Dehydration of diols catalyzed by CeO2

Article abstract of DOI:10.1016/j.molcata.2004.07.004

Dehydration of several 1,3-diols into unsaturated alcohols was studied over pure CeO₂ at 325°-425°C. 1,3-Diols were more reactive than other diols and monoalcohols over CeO₂. In the dehydration of 1,3-propanediol, 1,3-butanediol, 3-m

Full text of DOI:10.1016/j.molcata.2004.07.004

Journal of Molecular Catalysis A: Chemical 221 (2004) 177–183
Dehydration of diols catalyzed by CeO2
∗
Satoshi Sato , Ryoji Takahashi, Toshiaki Sodesawa, Nozomi Honda
Department of Applied Chemistry, Faculty of Engineering, Chiba University, Yayoi, Inage, Chiba 263-8522, Japan
Received 15 April 2004; received in revised form 5 July 2004; accepted 6 July 2004
Available online 7 August 2004
Abstract
Dehydration of several 1,3-diols into unsaturated alcohols was investigated over pure CeO
◦
2
at 325–425 C. 1,3-Diols are more reactive than
other diols and monoalcohols over CeO
and 2-methyl-2,4-pentanediol, unsaturated alcohols are selectively produced at 325 C. In the dehydration of 2-methyl-1,3-propanediol, the
corresponding unsaturated alcohol is produced with low selectivity: decomposition simultaneously proceeds. TPR experiment reveals that
2
. In the dehydration of 1,3-propanediol, 1,3-butanediol, 3-methyl-1,3-butanediol, 2,4-pentanediol,
◦
4
+
4+
3+
active CeO
affects the dehydration of 1,3-diols.
2004 Elsevier B.V. All rights reserved.
2
surface is maintained at high valence of Ce in the water-producing reaction. It is speculated that redox nature between Ce –Ce
©
Keywords: CeO2; Dehydration; Diol; Unsaturated alcohol; TPR; Ce4 –Ce redox property
+
3+
1
. Introduction
Syntheses of unsaturated alcohols have been widely
investigated. It is known that both isomerization of epoxy
compounds such as 1,2-epoxypropane [14,15] and partial
hydrogenation of unsaturated aldehydes such as 2-butenal
[16–18] are efficient for the synthesis. However, some
epoxides and unsaturated aldehydes are expensive as raw
materials. As long as using inexpensive diols, we expect that
the dehydration of diols is an alternative for the production
of unsaturated alcohols.
Cerium(IV) oxide itself has attractive features in catal-
yses such as CO hydrogenation to hydrocarbons [1],
ortho-selective alkylation of phenol with alcohols [2–4],
and ketone formation through dimerization of alcohol
[
4–9], aldehyde, ester [9], and carboxylic acid [10,11]. In
the reaction of 1-propanol, 1-propanol was converted into
-pentanone with high selectivity over pure CeO2 catalyst
4]. In the vapor-phase conversion of 1,6-hexanediol over
3
[
ItiswellknownthatCeO2 componentwithoxygenstorage
capacity plays an important redox role in automotive exhaust
catalysts [19,20]. Both the redox ability and the basicity of
CeO2 cooperate to catalyze the ketone formation at tempera-
CeO2, cyclopentanone is formed with high selectivity [12].
We have recently reported that pure CeO2 selectively cat-
alyzes the formation of unsaturated alcohols in the dehydra-
tion of 1,3-diols [13]. In the dehydration of 1,3-propanediol,
◦
tures >400 C [8,9]: dehydrogenation of alcohol is the initial
2
-propen-1-ol is produced with 98.9 mol% selectivity over
reaction, followed by aldol addition of the resulting alde-
hyde, and the aldol is finally decomposed into ketone. CeO2
catalyzes dehydrogenation of primary alcohol to aldehyde,
while it does not catalyze the dehydration of the primary al-
◦
CeO2 at 325 C. In the catalytic reaction of 1,3-butanediol
over Al2O3 and MgO, 1,3-butanediol decomposes to gaseous
hydrocarbonssuchas1,3-butadienewithoutproducingunsat-
urated alcohols. Only CeO2 has specific catalytic activity for
the selective dehydration of 1,3-butanediol to 2-buten-1-ol
and 3-buten-2-ol with a small amount of 3-buten-2-one.
◦
cohol into olefin and ether even at high temperatures >400 C.
In contrast, 1,3-diols are readily dehydrated into unsaturated
◦
alcohols over CeO2 at low temperatures <400 C [13].
However, we have observed several by-products, which
had not been detected in the previous report [13], in reactions
of 1,3-diols in GC analysis using a different capillary column.
∗
Corresponding author. Tel.: +81-43-290-3376; fax: +81-43-290-3401.
E-mail address: satoshi@faculty.chiba-u.jp (S. Sato).
1
381-1169/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2004.07.004

1
78
S. Sato et al. / Journal of Molecular Catalysis A: Chemical 221 (2004) 177–183
In this paper, we describe catalytic feature of CeO2 in dehy-
dration of various monoalcohols and diols at 325–425 C. We
2.2. Catalytic reactions
◦
also examined the effect of reduction of CeO2 on the catalytic
activity, and characterized the CeO2 by using temperature-
programmedreduction(TPR). Then, wediscussedactivecen-
ters of CeO2 in the vapor-phase dehydration of 1,3-diols to
unsaturated alcohols.
Priortothereaction, aCeO2 sample(0.15 g)waspreheated
in a usual fixed bed flow reactor in an N2 flow typically at
◦
500 C for 1 h. A reactant fed into the reactor at flow rate
3
−1
−1
of 2.01 cm h together with an N2 flow of 73 mmol h
was contacted with the catalyst at a prescribed temperature
◦
between 325 and 425 C. The effluent collected periodically
was analyzed by gas chromatography (GC-8A, Shimadzu,
Japan) with a 30 m capillary column (TC-wax, GL Science,
Japan). Gaseous products such as 1,3-butadiene were ana-
lyzed by on-line gas chromatography (GC-8A) with a 1 m
packed column (Porapak Q).
2
. Experimental
2
.1. Catalyst samples
A reagent-grade powder of cerium(IV) oxide was pur-
chased from Wako Pure Chemical Industry Ltd., Japan. The
2
−1
specific surface area (SA) of the CeO2 was 20 m g by the
3. Results
◦
calculation with BET method using N2 isotherm at −196 C.
2
−1
Zirconium(IV) oxide, ZrO2, with SA of 44 m g was pre-
pared by conventional precipitation using zirconyl nitrate and
3.1. Dehydration of alcohols
◦
ammonia solution, followed by calcination in air at 500 C
Table 1 lists results of the reactions of several monoal-
cohols such as 1-butanol, 2-butanol, 2-buten-1-ol, and 3-
methoxy-1-butanol over CeO2 at 325–425 C. In the reaction
of 2-butanol, CeO2 catalyzes the dehydrogenation to produce
butanone, while butenes are formed at higher temperatures. In
the conversion of 1-butanol and 3-methoxy-1-butanol, CeO2
catalyzes only the dehydrogenation to produce butanal and
2-butenal. These monoalcohols are not dehydrated to butenes
at temperatures of 325–425 C. In the conversion of 2-buten-
1-ol, dehydration to 1,3-butadiene proceeds in addition to de-
hydrogenation. In contrast, 3-oxo-1-butanol is readily dehy-
drated into 3-buten-2-one at temperatures lower than 300 C,
together with decomposition into propanone.
for 3 h.
◦
A temperature-programmed reduction measurement was
done with a stepwise temperature program for the samples
of both fresh and treated with water vapor after reduction,
and the details are described elsewhere [21,22]. A mixture of
3
−1
H2/N2 (1/9) was flowed at rate of 10 cm min at ambient
pressure over a catalyst sample (30 mg) charged in a quartz
◦
◦
tube. The temperature was raised from 25 C to a prescribed
−
1
temperature at heating rate of 5 K min , and kept at the tem-
perature for 1 h. An amount of H2 consumed for reduction of
the sample was monitored with a thermal conductivity detec-
tor, and was calibrated by using complete reduction of a refer-
ence NiO sample. Average oxidation number of Ce in CeO2
was calculated from the consumption of H2 during the TPR
process.
◦
Table 2 summarizes results of the reactions of different
butanediols such as 1,2-, 1,3-, 1,4-, and 2,3-butanediol over
CeO2 at 325–425 C. CeO2 catalyzes the dehydration of
◦
Table 1
Dehydration of monoalcohols over CeO2
◦
Selectivitya
Reactant
Temperature ( C)
Conversion (%)
3
3
4
25
75
25
0.4
0.8
2.2
1 (68)
1 (36)
1 (41)
1
2
2
-Butanol
325
375
425
2.3
8.2
40.4
2 (95)
2 (30), 3 (63)
2 (17.6), 3 (76.3)
-Butanol
325
375
425
2.4
20.9
29.1
Unidentified
1 (19.4), 4 (19.1), 5 (12.9)
1 (12.7), 4 (12.5), 5 (15.5)
-Buten-1-ol
3
3
4
25
75
25
2.0
7.5
15.1
1 (7), 4 (47)
1 (12), 4 (7)
1 (13), 4 (9)
3
-Methoxy-1-butanol
-Oxo-1-butanol
3
275
25
51.8
87.2
6 (87.2), 7 (10.0)
6 (67.0), 7 (29.7)
3
Products: (1) butanal; (2) butanone; (3) 1-butene; (4) 2-butenal; (5) 1,3-butadiene; (6) 3-buten-2-one; (7) propanone.
a
Number in parenthesis indicates the selectivity (mol%) to the product.

S. Sato et al. / Journal of Molecular Catalysis A: Chemical 221 (2004) 177–183
179
Table 2
Dehydration of butanediols over CeO2
Reactant
Conversion (%)
Selectivitya
b
6
5.7
3.1
.4
2 (14)
1
,2-Butanediol
,3-Butanediol
c
1
5
1 (23), 2 (19), 8 (17), 9 (2)
1 (28.4), 2 (26.4), 8 (12.7), 9 (2.2)
d
b
3
61.0
6.9
10 (56.9), 11 (35.5), 12 (2.2), 6 (1.8), 2 (1.3), 7 (0.8), 8 (0.5)
10 (41.8), 11 (28.2), 12 (3.7), 6 (6.0), 2 (4.3), 7 (4.5), 8 (1.2), 4 (0.7), 5 (0.7)
10 (47.9), 11 (19.4), 12 (2.1), 6 (4.1), 2 (2.5), 7 (4.9), 8 (1.6), 4 (1.3), 5 (4.6)
c
1
d
9
3
6.5
3.5
c,e
10 (15.3), 11 (11.2), 12 (3.7), 6 (10.6), 2 (10.6), 7 (2.8), 8 (2.1), 5 (3.7), 13 (25.5)
b
c
d
2
9.0
4.0
.6
13 (84)
1
2
,4-Butanediol
,3-Butanediol
1
7
13 (36.2), 11 (1.1), 12 (1.7), 8 (1.9), 14 (2.7), 15 (50.4), 5 (3.0)
13 (57.1), 11 (2.8), 12 (4.7), 8 (3.5), 14 (3.0), 15 (17.4), 5 (3.2)
b
c
d
1
0.3
1.1
.5
2 (18), 10 (3)
2 (48), 7 (7), 10 (5), 6 (1)
2 (64.0), 7 (9.4), 10 (2.7), 6 (1.3)
1
5
Products: (1) butanal; (2) butanone; (4) 2-butenal; (5) 1,3-butadiene; (6) 3-buten-2-one; (7) propanone; (8) 1-butanol; (9) 2-butanol; (10) 3-buten-2-ol; (11)
trans-2-buten-1-ol; (12) cis-2-buten-1-ol; (13) 3-buten-1-ol; (14) ␥-butyrolactone; (15) tetrahydrofuran.
a
Number in parenthesis indicates the selectivity (mol%) to the product.
b
c
d
e
◦
Reacted at 325 C.
◦
Reacted at 375 C.
◦
Reacted at 425 C.
Catalyzed by ZrO2 prepared by precipitation.
1
,2-butanediol to produce mainly butanal and butanone,
alytic performance without decay of the conversion within
the initial 5 h. Both the conversion of 1,3-butanediol and the
selectivities to 3-buten-2-ol, trans-, and cis-2-buten-1-ol are
stabilized. In contrast, slight decays in the conversion are
where an enol form of the carbonyl products would be an
intermediate. 2,3-Butanediol is also converted to butanone
over CeO2. It is remarked that 2-buten-1-ol and 3-buten-2-
ol are rarely produced in the dehydration of 1,2-butanediol
and2,3-butanediol. Inaddition, 1,4-butanediolisconvertedto
◦
observed at 375 and 425 C.
Table 3 lists results of the reactions of reactive diols
such as 1,3-propanediol, 2,4-pentanediol, 3-methyl-1,3-
butanediol, and 2-methyl-2,4-pentanediol over CeO2 at
3-buten-1-ol with a small amount of tetrahydrofuran and 1,3-
◦
butadiene at high temperature as 425 C. In the conversion of
1
2
◦
,3-butanediol over CeO2, however, 3-buten-2-ol and trans-
-buten-1-ol are selectively produced while cis-2-buten-1-ol
325–425 C. In the reactions, CeO2 effectively catalyzes the
◦
dehydration to unsaturated alcohols even at 325 C. Table 4
is minimally formed. In contrast to CeO2, ZrO2 has dehydra-
tion ability for 1,3-butanediol at 375 C, while 3-buten-1-ol
is the major product together with other unsaturated alcohols
such as 3-buten-2-ol, trans-, and cis-2-buten-1-ol.
summarizes results of the reactions of other diols such as
1,2-propanediol, 2-methyl-1,3-propanediol, and 2-ethyl-1,3-
hexanediol, together with 1,2,3-propanetriol over CeO2. In
the conversion of 1,2-propanediol, propanal and propanone
are formed through enols. 1,2,3-Propanetriol is converted
into hydroxypropanone with moderate selectivity, and
several unknown products are detected. In the conversion
of 2-methyl-1,3-propanediol and 2-ethyl-1,3-hexanediol,
the corresponding unsaturated alcohols are produced with
moderate selectivity. However, the 1,3-diols with alkyl group
at 2-position are less reactive than the 1,3-diols having no
alkyl side chain listed in Table 3.
◦
Fig. 1 depicts the time dependence of conversion of 1,3-
◦
butandiol over CeO2 at 325 C. CeO2 shows attractive cat-
3.2. Dehydration of 1,3-butanediol over reduced CeO2
and its redox nature
Fig. 2 shows TPR profiles of CeO2. H2 consumption in the
TPR up to the prescribed temperature increases with raising
the reduction temperature: CeO2 is readily reduced at higher
temperature. Since the H2 consumption in the TPR can be
calibrated by the amount of H2 consumption in a reference
NiO, oxidation state of CeO2 treated at different tempera-
tures can be estimated by the H2 consumption. For example,
Fig. 1. Time dependence of conversion in the dehydration of 1,3-butanediol
over CeO2 at 325 C: (a) conversion of 1,3-butanediol; (b) selectivity to
◦
3
-buten-2-ol; (c) selectivity to trans-2-buten-1-ol; (d) selectivity to cis-2-
buten-1-ol.

1
80
S. Sato et al. / Journal of Molecular Catalysis A: Chemical 221 (2004) 177–183
Table 3
Dehydration of other reactive diols over CeO2
◦
Selectivitya
Reactant Temperature ( C)
Conversion (%)
325
375
425
50.6
59.6
78.1
16 (98.9)
1
,3-Propanediol
16 (65.5), 17 (4.3), 18 (3.1), 19 (7.6)
16 (54.0), 17 (6.2), 18 (5.5), 19 (10.1)
3
3
4
25
75
25
47.2
79.2
97.3
20 (86.8), 21 (7.4), 22 (1.4)
20 (78.9), 21 (7.5), 22 (2.9)
20 (60.6), 21 (7.1), 22 (8.3)
2
,4-Pentanediol
-Methyl-1,3-
3
325
375
4
42.3
75.4
87.3
23 (56.8), 24 (24.7)
23 (59.1), 24 (25.5)
23 (44.3), 24 (16.3)
butanediol
25
2
-Methyl-2,4-
325
375
28.3
59.7
81.8
25 (48.9), 26 (5.8), 27 (28.3), 28 (5.7), 29 (5.6)
25 (46.9), 26 (7.4), 27 (27.9), 28 (4.6), 29 (5.5)
25 (22.6), 26 (5.8), 27 (11.9), 28 (22.2), 29 (10.5)
pentanediol
425
Products: (16) 2-propen-1-ol; (17) 1-propanol; (18) propanal; (19) ethanol; (20) trans-3-penten-2-ol; (21) cis-3-penten-2-ol; (22) 1,3-pentadiene; (23) 2-methyl-
-buten-2-ol; (24) 3-methyl-2-buten-1-ol; (25) trans-2-methyl-3-penten-2-ol; (26) cis-2-methyl-3-penten-2-ol; (27) 4-methyl-3-penten-2-ol; (28) 2-methy-1,3-
3
pentadiene; (29) propanone.
a
Number in parenthesis indicates the selectivity (mol%) to the product.
◦
CeO2 is reduced to CeO1.79 at 900 C, where the average ox-
version decreases with raising pretreatment temperature. The
decrease in the catalytic activity is also caused by the decrease
in SA of the samples heated at high temperature. In addition,
H2 used as a carrier gas does not affect the catalytic activity
of CeO2.
idation number of Ce is estimated to be 3.58. This means that
+
3+
4
2% of the total Ce4 cations is reduced to Ce . The re-
◦
duction treatment at >500 C changes the sample color from
yellow to gray. Table 5 lists the average oxidation number of
Ce in the CeO2 reduced at different temperatures. The av-
erage oxidation number decreases with raising the reduction
temperature.
Fig. 3 shows TPR profiles of CeO2 samples treated un-
◦
der different conditions. When the sample reduced at 600 C
◦
are contacted with H2O at 325 C for 1 h, it has a reduc-
Table 5 also summarizes the effect of CeO2 pretreatment
on the catalytic activity in the conversion of 1,3-butanediol,
together with the selectivities to 3-buten-2-ol and trans-2-
tion peak similar to the original CeO2 sample (Fig. 3b).
The reduction peak at <600 C decreases with increasing
◦
reduction temperature (Fig. 3c and d), and TPR profile at
◦
◦
buten-1-ol. In the samples reduced by H2 at >500 C, the
>600 C is recovered. In addition, the H2O treatment changes
average conversion level in the initial 5 h decreases with rais-
ing reduction temperature while the SA decreases steeply.
In the N2-pretreatment of CeO2 at >700 C, the average con-
the sample color from gray to yellow. This indicates that
the reduced CeO2 surface is readily oxidized by H2O at
325 C.
◦
◦
Table 4
Dehydration of less reactive polyols over CeO2
Reactant
Conversion (%)
Selectivitya
b
3
.3
17 (21), 29 (5), 18 (3), 30 (2), 31 (31)
17 (23), 29 (14), 18 (11), 30 (3), 31 (18)
17 (18.7), 29 (19.0), 18 (18.2), 30 (2.2), 31 (4.7)
1
,2-Propanediol
c
1
4
1.3
7.4
d
b
2
-Methyl-1,3-
6.8
32 (61), 33 (4), 34 (7), 18 (6), 17 (23)
32 (64.9), 33 (6.4), 34 (8.4), 18 (7.4), 17 (12.0)
32 (36.4), 33 (17.2), 34 (11.4), 18 (13.6), 17 (17.3)
propanediol
48.0c
d
8
5.4
b
2
-Ethyl-1,3-
19.0
35 (54.1), 36 (22.5), 8 (3.6), 1 (3.8)
35 (47.2), 36 (22.1), 8 (7.3), 1 (3.0)
35 (37.3), 36 (18.2), 8 (9.9), 1 (9.2)
40.7c
hexanediol
d
8
1.9
b
c
d
3
1.6
9.7
.9
31 (50)
31 (36.8)
31 (26.0)
1
,2,3-Propanetriol
2
4
Products:(1)butanal;(8)1-butanol;(17)1-propanol;(18)propanal;(29)propanone;(30)2-propanol;(31)1-hydroxy-2-propanone;(32)2-methyl-2-propen-1-ol;
(
33) 2-methylpropanal; (34) 2-methylpropanol; (35) 2-ethyl-1-hexen-3-ol; (36), 2-ethyl-2-hexen-1-ol.
a
Number in parenthesis indicates the selectivity (mol%) to the product.
b
c
d
◦
Reacted at 325 C.
◦
Reacted at 375 C.
◦
Reacted at 425 C.

S. Sato et al. / Journal of Molecular Catalysis A: Chemical 221 (2004) 177–183
181
Table 5
◦
Effect of pretreatment of CeO2 on the catalytic reaction of 1,3-butanediol at 325 C
a
◦
Valence of Ce in CeOxb
c
d
2
−1
Pretreatment ( C)
Conversion (%)
Selectivity (mol%)
-Buten-2-ol
SA (m g )
3
trans-2-Buten-1-ol
H2
H2
H2
H2
H2
H2
H2
H2
100
250
325
500
600
700
800
900
4.000
4.000
3.994
3.940
3.910
3.762
3.658
3.582
61.6
60.0
60.3
59.4
57.5
41.0
29.6
10.8
56.1
56.2
56.2
56.1
54.5
53.9
52.3
51.8
35.6
34.9
34.9
35.4
35.3
36.7
36.4
35.2
20.4
–
–
20.3
18.4
9.0
2.3
2.1
H2
H2
H2
H2
325
600
700
800
3.994
3.910
3.762
3.658
61.4 e
56.3 e
40.0 e
29.9 e
55.8
53.9
54.3
51.3
35.2
35.0
36.5
36.8
–
–
–
–
N2
N2
N2
N2
N2
325
500
700
800
900
–
–
–
–
–
58.2
56.3
58.1
48.4
24.7
55.9
56.0
57.5
55.6
56.9
35.8
35.7
35.4
34.7
35.2
–
20.1
17.1
8.4
4.2
a
The pretreatment of catalyst samples was performed at the prescribed temperature for 1 h.
b
c
d
e
Average oxidation number of Ce in CeO2, calculated from the consumption of H2 during the TPR process (Fig. 2).
−1
The catalytic reaction was performed over 0.3 g of CeO2 catalyst in N2 flow of 73 mmol h
.
Specific surface area.
The catalytic reaction was carried out in H2 carrier gas of 73 mmol h
−1
.
Fig. 3. TPR profiles of CeO2 treated under different conditions. The TPR
−
1
was performed at the temperature-rising rate of 5 K min and then the
◦
temperature was held at 900 C for 1 h: (a) fresh CeO2; (b) treated with
H2O at 325 C for 1 h after being reduced by H2 at 600 C; (c) 700 C; (d)
◦
◦
◦
◦
8
00 C.
4. Discussion
4.1. Reactivity of alcohols over CeO2
In the dehydration over CeO2, alcohol reactants are cat-
egorized into four types: monoalcohols, 1,3-diols, 1,4-diol,
and others. Monoalcohols are less reactive, and they are dehy-
drogenated into aldehyde and ketone at higher temperatures
◦
(
Table 1). 1-Butanol is less reactive even at 425 C, and it
Fig. 2. Stepwise TPR profiles of CeO2. The TPR was performed at the
−1
produces butanal not olefin: 1-butanol can be converted to
4-heptanone through dimerization of butanal at 450 C [7,8].
It is noted that further dehydration of 2-buten-1-ol, a product
temperature-rising rate of 5 K min and then the temperature was held at a
◦
◦
◦
◦
◦
prescribed temperature for 1 h: (a) 325 C; (b) 500 C; (c) 600 C; (d) 700 C;
◦
◦
◦
(e) 750 C; (f) 800 C; (g) 900 C.

1
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S. Sato et al. / Journal of Molecular Catalysis A: Chemical 221 (2004) 177–183
in the dehydration of 1,3-butanediol, does not proceed over
CeO2, andthatmonoalcoholssuchas1-butanoland2-butanol
were not dehydrated to butenes over CeO2 at low tempera-
the intrinsic catalytic activity of CeO2 for the dehydration of
1,3-butanediol or not.
Then, we examined another TPR experiment for samples
with different treatment (Fig. 3). Contact of water with the re-
duced CeO2 surface regenerates the reduction peak at around
◦
tures <375 C. 1-Butene is a major product in the dehydration
◦
of 2-butanol over CeO2 at ≥375 C. It is also known that lan-
◦ 3+
500 C, and it induces the oxidation of Ce cations into
thanide oxides including CeO2 catalyze Hoffman elimination
to produce ␣-olefin [23].
4
+
Ce . This is consistent with the reports of Otsuka et al.
[24,25]: a reduced CeO2 powder is oxidized to CeO2 by wa-
Diols are more reactive than monoalcohols, and they are
dehydrated to either unsaturated alcohols or saturated ketones
◦
ter even at 300 C, and the oxidation by water occurs not
(
Tables 2–4). 1,3-Diols are basically reactive in the dehydra-
only on the surface but also in the bulk. The reduction peak
at <600 C would be concerned with surface CeO2 because
◦
tion to produce unsaturated alcohols. 1,4-Butanediol has spe-
cific reactivity: CeO2 catalyzes dehydration of 1,4-butanediol
to 3-buten-1-ol, which is not further dehydrated to 1,3-
reduction at high temperatures reduces both the reduction
peak (Fig. 3) and the specific surface area (Table 5). Since the
◦
3+
4+
butadiene, at 425 C. Polyols such as 1,2- and 2,3-butanediol,
surface Ce is readily oxidized to Ce by H2O produced
in the dehydration, it is reasonable that the CeO2 surface is
maintained at high oxidation state in the working state of the
dehydration.
and 1,2,3-propanetriol are dominantly dehydrated into ke-
tone through the enol form. Butanone would be directly
formed via 2-buten-2-ol in the dehydration of 2,3-butanediol:
3
-buten-2-ol is not an intermediate because it is observed as
a stable product in the reaction of 1,3-butanediol over CeO2
4.3. Reaction model in the dehydration of 1,3-diol
(Table 2).
over CeO2
CeO2 works with different catalytic functions depending
on the temperature as well as on the reactant (Tables 1–4). It
can be summarized that CeO2 catalyzes dehydration of 1,3-
ZrO2 and CeO2 have different catalytic features in dehy-
dration of 4-methylpentan-1-ol, while ZrO2 is much more
acidic and basic than CeO2 [26]. ZrO2 has a fluorite (CaF2)
structure similar to CeO2, and it also has ability for the dehy-
dration of 1,3-butanediol, while 3-buten-1-ol is formed in ad-
dition to 3-buten-2-ol, trans-, and cis-2-buten-1-ol (Table 2).
The product distribution over ZrO2 is explained by an-
other mechanism that an OH anion is initially eliminated;
acidic sites of ZrO2 probably activate the OH group of 1,3-
butanediol.
◦
diols to unsaturated alcohols at <400 C and dehydration of
◦
1
,4-butanediol to 3-buten-1-ol at >400 C. It also catalyzes
dehydration of 1,2- and 2,3-diols to aldehyde and ketone.
4
.2. Activation of alcohols over CeO2 and its
redox property
We suggested that the catalytic activity of CeO2 in
the activation of alcohols would be correlated with the
In contrast, CeO2 produces only 3-buten-2-ol and
2-buten-1-ol without producing 3-buten-1-ol. If an OH
group on the 3-position is eliminated first as an OH anion,
3-buten-1-ol has to be formed together with 2-buten-1-ol.
Thus, the product distribution cannot be explained by the
acid-catalyzed mechanism mentioned above. We speculate
that redox nature of CeO2 initially activates hydrogen
in the 2-position of 1,3-butanediol [13]: the dehydration
of 1,3-diols over CeO2 follows a radical mechanism; a
hydrogen atom located on the 2-position is abstracted first,
followed by the elimination of an OH radical (Fig. 4). Then,
redox feature [4,8,9]. In the alkylation of phenol with
◦
1
-propanol catalyzed by CeO2–MgO at 475 C, it has
been suggested that redox sites, not acid sites, activate the
alkylating reagent of 1-propanol [4]. A hydrogen atom is
eliminated from 1-propanol to produce radical species such
as 1-hydroxypropyl radical rather than propoxy radical. The
hydrogen atom can reduce Ce4 into Ce : Ce cation
oxidatively eliminates hydrogen from 1-propanol to form
proton. The 1-hydroxypropyl radical attacks the electron-rich
ortho-positions of phenol adsorbed perpendicularly on the
weak basic sites in the CeO2–MgO because the ␣-position
of 1-hydroxypropyl radical is slightly positive. A hydroxyl
radical is readily eliminated from the alkylated intermediate
to produce 2-n-propylphenol and water, together with the
+
3+
4+
it is reasonable that Ce4 is reducible by the eliminated
+
hydrogen radical in the catalytic cycle.
Here, we have a significant question: even monoalcohols,
instead of diols, may be dehydrated into olefin according to
the radical mechanism (Fig. 4). Actually, monoalcohols in-
cluding unsaturated alcohol are less reactive for dehydration
(Table 1). Dehydration of 1,3-diol proceeds at temperature as
oxidation of Ce3 to Ce
+
4+
.
In the TPR profile (Fig. 2), CeO2 is severely reduced at
◦
>
600 C. Both the average oxidation number of Ce and the
◦
catalytic activity of CeO2 in the dehydration of 1,3-diols de-
low as 325 C, while much higher temperatures are needed
◦
creased with raising the reduction temperature above 600 C
for the activation on monoalcohols. Since 1,3-diols are more
stabilized and activated than monoalcohols on the CeO2
surface, both of the OH groups in 1,3-diol could be inter-
acted with the surface of CeO2. We can correct the reaction
image of the dehydration of 1,3-diols (Fig. 5). It is remark-
able that 2-methyl-1,3-propanediol is less reactive than
(Table 5). Because SA also decreases with treatment temper-
ature, the reduced CeO2 seems to have the intrinsic catalytic
activity as active as the non-reduced one: the catalytic activ-
ity could be proportional to the SA. Unexpectedly, we still
have a question whether the oxidation state of CeO2 affects

S. Sato et al. / Journal of Molecular Catalysis A: Chemical 221 (2004) 177–183
183
Fig. 4. Possible mechanism of dehydration of 1,3-diol.
Fig. 5. Probable mechanism in the dehydration of 1,3-propanediol over CeO2 (R = H or CH3).
1
,3-butanediol and 1,3-propanediol (Table 4). The methyl
[5] H. Idriss, C. Diagne, J.P. Hindermann, A. Kiennemann, M. Barteau,
J. Catal. 155 (1995) 219–237.
group on 2-methyl-1,3-propanediol would obstruct the
adsorption on the surface because of the steric hindrance
[
[
6] A. Yee, S.J. Morrison, H. Idriss, J. Catal. 186 (1999) 279–295.
7] N. Plint, D. Ghavalas, T. Vally, V.D. Sokolovski, N.J. Coville, Catal.
Today 49 (1999) 71–77.
(Fig. 5).
There still remains a question: why are not the most acidic
[8] Y. Kamimura, S. Sato, R. Takahashi, T. Sodesawa, M. Fukui, Chem.
Lett. (2000) 232–233.
protons on the OH groups eliminated from 1,3-diols? The
speculative mechanism needs further investigation.
[9] Y. Kamimura, S. Sato, R. Takahashi, T. Sodesawa, T. Akashi, Appl.
Catal. A 252 (2003) 399–410.
[10] M. Glinski, J. Kijenski, A. Jakubowski, Appl. Catal. A 128 (1995)
2
09–217.
5
. Conclusions
[
[
11] T.S. Hendren, K.M. Dooley, Catal. Today 85 (2003) 333–351.
12] T. Akashi, S. Sato, R. Takahashi, T. Sodesawa, K. Inui, Catal. Com-
mun. 4 (2003) 411–416.
The dehydration of monoalcohols and diols catalyzed by
CeO2 was investigated. The dehydration of 1,3- and 2,4-
diols produces selectively unsaturated alcohols over CeO2
at 325 C. CeO2 has attractive performance without decay at
[13] S. Sato, R. Takahashi, T. Sodesawa, N. Honda, H. Shimizu, Catal.
Commun. 4 (2003) 77–81.
[14] K. Ueyama, N. Nisiyama, S. Torii, Tetrahedron Lett. 25 (1984)
◦
4137–4138.
lower temperatures, while other alcohols such as 1,2- and 1,4-
butanediol are activated at higher temperature. In the reaction
of monoalcohols such as 1-buanol, 2-butanol, 2-buten-1-ol,
and 3-methoxy-1-butanol, they are dehydrogenated into alde-
hyde and ketone at higher temperatures.
[
15] P. Mosset, S. Manna, J. Viala, J.R. Falck, Tetrahedron Lett. 27 (1986)
299–302.
[16] J.L. Margitfalvi, A. Tompos, I. Kolosova, J. Valyon, J. Catal. 174
1998) 246–249.
(
[17] C. Ando, H. Kurokawa, H. Miura, Appl. Catal. A 185 (1999)
L181–L183.
TPR measurement combined with H2O treatment of the
reduced CeO2 reveals that active CeO2 surface is maintained
[18] C. Ando, A. Ikumoto, H. Kurokawa, K. Sugiyama, H. Miura, Catal.
Commun. 2 (2001) 323–327.
at high valence of Ce4 . The redox cycle of Ce –Ce on
the surface would play a role for the dehydration concerning
the activation of diols in the form of radicals, as shown in
Fig. 5.
+
4+
3+
[19] H.C. Yao, Y.F.Y. Yao, J. Catal. 86 (1984) 254–265.
[
[
[
20] J.G. Nunan, H.J. Robota, M.J. Cohn, S.A. Bradley, J. Catal. 133
1992) 309–324.
21] T. Nakayama, N. Ichikuni, S. Sato, F. Nozaki, Appl. Catal. A 158
1997) 185–199.
22] S. Takenaka, S. Sato, R. Takahashi, T. Sodesawa, Phys. Chem. Chem.
Phys. 5 (2003) 4968–4973.
(
(
References
[23] A.J. Lundeen, R.V. Hoozer, J. Org. Chem. 32 (1967) 3386–
389.
3
[
1] K. Kushihashi, K. Maruya, K. Domen, T. Onishi, J. Chem. Soc.,
Chem. Commun. (1992) 259–260.
[24] K. Otsuka, M. Hatano, A. Morikawa, J. Catal. 79 (1983) 493–
496.
[2] S. Sato, K. Koizumi, F. Nozaki, Appl. Catal. A 133 (1995) L7–L10.
[3] S. Sato, K. Koizumi, F. Nozaki, J. Catal. 178 (1998) 264–274.
[4] S. Sato, R. Takahashi, T. Sodesawa, K. Matsumoto, Y. Kamimura,
J. Catal. 184 (1999) 180–188.
[25] K. Otsuka, M. Hatano, A. Morikawa, Inorg. Chem. Acta 109 (1985)
193–197.
[26] V. Solinas, E. Rombi, I. Ferino, M.G. Cutrufello, G. Colon, J.A.
Navio, J. Mol. Catal. A 204–205 (2003) 629–635.