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pressure. In case of O2 as an oxidant, reux condenser was tted
with O2 balloon. The reaction mixture contained 25 mL of TBHP
(5 mol% of reactant) as an initiator. For the recyclability tests,
the catalyst was ltered off, washed twice with fresh solvent,
Synthesis
The mesoporous TSC–ED-X was prepared through sol–gel
method where CTAB was used as the structure directing agent
to form mesoporous structure. Briey, 10 mmol of TEOS and 20
mmol of ED were dissolved in 20 mL ethanol and stirred for 30
min. To this, 5 mL ethanol solution containing 0.25 mmol of
TIP was added. The resulting light yellow solution was contin-
uously stirred at room temperature for 2 h. In another beaker
solution containing 5 mmol of CTAB in 56.8 mL of water heated
ꢀ
calcined at 500 C for 4 h in air, cooled down to room temper-
ature and reused under the same conditions. Aer reaction,
catalyst was separated from product mixture by centrifugation
and the products were analyzed by Agilent gas chromatograph
equipped with HP-5 column and ame ionization detector.
ꢀ
ꢀ
to 80 C for 2 h with stirring then cool to 50 C. Aer that ED
precursor solution was added drop wise to CTAB solution with
vigorous stirring for 4 h. The resulting white gel was kept for
aging overnight at room temperature. The resultant dry gel was
collected by centrifuge, washed with water and ethanol, and
dried in oven at 50 ꢀC. To obtain the nal mesostructured
material as synthesised dry solid was calcined in air at different
temperature ranging from 550 ꢀC to 850 ꢀC. For comparison
TSC-25 was also synthesized via sol–gel method by adding NH3
(20 mmol) as catalyst for hydrolysis and condensation without
addition of ED.
½C6H10ꢄ ꢁ ½ C6H10ꢄ
0
t
Conversion ð%Þ ¼ 100 ꢃ
½C6H10ꢄ
0
½C6H10ꢄ ¼ initial conc: of cyclohexene
0
½C6H10ꢄ ¼ conc: of cyclohexene at time t:
t
moles of individual product
moles of total products
Selectivity ð%Þ ¼ 100 ꢃ
Result and discussion
Catalyst characterization
Morphology of calcined TSC–ED-25 was analysed using SEM
(Fig. 1a). TSC–ED 25 appeared as aggregation of spherical
particles. The presence of Ti4+ can inuence the nal
morphology of silica.17 The formation of various periodic mes-
oporous materials starts with nucleation, which involves the
assembly of surfactant micelles and silicate species in a stable
packing. However, the presence of foreign ions in the synthesis
gel altered the action of the structure directing template. Small-
angle X-ray diffraction pattern for the as-synthesized TSC–ED-25
(Fig. 1b(i)) showed well-resolved peaks at low angle value that
can be indexed as (100) reection associated with the ordered
mesoporosity. From the 2q value, the d-spacing corresponding
to ordered pores was calculated to be 8.5 nm. Two well resolved
reections of low intensity corresponding to (110) and (200)
were also observed that were characteristic of ordered hexag-
onal pore system. Notably, aer calcination in air at 550 ꢀC for 6
h, trace ii in Fig. 1b conrmed mesostructured pores in TSC–
ED-25. TSC–ED-X samples exhibited a high surface area in the
range of 840–860 m2 gꢁ1 as compared to 512 m2 gꢁ1 for TSC-25.
The pore size distributed from 2–24 nm in TSC–ED-25. The
higher surface area of TSC–ED-X could have been contributed
by the thermal decomposition of ED ligands during calcina-
tions. TEM images of TSC–ED-25 are provided in Fig. 1c and
d where long channels of pores are clearly seen. There was no
direct evidence for formation of TiO2 nanoparticles or aggre-
gates blocking the pores from the microscopy images.
Low angle powder X-ray diffraction patterns of as-synthesized
and calcined samples were recorded on a Phillips PAN analyt-
˚
ical diffractometer, Ni-ltered Cu Ka radiation, l ¼ 1.5404 A,
between 0.5ꢀ and 10ꢀ (2q) with a scan rate of 1ꢀ minꢁ1. While
wide angle XRD patterns of samples having different Si : Ti
molar ratio and calcination temperature were recorded on
˚
a recorded on a Rigaku D MAX Cu Ka radiation, l ¼ 1.5404 A,
between 10 and 80 (2q) with a scan rate of 3ꢀ minꢁ1. Charac-
terization of morphology of the synthesized TSC–ED having
different nSi/nTi ratio was performed with a eld emission
scanning electron microscope (FESEM) and transmission elec-
tron microscope (TEM). SEM micrographs of the mesoporous
titanosilicate samples were obtained on JEOL-JSM-5200 instru-
ment while the TEM images were obtained on a TECNAI S-20
instrument. Infrared Spectroscopy measurements were done
using Bruker FT-IR. The samples were analyzed as KBr pellets.
Diffuse reectance UV-vis spectra were recorded in the range of
200–800 nm with a Shimadzu UV-2101 PC spectrometer
equipped with a diffuse reectance attachment, using BaSO4 as
the reference. The UV-resonance Raman spectra were measured
using 273.8 nm excitation wavelength generated by tuneable Ti-
sapphire laser (Indigo, Coherent Inc.). The average power used
was ꢂ0.6 mW. Calibration was done by recording spectra of
dimethylformamide, cyclohexane, indene, acetonitrile, trichlo-
roethylene, and isopropanol with the known band positions.
Wide angle powder XRD was used to study the crystalline
phases in the sample and more importantly to evaluate the
Catalytic oxidation of cyclohexene
The catalytic oxidation of cyclohexene was carried out in 25 mL efficiency of the method to prevent the formation of TiO2. The
two-neck round bottom ask equipped with a reux condenser. patterns presented in Fig. 2a correspond to TSC–ED with
In a typical reaction, 50 mg of catalyst was mixed with 5 mL of different values of X namely (i) 40, (ii) 25 and (iii) 10 respectively.
solvent (acetonitrile), 0.5 mL of cyclohexene (4.9 mmol) and It can be observed that the diffraction peaks corresponding to
5 mmol of TBHP (70% aqueous) or H2O2 (30% aqueous) as crystalline TiO2 phase are absent in the samples synthesized in
oxidant and stirred magnetically for 4 h at 60 ꢀC at atmospheric the presence of ED for different ratios of X. This shows that
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 92371–92377 | 92373
Gupta
