R. Ohno et al. / Catalysis Today 203 (2013) 60–65
61
R1
R2
2.4. Specific surface area
R3
C
O
BET surface area was evaluated by measuring N2 adsorption at
77 K with BELSORP-mini (BEL Japan) after calcination at 473 K in
50 ml/min of flowing N2 for 3 h.
-O
H+
O
C
O
2.5. Temperature programmed desorption
R3
O
R1
Temperature programmed desorption (TPD) of adsorbed NH3
was carried out to elucidate the acidity of the zeolites. TPD spec-
tra of adsorbed NH3 were measured in a static vacuum system.
Ammonia was adsorbed on a sample at 373 K and evacuated for
0.5 h. The amount of adsorption was evaluated as the difference
of total and reversible adsorption. The heating rate was 10 K/min
in the range of 373–773 K. The pressure of desorbed NH3 (des-
orption rate) was monitored by an ion gauge vacuum meter.
The TPD experiments of adsorbed cyclohexanone were also car-
ried out by a similar procedure. Cyclohexanone was adsorbed
on the catalysts at room temperature under vapour pressure of
cyclohexanone.
HO
C
C
O
R2
O
Scheme 1. Reaction mechanism of Baeyer–Villiger oxidation.
catalyst code of the reference catalyst is indicated as HBEA(75)-R.
Sodium type -zeolite was obtained by ion exchanging HBEA(75)-
R in 1.0 M of NaNO3 aqueous solution at 353 K for 1 h followed by
rinse with 3 l of hot deionized water. The obtained sample was
calcined at 773 K for 5 h (NaBEA(75)-R).
Synthesis of ˇ-zeolite: The -zeolites with various Si/Al ratios
were synthesized under hydrothermal condition [8] by using a
hydrothermal synthesis reactor KH-02 obtained from Hiro Com-
pany, Yokohama, Japan. A hydrogel mixture Al(OH)3 (Nakarai
Tesque, Kyoto, Japan), fumed silica (8.0 g, SIGMA, 0.007 m
of particle size) and tetraethylammonium hydroxide (TEAOH)
as a structure directing reagent (30.25 g of aqueous solution
(35%, Sigma–Aldrich) were stirred at room temperature for 4 h.
Then the aqueous solution of hydrofluoric acid (4.02 g Nakarai
Tesque 46%) was slowly added by drop wise in polyethylene
beaker with vigorous stirring. The composition of the hydrogel
was SiO2·yAl2O3·0.54TEAOH·0.54HF·9.3H2O (y = 0, 0.0025, 0.0033,
0.005, 0.0067, 0.01, and 0.02). The obtained gel was transferred
to a Teflon-coated stainless steel autoclave and heated at 423 K
for 7 days in the synthesis reactor. The obtained white solid
was filtrated and rinsed with 3 l of hot deionized water and
dried at 393 K for 24 h, followed by calcination in atmosphere at
853 K for 5 h to remove the residual structure directing reagent.
Sodium ions in the calcined samples were ion-exchanged with
H+ in an aqueous solution of NH4NO3 (1.0 mol/l) at 353 K for
6 h. This ion-exchange treatment was repeated twice. Finally, H-
type -zeolites were obtained by drying at 393 K, followed by
calcination at 773 K for 5 h. The catalyst code is indicated as
HBEA(x) (x = Si/Al).
2.6. Infrared spectroscopy for the adsorption of cyclohexane and
H2O2 on ˇ-zeolites
The infrared spectra of the catalysts were measured by using
a Pyrex glass in situ IR cell equipped with KBr single crystal win-
dows under transmission mode. A sample disc (13 mm in diameter)
was prepared by pressing 20 mg of -zeolite. The specimen was
evacuated in the IR cell at 523 K for 5 h. After the pre-treatment,
the specimen was transferred into a desiccator and the adsorption
of cyclohexanone or H2O2 under vapour pressure of each reactant
at ambient temperature. After the adsorption, the specimen was
transferred back to the IR cell, and then the spectra were accumu-
lated in 200 scans by Nicolet 380 FT-IR spectrometer equipped with
MCT highly sensitive detector. The resolution of the spectrometer
was 4 cm−1
.
2.7. BV oxidation of cyclohexanone by H2O2
The oxidation of cyclohexanone with H2O2 was carried out in
a Pyrex glass Erlenmeyer flask reactor. Cyclohexanone (0.2 mL,
2.0 mmol, Nakarai Tesque), 0.1 mL of 30% H2O2 aqueous solution
(1.2 mmol, Santoku Kagaku), 4.0 mL of acetonitrile (Nakarai Tesque)
and 20 mg of catalyst were charged in the reactor. The reactor was
purged by nitrogen gas several times in order to obtain anaero-
bic atmosphere. The reaction was started by dipping the reactor in
a thermostatically controlled oil bath at 303 K. After 20 h of reac-
tion time, the reaction mixture and catalyst were separated by
centrifugation and decantation. Products were analyzed by a gas
chromatograph equipped with G-300 capillary (40 m × 1.2 mm).
Ethanol was used as an internal standard for quantitative
analysis.
Ultra stable Y zeolite (HUSY (Si/Al = 15)) was also purchased
from ZEOLYST International and HZSM-5 (MFI (Si/Al = 75)) was
obtained by the hydrothermal synthesis with the gel mixture
of tetraethyl orthosilicate (TEOS), aluminum nitrate, tetrapropyl
ammonium bromide, and sodium hydroxide, to compare the activ-
ity over some zeolite catalysts.
2.2. X-ray fluorescence spectroscopy
The composition of zeolites were analysed by XRF spectrome-
ter, Primini (Rigaku) under 1.7 Pa of vacuum condition. Palladium
anode was operated at 40 kV and 1.25 mA.
Table 1
Catalytic activity of typical zeolite catalysts for BV oxidation of cyclohexane.
Catalyst
-Caprolactone yield (%)
H2O2 Conv. (%)
Efficiency (%)
2.3. X-ray diffraction powder pattern
HBEA(12.5)
HBEA(75)
HUSY(15)
MFI(75)
22.9
15.0
5.7
71.7
45.7
38.0
4.3
65.4
66.8
31.2
25.1
Structure of zeolites was checked by X-ray diffraction pow-
der pattern. The diffraction patterns were measured by RINT2000
diffract meter (Rigaku). The conventional Cu X-ray tube was oper-
ated at 40 kV and 40 mA.
0.5
Catalyst: 20 mg; cyclohexanone: 2.0 mmol; H2O2: 1.2 mmol in 30% aqueous solu-
tion; solvent: 4.0 ml of acetonitrile; React. Temp.: 303 K; React. time: 20 h.