G Model
CATTOD-9195; No. of Pages7
ARTICLE IN PRESS
S. Yamaguchi et al. / Catalysis Today xxx (2014) xxx–xxx
Table 1
2
[Fe(bpy)3]2+@Y was characterized by several methods and its cat-
alytic activity for oxidation of cyclohexene with H2O2 and O2 was
investigated in CH3CN and H2O solvents.
Experimental and theoretical values of Fe content, C/N and Fe/bpy in [Fe(bpy)3]2+@Y.
Fe content/wt%a
C/Nb
Fe/bpy molar ratio
Experimental
Theoretical
0.88
–
4.9
5.0
Fe:bpy = 1.0:2.8
Fe:bpy = 1.0:3.0
2. Experimental
a
ICP analysis results.
b
CHN elemental analysis results.
2.1. Materials and instruments
Na ion-exchanged Y-type zeolite (Na-Y) with SiO2/Al2O3 = 5.5
was supplied from Tosoh Co. All chemicals, FeSO4·7H2O (Wako,
>99%), 2,2ꢀ-bipyridine (Wako, 99.5%), methanol (Wako, 99.8%),
cyclohexene (Wako, 97.0%), 30% aqueous hydrogen peroxide
(Wako, 30–35.5%), cyclohexene oxide (TCL, >98%), 2-cyclohexen-1-
ol (Aldrich, 95%), 2-cyclohexen-1-one (Wako, 95%), mixture of cis
and trans-1,2-cyclohexan diols (Alfa Aesar), cis-1,2-cyclohexen diol
(Wako), 1-octanol (Wako, 98.0%), and acetonitrile (Wako, 99.5%),
were used as received. Cyclohexene was used as a substrate after
purification with treatment of activated alumina and distillation to
remove peroxide and oxidation species derived from cyclohexene.
The powder XRD patterns of catalysts were collected on a
Rigaku MiniFlex II diffractometer using CuK␣ radiation. UV–vis
spectra were recorded on a Hitachi U-4000 spectrometer for solid
samples or on Shimadzu U-1200 for liquid samples. GC analy-
sis was performed on Shimadzu GC-14B with a flame ionization
detector equipped with a Stabilwax capillary column (internal
diameter = 0.25 mm, length = 30 m) at the nature of polar liquid
phase. GC–MS spectra were recorded on Shimadzu GCMS-QP5050A
(ionization voltage = 70 eV) equipped with a DB-1MS capillary col-
umn (internal diameter = 0.25 mm, length = 30 m) at the nature of
non-polar liquid phase.
Fe K-edge X-ray Absorption Fine Structure (XAFS) spectra were
measured at room temperature in transmission mode at Kyushu
University Beamline (BL06) in the Kyushu Synchrotron Light
Research Center (SAGA-LS), Tosu, Japan (proposal no. 2012IK009).
Appropriate amount of powder samples and 80 mg of boron nitride
powder were mixed and pressed into pellets of 10 mm in diameter.
Synchrotron radiation was monochromated by a Si (111) double
crystal and a cylindrical mirror coated by rhodium was used to
eliminate higher harmonics. Extended X-ray absorption fine struc-
ture (EXAFS) data were analyzed using a data analysis program,
REX2000.
of the precipitate from CH3CN/diethylether gave needle-like red
single crystals, suitable for X-ray structural analysis.
Needle-like reddish solid; C30H24Cl2FeN6O8 (723.30) calcd. C
49.82, H 3.34, N 11.62; found C 49.51, H 3.37, N 11.64.
2.3. Catalytic oxidation
The catalytic oxidations were carried out with a glass tube
reactor. A typical procedure was as follows; catalyst (7.9 mol),
solvent (MeCN and/or H2O) (10 mL), and cyclohexene (7.9 mmol)
were charged, and 30% aqueous hydrogen peroxide (0.8 mmol)
was added in glass tube reactor under Ar or O2. The reaction was
carried out at 50 ◦C. After the reaction, triphenylphosphine as a
quencher was charged, and 1-octanol as an internal standard was
added in glass tube reactor. The reaction solution was analyzed
by GC in combination with mass spectroscopy. The products were
identified by the comparison of mass spectra with those authentic
samples. GC–MS condition was as follows: interface temperature
(150 ◦C), detector temperature (230 ◦C), oven temperature (85 ◦C
(hold for 10 min) to 220 ◦C at 30 ◦C/min (hold for 5 min)), and
retention times (2.5, 3.7, 4.0, 4.5, 8.3, 8.4, and 9.4 min for cyclohex-
ene, cyclohexene oxide, 2-cyclohexen-1-ol, 2-cyclohexen-1-one,
trans-1,2-cyclohexan diol, cis-1,2-cyclohexen diol, and 1-octanol
(internal standard), respectively). The carbon balance (mass bal-
ance) in each experiment was in the range of 95–100%.
Similarly, the reaction solution was analyzed by GC-FID in order
to confirm the presence or the absence of adipic acid as an oxidation
product of cyclohexene. GC-FID condition was as follows: interface
temperature (230 ◦C), detector temperature (250 ◦C), column tem-
perature (150 ◦C (hold for 1 min) to 245 ◦C at 30 ◦C/min (hold for
20 min)), and retention times (1.23, 1.41, 1.80, 1.84, 1.94, 10.8, and
13.6 min for cyclohexene, cyclohexene oxide, 2-cyclohexen-1-ol,
2-cyclohexen-1-one, 1-octanol (internal standard), triphenylphos-
phine, and adipic acid, respectively). In all oxidation reactions, very
little peak derived from adipic acid (TON < 0.015 with respect to
Fe) was observed. Remaining hydrogen peroxide after reaction was
analyzed by Ce4+/3+ titration.
2.2. Preparation of Fe-containing catalysts
Na-Y zeolite (5.0 g) was ion-exchanged by a conventional
method using aqueous solution (300 mL) of FeSO4·7H2O (0.2 g,
0.72 mmol) to yield iron(II) ion-exchanged Y-type zeolite (Fe-Y)
[35]. The prepared Fe-Y (1.0 g) was refluxed in an aqueous solution
(100 mL) of 2,2ꢀ-bipyridine (bpy) (0.47 g, 3.0 mmol) for 20 h, fol-
lowed by filtration, washing with water and methanol by Soxhlet
extractor, and drying at room temperature under vacuum to give
[Fe(bpy)3]2+@Y as a reddish-pink powder.
3. Results and discussion
3.1. Characterization of [Fe(bpy)3]2+@Y
ICP-AES and elemental analysis of [Fe(bpy)3]2+@Y were car-
ried out after the sample was dissolved into HF solution (Table 1).
[Fe(bpy)3]2+@Y sample contains 0.88 wt% iron(II) ions, 5.12 wt% C
atoms, and 1.22 wt% N atoms. This result indicates that the bpy/Fe
ratio is ca. 3, suggesting that Fe ion in zeolite Y was coordinated
Reddish-pink power ([Fe(bpy)3]2+@Y): elemental analyses. C,
5.12; H, 1.99; N, 1.22; Na, 5.38; Fe, 0.88; and Al, 8.08 wt%.
2.2.2. Preparation of [Fe(bpy)3](ClO4)2 as a control catalyst for
[Fe(bpy)3]2+@Y
IR spectra of [Fe(bpy)3]2+@Y, [Fe(bpy)3](ClO4)2 + Na-Y, Fe-Y, and
[Fe(bpy)3](ClO4)2 are shown in Fig. 1. [Fe(bpy)3](ClO4)2 complex
showed sharp bands in the range of 1400–1600 cm−1 (Fig. 1(d)),
which can be assigned to the ꢀ(C N) bands of the pyridine
ring in bpy [37–39]. Similar ꢀ(C N) bands were observed for
[Fe(bpy)3]2+@Y (Fig. 1(a)) and [Fe(bpy)3](ClO4)2 + Na-Y (Fig. 1(b)).
For [Fe(bpy)3]2+@Y, the IR peaks derived from [Fe(bpy)3]2+ com-
plex were observed even after Soxhlet extraction, suggesting that
[Fe(bpy)3]2+ ions were present in the supercage of zeolite Y. The
The complex [Fe(bpy)3](ClO4)2 for comparison with
[Fe(bpy)3]2+@Y was synthesized as described in previous work
[36]. 2,2ꢀ-Bipyridine (0.78 g, 5.0 mmol) was added into H2O solu-
tion (100 mL) of FeSO4·7H2O (0.42 g, 1.5 mmol) at about 60 ◦C and
stirred at the same temperature for 1 h. After the addition of sodium
perchlorate (0.85 g, 7.0 mmol) into the mixture solution, a reddish
precipitate formed immediately. After filtration, recrystallization
Please cite this article in press as: S. Yamaguchi, et al., Selective hydroxylation of cyclohexene over Fe-bipyridine complexes encapsulated