J. Math. Fund. Sci., Vol. 46, No. 1, 2014, 76-90
76
Influence of TiO2/TS-1 Calcination on Hydroxylation of
Phenol
Ratna Ediati1, Maria Ulfa1, Hamzah Fansuri1, Zainab Ramli2, Hadi Nur2 &
Didik Prasetyoko1
1
Department of Chemistry, Faculty of Mathematic and Natural Sciences,
Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo,
Surabaya 60111, Indonesia
2
Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia,
81310 UTM Skudai, Johor, Malaysia.
Email: rediati@chem.its.ac.id
Abstract. Titanium oxide (TiO2) was impregnated on the surface of
titanosilicate-1 (TiO2/TS-1) and used as catalyst for hydroxylation of phenol with
hydrogen peroxide. Calcination was conducted at various temperatures (400,
500, 600 and 700°C) in order to observe the effect on the structure and
physicochemical properties towards catalytic activity for producing
hydroquinone. The structure and physicochemical properties of the TiO2/TS-1
catalyst were characterized by several techniques, such as X-ray diffraction
(XRD), infrared spectroscopy, nitrogen adsorption, pyridine adsorption and
hydrophilic measurement. The results show that by increasing the calcination
temperature, the surface acidity of the catalyst was also increased. The TiO2/TS1 catalyst calcined at 500 °C proved to be optimal for hydroquinone production,
in which the anatase-rutile phase may be present dispersed on the MFI
framework.
Keywords: anatase; calcinations; phenol hydroxylation; rutile; TiO2/TS-1.
1
Introduction
Catechol and hydroquinone are used in a large number of applications in the
modern chemical industry, such as pharmaceuticals, photography and polymer
production [1]. Catechol and hydroquinone are commonly synthesized by a
phenol hydroxylation reaction using H2O2 as an oxidant [2]. H2O2 has many
advantages, such as having a high active oxygen content and being a stable
reagent and a green compound that only results in water as waste product from
the reaction [3]. TS-1 was first synthesized by Taramasso, et al. in 1983 [4] and
showed excellent catalytic activities in organic oxidation reactions using
hydrogen peroxide as oxidant under mild conditions. On the subject of organic
oxidation reactions such as the hydroxylation of phenol, many experiments have
been carried out to enhance phenol selectivity due to the importance for industry
of producing hydroquinone and cathecol. The ability of TS-1 to catalyze a wide
Received April 28th, 2013, 1st Revision February 26th, 2014, 2nd Revision March 18th, 2014, Accepted for
publication April 13th, 2014.
Copyright © 2014 Published by ITB Journal Publisher, ISSN: 2337-5760, DOI: 10.5614/j.math.fund.sci.2014.46.1.7
Influence of TiO2/TS-1 Calcination on Hydroxylation of Phenol 77
variety of oxidation transformations, including phenol hydroxylation with
aqueous hydrogen peroxide, has led to extensive research worldwide on
synthesis related to heterogeneous catalysts for liquid phase oxidation [4-8].
TS-1 has a relatively high phenol conversion activity and it can lessen the
production of tar and other side products that are potential pollutants [2].
However, TS-1 has a low reaction rate and catalytic selectivity in oxidation
reactions because of its hydrophobic nature [9]. Meanwhile, in the reaction
mechanism of phenol hydroxylation, TS-1 will decompose H2O2 (the oxidation
agent), which has a hydrophilic character, to form titanium-peroxo radicals
(initiation step), followed by propagation in solution [10]. Therefore, one way
to increase the phenol hydroxylation reaction rate of TS-1 catalyst is by making
it more hydrophilic.
Hydrophilic improvement of TS-1 catalyst can be carried out by addition of
metal oxide, which leads to an increase of acidity. The existence of metal oxide
in TS-1 catalyst can generate acid sites, which are capable of increasing catalyst
hydrophilicity. In earlier research, epoxydation of 1-octene with H2O2 has
shown that the presence of metal oxide in TS-1 catalyst can generate acid sites
and thus increase the hydrophilic nature of the catalyst, so that the adsorption of
reactants to the catalyst becomes faster [11,12]. Acid sites can be found in some
metal oxides, such as V2O5, Nb2O5, MoO3, WO3, Re2O7, TiO2 and Cr2O3/Al2O3
[13]. As for TiO2, many researchers have reported that TiO2/SiO2, TiO2/clay and
TiO2/Al-MCM-41 nanocomposites can increase catalytic activity in many
organic syntheses [14-16]. The activity of TiO2 depends on the calcination
temperature, which is correlated to phase transformation (anatase to rutile),
surface area, crystallite size, acidity, water sorption and hydroxyl groups [1719].
In this research, TS-1 catalyst was modified by addition of titanium oxide on
the surface. Also, the effect of the calcination temperature of titanium oxide on
the structure and properties of the catalyst was investigated.
2
Experiment
2.1
Synthesis of TS-1
TS-1 containing 1 mol% of titanium was prepared according to the procedure
described by Taramasso, et al. [4], using tetraethyl orthosilicates (TEOS,
Merck, 99%), tetraethyl orthotitanate (TEOT, Merck 99%), 2-propanol (Merck,
99%), tetrapropylammonium hydroxide (TPAOH, Merck, 40% in water) and
distilled water. The gel was charged into a 150 mL autoclave and heated at
175°C under static conditions. The material was recovered after 4 days by
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Ratna Ediati, et al.
centrifugation at 3000 rpm for 30 min and washed with excess distilled water.
White powder was obtained after drying in air at 100°C overnight. The solid
material was then calcined in air at 550°C for 4 h.
2.2
Preparation of TiO2/TS-1
TS-1 sample loaded with titanium oxide (TiO2/TS-1) was prepared using the
impregnation method, where tetraethyl orthotitanate is used as a precursor. The
calcined TS-1 was dried in an oven at 110°C for 24 h. The necessary amount of
TEOT (0.122 g) was then dissolved in 10 mL of 2-propanol to obtain the
desired metal loading; the required quantity of pre-dried TS-1 (3.612 g) was
immediately added. The obtained mixture was stirred at room temperature for 3
h, the solid was recovered by evaporation of the 2-propanol at 80°C. The acid
hydrolysis was performed by addition of 20 mL solution of 0.5 M HNO3 in
distilled water and the solution was aged overnight, followed by heating at
100°C until dry. The solid was then washed three times with distilled water and
finally dried at 110°C for 24 h. The white solid was calcined at 400, 500, 600
and 700°C for 4 h at a heating rate of 2°C/min. Titanium oxide was prepared by
hydrolysis of tetraethyl orthotitanate at room temperature for 24 h. The white
solid was recovered by filtration, washed with water, and dried at 100°C
overnight. Finally, the solid produced was calcined at 550°C for 4 h. The
samples were denoted as xTiO2/TS-1, where x refers to the calcination
temperature.
2.3
Characterization
All samples were characterized by X-ray diffraction with a Bruker Advance D8
diffractometer with CuKα (λ = 1.5405 Å) using a diffracted monochromatic
beam at 40 kV and 30 mA. The pattern was scanned in 2θ ranges from 5-50° in
steps of 0.02° and with a step time of 1 s. The infrared (IR) spectra of the
samples were collected with a Shimadzu Fourier Transform Infrared (FTIR)
spectrometer with a spectral resolution of 2 cm-1 and a scan speed of 10 s, with
the KBr self-supported wafer method. The infrared spectra of the samples were
recorded at room temperature in the framework region of 1400-400 cm-1. The
acidity of the samples was determined by FTIR using pyridine as the probe
molecule [20]. The wafer of the sample (10-12 mg) was locked in a cell and
evacuated at 400°C for 4 h, followed by adsorption of pyridine at room
temperature. After evacuation at 150°C for 3 h, the infrared spectra of the
samples were recorded at room temperature in the region of 1400-1700 cm-1. In
order to directly compare the surface coverage of the adsorbed species, all
spectra were normalized after activation using the overtone and combination
vibration of the MFI at around 1800 cm-1 [21]. The number of Brønsted or
Influence of TiO2/TS-1 Calcination on Hydroxylation of Phenol 79
Lewis acid sites was calculated using the equation proposed by Emeis [20], as
follows:
Number of acid sites (mmol / g ) =
B×L
× 10 −3
k×g
where:
B is peak area of Brønsted or Lewis acid absorption band (cm-1)
L is area of sample disk (cm2)
g is weight of sample disk (g)
k is molar extinction coefficient values of 1.67 cm µmol–1 for the 1545 cm-1
band characteristic of pyridine on the Brønsted acid sites or 2.22 cm µmol-1 for
the 1455 cm-1 band of pyridine on the Lewis acid sites.
The nitrogen adsorption-desorption isotherms were performed using a
Micromeritics ASAP 2010 instrument. The samples were previously outgased
at 200 °C under vacuum. The surface areas of the samples were determined by
BET equation. The catalyst hydrophilicity was analyzed by the sample
dispersion method using a mixture of water and xylene based on the method by
Wang, et al. [22]. In a typical experiment, the catalyst is dried in an oven at
110°C for 24 h to remove all the physically adsorbed water. After dehydration,
the sample is poured into the mixture of xylene and water. The catalyst motion
in each phase is visually monitored.
2.4
Catalytic Study
The phenol hydroxylation reactions were carried out in a 50 mL round bottom
flask equipped with condenser and magnetic stirrer. In every run, 1.3 g of
phenol (Merck, 99%) was mixed with 5 mL of methanol, 0.16 g of catalyst and
0.5 g of H2O2 (Merck, 30 wt% aqueous). All reactions were run at 70°C. The
products were taken out periodically after 1, 2, 3 and 4 h reaction time, and
analyzed by gas chromatography with an FID detector.
3
Results and Discussion
3.1
Structural Characterization and Properties
The XRD patterns of the TiO2, TS-1 and xTiO2/TS-1 samples are shown in
Figure 1. The diffraction patterns for the samples with a calcination temperature
of 400, 500, 600 and 700°C were found to be similar to those of the parent TS1, as indicated by the diffraction peaks at 2θ = 7.92º; 7.94º; 8.80º; 23.06º;
23.08º; 23.10º; 23.24º; 23.26º; and 23.28º. The presence of all the typical XRD
peaks in the samples containing TS-1 indicates that the framework structure was
still retained even after calcination. Meanwhile, the XRD pattern of the TiO2
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Ratna Ediati, et al.
sample exhibited a rutile structure of TiO2. In addition, samples xTiO2/TS-1 in
Figure 1 show that no diffraction lines for the anatase-rutile phases of titanium
oxide were observed. This suggests that the TiO2 was highly dispersed on the
surface of TS-1. It was found that the MFI structure of TS-1 was maintained
after the impregnation of titanium oxide and calcination preparation.
TS-1
Intensity (a.u)
400 TiO2/TS-1
500 TiO2/TS-1
600 TiO2/TS-1
700 TiO2/TS-1
TiO2
2θ, degree
Figure 1 Powder X-ray diffraction patterns of TiO2, TS-1 and TiO2/TS-1
calcined at different temperatures (400, 500, 600 and 700°C) for 3 h.
Influence of TiO2/TS-1 Calcination on Hydroxylation of Phenol 81
However, the diffraction peak intensities of TS-1 decreased along with the
increase in calcination temperature. This finding also suggests that either
titanium oxide was located on the surface of TS-1, or crystalline phase of TiO2
covered the surface of TS-1. Since the source of TiO2 is TEOT, which has a
molecular size (11.22 Ǻ) larger than that of the pore entrance of TS-1 (0.55 Ǻ),
the TiO2 should be attached to the external surface of TS-1.
The infrared spectra of the zeolite lattice vibrations between 1400 and 400 cm-1
are depicted in Figure 2.
Figure 2 Framework infrared spectra of TiO2, TS-1 and TiO2/TS-1 calcined at
different temperatures (400, 500, 600 and 700°C) for 3 h.
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The absorption bands at around 1100, 800, and 450 cm-1 were of lattice modes
associated to internal linkage in SiO4 or AlO4 tetrahedral, and were insensitive
to structural changes, whereas the absorption bands at around 1230 and 547
cm-1 were characteristics of the MFI type zeolite structure and were sensitive to
structural changes [23]. In addition, all samples revealed a band at around 970
cm-1. The vibration modes around this frequency maybe the result of several
contributions, such as the asymmetric stretching modes of Si-O-Ti linkages,
terminal Si-O stretching of Si-O-H-(HO)Ti ‘defective sites’ and titanyl (Ti=O)
vibrations [8,24-25]. However, the band at around 970 cm-1 could also be
attributed to the titanium in the framework, since silicate, a Ti free zeolite, did
not show any band around this frequency. Furthermore, impregnation of
titanium oxide on TS-1 followed by calcination at various temperatures resulted
in no significant change of the band at around 970 cm-1. Therefore, it is
concluded that the TS-1 sample contained Si-O-Ti connections. There was no
band shifting or additional band observed after impregnation of titanium oxide
on TS-1. This finding suggests that both the MFI structure and the titanium
framework remained unchanged after both the impregnation and the calcination.
The surface acidity of the samples was determined by infrared spectroscopy
after adsorption of pyridine on the samples and evacuation at 150°C (Figure 3).
As is shown in Figure 3, only characteristic absorption bands due to adsorbed
pyridine coordinated to the Lewis acid sites appearing at 1448 cm-1 were
observed in all samples, while the peak characteristic of the Brønsted acid sites
at around 1545 cm-1 was absent. The acid sites are associated to coordinatively
unsaturated surface metal ions [26]. The numbers of the Lewis acid sites
determined through the integration of the peak at around 1448 cm-1 are listed in
Table 1.
Table 1
Physical and chemical properties of the TiO2/TS-1 samples.
Sample
Surface
area
(m2/g)
Number of
Lewis acid
sites (µmol/g)
TS-1
431
13
TiO2
n.d.(a)
8
400TiO2/TS-1
394
14
500TiO2/TS-1
407
16
600TiO2/TS-1
389
20
700TiO2/TS-1
373
35
(a) Not determined
Hydrophilicity
Character
Partially
hydrophobic
Partially
hydrophilic
Partially
hydrophilic
Partially
hydrophilic
Partially
hydrophilic
Partially
hydrophilic
Index
Water
submerged
time (s)
5
98
5
107
5
66
5
64
5
89
5
92
Influence of TiO2/TS-1 Calcination on Hydroxylation of Phenol 83
Thermal treatment has been reported to affect the acidity of the material in
which the acidity generally decreases with the increase in calcination
temperature [27]. Our finding, however, proved to be contrary to the general
tendency reported by Maldonado-Hódar, et al. [27].
Figure 3 Infrared spectra of adsorbed pyridine of the TiO2, TS-1 and TiO2/TS-1
samples calcined at different temperatures (400, 500, 600 and 700°C) for 3 h.
As is shown in Table 1, the acidity of the catalysts increased with the increase in
calcination temperature. This phenomenon could be attributed to a polymorphic
transformation of TiO2 from anatase phase to rutile phase as the calcination
temperature increased from 500 to 700°C. Machado and Santana [17] have
reported that the acidity of the anatase phase is much lower as compared to the
rutile one. In this study, the acidity was correlated to the TiO2 structure because
the position of TiO2 was on the surface of TS-1, whereas the structure of TS-1
remained unchanged after calcination up to 700°C, as observed by XRD and
infrared spectroscopy.
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Ratna Ediati, et al.
The hydrophobicity of the samples was monitored by dispersion of the samples
in a mixture of xylene and water. The powder distribution of both TS-1 and
500TiO2/TS-1 suspended in the mixture after stirring is illustrated in Figure 4(a)
and Figure 4(b), respectively. In general, all samples (the TiO2, TS-1 and
TiO2/TS-1 catalysts) showed partially hydrophobic behavior in which each
catalyst was dispersed in the interlayer and suspended in the bottom of the
aqueous phase. The rates of sample dispersion, however, were different, as is
shown in Table 1. The dispersion behavior of TiO2/TS-1 shown in Table 1
indicates that there was a correlation between the hydrophilicity and the
calcination temperature. The 400TiO2/TS-1 sample took longer to disperse in
the aqueous phase than the 500TiO2/TS-1. This may be due to the low
interaction between titanium oxide and TS-1. The dispersion rate of the
TiO2/TS-1 sample in the aqueous phase decreased with the increase in
calcination temperature from 500 to 700 °C. This may be due to the phase
transformation of amorphous titanium oxide to the anatase and rutile phase, or
the alteration in the percentage of titanium oxide crystalline phase on the
surface of TS-1 [14,26,28].
Figure 4 Hydrophobicity testing results for sample after stirring: (a) TS-1 and
(b) 500TiO2/TS-1.
The calcination at 700°C resulted in a longer dispersion rate in the aqueous
phase as compared to the calcinations at 500-600°C. According to Machado and
Santana [17], this is mainly due to partial transformation of anatase to rutile
phase. In addition, as shown in Figure 4, it can be clearly seen that the amount
of adsorbed water in the TS-1 samples was significantly lower than that of the
400 and 500TiO2/TS-1 samples. This may indicate the anatase to rutile phase
transformation in the samples with a higher calcination temperature. Based on
the infrared data at the absorption band of around 960-970 cm-1 and by using a
standard curve, it was found that the Si/Ti was 0.8% [29]. The high rutile phase
of the samples at high calcination temperatures may result in the agglomeration
of titanium oxide on the surface of TS-1 [8]. Meanwhile, the TS-1 was not well
dispersed in the water phase, which indicates that the behavior of the TS-1 was
Influence of TiO2/TS-1 Calcination on Hydroxylation of Phenol 85
naturally hydrophobic. Impregnation of titanium oxide on the surface of the TS1 enhanced its hydrophilic character.
Textural analysis of the catalysts was carried out using N2 adsorption–
desorption at 77 K using Quantachrome Nova 1200 equipment. Surface area
measurement was made according to the BET method. The surface area of the
samples decreased with the increase in calcination temperature, as listed in
Table 1. This finding supports the hypothesis that there are sintering phenomena
when samples are calcined at a high temperature. Figure 5 displays the nitrogen
adsorption-desorption isotherms of the catalysts.
Figure 5 Nitrogen adsorption-desorption isotherms of TS-1 and TiO2/TS1samples calcined at different temperatures (400, 500, 600 and 700°C) for 3 h.
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Ratna Ediati, et al.
It can be seen that the TiO2/TS-1 samples calcined at 400 to 700°C exhibited a
type I of nitrogen isotherm with nitrogen uptake at relative pressure P/Po below
0.1 indicative of their microporosity. In addition, the hysteresis loop was
observed at P/Po higher than 0.9. The hysteresis phenomenon in the isotherms
is related to capillary condensation of N2 in mesoporous structures, in which the
adsorbed volume tends to reach a finite maximum value, corresponding to a
complete filling of the capillary.
3.2
Catalytic Activity
The catalytic activity of the TS-1 and the TiO2/TS-1 samples was evaluated
using hydroxylation of phenol with H2O2 as the oxidizing agent. The products
were analyzed by gas chromatography. In general, according to the literature,
the main products usually observed in the hydroxylation reaction are catechol,
hydroquinone, benzoquinone, and tar [16,28,30]. In this study, however, apart
from hydroquinone and catechol, no other products were observed, while in the
reaction without catalyst, no hydroquinone product was obtained. The amounts
of hydroquinone obtained using TiO2, TS-1, and TiO2/TS-1 catalysts at various
reaction times are depicted in Figure 6.
Generally, all catalysts exhibited catalytic activity for the hydroxylation of
phenol. The amount of hydroquinone product was higher at longer reaction
times. The TiO2 catalyst revealed the lowest amount of hydroquinone product
for all reaction times, while the highest amount of hydroquinone product was
observed when the 500TiO2/TS-1 catalyst was used. In addition, the TS-1,
400TiO2/TS-1 and 700TiO2/TS-1 catalysts produced similar amounts of
hydroquinone, which were lower than those of the 500TiO2/TS-1 and
600TiO2/TS-1 catalysts. Moreover, the 400TiO2/TS-1 catalyst revealed the
lowest activity among the TiO2/TS-1 catalysts, which may be a result of
incomplete organic removal or deposition of carbon on the surface of the
catalyst due to the lower calcination temperature of the catalyst. Consequently,
the amount of reactant accessing the active sites inside the pore system of the
catalyst was limited, because those sites were covered by the carbon deposit.
Meanwhile, the activity of the TiO2/TS-1 catalysts calcined at temperatures
higher than 500°C decreased. Machado and Santana [17] have reported that a
higher calcination temperature of TiO2 results in the production of a rutile solid
structure in which the TiO2 is less effective as a catalyst for the oxidation of
most organic compounds than in that of the anatase phase. Therefore, the
decrease in catalytic activity at the higher calcination temperatures was due to
the TiO2 structure. The sintering mechanism of TiO2 calcined at high
temperatures, which affects the properties of the catalyst, such as lowering the
crystallinity and the surface area, can also decrease the catalytic activity of the
TiO2/TS-1 catalyst. The better properties displayed by the 500TiO2/TS-1
Influence of TiO2/TS-1 Calcination on Hydroxylation of Phenol 87
catalyst were correlated to both the high surface area and high hydrophilicity,
leading to a high hydroquinone production.
Figure 6 Catalytic performance of TiO2, TS-1, and TiO2/TS-1 catalysts for
hydroquinone production from phenol hydroxylation reaction with H2O2 at 70°C.
4
Conclusions
The hydrophylic character of TS-1 catalysts was successfully improved by the
dispersion of titanium oxide on the surface of TS-1. The titanium located in the
silicate framework of the catalysts resulted in the existence of oxidative sites,
while octahedral titanium played a role as a hydrophilic site. The analysis of the
structure and properties of the TiO2/TS-1 catalysts suggests that there are
correlations between the calcination temperatures and the anatase to rutile phase
transformation and the sintering behavior that influences the catalytic activity.
The 500TiO2/TS-1 catalyst showed optimum hydroquinone formation.
Acknowledments
We gratefully acknowledge funding from the Directorate General of Higher
Education Indonesia under the Academic Recharging Program, Grant 2011 No.
3021/E4.2/2011.
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References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
Esposito, A., Taramasso, M. & Neri, C., Hydroxylating Aromatic
Hydrocarbons, US Patent No. 4.396.783, 1983.
Ray, S., Mapolie, S.F. & Darkwa, J., Catalytic Hydroxylation of Phenol
Using Immobilized Late Transition Metal Salicylaldimine Complexes,
Journal of Molecular Catalysis A: Chemical, 267, pp. 143-148, 2007.
Smith, G.V. & Notheisz, F., Heterogeneous Catalysis in Organic
Chemistry, Academic Press, London, pp. 229-239, 1999.
Taramasso, M., Perego, G. & Notari, B., Preparation of Porous
Crystalline Synthetic Material Comprised of Silicon and Titanium
Oxides, US Patent No. 4.410.501, 1983.
Van der Pol, A.J.H.P. & Van Hooff, J.H.C., Parameter Affecting the
Synthesis of Titanium Silicalite 1, Applied Catalysis A: General, 92, pp.
93-111, 1992.
Thangaraj, A., Kumar, R. & Sivasanker, S., Evidence for the
Simultaneous Incorporation of Al and Ti in MFI Structure (Al-TS-1),
Zeolites, 12, pp. 135-137, 1992.
Constantine, M., Popa, J.M. & Gubelmann, Hydroxylation of Phenols/
Phenol Ethers, US Patent 5.254.746, 1993.
Corma, A. & Garcia, H., Lewis Acids as Catalysts Oxidation Reaction:
from Homogeneous to Heterogeneous Systems, Chemical Review, 102,
pp. 3837-3892, 2002.
Liu, X., Wang, X., Guo, X. & Li, G., Effect of Solvent on The Propylene
Epoxidation over TS-1 Catalyst, Catalysis Today, 93-95, pp. 505-509,
2004.
Kurian, M. & Sugunan, S., Wet Peroxide Oxidation of Phenol over Mixed
Pillared Montmorillonites, Chemical Engineering Journal, 115, pp. 39146, 2006.
Nur, H., Prasetyoko, D., Ramli, Z. & Endud, S., Sulfation: A Simple
Methode to Enhance the Catalytic Activity of TS-1 in Epoxidation of 1Octene with Aqueous Hydrogen Peroxide, Catalysis Communication, 5,
pp. 725-728, 2004.
Prasetyoko, D., Ramli, Z., Endud, S. & Nur, H., Enhancement of
Catalytic Activity of Titanosilicalite-1-Sulfated Zirconia Combination
towards Epoxidation of 1-Octene with Aqueous Hydrogen Peroxide,
Reaction Kinetics Catalysis Letter, 86, pp. 83-89, 2005.
Kung, H.H., Transition Metal Oxides: Surface Chemistry and Catalysis,
Studies in Surface Science and Catalysis, 45, pp. 72-79, 1989.
Bonelli, B., Cozzolino, M., Tesser, R., Serio, M.D., Piumetti, M.,
Garrone, E. & Santacesaria, E., Study of the Surface Acidity of TiO2/SiO2
Catalysts by Means of FTIR Measurements of CO and NH3 Adsorption,
Journal of Catalysis, 246, pp. 293-300, 2007.
Influence of TiO2/TS-1 Calcination on Hydroxylation of Phenol 89
[15] Belessi, V., Lambropoulou, D., Konstantinou, I., Katsoulidis, A.,
Pomonis, P., Petridis, D. & Albanis, T., Structure and Photocatalytic
Performance of TiO2/Clay Nanocomposites for the Degradation of
Dimethachlor, Applied Catalysis B: Enviromental, 73, pp. 292-299,
2007.
[16] Sharma, M.V., Durgakumari, V. & Subrahmanyam, M., Photocatalytic
Degradation of Isoproturon Herbicide over TiO2/Al-MCM-41 Composite
Systems Using Solar Light, Chemosphere, 72, pp. 644-658, 2008.
[17] Machado, N.R.C. & Santana, S.V., Influence of Thermal Treatment on
The Structure and Photocatalytic Activity of TiO2 P25, Catalysis Today,
107-108, pp. 595-698, 2005.
[18] Hamadian, M., Reisi-Vanani, A. & Majedi, A., Synthesis,
Characterization and Effect of Calcination Temperature on Phase
Transformation and Photocatalytic Activity of Cu, S-codoped TiO2
Nanoparticles, Applied Surface Science, 256, pp. 1837-1844, 2010.
[19] Lamonier, J-F., Nguyen, T.B., Franco, M., Siffert, S., Cousin, R., Li, Y.,
Yang, X.Y., Su, B-L. & Giraudon, J-M., Influence of the MesoMacroporous ZrO2–TiO2 Calcination Temperature on the Pre-reduced
Pd/ZrO2–TiO2(1/1) Performances in Chlorobenzene Total Oxidation,
Catalysis Today, 164, pp. 566-570, 2011.
[20] Emeis, C.A., Determination of Integrated Molar Extinction Coefficients
for Infrared Absorption Bands of Pyridine Adsorbed on Solid Acid
Catalysts, Journal of Catalysis, 141, pp. 347-354, 1993.
[21] Jentys, A., Mukti, R.R., Tanaka, H. & Lercher, J.A., Energetic and
Entropic Contributions Controlling The Sorption of Benzene in Zeolites,
Microporous and Mesoporous Materials, 90, pp. 284-292, 2006.
[22] Wang, Z., Wang, T., Wang, Z. & Jin, Y., Organic Modification of
Ultrafine Particles Using Carbon-Dioxide as The Solvent, Journal of
Powder Technology, 139, pp. 148-155, 2004.
[23] Bekkum, H., Flanigen, E.M., & Jansen, J.C., Introduction to Zeolite:
Science and Practice, 2nd ed., Elsevier, Amsterdam, pp. 241-284, 1991.
[24] Atoguchi, T. & Yao, S., Phenol Oxidation over Titanosilicalite-1:
Experiment and DFT Study of Solvent, Journal of Molecular Catalysis A:
Chemical, 176, pp. 173-178, 2002.
[25] Drago, R.S., Dias, S.C., McGilvray, J.M. & Mateus, A.L.M.L., Acidity
and Hydrophobicity of TS-1, Journal of Physical Chemistry, 102, pp.
1508-1514, 1998.
[26] Lamberti, C., Bordiga, S., Zecchina, A., Artioli, G., Marra, G. & Spano,
G., Ti Location in the MFI Framework of Ti-Silicalite-1: A Neutron
Powder Diffraction Study, Journal of American Chemical Society, 123,
pp. 2204-2212, 2001.
[27] Maldonado-Hódar, F.J., Moreno-Castilla, C. & Rivera-Utrilla, J.,
Synthesis, Pore Texture and Surface Acid–Base Character of
90
Ratna Ediati, et al.
TiO2/Carbon Composite Xerogels and Aerogels and Their Carbonized
Derivatives, Applied Catalysis A: General, 203, pp. 151-159, 2000.
[28] Araña, J., Rendón, E.T., Rodríguez, J.M.D., Melián, J.A.H., Díaz, O.G. &
Peña, J.P., High Concentrated Phenol and 1,2-Propylene Glycol Water
Solutions Treatment by Photocatalysis: Catalyst Recovery and Re-use,
Applied Catalysis B: Environmental, 30, pp. 1-10, 2001.
[29] Prasetyoko, D., Ramli, Z., Endud, S. & Nur, H., Preparation and
Characterization of Bifunctional Oxidative and Acidic Catalysts
Nb2O5/TS-1 for Synthesis of Diols, Materials Chemistry and Physics, 93,
pp. 443-449, 2005.
[30] Chun, H., Yizhong, W. & Hongxiano, T., Destruction of Phenol Aqueous
Solution by Photocatalysis or Direct Photolysis, Chemosphere, 41, pp.
1205-1209, 2000.