Preparation and characterization of SO4 2-/Fe 2O3-TiO2-Nd2O3 catalyst

Article abstract of DOI:10.1007/s13738-012-0173-5

This paper reports on the preparation of SO₄ ^2-/Fe₂O₃-TiO₂-Nd₂O ₃ (SFTN) by combustion method. The effect of Nd content on catalytic activity was investigated. The prepared materials doped and undoped by Nd were compared by means of TG-DTG, XRD, FT-IR, NH₃-TPD and TEM techniques. Results indicated that the introduction of Nd improved the catalytic activities of the catalysts. Catalytic activity of SFTN was the highest with 98.3 % menthol conversion when Nd content was at 2 wt%. The introduction of Nd stabilized the coordination bond between the sulfate irons and the metallic oxides, helping in the formation of solid acid sites, enhancing the dispersion of catalyst particles, and inhibiting the growth of catalyst particles under heating.

Full text of DOI:10.1007/s13738-012-0173-5

J IRAN CHEM SOC (2013) 10:407–413
DOI 10.1007/s13738-012-0173-5
ORIGINAL PAPER
2
4
2
Preparation and characterization of SO /Fe O –TiO –Nd O
2 3
2 3
2
catalyst
C. H. Yang
•
M. Q. Fan
•
G. Chen L. Zhang
•
Received: 21 November 2011 / Accepted: 3 October 2012 / Published online: 9 November 2012
Ó Iranian Chemical Society 2012
2
-
Abstract This paper reports on the preparation of SO4
Fe O –TiO –Nd O (SFTN) by combustion method. The
/
activity for chlorobenzene condensation polymerization
because of the residual sulfate ions on the ferric oxide
surface. Later, they paid close attention to the roles of these
ions (such as Zr, Ti, Sn, Hf), which led to the successful
2
3
2
2 3
effect of Nd content on catalytic activity was investigated.
The prepared materials doped and undoped by Nd were
2
-
2-
compared by means of TG-DTG, XRD, FT-IR, NH -TPD
3
development of SO4 -promoted solid super acids (SO4
/
and TEM techniques. Results indicated that the introduc-
tion of Nd improved the catalytic activities of the catalysts.
Catalytic activity of SFTN was the highest with 98.3 %
menthol conversion when Nd content was at 2 wt%. The
introduction of Nd stabilized the coordination bond
between the sulfate irons and the metallic oxides, helping
in the formation of solid acid sites, enhancing the disper-
sion of catalyst particles, and inhibiting the growth of
catalyst particles under heating.
M O ) [2]. These catalysts show high activity and selec-
x
y
tivity in many acid catalytic reactions including acetylation
[3], light alkane isomerization [4], acylation [5], and
2
-
esterification [6]. In addition, as a solid super acid, SO4
/
M O may alleviate corrosion of apparatus and thus reduce
x
y
environmental pollution. Therefore, it is used as a new
catalytic material in a variety of acid catalytic reactions.
2
-
However, the effect of Nd on (SO4 /M O ), which is used
x
y
as a catalyst in esterification, has been rarely reported in
literature.
Keywords Schiff base Rare earth metal Nd Á Solid super
acid Á Esterification
Menthyl acetate is a monoterpene with the smell and
flavor of peppermint. This compound is often used as
tobacco flavoring because it possesses long-lasting flavor.
In the conventional approach for menthyl acetate produc-
tion, sulfuric acid [7] is always used as a catalyst, resulting
in serious environment pollution and equipment corrosion
problems. The flavor and color of the menthyl acetate
product is not satisfactory with sulfuric acid. Therefore, it
is necessary to develop new and environmentally benign
catalysts for the production of menthyl acetate.
Introduction
Hino et al. [1] reported that ferric oxide prepared by the
calcination of iron sulfate to 700 °C exhibits very high
In this paper, a series of solid super acid catalysts
2
C. H. Yang Á L. Zhang (&)
-
2-
School of Chemistry, Northeast Normal University,
Changchun 130024, People’s Republic of China
e-mail: zhanglongzhl@163.com
including SO4 /Fe O –TiO (SFT) and SO4 /Fe O –
2 3 2 2 3
TiO –Nd O (SFTN) was prepared. The catalytic proper-
2 2 3
ties were explored in the esterification of menthol and
acetic acid. Thermal decomposition behavior, textural
properties, crystalline structure, existing state of sulfur
ions, acidic characteristics, and sample sizes were exam-
C. H. Yang Á M. Q. Fan Á G. Chen
Jilin Vocational College of Industry and Technology,
Jilin 132013, People’s Republic of China
ined by TG-DTG, XRD, FT-IR, NH -TPD, and TEM
3
L. Zhang
School of Chemical Engineering, Changchun University
of Technology, Changchun 130012, People’s Republic of China
techniques. Moreover, the lifetime of solid acid catalysts
was studied.
123

4
08
J IRAN CHEM SOC (2013) 10:407–413
Experimental
NH
3
-TPD studies
-TPD profiles were carried out by ramping the tem-
3
Preparation of SFT and SFTN
NH
perature from 393 to 873 K at a rate of 10 K/min.
3
.37 g Fe(NO ) Á9H O, 5.02 g C H O ÁH O, 2.84 mL
3
3
2
6
8
7
2
[
CH (CH ) O] Ti and x mol Nd(NO ) Á6H O were well
TEM studies
3
2 2
4
3 3
2
mixed with 20 mL anhydrous ethanol to obtain the
homogeneous solution with a molar composition of
Transmission electron microscopy (TEM) and high-reso-
lution transmission electron microscopy (HRTEM) exper-
iments were performed on a PHILIPS CM 200 FEG
electron microscope with an acceleration voltage of
200 kV. Samples were dispersed in ethanol. Carbon-coated
copper grids were used as the sample holder.
[
CH (CH ) O] Ti:Fe(NO ) Á9H O: x mol Nd(NO ) Á6H O
3
2 2
4
3 3
2
3 3
2
=
1:2:x. SFTN was obtained by heating the homogeneous
solution above to combustion on the electric stove, col-
lecting the ash followed by impregnating in 1.5 mol/L
(
NH ) SO solution for 18 h and calcining at 600 °C for
4
2
4
3
h. The Nd loading was changed by modifying the amount
2
-
2-
of Nd(NO ) Á6H O added. SO /Fe O (SF), SO /TiO2
3
3
2
4
2
3
4
2
-
ST), SO /Nd O (SN) and SFT were prepared according
(
Results and discussion
4
2 3
to the above mentioned method.
Effect of Nd O content on the catalytic activity
2
3
Catalytic activity test
The catalyst samples of different Nd contents were syn-
thesized by changing the amount of Nd(NO O added
Á6H
at the 1:2 mol ratio of [CH (CH O] Ti to Fe(NO
9H O .
The effect of Nd
The esterification of 8.01 mL acetic acid and 15.6 g
menthol in a molar ratio of 3:1 on 1 g catalyst was per-
formed in a three-necked flask with a thermometer reflux
condenser and magnetic stirrer at 405 K for 6 h. The
liquid product was obtained by separating the catalyst,
which could be reused, from the reaction mixture. The
liquid product was analyzed using a gas chromatograph
with a flame ionization detector (Simadzu 8A) and a
Porapak QS column.
3
)
3
2
)
)
3
Á
3
2
2
4
3
2
O content of SFT on the catalytic
2 3
activity is shown in Fig. 1. Results showed that the cata-
lytic activity of SFTN is highest with a menthyl acetate
yield of 98.30 % when the Nd O is 2 wt%.
2 3
Effect of SF, ST, SN and SFT on the catalytic activity
Different catalytic samples such as SF, ST, SN and SFT
were tried for the esterification of acetic acid and menthol.
The effect of catalytic samples on the catalytic activity is
shown in Table 1. Using SF, ST, SN and SFT as catalysts
for the esterification only 72.12, 70.53, 71.32 and 89.21 %
menthyl acetate yield took place, while the highest menthyl
Characterizations
TG-DTG studies
Thermal gravity analysis (TG) of the as-synthesized sam-
ple (9 mg) was performed on a NEZSCH STA 409PC
thermo analyzer. The analysis was carried out in Ar
atmosphere in the temperature range of 30–730 °C with a
heating rate of 10 °C/min.
100
9
9
9
8
6
4
XRD studies
Powder X-ray diffraction (XRD) patterns were recorded on
a Rigaku D/max-IIIB diffractometer using Cu Ka radiation
˚
(
k = 1.5406 A).
92
90
FT-IR studies
8
8
The samples were characterized by FT-IR spectroscopy
using a PE-783 IR spectrometer. Then, the samples were
mixed with KBr, made a piece, and the spectra taken at
room temperature.
0
1
2
3
4
5
The Nd content/wt%
Fig. 1 Menthyl acetate yield as a function of the Nd content of SFT
1
23

J IRAN CHEM SOC (2013) 10:407–413
409
Table 1 The effect of SF, ST, SN and SFT samples on the catalytic
activity
1.0
100
TG
0
.5
Catalytic samples
SF
ST
SN
SFT
9
9
8
5
0
5
0.0
DTG
Menthyl acetate yield/%
72.12
70.53
71.32
89.21
-
0.5
1.0
47
-
acetate yield of 98.30 % was obtained using SFTN as the
esterification of acetic acid and menthol (Nd O 2 wt%) (as
-1.5
2.0
-2.5
3.0
2
3
shown in Fig. 1).
80
-
349
7
5
449
548
TG-DTG of samples
-
0
100
200
300
400
500
600
700
800
The thermal decomposition behavior of samples was
examined by TG-DTG. Results are shown in Figs. 2 and 3.
There are three main gradients of weight loss. The first
gradient is at temperature under 351 °C (Fig. 2) and
Temperature/°C
Fig. 2 TGA curves of SFT
3
41 °C (Fig. 3) corresponding to the behavior, which can
1
.0
be ascribed to the release of crystal water and the water
adsorbed on the surface of the samples. The second gra-
dient appears between 340 and 500 °C. This scope is
characterized by endothermic peaks corresponding to the
TG
1
00
0.5
0.0
95
DTG
-0.5
decomposition reaction of (NH ) SO . The exothermic
4
2
4
90
85
peaks at 548 °C (Fig. 2) and 578 °C (Fig. 3) are due to the
combustion of sulfate ions and the metallic constituents
with a further weight loss in the last gradient. Figures 2 and
-1.0
341
-1.5
8
7
0
5
-2.0
-2.5
3
show that at 578 and 548 °C, respectively, corresponding
5
78
to a 30 °C difference, the introduction of Nd stabilizes the
coordination bond between sulfate and metallic irons,
which is consistent with the results of FT-IR.
4
55
-3.0
0
100
200
300
400
500
600
700
800
Temperature/
Fig. 3 TGA curves of SFTN
°C
XRD of samples
Figure 4 represents the XRD patterns of the samples cal-
cined at 600 °C. As shown in SFT, several peaks are
observed, which are ascribed to Fe O (JCPDS File No.
1
01
104
110
Fe O3
anatase
2
2
3
8
4-0309), anatase (JCPDS File No. 21-1272), rutile
Fe TiO5
2
(
JCPDS File No. 21-1276), and pseudobrookite (Fe TiO ,
2
5
1
10
rutile
JCPDS File No. 41-1432). The formation of the Fe TiO
2
5
0
24
1
03
214
300
phase can be explained by the fact that a certain percentage
?
200
0
04
3
211
211
of Fe
ions diffuses into the bulk TiO , producing a
2
a
3
substitutional solid solution in which Fe is dispersed in
3
the lattice of TiO . In fact, as the Fe radius is similar to
?
?
2
4
?
012
that of Ti [8], the substitution of iron in the matrix of
TiO is a favorable process. The Fe TiO peaks disappear
2
2
5
b
for SFTN because of the Nd additives. Moreover, the
addition of Nd O leads to a decrease in the intensity of
2
3
peak height for Fe O , anatase, and rutile phases. Results
2
20
30
40
50
60
70
3
reveal that the addition of Nd O limits the growth of the
2
2θ /degree
3
crystal, and increases the specific surface area. On the other
hand, the disappearance of Fe TiO adds the acid sites
Fig. 4 XRD patterns of the samples calcined at 600 °C (a SFT, b
SFTN)
2
5
[
9, 10], which agree with FT-IR.
123

4
10
J IRAN CHEM SOC (2013) 10:407–413
Figure 5 represents the XRD patterns of the recyclable
samples after five times. As shown in SFT, the back bottom
baseline is uneven and peak type is mixed and disorder,
which reveals that crystal structures are almost destroyed.
Water produced and stirring during the reaction process are
the main factors for destruction of the crystal structure. As
can be seen in recyclable SFTN after five times, the
destruction of the crystal structure is less than that of SFT.
Figure 6 represents the XRD patterns of the recyclable
samples after ten times. As shown in Fig. 6, the back
bottom baseline is uneven and peak type is mixed and
disorder, which reveals that crystal structures are almost
destroyed. Much more reuse times, water produced and
stirring during the reaction process are the main factors for
destruction of the crystal structure.
20
30
40
50
60
2
θ /degree
Fig. 6 XRD patterns of recyclable SFTN after ten times
FT-IR of samples
H
H
When the sample was heated at higher temperature, the
sulfate species structure on the surface of the catalyst will
change in the process of dehydration by forming strong
Lewis acid sites (Scheme 1) [11]. Sulfate species must
possess a strong covalence S=O bond that has a strong
ability to induce electrons for the formation of solid super
acid, which will enhance Lewis acidity of the metal center
ion.
O
M
Lewis acid
O
O
O
O
O
M
heat
H O
O
S
S
-
2
O
O
O
O
O
O
O
O
Scheme 1 The forming process of the catalysts
Figure 7 shows that there are two characteristic bands
-
between 800 and 1,450 cm in the SFTN and SFT spec-
1
tra, respectively, which were recorded at 1,122 and
-
,386 cm indicating that there are sulfate species in both
1
1
8
7
0
8
-
1
samples [12]. The band at 1,122 and 1,386 cm can be
attributed to the asymmetry stretch and shrink vibration of
S=O bond. These S=O bonds have similar characteristics
b
a
76
7
7
7
6
6
4
2
0
8
6
a
500
1000
1500
2000
2500
3000
3500
4000
Wavenumber/cm-1
Fig. 7 The FT-IR spectrum of the samples (a SFT, b SFTN)
b
with the covalence bond. Therefore, the strong acidic
center is formed on the surface of the catalyst.
2
0
30
40
50
60
According to literature [13], before TiO was impreg-
2
2
θ /degree
2-
nated with SO , the vibration peak of Ti–O was at
4
-
1
2-
50 cm , but after impregnating with SO , this peak
6
Fig. 5 XRD patterns of the recyclable samples after five times
a SFT, b SFTN)
4
-
shifted to a lower frequency of 616 cm as illustrated in
1
(
1
23

J IRAN CHEM SOC (2013) 10:407–413
411
1
0
8
6
4
2
0
Lewis acid sites [14]. There is also a distinct high-tem-
perature (HT) peak (at the range of 700–1,200 °C), which
is attributed to the presence of Brønsted acid sites [14, 16].
Riemer et al. [17] have studied that the ‘‘very strong’’ acid
sites found in solid acid are mostly due to the presence of
Brønsted acid sites. Moreover, there is an obvious differ-
ence in the strength of the acid sites between both samples.
The peaks at both LT and HT for SFTN are higher than
those for SFT, and the peak areas in the TPD profiles of
SFTN are larger than those of SFT. This suggests that the
strength of acid sites of SFTN is stronger than that of SFT,
and indicates that the addition of Nd O to SFT results in
b
a
2
3
an increase of acidity of the catalyst responsible for the
better esterification reaction activity.
200
400
600
800
1000
Temperature/°C
3
-TPD of the samples (a SFT, b SFTN)
TEM of samples
Fig. 8 The NH
-
1
SFT spectrum of Fig. 7. The band at 541 cm in SFT
spectrum was the stretching vibration of Fe–O bond [14].
However, small peaks have been observed in the region of
Representative TEM and HRTEM images of the SFT and
SFTN calcined at 600 °C are shown in Figs. 9 and 10,
respectively. In Fig. 9, the micrograph at low magnification
shows uniform lamellar crystals of about 50 nm in diam-
eter. The HRTEM image and the corresponding Fourier
filtered transformed image can be consistently indexed
using the structural data of crystals (Fig. 4). Increasing
Nd O (Fig. 10) shrinks grain size down to 30 nm. The
-
1
-1
5
41–616 cm instead of peaks at 541 and 616 cm in
SFTN, as shown in the spectrum of Fig. 2.
The presence of the small peaks can be attributed to the
introduction of Nd O into the SFT. The strong absorption
2
3
-
1
-1
peak at 3,432 cm
and peak at 1,643 cm
might be
2
3
assigned to the dissociative hydroxyl of H O absorbed on
2
HRTEM observation indicates that the lattice spacing of
SFTN is clearly observed and supported in the laminated
matrix with interphase spacings of d (104) = 0.268 nm,
which is agreement with XRD.
the solid super acid (shown in Fig. 7), indicating that the
prepared solid super acid catalysts could both act as
Bronsted acid and Lewis acid in the catalytic reaction [15].
TEM and SEM images of the SFT and SFTN reused are
shown in Fig. 11. Compared with that of fresh catalysts
NH -TPD of samples
3
(Figs. 9, 10), smaller catalytic particles can be observed
The NH -TPD technique is used to compare the acidic
3
from Fig. 9. However, lots of tiny flocculent particles can
be seen in Fig. 11d of SFT, which is bad for the catalytic
activity of SFT. The particle edge is sharp and there is
crack on the surface of the particle in SEM of SFTN, which
is caused by stirring during the reaction process.
characteristics of the SFT and SFTN catalysts. In Fig. 8,
two desorption peaks can be observed in the samples: the
first broad low-temperature (LT) desorption peak at
2
00–300 °C, which is attributed to NH adsorbed on weak
3
Fig. 9 TEM and HRTEM of
SFT calcined at 600 °C
123

4
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J IRAN CHEM SOC (2013) 10:407–413
Fig. 10 TEM and HRTEM of
SFTN calcined at 600 °C
Fig. 11 TEM and SEM of
recyclable samples: a TEM of
recyclable SFT after 5 times,
b TEM of recyclable SFTN
after five times, c TEM of
recyclable SFTN after ten times;
d SEM of recyclable SFT after
five times e SEM of recyclable
SFTN after five times and
f SEM of recyclable SFTN after
ten times
1
23

J IRAN CHEM SOC (2013) 10:407–413
413
catalytic activity was also investigated. Results indicated
that the introduction of Nd O improved the acidic prop-
1
00
2
3
erties of the catalysts. SFTN kept the typical covalence
-
2
9
8
7
6
5
0
0
0
0
0
S=O bond structure of SO4 /M O (SM) solid acids, and
x y
both Lewis and Brønsted acid sites existed. SFTN exhib-
ited higher activity for the esterification of acetic acid and
menthol, with 98.30 % yield of menthyl acetate. If SFTN
can be easily separated from reaction mixture and reused,
then the compound can be a desirable catalyst for the green
synthesis of menthyl acetate.
Acknowledgments The author (C.Y.) acknowledges the financial
support from the Department of Education of Jilin Province for the
a
b
‘
(
‘the Eleventh Five’’ Scientific and Technological Research Projects
2007-444).
0
1
2
3
4
5
6
7
8
9
10
11
Recycle time
Fig. 12 Menthyl acetate yield as a function of time of the catalyst
reuse cycle (a SFT, b SFTN)
References
1
. M. Hino, S. Kobayashi, K. Arata, J. Am. Chem. Soc. 101,
439–6441 (1979)
. M. Hino, K. Arata, J. Chem. Soc. Chem. Commun. 2, 851–852
1980)
3. J. Zhao, Y. Yue, W. Hua, H. He, Z. Gao, Appl. Catal. A Gen.
36, 133–139 (2008)
. T. Løften, E.A. Blekkan, Appl. Catal. A Gen. 299, 250–257
2006)
6
Reuse of the catalysts
2
(
Figure 12 shows that the yield of menthyl acetate over SFT
catalyst quickly decreases with the increase of catalyst
reuse times. After the fifth time for the catalyst reuse cycle,
the menthyl acetate yield reduces to 49.50 %, which is
approximately half of the yield (89.20 %) achieved on the
fresh catalyst.
3
4
5
6
(
. H. Guo, P. Yan, X. Hao, Z. Wang, Mater. Chem. Phys. 112,
1065–1068 (2008)
. S. Furuta, H. Matsuhashi, K. Arata, Appl. Catal. A Gen. 269,
1
87–191 (2004)
As for SFTN, the menthyl acetate yield shows only a
mild change after five times reuse cycle. It decreased only
from 98.30 to 96.80 % after the sixth of the catalyst reuse.
Moreover, the menthyl acetate yield rapidly decreased and
reached 49.90 % at the tenth reuse. These results indicate
that the catalytic activity decomposes after several times of
catalysts reuse. However, the SFTN catalyst shows more
stable activity than the SFT catalyst and can be reused
effectively up to five times.
7
8
. Z. Wang, S. Shao, H. Xing, Tianjin Chem. Ind. 4, 6–7 (2002)
. Y. Yin, S. Chen. Y. Liu, 3rd edn (Chemical Industry Press,
Beijing, 2004), p. 58
9
. C. Du, Y. Qin, Y. He, Chin. J. Chem. Phys. 16, 504–508 (2003)
1
1
1
0. J.C. Yu, L. Zang, J. Yu. New J. Chem. 26, 416–420 (2002)
1. F. Haase, J. Sauer, J. Am. Chem. Soc. 120, 13503–13512 (1998)
2. B. Fr e´ d e´ ric, C. Gisele, J.C. Vedrine, J. Catal. 152, 341–349
(1995)
3. H. Yin, Z. Tan, Y. Liao, Y. Feng, J. Environ. Radioactiv. 87,
2
4. W. Chen, H.H. Ko, A. Sakthivel, S.J. Huang, S. Liu, A.Y. Lo,
T.C. Tsai, S. Liu, Catal. Today 116, 111–120 (2006)
5. H. Ma, F. Chen, B. Wang, Q. Zhuo, J. Hazard. Mater. 145,
53–458 (2007)
6. R. Barthos, F. L o´ nyi, G. Onyesty a´ k, J. Valyon, Solid State Ion.
41, 253–258 (2001)
1
1
1
1
1
27–235 (2006)
4
Conclusions
1
SFTN solid super acid catalysts were prepared by com-
7. T. Riemer, D. Spielbauer, M. Hunger, G.A.H. Mekhemer, J.
Chem. Soc. chem. Commun. 1181–1182 (1994)
bustion method. The effect of Nd O3 content on the
2
123