Synthesis and characterization of S2O82 -/ZnFexAl2 - XO4 solid acid catalysts for the esterification of acetic acid with n-butanol

Article abstract of DOI:10.1016/j.catcom.2015.01.009

New spinel-types of S₂O₈^{2 -}/ZnFe_xAl_{2 - x}O₄ solid acid catalysts were prepared by sol-gel method. Their catalytic performances for the synthesis of n-butyl acetate were investigated. The cat

Full text of DOI:10.1016/j.catcom.2015.01.009

Catalysis Communications 62 (2015) 29–33
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
2
−
Synthesis and characterization of S O /ZnFe Al O solid acid
2 − x 4
2
8
x
catalysts for the esterification of acetic acid with n-butanol
a,
a,b
a
a
a
a
Junxia Wang ⁎, Hui Pan , Anqi Wang , Xiaoyun Tian , Xiuling Wu , Yongqian Wang
a
Faculty of Materials Science and Chemistry, Engineering Research Center of Nano-Geomaterials of Ministry of Education, China University of Geosciences, Wuhan 430074, China
College of Chemistry and Chemical Engineering, Xinjiang Normal University, Urumqi 830054, China
b
a r t i c l e i n f o
a b s t r a c t
New spinel-types of S O2 /ZnFe Al2 − xO4 solid acid catalysts were prepared by sol–gel method. Their catalytic
−
Article history:
2
8
x
Received 10 November 2014
Received in revised form 5 January 2015
Accepted 6 January 2015
performances for the synthesis of n-butyl acetate were investigated. The catalysts were characterized by
means of XRD, IR, XPS, FT-IR of adsorbed pyridine and NH -TPD. The experimental results showed that S O /
3 2 8
2−
ZnFe
x
Al2 − x
O
4
x 4
solid acid catalysts maintained the spinel structure as well as the support of ZnFe Al2 − xO .
Available online 8 January 2015
3
+
2−
Fe ions were well incorporated and highly dispersed into the spinel lattice. S
O
2 8
/ZnFe0.15Al1.85
showed better reusability,
which remained above 72.7% conversion of acetic acid even after being used five times.
© 2015 Published by Elsevier B.V.
4
O exhibited
2
−
2 8 4
the maximum conversion of acetic acid with 98.2%. Moreover, S O /ZnFe0.15Al1.85O
Keywords:
Solid acid
2
−
S
2
O
8
/ZnFe
Synthesis
Characterization
Catalytic properties
x
Al2 − x
O
4
1
. Introduction
crystal form of simple oxides are complex and difficult to control. There-
fore, researchers in this field are focusing on looking for a new type of
support.
2
−/M
SO
4
O
x y
solid acid catalysts have received extensive interests in
recent years because of their strong acidity, high catalytic activity, easy
separation, low waste generation, good environmental friendliness,
Spinel compound oxides have the advantage of stable structure,
single crystal shape and easy modification, which can generally be de-
scribed by the chemical formula of AB O [12–15]. Recently, some
2 4
etc. [1,2]. Among them, SO2
−
/ZrO
, SO
2−
/SnO
and SO
2−
/TiO
have
4
2
4
2
4
2
drawn significant attention due to their good catalytic performances
in many reactions [3–5]. However, they have similar disadvantages of
rapid deactivation and low service life, which limit their practical appli-
cation [6]. The modification by the addition of other metal ions is usually
considered as an effective method to overcome their limitation. How-
ever, the crystal type is easily changed and difficult to control in the pro-
scholars found that spinel compound oxides could be used in the syn-
2
4
−
thesis of SO
/M
x y
O solid acid. For example, Lin et al. reported that
2
−
SO
4
2
/CoFe O
4
solid acid displayed certain acid strength and good cata-
lytic activity in the synthesis of ethyl acetate reaction [16]. Lee et al.
found that sulfated ZnFe showed a better catalytic performance in
2 4
O
the oxidative dehydrogenation of n-butene because of its good acidity
[17]. Nanosized SO2
−
/ZnFe
catalyst was found to be highly active
cess of doping with other metal ions, which has a great influence on the
4
2
O
4
formation of acid sites and catalytic performances of SO2
−
/M
O
y
. For
in some important acid catalyzed reactions [18]. From the literature
mentioned above, it could be seen that spinel oxides could be used
as a new support for the preparation of solid acid catalyst. Neverthe-
less, there is still little information about this aspect of research in
4
x
2 2
instance the monochromic in ZrO and SnO crystallization is not
conducive to the formation of acid centers. By comparison, the classical
tetragonal phase is beneficial to improve the acid catalytic activity of
2
−
2−
SO
4
/ZrO
2
and SO
4
/SnO
2
[7–9]. TiO
2
has three main forms of crystal,
the literature.
2
−/ZnFe
including the anatase, rutile, and brookite. Among them, the anatase is
In this paper, new spinel-types of S
2
O
8
Al2 − xO
x 4
solid acid
conducive to improve the catalytic performance of SO2
−
/TiO
[10].
catalysts were prepared and applied in the synthesis of n-butyl acetate.
4
2
2
−
In order to control the crystal transformation, scholars have performed
The effects of x value on the catalytic activities of S
2 8 x 4
O /ZnFe Al2 − xO
much research [10,11]. Nevertheless, the factors that influence the
were studied. In addition, the structure, the acidity, and the stability of
2
−
S
2
O
8
/ZnFe
been paid to the study of S
This study was aimed to provide some valuable information on the ap-
x 4
Al2 − xO were evaluated. At present, little attention has
2
−
2 8 x 4
O /ZnFe Al2 − xO solid acid catalyst.
⁎
Corresponding author.
2
−
E-mail address: jxwyqh@sina.com (J. Wang).
2 8 x 4
plication of S O /ZnFe Al2 − xO in the esterification reaction.
http://dx.doi.org/10.1016/j.catcom.2015.01.009
566-7367/© 2015 Published by Elsevier B.V.
1

30
J. Wang et al. / Catalysis Communications 62 (2015) 29–33
2
. Experimental
Frontier FT-IR spectrometer. Before measurement, the sample was
pretreated at 300 °C for 1 h in a vacuum. Then the samples were cooled
to 30 °C and adsorbed pyridine vapor for 0.5 h. The adsorbed pyridine
was subsequently removed by degassing for 1 h at 150 °C. Then, the
FT-IR spectra of the adsorbed pyridine were recorded. The X-ray photo-
electron spectroscopy (XPS) was performed in a VG Multilab 2000. The
2
.1. Catalyst preparation
Spinel ZnFe
lows: Al(NO
x
Al2 − x
O
4
(x = 0, 0.1, 0.15, 0.2) were prepared as fol-
3
)
3
·9H
2
O, Zn(NO ·6H O and Fe(NO) ·9H O were dis-
3
)
3
2
3
2
solved in alcohol. 5 wt.% of polyethylene glycol was then slowly added
to the solution under magnetic stirring at room temperature for 4 h.
The obtained mixture was further stirred for 2 h in a water bath at
3 3
NH temperature programmed desorption (NH -TPD) experiments
were carried out using a Micromeritics AutoChem II 2920 quipped with
a TCD detector. The samples were treated in helium flow (50 mL/min)
6
0 °C. After the mixture was dried at 120 °C, the precursor was ob-
at 400 °C for 1 h and exposed to NH
for 1 h, and then followed by helium to remove gas-phase and physically
adsorbed NH . Measurements were started in helium with a heating rate
of 10 °C/min.
3
(50 mL/min) at room temperature
tained. After being ground into a fine powder, the obtained powder
was calcined at 600 °C for 5 h in air sequentially to obtain the pow-
der samples. The obtained spinel compound oxides were designated
3
as ZnFe
Fe (based on the compositions of ZnAl
catalysts were prepared by impregnating calcined ZnFe
x 4
Al2 − xO , where x represented the different molar ratios of
2
−
2
O
4
). S
2
O
8
/ZnFe
x
Al2 − x
Al2 − x
O
O
4
x
4
2.3. Catalytic activity test
sample using 1.50 mol/L aqueous ammonium persulfate ((NH
solution. Sulfation was done by immersing 1 g of ZnFe
0 mL of ammonium persulfate solution for 12 h. After been filtered
and dried, the obtained samples were calcined at 550 °C for 5 h to get
4
)
2
S
O
2
O
8
)
x
Al2 − x
4
in
The esterification reaction was carried out in a three-necked flask
under atmospheric pressure, which is equipped with a magnetic stirrer,
a thermometer and a refluxing condenser tube. The reaction conditions
were as follows: the reaction temperatures were 115–118 °C, the molar
ratio of n-butanol to acetic acid was 3:1, the reaction time was 3 h and
the catalyst amount was 1.55 wt.% (weight percentage of the reaction
mixture). After the reaction, the catalyst was immediately separated
from the reaction mixture by filtering. Then, the titration experiment
was rapidly performed, which was used to determine the residual
acid. Namely, 0.50 mL reaction mixture was added in 20.00 mL absolute
alcohol and titrated by 0.10 mol/L NaOH solution using phenolphthalein
as an indicator. Then, the conversion of acetic acid was measured using
the following equation [19,20]:
1
2
−
S O
2 8
/ZnFe
x
Al2 − x
4
O .
2
.2. Catalyst characterization
XRD measurements were performed on a Dmax-3β diffractometer.
IR spectra of the catalysts were recorded by a Nicolet 6700 spectrometer
using KBr pellets. FT-IR of adsorbed pyridine spectra were recorded on a
M −M
0
1
The conversion of acetic acidð%Þ ¼
ꢀ 100
M
0
where M
and M was the dissipative volume of NaOH solution after reaction.
In order to test the stability, S
were repeatedly used for the batch reaction process. After
0
was the dissipative volume of NaOH solution before reaction
1
2
−
2−
2 8 2 4 2 8
O /ZnAl O and S O /ZnFe0.15
Al1.85O
4
each catalytic evaluation was finished, the catalyst was filtered from
the reaction mixture, and dried at 60 °C for 12 h in air. Then, the catalyst
without any further intermediate reactivation was reused in a new reac-
tion cycle under the same reaction conditions.
2
−/ZnFe
, (e) S
Fig. 2. IR spectra of ZnFe
x
Al
2
−
x
O
4
and S
2
O
8
x
Al
2
−
x
O
4
. (a) ZnFe0.2Al1.8
O
4
,
/
2
−
2−
2 8
(b) ZnFe0.15Al1.85
O
4
, (c) ZnFe0.1Al1.9
O
4
, (d) ZnAl
, and (h) S
2
O
4
2
O
8
/ZnAl
2
O
4
, (f) S
O
2
−/ZnFe
2−
2−
Fig. 1. XRD patterns of ZnFe Al2 − xO
x 4
(a) and S
2
O
8
Al2 − xO
x 4
(b).
ZnFe0.1Al1.9 , (g) S
O
4
O
2 8
/ZnFe0.15Al1.85
O
4
2 8
O
4
/ZnFe0.2Al1.8O .

J. Wang et al. / Catalysis Communications 62 (2015) 29–33
31
2
−/ZnFe
3
. Results and discussion
.1. Catalyst characterization
The XRD patterns of ZnFe
The IR spectra of ZnFe
x
Al2 − x
O
4
and S
2
O
8
x
Al2 − x
−1
O
4
are
−
1
−1
shown in Fig. 2. Bands at 672 cm , 556 cm and 493 cm are related
to Al\O stretching vibrations, Zn\O stretching vibrations and Al\O
bending vibrations respectively [22,23]. In addition, spectra of the
2 8 x 4
S O /ZnFe Al2 − xO exhibit the special bands in the range of 900–
1400 cm , which are associated with the acid structures of the cata-
lysts [24–26]. The specific bands in this region are attributed to the
strong interaction between sulfuric groups and metal ions, which are
correlated to their high catalytic activities. Among them, the bands at
987 cm , 1102 cm and 1145 cm are assigned to the stretching vi-
bration of S\O. In the meantime, the band at 1220 cm is assigned to
3
2
−/ZnFe
2−
x
Al2 − x
O
4
and S O
2 8
x
Al2 − x
O
4
are
−
1
present in Fig. 1. As shown in Fig. 1(a), all the reflection peaks of
ZnFe match well with the standard JCPDS card No. 82-1043 of
spinel ZnAl , indicating that all the samples of ZnFe crystallize
single spinel structure. Furthermore, there are no apparent changes in the
intensity and the position of the characteristic peaks with the x-value in-
crease, indicating that Fe3 ions are well incorporated and highly dis-
Al2 − xO
x 4
2
O
4
x 4
Al2 − xO
−
1
−1
−1
+
−1
2
−
2−
persed into the spinel lattice. As shown in Fig. 1(b), S
2
O
8
/ZnFe
x
Al2 −
Al2 −
the stretching vibration of S_O, indicating that S
2
O
8
ion coordinates to
x
O
4
maintained the spinel structure as well as the support of ZnFe
x
metal ions and forms the bidentate structure [25]. Such a bidentate struc-
ture is believed to be a driving force in the generation of many acidic sites
on surface of sulfated metal oxides, making the samples possess acidity.
Noticeably, the typical bands in the range of 900–1400 cm are not ob-
x 4
served in the case of ZnFe Al2 − xO . However, upon impregnation with
x
O
4
. However, Al
2
(SO
4
)
3
and ZnSO
/ZnFe
4
·H
2
O crystalline phases are observed
, which might be attributed to
and metal ions. A similar phenom-
solid acid [21].
2
−
in all samples of S
2
O
8
x
Al2 − x
O
4
2
−
−1
the interaction between excess S
2
O
8
enon is observed in other SO2
−
/M O
x y
4
2
−/ZnAl
2−
4
/ZnFe0.15Al1.85O . (a) The whole XPS spectra, (b) Zn 2p spectra, (c) Al 2p spectra, (d) O 1s spectra, (e) Fe 2p spectra, and (f) S 2p spectra.
Fig. 3. XPS spectra of S
2
O
8
O
2 4
and S O
2 8

3
2
J. Wang et al. / Catalysis Communications 62 (2015) 29–33
Table 1
ammonium persulfate, there is a drastic change in the IR spectra of the
samples. All related bands in the range of 900–1400 cm become obvi-
ous in S
interaction of surface sulfate species with metal ions, which is the sig-
nificant reason for the formation of the active acid center on the surface
of S
other SO
The XPS analysis of S
2
−
−
1
The effect of x value on the catalytic activities of S O /ZnFe Al2 − xO4 solid acids.
2
8
x
2
−
2
O
8
/ZnFe
x
Al2 − x
O
4
samples. This result indicates a very strong
Catalysts
No
The conversion of acetic acid (%)
38.8%
47.5%
91.4%
95.2%
98.2%
92.5%
ZnFe0.15Al1.85O
4
2
−
2−
2
O
8
/ZnFe
x
Al2 − x
O
4
. The similar conclusion was also proved by
S
S
S
S
2
O
2
O
2
O
2
O
8
2 4
/ZnAl O
2
−
2−
8
/ZnFe0.1Al1.9O
4
4
x y
/M O systems [27].
2
−
−
2
−/ZnAl
2−
4
/ZnFe0.15Al1.85O is
8
2
8
/ZnFe0.15Al1.85O
4
/ZnFe0.2Al1.8O
4
2
O
8
2
O
4
and S
2
O
8
2
−
shown in Fig. 3. For S O /ZnAl O , the Zn 2p3/2 and Zn 2p1/2 binding
2 8 2 4
energies are located at 1021.9 eV and 1045.1 eV, respectively, which
are close to the standard data for Zn2 (Fig. 3(b)) [28]. The peaks
located at 75.0 eV and 531.3 eV are attributed to the Al 2p (Fig. 3(c))
and O 1s (Fig. 3(d)) binding energies, respectively [29,30]. Compared
+
oxidation state of +6 plays a key role on the formation of the strong
acidity [32]. This result is in good agreement with the IR results.
FT-IR spectra of adsorbed pyridine made it possible to distinguish be-
tween Brönsted and Lewis acid sites. As shown in Fig. 4(a), the peak at
2
−
2−
4
/ZnFe0.15Al1.85O sample
with S O
2 8
/ZnAl
2
O
4
, the XPS spectra of S
O
2 8
−
1
−1
show no significant differences in the binding energies of the Zn 2p3/2
and Zn 2p1/2. However, the Al 2p shifts to the lower binding energy
and the O 1s shifts to the higher binding energy. From the above result,
we speculate that the introduction of iron instead of aluminum in the
spinel lattice could change the chemical environment of the measured
atoms in the crystal lattice, which may be a reason for the influence of
1540 cm is attributable to Brönsted acid sites. The peak at 1450 cm
−
1
is assigned to Lewis acid sites [33,34]. The band at 1490 cm is attributed
to both Brönsted and Lewis acid sites. FT-IR spectra of the adsorbed pyri-
dine therefore indicate that both Brönsted and Lewis acid sites are present
2
−
on the surface of S
2 8 x 4
O /ZnFe Al2 − xO . Obviously, the concentration of
2
−
Brönsted and Lewis acid sites of S
O
2 8
/ZnAl O
2 4
is the lowest among all
has the larger number of
acid sites, resulting in its highest catalytic activities. This result is also con-
firmed by the NH -TPD results.
The acid strength distribution obtained from the NH
2
−
the acid properties and catalytic activities. The peaks at 711.5 and
2 8 4
samples. Meanwhile, S O /ZnFe0.15Al1.85O
+
7
25.8 eV are corresponding to the Fe 2p3/2 and Fe 2p1/2 for Fe3 res-
pectively (Fig. 3(e)) [31]. In the meantime, the peak at 169.1 eV is mea-
sured for S 2p binding energy in the two samples (Fig. 3(f)), which is
attributable to the sulfur oxidation state of +6. Specifically, the sulfur
3
3
-TPD spectra of
is shown in Fig. 4(b). The
peaks in each of the profiles correspond to desorption of NH bound
to the acid sites of oxide surface. The desorption temperature indicates
the acid strength of the catalyst. Generally, NH adsorbed on the
weak acid sites is desorbed at low temperature. Correspondingly, NH
2
−
4 2 8 x 4
ZnFe0.15Al1.85O and S O /ZnFe Al2 − xO
3
3
3
adsorbed on strong acid sites is desorbed at high temperature. The
higher temperature of desorption is, the stronger the acid strength is.
As shown in Fig. 4(b), ZnFe0.15Al1.85
4
O exhibits almost no desorption
peaks in the range of 100 °C and 800 °C, which could be one reason
2
−
for its lower catalytic activity (as shown in Table 1). However, S
ZnFe all show broad desorption peaks in the range of 100 °C
and 800 °C, indicating that S
forms the acid structures. The NH
2 8
O /
Al2 − xO
x 4
2
−
2
O
8
ion coordinates to metal ions and
-TPD results are consistent very well
3
with the IR results. The peaks below 450 °C are corresponding to the
weak and middle strength acid sites. The peaks between 450 °C and
6
50 °C are attributable to strong acidic sites. The peaks above 700 °C
2
−
2 8
are associated with very strong acidic sites. Compared with S O /
ZnAl O , S O /ZnFe Al2 − xO (x = 0.1, 0.15, 0.2) shows the stronger
2 4 2 8 x 4
2
−
acid strength and a greater number of acid sites. It demonstrates that
the appropriate addition of Fe results in increasing the amount of acid
sites and strengthening the acidity. This result indicates that a certain
addition of Fe plays a prior effect on the interaction of the active sulfur
2
−/ZnFe
Fig. 4. The pyridine adsorption FT-IR spectra of S
2
O
O
8
x
Al2 − x
O
4
(a) and NH
3
-TPD
2
−
2−
2−
spectra of ZnFe0.15Al1.85
O
4
and S O
2 8
x
/ZnFe Al2 − x
4
(b). (1) S
O
2 8
/ZnAl , (2) S
O
2 4
2
O
8
/
2
−
2−
2−
2−
4
/ZnFe0.15Al1.85O .
ZnFe0.2Al1.8O , (3) S O
4 2 8
/ZnFe0.15Al1.85 , and (4) S
O
4
2
O
8
/ZnFe0.1Al1.9
O
4
.
Fig. 5. The reusability of S
2
O
8
/ZnAl O
2 4
and S O
2 8

J. Wang et al. / Catalysis Communications 62 (2015) 29–33
33
2
−/
2−
species with metal oxides. Furthermore, the total acid sites of S
2
O
8
site number. Correspondingly, S
2
O
8
/ZnFe
x
Al2 − x
O
4
(x = 0.1, 0.15,
ZnFe0.15Al1.85
with the FT-IR of adsorbed pyridine. Accordingly, S
shows the highest activity in all samples.
O
4
are the maximum in all samples, which is consistent
0.2) solid acid catalysts showed the higher catalytic activity than
2
−
2−
O
2 8
/ZnFe0.15Al1.85
O
4
2 8 2 4
S O /ZnAl O catalyst for the esterification of n-butanol with acetic
2
−
2 8 4
acid. Among them, S O /ZnFe0.15Al1.85O showed the highest activity
and improved reusability, which has potential applications for other
acid catalyzed reactions, either Brönsted acid or Lewis acid.
3
.2. Catalytic activities and reusability
2 8
O
−/
2
Table 1 gives the effect of x value on the catalytic activity of S
ZnFe in esterification of acetic acid with n-butanol. For com-
parison, the catalytic activities of ZnFe0.15Al1.85 and no catalyst are
also added in Table 1. It is found that the conversion of acetic acid is
less than 40% in the absence of catalyst. Additionally, the support of
Acknowledgments
Al2 − xO
x 4
O
4
The authors gratefully acknowledge the financial support from NSFC
(
2
21203170, 41172051), SFBSRCC (CUGL090227), ERCNGME (CUGNGM
0133), Self-DIRFC (2013-09) and NCSITP (201310491019).
4
ZnFe0.15Al1.85O also shows lower catalytic activity with 47.5% conver-
2
−
2 8 x 4
sion of acetic acid. However, S O /ZnFe Al2 − xO catalysts all exhibit
significantly high catalytic activities with above 90% conversion of acetic
acid. It is well known that acid property of metal oxides is promoted by
the surface modification with sulfate ion. According to the IR results,
References
[
1] S.D. Salim, K.G. Akamanchi, Catal. Commun. 12 (2011) 1153–1156.
2
−
S
2
O
8
/ZnFe
dicating that there are strong interactions between sulfuric groups and
metal ions. So, the enhanced acidities of sulfated ZnFe cata-
lysts may be responsible for their higher catalytic activities. By compar-
x
Al2 − x
O
4
catalysts exhibit the apparent acid structures, in-
[2] D.C. Boffito, V. Crocellà, C. Pirola, B. Neppolian, G. Cerrato, M. Ashokkumar, C.L.
Bianchi, J. Catal. 297 (2013) 17–26.
[
[
3] V.G. Devulapelli, H.S. Weng, Catal. Commun. 10 (2009) 1711–1717.
4] F.H. Alhassan, U. Rashid, M.S. Al-Qubaisi, A. Rasedee, Y.H. Taufiq-Yap, Powder
Technol. 253 (2014) 809–813.
Al2 − xO
x 4
2
−
2−
[5] M.K. Lam, K.T. Lee, A.R. Mohamed, Appl. Catal. B 93 (2009) 134–139.
6] X.J. Shi, Y.L. Wua, P.P. Li, H.F. Yi, M.D. Yang, G.H. Wang, Carbohydr. Res. 346 (2011)
80–487.
[7] F. Ye, Z.W. Dong, H.J. Zhang, Catal. Commun. 10 (2009) 2056–2059.
8] B.M. Reddy, G.K. Reddy, K.N. Rao, L. Katta, J. Mol. Catal. A 306 (2009) 62–68.
2 8 2 4 2 8 x 4
ison of S O /ZnAl O , S O /ZnFe Al2 − xO (x = 0.1–0.2) catalysts
[
present better catalytic activities, which is well associated with their
more amount of acid sites. Combined with the characterization results,
we could deduce that there might be two main reasons for this
4
[
phenomenon. First reason is that Fe3 ions instead of Al in the spinel
+
3+
[9] C.H. Li, Y.X. Zhao, B. Dai, J. Ind. Eng. Chem. 18 (2012) 520–525.
10] J.R. Sohn, D.C. Shin, Appl. Catal. B 77 (2008) 386–394.
[
lattice change the chemical state of the exterior atom and enhance the
[11] N. Thimmaraju, S.Z. Mohamed Shamshuddin, S.R. Pratap Venkatesh, J. Mol. Catal. A
91 (2014) 55–65.
2
−
3
acidities of S
2 8 x 4
O /ZnFe Al2 − xO . Second, the mixture of different
[
[
12] G.L. Fan, J. Wang, F. Li, Catal. Commun. 15 (2011) 113–117.
13] R.T. Kumar, N.C.S. Selvam, C. Ragupathi, L.J. Kennedy, J.J. Vijaya, Powder Technol. 224
(2012) 147–154.
metal ions also modifies acid sites and indirectly helps to improve the
2
−
catalytic activities [35]. Furthermore, S
the highest catalytic activity with 98.2% conversion of acetic acid.
Based on the results of FT-IR of adsorbed pyridine and NH -TPD, this re-
2 8 4
O /ZnFe0.15Al1.85O exhibits
[14] F. Davar, M. Salavati-Niasari, J. Alloys Compd. 509 (2011) 2487–2492.
[15] A. Ghasemin, M. Mousavinia, Ceram. Int. l40 (2014) 2825–2834.
[16] D.J. Lin, S.F. Shen, H.B. Pan, N.S. Chen, Chin. J. Inorg. Chem. 16 (2000) 757–762.
[17] H. Lee, J.C. Jung, I.K. Song, Catal. Lett. 133 (2009) 321–327.
3
sult may be owing to its strongest acid strength and its maximum
amount of acid sites in all samples.
[18] S.V. Jadhav, K.M. Jinka, H.C. Bajaj, Catal. Today 198 (2012) 98–105.
[19] S. Praserthdam, B. Jongsomjit, Catal. Lett. 130 (2009) 583–587.
It is well known that SO2
−
4
x y
/M O solid acid catalysts suffer from poor
[
[
20] H.Q. Yang, H.Y. Song, H. Zhang, P. Chen, Z.X. Zhao, J. Mol. Catal. A 381 (2014) 54–60.
21] R.P. Yao, M.J. Zhang, J. Yang, D.L. Yi, J. Xu, F. Deng, Y. Yue, C.H. Ye, Acta Chim. Sin. 63
(2005) 269–273.
reusability and ongoing deactivation, which is mainly due to the loss of
sulfur species as well as carbon deposition [6]. However, there is little
recycling data about SO2
−
[22] A.G. Khaledi, S. Afshar, H.S. Jahromi, Mater. Chem. Phys. 135 (2012) 855–862.
[23] X.Y. Li, Z.R. Zhu, Q.D. Zhao, L.Z. Wang, J. Hazard. Mater. 186 (2011) 2089–2096.
4
x y
/M O solid acid catalysts in the literature,
2
−
2 8
which is vital in the evaluation of a catalyst lifetime. Therefore, S O /
[
[
[
24] P.F. Chen, M.X. Du, H. Lei, Y. Wang, G.L. Zhang, F.B. Zhang, X.B. Fan, Catal. Commun.
2
−
ZnAl
2 4 2 8 4
O and S O /ZnFe0.15Al1.85O solid acid catalysts were recycled
18 (2012) 47–50.
25] O.V. Manoilova, R. Olindoa, C.O. Areán, J.A. Lercher, Catal. Commun. 8 (2007)
865–870.
26] J.R. Sohn, W.C. Park, Appl. Catal. A 239 (2003) 269–278.
to study their stability under use. The results are shown in Fig. 5.
2
−
2−
2 8 2 4 2 8 4
Compared with S O /ZnAl O , S O /ZnFe0.15Al1.85O shows better
reusability, which remains above 72.7% conversion of acetic acid even
after being used five times. This above result indicates that the addition
of Fe can also enhance the stability of S
catalyst.
[27] G.D. Yadav, B.A. Gawade, Catal. Today 207 (2013) 145–152.
[28] Z.R. Zhu, X.Y. Li, Q.D. Zhao, S.M. Liu, X.J. Hu, G.H. Chen, Mater. Lett. 65 (2011)
194–197.
2
−
2 8 x 4
O /ZnFe Al2 − xO solid acid
[
29] L.C. Peng, L. Lin, J.H. Zhang, J.B. Shi, S.J. Liu, Appl. Catal. A 397 (2011) 259–265.
[30] Q. Yu, X.J. Yao, H.L. Zhang, F. Gao, L. Dong, Appl. Catal. A 423–424 (2012) 42–51.
[
[
31] C.Z. Liu, D.W. Meng, H.X. Pang, X.L. Wu, J. Xie, X.H. Yu, L. Chen, X.Y. Liu, J. Magn.
Magn. Mater. 324 (2012) 3356–3360.
32] O.B. Belskaya, I.G. Danilova, M.O. Kazakov, T.I. Gulyaeva, L.S. Kibis, A.I. Boronin, A.V.
Lavrenov, V.A. Likholobov, Appl. Catal. A 387 (2010) 5–12.
4
. Conclusions
2
−/ZnFe
All the samples of ZnFe
x
Al
2
−
x
O
4
and S
2
O
8
x
Al
2
−
x
O
4
[33] M.Y. Smirnova, A.V. Toktarev, A.B. Ayupov, G.V. Echevsky, Catal. Today 152 (2010)
7–23.
1
belonged to the stable and unique spinel structure. The introduction of
Fe in the crystal lattice of spinel changed the chemical environment of
the atoms, which led to an increase of the acid strength and the acid
[
[
34] M.L. Zhua, S. Li, Z.X. Li, X.M. Lu, S.J. Zhang, Chem. Eng. J. 185–186 (2012) 168–177.
35] P.C. Wang, K. Yao, J. Zhu, X. Liu, T.T. Lu, M. Lu, Catal. Commun. 39 (2013) 90–95.