Preparation of Sn-Β-zeolite via immobilization of Sn/choline chloride complex for glucose-fructose isomerization reaction

Article abstract of DOI:10.1016/S1872-2067(17)62754-2

Well dispersion of tin species in an isolated form is a quite challenge since tin salts are easily hydrolyzed into (hydr)oxides during aqueous stannation of β-zeolite. In this study, immobilization of tin species on high silica commercial β-zeolite by using SnCl₂/Choline chloride (ChCl) complex followed with calcination provided a convenient way to get well dispersed Sn in β-zeolite in the aqueous condition, which was observed based on electron microscopy images, UV visible spectra and X-ray diffraction pattern. The existence of ChCl facilitated tin species to incorporate into zeolite. (1?2) wt% of Sn loaded β-zeolites exhibited good catalytic activity and high selectivity for glucose-fructose isomerization reaction.

Full text of DOI:10.1016/S1872-2067(17)62754-2

Chinese Journal of Catalysis 38 (2017) 426–433
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article (Special Column on Novel Catalysts for Energy and Environmental Issues)
Preparation of Sn‐‐zeolite via immobilization of Sn/choline
chloride complex for glucose‐fructose isomerization reaction
Asep Bayua, Surachai Karnjanakoma, Katsuki Kusakabec, Abuliti Abudula a, Guoqing Guana,b,
*
a Graduate School of Science and Technology, Hirosaki University, Hirosaki 036‐8560, Japan
b North Japan Research Institute for Sustainable Energy (NJRISE), Hirosaki University, 2‐1‐3, Matsubara, Aomori 030‐0813, Japan
c Department of Nanoscience, Sojo University, 4‐22‐1 Ikeda, Nishi‐ku, Kumamoto 860‐0082, Japan
A R T I C L E I N F O
A B S T R A C T
Article history:
Well dispersion of tin species in an isolated form is a quite challenge since tin salts are easily hydro‐
lyzed into (hydr)oxides during aqueous stannation of ‐zeolite. In this study, immobilization of tin
species on high silica commercial ‐zeolite by using SnCl2/Choline chloride (ChCl) complex followed
with calcination provided a convenient way to get well dispersed Sn in ‐zeolite in the aqueous
condition, which was observed based on electron microscopy images, UV visible spectra and X‐ray
diffraction pattern. The existence of ChCl facilitated tin species to incorporate into zeolite. (12)
wt% of Sn loaded ‐zeolites exhibited good catalytic activity and high selectivity for glu‐
cose‐fructose isomerization reaction.
Received 31 September 2016
Accepted 23 November 2016
Published 5 March 2017
Keywords:
Sn‐ zeolite
Immobilization
Choline chloride
Glucose
© 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
Isomerization
Fructose
1. Introduction
be achieved with only small amount of grafted tin (i.e. (0.52)
wt%) [4,5]. For high tin loaded materials (i.e. >5 wt%), inactive
The preparation of Sn‐‐zeolite via post‐synthetic ap‐
proaches has been attracted much interest since it is simpler,
faster and scalable way compared with the hydrothermal route.
The general method to add tin as the Lewis acid site in ‐zeolite
is based on a two‐step way consisted of dealumination of high
alumina commercial ‐zeolite to generate silanol nest, followed
with stannation [15]. For instances, Sn‐‐zeolite can be ob‐
tained via gas‐solid deposition of SnCl4 at 400500 °C [1]. Also,
a solid state ion exchange method can result up to 10 wt% of
tin incorporated into the framework of zeolite [2,3]. It is re‐
ported that (56) wt% tin loaded ‐zeolites always have high
activity [13] but the highest turnover frequency (TOF) could
species (e.g. extraframework [1], oligomeric SnxOy [3], oxide
form SnO2) and/or other physical barriers (i.e. loss of mi‐
cropore access) [3,5] are usually observed which make it ineffi‐
cient in term of tin sustainability. Particularly, such problems
could occur in liquid‐stannation processes, especially in the
presence of water [5,7] or hydroxide ion [6] since tin is easily
hydrolyzed and as a result, precipitate is easily formed at this
state [7]. Therefore, to obtain Sn‐‐zeolite catalyst with good
performance, it is important to well disperse tin on the sup‐
ports and avoid the formation of unwanted tin species during
the treatments in aqueous solutions [4,8].
Recently, it is found that the addition of ChCl, a safe and
* Corresponding author. Tel: +81‐17‐7353362; Fax: +81‐17‐7355411; E‐mail: guan@hirosaki‐u.ac.jp
This work was supported by Aomori City Government, and the Doctoral Program of Ministry of Education, Culture, Sport, Science, and Technology
(MEXT), Japan.
The authors thank Professor Seiichiro Ioka at NJRISE, Hirosaki University helped ICP measurements.
DOI: 10.1016/S1872‐2067(17)62754‐2 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 38, No. 3, March 2017

Asep Bayu et al. / Chinese Journal of Catalysis 38 (2017) 426–433
427
cheap quaternary ammonium chloride [10], can improve tin
solubility in aqueous media, specifically for SnCl2 [9]. When
(4050) wt% of ChCl is added to the water, SnCl2 can be com‐
pletely dissolved in it due to the good interaction between ChCl
and SnII ion and the formation of complex as found in other
Lewis acid metal chlorides/ChCl systems [10,11].
Co‐impregnation of AlCl3‐ChCl on silica was also demonstrated
as an effective Lewis acid solid catalyst for dehydration of car‐
bohydrates to 5‐hydroxymethylfurfural (HMF) [12]. In this
study, SnCl2/ChCl aqueous solution was used as the precursor
for immobilization of Sn species on ‐zeolite. It is expected to
obtain high performance Sn‐‐zeolite catalyst for glu‐
cose‐fructose isomerization reaction.
90 °C for overnight. Meanwhile, Fourier Transform Infrared
(FTIR) spectra were obtained by using JASCO FT/IR‐4200 in‐
frared spectrophotometer with wavenumber in the range of
5004000 cm–1. In this context, the sample was mixed with KBr
followed by pressing the mixture into thin pellet. To check the
total acidity value, NH3‐temperature program desorption
(NH3‐TPD) was conducted (Belcat, Japan) according to the re‐
ported procedure [13]. Surface morphology of materials were
observed with a scanning electron microscope (SEM, SU8010,
Hitachi, Japan) while transmission electron microscope (TEM)
images were obtained using a JEM‐2100F transmission elec‐
tron microscope JEOL operating at 200 kV. ICP‐OES measure‐
ment was performed using a Perkin Elmer Optima DV 7000 at
189.927 nm for Sn.
2. Experimental
2.4. Chemical reaction
2.1. Materials
Reaction was performed in an autoclave reactor (Berghof,
Germany). About 5 wt% of substrate was added into 10 mL of
water containing 1 wt% of catalyst. The mixtures were heated
and stirred at several operation conditions. After finished, the
products were separated and analyzed using a Shimadzu
Prominence HPLC according to our previous protocols [9]. In
brief, the liquid product was filtrated using cellulose acetate
membrane filter (0.2 m) prior injected into HPLC. RID‐10A
(Shimadzu) and Supelcogel C610‐H (30 cm  7.8 mm) (Sigma)
were used as the detector and the column, respectively. The
oven CTO‐20A was operated at 40 °C and H3PO4 (0.05%) was
selected as the eluent.
Glucose (98%), fructose (99%), mannose, dihydroxyacetone
(dimer form) (DHA), lactic acid (LacA) (L‐form, (8592)%),
formic acid (FA) (99.5%), levulinic acid (LevA) (95%),
5‐hydroxymethylfurfural (HMF), Choline chloride (ChCl)
(95%), tin(II) chloride (SnCl2) (97%), tin(IV) chloride pen‐
tahydrate (SnCl4·5H2O) (98%), isopropanol (99.7%), tin(IV)
oxide (SnO2) (98%) were purchased from WAKO Chemicals.
High‐silica ‐zeolite with Si/Al ratio = 1700 in protonic form
(HSZ‐990 HOA) was obtained from Tosoh Corp. Distilled water
was used in all experiments.
2.2. Catalyst preparation
3. Results and discussion
Here, SnCl2, which is very easy to precipitate as
(hydr)oxides in the presence of water, was selected as the pre‐
cursor to identify the advantage of the present method. Mean‐
while, SnCl4 was also used for comparison. Firstly, SnCl2 was
added into 20 mL of ChCl aqueous solution (50 wt%) and
stirred until a homogeneous solution was obtained. Subse‐
quently, 10 g of zeolite was added and stirred at room temper‐
ature for 12 h. Thereafter, the liquid was separated by filtra‐
tion, and the obtained sticky gel was washed with isopropanol
using Soxhlet apparatus for at least 2 h and then, dried at 50 °C
for overnight. The obtained solid material is called as
xSn‐Z‐UC, in which x represents the loading amount of tin (in
this study, x = (0.6, 1.3, 1.9, 3.1 and 6.3) wt%). Furthermore,
calcination was conducted in air at 550 °C for 6 h with a heating
rate of 2 °C/min. The obtained powder is called as xSn‐Z‐C.
Here, the parent ‐zeolite was prepared by direct calcination of
the commercial zeolite at the same conditions.
3.1. Catalyst synthesis and characterization results
Fig. 1(a) shows the XRD patterns of all the materials. Alt‐
hough the treated zeolites still conserved ‐topology pattern,
the diffraction peaks were shifted to the low angle when com‐
pared with the parent one, implying the changes of their struc‐
tures to some extent. Interestingly, the peaks at 2 values of
13.5° and 14.8° were disappeared while some new peaks (i.e. at
2 values of 16.9°, 17.2°, 18.6°, 22.2°, 28.5° and 29.3°) were
observed on 1.3Sn‐Z‐UC. However, it should be noted that the
peaks at 13.5° and 14.8° reappeared while those new peaks
vanished again after calcination, indicating the presence of
crystalline organic substance on zeolite before calcination. The
new XRD peak of 1.3Sn‐Z‐UC at 29.3° was confirmed as the
main diffraction of ChCl. Furthermore, FTIR results suggested
that ChCl was immobilized at first, and then removed after
heated (Fig. 1(b)). Herein, the existence of ChCl after using
1.3Sn‐Z‐UC was also detected in the product by HPLC. On the
other hand, owing to the ability of ChCl to form Lewis‐acidic
ionic complexes with SnCl2 [14], it can assist tin species to well
disperse into zeolite. At this state, it is found that no significant
loss of Sn observed in the liquid after reaction by ICP meas‐
urement. Noted, the similar phenomenon has also reported by
Yang et al. [12] for silica‐based catalyst. In this context, the cal‐
cination facilitated tin species to get into the framework of zeo‐
2.3. Catalyst characterization
Crystalline X‐ray diffraction (XRD) patterns were checked
on X‐ray Rigaku diffractometer (Smartlab, Rigaku, Japan) using
Cu K radiation source (λ = 1.5405 Å). Diffuse reflectance
UV‐visible (DRUV) was recorded on a JASCO V‐650 spectro‐
photometer using ISV‐722 integrating spheres coated with
BaSO4. Before measurement, the sample was vacuum‐dried at

428
Asep Bayu et al. / Chinese Journal of Catalysis 38 (2017) 426–433
(a)
(6)
T-O-T
(T=Si, M)
SiO-H
T-O-T
(T=Si, M)
-OH
(b)
(5)
*
*
(5)
(4)
(3)
**
*
*
(4)
(3)
(2)
(1)
-CH2
-CN
-CH
-OH
(2)
-CH
-CH2
-OH
-CN
(1)
10 12 14 16 18 20 22 24 26 28 30 32 34 21 22 23 24 25 26
2
4000 3600 3200 2800 2400 2000 1600 1200 800
Wavenumber (cm1)
400
2
Fig. 1. (a) XRD patterns of SnO2 (1), crystalline ChCl (2), SnCl2 (3), parent ‐zeolite (4), 1.3Sn‐Z‐UC (5) and 1.3Sn‐Z‐C (6). The appearances of new
peaks are marked as a star point. (b) FTIR spectra of SnO2 (1), ChCl (2), parent ‐zeolite (3), 1.3Sn‐Z‐UC (4) and 1.3Sn‐Z‐C (5). xSn indicates the
loading amount value in wt% unit.
lite as indicated from the shifting peaks of XRD as well as the
typical signal of DRUV spectra. Meanwhile, the typical diffrac‐
tion of SnO2 was not observed for all treated zeolites, indicating
the effectiveness of this method to prevent the hydrolysis of tin
into (hydr)oxides [7,9] or other polymeric substances [4] dur‐
ing the treatment and thus minimizing the formation of un‐
wanted tin species. However, it should be noted that the exist‐
ence of some aggregates of Sn‐O‐Sn or other tin species was not
hindered which were indicated from the DRUV spectra as well
as TEM images. Detail explanations will be presented further in
the following section.
DRUV measurement was carried out as one of common
tools to get qualitative assessment of tin species on zeolite
[1,4,15,16] and the results are depicted in Fig. 2(a, b). To make
Sn state more clearly, the spectra of Sn‐ChCl‐treated zeolites
were corrected with the ChCl‐treated zeolite without Sn loaded
(notified as 0Sn‐Z) (Fig. 2(b)). It can be seen that the peak at
200 nm, assigned to the Sn in the tetrahedrally coordinated
framework [1,15,16], was observed and increased aligned with
tin loading amount on zeolite. Interestingly, in the case with
low tin loading (i.e. <3.1 wt%), the different absorption band
was observed in the region of 215340 nm when compared
with the parent one as well as the catalysts prepared in pure
water (Fig. 2(a)), and it was similar with that of 0Sn‐Z catalyst,
indicating that neither the tin oxide nor other tin species af‐
fected this absorption. Recently, it is reported that the interca‐
lation of choline followed by calcination can favor the desired
‘shifted’ orientation structure of IPC‐1P zeolite, a kind of lay‐
ered structure material, and produce new ‘unfeasible’ structure
of zeolite [17]. Moreover, it also promoted dealumination pro‐
cess which affected the acidity of zeolite, indicating the great
interaction between choline and silanol group in zeolite. In this
study, the decrease in acidity was observed from the NH3‐TPD
analysis result of 0Sn‐Z zeolite (Fig. 5), also indicating the
possible occurrence of this phenomena. Considering these re‐
sults, immobilization of ChCl followed by calcination can
change the silica structure of ‐zeolite, which opens a new way
to incorporate tin into the zeolite.
For comparison, loading of tin was also performed in pure
water. As expected, the DRUV absorption pattern was totally
different from those of ChCl‐treated zeolite as well as the par‐
ent one (Fig. 2(a)). Although no obvious peaks of SnO2 were
observed on XRD patterns (Fig. 2(c)), DRUV spectra showed
low signal and the broad band at 200 and 260 nm, respectively,
indicating the formation of other inactive tin species besides
the isolated form. For example, the signals in the range of
240350 nm should be assigned as the typical absorption of
oligomeric tin compounds [5]. Specifically, the extraframework
and polymeric Sn‐O‐Sn always had the high absorption peaks in
the ranges of 255260 nm [4,5,18], and 270280 nm [4,15,18],
(c)
(b)
(a)
(8)
(7)
(9)
(6)
(5)
(4)
(8)
(7)
(8)
(7)

(4)
(3)
(6)
(3)
(2)



(5)


(1)
200
250
300
350
 (nm)
400
450
500
10 15 20 25 30 35 40 45 5021
22
2/( o
23
200 210 220 230 240 250 260 270 280 290 300 310
2/( o
)
)
 (nm)
Fig. 2. DRUV spectra (a, b) and XRD patterns (c) of parent (1) compared with ChCl‐treated zeolite with different loading amounts of Sn (wt%): 0 (2),
0.6 (3), 1.3 (4) 1.9 (5) 3.1 (6) 6.3 (7), H2O‐prepared zeolite with 1.3 wt% of Sn (8) and SnO2 (9). (b) is obtained after corrected with the ChCl‐treated
zeolite without the addition of Sn. The appearance of SnO2 diffraction peak on (c) is showed by the arrow.

Asep Bayu et al. / Chinese Journal of Catalysis 38 (2017) 426–433
429
respectively. The peaks on the latter range were considered
sion of tin on zeolite.
from the hydrated form of tin or even octahedral extraframe‐
work SnO2 [4,5,18]. The absorption band at 260 nm should be
correlated with the precipitation of Sn2+ ions soon after the salt
was added in pure water, i.e., the hydrolysis to (hydr)oxides [7],
and as such, the agglomeration should occur, which was sup‐
ported by the TEM images (Fig. 3(c) and (d)). On the other
hand, it is found that the good solubility of SnCl2 in ChCl solu‐
tion can minimize the formation of those inactive species as
long as the amount of tin was lower than 3.1 wt% in this study.
Other works reported that the solubility of tin had great re‐
sponsibility to the morphology as well as the catalytic activity
of tin‐‐zeolite prepared via hydrothermal route [19]. Moreo‐
ver, the isolated tin species in the framework were difficult to
be formed when performing the grafting in pure water [5].
As shown in Fig. 3(c), Sn species were dispersed with ran‐
dom sizes on zeolite when Sn‐‐zeolite was prepared in pure
water without ChCl. Moreover, some Sn particles were obvi‐
ously observed on the surface of zeolite (Fig. 3(d)), indicating
the agglomeration of tin species which typical DRUV absorption
signals have been discussed above. On the contrary, smaller
and more uniform Sn particles were found to be well dispersed
on zeolite when Sn‐‐zeolite was prepared in the ChCl aqueous
solution (inset of Fig. 3(b)). It is indicated that the formation of
other tin species besides isolated form could be suppressed
although a small aggregate could not be hindered even at this
state. Thus, maintaining tin solubility in the solvent should be
considered strictly to obtain Sn‐‐zeolite with well metal dis‐
persion. These results indicated that the performing of stanna‐
tion through the present route can result in a very well disper‐
On the other hand, when Sn loading amount was over 3.1
wt%, as shown in Fig. 2, it is found that the peak at around
270280 nm was observed on DRUV spectrum. Moreover, a
broad peak at around 280 nm, which corresponds to the typical
SnO2 species, appeared when the Sn loading amount was 6.3
wt%. It was also supported by SEM images, on which some
disordered bright objects were observed (Fig. 4), indicating
that some SnO2 formed on the outside of zeolite as also found
by others [5]. As reported by others [1,3,5], in this study, 5 wt%
loading amount seemed to be the limit amount to prevent the
formation of such inactive tin species.
Fig. 5 shows NH3‐TPD profiles of parent zeolite and
Sn‐‐zeolite prepared in ChCl aqueous solutions with different
tin loading amounts. Since the parent one was a protonic form
of ‐zeolite with low aluminum content as the Lewis acid
source, it had low total acidity value. With the increase in tin
loading amount, the acidity was also increased. Here, the high
intensity peak at around 205225 °C indicates the presence of
Lewis acid sites [20,21], which also indicated the total acidity
value of the prepared Sn‐‐zeolite. In this context, Lewis acid
sites from tin species should have great contribution to the
obtained value. One can see that the acidity decreased to some
extent after the zeolite was only treated with ChCl, which
should be resulted from the great interaction between choline
and silanol bonds in the zeolite [17].
3.2. Catalytic Activity
Table 1 shows the catalytic activity of the prepared
(b)
(a)
(c)
(d)
20 nm
Fig. 3. TEM images of parent ‐zeolite (a), 1.3Sn‐Z‐C prepared in ChCl solution (b) and in pure water (c, d).

430
Asep Bayu et al. / Chinese Journal of Catalysis 38 (2017) 426–433
0.06
(7)
(a)
Sn
(wt%)
Total acidity
(mmol/g)
Code
(1)
(2)
(3)
(4)
(5)
(6)
(7)
parent
0
0.047
0.036
0.081
0.110
0.169
0.170
0.274
0.05
0
0.6
1.3
1.9
3.1
6.3
ChCl-
treated
(6)
(5)
0.04
0.03
0.02
0.01
0.00
(4)
(3)
(1)
(2)
100
200
300
400
500
600
700
Temperature (oC)
(b)
Fig. 5. NH3‐TPD profiles of parent zeolite (1) and Sn‐‐zeolite prepared
in ChCl aqueous solutions with different tin loading amounts (2–7).
SnCl2/ChCl was found to have high activity for aqueous catalyt‐
ic reaction of glucose [9]. For comparison, the catalytic activity
of Sn‐‐zeolite prepared in pure water was also investigated. It
had lower activity than those prepared in ChCl aqueous solu‐
tions (Table 1, entries 8 and 9) due to the low Sn content on it
based on ICP measurement (i.e. (0.13 and 0.40) wt%, respec‐
tively). However, it showed high selectivity for fructose for‐
mation, indicating that different active species should be
formed as discussed above. These results identified that the
catalytic activity of Sn‐‐zeolite should be related with the
presence of active sites of tin as the Lewis acid, especially in its
isolated form.
The prepared catalysts were also used for the conversions
of other hexoses in this study. When fructose was used as the
substrate, a large amount of glucose was found to be produced
(Table 1, entry 4) since this reaction is an equilibrium reaction
[22,23]. This result indicates that this catalyst is benefit for the
glucose‐fructose isomerization reaction as typically observed
for the common Sn‐‐zeolite [4,22]. It is supported from the
high selectivity fructose formation when reaction was carried
Fig. 4. SEM images of 6.3Sn‐Z‐C (a) and 1.3Sn‐Z‐C (b).
Sn‐‐zeolite for aqueous hexoses conversion reaction. One can
see that the parent ‐zeolite had very low performance due to
its low acidity, especially the Lewis acid site (Table 1, entry 1).
After Sn loading, the activity increased either with or without
calcination (Table 1, entries 3 and 2, respectively). However,
the calcination seemed to have a great effect to induce the gen‐
eration of Sn active sites in ‐zeolite while SnCl2/ChCl played
an important role in improvement of the catalytic performance
in the case without calcination. In our previous work,
Table 1
Catalytic performance for hexoses conversion reaction in aqueous solutions.
T
(°C)
Conv.
(mol%)
9.5
Yield (mol%)
Selectivity a
Entry
Hexoses
Catalyst
Gluc
Fruc
2.5
15.7
41.4
DHA
—
<1
1.5
1.6
1
<1
1.7
—
LacA
—
—
HMF
—
—
(%)
26
51
1
2
Gluc
Gluc
Gluc
Fruc
Gluc
Gluc
Mann
Gluc
Gluc
Gluc
Gluc
Gluc
Gluc
Parent
145
145
145
145
125
125
125
125
145
125
145
125
145
1.3Sn‐Z‐UC
1.3Sn‐Z‐C
1.3Sn‐Z‐C
1.3Sn‐Z‐C
1.3Sn‐Z‐C
1.3Sn‐Z‐C
1.3Sn‐Z‐C
1.3Sn‐Z‐C
1.3Sn‐Z‐C
1.3Sn‐Z‐C
1.3Sn‐Z‐C
1.3Sn‐Z‐C
30.5
72.1
55.4
58.6
54.6
36.0
19.2
30.3
35.8
57.4
19.5
25.3
3
4
5
6 b
5.5
3.9
7.8
<1
<1
—
—
—
—
57
17.8
—
—
9.2
4.1
2.0
5.1
46.3
47.1
—
16.0
22.9
30.2
37.3
11.9
17.2
79
86
7
18.8
8 c
9 c
10 d
11 d
12 c,d
13 c,d
—
83
76
84
65
61
75
—
—
<1
4.3
—
—
<1
<1
—
3.3
—
—
—
Reactions: 5 wt% of hexoses, 1 wt% of catalyst, 10 mL of water, 1.5 h in autogenous state. Gluc, Fruc, Mann, T, and Conv. are the abbreviations of glu‐
cose, fructose, mannose, reaction temperature and conversion, respectively.
a For fructose formation; b after 1 h of reaction time; c prepared in pure water; d using SnCl4 as the precursor in equimolar condition.

Asep Bayu et al. / Chinese Journal of Catalysis 38 (2017) 426–433
431
60
50
40
30
20
10
0
(b)
0
30
60
90
120
Reaction time (min)
Fig. 6. Product evolution (a) and heterogeneity test (b) for aqueous glucose conversion using 1.3Sn‐‐zeolite. Reactions: 5wt% of glucose, 1 wt% of
catalyst, 10 mL of water at 125 °C. Heterogeneity test was conducted based on the reported protocol [4].
out at low reaction temperature (Table 1, entry 5 and 6). In this
case, about (4547)% of fructose was obtained after 6090
min of reaction (Fig. 6(a)). With further extending of the reac‐
tion time, the yield and selectivity decreased slightly and other
products such as HMF were observed in significant amounts,
indicating that fructose was further transformed to other side
products. In this context, as shown in Fig. 6(b), it is obviously
observed that the reaction occurred via heterogeneity state of
zeolite.
Meanwhile, a significant amount of glucose was obtained
from mannose by using this Sn‐‐zeolite (Table 1, entries 7). In
contrast with other results [4], mannose was not detected in
the product obtained from glucose as the substrate, presuma‐
bly small peak of mannose could not be detected in our HPLC
condition since it has a close retention time as that of fructose
(i.e. 11.53 and 11.60 min, respectively). Considering its low
activity for glucose‐mannose reaction in the case without some
additives [24] and its good ability for glucose‐fructose reaction
[4], it is hypothesized that the nature of ‐topology of zeolite
and the isolated tin active sites on it have great contribution to
the isomerization of glucose to fructose rather than epimeriza‐
tion reaction. In this context, since these reactions generally
occur competitively [24], glucose isomerization seems to be
more preferable to occur due to the high energy barrier of the
latter reaction. It should be noted that intramolecular
1,2‐hydride shift [23] and 1,2‐carbon shift [24] could happen
for the isomerization and epimerization, respectively, which
have different thermodynamical activation energy.
thermore, a higher selectivity for fructose formation and a
higher TOFSn value were found for SnCl4 than SnCl2 (i.e.
265331 and 228255 h–1, respectively) indicated that the
oxidation state of Sn also contributed to the Sn active site for‐
mation during the calcination step. In this study, the variation
of Sn precursor clearly showed that different precursors have
different interaction with zeolite framework, which affected the
physical and catalytic behaviors of the obtained Sn‐‐zeolites as
prepared via alcoholic grafting method [5]. Meanwhile, per‐
forming stannation in pure water with SnCl4 also resulted in
higher TOFSn when compared with SnCl2 (i.e. 281 and 274 h–1 at
125 °C for 1.5 h, respectively), indicating the possible different
Sn dispersions as well as active forms on zeolite. As described
above, white precipitate appeared shortly after adding SnCl2
into pure water, however, such phenomenon was not soon
observed in the case of SnCl4, where white suspension ap‐
peared after storing the solution for 2 days, indicating its lower
hydrolysis rate than SnCl2. Therefore, considering these results
and other reports [5], the solubility or choosing an appropriate
solvent for tin salts should be important for the preparation of
Sn‐‐zeolite with high performance.
The catalytic activity of catalyst with different tin loading
amounts was also investigated. Although the yields of fructose
as well as the conversion value were not significantly different,
side products such as FA as well as HMF were significantly
formed when the Sn loading amount was increased. Moreover,
LacA was also detected and increased slightly, confirming the
existence of other reactions besides glucose‐fructose isomeri‐
zation. As indicated above, more other tin species were possi‐
bly formed at high Sn loading amounts. Since the speciation of
tin species on zeolite (e.g. isolated or extraframework) could
affect the activity as well as selectivity [15], other side reactions
could be catalyzed by them so that other products were de‐
tected as shown in Fig. 7. Considering of these results, 1.3 wt%
of tin loading amount should be the optimum one for the
aqueous glucose‐fructose isomerization reaction.
Since tin chlorides are available in two forms of oxidation
state, Sn‐‐zeolite was also prepared by using SnCl4 as the pre‐
cursor. It is found that the obtained catalysts had lower activity
than those obtained from immobilization of SnCl2 (Table 1,
entries 10,11 and 3,5, respectively). It is possible that the two
kinds of tin chlorides have different interactions with ChCl,
which affect Sn dispersion during the loading process. ICP
measurement confirmed the different tin contents observed for
both catalysts (i.e. (0.24 and 0.40) wt%, respectively). Here, the
SnCl2 is able to form an eutectic salt with ChCl [14], however,
such a complex was not commonly reported for SnCl4. Fur‐
The reusability of the prepared catalyst was also investi‐
gated. Relative activity is used to see the catalytic performances
of the reused as well as recycled catalyst compared with the

432
Asep Bayu et al. / Chinese Journal of Catalysis 38 (2017) 426–433
Fig. 8. The reusability of 1.3Sn‐Z‐C in aqueous glucose conversion.
Recycle test was performed after calcining the zeolite from reuse 2.
Reaction conditions: 5 wt% of glucose, 1 wt% of catalyst, 125 °C.
Fig. 7. Effect of Sn loading amount on the catalytic activity of
Sn‐‐zeolite. Reactions conditions: 5 wt% of glucose, 1 wt% of catalyst,
145 °C.
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fresh one. It is found that the activity of catalyst decreased to
some extent (Fig. 8) and the color changed to brown after re‐
used, indicating the loss of activity due to the existence of some
impurities formed on the catalyst. These impurities could cover
the active sites of the catalyst, and lower its activity. After the
spent catalyst was calcined and reused, as shown in Fig. 8, the
activity recovered to some extent but was still lower than the
fresh one. It is possible that some active sites were lost and/or
the structure was changed as reported by others [25]. ICP
measurement confirmed that some amount of tin (i.e. ~1 wt%)
was lost from the fresh catalyst. However, it should be noted
that the selectivity for fructose formation remained relatively
constant.
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Immobilization of SnCl2/ChCl into high‐silica commercial
‐zeolite followed by calcination was identified as an effective
way to prepare well Sn dispersed zeolite catalysts. 1.3 wt% of
Sn loading amount was found to be the optimum one, in which
not only well dispersion of Sn species was realized but also less
inactive tin species were formed on zeolite. The obtained
Sn‐‐zeolite shows good catalytic activity as well as selectivity
for aqueous glucose‐fructose isomerization reaction. The pre‐
sent method should be a novel alternative process for prepar‐
ing Sn loaded catalyst with high performance.
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Graphical Abstract
Chin. J. Catal., 2017, 38: 426–433 doi: 10.1016/S1872‐2067(17)62754‐2
Preparation of Sn‐‐zeolite via immobilization of Sn/choline chloride complex for glucose‐fructose isomerization reaction
Asep Bayu, Surachai Karnjanakom, Katsuki Kusakabe, Abuliti Abudula, Guoqing Guan *
Hirosaki University; North Japan Research Institute for Sustainable Energy (NJRISE)
Sn‐‐zeolite prepared by immobilization of SnCl2/ChCl followed by calcination showed good activity and high selectivity for glu‐
cose‐fructose isomerization.
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