N-Butyraldehyde self-condensation catalyzed by Ce-modified γ-Al2O3

Article abstract of DOI:10.1039/c5ra21125e

Self-condensation of n-butyraldehyde is an important process for the industrial production of 2-ethylhexanol. The catalytic performance of some solid acids such as γ-Al₂O₃ and molecular sieves for the self-condensation of n-butyraldehyde was investigated and the results showed that γ-Al₂O₃ was the best one. Then the effect of preparation conditions on the catalytic performance of γ-Al₂O₃ and the effect of reaction conditions on the self-condensation of n-butyraldehyde were discussed. In order to improve the catalytic performance, γ-Al₂O₃ was modified by different substances and Ce-Al₂O₃ was found to show the best catalytic performance; the conversion of n-butyraldehyde and the yield of 2-ethyl-2-hexenal could reach 93.8% and 88.6%, respectively. Moreover, the Ce-Al₂O₃ catalyst had excellent reusability. The XPS analysis of Ce3d demonstrated that the valence state of cerium affected the catalytic performance of Ce-Al₂O₃ to some extent but not predominantly. Instead the acid-base property of Ce-Al₂O₃ played a dominant role in the catalytic performance. The reaction components formed over the Ce-Al₂O₃ catalyst were identified by GC-MS and then some side-reactions were speculated and a reaction network for n-butyraldehyde self-condensation catalyzed by Ce-Al₂O₃ was proposed. Subsequently, the research on the intrinsic kinetics of n-butyraldehyde self-condensation catalyzed by Ce-Al₂O₃ showed that both the forward and backward reactions are second order and the corresponding activation energy is separately 79.60 kJ mol^-1 and 74.30 kJ mol^-1, which is higher than that of the reaction catalyzed by an aqueous base or acid.

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n-Butyraldehyde Self-Condensation Catalyzed by Ce-Modified γ-
Al O
2
3
Received 00th January 20xx,
Accepted 00th January 20xx
Chao Xiong, Ning Liang, Hualiang An, Xinqiang Zhao*, Yanji Wang
DOI: 10.1039/x0xx00000x
Self-condensation of n-butyraldehyde is one of the important processes for the industrial production of 2-ethylhexanol.
The catalytic performance of some solid acids such as γ-Al
butyraldehyde was investigated and the results showed that γ-Al
conditions on the catalytic performance of γ-Al and the effect of reaction conditions on the self-condensation of n-
butyraldehyde were discussed. In order to improve the catalytic performance, γ-Al was modified by different
substances and Ce-Al was found to show the best catalytic performance; the conversion of n-butyraldehyde and the
yield of 2-ethyl-2-hexenal could reach 93.8% and 88.6%, respectively. Moreover, Ce-Al catalyst had excellent
reusability. The XPS analysis of Ce3d demonstrated that the valence state of cerium affected the catalytic performance of
Ce-Al to some extent but not predominantly. Instead the acid-base property of Ce-Al played a dominant role in the
catalytic performance. The reaction components formed over Ce-Al catalyst were identified by GC-MS and then some
side-reactions were speculated and a reaction network for n-butyraldehyde self-condensation catalyzed by Ce-Al was
proposed. Subsequently, the research on the intrinsic kinetic of n-butyraldehyde self-condensation catalyzed by Ce-Al
2
O
3
and molecular sieves for the self-condensation of n-
www.rsc.org/
2
O
3
was the best one. Then the effect of preparation
2
O
3
2
O
3
2
O
3
2
O
3
2
O
3
2 3
O
2 3
O
2 3
O
2 3
O
showed that both the forward and backward reactions are second order and the corresponding activation energy is
separately 79.60 kJ/mol and 74.30 kJ/mol, which is higher than that of the reaction catalyzed by an aqueous base or acid.
Introduction
ease of separation. The reported solid base catalysts used for the
2
-4
self-condensation of n-butyraldehyde include inorganic
and
As an important chemical, 2-ethylhexanol is mainly used for the
production of diethylhexyl phthalate (generally known as dioctyl
phthalate, DOP) which serves as a plasticizer for PVC. In addition, 2-
ethylhexanol is also used to produce adhesives, surfactants,
5
-6
organic solid bases. However, the solid base catalysts show poor
hydrothermal stability and reusability in spite of their high activity,
hindering their industrial applications.
antioxidants, cosmetics as well as additives of diesel and lubricating
1
The self-condensation of n-butyraldehyde is a typical aldol
oil . The industrial manufacture of 2-ethylhexanol mainly relies on condensation reaction. Aldol condensation reaction can be
carbonyl synthesis technology and aldehyde condensation catalyzed by a basic or an acidic catalyst from the viewpoint of
technology. Whichever technology is adopted, self-condensation of reaction mechanism. The literatures about the self-condensation of
7
-9
n-butyraldehyde is an essential step. At present, an aqueous caustic n-butyraldehyde catalyzed by a solid acid are very few, but there
alkali catalyst is used for the self-condensation of n-butyraldehyde are a lot of reports about solid acid-catalyzed other aldol
10-13
7
in industry and some drawbacks exist inherently. When the liquid condensation reactions
. Swift et al. prepared some kinds of
alkali concentration is lower, the condensation reaction proceeds supported SnO catalysts to catalyze the self-condensation of n-
2
insufficiently and the conversion of n-butyraldehyde is lower. When butyraldehyde and found that acid-base property of a support had a
the liquid alkali concentration is much higher, the condensation great effect on the catalytic activity: the activity of SnO supported
2
reaction will take place drastically and the formation of byproducts on an acidic or a basic support was very low while that of neutral
2
may lead to a low selectivity of 2-ethyl-2-hexenal. Besides, liquid silica-supported SnO was much higher. Under the suitable reaction
alkali can corrode reaction apparatus and a lot of liquid acid will be conditions, the conversion of n-butyraldehyde and the selectivity of
required for handling the spent liquid alkali catalyst. In order to 2-ethyl-2-hexenal could separately reach 75% and 98% over
8
solve the problems resulted from the liquid alkali catalyst, solid SnO
base catalysts have drawn much attention for their high activity and of H
in supercritical carbon dioxide and obtained
2
/SiO
2
catalyst. Musko et al. studied the catalytic performance
4
SiW12
O
40/MCM-41 in the self-condensation of n-butyraldehyde
27% of n-
a
butyraldehyde conversion and 100% of 2-ethyl-2-hexenal selectivity
under the suitable conditions. Compared with the work of Musko et
C. Xiong. N. Liang.H.An. Y.Wang.Prof. Dr. X. Zhao
School of Chemical Engineering and Technology
Hebei University of Technology
8
9
4 2
al. , Chen et al. in our group selected H SiW12O40/SiO to catalyze
the self-condensation of n-butyraldehyde and obtained a better
result. Under the suitable conditions, the conversion of n-
GuangRong Dao 8, Hongqiao District
Tianjin 300130, P. R. China.
*
Corresponding author e-mail address: zhaoxq@hebut.edu.cn.
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butyraldehyde and selectivity of 2-ethyl-2-hexenal could attain
0.4% and 89.2%, respectively. However, the reusability of
40/SiO was poor due to the loss of silicotungstic acid.
Materials Characterization
9
The textural properties of the catalysts were measured using an
ASAP 2020 specific surface area and porosity analyzer made in
Micromeritics Company in America. Prior to the test, 0.2 g of the
sample was degassed at 150 ℃ for 4 h in vacuum to remove the
H
4
SiW12
O
2
1
0
Kikhtyanin et al. evaluated the catalytic performance of a series of
molecular sieve catalysts for the aldol condensation of furfural with
acetone and found that HBEA(25) showed the best catalytic
performance. Under the suitable conditions, the conversion of
furfural and the yield of 4-(2-furyl)-3-buten-2-on could reach 50%
2
impurities adsorbed on the sample surface. Then N adsorption-
desorption test was performed at -195.8 ℃. The specific surface
area was calculated by the Brunauer-Emmer-Teller (BET) method
while the pore volume and pore diameter were calculated by the
Barrett-Joyner-Halenda (BJH) method.
1
1
and 36%, respectively. Lahyani et al. selected acidic resins
Amberlyst-15 and Amberlite-200C to catalyze the cross aldol
condensation of benzaldehyde with acetophenone. The conversion
of benzaldehyde and the yield of chalcone could separately reach
The basicity and acidity of a catalyst were measured by a
temperature programmed desorption using CO
molecule (CO -TPD, NH -TPD) performed on an Auto ChemⅡ 2920
chemical adsorption instrument made in Micromeritics Company in
America. Taking the test of CO -TPD as example, a typical procedure
2 3
or NH as a probe
100% and 98% at a reaction temperature = 100 ℃ and a reaction
2
3
time = 1 h. However, the yield of chalcone dropped to 72.4% over
Amberlyst-15 catalyst and to 77.5% over Amberlyst-200C catalyst
after reused for four times. It was evident that the reusability of the
2
1
2
is described as follows. 0.1 g of the sample was placed in a quartz
sample tube under nitrogen atmosphere with a flow of 25 mL/min
and then the temperature was increased as follows in order to
remove the impurities adsorbed on the sample surface: increased
from room temperature to 500 ℃ at a heating-rate of 10 ℃/min
and then kept for 1 h. Next the temperature was decreased to
two acidic resins was poor. Li et al. prepared Zr-Fe-Cs/SBA-15 by a
wetness impregnation to catalyze the aldol condensation of
formaldehyde with methyl propionate on a fixed bed reactor and
got a 26% of formaldehyde conversion and a 96% of methyl
methacrylate selectivity under the suitable conditions. Rekoske et
1
3
2
al. utilized anatase TiO to catalyze the self-condensation of
1
10 ℃. Subsequently the sample was saturated with CO
flow of 25 mL/min for 30 min. Then the sample was purged by
helium with a flow of 50 mL/min for about 1 h to remove the CO
absorbed physically. After that, the temperature was increased to
00 ℃at a heating-rate of 10 ℃/min. The test of NH -TPD is similar
to CO -TPD.
The X-ray diffraction (XRD) analysis was performed on a Rigaku
2
with a
acetaldehyde and obtained a 26% of conversion and a 96% of
crotonaldehyde selectivity at a reaction pressure = 0.202 MPa, a
reaction temperature = 150 ℃ and a contact time = 1 min.
2
However, the TiO
2
catalyst exhibited a rapid deactivation within the
and Zr-Fe-
7
3
first 10 min. In conclusion, HBEA(25), anatase TiO
2
2
Cs/SBA-15 showed poor catalytic activity while Amberlyst-15 and
Amberlite-200C exhibited a poor reusability. So a catalyst with both
high activity and good reusability is expected for aldol condensation D/max-2500 X-ray diffractometer using Cu Kα radiation and a
reaction.
In this work, we prepared a Ce-modified γ-Al
showed good catalytic activity and excellent reusability for the self-
condensation of n-butyraldehyde. Based on the analysis of the with
reaction system, a reaction network was proposed and the intrinsic monochromatic Al KαX-rays (1486.6 eV) operated at 150 W and 15
graphite monochromator at 40 kV and 100 mA. The scan range
covered from 10° to 90° at a rate of 4 °/min.
2
3
O catalyst which
X-ray photoelectron spectroscopy (XPS) spectra were recorded
a
Physical Electronics Kratos Axis Ultra DLD using
kinetics equation was established.
kV. All the spectra with a scan range of 0-1200 eV were obtained
with a pass energy of 80 eV and step increment of 1 eV while the
narrow-spectra were obtained with a pass energy of 40 eV and 100
mV. The binding energy of C1s (284.6 eV) was used as calibration
standard. The obtained XPS peaks were fitted with Peak 4.1
software.
Experimental Section
Preparation of catalysts
2 3
γ-Al O catalyst was prepared by calcinating pseudo-boehmite on
a muffle furnace under air atmosphere. The temperature was n-Butyraldehyde self-condensation reaction
controlled as follows: increased from room temperature to 500 ℃
The self-condensation of n-butyraldehyde was conducted in a
at a heating-rate of 10 ℃/min and then kept for 4 h.
Modified γ-Al catalysts were prepared by an incipient follows: 40 mL (about 30 g) n-butyraldehyde and 4.5 g catalyst were
impregnation of γ-Al with an aqueous solution of modifier added into the autoclave and then the air inside was replaced with
1
00 mL stainless steel autoclave. A typical procedure is described as
2
O
3
2 3
O
precursor including potassium nitrate, magnesium nitrate, barium nitrogen. The reaction was conducted at 180 ℃ for 8 h with a
nitrate, zinc nitrate, ammonium fluoride, cerium nitrate and boracic stirring agitation of 400 rpm. After the completion of reaction, the
acid. The loading of the modifier (in a state of oxide except for mixture was cooled to room temperature. The catalyst was
fluorine) is 5% (wt). Taking Ce-Al
procedure is described as follows. 8 g γ-Al
.6 mL of 0.24 M aqueous solution of Ce(NO
at room temperature for 24 h, dried at 110 ℃for 8 h and calcinated
at 550 ℃ for 4 h. The preparation of γ-Al modified by other
substances was similar to Ce-Al
2
O
3
as an example, the preparation separated by vacuum filter and the liquid was quantitatively
2 3
O
was impregnated with analyzed by a gas chromatograph.
9
3 3
) first and then aged
Product analysis
A qualitative analysis of the reaction products was conducted on
a GC-MS (ThermoFinnigan TRACE DSQ). EI ionization source was
used in the mass spectrometry with anion source temperature of
2
O
3
2 3
O .
2
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200 ℃. The mass spectrum was recorded in the range of 40- the acid strength of HZSM-5 decreased, and the selectivity and the
500 amu. The temperature of both the vaporizing chamber and the yield of 2-ethyl-2-hexenal increased because of restraining the
transmission line was controlled at 250 ℃. A BPX5 capillary column occurrence of side-reactions. Therefore, the weak acid sites could
was used for separation of the components and the column contribute to the self-condensation of n-butyraldehyde. Ungureanu
1
6
temperature was controlled according to the following program: an et al. obtained a similar conclusion using UL-ZSM-5 to catalyze the
initial temperature of 40 ℃and then heated to 250 ℃in a ramp of aldol condensation of formaldehyde with acetaldehyde. Thereby, γ-
10 ℃/min and held for 5 min.
2 3
Al O was chosen as the catalyst to do a further research in this
work.
A quantitative analysis of the reaction products was carried out
using a SP-2100 gas chromatograph (Beijing Beifen-Ruili Analytical Table 1 Catalytic performance of different solid acid catalysts
Instrument (Group) Co., Ltd). The product mixture was separated in
Catalyst
None
X
BA/%
Y
2E2H/%
12.6
70.8
51.6
29.2
28.1
21.9
14.9
9.6
S2E2H/%
a KB-1 capillary column whose temperature was controlled
according to the following program: an initial temperature of 80 ℃
and held for 3 min, heated to 160 ℃ in a ramp of 10 ℃/min and
held for 10 min. Nitrogen was used as a carrier gas and its flow rate
was 30 mL/min. The components were analyzed in a flame
ionization detector (FID).
41.3
83.5
77.3
52.9
62.6
57.8
53.3
49.3
30.5
84.9
66.8
55.3
45.0
37.8
28.0
19.6
γ-Al O
2
3
Hβ
HY
HZSM-5（360）
HZSM-5（150）
HZSM-5(38)
Results and discussion
1.Screening of catalysts
HZSM-5(25)
2 3
The catalytic performance of some solid acids such as γ-Al O , Hβ,
HY and HZSM-5 with different molar ratios of Si/Al for the self- Reaction conditions: a weight percentage of catalyst = 10%，T =
1
80 ℃，t = 6 h.
condensation of n-butyraldehyde was separately investigated and
BA: n-butyraldehyde; 2E2H: 2-ethyl-2-hexenal；X: conversion;
the results are listed in Table 1. It can be seen that the conversion
Y: yield; S: selectivity.
2 3
of n-butyraldehyde decreased in the following order: γ-Al O ＞Hβ
＞
HZSM-5(360)＞HZSM-5(150)＞HZSM-5(38)＞HY＞HZSM-5(25)＞ 2. Preparation and catalytic performance of γ-Al O3
2
None, and the selectivity of 2-ethyl-2-hexenal lessened as follows:
γ-Al ＞Hβ＞HY＞HZSM-5(360)＞HZSM-5(150)＞None＞HZSM-
(38)＞HZSM-5(25). It is obvious that γ-Al showed the best
2 3
γ-Al O catalyst was prepared by calcinating pseudo-boehmite as
2 3
O
described in Experimental Section. The effect of calcination
temperature and calcination time on the textural structure and
5
2 3
O
catalytic performance; the conversion of n-butyraldehyde and the
selectivity of 2-ethyl-2-hexenal reached 83.5% and 84.9%,
respectively. Among the three kinds of molecular sieves, HZSM-5
showed the worst catalytic activity. With the increase of the molar
ratio of Si/Al, the catalytic activity of HZSM-5 increased gradually,
suggesting that strong acidity is unfavorable to the self-
catalytic performance γ-Al
enclosed in the Supporting Information. As a result, the suitable
preparation conditions of γ-Al were as follows: pseudo-
boehmite was calcinated at 500 ℃ for 4 h. The catalytic
performance of γ-Al prepared at above conditions was evaluated
2 3
O was investigated and the details are
2
O
3
2 3
O
at different reaction conditions. The effect of reaction parameters
on the catalytic performance is enclosed in the Supporting
3
condensation of n-butyraldehyde. Shen et al. studied the vapor
phase self-condensation of n-butyraldehyde and found that an ideal
catalyst should be neither a strong acid nor a strong base.
Furthermore, the catalytic performance of Hβ was higher than HY,
Information. The results showed that γ-Al
temperature, and reaction time exerted different influence on the
catalytic performance of γ-Al . The suitable reaction conditions
for n-butyraldehyde self-condensation over γ-Al catalyst were
obtained as follows: a weight percentage of γ-Al catalyst = 15%,
a reaction temperature = 180 ℃, and a reaction time = 8 h. The
n-butyraldehyde
-TPD and the measurement data conversion of 87% under the above reaction conditions.
2 3
O dosage, reaction
2
O
3
1
4
in accordance with the result of Komatsu et al. A lower activity of
HY may be due to its micropore which hindered the diffusion of the
reaction substances.
2 3
O
2 3
O
The acidity of γ-Al
2 3
O , Hβ, HY and HZSM-5(25) was separately yield of 2-ethyl-2-hexenal was 76.6% at
a
measured and the profiles of NH
3
are separately shown in Fig.S1 and Table 2. It can be seen that the
acid amount of the four solid acids decreased in the following order:
3
2 3
. Modification of γ-Al O
As mentioned above, the yield of 2-ethyl-2-hexenal was merely
6.6% under the suitable reaction conditions, lower than the data
HY > HZSM-5 > Hβ > γ-Al
follows: HZSM-5 > HY > Hβ > γ-Al
amount and the acid strength of the three molecular sieves was in
2
O
3
while the acid strength declined as
7
2
O
3
. The sequence of the acid
obtained from the industrial aqueous caustic alkali, indicating that
1
5
the catalytic performance of γ-Al O was not satisfactory. Thereby,
2
3
consistence with the result determined by Castano et al.
2 3
a modification of γ-Al O is needed in order to improve its catalytic
Combined with the catalytic performance, it was inferred that the
stronger the acidity, the lower the yield of 2-ethyl-2-hexenal. A
performance.
stronger acidity will give rise to the trimerization of n- 3.1 Screening of modifier
butyraldehyde, reducing the selectivity of 2-ethyl-2-hexenal. A
Aldol condensation reaction can be catalyzed by either acid or
base, so the acidity and basicity of a catalyst will have a great
2 3
weaker acidity of γ-Al O is responsible for its better catalytic
performance. Besides, with the increase of the molar ratio of Si/Al,
2 3
impact on its catalytic performance. γ-Al O is traditionally
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considered as a weak solid acid butthere are both acid sites and magnesium oxide, and barium oxide while introducing boric oxide
base sites on its surface. Therefore, it is expected to enhance its and fluorine could increase the acidity of γ-Al . A fine tuning of
2 3
O
catalytic performance by introducing a kind of modifier to tune its the acidity and basicity of γ-Al
superficial acidity and basicity. A promotion in the basicity of γ- zinc oxide and cerium oxide.
2
O
3
might be achieved by introducing
2 3
Al O was expected by the introduction of potassium oxide,
Table 2 Acidic properties of some solid acid catalysts
NH desorption peak at lower
NH desorption peak at higher
3
3
temperature
Catalyst
temperature
Total acid
amount
Weak acid
Strong acid
amount
.
-1
Peak top temperature
Peak top temperature
/μmol g
amount
/℃
.
-1
/
℃
.
-1
/μmol g
/μmol g
γ-Al
Hβ
HY
2
O
3
176.1
179.2
192.0
195.5
386.6
359.4
838.8
680.7
/
/
386.6
707.8
2065.3
1438.3
273.4
334.1
398.2
348.1
1226.5
757.6
HZSM-5(25)
Table 3 Catalytic performance of the modified γ-Al
2
O
3
catalysts
Catalyst
X
BA/%
Y
2E2H/%
S
2E2H/%
87.5
82.5
83.9
87.6
87.5
90.0
89.8
γ-Al
2
O
3
87.5
81.3
88.0
86.3
84.9
86.7
87.6
76.6
67.1
73.9
75.6
74.4
78.1
78.7
B-Al
F-Al
2
O
O
3
2
3
2 3
Zn-Al O
Ba- Al O
2 3
Mg-Al
2
O
3
K-Al O
2 3
Ce- Al
2
O
3
93.8
83.1
88.6
Reaction conditions: a weight percentage of catalyst =15%，T=180℃，t=8 h.
BA: n-butyraldehyde 2E2H: 2-ethyl-2-hexenal X: conversion; Y: yield; S: selectivity
；
；
Table 4 Acid and base properties of different modified γ-Al O catalysts
2
3
Acid property
Base property
CO desorption peak at
higher temperature
CO
2
desorption peak at
2
lower temperature
Total
base
NH
3
Total
Catalyst
desorption
acid
Strong
amount
peak
amount/
Peak top
Weak
Peak top
.
-1
base
/μmol g
.
-1
/℃
μmol g
temperature base amount temperature
.
-1
amount
/℃
/μmol g
/℃
.
-1
/
μmol g
γ-Al
B-Al
2
O
3
176.1
181.6
386.6
500.4
163.3
—
29.1
—
378.0
331.1
179.1
113.7
178.2
113.7
2
O
3
1
4
81.0
68.9
F-Al
2
O
3
306.6
—
—
317.7
116.1
116.1
Zn-Al
Ba-Al
2
O
O
3
191.4
186.8
189.3
187.0
191.9
463.0
254.8
484.0
100.8
404.8
167.6
172.3
171.6
167.3
172.7
19.3
18.7
336.6
281.9
—
162.7
142.8
—
182.0
161.5
756.1
641.3
540.3
2
3
Mg-Al
K-Al
Ce-Al
2
O
3
756.1
641.3
540.3
2
O
3
—
—
2
O
3
—
—
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The catalytic performances of γ-Al
2
O
3
modified by different amount, the selectivity of 2-ethyl-2-hexenal was higher over Mg-
, K-Al and Ce-Al catalysts with higher base amount. As a
. It was consequence, it was inferred that the base amount of the modified
obvious that modifier had an important influence on the catalytic γ-Al is the key factor influencing the selectivity of 2-ethyl-2-
performance of γ-Al 3. The catalytic performance of γ-Al hexenal; the bigger the base amount, the higher the selectivity of 2-
modified by nonmetal B and F was the worst; the selectivity of 2- ethyl-2-hexenal. Climentet al. compared the selectivity of MgO
ethyl-2-hexenal decreased. Especially for B-Al , the selectivity and and NaCsX zeolite in the aldol condensation of heptanal with
yield of 2-ethyl-2-hexenal were merely 82.5% and 67.1%. In benzaldehyde and found that base strength certainly had an
contrast, the γ-Al modified by metallic oxide showed good important influence on the selectivity. In this study, it is found that
catalytic performance. The selectivity of 2-ethyl-2-hexenal reached weak base amount played a crucial role in the selectivity. Not only
the highest, 90.0%, over Mg-Al catalyst. Moreover, Ce-Al does Ce-Al have relatively higher base amount, but also its 4f
exhibited the best catalytic performance and the yield of 2-ethyl-2- electronic structure is beneficial to the polarization of a carbonyl
substances are listed in Table 3. The loading of the modifier (based Al
on oxide except for F) accounted for 5% (wt) of γ-Al
2
O
3
2
O
3
2 3
O
2 3
O
2
O
3
2
O
2 3
O
1
8
2 3
O
2
O
3
2
O
3
2
O
3
2 3
O
1
9
hexenal was the highest, up to 83.1%. So Ce was determined to be group, promoting the formation of enol structure which is good
the suitable modifier.
for the enhancement of the conversion of n-butyraldehyde. In
addition, the excellent catalytic performance of Ce-Al is possibly
2
O
3
Acid and base properties of the modified γ-Al
2
O
3
catalysts were
-TPD are separately
shown in Fig.S6, Fig.S7, Fig.S8, Fig.S9,Fig.S10 and Fig.S11 while the
attributed to its suitable and matched acid-base properties on the
surface.
3 2
measured and the profiles of NH -TPD and CO
measurement data are summarized in Table 4. After modified by 3.2 Effect of Ce loading
nonmetal B and F, the total base amount of γ-Al O dropped
2
3
2 3
The catalytic performance of Ce-Al O with different loading
distinctly and the base strength also decreased and the weak base
sites of γ-Al O disappeared. The total acid amount rose for the γ-
amounts of Ce was evaluated and the results are shown in Fig. 1.
With the increase of the loading amount of Ce, the conversion of n-
butyraldehyde increased at first and then decreased, similar to the
selectivity of 2-ethyl-2-hexenal. The conversion of n-butyraldehyde
reached the maximum over the Ce-Al O with the Ce loading
2
3
Al O modified by B but decreased for the γ-Al O modified by F.
2
3
2 3
Furthermore, a new strong acid site appeared and the acid strength
1
7
was enhanced after modified by F. Jian et al. studied the role of F
in the γ-Al O catalyst and obtained a similar conclusion. They
2
3
2
3
amount of 5% while the selectivity of 2-ethyl-2-hexenal attained the
maximum over the Ce-Al O with the Ce loading amount of 7%.
considered that the lone pair electrons of F was in coordination
with the acid sites on the surface of γ-Al O and the acid sites of γ-
2
3
2
3
Since the yield of 2-ethyl-2-hexenal achieved the maximum over the
Ce-Al O with the Ce loading amount of 5%, 5% was chosen as the
Al O were covered partly, causing the reduction of the acid amount.
2
3
2
3
Meanwhile, the higher electro-negativity of F had a great inductive
effect and could make the strength of acid site nearby stronger.
When modified by transition metal Zn, the total acid amount of γ-
Al O rose but the total base amount and base strength changed a
suitable loading amount of Ce. In order to elucidate the role of Ce in
Ce-Al O CeO2 was used to catalyze the self-condensation of n-
2
3,
butyraldehyde under the suitable reaction conditions. The
conversion of n-butyraldehyde and the yield of 2-ethyl-2-hexenal
attained 71.3% and 29.9%, respectively, far lower than the catalytic
performance of γ-Al O . It is obvious that CeO played a role of a
2
3
little. Through the modification of alkaline earth metal Ba, the total
acid amount of γ-Al O dropped severely but the total base amount
2
3
2
3
2
declined slightly. After modified by alkali metal K, alkaline earth Mg
promoter not a major active species.
.3 Analysis of Ce function
Fig.S12 presents deconvoluted XPS spectra of Ce3d of the fresh
. The spin–orbit peaks of ‘a’ and ‘e’ centered at 898.3 eV
by K. Shen et al. found that the silica-supported MgO and SrO and 916.4 eV are attributed to the primary photoionization from
and rare-earth metal Ce, all the desorption peaks of CO at higher
2
3
temperature disappeared but the total base amount increased
drastically. In addition, the total acid amount of γ-Al O modified by
2
3
2 3
Mg and Ce increased to some extent but decreased when modified Ce-Al O
3
4
+
9
0
6
20
catalysts had a dramatically increased NH uptake because of the Ce with Ce3d 4f O2p final state . The spin–orbit peaks of f-b, i-d
3
9
1
5
formation of extra acid sites. It was also observed in Table 4 that and g-h with lower binding energy are assigned to the Ce3d 4f O2p
9
2
4
20
the influence of different substances on the base amount of γ-Al O
and Ce3d 4f O2p final states shake-down satellite features .
2
3
was much greater than that on its acid amount. The base amount Those satellite peaks are caused by the charge transfer from ligand
declined in the following order: Mg-Al O > K-Al O > Ce-Al O > Zn- (O2p) to metal (Ce4f) in the primary photoionization process. The
2
3
2
3
2 3
Al O >γ-Al O > Ba-Al O > F-Al O ≈ B-Al O Combined with the peaks of ‘c’ and ‘i’ centered at 885.5 eV and 903.9 eV are associated
2
3
2
3
2
3
2
3
2
3.
3
+
catalytic performance, we can see that the base amount played a with Ce final states. In this sense, c-i spin-orbit doublet peaks are
major role in the improvement of the selectivity of 2-ethyl-2- assigned to the main photoionization from Ce3d 4f O2p final
hexenal. With respect to B-Al O and F-Al O with lower base state . Fig.S13 shows the XPS spectra of Ce3d of the recovered Ce-
9
1
6
2
0
2
3
2
3
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Journal Name
4
+
Al
2
O
3
without calcination. Compared with Fig.S12, it is not difficult
It is known from the calculation result that the percentage of Ce
, and dropped to 10% in the
without calcination and increased back to 42%
in the recovered Ce-Al after calcination. It can be seen from
to find that the peak of ‘a’ at 916.4 eV completely disappears in species was 94% in the fresh Ce-Al
2 3
O
0
2 3
Fig.S13, probably due to the lack of 4f configuration in the recovered Ce-Al O
3
+
0
formation of Ce state. Thus, any transitions involving the 4f
2 3
O
21
configuration will not appear in the spectra . Meanwhile, the area Table 8 that the conversion of n-butyraldehyde decreased to some
of peak ‘e’ at 898.3 eV decreases drastically while that of peaks at extent while the selectivity of 2-ethyl-2-hexenal decreased greatly
3
+
the 903.9 eV and 885.4 eV corresponding to Ce species increases for the recovered Ce-Al
greatly. Cerium oxide is known to possess a very high oxygen the fresh Ce-Al . Thus, it is certain that the Ce speices are the
exchange capacity which is related to the ability of reversible active sites in Ce-Al
2 3
O without calcination as compared with
4
+
2
O
3
4
+
2
O
3
. On the other hand, the percentage of Ce
change of oxidation states of cerium between Ce and Ce . species in the recovered Ce-Al after calcination is less than half
Additionally, the reduction of Ce species is not resulted from a of that in the fresh Ce-Al but the catalytic activity of the
direct release of O to the gas phase but from a surface reaction recovered Ce-Al after calcination is almost the same as the fresh
4
+
3+
2
O
3
2
O
3
2
2 3
O
2
2
with a reductant such as CO or a hydrocarbon . Therefore, it is one. Therefore, it is inferred that the valence state of Ce affects the
speculated that some kind of reductants existing in the reaction catalytic performance of Ce-Al O to some extent but it does not
2
3
system of n-butyraldehyde self-condensation reduced Ce species play a key role in the catalytic performance. As mentioned above,
4
+
3+
21
from Ce to Ce . Shyu et al. obtained a similar conclusion that the acid and base property of γ-Al O catalyst exerts a great effect
2
3
CeAlO was formed from CeO -Al O in H2 or under vacuum at on the catalytic performance and furthermore the base amount is
3
2
2
3
elevated temperatures. Fig.S14 shows the XPS spectra of Ce3d of the key factor influencing the selectivity of 2-ethyl-2-hexenal.
the recovered Ce-Al calcinated at 550 for 4 h. Compared with Therefore, it is speculated that the acid and base property of Ce-
Fig.S13, it can be observed that the peak area of Ce spices at 903.9 Al O play a dominant role in its catalytic performance.
2
O
3
℃
3
+
2
3
eV and 885.4 eV decreases to a small degree while other peaks
change little. New peaks of ‘A’ and ‘C’ appear which belong to the
Acid and base properties of the fresh and the recovered Ce-Al O
2
3
catalysts were measured and the profiles of CO -TPD and NH -TPD
2
3
4
+
3+
Ce spices. It is obvious that Ce spieces could be transformed to
are separately shown in Fig.S15 and Fig.S16 while the measurement
data are summarized in Table S2. As compared with the fresh Ce-
Al O , the total acid amount decreased to some extent and what is
4
+
23
Ce spices after the recovered Ce-Al O was calcinated. He et al.
2
3
thought that trivalent cerium species could convert into tetravalent
cerium species in the presence of the oxidants such as oxygen
2
3
more, a new strong acid site appeared while the total base amount
increased greatly but the base strength increased a little in the
2
1
under alkaline conditions. Shyu et al. gained a similar conclusion
that CeAlO precursor could be reoxidized to CeO even at room
3
2
recovered Ce-Al O without calcination. After calcinated at 550
℃
2
3
temperature upon exposure to oxidizing environments.
for 4 h, both the base amount and strength decreased and
furthermore the base strength restored to that of the fresh Ce-
Al O . The new strong acid site disappeared and both the weak acid
98
96
94
92
90
88
86
84
82
80
78
XBA
Y2E2H
S
2
3
2E2H
amount and strength increased and furthermore the weak acid
strength restored to that of the fresh Ce-Al . In a word, the acid
and base properties of the recovered Ce-Al O after calcination
O
3
2
2
3
restored almost to those of the fresh Ce-Al O .
2
3
γ-Al O can be hydrated with the byproduct water to form
2
3
3
2
boehmite phase in the aldol cndensation of n-butyraldehyde.
3
3
Since the acid amount of γ-Al O is more than boehmite , it is
2
3
2
4
6
8
10
speculated that the increase of the base amount and the decrease
of the acid amount in the recovered Ce-Al O without calcination is
CeO loading/%
2
2
3
Fig. 1 Effect of CeO loading on the catalytic performance of γ-Al O
2 3
2
related to the formation of boehmite. Boehmite can decompose to
catalyst
Reaction conditions: a weight percentage of catalyst = 15%, T = 180
, t = 8 h.
3
4
γ-Al
2
O
3
after calcination , so the base amount decreased and acid
after calcination.
amount increased in the recovered Ce-Al
2
O
3
℃
Combined with the result of Table S2 and Table 8, it is inferred that
the strong acid site does harm to the self-condensation of n-
butyraldehyde, causing the side-reactions to reduce the selectivity
X: conversion; Y: yield; S: selectivity;
BA: n-butyraldehyde;2E2H: 2-ethyl-2-hexenal.
4
+
3+
The peak areas (A) of Ce and Ce species are used to estimate
their relative contents (C) in the Ce-Al using the following
equations and the results in the fresh Ce-Al , the recovered Ce-
Al without calcination and the recovered Ce-Al
3
5
of 2-ethyl-2-hexenal. Zeidan et. al selected the acid-base
bifunctionalized mesoporous SBA-15 to catalyze the aldol
condensation of 4-nitrobenzaldehyde with acetone and found that
the catalytic activity of bifunctionalized materials increased
gradually with the decrease of the acidity.
2
O
3
2
O
3
2
O
3
2
O
3
after
calcination are separately listed in Table 5, Table 6 and Table 7.
∑ ACe
4
+
It can be seen from Table 8 that the conversion of n-
CCe4
+
=
butyraldehyde changed little while the selectivity of 2-ethyl-2-
hexenal decreased greatly over the recovered Ce-Al
calcination as compared with the fresh Ce-Al . Despite the fact
that the total base amount increased for the recovered Ce-Al O
3
2 3
O without
∑ ACe4+ ∑ ACe3+
+
2 3
O
2
6
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without calcination, the appearance of the strong acid site reduced Table 8 Catalytic performance of different catalysts for the self-
its catalytic activity, so its selectivity of 2-ethyl-2-hexenal decreased. condensation of n-butyraldehyde
After calcinated at 550
decreased and was slightly more than that of the fresh Ce-Al
while the strong acid site disappeared, so the catalytic performance
was restored for the recovered Ce-Al after calcination. In
conclusion, matchable acid and base properties are the key factor
to achieve a good catalytic performance of Ce-Al
Table 5 Binding energies, valence states and relative contents of
Ce3d in the fresh Ce-Al
℃ for 4 h, the total base site amount
Catalyst
X
BA/%
Y
2E2H/%
S
2E2H/%
2 3
O
Fresh Ce-Al O
93.7
80.3
85.7
2
3
2
O
3
Recovered Ce-Al O
2
3
3
Without
90.3
71.1
78.8
2 3
O .
calcination
Recovered Ce-Al O
2
O
3
2
9
3.3
83.0
72.9
88.9
84.2
after calcination
Binding energy
(eV)
CCex+ (%)
Peak assignment Ce species
Refs
γ-Al O
86.6
2
3
Reaction conditions: a weight percentage of catalyst = 15%
，T =
4
4
3
4
4
4
4
4
3
4
+
+
+
+
+
+
+
+
+
+
a
b
c
d
e
f
Ce
Ce
Ce
Ce
Ce
Ce
Ce
Ce
Ce
Ce
916.4
906.1
903.9
901.0
898.3
889.1
887.6
886.7
885.4
882.4
15
15
2
23
20
24
25
26
27
28
29
22
30
1
80 ℃，t = 8 h.
BA: n-butyraldehyde; 2E2H: 2-ethyl-2-hexenal
；X: conversion; Y:
yield; S: selectivity.
14
15
6
3
.4 Reusability of Ce-Al
2 3
O
The reusability of Ce-Al
O after calcination was investigated
3
2
and the results are listed in Table 9. It can be seen that after reused
for several times, the selectivity of 2-ethyl-2-hexenal rose slightly
while the conversion of n-butyraldehyde declined a little. The
increase of the selectivity is in accordance with the increase of the
base amount of the recovered Ce-Al O after calcination (see Table
g
h
i
1
4
4
j
24
2
3
S2). On the whole, the catalyst Ce-Al O showed good stability: the
2
3
yield of 2-ethyl-2-hexenal decreased merely by 0.6% when reused
for four times.
Table 6 Binding energies, valence states and relative contents of
Ce3d in the recovered Ce-Al
2
O
3
without calcination
Table 9 Reusability of Ce modified γ-Al O
2
3
Binding energy
CCex+ (%)
Peak assignment Ce species
Refs
Run
1
X /%
Y2E2H/%
83.1
S2E2H/%
88.6
(
eV)
BA
93.8
93.3
92.4
91.3
91.0
3
4
4
3
4
3
+
+
+
+
+
+
1
2
3
4
5
6
Ce
Ce
Ce
Ce
Ce
Ce
904.1
901.7
899.0
885.5
883.1
881.3
38
3
24
25
26
24
23
30
2
83.0
88.9
3
82.5
89.2
3
4
82.5
90.4
48
4
5
82.5
90.7
Reaction conditions: a weight percentage of catalyst = 15%, T =
80 , t = 8 h.
4
1
℃
BA: n-butyraldehyde
；2E2H: 2-ethyl-2-hexenal；X: conversion; Y:
Table 7 Binding energies, valence states and relative contents of
Ce3d in the recovered Ce-Al after calcination
yield; S: selectivity.
2
O
3
4. Analysis of reaction system
The reaction liquid obtained from the self-condensation of n-
butyraldehyde catalyzed by Ce-Al was analyzed by GC-MS and
Binding
energy
CCex+
Peak
Ce
2 3
O
Refs
assignment
species
(%)
results listed in Table S3 show that several by-products were found
such as butyl butyrate, 4-heptanone, 3-heptylene, 2-ethyl-3-
hydroxyhexyl butyrate and so on. Based on the analysis results of
GC-MS, some side-reactions (1)~(4) were speculated as Scheme 1.
36
(eV)
4
4
4
3
4
4
3
4
3
+
+
+
+
+
+
+
+
+
A
B
C
D
E
F
Ce
Ce
Ce
Ce
Ce
Ce
Ce
Ce
Ce
916.8
911.8
907.9
904.1
901.4
898.6
885.5
882.8
881.3
7
2
23
31
20
24
25
26
24
22
30
5
2 3
Tsuji et al. thought that Al O can catalyze the Tishchenko
29
5
reaction of n-butyraldehyde to produce butyl butyrate, so the
3
reaction (1) was speculated. Shen et al. probed into the vapor
phase self-condensation of n-butyraldehyde catalyzed by alkaline
earth metal oxide and discovered that the reaction system
contained C7 alkene byproduct. At present, there is a dispute on
10
28
13
1
G
H
I
37
the formation of C7 alkene. Idriss et al. considered that C7 alkene
came from the reductive coupling reaction of n-butyraldehyde. Luo
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8
et al. believed that the reductive coupling reaction was prone to 5. Kinetic study
occurrence on the surface of a reductant and there was a great
In order to get an intensive investigation of the n-butyraldehyde
self-condensation reaction catalyzed by Ce-Al , its intrinsic
possibility that C7 alkene was originated from these side-reactions
2
O
3
3
such as dehydroxylation and decarbonylation. Shen et al. deemed
reaction kinetics was established. The influence of internal and
external diffusion was eliminated prior to the kinetic experiments.
that C7 alkene may be derived from the hydrogenation/dehydration
of heptanone generated from the ketonization of butyl butyrate.
3
9
5.1 Establishment of kinetic model and estimation of parameters
Glinski et al. studied the ketonization of ethyl heptanoate
catalyzed by Ce or Zr loaded Al and found the formation of 13
2
O
3
The n-butyraldehyde self-condensation reaction can be described
ketone, ethylene, carbon dioxide and water. On the basis of above as follows:
discussion, the reaction (2) was inferred. Namely the ketonization
of butyl butyrate generated carbon dioxide, water, 1-butene and
heptanone followed by a hydrogenation/dehydration to produce C7
alkene. The hydrogen used for the hydrogenation was derived from
3
7
the decomposition of n-butyraldehyde. The formation of 2-ethyl-
-hexenal comprises two reaction steps: the condensation of n-
2
butyraldehyde to 2-ethyl-3-hydroxyhexanal and the dehydration of
the intermediate to 2-ethyl-2-hexenal. Part of 2-ethyl-3-
hydroxyhexanal could react with n-butyraldehyde to produce 2-
ethyl-3-hydroxyhexyl butyrate by the Tishchenko reaction,
described as reaction (4), in accordance with the result obtained by
The rate of a chemical reaction (r
concentration of reaction components (CA
reaction temperature (T). CA C2E2H and CW can be expressed by
A
) is the function of the
，
C2E2H CW) and
，
，
means of the conversion of n-butyraldehyde (x
A
). The reaction
4
0
36
40
rate equation can be described as follows:
Zhu et al. and Tsuji et al. Zhu et al. used rare earth compound
to catalyze aldol condensation-Tishchenko reaction of n-
butyraldehyde and found that 2-ethyl-3-hydroxyhexyl butyrate was
1 dnA nA0 dxA
m
P
q
（5）
rA = −
=
= k C − k C
+
A
−
Cw
2E 2H
V dt
V
dt
3
6
formed. Tsuji et al. concluded that Al O could catalyze the
n2E2H nA0 ×xA
xA
2
3
because C2E2H
=
=
=CA0
×
=C ，eq (5) can be converted to eq (6)：
W
Tishchenko reaction of n-butyraldehyde to produce 2-ethyl-3-
hydroxyhexyl butyrate and furthermore n-butyraldehyde preferred
to react with 2-ethyl-3-hydroxyhexanal by the cross-Tishchenko
reaction, compared with the self-Tishchenko reaction of n-
butyraldehyde.
V
2V
2
dxA
xA
m
m
( p+q )
( p+q)
（6）
CA0
= k C (1− x ) − k C
(
)
+
A0
A
−
A0
dt
2
Suppose p+q=n, eq (6) can be changed as follows:
Based on the results of product analysis and discussion above, a
possible reaction network for self-condensation of n-butyraldehyde
catalyzed by Ce-Al O was proposed as shown in Scheme 1. A
dxA
m
xA n
m
n
CA0
= k+CA0
(
1− xA
)
−k−CA0
(
)
2
3
(7)
dt
2
majority of n-butyraldehyde undertakes aldol condensation to 2-
ethyl-3-hydroxyhexanal followed by a dehydration reaction to 2-
ethyl-2-hexenal. Simultaneously, a minority of n-butyraldehyde will
be converted to butyl butyrate by the Tishchenko reaction and then
butyl butyrate can transform to heptanone from the ketonization
followed by a hydrogenation/dehydration to C7 alkene. In addition,
a small quantity of 2-ethyl-3-hydroxyhexanal can react with one
molecule of n-butyraldehyde by the Tishchenko reaction to produce
− Ea
RT
When the Arrhenius equation
) is put into eq
k = A exp(
(
7), the differential equation to be fitted can be shown as follows:
dxA
ꢀEa+
mꢀ1
m
ꢀEa
nꢀ1 xA
n
ꢀ
= A
exp(
)CA0
(
1− x
)
− A
exp(
)CA0
(
)
+
A
ꢀ
（
8）
dt
RT
RT
2
Where x
separately the reaction time and reaction temperature. The pre-
exponential factor A and A , the activation energy Ea and Ea and
A
is the conversion of n-butyraldehyde, t and T are
2
-ethyl-3-hydroxyhexyl butyrate.
+
-
+
-
the reaction order m and n are the parameters to be determined. It
has been known that R = 8.314 J/(mol.K) and the initial
concentration of n-butyraldehyde CA0 = 11.09 mol/L. The kinetic
experiment was conducted on an autoclave and the time when the
temperature inside the autoclave reached the reaction temperature
was set as t=0. The conversions of n-butyraldehyde at different
reaction times and reaction temperatures were experimentally
measured and the results are listed in Table S4.
The kinetic equation is an initialꢀvalue problem of a firstꢀorder
ordinary differential equation. When the initial values of the
Scheme1 Reaction network of n-butyraldehyde self-condensation
catalyzed by Ce-Al
+ ꢀ + ꢀ
parameters A , A , Ea , Ea , m and n are given, the conversion of nꢀ
butyraldehyde at t = 3600 s can be obtained by integrating the set of
the firstꢀorder ordinary differential equations using a fourthꢀorder
Runge−Kutta method in the time interval of [0, 3600]. Similarly, the
2
O
3
8
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conversion of nꢀbutyraldehyde at t = i can be attained in the time and t is linear, indicating that the hypothesis for second-order
interval of [0, i], which is the corresponding estimated values of the reaction is correct.
reaction kinetics model. The experimental data (the conversions of
5
.3 Test of kinetic model
nꢀbutyraldehyde) at t = i were obtained by GC analyses. Then the
objective function for parameter estimation is expressed as follows:
The relationship between the experimentally measured and the
estimated conversion of n-butyraldehyde is shown in Fig.2. It can be
seen that a majority of dot are uniformly located in the both side of
diagonal, demonstrating that the experimental data is well in
T
t
f
=
2
ꢀ xA,exp
)
∑
∑ (xA ,est
accordance with the estimated data.
where,
x
A,est represents the estimated conversion of n-
1
butyraldehyde calculated from the model and xA,exp represents the
measured conversion of n-butyraldehyde from the experiment. The
parameters can be estimated by minimizing this function using
MATLAB software.
0.9
0.8
0.7
0.6
0.5
4
1
Zhang et al. studied the kinetic of n-butyraldehyde self-
condensation catalyzed by a sulfonic acid functionalized ionic liquids
and found that both the forward and backward reactions are second
order. In this study, the forward and backward reactions are
supposed to be second order first and then the assumption will be
verified. As a result, The estimated kinetic parameters (activation
energy and pre-exponential factor of the forward and reverse
0.4
0.3
0.2
0.1
0
0
0.1
0.2
0.3
0.4
0.5
x(est)
0.6
0.7
0.8
0.9
1
5
3
Fig.2 Comparison between the experimental and the estimated
conversion of n-butyraldehyde.
reactions) are listed as follows: A
+
= 5.745×10 m /(kmol.s); Ea
= 2.146×10 m /(kmol.s); Ea = 74.30 kJ/mol.
.2 Verification of reaction order
Substituting m = 2 and n = 2 to eq (7), the reaction rate equation
+
=
4
3
7
9.60 kJ/mol; A
-
-
x: conversion of n-butyraldehyde; est: estimated values, exp:
5
experimental values.
can be expressed as follows:
The results of variation analysis and the F-test on the kinetic
model are listed in Table 10. As we know from the variation analysis
theory, the larger the absolute value of the correlation index and
test value of F, the better the regression effect. If the correlation
dxA
2
xA
2
=
k+CA0
(
1−xA
)
−k C (
)
−
A0
dt
2
Then the above equation can be integrated to
index r is larger than 0.9 and F > 10 F , the model is considered to
α
be suitable to the α level. In this study,
2
1
2
（x − a）− a − a
CA0
a
A
ln
=
t + C
Re g.SS / 3 = 349.96.
F=
2
2
a − a （x − a）+ a − a
(
A
)
RSS / 31
k+
It can be seen that F is much bigger than F0.05(3, 31) and the
correlation index r is larger than 0.9. Therefore, the kinetic model is
significant to the level α = 0.05 and thus is able to describe the n-
butyraldehyde self-condensation reaction process.
where a =
，
C is the integration constant.
k−
k+ −
4
2
（
x A
−
−
a ）−
a ）+
a
a
−
−
a
a
Suppose
b
=
then
2
（
( x
A
)
1
C A 0
a
ln b =
t + C
2
2
a
− a
Substituting the conversion of n-butyraldehyde x determined by
A
GC to the above equation, it is found that the relation between lnb
Table 10 Model Statistics
Free
Experiment
No.
Regression
Residual
Correlation
index
Variance
2.0538
F0.05(3, 31)
squares sum
squares sum
variation No.
35
4
2.0591
0.0608
0.9856
2.91
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.4 Comparison with literature values
Journal Name
5
and backward reactions are second order and the corresponding
activation energy is separately 79.60 kJ/mol and 74.30 kJ/mol,
higher than its homogeneous catalytic reaction system. The preꢀ
exponential factor of the forward and backward reaction is
42
Lee et al. studied the aldol condensation of n-butyraldehyde
catalyzed by an aqueous solution of sodium hydroxide with a
concentration range of 0.76 1.9 M and estimated that the
activation energy was 56.80 ± 1.671 kJ/mol and the pre-exponential
～
5
3
4
3
separately 5.745× 10 m /(kmol.s) and 2.146 × 10 m /(kmol.s),
lower than the acid and base aqueous homogeneous catalytic
reaction system but equivalent to the sulfonic acid functionalized
ionic liquid system. The lower preꢀexponential factors are due to the
liquidꢀsolid heterogeneous phase catalytic system. In conclusion, not
8
3
factor was 1.712× 10 m /(kmol.s) in the temperature range of
4
3
1
10
of n-butyraldehyde catalyzed by an aqueous solution of H
wt %) in the temperature range of -24 42 and found that the
activation energy and the pre-exponential factor were 53.79±7.82
～
150
℃
. Casale et al. studied the kinetic of self-condensation
2
4
SO (85
～
℃
2 3
only does CeꢀAl O show good catalytic performance, but also it can
overcome the disadvantage of the corrosion of apparatus caused by
an inorganic acid or base. Therefore, CeꢀAl O has a bright industrial
8
3
kJ/mol and 3.594× 10 m /(kmol.s), respectively. In addition, Zhang
4
1
2
3
et al. studied the kinetic of n-butyraldehyde self-condensation
prospect for the selfꢀcondensation of nꢀbutyraldehyde.
catalyzed by a sulfonic acid functionalized ionic liquid in the
temperature range of 90
～120 ℃ and obtained that the activation
energy of the forward and backward reaction was separately 60.29 Acknowledgments
kJ/mol and 62.94 kJ/mol, and the corresponding pre-exponential
This work was financially supported by National Natural Science
Foundation of China (Grant No. 21476058, 21236001) and Key Basic
Research Project of Applied Basic Research Plan of Hebei Province
4
3
4
factor was separately 1.999× 10 m /(kmol.s) and 1.001× 10
3
m /(kmol.s).
Compared with the kinetic parameters obtained from the
conventional inorganic acid and base catalysts and the sulfonic acid
functionalized ionic liquid, it is observed that the activation energy
(
Grant No. 12965642D). The authors are gratefully appreciative of
their contributions
Notes and references
2 3
of the self-condensation of n-butyraldehyde catalyzed by Ce-Al O is
higher, indicating that the energy barrier of such a liquid-solid phase 1. S. Liu, C. Xie, S. Yu, F. Liu, Z. Song, Ind. Eng. Chem. Res., 2010, 50
,
catalytic reaction is higher and an elevated reaction temperature
will be required correspondingly. Pre-exponential factor reflects the
collision frequency of the reactants in a reaction system. The pre-
2478-2481.
2
3
. G. J. Kelly, F. King, M. Kett, Green Chem., 2002, 4, 392-399.
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exponential factor of this aldol condensation catalyzed by Ce-Al O
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acid functionalized ionic liquid. This is also because that the self-
4
5
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condensation of n-butyraldehyde catalyzed by Ce-Al O is a liquid-
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solid heterogeneous catalytic reaction and the resistance of mass
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2
Conclusions
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1
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6
5
boehmite was calcinated at 500
reaction conditions of dosage of γꢀAl
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℃
for 4 h. Under the suitable
0. O. Kikhtyanin, V. Kelbichová, D. Vitvarová, M. Kubu, D. Kubicka,
2
3
O catalyst = 15 wt.%, reaction
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℃
butyraldehyde and the yield of 2ꢀethylꢀ2ꢀhexenal attained 87.5% and 11. A. Lahyani, M. Chtourou, M. H. Frikha, M. Trabelsi, Ultrason.
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6.6% respectively. When γꢀAl
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yield of 2ꢀethylꢀ2ꢀhexenal could reach 83.1%. Moreover, CeꢀAl O
3
2
O
3
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Sonochem., 2013, 20, 1296. -1301
1
2. B. Li, R. Yan, L. Wang, Y. Diao, Z. Li, S. Zhang, Ind. Eng. Chem.
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showed an excellent reusability. The XPS analyses of Ce3d
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3. J. E. Rekoske, M. A. Barteau, Ind. Eng. Chem. Res., 2011, 50, 41-
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1.
performance of CeꢀAl
properties of CeꢀAl
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O
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O
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