I2/ionic liquid as a highly efficient catalyst for per-O-acetylation of sugar under microwave irradiation

Article abstract of DOI:10.1016/S1872-2067(14)60219-9

A practical and highly efficient approach was developed to synthesize peracetylated sugar derivatives using a recyclable iodine/PEG₄₀₀-based ionic liquid catalyst (I₂/IL). The peracetylated sugars were readily obtained in a few minutes in excellent yields (90%-99%, 13 examples) on a multi-gram scale (50.0 mmol) by the reaction of sugar and acetic anhydride under microwave irradiation in the absence of a volatile organic solvent. The desired product was easily obtained by simple extraction with toluene from the reaction mixture, and I₂/ILs can be readily recovered and reused at least six times without obvious loss in the yield. When the scale of the per-O-acetylation reaction was increased to 50.0 mmol, the desired product was still obtained in 90% yield after five recycles.

Full text of DOI:10.1016/S1872-2067(14)60219-9

Chinese Journal of Catalysis 36 (2015) 237–243
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
I2/ionic liquid as a highly efficient catalyst for per‐O‐acetylation of
sugar under microwave irradiation
Xingquan Xiong*, Chao Yi, Qian Han, Lin Shi, Sizhong Li
College of Materials Science and Engineering, Huaqiao University, Xiamen 361021, Fujian, China
A R T I C L E I N F O
A B S T R A C T
Article history:
A practical and highly efficient approach was developed to synthesize peracetylated sugar deriva‐
tives using a recyclable iodine/PEG400‐based ionic liquid catalyst (I2/IL). The peracetylated sugars
were readily obtained in a few minutes in excellent yields (90%‒99%, 13 examples) on a mul‐
ti‐gram scale (50.0 mmol) by the reaction of sugar and acetic anhydride under microwave irradia‐
tion in the absence of a volatile organic solvent. The desired product was easily obtained by simple
extraction with toluene from the reaction mixture, and I2/ILs can be readily recovered and reused at
least six times without obvious loss in the yield. When the scale of the per‐O‐acetylation reaction
was increased to 50.0 mmol, the desired product was still obtained in 90% yield after five recycles.
© 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 19 June 2014
Accepted 29 August 2014
Published 20 February 2015
Keywords:
Peracetylated sugar
Iodine
Ionic liquid
Microwave irradiation
Published by Elsevier B.V. All rights reserved.
1. Introduction
H2SO4 [13], and HClO4 [14]. Although the above catalysts have
been widely applied to prepare peracetylated sugars, many of
Per‐O‐acetylation of sugar is a frequently used transform‐
ation in carbohydrate chemistry as it provides an efficient and
cheap means for protecting the hydroxy groups of sugars [1].
Peracetylated sugars are widely used as important and inex‐
pensive building blocks to synthesize biologically important
oligosaccharides and oligosaccharides and many bioactive nat‐
ural products [2‒5]. Therefore the synthesis of peracetylated
sugars is an important topic in the preparation of functional
glycoconjugates and oligosaccharides [6,7]. Considerable ef‐
forts have been made in the development of efficient and mild
strategies for the per‐O‐acetylation of sugars [8‒10].
these are associated with several obvious shortcomings, such
as environmental toxicity, unpleasant odour, equipment corr‐
osion, formation of unwanted side products, and incomp‐
atibility with carbohydrate derivatives containing acid‐labile
functional groups.
A variety of Lewis acid catalysts such as InCl3 [15],In(OTf)3
[16], ZnCl2 [17], Fe2(SO4)3 [18], FeCl3 [19], Bi(OTf)3 [20], Sc(OTf)3
[21], (CH3)3SiOTf [22], Cu(OTf)3 [23], Ce(OTf)3 [24], and
BF3∙Et2O [25] have been introduced for the acid catalyzed
per‐O‐acetylation of sugars. However, these catalysts also suffer
from significant drawbacks, such as expensive reagent, long
reaction time, harsh reaction conditions, and difficulty in the
recovery and reusability of the catalyst. Solid acid catalysts can
mitigate these problems as they are inexpensive and allow the
In general, a large excess of acetic anhydride is routinely
used as acylating agent and solvent in the presence of an acidic
or basic catalyst, such as pyridine [11], sodium acetate [12],
*Corresponding author. Tel/Fax: +86‐592‐6162225; E‐mail: xxqluli@hqu.edu.cn
This work was supported by the National Natural Science Foundation of China (21004024), the Natural Science Foundation of Fujian Province
(2011J01046), the Program for New Century Excellent Talents in University of Fujian Province (2012FJ‐NCET‐ZR03), the Promotion Program for
Young and Middle‐Aged Teachers in Science and Technology Research of Huaqiao University (ZQN‐YX103), and the Special Foundation for Young
Scientists of Fujian Province (2011J05131).
DOI: 10.1016/S1872‐2067(14)60219‐9| http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 2, February 2015

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Xingquan Xiong et al. / Chinese Journal of Catalysis 36 (2015) 237–243
straightforward removal of the catalysts from the reaction sys‐
tem [26–30].
reactor equipped with a stirring bar and were monitored by
TLC. The MW bench top reactor (MAS‐II) was manufactured by
Sineo Microwave Chemistry Technology (Shanghai) Co. IR
spectra were obtained using a Fourier transform infrared
(FT‐IR, 4000–400 cm–1) spectrometer (Nicolet Nexus FTIR
spectrometer, USA) using 4 cm–1 resolution and 32 scans. Sam‐
ples were prepared using the KBr disc method. NMR spectra
were acquired in CDCl3 on a Bruker DMX‐400 spectrometer at
400 MHz for 1H NMR. The chemical shifts were given in δ val‐
ues from TMS as an internal standard.
Recently, molecular I2 has drawn considerable attention as
an efficient, mild, and readily available Lewis acid catalyst for
various organic reactions [31]. In 1997, I2 was used successfully
for the synthesis of per‐O‐acetylated sugars in excellent yield
with a short reaction time [32]. However, it is difficult to use I2
because it has good solubility in most organic solvents and
easily sublimate at high temperature. In addition, the used I2 in
the reaction mixture was not recovered. It was difficult to use I2
in large scale synthesis due to environmental and economic
concerns. Therefore, there is a need to find a simple and effi‐
cient support for reusable I2 in the per‐O‐acetylation of sugars.
As a non‐conventional energy source, microwave (MW) ir‐
radiation leads to a large reduction in reaction time and obvi‐
ous enhancement in conversion, and has emerged as a useful
technology in organic chemistry [33–39]. As a part of our con‐
tinuing interest in improving the practicability and efficiency of
MW irradiation technology [40–43], we report here a simple,
rapid, and scalable strategy for the synthesis of per‐O‐acetylat‐
2.2. Preparation of IL400
The revised route for the preparation of IL400 is outlined in
Scheme 2. To a solution of PEG400 (60 mmol) and Et3N (120
mmol) in toluene (200 mL) was added methylsulfonyl chloride
(120 mmol) dropwise in 30 min under N2 atmosphere. Then
the mixture was stirred at room temperature. After 3 h, the
mixture was filtered. The filtrate was added to N‐methyli‐
midazol (120 mmol), and the mixture was stirred at 80 °C for
30 min under MW irradiation (200 W). After the reaction, the
ionic liquid layer was separated and washed with petroleum
ether (PE, 3×10 mL). Evaporation of residual PE under reduced
pressure gave the desired pure product IL400 in 90% yield.
ed sugars catalyzed by I2 in PEG400‐based ionic liquid (I2/IL400
)
under MW irradiation (Scheme 1). IL400 is an appealing polar
solvent. It is ambience friendly because it has a high boiling
point and has low toxicity and is biodegradable. Interestingly,
the IL400 and toluene system gives heterogeneous phases at
room temperature, such that the product can be easily recov‐
ered from the reaction mixture by simple extraction with tolu‐
ene while the catalyst I2 remains in IL400 and can be reused in
the next cycle. I2/IL400 can be reused at least six times without
significant loss of its catalytic activity. No previous example of a
rapid and efficient synthesis of fully acetylated sugars catalyzed
by recyclable I2/IL400 has been reported.
2.3. Typical procedure for per‐O‐acetylation of D‐glucose
To a 10.0 mL round bottom flask, D‐glucose (2.0 mmol) and
acetic anhydride (12.0 mmol, 1.2 equiv. per OH) in the IL400 (2.0
mL) was added I2 (0.05 mmol) at room temperature. Then the
mixture was heated to 50 °C under MW irradiation (200 W)
until the TLC analysis showed that the reaction was complete.
Then the reaction mixture was cooled to room temperature,
and toluene (2.0 mL × 3) was added. The mixture was vigor‐
ously stirred for several minutes and then kept stationary. The
upper toluene layer containing the product was collected. Tolu‐
ene was removed by a rotary evaporator, and the crude prod‐
uct was purified by recrystallization in ethyl alcohol. The desi‐
red peracetylated sugars were obtained in 90%–99% yields.
The bottom phase was the ionic liquid containing the I2 catalyst
2. Experimental
2.1. Materials and instrumentation
All reagents and solvents were obtained from commercial
sources and used without further purification. All the per‐O‐
acetylation reactions were carried out in a commercial MW
Scheme 1. Synthesis of peracetylated sugars catalyzed by I2/IL400 under MW irradiation.
Scheme 2. Synthesis of IL400 by a revised method under MW irradiation.

Xingquan Xiong et al. / Chinese Journal of Catalysis 36 (2015) 237–243
239
and produced acetic acid. The I2/IL400 system was reused after
the removal of the acetic acid under reduced pressure.
1 shows the FT‐IR spectra of PEG400 and IL400. The peaks at
1043 and 1109 cm–1 of IL400 were the characteristic absorption
bands of S=O. In the case of IL400, the broad band at 2900 cm–1
can be attributed to the C–H stretching of the –CH2– group, and
the peak at 1196 cm–1 was from the C–O stretch in PEG400. The
peak at 3107 cm–1 was assigned to C–H stretching of the imid‐
azole ring. The IL400 also exhibited other characteristic absorp‐
tion bands at 1350 cm–1, which was assigned to the symmetric
stretching of –CH3. The peaks at 1537 and 1653 cm–1 which
appeared, were related to the band of C=C and C=N, respec‐
tively.
2.4. Typical procedure of the scale up of per‐O‐acetylation of
sugars
To a 100 mL round bottom flask, the D‐glucose (50 mmol)
and acetic anhydride (0.25 mol) in the IL400 (20 mL) were add‐
ed I2 (0.25 mmol) at room temperature. Then the mixture was
heated to 50 °C under MW irradiation (200 W) until the TLC
analysis showed that the reaction was complete. The work‐up
of the reaction mixture was carried out by the same procedure
as the model reaction.
1
The H NMR spectrum (not shown) showed the peaks at
9.48, 7.67, and 7.52 ppm assigned to Himid. The single peak at
3.99 ppm was assigned to the protons of NCH3. The peaks be‐
tween 3.88 and 3.55 ppm were due to PEG–H. The single peak
at 2.71 ppm was assigned to the protons of –SO2CH3. The re‐
3. Results and discussion
3.1. Preparation and characterization of IL400
sults confirmed the successful preparation of IL400.
In general, IL400 is prepared by nucleophilic substitution
between CH3SO2–OPEG400O–SO2CH3 and substituted imidazoles
under conventional heating conditions. However, this synthesis
method has an obvious disadvantage in that it needed a long
reaction time (several hours to 2 d) and harsh reaction condi‐
tion (> 80 °C).
In this work, a modified method was developed to synth‐
esize PEG400 imidazolium salt ionic liquid, as depicted in
Scheme 2. First, CH3SO2–OPEG400O–SO2CH3 was synthesized by
a reaction of HO–PEG400–OH with methanesulfonyl chloride
using Et3N as a base in toluene at 0 °C under N2 atmosphere.
After completion of the reaction, the white solid byproduct was
removed by filtration. Without any purification, the filtrate was
added to 1‐methylimidazol, the mixture was then heated to 80
°C under MW irradiation (200 W) for 30 min, and the desired
IL400 was obtained. Compared to the traditional heating meth‐
od, the use of MW irradiation dramatically reduced the reaction
time. In the synthesis of IL400, the key step was the nucleophilic
substitution between CH3SO2–OPEG400O–SO2CH3 and 1‐me‐
thylimidazol under MW irradiation.
3.2. Per‐O‐acetylation of glucose catalyzed by various catalysts
First, the per‐O‐acetylation reaction of glucose with acetic
anhydride was chosen as a model reaction to screen the cata‐
lysts. The reaction was performed under MW irradiation. The
per‐O‐acetylation reaction was simply performed by stirring
the mixture of glucose with a slight excess of acetic anhydride
(1.2 equiv. per OH), and by using different catalysts in IL400 at
50 °C. The results are summarized in Table 1.
The optimization study revealed that per‐O‐acetylated glu‐
cose was only obtained in 60% yield using acetic anhydride in
the absence of a metal salt catalyst at 50 °C after 3 min under
MW irradiation. It was also observed that when the per‐O‐acet‐
ylation of glucose was carried out using metal salts catalysts
such as Co(OAc)2, FeCl3, Cu(OAc)2, and ZnCl2 under the same
condition, per‐O‐acetylated glucose was prepared in moderate
yields (67%–77%). To our delight, after the screening experi‐
ment with the target catalyst, that is I2, the reaction occurred
the most efficiently and yielded the product in 99% isolated
yield. Thus I2 was reasonably chosen as the best catalyst for
sugar per‐O‐acetylation under MW irradiation due to its high
efficiency, low toxicity, and easy recyclability.
The IL400 was characterized using FT‐IR and1H NMR. Figure
Table 1
PEG400
IL400
Effect of the various catalysts on the per‐O‐acetylation of glucose with
acetic anhydride under MW irradiation.
OH
OAc
O
O
O
Cat, IL400
MW, 50 o
HO
HO
O
AcO
AcO
OH
OAc
O
C
OH
OAc
Entry
Catalyst
—
Co(OAc)2
FeCl3
Cu(OAc)2
ZnCl2
Isolated yield (%)
1
2
3
4
5
6
60
73
70
77
67
99
1653
1537
1350
1196
1043
1109
3107
2900
I2
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm1)
Reaction conditions: D‐glucose (2.0 mmol), acetic anhydride (1.2 equiv.
per OH), and catalyst (5 mol%) in IL400 (2.0 mL) at 50 °C for 3 min un‐
der MW irradiation (200 W).
Fig. 1. FT‐IR spectra of PEG400 and IL400
.

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Xingquan Xiong et al. / Chinese Journal of Catalysis 36 (2015) 237–243
3.3. Effect of I2 concentration on the per‐O‐acetylation of
D‐glucose
quantitative conversion rate. A 99% isolated yield was ob‐
tained when the catalyst amount was 5.0 mol%; it took a longer
time (10 min, 62%) when the catalyst was used in the amount
of 1.0 mol%. Thus, the per‐O‐acetylation of sugar was per‐
formed in the presence of 5 mol% of I2. However, the reaction
gave only 60% and 70% yields under I2‐free conditions and a
conventional heating condition, respectively (entries 8 and 9).
The results showed that combining the I2/IL400 catalytic system
with the use of microwave irradiation dramatically improved
the yield of the reaction.
To optimize the reaction conditions, we first determined the
optimum dosage of catalyst. The acetylation of D‐glucose was
chosen as a model reaction to react with a slight excess of acetic
anhydride in the presence of 1.0, 3.0, 5.0, and 7.0 mol% of I2 in
IL400 at 50 °C under MW irradiation. The results are summa‐
rized in Table 2. To our delight, thin layer chromatography
(TLC) showed that the reaction was completed within 3 min in
Table 3
Per‐O‐acetylation of sugars and sugar alcohols using I2/IL400 as catalyst at 50 °C under MW irradiation.
Entry
Substance
Product
Time a (min)
Isolated yield (%)
99
α/β
OH
OAc
O
O
1
1a
2a
3a
1b
2b
3b
3
1/1.8
HO
HO
AcO
AcO
OH
OH
OAc
OAc
OH
O
OAc
O
HO
HO
AcO
AcO
2
3
5
4
96
90
2/1
OAc
OH
OAc
OH
O
O
1.3/1
HO
OH
AcO
OAc
OH
OAc
OAc
OH
O
O
4
5
4a
5a
4b
5b
5
6
90
96
6/1
—
HO
AcO
AcO
OH
OAc
HO
NHAc
NHAc
OAc
OH
O
AcO
AcO
OAc
O
HO
HO
OH
N
C
OCH3
N
C
OCH3
H
H
OAc
O
OH
O
HO
HO
AcO
AcO
OH
O
OAc
O
6
6a
6b
10
96
—
HO
OH
AcO
OAc
O
O
OH
OAc
OH
OAc
OAc
OAc
OH
OAc
O
OH
O
OH
O
O
O
O
7
8
7a
8a
7b
8b
10
12
97
94
4/1
1/1
OH
OAc
HO
AcO
HO
AcO
OH
OAc
OH
OAc
OH
O
OAc
O
HO
HO
AcO
AcO
OAc
O
OH
O
OH
OAc
O
O
AcO
HO
OAc
OH
OAc
OH
OAc
O
OH
O
HO
HO
AcO
AcO
OH
OAc
OAc
OAc
9
9a
9b
10
10
93
95
—
OH
OH
OAc
O
O
HO
OH
AcO
OH
OAc
OAc
O
OH
O
AcO
AcO
HO
HO
HO
AcO
O
O
10
10a
10b
2/1
OH
OAc
OH
OH
OAc
OAc
O
O
HO
OH
AcO
OAc
11
12
13
11a
12a
13a
11b
12b
13b
5
5
5
93
95
93
—
—
—
HO
OH
AcO
AcO
OAc
OH OH
OH OH
OAc OAc
OAc OAc
HO
OH
OH
OAc
OAc
OH OH
OH OH
OAc OAc
OAc OAc
HO
AcO
OH OH
OAc OAc
Reaction conditions: carbohydrate (2.0 mmol), acetic anhydride (1.2 equiv. per OH) and I2 (5 mol%) in IL400 (2.0 mL) at 50 °C under MW irradiation
(200 W). a Overall time including heating time an incubating time.

Xingquan Xiong et al. / Chinese Journal of Catalysis 36 (2015) 237–243
241
100
Table 2
Optimization of the reaction conditions for the per‐O‐acetylation of
D‐glucose.
95
90
85
80
OAc
OH
O
O
I2/IL400
O
O
AcO
AcO
HO
HO
OAc
OH
MW, T
O
OAc
OH
Entry
I2 (mol%)
Temperature (°C)
Isolated yield (%)
1
2
3
4
5
6
7
8
9
1
3
5
7
5
5
5
0
5
50
50
50
50
RT
40
60
50
50
62
75
99
99
63
80
99
60
70a
1
2
3
4
5
6
Cycle
Fig. 2. Reusability of I2 in IL400 for per‐O‐acetylation of D‐glucose.
removing the byproduct acetic acid. After completion of the
model reaction in the first run, the product was extracted using
toluene, and the I2/IL400 system was easily recovered by re‐
moving the acetic acid under reduced pressure without any
further purification. Then the I2/IL400 system was subjected to
the next reaction cycle with new reactants. As shown in Figure
2, the catalyst can be recycled and reused at least six times
without significant loss in product yield (90%–99%).
Reaction conditions: glucose (2.0 mmol), acetic anhydride (1.2 equiv.
per OH) and I2 in IL400 (2.0 mL) at 50 °C for 3 min under MW irradiation
(200 W).
a Using the traditional heating method.
It is worth mentioning that the reaction mixture was ex‐
tracted three times with toluene (2.0 mL × 3) and then the ob‐
tained toluene solution was titrated with a standard Na2S2O3
solution. It was found that only about 1.5 mg I2 existed in the
toluene, which was obviously lower than in the I2/IL400 catalyt‐
ic system (25.4 mg). Thus, this makes the process stable, of low
toxicity, and cost effective.
3.5. Scale up of per‐O‐acetylation of D‐glucose catalyzed by
I2/IL400
Peracetylated sugars are important building blocks in car‐
bohydrate chemistry, so it is significant for the per‐O‐acet‐
ylation to be performed on the many‐gram scale. From the ex‐
cellent results of the I2/IL400 catalytic system, we set out to fur‐
ther investigate the practicality of the system. To extend this
strategy to the many‐gram scale synthesis, the scale up synthe‐
sis of glucopyranose pentaacetate as a model reaction was in‐
vestigated. As demonstrated in Table 4, we have shown that
glucose was peracetylated on 1, 2, and 20 g scales to afford
excellent yields. Most importantly, when the scale of the
per‐O‐acetylation of glucose was increased to 50.0 mmol, the
per‐O‐acetylation was found to proceed successfully and glu‐
copyranose pentaacetate was still obtained in 90% yield even
after 6 recycles.
From a practical perspective, the I2/IL400 catalytic system
should be used in a wide variety of sugars and sugar alcohols.
Thus, with the optimum per‐O‐acetylation conditions, the sub‐
strate scope of the per‐O‐acetylation reactions between acetic
anhydride and various carbohydrate substrates was explored
with the I2/IL400 catalytic system (Table 2). The results are
summarized in Table 3. The monosaccharides (1a–4a), disac‐
charides (6a–10a), and sugar alcohols (11a–13a) were
peracetylated in excellent yields (90%–99%). Interestingly,
saccharide with an acid sensitive protecting group (such as a
Schiff base) (5a) can also be peracetylated with high yields
(96%). In addition, in the case of reducing sugars, the per‐O‐
acetylation reactions gave a mixture of α‐ and β‐acetate
anomers. In all cases, pure products were obtained by a simple
extraction with toluene and recrystallization. The configura‐
tions and ratios of these in Table 3 were determined by 1H NMR
spectral analysis (400 MHz). The production of all known
Table 4
Per‐O‐acetylation of D‐glucose on large scales.
1
OH
compounds gave H NMR spectra that matched data reported
in the cited references.
OAc
O
O
O
I2/IL400
MW, 50 o
HO
HO
O
AcO
AcO
OH
OAc
O
C
OH
OAc
3.4. Reusability of I2/IL400 for per‐O‐acetylation of D‐glucose
Scale
(mmol)
2
Time
(min)
3
Isolated
product (g)
0.8
Isolated
yield (%)
99
Entry
The recovery and reusability of the catalyst is a very signifi‐
cant factor for a catalytic process. In order to make the I2/IL400
catalytic system highly efficient and economical, we focused on
the reusability of I2/IL400 using the per‐O‐acetylation of
D‐glucose and acetic anhydride. Thus, a set of experiments
were performed for the per‐O‐acetylation of D‐glucose using a
recycled I2/IL400 system. We found that the I2/IL400 system can
be easily recovered by extracting the product with toluene and
1
2
5
5
2.0
98
3
50
50
50
50
15
15
15
15
15
18.5
18.2
18.1
18.0
95
93
93
92
4 a
5 b
6 c
7 d
50
17.6
90
a Catalyst was recycled from entry 3 and used for second run.
b Third run. c Fourth run. d Fifth run.

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Xingquan Xiong et al. / Chinese Journal of Catalysis 36 (2015) 237–243
127: 9692
3.6. Mechanism of I2/IL400 catalysis of sugars and acetic
anhydride
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In the acetylation, I2 served as an extremely powerful cata‐
lyst for the per‐O‐acetylation of sugars. The initial step was the
activation of acetic anhydride by I2 to afford a more active in‐
termediate, which reacted faster with the hydroxyl groups on
the sugars. In addition, I2 is also known to absorb microwave
energy. Thus, the per‐O‐acetylation reaction can be completed
quickly under I2/IL400 and microwave irradiation conditions.
4. Conclusions
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We have developed a simple, highly efficient, and eco‐fri‐
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This method gave excellent yields, and the I2/IL400 catalytic
system can be reused and recovered at least six times with no
loss of catalytic performance. When the scale of the per‐O‐acet‐
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Graphical Abstract
Chin. J. Catal., 2015, 36: 237–243 doi: 10.1016/S1872‐2067(14)60219‐9
I2/ionic liquid as a highly efficient catalyst for per‐O‐acetylation of sugar
under microwave irradiation
Toluen
e
6 cycles
>90% yields
Multi-gram scale
Xingquan Xiong*, Chao Yi, Qian Han, Lin Shi, Sizhong Li
Huaqiao University
A mild, practical, and highly efficient approach was developed to synthesize
peracetylated sugar derivatives using a recyclable iodine/PEG400‐based ionic
liquid catalyst (I2/IL400) under microwave irradiation.

Xingquan Xiong et al. / Chinese Journal of Catalysis 36 (2015) 237–243
243
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