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Preparation of Nano Particles Sulfated Titania Catalyst Aerogel for
Synthesis of Glycerol Mono Oleate (Gmo)
Rakhman Sarwono
1
, Silvester Tursiloadi
1
, Dewi Sondari
2
1
Research Center for Chemistry, National Research and Innovation Agency-BRIN Kawasan Puspiptek, Serpong,
Tangerang 15314, Indonesia
2
Research Centre for Biomaterial, National Research and Innovation Agency, Cibinong Science Centre, Jl.Raya Jakarta-
Bogor, km 143, West Jawa, Indonesia
DOI: https://doi.org/10.51583/IJLTEMAS.2025.140500052
Received: 21 May 2025; Accepted: 24 May 2025; Published: 11 June 2025
Abstract: Catalysts nanoparticle sulfated titania aerogel have been prepared through one-step synthesis by the sol-gel method using
sulfuric acid as catalyst followed by the one-step CO
2
supercritical extraction. The catalysts were tested in reaction of oleic acid
with glycerol to produce glycerol mono oleate (GMO). Thermal evolution of the gels was evaluated by TGA-DTA, N
2
adsorption,
TEM and XRD, and the IR absorption spectra measurements were made to discuss the structure of sulfated titania. The anatase
phase is stable after calcination at temperatures up to 700
o
C, and the specific surface area, total pore volume and average pore
diameter of anatase phase do not change significantly after calcination at 600
o
C. Thermally stable and highly acidic sulfated titania
aerogel is attractive as catalyst. The aerogels calcined at 500, 700 and 750
o
C have similar activities for synthesis of glycerol mono
oleate surfactant. However, the activity of the aerogel calcined at 600
o
C is low. At 500
o
C, a relatively large amount of sulfate
remains, and the aerogel has high activity.
Keywords: Nanoparticle sulfated titania, one-step CO
2
supercritical extraction, glycerol mono oleate.
I. Introduction
A catalyst has an important role in the chemical reaction. One type of catalyst is that widely used is the catalyst in the esterification
process. Sulfated titania as solid acid catalyst is one of the modified titania gel products by reacting titania gel with sulfuric acid.
Anatase titania has attracted much attention for its wide applications as key material in photocatalyst,
1
solar cells,
2
gas sensors
3
and electrochromic devices.
4
The acid strengths of sulfated titania anatase are high. New types of nonzeolitic solid superacids,
namely single or binary metal oxides (ZrO
2
, TiO
2
, Fe
2
O
3
, TiO
2
–SiO
2
, NiO–ZrO
2
etc.) modified by sulfate ions, have been
developed.
5-12
These materials exhibit extremely high activities for various acid-catalyzed reactions such as skeletal isomerization
of butane, ring-opening isomerization of cyclopropane, alkylation of benzene derivatives, cracking of paraffins, and dimerization
of ethylene.
13-19
Recently, considerable research attention has been directed towards several sulfated metal oxide systems.
20-26
The
sulfated TiO
2
, in which covalent surface sulfates such as TiOSO
4
can be formed by the sulfuric acid treatment, possesses acid
centers of high acid strength in the range -16.04 <H
0
< -14.52,
6
similar to sulfated zirconia, and has redox sites of Ti
4+
/Ti
3+
as well
as SO
4
2-
type. Here H
0
is the Hammett acidity function. Ho is used to describe the strength of superacids which is actually equivalent
to pH for aqueous solutions. However, the disadvantage of anatase phase TiO
2
is its relatively low surface area, usually smaller
than 55m
2
/g,
27
and the poor stability of anatase at high temperatures, stable only below 500
o
C.
28
The aerogels, prepared by the sol-gel method followed by supercritical drying, consist of nanoparticles and have large surface area
and high porosity. The first step in the preparation is the formation of an alcogel through the sol-gel chemistry, hydrolysis and
subsequent condensation in alcoholic solutions. For catalytic uses, the solvent must be removed from the gel. During conventional
drying, a liquid-vapor interface is formed in the pores, and the corresponding surface tension collapses the oxide network, thereby
reducing its porosity and surface area. However, in the supercritical drying process, the liquid solvent is replaced with a supercritical
fluid, and the liquid-vapor interface is eliminated. This supercritical fluid can then be safely removed from the pores leaving the
oxide network intact. The resulting material, aerogel, can have high porosity, >90%, very low density and extremely large surface
area.
29
In this work, the catalytic activities of resulting materials were evaluated for the esterification of oleic acid with glycerol to produce
glycerol mono oleate. Palm oil in Indonesia is the largest plantation that spreads throughout the province. Indonesia is currently the
world's largest producer of palm oil, with an area of 11.4 million ha. Indonesia's palm oil production in 2015 reached 31.9 million
tons.
30
Most of Indonesia's palm oil production is still in the form of CPO (crude palm oil), this causes the added value of Indonesian
palm oil is still low. One of the efforts undertaken to improve oil palm based agribusiness is to increase the added value of palm oil
such as producing derivative products of palm oil.
One type of surfactant is a Glycerol mono oleate(GMO). GMO is a synthetic compound that is considered a monoglyceride. The
petitioned purpose is for use as a defoamer, but the substance has a number of food applications, as well as application as an
excipient in pharmaceutical products. The structure of glycerol mono oleate (GMO). The activity and selectivity of catalysts were
compared by varying calcination temperature.
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II. Methodology
Materials
The materials used in this study were titanium tetra-n-butoxide (TNB), Ti(n-OC
4
H
9
)
4
, aquadest, sodium hydroxide (NaOH), sulfuric
acid (H
2
SO
4
) 96%, 70% ethanol, CO
2
and hydrogen.
Material Preparation
Titania sol-gel synthesis has been developed from inorganic precursors and from metal organic Ti(OR)4.
31
The sulfated-TiO
2
wet
gel was prepared by hydrolysis of titanium tetra-n-butoxide (TNB), Ti(n-OC
4
H
9
)
4
, in a methanol solution with sulfuric acid catalyst.
The molar ratios used for the synthesis were [TNB]: [H
2
O]: solvent = 1:13.4:12.7 and [H
2
SO
4
]: [TNB] = 0.06. At first, TNB was
dissolved into methanol at room temperature. A mixture of the catalyst solution, remaining methanol, H
2
O and H
2
SO
4
, was added
to the TNB solution, and then stirred for 1h. The solution was completely gelled in 24h after addition of the catalyst. The un-
sulfated-TiO
2
wet gel was prepared in the same condition using HNO
3
as catalyst for hydrolysis. The solution was completely
gelled in 2 min after addition of the catalyst. The gel time was defined as the time required after mixing for the vortex created by
the stirring to disappear completely. After aging at room temperature for 24h, the wet gels were supercritically extracted by flowing
supercritical carbon dioxide at 60
o
C and 22Mpa for 4h using a supercritical extraction system. Schematic equipment (Supercritical
Fluid Extraction System, Newport Scientific Inc.) as shown in Figure 1.
Fig.1. Supercritical Fluid Extraction System, Newport Scientific Inc.
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Changes in the nanostructure of the aerogel during heating were evaluated using thermo gravimetric and differential thermal
analyses (TG-DTA, Seiko Exstar 6000 TG/DTA 6200 system) and N
2
adsorption measurements (Quantachrome, Autosorb). TG-
DTA measurements were carried out under airflow of 300 ml min
-1
, with a heating rate of 10
o
C min
-1
. The specific surface area,
pore volume and pore size distribution of the gels, before and after calcination, were estimated by the BET and Barret-Joyner-
Halenda (BJH) method using N
2
adsorption-desorption curves.
32
Infrared spectra of the sulfated gels were measured by the KBr disc method with a Fourier transform infrared spectrometer (FTIR,
BIO-RAD FTS-60A). The grain size of the extracted samples was estimated from the images observed by a transmission electron
microscope (TEM, Philips, TECNAI F20). Crystallization behaviors of the aerogels were investigated by X-ray diffractometry
(Rigaku, RAD-C) after calcination at temperatures in the range from 500 to 800
o
C with a heating rate of 10 °C min
-
1
, holding time
of 2 h and a cooling rate of 10 °C min
-
1
.
The catalytic activity of sulfated titania as-prepared and after calcination at various temperature, were evaluated for the reaction of
oleic acid with glycerol to produce glycerol-mono-oleate when the molar ratio of oleic acid and glycerol was 1:1. The operational
temperature was 180
o
C. During the reaction, sampling was performed every one hour for 7h. Each sample was analyzed for its acid
saponification values and percentage of the produced esters (yield).
III. Results and Discussion
Catalyst characterization
Gelling time of sulfated titania 24 h is much longer than that of un-sulfated titania e.g. 2 minutes. This showed that by using sulfuric
acid as the catalyst for hydrolysis, the ion sulfate was coordinated to Ti
4+
and formed bidentate sulfate (steric hindrance factor),
19
and then obstructed the reaction of formation polymerization of gel. The specific surface area of the sulfated and un-sulfated titania
aerogel (Fig. 7a) are as large as those of the usual titania aerogels, e.g. the specific surface area was about 160 m
2
g
-1
for the as-dried
aerogel prepared by supercritical drying in ethanol.
33
The simple process of one-step CO
2
supercritical extraction of titania gels is
as good as the usual supercritical drying method. The advantage of this method is a simple one-step-process, and it needs shorter
processing time, safety and low cost. The direct extraction of solvent in wet gels with supercritical CO
2
will be a good alternative
method for the usual “aerogel” method.
TG-DTA profiles of the sulfated and un-sulfated aerogel are given in Fig. 2. For the sulfated aerogel (Fig. 2a), a broad endothermic
peak with gradual weight losses about 10% at 100
o
C, a sharp exothermic peak and a weight loss about 10% at 240
o
C were observed.
A broad and small exothermic peak at 400
o
C and a small exothermic peak at 500
o
C accompanied with a gradual weight loss were
observed. The total weight loss at temperatures up to 750
o
C was about 40%, and practically no more weight loss was observed at
temperatures higher than 750
o
C. For the un-sulfated aerogel (Fig. 2b), weight loss about 5% was observed around 80
o
C. In the
temperature range between 150 and 400
o
C, several small exothermic peaks and a gradual weight loss about 10% were observed.
Beyond 400
o
C, the un-sulfated aerogel practically lose no more weight.
Solvent and other organic residue in the un-sulfated aerogel can be eliminated at temperatures up to 400
o
C (Fig. 2b). The first two
weight losses observed for the sulfated aerogel, about 100
o
C accompanied with a small endothermic peak and up to 250
o
C
accompanied with a strong exothermic peak, can be attributed to the evaporation and combustion of the solvent ethanol and sulfuric
acid residue (Fig. 2a).
Fig. 2 TG-DTA profile of (a) sulfated titania aerogel and (b) un-sulfated aerogel.
Fig. 3. shows the FT-IR spectra of the sulfated gel as-extracted, calcined at 500, 600, 700 and 800
o
C for 2h in the range from
4000cm
-1
to 400cm
-1
. The broad absorption band around 3400 cm
-1
for all samples indicates the OH groups, the occluded water
and surface = Ti-OH groups with H-bonding. Infrared spectra of sulfated metal oxides generally show a strong absorption band at
1380-1370cm
-1
and broad bands at 1250-900cm
-1
.
5, 34
The former is attributed to the stretching frequency of S=O and the latter
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bands are the characteristic frequencies of SO
4
2-
.
5, 35
The as-extracted sample shows the presence of the absorption bands in the
range from 1250 to 900 cm
-1
, 1250, 1128, 1058, and 900 cm
-1
, and strong peaks at 1635 cm
-1
and at 1461cm
-1
, attributed to the
characteristic frequencies of SO
4
2-
, and stretching of -OH and vibration of -C-H, respectively.
5
After calcination at 500
o
C, the peak
at 1461cm
-1
disappeared, but the peaks at 3400cm
-1
and at 1635cm
-1
ascribed to OH group still existed and strong peak at 400-600
cm
-1
attributed to metal-oxygen bonds of Ti-O was found.
36
Fig. 3. IR absorption spectra of sulfated titania aerogel after calcination at various temperatures (a) as-prepared, (b) 500
o
C, (c)
600
o
C, (d) 700
o
C, and (e) 800
o
C
The X-ray powder diffraction pattern for the sulfated titania aerogel calcined at 500
o
C shows the diffraction peaks of anatase (Fig.
4b). The anatase structure was stable after calcination up to 700
o
C (Fig. 4d). After calcination at 800
o
C, the diffraction peaks of
anatase disappeared (Fig. 4e).
5
The wide peaks that appear at 2h = 25, 37, 47, 55, and 62_ are corresponded to the pure anatase
crystalline phase.
37
Anatase is the most stable form by 8-12 KJ mol
-1
,
38
and can be converted to rutile by heating up to temperatures
~ 700
o
C.
39
Fig. 4 XRD patterns of sulfated titania aerogel; (a) as-extracted, (b)500
o
C, (c)600
o
C, (d)700
o
Cand (e) 800oC. ; anatase ;
rutile.
After calcinations at 600
o
C, the small diffraction peaks of rutile were found (Fig. 5c). After calcination at 700
o
C, the anatase peaks
disappeared (Fig. 5d).
5
Therefore, anatase is obtained in processes under kinetic control, whereas processes involving Ostwald
riping lead to the equilibrium phase, i.e., rutile.
40
Fig.5 XRD patterns of un-sulfated titania aerogel; (a) as-extracted, (b) 500
o
C, (c) 600
o
C, (d) 700
o
C and (e) 800
o
C.; anatase *;
rutile
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The X-ray diffraction peaks of anatase were found for the un-sulfated titania aerogel as-extracted (Fig. 5a). In fact, crystallization
is highly influenced by the hydrolysis condition.
41
The anatase structure was stable after calcination at temperatures up to 500
o
C
(Fig. 5b).
Figs. 6 show the TEM images and electron diffraction patterns of sulfated and un-sulfated TiO
2
aerogels as-extracted respectively.
The as-extracted sulfated titania aerogel is in aggregate form and amorphous. For the as-extracted un-sulfated titania aerogel, many
small crystalline particles were observed. The electron diffraction pattern also showed crystals with d = 0.362nm. The particle size
of the un-sulfated TiO
2
aerogel as-extracted was ca. 5nm in diameter.
Fig.6 TEM image and electron diffraction pattern of (a) sulfated and (b) un-sulfated titania aerogel as-extracted.
Fig. 7 a,b,c show the specific surface area, cumulative pore volume and average pore diameter of the sulfated- and the un-sulfated
TiO
2
gels as-extracted and after calcination at various temperatures for 2h. The specific surface area, average pore diameter and
pore volume of the as-extracted sulfated titania aerogel were 469 m
2
g
1
, 11.9 nm and 1.60 cm
3
g
-1
, respectively. The specific surface
area and the pore volume of the sulfated titania are larger than those of the un-sulfated titania, 195 m
2
g
-1
and 0.55 cm
3
g
-1
,
respectively, more than two and three times, respectively (Fig. 7 a,b). After calcination at 500
o
C, the specific surface area and the
pore volume of the sulfated titania, about 175 m
2
g
-1
and 0.94 cm
3
g
-1
, are two times larger than those of the un-sulfated titania. After
calcination at 600
o
C, the specific surface area and pore volume of the sulfated titania, about 117 m
2
g
-1
and 0.74 cm
3
g
-1
, are two
times larger than those of the un-sulfated titania. After calcination at 700
o
C, the specific surface area and pore volume of the
sulfated titania, about 65 m
2
g
-1
and 0.4 cm
3
g
-1
, are more than three and two times larger than those of the un-sulfated titania,
respectively. After calcination at 800
o
C, the specific surface area and the pore volume of the sulfated titania are almost the same
as those of the un-sulfated titania (Fig. 7 a,b). The specific surface area and the cumulative pore volume of the sulfated titania were
much larger than those of the un-sulfated titania, and gradually decreased with increasing calcination temperature up to 700
o
C.
The average pore size of the sulfated and the un-sulfated titania aerogels increased with increasing calcination temperature (Fig.
7c).
(a)
0
50
100
150
200
250
300
350
400
450
500
0 100 200 300 400 500 600 700 800 900
Temperature (
o
C)
Specific Surface Area (m
2
/g)
TiO2
TiO2-SO4
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(b)
(c)
Fig. 7. Effect temperatures calcination: (a) on surface specific area; (b)pore volume ;(c) average pore size of sulfated titania and
un-sulfated titania aerogel.
Catalysts activities
The effect of activation temperature of the sulfated titania on the catalytic activity for the reaction of oleic acid (C
18
H
34
O
2
) with
glycerol (C
3
H
8
O
3
) to produce glycerol mono oleate.
5
Oleic acid (CH
3
(CH
2
)
7
CHCH(CH
2
)
7
COOH) react readily with glycerol
(CH
2
OHCHOHCH
2
OH) in the presence of catalytic amount of sulfated titania acids to yield compounds called Glycerol mono
oleate (GMO)(CH
3
(CH
2
)
7
CHCH(CH
2
)
7
COO CH
2
OHCHOHCH
2
).
where R is CH
3
(CH
2
)
7
CHCH(CH
2
)
7
and R’ is CH
2
OHCHOHCH
2
. The as-prepared sulfated TiO
2
aerogel shows the high activity.
The calcined sample at 800
o
C shows the lowest activity than the others.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 100 200 300 400 500 600 700 800 900
Temperature (
o
C)
Pore Volume (cm
3
/g)
TiO2
TiO2-SO4
0
10
20
30
40
50
60
0 100 200 300 400 500 600 700 800 900
Temperature (
o
C)
Average pore diameter (nm)
TiO2
TiO2-SO4l
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Fig.8.Effect of activation temperatures of the sulfated titania on the catalytic activity on production of glycerol mono oleate.
Glycerol monooleate (GMO) synthesized via esterification involves reaction between glycerol and oleic acid, the esterification
reaction is intrinsically slow, requiring the use of catalyst to decrease the activation energy.
42
The catalyst based on zeolites with
many modification.
42,43
Using Mordenite natural zeolite, catalyst loading of 2 wt%, resulted GMO conversion of 75.09 %.
43
Zirconia-Silica and commercial acid catalysts used for esterification of glycerol with oleic acid resulted conversion of GMO 59.4
%.
44
Esterification reaction of oleic acid and glycerol produced of GMO using H-ZSM-5 catalyst and microwave as a heat source,
1% catalyst weight, ratio of reactant 2:1, reaction time of 50 minutes, and temperature of 160
o
C resulted a yield value of 92,02
%.
45
Natural zeolite used as catalyst for glycerolysis at temperature of 220
o
C resulted the conversion value of 95 %.
46
The sulfated titania catalysts with several treatment used for catalytic of the conversion of GMO as shown in Figure 8. The
activities of catalysts were changed by changing of heat treatment. The specific area and pore volume were decreased drastically
after calcination of 500
o
C and nearly zero in the heat treatmecayalyst and microvant of 800
o
C (Fig.7 a,b), but average pore
diameters were increased by increasing calcination temperature (Fig.7c). The catalysts activity was not inherent with the decreasing
of specific area and pore volume. Catalysts calcined at 750
o
C has hgher yield than catalysts at 600 and 700
o
C. Eventhough
catalysts calcined at 600 and 700 have higher surface area and pore volume. The extracted catalysts have higher yield, followed
by 500
o
C and 700
o
C heat treatment. The lower yield laid on the 600 and 800
o
C heat treatment.
After calcination at 500
o
C, the most sulfates in the titania particles is expelled onto the surface of titania nanoparticles with
crystallization (Fig. 4b). During this process, some sulfate is lost (Fig. 2a) and some dehydroxylation occurs. The majority of the
sulfate is expelled onto the surface. Now, sulfate is on the surface, and the sulfate transformed into an active state. There are showed
that calcination at 500
o
C gave higher yield. The structural stability of the sulfated aerogel is due to the stability of anatase phase.
The grain growth and phase transformation of anatase are restrained with the surface sulfate, Ti
2
SO
4
.
6,19
The TG profile (Fig. 2a) shows that the decomposition of sulfate phase in the TiO
2
continues up to 750
o
C. As long as sulfate was
present, the phase transformation from anatase to rutile is retarded. And, when the entire sulfate is removed after calcinations at
800
o
C, the aerogel converted to the rutile phase. After calcination at 800
o
C, the absorption bands 1250, 1128, 1058, and 900 cm
-1
attributed to the sulfate are disappeared. The aerogel calcined at 800
o
C shows the lowest activity for synthesis of glycerol mono
oleate surfactant because that the entire sulfate is removed.
IV. Conclusions
Sulfated titania (TiO
2
-SO
4
2-
) aerogel has been prepared by one-step synthesis through the sol-gel method using sulfuric acid as
hydrolysis catalyst followed by the one-step CO
2
supercritical extraction. The introduction of sulfuric acid into the titania aerogel
results in the formation of sulfate phase, bridged bidentate Ti
2
SO
4
. Sulfate ions can be anchored to anatase, because they have short
O-O atomic bond lengths that are slightly larger than the largest O-O bond length of the sulfate ion. The specific sulfate phase in
the sulfated TiO
2
aerogel is stable up to 700
o
C, and the decomposition temperature is much higher than that of the sulfated TiO
2
gel
prepared by impregnation. It makes them attractive from the catalytic point of view. The presence of sulfate in amorphous titania
prevents the crystallization of anatase at low temperature during supercritical extraction. The porous structure of the sulfated aerogel
is thermally stable in comparison with the un-sulfated aerogel. The sulfate phase, Ti
2
SO
4
, restrains the crystallization and the grain
growth of anatase, and retards the phase transformation from anatase to rutile. The aerogels calcined at 500, 700 and 750
o
C have
similar activities for synthesis of glycerol mono oleate surfactant. However, the activity of the aerogel calcined at 600
o
C is low. At
500
o
C, a relatively large amount of sulfate remains and the aerogel has high activity.
0.0000
10.0000
20.0000
30.0000
40.0000
50.0000
60.0000
70.0000
80.0000
90.0000
100.0000
1 2 3 4 5 6 7 8
Time (Hour)
Yield (%)
Extracted
500C
600C
700C
750C
800C
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