Hydrophilic sulfonic acid-functionalized micro-bead silica for dehydration of sorbitol to isosorbide

Article abstract of DOI:10.1039/c5ra27510e

Different (3-mercaptopropyl)trimethoxysilane (MPTS) loadings of sulfonic acid-functionalized micro-bead silica (SA-SiO₂) were prepared by silylation and oxidation, and characterized by elemental analysis, SEM, FT-IR, TGA, NH₃-TPD, BET N₂ adsorption-desorption and ¹³C NMR CP/MAS. The as-prepared SA-SiO₂ showed strong hydrophilic nature and excellent catalytic performance for dehydration of sorbitol to isosorbide. The selectivity to isosorbide is obviously affected by the MPTS loading. Using SA-SiO₂ as a solid catalyst with 60.5% MPTS loading, 100% sorbitol conversion and 84% yield of isosorbide are achieved at 120 °C for 10 h under vacuum. The catalyst was reused 10 times without noticeable loss of activity and selectivity.

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PAPER
Hydrophilic Sulfonic Acid- Functionalized Micro-Bead Silica for
Dehydration of Sorbitol to Isosorbide
Received 00th January 20xx,
Accepted 00th January 20xx
Jun Shi, Yuhua Shan*, Yuan Tian, Yu Wan, Yitian Zheng and Yangyang Feng
Different (3-Mercaptopropyl) trimethoxysilane (MPTS) loadings of sulfonic acid-functionalized micro-bead silica (SA-SiO2)
were prepared by silylation and oxidation, and characterized by Elemental analysis, SEM, FT-IR, TGA, NH3-TPD, BET N2
adsorption-desorption and 13C NMR CP/MAS. The as-prepared SA-SiO2 showed high hydrophilic nature and excellent
catalytic perfomance for dehydration of sorbitol to isosorbide. The selectivity to isosorbide is obviously affected by the
MPTS loading. Using SA-SiO2 as a solid catalyst with 60.5% MPTS loading, 100% sorbitol conversion and 84% yield of
isosorbide are achieved at 120 ℃ for 10 h under vacuum. The catalyst was reused for 10 times without noticeable loss of
activity and selectivity.
DOI: 10.1039/x0xx00000x
www.rsc.org/advances
catalysts have been reported with different yields of isosorbide
at suitable temperatures, such as sulfated copper oxides (67.3%,
Introduction
200
oxide (65%, 180
molten salt hydrate medium (85%, 200
Amberlystꢀ15 resin (71.8%, 250
).31
However, most of these catalysts require comparatively high
reaction temperature (200ꢀ300 ) and yield of isosorbide is not
℃
),17 sulphated zirconia (61%, 210
℃
),24 sulfated tin
),28
and
With environmental concerns, use of green and renewable
raw materials to produce chemicals has become the trend of the
times. Therefore, the interest in biomass conversion into
chemicals increased rapidly during the last few years.1ꢀ6 Today,
sorbitol, can be conveniently obtained from cellulose
(considered the most abundant and cheap carbon source
glucose, is one of the “top ten” platform chemicals in
biorefinery by US Department of Energy,10ꢀ14 and its most
popular dehydrated production is isosorbide15
platform chemical for the replacement of traditional oil
resource products in the future.16ꢀ20
℃
),25 metal phosphate (70.3%, 250
℃
29, 30
℃
),27,
℃
℃
7ꢀ9
)
via
high. Therefore, the development of efficient solid acid catalyst
which catalyzed this reaction at moderate reaction conditions
and obtained high yield of isosorbide is highly desirable.
Polymerꢀsupported Brønsted acid catalysts: SO3H–PS–
- an important
SO3H32 have been used for dehydration of sorbitol at 150
℃,
with a maximum yield of 1,4ꢀanhydroꢀDꢀsorbitol of 90% within
4 h. However, the yield of isosorbide is not high. Alternatively,
a super hydrophobic mesoporous acid catalyst named as Pꢀ
SO3H has been synthesized and used for dehydration of sorbitol
to isosoride,33 with a maximum yield (87%) of isosorbide at
The dehydration of sorbitol to isosorbide (Scheme 1) is
conventionally using liquid acid like sulphuric acid,
hydrochloric acid and pꢀtoluenesulfonic acid as a homogeneous
catalyst in industrial production, which provides a yield of
isosorbide (70ꢀ77%) at 130
℃ under high vacuum conditions
140
℃ within 10 h. Although these hydrophobic polymerꢀ
within a few hours.21 But use of homogeneous catalysts
introduces many troubles such as difficulties in product
separation, a corrosive hazardous for the reactors and catalyst
regeneration from the reaction system.20 Without adding any
acid catalyst, dehydration of sorbitol in high temperature water
supported sulfonic acid catalysts show high yield, they are
deactivation quickly for their surface affinity to humins and
cokings.
The silica sulfuric acid (SSA) catalysts have widely been
studied for a great number of acid catalyzed organic reactions
due to their heterogeneous nature, cheapness and availability of
the reagent.34 A simple in situ method to prepare waterꢀstable
acidic mesoporous sulfonated silica without any surfactant or
template was reported by Hasan,35 and it has good catalytic
performance of hydrolysis and alkylation reaction. Microꢀbead
silica has the advantage of hydrophilic, high BETꢀsurface area
and special porous structure.36, 37 And chemical bond linking
method has good prospects for industrial application since it
can fix the organic groups on the carrier surface firmly.38, 39 In
this work, we report a simple and lowꢀcost synthesis of a
hydrophilic sulfonic acidꢀfunctionalized microꢀbead silica
(250ꢀ300
℃) for 1 h, 57% yield of isosorbide was obtained,
reported by Yamaguchi et al.20, 22 In addition, dehydration of
pure sorbitol under microwave at 160
℃ showed sorbitol
conversion and isosorbide selectivity of 100% and 60%,23
respectively.
Therefore, the research of sorbitol dehydration has been
focused on developing solid acid catalysts.17, 24ꢀ27 Many solid
Advanced catalysis and Green Manufacturing Collaborative Innovation Center,
Changzhou University, Changzhou 213164, China E-mail: yhshan@cczu.edu.cn
Electronic Supplementary Information (ESI) available. See
DOI: 10.1039/x0xx00000x
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Scheme 1 Reaction pathway of sorbitol dehydration.
catalyst named SAꢀSiO2 and evaluated its catalytic performance route is shown in Scheme 2(A). The X represents the amount of
in dehydration of sobitol to isosorbide in solvent free condition. MPTS loading. As a typical run, 20.0 g microꢀbead silica (after
As we expected, the SAꢀSiO2 gives good sorbitol conversion washing with nitrate and roasting at 250
℃ ) and 100 ml
and isosorbide selectivity, excellent recyclability, compared anhydrous toluene was charged into the flask and stirred for 30
with those reported catalysts.
min at room temperature. After adding 12.10 g MPTS, the
mixture was refluxed under nitrogen over night.38 Then, 20.94 g
hydrogen peroxide and 3.50 g acetic acid was added dropwise
and stirred for another 6 h. After washing thoroughly with
acetonitrile (after drying by CaH2 and redistilled) for 5 times
and drying at 0.09 MPa for 5 h, the final product designated as
SAꢀSiO2ꢀ60.5 was obtained.
By adjusting the ratio of MPTS to microꢀbead silica,
different SAꢀSiO2ꢀX was obtained. For example, the catalyst
loading of 60.5% MPTS was represented as SAꢀSiO2ꢀ60.5. The
elemental analysis of the SAꢀSiO2 catalysts is shown in Table
1S.
Experimental Details
Materials
Hβ (Si/Al=25), HZSMꢀ5 (Si/Al=40), MCMꢀ49 (Si/Al=30) were
bought from Chinese NanKai University. Microꢀbead silica
(280~600µm) were purchased from Qingdao Haiyang Chemical
Co., Ltd. (3ꢀMercaptopropyl) trimethoxysilane (MPTS) were
purchased from Shanghai Ziyiꢀreagent Chemical Co., Ltd.
Amberlystꢀ15 resin was purchased from Shanghai Host
Chemical Co., Ltd. Calcium hydride (CaH2), hydrogen
peroxide (30% H2O2), hydrochloric acid (37% HCl), sulfuric
acid (98% H2SO4), acetic acid, acetonitrile, toluene, glycol
dimethyl ether, tergitol(tm)xhꢀ(nonionic) (P123) and tetraethyl
orthosilicate (TEOS) were bought from SCRC (Sinopharm
Chemical Reagent Co., Ltd, Shanghai).
Synthesis of SBA-15-SO3H. The synthesis was carried out
according to an established procedure,33 and the synthetic route
is shown in Scheme 2(B). As a typical run, 2.00 g P123 was
dissolved in 39.75 g deionized water, and stirred for 2 h at room
temperature. Then 30.0 g H2O was added and stirred for
another 1 h. After adding 3.84 g TEOS, the mixture was
continued to stir for 45 min. Next, 0.40 g MPTS and 4.15 g
Catalyst preparation
H2O2 was added sequentially and stirred for 24 h at 40
last, the mixture was transferred into a hydrothermal reaction
kettle and maintained at 100 for 24 h. The template (P123)
℃. At
Synthesis of SA-SiO2-X. The SAꢀSiO2ꢀX, sulfonic acidꢀ
functionalized microꢀbead silica with different acid
concentrations were prepared by loading different amount of
MPTS according to the previous report,40 and the synthetic
℃
was removed by soxhlet extraction by the mixture of
(A)
Si
Si
Si
Si
OH
OH
OH
Si
Si
Si
O
O
O
O
O
H2O2
HAc.
reflux
Si
Si
O
O
Si
SO3H
Si
SH
Si
SH
O
O
toluene
(SA-SiO2-X)
(MPTS)
(B)
O
O
O
O
O
O
H2O2
heating
OH
OH
OH
TEOS
stirring
HCl
Si
SO3H
P 123
H2O
Si
SH
(MPTS)
(SBA-15-SO3H)
Scheme 2 Synthetic route of SA-SiO2-X and SBA-15-SO3H.
2 | J. Name., 2012, 00, 1-3
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Fig. 1 FT-IR spectra of SA-SiO2 catalyst. (a) SA-SiO2-60.5, (b) SA-SiO2-
Scheme 3 The process of sorbitol dehydration to isosorbide.
60.5 after ten recycles.
hydrochloric acid and ethanol (VHCl/Vethanol=2/100). The final
product designated as SBAꢀ15ꢀSO3H was obtained after drying
at 60
℃for 8 h.
Catalyst characterization
NMR spectra were collected by using a Bruker instrument
(Avance
Ⅲ 500MHz). The Brunauer–Emmett–Teller (BET)
surface areas of catalysts were calculated according to the
nitrogen adsorption–desorption isotherms method using
Micromeritics ASAP2010C equipment. And before this
analysis,41 the samples were degassed at 150
℃for at least 10 h
to remove the moisture and volatile impurities. Pore size
distribution and pole volume were determined by the Density
functional theory method. FTꢀIR spectra were carried out using
a Bruker FTꢀIR spectrometer (TENSOR27) with a high
temperature vacuum chamber.42 Thermogravimetric analysis
(TGA) measurements were carried out by a SDT Q600
instrument in the nitrogen atmosphere and the constant heating
Fig. 2 SEM images of (a) and (c) micro-bead silica, (b) and (d) SA-
SiO2-60.5.
rate was 10
℃
minꢀ1. NH3ꢀTPD was carried out in the BEꢀCATꢀ
Bꢀ82 instrument equipped with a thermal conductivity detector.
The scanning electron microscopy (SEM) experiments were
used by scanning electron microscope (SUPRA 55
SAPPHIRE). The composition of the catalysts were analyzed
by inductively coupled plasma analysis (ICP) using
V0: Standard NaOH solution volume consumed by blank
sample (ml).
V1: Standard NaOH solution volume consumed by test
sample (ml).
CNaOH: Concentration of standard NaOH solution (mol/L).
W: Weight of test sample (g).
PerkinElmer 2400 Series
Ⅱ CHNS device. The surface
hydrophilicity of catalyst was measured by liquid contact angle
measurement using Drop Shape Analyzer (DSA100ꢀKRÜSS
GmbH). The operation was carried out according the procedure:
SAꢀSiO2 powders were pressed into a sheet then the sheet and
Catalyst performance evaluation and product analysis
The catalytic reaction was carried out in a 250 mL roundꢀ
bottom flask equipped with a vacuum pump (in order to
maintain the reaction pressure below 1000 Pa) with a magnetic
stirrer (300 r.p.m.). Sorbitol (50 g) was added in a threeꢀneck
sorbitol/ isosorbide were putted in 100
℃constant temperature
box for 1 h The molten sorbitol/ isosorbide were dropped onto
.
the SAꢀSiO2 sheet surface rapidly and take the picture quickly.
Diagram of the apparatus is shown in Fig. S6.
The acidity of the SAꢀSiO2 catalysts was determined by acidꢀ
base titration in ultrasonic pool, according to the following
definition:
flask, followed by heating at 100
℃ to yield clear melt. Then,
the catalyst was added and the reactor was heated to reaction
temperature with an oil bath pot. During the heating reaction,
water was continuously removed off under reduced pressure to
promote the reaction equilibrium shift to the positive direction.
Total acidity ꢀ ꢁVꢂ ꢃ Vꢄꢅ ꢆ Cꢇꢈꢉꢊ /W
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Fig. 4 DSC-TGA curves of SA-SiO2-60.5
Catalyst characterization
The sulfonic acidꢀfunctionalized catalyst was characterized by
various physicochemical analyses. Fig.1 shows FTꢀIR spectra
of SAꢀSiO2ꢀ60.5 and SAꢀSiO2ꢀ60.5 after ten recycles. The
oxidation product of MPTS displays characteristic bands at
1360~960 cmꢀ1 and 800~510 cmꢀ1. The bands at 601 cmꢀ1 and
526 cmꢀ1 indicate the presence of CꢀS stretching vibrations
bond, while the absorbance peak at about 1170 cmꢀ1 is
associated with a sulfonic acid group because of the presence of
O=S=O bond.43 The strong and broad peak at around 3440 cmꢀ1
is assigned to the stretching vibration of –OH. Furthermore, the
SAꢀSiO2ꢀ60.5 catalyst shows absorbance peaks at 688, 601, and
526 cmꢀ1. In addition, these absorbance peaks all show red
shifts due to the electron inductive effect of O=S=O double
band.44 All the results indicate successful introduction of
sulfonic acid groups in the SAꢀSiO2ꢀ60.5 sample.
Fig. 3 13C NMR CP/MAS spectrum of SA-SiO2-60.5 and its precursor.
Products were analyzed by HPLC (Agilent LC1260)
equipped with a Zorbax NH2 column (4.6*200mm, 5µm
particle size) and an Evaporative Lightꢀscattering Detector
(ELSD). The sugar products were separated by reversedꢀphase
mode. The mobile phase was acetonitrileꢀwater (80:20) with a
flow rate of 0.5 ml/min. The column was thermostated at room
temperature. The selectivity or yield of sorbitan or isosorbide
was based on molar composition. The isolated yield is
calculated by the following definition:
The SEM images of SiO2 and SAꢀSiO2ꢀ60.5 are shown in
Fig. 2. From the SEM images, it can be seen that the surface of
SAꢀSiO2ꢀ60.5 catalyst is rough while that of the microꢀbead
silica is relatively smooth. It is caused by the sulfonic acid
groups chemically bonded on the microꢀbead silica.
The (CP/MAS) 13CꢀNMR spectrum of SAꢀSiO2ꢀ60.5 and its
precursor (unoxidized product) is shown in Fig. 3. The
chemical shifts of saturated carbon are generally at 0~70, while
that of the unsaturated carbon are usually at 100~165. As
shown in Fig. 3A, the chemical shift peaks at 16.49 and 23.42
are associated with the saturated carbon atom attached to a
silicon atom and saturated carbon atom attached to a carbon
atom of both ends, respectively. At last, the chemical shift peak
at 58.95 is the saturated carbon atom attached to an oxidized
sulphur atom.45 Compared with that shown in Fig. 3A, Fig. 3B
shows the chemical shift peak at 47.61, which is associated
with a saturated carbon atom attached to an unoxidized sulphur
atom. Interestingly the peaks of other carbon atoms in Fig. 3B
show red shifts because of the oxidation of sulphur atom. In a
word, we can confirm that the product of MPTS loading is
oxidized and propylꢀsulfonic acid group is connected to SiO2
by chemical bonding successfully
yieldꢋꢌꢍꢎꢈꢏꢐꢑ
ꢀ
ꢁmol of isolated productꢅ/ꢁmol of sorbitolꢅ ꢆ 100%
Procedure for catalyst regeneration
To better test the stability of used catalyst, regeneration was
performed with the following procedure: After reaction, the
used catalyst was recycled by filtration, and washed in
ultrasonic pool with water, glycol dimethyl ether, and water,
sequentially to remove the coke formed in reaction, then dried
at 100
℃ for the next run.
Results and discussion
4 | J. Name., 2012, 00, 1-3
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Table 1 The textural and acidic parameters of various acid catalysts.
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Acidity density
(µmol/m2)
SBET
Vp
Mean Dp
(nm)
Total acidity
(µmol/g) a
Entry
Catalyst
(m2/g)
(cm3/g)
c
c
1
Microꢀbead silica
SAꢀSiO2ꢀ10.6
SAꢀSiO2ꢀ22.5
SAꢀSiO2ꢀ33.1
SAꢀSiO2ꢀ40.9
SAꢀSiO2ꢀ52.0
SAꢀSiO2ꢀ60.5
SAꢀSiO2ꢀ71.9
SAꢀSiO2ꢀ83.3
H2SO4
350.9
345.0
310.3
273.7
221.1
160.5
140.9
109.7
48.3
0.84
0.68
0.51
0.43
0.39
0.33
0.29
0.17
0.09
11.3
11.1
10.5
9.9
_
_
2
230
340
490
610
710
840
970
1290
20000
4530
810
490
320
435
790
150
0.66
1.10
1.79
2.76
4.42
5.96
8.84
26.71
3
4
5
9.6
6
8.1
7
7.3
8
6.0
9
4.9
c
c
c
c
10
11
12
13
14
15
16
17
_
_
_
_
Amberlystꢀ15
SBAꢀ15ꢀSO3H
Hβ (25)
49.1
0.29
0.92
0.25
0.14
0.46
0.26
0.69
40.0
3.8
92.26
2.13
0.75
0.71
0.95
5.64
0.49
379.6
650.9
451.7
457
0.65
0.54
0.71
7.1
HZSMꢀ5 (40)
MCMꢀ49 (30)
SAꢀSiO2ꢀ60.5 d
SBAꢀ15ꢀSO3H d
140.1
303.6
3.1
a Determined by NH3ꢀTPD (Fig. 3S) except SAꢀSiO2ꢀ60.5. b Acidity density=total acid amount/BET surface area. c Undetectable. d After ten
recycles.
The thermogravimetric analysis (TGA) of SAꢀSiO2ꢀ60.5
catalyst is shown in Fig. 4. Firstly, a slow weight loss in the various acid catalysts are shown in Table 1. The sulphonic
range of 0~250 was noticed. Then a sharp weight loss was resin has the maximum acidity (4530 µmol/g) among these
observed between 250 and 400
, which indicates desorption solid catalysts while its surface area is very poor (49.1m2/g).
of the sulfonic groups on the surface of the microꢀbead silica. Compared with the Amberlystꢀ15 resin, the SAꢀSiO2 has larger
The acidity, surface area, pore volume and pore size of
℃
℃
The weight loss above 400
℃ is due to the dehydration of surface area and exhibits an appropriate high acidity and pore
hydroxyl groups in the pore walls of microꢀbead silica.40 Thus it size. Furthermore, as shown in Table 1 (Entries 1, 2, 3, 4, 5, 6,
can be concluded that the SAꢀSiO2ꢀ60.5 catalyst is thermally 7, 8 and 9), the acid concentration can be adjusted, and the
stable and suitable for use at less than 250
℃.
acidity are varied from 230µmol/g to 1290µmol/g. The pore
Table 2 Catalytic performance of various sulfo-based catalysts and zeolites in the dehydration of sorbitol.a
Yield. (%)
Entry Catalyst
Sorbitol Conv. (%)
Others (%) b
Isosorbide
Sorbitan
11
1
2
3
4
5
6
7
8
9
SAꢀSiO2ꢀ60.5
100
100
93
84
90
71
70
25
9
5
c
H2SO4
_
7
Amberlystꢀ15
SBAꢀ15ꢀSO3H
Hβ (25)
5
24
11
22
4
c
95
_
69
22
17
29
20
37
HZSMꢀ5 (40)
MCMꢀ49 (30)
SAꢀSiO2ꢀ60.5 d
SBAꢀ15ꢀSO3H d
30
c
73
_
14
5
100
77
75
31
9
a Reaction condition: 120 ℃, 10 h, 1000 Pa, 50 g of sorbitol, 1.0 g of catalyst. b The byꢀproducts are 2,5ꢀanhydroꢀdꢀsorbitol, 1,5ꢀanhydroꢀdꢀ
sorbitol, and some others. c Undetectable. d After ten recycles.
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Fig. 5 Effect of different MPTS loadings on the performance of
sorbitol dehydration. Reaction condition: 50 g sorbitol, 1.0 g
catalyst, 120
℃, 10 h.
volume and pore size are decreased with the rise of MPTS
content. Pore size distributions of used SAꢀSiO2ꢀ60.5 and SBAꢀ
15ꢀSO3H are shown in Fig. S4.
Catalyst performance
The catalytic performance of SAꢀSiO2 catalysts for dehydration
of sorbitol to isosorbide was evaluated in solvent free and
vacuum conditions, which is helpful to remove off water from
the reaction system to promote the reaction equilibrium shift to
the positive direction. As shown in Scheme 1, the major
dehydrated products identified are isosorbide, 1, 4ꢀsorbitan and
along with a very small amount of 3, 6ꢀsorbitan. 2, 5ꢀanhydroꢀ
dꢀsorbitol, 1, 5ꢀanhydroꢀdꢀsorbitol and some non identified
substances were all termed here as “others”. To compare
different catalysts, we chose various acid catalysts such as
H2SO4, Amberlystꢀ15 resin, Hβ and HZSMꢀ5 zeolites. The
results listed in Table 2 show that Hβ(Si/Al=25) and HZSMꢀ
5(Si/Al=40) give a relatively low sorbitol conversion and yield
of isosorbide. Both Amberlystꢀ15 resin and SBAꢀ15ꢀSO3H have
high reactivity, but yield of isosorbide is low. Compared with
those solid catalysts, the SAꢀSiO2ꢀ60.5 catalyst exhibits the
highest sorbitol conversion (100%) and yield of isosorbide
(84%). This reactivity is very close to traditional homogeneous
catalyst such as H2SO4.
It is worth note that although SAꢀSiO2ꢀ60.5 doesn't offer the
maximum acidity, but displays good reaction performance (see
Table 2). Compared other reported hydrophilic catalysts in
Table S2, SAꢀSiO2ꢀ60.5 provides a higher yield of isosorbide
and the reaction condition is moderate. This should be
attributed to its suitable large pore size and high surface area
(see Tab 1). Thus it is beneficial to mass transfer process,
thereby inhibiting coke forming.
Fig. 6 Effect of reaction temperature on the performance of
sorbitol dehydration. Reaction condition: 10 g sorbitol, 0.2 g
catalyst, sorbitol conversion (a), yield of isosorbide (b), yield of
sorbitan (c).
40.9% to 60.5%, the growth rate of isosorbide yield slows
down. Thereafter, with the continued increase of MPTS loading,
the yield of isosorbide is decreased. Yield of isosorbide and
conversion of sorbitol are maximised at 60.5% MPTS loading.
Fig. 5 shows the activity of dehydration of sorbitol over
various SAꢀSiO2ꢀX at 120
℃ for 10 h. With increasing the
MPTS loading from 10.6% to 40.9%, the yield of isosorbide
increases obviously. When the MPTS loading increases from
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Fig. 7 Reuse of SA-SiO2-60.5 in the dehydration of sorbitol at 120
℃for 10 h under vacuum.
This phenomenon suggests that the further increase of MPTS
loading (above 60.5%) will block the pore of microꢀbead silica
in physics.40 Thus it seriously obstructs the internal diffusion
and transfer of reactants and decreases the yield of isosorbide.
The influence of reaction temperature on the dehydration
reaction was investigated, and the results are shown in Fig. 6.
As shown in Fig. 6a, the conversion of sorbitol is 100% at
Fig. 8 Sorbitol droplet contact angle (CA) on SA-SiO2-60.5 (a) and
isosorbide droplet contact angle on SA-SiO2-60.5 (b).
34.5°, respectively. This indicates that SAꢀSiO2ꢀ60.5 has a high
hydrophilic surface, and its surface affinity to sorbitol is
stronger than that to isosorbide. Scheme 3 shows the process of
sorbitol dehydration to isosorbide. The high surface
hydrophilicity and different surface affinity of SAꢀSiO2ꢀ60.5
catalyst is in favor of the feed (sorbitol) reaching and the
product (isosorbide) leaving active site rapidly, thus suppresses
the sequential reactions which cause coke formation. Under the
100~160
With increasing the dehydration reaction temperature to 120
the yield of isosorbide reaches the highest value (84%), and
then decreases with further increasing the temperature to 160
℃. At 100 ℃, the yield of isosorbide is low, ca. 60%.
℃,
℃
(see Fig. 6b), since more coke during the test is formed. But the
sorbitan yield, a main intermediate product,29, 46 decreases as
the temperature increasing (see Fig. 6c). These demonstrated
that an appropriate reaction temperature was crucial for
achieving a high yield of isosorbide.47 The highest catalytic
reaction conditions (100~160
℃, 650~1000 Pa), water, formed
in the reaction, can be removed out of the reactor instantly,
although it is a more polar molecule than sorbitol and
isosorbide. This avoids the competitive adsorption of water on
the surface of the catalyst with high hydrophilicity. As a
regeneration treatment in each cycle, the catalyst was washed
with water and glycol dimethyl ether. Moreover, the high
surface hydrophilicity of SAꢀSiO2ꢀ60.5 catalyst makes the
depositing coke, which is hydrophobic, washed away easily.
So the catalyst activity is restored. Therefore, the physical and
chemical properties of SAꢀSiO2ꢀ60.5 are also stable. For
example, after recycle for ten times, the SAꢀSiO2ꢀ60.5 still gave
acid site at 790 µmol/g, which slightly lower than that of the
fresh catalyst (840 µmol/g). On the contrary, the acid site of
SBAꢀ15ꢀSO3H almost decreased to none, and its recyclability
was very poor. From the TGA (Fig. S1) and FTꢀIR curves (Fig.
1b), the curves of SAꢀSiO2ꢀ60.5 remain almost unchanged after
ten recycles respectively. It can be concluded that the SAꢀSiO2ꢀ
60.5 is easily regenerated and exhibits good stability.
performance is observed at 120
℃for 10 h under vacuum with
2% SAꢀSiO2ꢀ60.5 (100% conversion of sorbitol and 84% yield
of isosorbide).
The recyclability is of great importance for applying a solid
catalyst in industrial production. After reaction, the SAꢀSiO2ꢀ
60.5 has been washed in ultrasonic pool with water and glycol
dimethyl ether to evaluate its recyclability, and the results are
shown in Fig. 7. After being reused for 10 times, sorbitol
conversion is still 100% and the yield of isosorbide decreases
only slightly. Compared with other zeolites,48 the regeneration
process does not require calcination and the synthesis does not
need surfactant or template so that the cost can be reduced. All
the results indicate that the SAꢀSiO2ꢀ60.5 exhibits excellent
stability and lowꢀcost.
As shown in Table S2, most of the hydrophilic catalysts
such as oxides, phosphates and sulfated materials showed a
relatively high reactivity compared with other hydrophobic
catalysts, which makes us believe that the high reactivity and
stability of SAꢀSiO2ꢀ60.5 is derived from its high surface
hydrophilicity. As observed in Fig. 8, the sorbitol and
isosorbide contact angle on SAꢀSiO2ꢀ60.5 is about 12.1° and
Conclusions
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7

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DOI: 10.1039/C5RA27510E
ARTICLE
Journal Name
We have found that SA-SiO2-60.5 is a highly effective solid acid 18.
catalyst for dehydration of sorbitol into isosorbide in solvent-free
M. Rose and R. Palkovits, ChemSusChem, 2012, 5, 167-
176.
19.
P. Sun, X. Long, H. He, C. Xia and F. Li, ChemSusChem
2013, 6, 2190-2197.
A. Yamaguchi, N. Hiyoshi, O. Sato and M. Shirai, Green
Chemistry, 2011, 13, 873-881.
G. Flèche and M. Huchette, Starch - Stärke, 1986, 38, 26-
30.
,
condition. The used catalyst can be easily regenerated by washing
with water and glycol dimethyl ether. And the catalyst displays
20.
good stability because it can be reused for 10 times without
significant loss of activity and selectivity. The excellent performance
21.
of the SA-SiO2-60.5 is attributed to its suitable large pore diameter
22.
23.
A. Yamaguchi, O. Sato, N. Mimura and M. Shirai, RSC
Advances, 2014, 4, 45575-45578.
A. Kamimura, K. Murata, Y. Tanaka, T. Okagawa, H.
and high surface hydrophilicity that is beneficial to the feed
adsorption and the product desorption, and inhibits the deposition
of coke. Thus, the catalyst—SA-SiO2 prepared in this work, has high
potential for conversion of the most abundant biomass into the
platform chemicals.
Matsumoto, K. Kaiso and M. Yoshimoto, ChemSusChem
2014, 7, 3257-3259.
,
24.
N. A. Khan, D. K. Mishra, I. Ahmed, J. W. Yoon, J.-S. Hwang
and S. H. Jhung, Applied Catalysis A: General, 2013, 452,
34-38.
Acknowledgements
25.
26.
27.
28.
A. A. Dabbawala, D. K. Mishra and J.-S. Hwang, Catalysis
Communications, 2013, 42, 1-5.
This work was supported by Jiangsu province science &
technology innovation project (BY2014037ꢀ12), and the Project
Funded by the Priority Academic Program Development of
Jiangsu Higher Education Institutions.
X. Zhang, D. Yu, J. Zhao, W. Zhang, Y. Dong and H. Huang,
Catalysis Communications, 2014, 43, 29-33.
J. Li, A. Spina, J. A. Moulijn and M. Makkee, Catalysis
Science & Technology, 2013, 3, 1540-1546.
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Graphical Abstract
Large pore diameter and hydrophilic surface of SA-SiO2-60.5 is beneficial to sorbitol
adsorption and isosorbide desorption, and inhibits deposition of coke.