-butanediol on Er2O3 using density functional the-
ory (DFT) and paired interacting orbitals (PIO) calculations [45].
The adsorption of 1,4-butanediol proceeds via tridentate coordina-
tion: three attractive interactions between a position-2 hydrogen
atom of 1,4-butanediol and an oxygen anion on Er2O3 surface and
between each OH group of 1,4-butanediol and erbium cations on
Er2O3 are observed. We also speculate that similar interactions
could be formed between 2,3-BDO and Sc2O3. In order to prove the
speculation, DFT and PIO calculations of adsorption of 2,3-BDO on
Sc2O3 are executed to discuss the issue. The results and the related
discussion will be presented in the near future.
4.2. Intermediates during the dehydration of 2,3-BDO to BD
In the dehydration of 2,3-BDO at 325 ◦C, high selectivities to
3B2OL have also been obtained over In2O3 [32] and ZrO2 [36], in
which the ionic radii of In2O3 (0.0800 nm) and ZrO2 (0.0840 nm) are
between that of Sc2O3 (0.0745 nm) and Lu2O3 (0.0861 nm). Sc2O3
and Lu2O3 show the BD selectivities of 58.2 and 28.2 mol% at 425 ◦C,
respectively (Table 1), while ZrO2 shows the 2,3-BDO conversion
of 98.6% and the selectivities to BD, 3B2Ol, and MEK of 13.9, 19.6,
and 33.3 mol% at 400 ◦C, respectively [36]. In2O3, however, shows
at most 4.7% for the BD selectivity (Table 2), because In2O3 has an
ability of hydrogenation of BD to butene isomers. In2O3 actually has
redox catalytic property: 1,4-butanediol is dehydrogenated into
␥-butyrolactone and 1-butanol can be dehydrogenated to butanal
[44].
In the pioneering work of Winfield, 3B2OL is mainly obtained
in the dehydration of 2,3-BDO over ThO2 at 350 ◦C while the main
product shifts to BD at a high temperature of 500 ◦C [26]. How-
ever, other research groups also disclosed their results with high
MEK selectivity but rare or no 3B2OL [28,14,29]. Some researchers
believed that MEK had been the intermediate from the dehydra-
tion of 2,3-BDO [27]. Bouns reported that MEK was obtained with a
yield of 86% in the dehydration of 2,3-BDO over mineral acids such
as bentonite at 225 ◦C, and it was converted into BD of 20% at 700 ◦C
with water as a diluent [27]. It seems that both MEK and 3B2OL can
be considered as the intermediates for the formation of BD from
2,3-BDO.
Fig. 7 summarizes the relationship between the ionic radii of
REOs and their formation rate of BD. Sc2O3, Sc2−xYbxO3, and Lu2O3
have the same cubic crystal phase, as shown in Table 1. Among
the REO catalysts, Sc2O3 with the smallest ionic radius showed
the highest BD selectivity. Lu2O3 also showed the selectivity to BD
while the others with larger ionic radii showed no catalytic abilities
to produce BD. It can be said that only Sc2O3 is selective to BD. In
this study, the highest formation rate of BD is obtained over Sc2O3
at 411 ◦C (Fig. 7). Thus, Sc2O3 with the smallest ionic radius of Sc3+
would provide a suitable adsorption site of 2,3-BDO on the surface
for the formation of 3B2OL and BD.
Table 4 and Fig. 5 clearly indicate that BD is formed from 3B2OL
but not from MEK over Sc2O3. Therefore, it is obvious that 3B2OL
is the intermediate from 2,3-BDO to BD over Sc2O3, whereas MEK
is not appropriate to be the intermediate to BD. Scheme 1 sum-
marizes the probable reaction routes to the major products over
Sc2O3. Butene isomers could come from butanols via dehydration.
2-Butanol and 2-methyl-1-propanol are actually detected in the
products (Tables 2 and 3). It is speculated that propylene could be
formed via the dehydration of 1-propanol through propanal, which
can be produced via pinacol rearrangement with the elimination of
methanol instead of water.
There are several examples that well-crystallized oxide surface
calcined at high temperatures shows high selectivity to a specific
product in the dehydration of diols [32,36,39–43]. In the dehydra-
tion of 1,4-butanediol over REO catalysts [39], we have reported
that a high calcination temperature results in high selectivity to
3-buten-1-ol in spite of growth of REO particles with a well-
crystallized cubic phase. A proper calcination temperature could
lead to the well-crystallized monoclinic ZrO2 for the adsorption of
the reactant 2,3-BDO [36]. In our previous work, it is confirmed
that Sc2O3 calcined at 800 ◦C with better crystallized cubic phase
has high selectivity to 3B2OL from 2,3-BDO [32] as well as the high
selectivity to BD from 2,3-BDO (Table 3).
Winfield has also pointed out that the equilibrium constant for
the dehydration of 2,3-BDO to MEK is 105 times greater than that for
the reaction to 3B2OL at 500 ◦C, and that the equilibrium constant
for the dehydration of 3B2OL to BD is 104 times greater than that
for the reaction of MEK to BD at 500 ◦C [26]. Thus, it is considerable
that the formation of MEK from 2,3-BDO readily proceeds but the
formation of BD from MEK is difficult. The BD formation from MEK
needs a high reaction temperature. Winfield has already considered
that 3B2OL rather than MEK is probably the intermediate in the
dehydration from 2,3-BDO to BD [26]. These are also well consistent
with the results of Table 4 and Fig. 5.
In Fig. 6, we have demonstrated that the dehydration of 2,3-BDO
to produce BD proceeds over the double-bed catalysts at 318 ◦C
in order to overcome the decomposition of the intermediates. The
In the dehydration of 1,4-butanediol into 3-buten-1-ol over
rare earth oxides such as Er2O3, we have already investigated the

H. Duan et al. / Applied Catalysis A: General 491 (2015) 163–169
[3] V.K. Srivastava, M. Maiti, R.V. Jasra, Eur. Polym. J. 47 (2011) 2342–2350.
169
main by-products such as MEK and propylene observed in Fig. 2 are
greatly reduced in the double-bed catalysts (Fig. 6). BD is obtained
with a selectivity higher than 94%. This is probably because Al2O3
catalyst in the lower bed converted 3B2OL into BD efficiently. The
present double-bed catalyst system consisting of Sc2O3 and Al2O3
would be a candidate in the manufacture of BD from bio-based
2,3-BDO. In our previous report, on the other hand, 3B2OL and
2-buten-1-ol are readily dehydrated to produce BD over acidic
catalysts such as silica-alumina, while 3-buten-1-ol is preferably
decomposed into propylene [46]. Therefore, it can be proposed that
3B2OL and 2-buten-1-ol are preferable intermediates in a selective
production of BD rather than 3-buten-1-ol. Since 1,3-butanediol
can be selectively dehydrated into 3B2OL and 2-buten-1-ol over
CeO2 catalyst [40,43], 1,3-butanediol is also introduced to be a
potential reactant for the production of BD [30,31].
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5. Conclusions
Vapor-phase catalytic dehydration of 2,3-BDO was investi-
gated over all the REO catalysts and In2O3 at high temperatures
around 425 ◦C. In the dehydration of 2,3-BDO, BD was mainly pro-
duced, together with MEK, 2-methyl-propanal, 2-methyl-propanol,
3B2OL, and butene isomers over Sc2O3. It was only Sc2O3 cata-
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H2 flow with a flow rate of 45 cm3 min−1. BD yield exceeded 90%
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