Cellulose hydrolysis over silica modified with chlorosulphonic acid in one pot synthesis

Article abstract of DOI:10.1016/j.apcata.2014.01.035

Titration of chlorosulphonic acid against sodium silicate was carried out via a simple one pot synthesis at room temperature to form an acid catalyst denoted as RHSO₃H. The BET measurements of the catalyst showed the surface area to be 80 m² g^-1. The FT-IR clearly showed the presence of -SO₂- absorption band at the expected range. The XPS showed the presence of O, Si, and S. The presence of S 2p on the XPS spectra indicated that the sulphonic acid groups (-SO₃H) are included into the catalyst structure. The RHSO₃H was efficient for the hydrolysis of cellulose, with maximum glucose yields over 99% at 120 C with 100% selectivity. As the solubility of cellulose is very important factor to make the hydrolysis much more easily. It was observed that the mixture of DMF/LiCl or cyclohexanol/LiCl has high ability to dissolve cellulose. The catalyst was simple in its preparation, stable during the cellulose hydrolysis in addition to repeatedly without a significant loss of its catalytic activity.

Full text of DOI:10.1016/j.apcata.2014.01.035

Applied Catalysis A: General 475 (2014) 226–234
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Cellulose hydrolysis over silica modified with chlorosulphonic acid in
one pot synthesis
Kasim Mohammed Helloa,∗, Hathama Rzooki Hasanb, Muna Hasoon Sauodib,
Per Morgenc
a Chemistry Department, College of Science, Al-Muthanna University, Al-Samawa, Iraq
b Chemistry Department, College of Science, University of Baghdad, Baghdad, Iraq
c Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, Odense M, Denmark
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 October 2013
Received in revised form 13 January 2014
Accepted 16 January 2014
Available online 24 January 2014
Titration of chlorosulphonic acid against sodium silicate was carried out via a simple one pot synthesis
at room temperature to form an acid catalyst denoted as RHSO3H. The BET measurements of the catalyst
showed the surface area to be 80 m2 g−1. The FT-IR clearly showed the presence of –SO2– absorption
band at the expected range. The XPS showed the presence of O, Si, and S. The presence of S 2p on the XPS
spectra indicated that the sulphonic acid groups (–SO3H) are included into the catalyst structure. The
RHSO3H was efficient for the hydrolysis of cellulose, with maximum glucose yields over 99% at 120 ◦C
with 100% selectivity. As the solubility of cellulose is very important factor to make the hydrolysis much
more easily. It was observed that the mixture of DMF/LiCl or cyclohexanol/LiCl has high ability to dissolve
cellulose. The catalyst was simple in its preparation, stable during the cellulose hydrolysis in addition to
repeatedly without a significant loss of its catalytic activity.
Keywords:
Surface modification
Cellulose
Rice husk ash
Chlorosulphonic acid
Glucose
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
cellulose, lignin, and hemicellulose in addition to low quantities of
pectin, pigments and extracts.
Over the last two decades, a special attention has been paid to
the rice husk (RH). Due to it being available free, with a high silica
content and suitable for recycling makes it economically viable to
be used as a raw material [1]. The controlled burning of RH in air
leads to the formation of rice husk ash (RHA), which contains ca. 95%
silica [2]. RHA is a great environment threat causing damage to land
and surrounding area where it is dumped. Therefore, commercial
use of RH and its ash is the alternative solution to disposal problem.
Nowadays the environmental benefits of wood or other forms of
biomass/agricultural wastes associated with the producing of solid,
liquid and gaseous fuels which is attracting wide attention. Agricul-
tural waste has an important contributor into the world economy.
Today, various forms of agricultural wastes energy are consumed
all over the world [3]. Cellulose is a bioorganic molecule with a
long linear chain polymer of several monomeric d-glucose units
linked by ␤-1,4-glycosidic bonds. It is the most abundant organic
compound in nature and does exist in the cell wall of plants as
complex fibrous carbohydrates [4]. Natural fibers mainly consist of
Cellulose hydrolysis can be achieved by using enzymes [5], or by
diluting and concentrating acids [6]. In a preliminary experiment,
cellulose was hydrolyzed using 70% w/w sulphuric acid in a sealed
reactor. After 9 h of hydrolysis, there was approximately 31% of the
glucose has been obtained [7]. A new route to high yield sugars from
cellulose based upon the use of phosphoric acid 60% and sulphuric
acid 70% at 85 ◦C for hydrolysis, this route produced glucose with a
yield of approximately 90% after about 4 h of hydrolysis [8]. While
Changzhi et al. [9] hydrolyzed cellulose at 175 ◦C for 7 h using 85%
H3PO4 as a catalyst, there is only16% of the glucose was obtained
under these conditions.
In the present study, the modification of silica extracted from
RH with chlorosulphonic acid was described in more direct and
simple method. As the product is a solid acid, it can be applied in
the hydrolysis of cellulose to glucose.
2. Materials and method
2.1. Raw materials
The chemicals used in this study were Sodium hydroxide (Sys-
term, 99%), Aceton (GCC, 99%), Nitric acid (Scharlau, 65%), 1-Butanol
(Fluka, 99%), Cellulose (Riedle-De Haen 99%), Chlorosulphonic acid
∗
Corresponding author. Tel.: +964 7801274886.
E-mail addresses: kasimhello@gmail.com, kasimaz@yahoo.com (K.M. Hello).
http://dx.doi.org/10.1016/j.apcata.2014.01.035
0926-860X/© 2014 Elsevier B.V. All rights reserved.

K.M. Hello et al. / Applied Catalysis A: General 475 (2014) 226–234
227
(J.T. Baker, 99.8%), Cyclohexanol (Riedle-De Haen, 99%), Dimethyl-
formamide (DMF) (Systerm, 99.5%), Dinitrosalycilic acid (DNS)
(BDH, 99%), Dioxane (Riedel-De Haen, 99.5%), Glucose (BDH, 99%),
Lithum chloride (Sigma, 99%), Sulphuric acid (Poch, 95%), Toluene
(GCC, 95%). The RH was collected from a rice mill in Samawah, Iraq.
All other chemicals used were AR grade or of high purity and were
used directly without further purification.
with standard NaOH solution. An average of three separate titra-
tions was performed to obtain an average value for the CEC of
RHSO3H.
2.3.2. Pyridine acidity test
The sample, together with a beaker containing pyridine was
placed in a dessicator equipped with a valve connected to a
membrane vacuum pump (AMB Greiffenberger Antriebstechnik,
MZ2C, CE 2002/06). The system was evacuated for 1 h at a rate of
1.7 m3 h−1. The system was kept under closed vacuum for 48 h. The
atmosphere in the desicator was evacuated again for 1 h at the same
pump rate. The sample was then removed and analyzed by FT-IR in
KBr disc.
2.2. Extraction and modification of silica from RHA
2.2.1. Sources of silica
The RH was chosen as the source of amorphous silica [10] as
it was available in abundance. The silica was extracted from RH
according to a reported method [11,12].
2.4. Catalytic hydrolysis procedure
2.2.2. The one-step preparation of solid silica-sulphonic acid
About 3.0 g of RHA was added to 100 mL of 1.0 M NaOH in a
plastic container and stirred for 30 min at room temperature to
converted silica to sodium silicate. The sodium silicate formed was
filtered to remove undissolved particles. The solution was then
titrated slowly with 3.0 M nitric acid and 3.0 mL (51.0 mmol) of
chlorosulphonic acid with constant stirring. The change in pH was
monitored by using a pH meter. A white gel started to form when
the pH reached 10.0. The titration was continued until the pH of
the solution reached 3.0. The gel was aged for 24 h at room temper-
ature. It was later separated by centrifuge. The separation process
was repeated 6 times with copious amount of distilled water, and
the final washing was done with acetone. The sample was then
dried at 110 ◦C for 24 h and finally, it was ground to a fine powder,
which weighed 6.4 g. It was labelled as RHSO3H.
2.4.1. Hydrolysis of cellulose
The cellulose hydrolysis was carried out in liquid-phase in a
50 mL round bottom flask equipped with magnetic stirrer and
water condenser. 20 mL of DMF, 0.2 g of LiCl and cellulose (0.18 g,
20 mmol) were separately transferred to the round bottom flask
containing 0.2 g of the catalyst (pre-dried at 110 ◦C for 24 h and
cooled in desiccators to minimize moisture content). The hydrolysis
temperature fixed at 120 ◦C. The hydrolysis mixture was refluxed
for 8 h. A 0.5 mL portion of the clear hydrolyte solution from the
reaction mixture was transferred into a vial and 2.0 mL of deion-
ized water was added. To this solution 2.0 mL of DNS reagent and
2.0 mL of 2.0 N NaOH were added and the mixture was incubated in
a water bath maintained at 90 ◦C for 5 min [13,14]. The DNS reagent
was prepared according to an IUPAC method [15]. The reagent blank
sample was prepared with 2.0 mL of deionized water, 2.0 mL of DNS
reagent and 2.0 mL of 2.0 N NaOH and heated similar to the samples.
Then the absorbance was measured at 540 nm, against the reagent
blank, and glucose concentrations in solutions were calculated by
employing a standard curve prepared using glucose. The catalytic
activity with different mass of catalyst (50, 100, 150, and 200 mg),
different temperatures (RT, 100, 110, and 120 ◦C), different solvents
i.e. (toluene, dioxane, 1-butanol, cyclohexanol, and ethanol), and
RHA-blank catalyst were studied by using the same procedure as
in above.
2.3. Sample characterization
The RHSO3H was characterized by Powder X-ray diffraction
(Systerm). XPS was performed in a SPECS system, including a Phoi-
bos 100 analyzer. The samples were in the form of a white small
size grained powder. This powder was deposited on the top sur-
face of a double sided sticky carbon tape attached to a stainless
steel sample holder. The deposited powder was uniformly cover-
ing the carbon tape and inserted in the vacuum system and pumped
down to 3 × 10−10 Torr overnight. XPS spectra were recorded with
Mg Kalpha and Al Kalpha radiation, and the spectra were compared to
discriminate between Auger and photoemission peaks. Two spec-
tra are shown: A wide scan spectrum covering a wide range of
binding (and kinetic-) energies, recorded with Al Kalpha radiation,
and a resolution of around 2.5 eV, for monitoring the concentra-
tion of the elements in the sample, and a detailed scan with a
resolution of 1.4 eV, which serves to detect chemical shifts and
to separate overlapping peaks. The latter spectrum was recorded
with Mg Kalpha radiation, which gives a slightly better resolution
than for Al Kalpha. The resolution for the survey scans was 2.5 eV.
Element peaks were identified with the CasaXPS software. The FT-
IR spectra were recorded on a 8400 S Shimadzu using KBr disk.
UV–visible was recorded on a I65o pc Shimadzu. The scanning
electron microscopy (SEM) was recorded on a (Leica Cambridge
S360) and energy dispersive spectrometry (EDX) (Edax Falcon Sys-
tem). The Atomic Force Microscopy (AFM) were obtained using
CSPM-AA3000, SEM/EDX (Leo 35VP from Zeiss) AEM (PHI Model
560).
2.4.2. The reusability of the catalyst
Reusability experiment was conducted by running the hydroly-
sis successively with the same catalyst under the same hydrolysis
condition. The hydrolysis was first run with the fresh catalyst to
complete conversion and then the catalyst was filtered and washed
with hot dioxane then with hot mixture of DMF and LiCl and dried
at 110 ◦C. After regeneration, the catalysts were reused under the
optimised reaction conditions.
2.4.3. Hydrolysis procedure for homogenous catalyst
The hydrolysis using homogenous catalyst was studied with sul-
phuric acid. Typically, a 50 mL capacity two necked round-bottom
flask, equipped with a magnetic stirrer (700 rpm) and water con-
denser was used. 20 mL of DMF was transferred by pipette into the
round bottom flask containing 8.8 mg (6.9 mmol) of sulphuric acid.
After the reaction temperature reached 120 ◦C, 0.18 g (20.0 mmol)
of cellulose was added. The hydrolysis mixture was refluxed. Sam-
ples for analysis (∼0.50 mL) were withdrawn at regular intervals
from the hydrolysis mixture by means of a syringe equipped with
filter (cotton wool). To this solution 2.0 mL of DNS reagent and
2.0 mL of 2.0 N NaOH were added and the mixture was incubated in
a water bath maintained at 90 ◦C for 5 min. The glucose concentra-
tions in solutions were calculated by employing a standard curve
prepared using glucose.
2.3.1. Cation exchange capacity (CEC)
1.0 g of sodium chloride was dissolved in 25 mL of distilled water
in a conical flask with a magnetic stirrer. 1.0 g ( 10 mg) sample of
RHSO3H was added to the solution and left to stir for 30 min. 2–3
drops of phenolphthalein was added and the sample was titrated

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K.M. Hello et al. / Applied Catalysis A: General 475 (2014) 226–234
-
+
+
O Na
OSO3H
-
+
RT/30 min
ClSO3H/ 1M HNO3
pH = 3 / 20 min.
Sodium
Silicate
O Na
+ NaCl
OSO3H
OSO3H
SiO2
RHA + NaOH
-
O Na
Scheme 1. The reaction sequence for the direct synthesis of RHSO3H. The approximate time taken for the completion of the experimental process was less than 60 min.
3. Results and discussion
This result was supported by XPS result as will explain latter. Both
NaCl and Na2SiO3 were come from the synthesis of the catalyst. This
result is in agreement well with the literature [19]. The patterns at
2ꢀ angle of ca. 14◦, 19◦ were due to the presence of sulphur onto
silica surface [20]. The presence of sulphur may indicate that the
sulphonic acid was immobilized onto silica.
3.1. The synthesis
Silica which extracted from RHA has been modified with chloro-
sulphonic acid in one pot synthesis at room temperature and
pressure. Scheme 1 shows the synthesis of RHSO3H. The RHA has
been characterized elsewhere [16].
3.3. The nitrogen adsorption analysis
3.2. Powder X-ray diffraction (XRD)
Fig. 2 shows the nitrogen adsorption isotherm obtained for
RHSO3H and inset is shown the pore size distribution graph. The
hysteresis loop observed in the range of 0.4 < P/Po < 1.0, is associ-
ated with capillary condensation according to IUPAC classification.
The isotherm shown is of type IV and exhibited an H3 hystereis
loop [21].
The BET analysis showed the specific surface area of RHSO3H
was 80 m2 g−1, while the specific surface area of RHA which was
reported to be 347 m2 g−1 [16]. The decrease in the surface area of
Fig. 1(a and b) shows XRD pattern of RHA and RHSO3H. A broad
diffraction band at 2ꢀ angle of ca. 22◦ in Fig. 1(a and b) was observed.
This was typically referred to amorphous silica. This similar to the
observation was cited by Adam et al. [17] and Yalc¸ in, et al. [18].
According the JCPDS files in Fig. 1(b), the patterns at 2ꢀ angle of ca.
28◦, 33◦ were due to the formation of NaCl. While the patterns at 2ꢀ
angle of ca. 29◦, 34◦, 38◦, 48◦ were due to the formation of Na2SiO3.
Fig. 1. The X-ray diffraction pattern for RHA and RHSO3H. (a) XRD of RHA, (b) XRD of RHSO3H.

K.M. Hello et al. / Applied Catalysis A: General 475 (2014) 226–234
229
140
120
100
80
the chemical transformation that is taking place adjacent to the
–Si–O–Si– framework by chlorosulphonic acid.
0.20
0.15
0.10
0.05
0.00
3.5. X-ray photoelectron spectra (XPS)
The photoelectron peaks of O 1s, Si 2p, S 2p of the catalyst
are presented in Fig. 4(a and b). The formation of sulphur–oxygen
species, which typically have binding energy in region 167–169 eV,
is already seen. Spectral peak of S 2p XPS of RHSO3H has been
occurred at ca. 168–169 eV associated with sulphate (S 6+) species
due to sulphonic acid groups (–SO3H). This result was consistent
with a previous study [23]. The O 1s binding energy was found at
532.3 eV for RHSO3H while the Si 2p binding energy at 102.7 eV
that was obtained from an overlap of Si 2p3/2 and Si 2p1/2 binding
energy [24]. The XPS has also shown a peak at ca. 1070 eV associ-
ated with Na 1s species, the presence of Na due to synthesis process
of the catalyst. In order to better observation of sulphonic groups,
the XPS spectrum between 250 and 0 eV was included (Fig. 4b). The
positions of all the peaks in the spectra have been shifted (around
5 eV) to compensate for charging of the sample due to the X-ray
beam, and a low conductivity of the powder sample. With this shift
the O 1s line is brought to a position of a 532 eV binding energy. The
S and Si peaks are shifted about 4 eV with respect to their neutral
positions, after this alignment of the spectrum for the O 1s peak
position. This indicates that all Si and S present in the sample are
oxidized. The XPS results imply that the chlorosulphonic acid was
immobilized onto silica.
60
10
20
30
40
50
60
70
80
Pore diameter (nm)
40
20
0
0.0
0.2
0.4
0.6
0.8
1.0
P/Po
Fig. 2. The N2 adsorption/desorption isotherms of RHSO3H with the corresponding
pore size distribution inset.
RHSO3H, however, could be due to the reduction of the surface sites
by chlorosulphonic acid causing the surface to be over crowded
with the ligand network on the surface and thus blocked the pores.
The RHSO3H (Fig. 2) showed a broad pore size range from 10 to
50 nm which is in the mesoporous range.
3.4. Fourier transformed infrared spectroscopy analysis (FT-IR)
3.6. Scanning electron microscope (SEM)
Fig. 3 shows the FT-IR spectra of RHA and RHSO3H spec-
trum. The strong and broad band in the range of 3500–3455 cm−1
region corresponds to the hydrogen bonded from SiO–H and
HO–H of adsorbed water. The band at 1639 cm−1 is due to the
HO–H of adsorbed water. The RHSO3H spectrum shows bands at
1384–1201 cm−1 is due to the asymmetric and symmetric stretch-
ing bands of –SO2– moieties, which confirm the formation of
sulphonic acid [22]. The RHA spectrum does not show these bands.
In RHA the Si–O–Si vibration appears at 1099 cm−1 [11]. This vibra-
tion was observed displaced to 1051 cm−1 in RHSO3H. This reflects
The SEM of RHSO3H was shown in Fig. 5. It seems that the cata-
lyst has shown some rocky particles appear on the surface. It is also
indicated that the surface was highly rough and porous.
3.7. Atomic force microscopy imaging (AFM)
The AFM images technique was used to characterize topograph-
ical and morphological on the RHSO3H surfaces. Sup. 1(a, b and c)
Smooth
ma74
7.5
%T
6
RHA
4.5
3
RHSO H
3
1.5
0
-1.5
4000
ka
3500
3000
2500
2000
1750
1500
1250
1000
750
500
1/cm
Fig. 3. The FT-IR of RHA and RHSO3H.

230
K.M. Hello et al. / Applied Catalysis A: General 475 (2014) 226–234
Fig. 4. The XPS spectrum of RHSO3H. The Si, S and O content are shown. (a) A wide scan spectrum, (b) the XPS spectrum between 250 and 0 eV.
in absorbance mode using KBr disc at the range of 1700–1400 cm−1
.
shows the AFM of RHSO3H a relative layer surface with a mean
value of surface roughness (Rq) 1.09 nm. The granularity accumu-
lation distribution chart Sup. 1(c) shows the distribution of the
particle size. It was observed that the particles were distributed in
the range of 70–160 nm. This indicates that the most of the catalyst
particles were in nano size.
The FT-IR shows bands of the pyridinium ion can be distinguished
at 1633 and 1547 cm−1 which corresponding to the Brönsted acid
species. The band at 1433 cm−1 corresponding to hydrogen bonded
pyridine [25]. The band at 1494 cm−1 [26] was due to the interac-
tion of silanol with Pyridine. These bands did not show up in the
spectra before the Pyridine test.
3.8. Pyridine test
3.9. Cation exchange capacity (CEC)
The easiest and direct method to distinguish between Brönsted
and Lewis acid species is the IR spectroscopy of chemisorbed pyri-
dine. Sup. 2 shows the RHSO3H after and before pyridine acidity test
The base titration is generally regarded as a technique that can
reasonably be used to calculate the concentrations of acid sites of

K.M. Hello et al. / Applied Catalysis A: General 475 (2014) 226–234
231
Fig. 5. The SEM micrographs of RHSO3H at different magnification.
related solid acids. In this work, NaOH as the basic probe compound
was used [27]. The CEC was determined by using the following
formula [28].
cellulose to glucose was 100% at the optimum time of the hydrol-
ysis. In our previous studies, we had been immobilized different
silica-SO3H acid catalysts for different purposes [1,2,29,33]. Even
these catalysts had low acid density; they had shown very good
catalytic activities. Therefore, it is saved to conclude that the activ-
ity of silica–SO3H could be due to the strong acid character of the
active sulphonated sites. This phenomenon could explain the activ-
ity of RHSO3H which has low CEC and show high activity during the
cellulose hydrolysis.
The maximum hydrolysis of cellulose over DMF without catalyst
was 14% in 8 h. It was observed that the hydrolysis over RHA-balnk
was found to be 20% in 8 h. The activity of RHA could be related to
the weak acidity of the silanol group over the surface of silica.
Normality of NaOH × Volume of NaOH
CEC =
g of material
The concentrations of acid sites on the RHSO3H was determined
in water, by exchanging with excess Na+ (from NaCl) followed by
titration with a standard NaOH solution. The CEC was found to be
0.07 mequiv/g. However, the low CEC value can be attributed to the
poor accessibility of the sulphonic acid group by the titrating base
[29]. Some authors cited that the low CEC results associated with
sulphonic acid groups buried deep within the silica frame work
[30,31]. Another possible explanation is the crowdedness of sul-
phonic groups in the pore walls of the catalyst thereby limiting
the exchange capacity between NaCl and the sulphonic acid group
before the titration [32].
3.10.2. Effect of catalyst mass
The hydrolysis of cellulose was carried out by varying the
amount of RHSO3H between 50 and 200 mg while keeping the other
parameter fixed as, 8 h hydrolysis time at 120 ◦C. The effect of the
amount of catalyst on the hydrolysis of cellulose is shown in Fig. 7.
When the catalyst mass was increased from 50 to 200 mg, the cel-
lulose hydrolysis increased from 75% to 99%. Further increase of the
catalyst mass had no significant effect. The increased in the conver-
sion with the catalyst mass could be attributed to the availability
of a greater number of catalytically active sites. Therefore 200 mg
was choosing as the optimum mass of the catalyst.
3.10. Hydrolysis of cellulose over RHSO3H catalyst
The RHSO3H was used to hydrolyze cellulose in liquid-phase
reaction using new solvent system. Further various parameters
such as effect of hydrolysis time, mass of catalyst, temperature,
solvents effects on glucose formation were evaluated to optimize
the hydrolysis conditions.
3.10.1. Influence of hydrolysis time
100
Variable
The effect of the hydrolysis time on the hydrolysis of cellulose
over RHSO3H, RHA-Blank as well as homogenous sulphuric acid
and the new solvent system without catalyst (DMF/LiCl) are shown
in Fig. 6. The hydrolysis was carried out with 200 mg catalyst using
a DMF/LiCl as a solvent at 120 ◦C. The initial hydrolysis of cellulose
during the first hour was 2% and it reached the maximum hydroly-
sis 99% in 8 h. The homogeneous sulphuric acid (8.8 mg, 6.9 mmol)
showed 80% at 4 h and then the hydrolysis was decreased due to the
hydrolysis of glucose itself. It was well known that the homogenous
catalyst is more effective than the heterogeneous one. The hydrol-
ysis of cellulose over H2SO4 was reached to the optimum at the
4 h of the hydrolysis time then it decrease due to the hydrolysis of
the glucose to another products. The hydrolysis of cellulose over
RHSO3H was reached to the optimum at the 8 h of the hydrolysis
time. At this point the behaviour of both catalysts is same the only
difference is time. At the optimum time of the cellulose hydroly-
sis over RHSO3H, we did not deduct any hydrolysis of glucose. After
the optimum time of the cellulose hydrolysis over RHSO3H, the glu-
cose was started to hydrolyze to other products too. Such a work is
under process on our laboratory. The selectivity of the hydrolysis of
RHSO3H
Homogeneous H2SO4
RHA-Blank
80
With out catalyst
60
40
20
0
0
1
2
3
4
5
6
7
8
9
Time (h)
Fig. 6. The hydrolysis of cellulose to glucose over RHSO3H, RHA-blank, sulphuric
acid and DMF without catalyst as a function of hydrolysis time. The hydrolysis con-
ditions were: catalyst 200 mg, H2SO4 (8.8 mg, 6.9 mmol), and reaction temperature
(120 ◦C).

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K.M. Hello et al. / Applied Catalysis A: General 475 (2014) 226–234
100
80
60
40
20
0
Variable
50 mg
100 mg
150 mg
200 mg
0
1
2
3
4
5
6
7
8
9
Time (h)
Fig. 7. The hydrolysis of cellulose to glucose over RHSO3H, as a function of mass of
Fig. 9. The hydrolysis of cellulose to glucose over RHSO3H, at different solvents. The
catalyst. The hydrolysis conditions were: 8 h hydrolysis time at 120 ◦C.
hydrolysis conditions were: catalyst 200 mg, 120 ◦C and 8 h reaction time.
3.10.3. Influence of hydrolysis temperature
In this study it is found that the cellulose was highly soluble in
DMF or cyclohexanol containing LiCl. This phenomenon was not
cited before. The solvent–lithium interaction and the chloride ion
were playing a vital role in the solubility of cellulose. The lithium
ions are tightly linked with the carbonyl group of DMF while the
chloride ions are left unencumbered. Thereby Cl− is highly active as
nucleophilic base and plays a major role by breaking up the inter-
and intra-hydrogen bonds [39]. This could make the hydrolysis of
cellulose much more easily.
The effect of the solvent on the hydrolysis of cellulose over
RHSO3H was shown in Fig. 9. The hydrolysis was studied over dif-
ferent solvents i.e. 1-butanol, ethanol, cyclohexanol, dioxane and
toluene as well as DMF. All these solvents contain LiCl. It was
observed that the hydrolysis of cellulose over these solvents was
increased according the following order:
The effect of temperature on the hydrolysis of cellulose over
RHSO3H is shown in Fig. 8. The hydrolysis increased when the
reaction temperature was increased from room temperature to
120 ◦C. The hydrolysis was ca. 99% at 120 ◦C. Most researchers
set the hydrolysis temperature at 100 ◦C. To confirm the effect of
hydrolysis temperature on the yield of glucose, comparing with
Xia and co-workers [34] who they have been used different SO3H-
functionalized acidic ionic liquids as a homogeneous catalyst for
cellulose hydrolysis. The maximum sugar yields at 100 ◦C were 83%
at 2 h. By using RHSO3H the sugar was reach ≈80% at 100 ◦C and
99% at 120 ◦C in 8 h. Taken into account the nature of the RHSO3H
catalyst used (heterogeneous catalyst) in this study. This clearly
indicates that the using of RHSO3H is effective to promote the
hydrolysis of cellulose.
DMF > cyclohexanol > ethanol > dioxane > 1-butanol > toluene
3.10.4. Influence of the solvents effect
Most of our dissolution system could form hydrogen bonding
between layers of cellulose chains and the solvents. The DMF con-
tains more than one centre able to form a hydrogen bonding with
the cellulose and this could lead to increasing the solubility of cel-
lulose which makes the hydrolysis easier. The other solvents have
only one centre able to form a hydrogen bond with cellulose. While
the toluene could not form a hydrogen bond and it has a very low
solubility of cellulose.
The hydrolysis of cellulose is varying according to its solubility
into different solvents. Cellulose can be dissolved in several com-
plex solvents, such as Cu(NH3)4(OH)2, [NH2CH2CH2NH2]Cu(OH)2,
[NH2CH2CH2NH2]Zn(OH)2, and ([Pd(NH2(CH2)2NH2)](OH)2 [35]. It
was mentioned that the cellulose was completely soluble in the
N,N-diethylacetamide containing LiCl [36]. Since 1972 up to date
lithium chloride/N,N-diethylacetamide has become very popular to
dissolve cellulose [37,38]. These early studies showed the unique-
ness of LiCl/N,N-diethylacetamide as solvent system.
3.10.5. Catalyst recycles experiments
Fig. 10 shows the RHSO3H recycles experiments. After the first
reaction was run using the catalyst at 120 ◦C for 8 h, the mixture,
including the solid catalyst and the cellulose residue, was then
filtered and washed with hot dioxane then with hot mixture of
DMF and LiCl (repeated three times) and the catalyst was heated at
100 ◦C for 24 h. Next, fresh cellulose and DMF with LiCl were added
to the catalyst obtained and a second run was conducted, as well
as a third run, using the same procedure. As shown in Fig. 10, the
product yields in the second and third runs were similar to that
in the first run, without any loss in the catalytic activity. These
results indicated that catalytic performance was not lost in the
course of the catalytic runs. Since the evaluation of the catalyst sta-
bility is important for practical catalyst use, further studied on the
stability of the RHSO3H catalysts in repeated runs was done. The
pre-treated RHSO3H catalysts were characterized by FT-IR analy-
sis (see supplementary data, Sup. 3). The FT-IR of the catalysts was
not changed after pre-treatment. The analysis data of the textural
properties demonstrated that the RHSO3H catalyst had excellent
stability during the pre-treatment.
100
Variable
100 C
110 C
120 C
80
RT
60
40
20
0
3
4
5
6
7
8
Time (h)
Fig. 8. The hydrolysis of cellulose to glucose over RHSO3H, at different temperatures.
The hydrolysis conditions were: catalyst 200 mg, and 8 h reaction time.

K.M. Hello et al. / Applied Catalysis A: General 475 (2014) 226–234
233
O
O
H
O
HO
SiO
S
2
O
O
O
OH
HO
SiO2
O
OH
S
HO
SiO2
OH
O
OH
S
HO
HO
O
O
OH
HO
O
HO
HO
HO
O
O
O
OH
HO
O
OH
O
n
OH
OH
O
OH
OH
HO
OH
O
HO
HO
HO
O
O
HO
HO
HO
O+
OH
O
HO
OH
OH
n
OH
O
HO3SO
OSO3H
SiO
SiO
2
2
OH
O
HO
HO
OH
OH
Scheme 2. The possible mechanism of the cellulose hydrolysis to glucose over RHSO3H.
specific surface area. The XPS shows the presence of O, Si, S peaks.
The presence of S 2p on the XPS spectra indicated that the sulphur
has +6 oxidation state which corresponded to the sulphonic acid
groups (–SO2–).The FT-IR clearly showed the presence of –SO2–
absorption band at the expected range. The RHSO3H was used to
hydrolyze of cellulose to glucose at 120 ◦C for 8 h. The catalytic
activity of the catalyst reach to 99% of glucose and the selectivity
was 100%. It was found that the hydrolysis of cellulose became
much more easily when DMF or cyclohexanol containing LiCl were
used as a solvent. The catalyst was simple in the preparation, stable
during the hydrolysis and could be used several times without
significant loss of its catalytic activity.
Acknowledgments
The Authors would like to thank Dr. T. Radika (Scientific Society
under M/o Communications and Information Technology, India) for
doing some analysis. Special thanks to Dr. Jawad Kadhim (Depart-
ment of Chemistry, College of Science, Al-Muthanna University) for
the critical discussion regarding the manuscript.
Fig. 10. The hydrolysis of cellulose to glucose over RHSO3H, reusability. The hydrol-
ysis conditions were: catalyst 200 mg, 120 ◦C and 8 h reaction time.
3.10.6. The mechanism of the hydrolysis of cellulose over RHSO3H
As shown in the characterization techniques which used above,
the RHSO3H has Brönsted acid sites. These acid sites could inter-
act rapidly with the glycosidic oxygen linking two sugar units
via a hydrogen bonding between layers of cellulose chains. Then
the cleavage of the C–O bond to the cyclic carbonium ion takes
place. Finally the yield of monosaccharides after partial hydrolysis
is occurred and the catalyst could hydrolyze new cellulose chains
as in Scheme 2.
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