Catalytic activity comparison of Zr-SBA-15 immobilized by a Br?nsted-Lewis acidic ionic liquid in different esterifications

Article abstract of DOI:10.1039/c7ra04950a

Zirconium-incorporated SBA-15 mesoporous molecular sieves (Zr-SBA-15) with different Si/Zr molar ratios were one-pot synthesized and characterized by XRD, TEM and N₂ physical adsorption. The Br?nsted-Lewis acidic ionic liquid 1-(3-sulfonic acid)-propy l-3-methylimidazole chlorozincinate ([mim-ps]Cl-ZnCl₂) was prepared by a hydrothermal process and its acidity was measured by FT-IR spectroscopy using acetonitrile and pyridine as probes. The Zr-SBA-15 catalyst immobilized by [mim-ps]Cl-ZnCl₂ (Zr-SBA-15/[mim-ps]Cl-ZnCl₂) was prepared by a wet impregnation method and characterized by XRD, BET, FT-IR spectroscopy, TEM, XPS and TG. In particular, the catalytic activities of Zr-SBA-15 and Zr-SBA-15/[mim-ps]Cl-ZnCl₂ in the esterification of acetic acid were evaluated with n-butyl alcohol (n-BuOH), benzyl alcohol (BnOH) and cyclohexanol (Naxol). The results show that Zr-SBA-15/[mim-ps]Cl-ZnCl₂ exhibited enhanced catalytic properties compared to Zr-SBA-15. Under optimal conditions, the acetic acid conversion over Zr-SBA-15/[mim-ps]Cl-ZnCl₂ reached 89.7, 93.6, and 84.9% for n-BuOH, BnOH and Naxol, respectively. After 5 cycles, the acetic acid conversion decreased slightly. Zr-SBA-15/[mim-ps]Cl-ZnCl₂ was found to be an outstanding catalyst for esterification.

Full text of DOI:10.1039/c7ra04950a

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Catalytic activity comparison of Zr–SBA-15
immobilized by a Brønsted–Lewis acidic ionic
liquid in different esterifications
Cite this: RSC Adv., 2017, 7, 32427
Liming Dai, Qian Zhao, Minglan Fang, Ruifeng Liu, Mingfeng Dong
and Tingshun Jiang
*
Zirconium-incorporated SBA-15 mesoporous molecular sieves (Zr–SBA-15) with different Si/Zr molar ratios
were one-pot synthesized and characterized by XRD, TEM and N physical adsorption. The Brønsted–Lewis
acidic ionic liquid 1-(3-sulfonic acid)-propy l-3-methylimidazole chlorozincinate ([mim-ps]Cl–ZnCl ) was
prepared by a hydrothermal process and its acidity was measured by FT-IR spectroscopy using
acetonitrile and pyridine as probes. The Zr–SBA-15 catalyst immobilized by [mim-ps]Cl–ZnCl (Zr–SBA-
5/[mim-ps]Cl–ZnCl ) was prepared by a wet impregnation method and characterized by XRD, BET, FT-
IR spectroscopy, TEM, XPS and TG. In particular, the catalytic activities of Zr–SBA-15 and Zr–SBA-15/
mim-ps]Cl–ZnCl in the esterification of acetic acid were evaluated with n-butyl alcohol (n-BuOH),
benzyl alcohol (BnOH) and cyclohexanol (Naxol). The results show that Zr–SBA-15/[mim-ps]Cl–ZnCl
exhibited enhanced catalytic properties compared to Zr–SBA-15. Under optimal conditions, the acetic
acid conversion over Zr–SBA-15/[mim-ps]Cl–ZnCl reached 89.7, 93.6, and 84.9% for n-BuOH, BnOH
and Naxol, respectively. After 5 cycles, the acetic acid conversion decreased slightly. Zr–SBA-15/[mim-
ps]Cl–ZnCl was found to be an outstanding catalyst for esterification.
2
2
2
1
2
[
2
2
Received 2nd May 2017
Accepted 9th June 2017
2
DOI: 10.1039/c7ra04950a
rsc.li/rsc-advances
2
aluminate acidic ionic liquid modied by HCl as a catalyst for
alkylations of benzene and found that this ionic liquid had
Organic esters are an important class of intermediate species, better catalytic activity in comparison with an anhydrous
1
. Introduction
11
commonly used in ne chemicals, perfumes, medicines, surfac- aluminium chloride catalyst. Lunagariya et al. used a sulfonic
tants, and cosmetics. With the recent increase in consumption, acid group functionalized ionic liquid catalyst for the esteri-
1
there is a great demand for organic esters. In order to reduce the cation of n-butanol with acetic acid and obtained a high
12
reaction temperature and reaction time, strong acid catalysts are conversion. Recently, a class of acidic ionic liquids with both
usually added to accelerate the process. However, due to their Lewis and Brønsted acid sites has received much attention, for
disadvantages such as having difficult separations, being hard to it combined the advantages of Lewis and Brønsted acid
13–16
reuse and causing the corrosion of reactors and pollution, tradi- sites.
As we all know, both Lewis and Brønsted acids can
tional catalysts such as homogeneous acid catalysts (e.g. sulfuric accelerate the process of esterication. For example, Deng et al.
2–4
acid, p-TSA, etc.) are not entirely satisfactory. Besides, some reported that the room temperature ionic liquid 1-butylpyr-
strong solid acid catalysts like Naon resin catalysts show high idinium chloride-aluminium(III) chloride was a good catalyst for
catalytic activity for esterication. Nevertheless, they are known to various esterications, enabling high conversion and selec-
5,6
17
suffer great deactivation easily. Therefore, an efficient and tivity. Gui et al. used three Brønsted acidic ionic liquids as
environment-friendly catalyst is necessary.
catalysts for the esterication of carboxylic acids and obtained
18
Ionic liquids have been proved to be very useful and envi- good carboxylic acid conversion and high selectivity. There-
ronmentally friendly catalysts due to their low vapor pressure fore, the class of ionic liquid, which is both a Lewis and
7,8
and non-ammable nature. On the other hand, ionic liquids, Brønsted acid, is of value for esterications. Nevertheless, some
which are completely composed of ions, can be designed to drawbacks restrict their widespread applications. Firstly, most
possess a denite set of properties. In this manner some acidic ionic liquids have high liquid viscosity, which can increase their
groups like chloride or sulfonic alkyl groups can be introduced mass and heat transfer rate. Secondly, ionic liquid catalysts are
9,10
into ionic liquids. For example, Qiao et al. applied a chlorine- harder to recycle and separate from reaction systems than solid
catalysts, which can increase the number of separation and
neutralization steps. Besides, most ionic liquids are expensive,
School of Chemistry and Chemical Engineering, Jiangsu University, 301 Xuefu Road,
19,20
which can vastly affect the cost of industrialization.
To
Zhenjiang 212013, Jiangsu, P. R. China. E-mail: tshjiang@ujs.edu.cn; Fax: +86-
511-88791800; Tel: +86-0511-88791800
solve these problems, some studies reported the concept of
0
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 32427–32435 | 32427

View Article Online
RSC Advances
Paper
21,22
immobilized ionic liquids.
The immobilization process directing agent in the Zr–SBA-15 synthesis process, was
could transfer the desired properties of the ionic liquid to the purchased from Aldrich Company. 1-methylimidazole (>99%),
carrier and convert the homogeneous catalyst to a heteroge- 1,3-propane sulfone (>99%), zinc chloride, toluene (98%), tet-
neous one, which would greatly reduce waste and pollution.
raethoxy silane (TEOS), zirconium oxychloride, sodium chlo-
Mesoporous molecular sieves (e.g. MCM-41, and SBA-15, etc.) ride, hydrochloric acid (37 wt%), anhydrous ether (98%), methyl
are oen used as excellent carriers due to their large specic alcohol (98%), acetic acid (98%), n-butyl alcohol (98%), benzyl
23,24
surface areas and pore sizes.
Recently, many researchers alcohol (98%) and cyclohexanol (98%), used in the experiment,
have introduced metals or other acid functional groups into were of analytical grade and were purchased from the Shanghai
pore structures to change the properties of mesoporous Chemical Reagent Corporation, China.
25,26
molecular sieves.
For example, Mutlu et al. reported that Zr–
SBA-15 was used as a catalyst for the esterication of cetyl
2.2 Synthesis of Zr–SBA-15
27
alcohol with palmitic acid in 63.1% yield. However, there is
still some efforts required to enhance their performance. The
concept of introducing ionic liquids into mesoporous molec-
ular sieves or metal doped mesoporous molecular sieves
combines the advantages of two materials, which could exhibit
more outstanding performances.
Zr–SBA-15 molecular sieves with different amounts of Zr were
28
synthesized in a self-generated acidic environment. Typically,
ꢀ
2
.0 g of P123 was dissolved in 90 mL of distilled water at 35 C to
form a transparent solution. Then, 1.18 g of NaCl and various
amounts of ZrOCl2 were added to the above solution. Aer
ꢀ
stirring for 2 h at 35 C, 4.5 mL of TEOS was added to the mixed
In this study, a Brønsted and Lewis acid ionic liquid [mim-
solution. The mixture was stirred for 24 h, and then transferred
ps]Cl–ZnCl was synthesized and immobilized on the Zr–SBA-15
2
into a 100 mL Teon-lined autoclave and crystallized for 24 h at
mesoporous molecular sieves for the rst time. The catalytic
activity of Zr–SBA-15/[mim-ps]Cl–ZnCl is investigated in the
2
ꢀ
90
C. Aer cooling to room temperature, the product was

ltered and washed with a large amount of distilled water and
esterication of acetic acid with n-BuOH (or BnOH, Naxol). The
effect of the reaction time, reaction temperature, dose of the
catalyst and reactant molar ratio on the esterication was
systematically studied. The results showed that, among three
kinds of esterication, the esterication of acetic acid with
BnOH on the Zr–SBA-15/[mim-ps]Cl–ZnCl2 catalyst exhibited
the highest acetic acid conversion with 93.6%. The catalytic
ꢀ
dried at 50–60 C for 24 h. The as-synthesized Zr–SBA-15 sample
was heated to 550 C at a heating rate of 2 C min and
calcined at 550 C in air for 6 h to remove the template. The
ꢀ
ꢀ
ꢁ1
ꢀ
resulting sample was denoted as Zr–SBA-15(X), where X is the Si/
Zr molar ratio in the synthesis gel from 40, 20 to 10.
activity of the Zr–SBA-15/[mim-ps]Cl–ZnCl
higher than that of Zr–SBA-15.
2
sample is much
2
.3 Synthesis of [mim-ps]Cl–ZnCl
The synthesis of the Lewis and Brønsted acid ionic liquid [mim-
ps]Cl–ZnCl was carried out according to ref. 16. Briey, 6.1 g of
,3-propane sulfone was added to 30 mL toluene with vigorous
2
2
1
2. Experimental
ꢀ
stirring to obtain a transparent solution at 50 C. Then, 4.1 g of
N-methylimidazole was dropped slowly into the above solution.
2.1 Materials
The poly(ethylene glycol)-block-poly(propylene glycol)-block- Aer stirring for 3 h, the resulting white precipitate was ltered
ꢀ
poly(ethylene glycol) (Pluronic P123), used as the structure- and washed with 25 mL diethyl ether 3 times, and dried at 60 C
2
Scheme 1 A possible synthesis process of [mim-ps]Cl–ZnCl .
32428 | RSC Adv., 2017, 7, 32427–32435
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
for 6 h to obtain the dried sample. Aer that, a stoichiometric
amount of HCl was added slowly to the precursor solid under
stirring to form a transparent solution at room temperature.
ꢀ
The above solution was stirred at 80 C for 3 h and dried under
ꢀ
vacuum at 90 C to generate [mim-ps]Cl. Then, under stirring,
ꢀ
two equiv. of ZnCl
2
was added slowly to [mim-ps]Cl at 80 C for
4
h to form [mim-ps]Cl–ZnCl
2
. According to the above prepa-
ration details, a possible synthesis process of [mim-ps]Cl–ZnCl
2
is displayed in Scheme 1.
2
.4 Synthesis of the Zr–SBA-15/[mim-ps]Cl–ZnCl catalyst
2
2
Zr–SBA-15(X)/[mim-ps]Cl–ZnCl was synthesized according to
the mass ratio of 1 g Zr–SBA-15(X) : 1.5 g [mim-ps]Cl–ZnCl . In
2
a typical preparation process: 6 g of [mim-ps]Cl–ZnCl was
2
ꢀ
added to 50 mL methyl alcohol at 40 C. Aer stirring for
30 min, a transparent solution was obtained, and then 4 g of Zr–
SBA-15(X) was added to the solution. Thereaer, the mixture
was continuously stirred for 24 h at 40 C. Finally, methyl
Scheme 2 The esterification of acetic acid with n-butyl alcohol,
benzyl alcohol and cyclohexanol.
ꢀ
alcohol was distilled, and the resulting solid was washed three
ꢀ
times with 20 mL diethyl ether and dried at 60 C for 12 h.
10.8 g of benzyl alcohol and 0.4 g of catalyst were added to the
above solution. Aer reacting for 5 h, the solution was cooled
down to room temperature and centrifuged to obtain the cata-
lyst. The catalyst was washed with 20 mL of diethyl ether and
2
.5 Characterization
The functional groups of the samples were characterized by FT-IR
spectroscopy using a (Nexus FT-IR 470) spectrometer, made by
Nicolet Corporation (USA) with a KBr pellet technique in the
frequency range of 4000–400 cm . The surface areas and pore
sizes of the samples were measured using a surface area and
porosity analyzer (ASAP 2020 HD88, made by Micromeritics
Instrument Corporation, USA). The surface areas and pore sizes
were calculated using the Brunauer–Emmett–Teller (BET) and
Barrett–Joyner–Halenda (BJH) methods, respectively. The powder
X-ray diffraction (XRD) was performed with a Rigaku D/MAX
ꢀ
dried under 60 C for reuse. The product was analyzed by an SP-
2000 gas chromatograph tted with an SE-54 capillary column
ꢁ
1
coupled with FID. It may be speculated that in the mechanism
of esterication with a solid acid catalyst the protonated
carboxylic acid and the protonated alcohol intermediate
compete to form in the Brønsted and Lewis sites in the solid
29,30
acid catalyst,
and the presence of an ionic liquid could
greatly accelerate this process. A probable mechanism for the
esterication is shown in Scheme 2.
2
500PC instrument using Cu Ka radiation (l ¼ 0.15418 nm),
ꢀ
ꢀ
operated at 40 kV and 50 mA with a scan step of 0.02 from 0.5 to
ꢀ
ꢀ
ꢁ1
5
(2q) at a speed of 1 min . Transmission electron microscopy 3. Results and discussion
(TEM) microphotographs were obtained using a Philips
3.1 XRD analysis
TEMCNAI-12 microscope with an acceleration voltage of 120 kV.
X-ray photoelectron spectroscopy (XPS) measurements were
recorded on an ESCALAB 250 (Thermal Electron Corp.) spec-
trometer equipped with an Al Ka X-ray source, operating at 150 W.
The binding energies were referenced to the C 1s binding energy
at 284.8 eV. The elemental analysis of a sample was determined
using the inductive coupled plasma (ICP) technique (Vista-MPX,
Australia), and the detector was an MPX CCD. The thermal
properties of the samples were measured on a thermogravimetric
The XRD patterns of all of the samples are displayed in Fig. 1. As
shown in Fig. 1, all of the samples had diffraction peaks at ca.
ꢀ
ꢀ
ꢀ
0
.9 , 1.51 , and 1.75 indexed to (100), (110) and (200), respec-
tively. It indicates that all of the samples had a 2D-hexagonal
31
p6mm structure. Furthermore, it is noted from Fig. 1 that
little difference is observed in the XRD patterns of the Zr–SBA-
15(10), Zr–SBA-15(20) and Zr–SBA-15(40) samples, and this
probably suggests that, to some extent, increasing Zr incorpo-
ration does not affect the mesoporous ordering of the samples;
the same results were also observed in ref. 32. However, aer
ꢁ
1
analyser (TGA-DSC, STA 449C) in air (50 mL min ) from 0 to
ꢀ
ꢀ
ꢁ1
8
00 C with a heating rate of 10 C min , held for 5 min and
2
introducing [mim-ps]Cl–ZnCl into the Zr–SBA-15 mesoporous
cooled down to room temperature.
materials, the resulting Zr–SBA-15/[mim-ps]Cl–ZnCl2 samples
had mesoporous structures, but the peak intensities greatly
declined. This may be due to the occupation of the ionic liquid
2.6 Esterication of acetic acid with n-butyl alcohol, benzyl
alcohol and cyclohexanol
33
in the pore structure.
The reaction was carried out in liquid phase under atmospheric
pressure. Taking the esterication of acetic acid with benzyl
alcohol as an example, 6 g of acetic acid was added to a 3-neck
3
.2 Analysis of physical nitrogen adsorption
adsorption–desorption isotherms of all of the samples
condensing tube. Aer heating to the required temperature, are shown in Fig. 2. As shown in Fig. 2, all of the isotherms were
boiling ask equipped with magnetic stirring and a reux The N
2
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 32427–32435 | 32429

View Article Online
RSC Advances
Paper
size gradually increased. Compared to the corresponding
carrier, the specic surface area of the composite catalyst ob-
tained aer loading the ionic liquid greatly decreased and the
average pore size increased a lot. On the other hand, the
amount of Zn ions was detected by ICP-AES, and from this value
the [mim-ps]Cl–ZnCl
Table 1, it is noted that the [mim-ps]Cl–ZnCl
SBA-15(10)/[mim-ps]Cl–ZnCl , Zr–SBA-15(20)/[mim-ps]Cl–ZnCl
2
content was calculated. As shown in
2
content in Zr–
2
2
2
and Zr–SBA-15(40)/[mim-ps]Cl–ZnCl was 44%, 47% and 49%,
respectively.
Fig. 1 XRD patterns of various samples.
3
.3 FT-IR analysis
Fig. 3 displays the FT-IR spectra of Zr–SBA-15(10), [mim-ps]Cl–
ZnCl and Zr–SBA-15(10)/[mim-ps]Cl–ZnCl . The peak at 2961
was caused by the C–H stretching
vibration of straight-chain paraffin. Its exural vibration was
typical IV isotherms with a H1 hysteresis loop as dened by
2
2
34
IUPAC, which was analogous to conventional SBA-15. The
corresponding textural properties are summarized in Table 1,
including surface area, average pore size, and pore volume.
Table 1 shows that with an increase of Zr doping in the silicate
species, the specic surface area decreased and the average pore
ꢁ1
cm for [mim-ps]Cl–ZnCl
2
ꢁ1
ꢁ1
observed at 1337 cm
adsorption bands at 3111 cm and 3154 cm were charac-
and 1460 cm , respectively. The
ꢁ1
ꢁ1
teristic of the C–H stretching vibration of the imidazole ring and
Fig. 2
N
2
adsorption–desorption isotherms of various samples (a) Zr–SBA-15(10); (b) Zr–SBA-15(10)/[mim-ps]Cl–ZnCl
2
; (c) Zr–SBA-15(20); (d)
2
Zr–SBA-15(20)/[mim-ps]Cl–ZnCl ; (e) Zr–SBA-15(40); (f) Zr–SBA-15(40)/[mim-ps]Cl–ZnCl
2
.
32430 | RSC Adv., 2017, 7, 32427–32435
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Table 1 Textural properties of various samples and the ionic liquid content in the composites
[
mim-ps]Cl–ZnCl
2
Surface area
Average pore
size (nm)
Pore volume
2
ꢁ1
3
ꢁ1
Sample
wt%
(m g
)
(cm g
)
1
2
4
1
2
4
0-Zr–SBA-15
0-Zr–SBA-15
0-Zr–SBA-15
0-Zr–SBA-15/[mim-ps]Cl–ZnCl
0-Zr–SBA-15/[mim-ps]Cl–ZnCl
0-Zr–SBA-15/[mim-ps]Cl–ZnCl
—
—
—
44
47
49
716.3
782.0
845.6
49.9
104.7
137.2
5.4
5.0
4.2
7.4
7.6
7.7
0.82
0.90
0.95
0.11
0.22
0.31
2
2
2
3.5 Acidity measurements
Fig. 5 shows the FT-IR spectra of [mim-ps]Cl–ZnCl2 using
ꢁ
1
acetonitrile as a probe. Two characteristic peaks at 2253 cm
ꢁ
1
and 2293 cm were observed in the FT-IR spectra of acetoni-
trile, due to the CN stretching vibrations, while a new absorp-
tion band at 2293 cm appeared when [mim-ps]Cl–ZnCl was
2
ꢁ1
added to acetonitrile. This was attributed to acetonitrile coor-
dinating with the Lewis acid sites, suggesting that [mim-ps]Cl–
ZnCl had Lewis acidity. Fig. 6 presents the FT-IR spectra of
2
[
mim-ps]Cl–ZnCl using pyridine as a probe. The absorption
2
ꢁ
1
peak at 1437 cm was observed in the FT-IR spectra of pyridine.
Furthermore, we found that when [mim-ps]Cl–ZnCl was added
to the pyridine, this band shied to 1450 cm , which was
known as the characteristic peak of pyridine coordinated with
the Lewis acid sites, agreeing with the result of the FT-IR spectra
Fig. 3 FT-IR spectra of Zr–SBA-15(10), [mim-ps]Cl–ZnCl
SBA-15(10)/[mim-ps]Cl–ZnCl
2
and Zr–
2
.
2
ꢁ1
ꢁ
1
the peak at 3411 cm was attributed to water absorbed in the
of [mim-ps]Cl–ZnCl using acetonitrile as a probe. At the same
2
ꢁ
1
ꢁ1
ionic liquid. The adsorption bands at 1637 cm and 1571 cm
were assigned to C]C and C]N bonds. Besides, the bands
around 1038 cm and 1174 cm were attributed to the S]O
time, the characteristic peak of pyridine coordinated with the
ꢁ1
Brønsted acid sites was observed at 1539 cm , which suggested
ꢁ
1
ꢁ1
39
2
that the [mim-ps]Cl–ZnCl had Brønsted acidity.
asymmetric and symmetric stretching vibrations of the –SO H
3
group. Also, it can be noted that the above peaks were observed
3
.6 TG analysis
The TGA curves of the Zr–SBA-15(10) and Zr–SBA-15(10)/[mim-
ps]Cl–ZnCl samples are shown in Fig. 7. A weight loss at
2
in the FT-IR spectra of Zr–SBA-15/[mim-ps]Cl–ZnCl , suggesting
that [mim-ps]Cl–ZnCl was successfully attached to the
2
35,36
2
carriers.
ꢀ
around 100 C was observed for both the catalyst and carrier
and was assigned to the loss of moisture. In contrast to Zr–SBA-
3
.4 XPS analysis
Fig. 4 shows the high-resolution XPS spectra of the Zr–SBA-
5(10)/[mim-ps]Cl–ZnCl sample. As shown in Fig. 4a, it was
1
2
5(10), Zr–SBA-15(10)/[mim-ps]Cl–ZnCl had a more than 30%
ꢀ
ꢀ
weight loss at about 360 C to 600 C and it was attributed to the
1
2
degradation of [mim-ps]Cl–ZnCl2.
noted that the surface of the sample consisted of O, Si, Zr, C,
N, S, Cl and Zn elements. The N, Zn, S, and Cl elements mainly
3
.7 TEM analysis
The TEM images of the Zr–SBA-15(10) and Zr–SBA-15(10)/[mim-
ps]Cl–ZnCl samples are shown in Fig. 8. As shown in Fig. 8a,
came from the immobilized [mim-ps]Cl–ZnCl
2
. The C may be
due to the immobilized [mim-ps]Cl–ZnCl and the C absorbed
2
2
in the air. O, Si and Zr elements were primarily attributed to
Zr–SBA-15. Besides, Fig. 4b shows the XPS Zr 3d high resolu-
clear pore arrays were observed, suggesting the formation of an
ordered mesoporous framework, and this is in agreement with
the results of the XRD and BET. At the same time, it was also
seen from Fig. 8b that Zr–SBA-15/[mim-ps]Cl–ZnCl still had
2
a highly ordered mesoporous structure.
tion spectra of Zr–SBA-15/[mim-ps]Cl–ZnCl with deconvolu-
2
tion peaks. According to Fig. 4b, the binding energy of Zr 3d5/2
was 183.28 eV, which was in close proximity to that of ZrSiO
4
3
7
(
183.3 eV), suggesting that Zr ions were incorporated into
the framework of SBA-15. Furthermore, the XPS Zn 2p high
resolution spectra are presented in Fig. 4c. The binding
3
.8 Catalytic activity
3.8.1 Effect of different catalysts on the esterication.
1021.7 eV), which was probably because the Cl ions in [mim- Table 2 lists the results of the esterication of acetic acid with n-
ps]Cl were combined with ZnCl which increased the binding BuOH, BnOH and Naxol for all of the samples. To evaluate the
energy of Zn 2p3/2 (1022.4 eV) was higher than that of ZnCl
2
(
2
3
8
energy of Zn 2p3/2
Cl–ZnCl
.
This indicated the formation of [mim-ps] performance of these catalysts, the results of the esterication
of acetic acid with n-BuOH, BnOH and Naxol over concentrated
2
.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 32427–32435 | 32431

View Article Online
RSC Advances
Paper
Fig.
a probe (a) [mim-ps]Cl–ZnCl
mim-ps]Cl–ZnCl where acetonitrile is 2/3 as a mole fraction.
5
FT-IR spectra of [mim-ps]Cl–ZnCl
2
using acetonitrile as
2
; (b) pure acetonitrile; (c) acetonitrile/
[
2
Fig. 6 FT-IR spectra of [mim-ps]Cl–ZnCl
mim-ps]Cl–ZnCl ; (e) pyridine/[mim-ps]Cl–ZnCl
as a mole fraction; (f) pure pyridine.
2
using pyridine as a probe (d)
[
3
2
2
where pyridine is 2/
Fig. 7 TGA curves of the Zr–SBA-15(10) and Zr–SBA-15(10)/[mim-ps]
Cl–ZnCl samples.
2
Table 2, Zr–SBA-15(10) exhibited the highest catalytic activity
among the three Zr–SBA-15 catalysts for three different esteri-

cations, along with an acetic acid conversion of 61.7%, 63.3%
and 55.9% with n-BuOH, BnOH and Naxol, respectively. The
catalytic activities of the three Zr–SBA-15 catalysts are much
higher than that of the SBA-15 catalyst. However, it was noted
that the catalytic activities of the three Zr–SBA-15/[mim-ps]Cl–
Fig.
4 XPS spectra of several Zr–SBA-15(10)/[mim-ps]Cl–ZnCl
2
samples (a) survey of samples; (b) Zr 3d; (c) Zn 2p.
ZnCl
corresponding carriers, which may be due to the introduction of
mim-ps]Cl–ZnCl into the Zr–SBA-15 samples, leading to an
increase in the amount of acid in the resulting samples. Among
all of the samples, Zr–SBA-15(10)/[mim-ps]Cl–ZnCl exhibited
2
samples were signicantly enhanced compared to their
sulfuric acid, SBA-15 and a pure ionic liquid were carried out
and are also listed in Table 2. In these reactions, a 1.2 : 1 molar
ratio of the alcohol to acetic acid (6 g) and 0.4 g of the catalyst
[
2
2
were added into the reactor sequentially; the reaction time was
ꢀ
the highest catalytic activity in the three types of esterication
3
00 min and the reaction temperature was 100 C. According to
32432 | RSC Adv., 2017, 7, 32427–32435
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Fig. 9 The effect of temperature on esterification of acetic acid with
Fig. 8 TEM images of (a) Zr–SBA-15(10) and (b) Zr–SBA-15(10)/[mim-
ps]Cl–ZnCl .
2
n-BuOH, BnOH and Naxol over Zr–SBA-15(10)/[mim-ps]Cl–ZnCl
2
catalyst (reaction condition: catalyst dose ¼ 0.4 g; time ¼ 300 min;
nalcohol/nacetic acid ¼ 1.2).
under comparable conditions, and gives a maximum acetic acid
conversion of 89.7, 93.6, and 84.9% with n-BuOH, BnOH and 120 C, which is probably due to the enhancement of some side-
Naxol, respectively. Furthermore, according to Table 2, we reaction (e.g. dehydration of alcohol to ether).
found that the catalytic activity of concentrated sulfuric acid for
3.8.3 Effect of molar ratio of alcohol to acetic acid. The
ꢀ
40
the three esterications was low compared to the three results of effect of the molar ratio of alcohol to acetic acid on the
composite catalysts. On the other hand, 0.176 g of pure ionic esterication of acetic acid with n-BuOH, BnOH and Naxol over
liquid was also applied as the catalyst which is the same ionic the Zr–SBA-15(10)/[mim-ps]Cl–ZnCl
catalyst are shown in
2
liquid content in Zr–SBA-15(10)/[mim-ps]Cl–ZnCl
2
. The results Fig. 10. Obviously, a common trend for the three esterications
showed that the acetic acid conversions were much lower than is that the conversion of acetic acid increased as the molar ratio
those for Zr–SBA-15(10)/[mim-ps]Cl–ZnCl , at 76.0, 80.8, and of alcohol to acetic acid increased from 1.1 to 1.2, and then
2
74.1% with n-BuOH, BnOH and Naxol, respectively.
gradually decreased from 1.2 to 1.8. The decrease in acetic acid
3
.8.2 Effect of temperature on the esterication. Fig. 9 conversion may be due to excess alcohol in the reactant,
shows the effect of temperature on the esterication of acetic resulting in the dilution of acetic acid and the catalyst. In
acid with n-BuOH, BnOH and Naxol over Zr–SBA-15(10)/[mim- particular, a maximum conversion of acetic acid was noted
ps]Cl–ZnCl
7
2
at various reaction temperatures, ranging from when the molar ratio of alcohol to acetic acid was 1.2. Among
0 C to 120 C. In the three esterications, we found from Fig. 9 the three esterications, the conversion of acetic acid in the
ꢀ
ꢀ
that the conversion of acetic acid gradually increased with esterication of acetic acid with BnOH is the highest and
ꢀ
ꢀ
temperature from 70 C to 100 C. This may be because the reached 93.6%, suggesting that Zr–SBA-15(10)/[mim-ps]Cl–
increase in the reaction temperature could enhance the ZnCl is a promising catalyst for the esterication of acetic acid
2
molecular collisions and the miscibility of the reactants. When with BnOH.
ꢀ
the reaction temperature was increased to 100 C, the conver-
3.8.4 Effect of catalyst dose on the esterication. The effect
sion of acetic acid in the esterication of acetic acid with n- of the catalyst dose on the esterication of acetic acid with n-
BuOH, BnOH and Naxol over Zr–SBA-15(10)/[mim-ps]Cl–ZnCl
was 89.7%, 93.6% and 84.9%, respectively. Further, it was noted ZnCl
2
BuOH, BnOH and Naxol over the Zr–SBA-15(10)/[mim-ps]Cl–
2
catalyst is shown in Fig. 11. The acetic acid conversion in
that the conversion of acetic acid in all cases remained almost the three esterications quickly increased as the amount of
ꢀ
unchanged with the increase in temperature from 100 C to catalyst increased from 0.1 to 0.4 g, maybe owing to the increase
a
Table 2 Catalytic activities of the different catalysts
Conversion of acetic
acid with n-BuOH (%)
Conversion of acetic
acid with BnOH (%)
Conversion of acetic
acid with Naxol (%)
Catalyst
Zr–SBA-15(10)
Zr–SBA-15(20)
Zr–SBA-15(40)
Zr–SBA-15(10)/[mim-ps]Cl–ZnCl
Zr–SBA-15(20)/[mim-ps]Cl–ZnCl
Zr–SBA-15(40)/[mim-ps]Cl–ZnCl
61.7
54.5
41.3
89.7
88.9
88.3
76.0
83.5
22.7
63.3
58.4
49.0
93.6
93.1
92.1
80.8
90.0
30.3
55.9
49.7
32.7
84.9
83.7
82.1
74.1
80.9
20.1
2
2
2
[
mim-ps]Cl–ZnCl
2
Concentrated sulfuric acid
SBA-15
a
All error ranges were within 1%. Product selectivity using the composite catalysts for BnOH and Naxol was higher than 99%. Product selectivity for
n-BuOH was around 96%.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 32427–32435 | 32433

View Article Online
RSC Advances
Paper
Fig. 12 The effect of reaction time on the esterification of acetic acid
with n-BuOH, BnOH and Naxol over the Zr–SBA-15(10)/[mim-ps]Cl–
Fig. 10 The effect of the molar ratio of alcohol to acetic acid on the
esterification of acetic acid with n-BuOH, BnOH and Naxol over the
ZnCl
2
catalyst (reaction conditions: nalcohol/nacetic acid ¼ 1.2; catalyst
2
Zr–SBA-15(10)/[mim-ps]Cl–ZnCl catalyst (reaction conditions: cata-
ꢀ
ꢀ
dose ¼ 0.4 g; temperature ¼ 100 C).
lyst dose ¼ 0.4 g; time ¼ 300 min; temperature ¼ 100 C).
of active sites in the catalyst caused by the increase in the
catalyst dose. However, the acetic acid conversion was almost
unchanged when the catalyst dose was in the range of 0.4–0.8 g.
This might due to the esterication reaching equilibrium when
the catalyst dose is 0.4 g.
3
.8.5 Effect of reaction time on the esterication. The
esterication of acetic acid with n-BuOH, BnOH and Naxol over
the Zr–SBA-15(10)/[mim-ps]Cl–ZnCl catalyst was carried out for
2
a reaction time of 420 min and the results are presented in
Fig. 12. As shown in Fig. 12, we found that, in all cases, the
acetic acid conversion quickly increased within 180 min, and
then gradually increased to a maximum of 89.7, 93.6, and 84.9%
for n-BuOH, BnOH and Naxol in 300 min, respectively. The
acetic acid conversion in the three esterications was almost
unchanged in the reaction time range of 300–420 min, sug- catalyst (reaction conditions: nalcohol/n
Fig. 13 The reusability of the Zr–SBA-15(10)/[mim-ps]Cl–ZnCl
2
acetic acid
ꢀ
¼ 1.2; catalyst dose ¼
gesting that the esterication reaction reached equilibrium in 0.4 g; time ¼ 300 min; temperature ¼ 100 C).
300 min.
under optimal experimental conditions and the results are
shown in Fig. 13. According to Fig. 13, it is noted that the acetic
3.9 Reusability of the catalyst
The reusability of the Zr–SBA-15(10)/[mim-ps]Cl–ZnCl
2
catalyst acid conversion decreased from 93.6% to 89.1% aer 5 recycling
was evaluated using the esterication of acetic acid with BnOH runs, a decrease of only 4.5% in acetic acid conversion. This
suggested that the Zr–SBA-15(10)/[mim-ps]Cl–ZnCl catalyst has
2
good stability and reusability. The decrease in acetic acid
conversion may be due to the loss of the Zr–SBA-15(10)/[mim-
ps]Cl–ZnCl catalyst during the recycling.
2
4. Conclusions
Zr–SBA-15 mesoporous molecular sieves with different Si/Zr
molar ratios were hydrothermally synthesized and several Zr–
SBA-15/[mim-ps]Cl–ZnCl
ionic liquids were synthesized by the wet impregnation method.
physical adsorption, XRD and TEM analysis revealed that the
resulting Zr–SBA-15/[mim-ps]Cl–ZnCl catalysts still had good
2
catalysts with Brønsted–Lewis acidic
N
2
2
mesoporous frameworks. Compared to the Zr–SBA-15 meso-
porous molecular sieve, the catalytic activity of the Zr–SBA-15/
Fig. 11 The effect of catalyst dose on the esterification of acetic acid
with n-BuOH, BnOH and Naxol over the Zr–SBA-15(10)/[mim-ps]Cl–
2
[mim-ps]Cl–ZnCl catalyst in the esterication of acetic acid
ZnCl
2
catalyst (reaction conditions: nalcohol/nacetic acid ¼ 1.2; time ¼
ꢀ
3
00 min; temperature ¼ 100 C).
with n-BuOH, BnOH and Naxol was obviously enhanced. The
32434 | RSC Adv., 2017, 7, 32427–32435
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
optimal reaction conditions are as follows: the molar ratio of 17 Y. H. Deng, F. Shi, J. J. Beng and K. Qiao, J. Mol. Catal. A:
alcohol to acetic acid ¼ 1.2, time ¼ 300 min, temperature ¼
Chem., 2001, 165, 33–36.
ꢀ
1
00 C, and catalyst dose ¼ 0.4 g. Under comparable conditions, 18 J. Z. Gui, X. H. Gong, D. Liu, X. T. Zhang, Z. D. Hu and
the Zr–SBA-15(10)/[mim-ps]Cl–ZnCl catalyst exhibited the
Z. L. Sun, Catal. Commun., 2004, 5, 473–477.
2
highest catalytic activity among the three esterications and 19 C. V. Doorslaer, J. Wahlen, P. Mertens, K. Binnemans and
a maximum acetic acid conversion of 93.6% was achieved in the D. D. Vos, Dalton Trans., 2010, 39, 8377–8390.
esterication of acetic acid with BnOH. Zr–SBA-15/[mim-ps]Cl– 20 H. Li, P. S. Bhadury, B. A. Song and S. Yang, RSC Adv., 2012,
ZnCl is a promising catalyst for the esterication of acetic acid 2, 12525–12551.
with BnOH. The reusability test suggested that Zr–SBA-15/[mim- 21 A. Riisager, R. Fehrmann, M. Haumann and
2
ps]Cl–ZnCl had good stability.
P. Wasserscheid, Top. Catal., 2006, 40, 91–102.
2
2
2
2 C. Y. Yuan, Z. W. Huang and J. Chen, Catal. Commun., 2012,
24, 56–60.
Acknowledgements
3 J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz,
C. T. Kresge, K. D. Schmitt, C. T.-W. Chu, D. H. Olson,
E. W. Sheppard, S. B. McCullen, J. B. Higgins and
J. L. Schlenkert, J. Am. Chem. Soc., 1992, 114, 10834–10843.
4 M. Kruk, M. Jaroniec, C. H. Ko and R. Ryoo, Chem. Mater.,
Financial support from Project supported by the National
Natural Science Foundation of China (51572115) is gratefully
acknowledged.
2
2
2
2
2
2
2000, 12, 1961–1968.
5 Q. Zhao, X. P. Zhou, M. R. Ji, D. L. Wu, T. S. Jiang and
H. B. Yin, Colloids Surf., A, 2011, 384, 513–518.
6 S. Kaiprommarat, S. Kongparakul, P. Reubroycharoen,
G. Q. Guan and C. Samart, Fuel, 2016, 174, 189–196.
7 V. N. Mutlu and S. Yilmaz, Appl. Catal., A, 2016, 522, 194–
References
1
2
3
4
5
6
7
8
9
S. R. Kirumakki, N. Nagaraju, K. V. V. S. B. S. R. Murthy and
S. Narayanan, Appl. Catal., A, 2002, 226, 175–182.
T. S. Jiang, Q. Zhao, M. Li and H. B. Yin, J. Hazard. Mater.,
2008, 159, 204–209.
2
00.
8 S. Y. Chen, L. Y. Jang and S. Cheng, Chem. Mater., 2004, 16,
174–4180.
9 W. L. Chu, X. G. Yang, X. K. Ye and Y. Wu, Appl. Catal., A,
996, 145, 125–140.
S. Zheng, M. Kates, M. A. Dub ´e and D. D. McLean, Biomass
Bioenergy, 2006, 30, 267–272.
D. E. L ´o pez, K. Suwannakarn, D. A. Bruce and J. G. Goodwin,
J. Catal., 2007, 247, 43–50.
J. Gangadwala, S. Mankar and S. Mahajani, Ind. Eng. Chem.
Res., 2003, 42, 2146–2155.
M. Mazzotti, B. Neri, D. Gelosa, A. Kruglov and
M. Morbidelli, Ind. Eng. Chem. Res., 1997, 36, 3–10.
M. Petkovic, K. R. Seddon, L. P. N. Rebelo and C. S. Pereira,
Chem. Soc. Rev., 2011, 40, 1383–1403.
4
1
3
3
0 H. T. R. Teo and B. Saha, J. Catal., 2004, 228, 174–182.
1 D. Y. Zhao, J. Y. Sun, Q. Z. Li and G. D. Stucky, Chem. Mater.,
2
000, 12, 275–279.
2 S. Y. Chen, J. F. Lee and S. F. Cheng, J. Catal., 2010, 270, 196–
05.
3
3
3
3
3
3
2
3 B. Zhou, D. H. Yu, J. J. Xia, S. S. Tang, W. M. Liu and
H. Huang, Biochem. Eng. J., 2010, 53, 150–153.
4 Y. C. Du, S. Liu, Y. L. Zhang, F. Nawaz, Y. Y. Ji and F. S. Xiao,
Microporous Mesoporous Mater., 2009, 121, 185–193.
5 C. Cai, H. Wang and J. Y. Han, Appl. Surf. Sci., 2011, 257,
N. V. Plechkova and K. R. Seddon, Chem. Soc. Rev., 2008, 37,
1
23–150.
T. Welton, Coord. Chem. Rev., 2004, 248, 2459–2477.
0 J. Dupont, R. F. Souza and P. A. Z. Suarez, Chem. Rev., 2002,
02, 3667–3692.
1 K. Qiao and Y. Q. Deng, J. Mol. Catal. A: Chem., 2001, 171, 81–
4.
2 J. Lunagariya, A. Dhar and R. L. Vekariya, RSC Adv., 2017, 7,
412–5420.
1
1
1
1
1
9802–9808.
6 L. Zhang, Y. D. Cui, C. P. Zhang, L. Wang, H. Wan and
G. F. Guan, Ind. Eng. Chem. Res., 2012, 51, 16590–16596.
7 D. J. Jones, J. J. Jim ´e nez, A. J. L ´o pez, P. M. Torres,
P. O. Pastor, E. R. Castell ´o nb and J. Rozi `e re, Chem.
Commun., 1997, 431–432.
8
5
3 X. Y. Jiang, W. D. Ye, X. H. Song, W. X. Ma, X. J. Lao and
R. P. Shen, Int. J. Mol. Sci., 2011, 12, 7438–7444.
3
3
8 J. C. Klein and D. M. Hercules, J. Catal., 1983, 82, 424–441.
9 Y. L. Yang, X. H. Wang and Y. Kou, Chem. Commun., 2004,
1
1
4 X. Z. Liang and C. Z. Qi, Catal. Commun., 2011, 12, 808–812.
5 K. P. Boroujeni and P. Ghasemi, Catal. Commun., 2013, 37,
226–227.
5
0–54.
6 N. Azizi, M. A. Senejani and F. Abbasi, Tetrahedron Lett.,
016, 57, 5009–5011.
4
0 J. Z. Gui, X. H. Cong, D. Liu, X. T. Zhang, Z. D. Hu and
Z. L. Sun, Catal. Commun., 2004, 5, 473–477.
1
2
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 32427–32435 | 32435