22
H. Yang et al. / Applied Catalysis A: General 457 (2013) 21–25
POM anion exhibited excellent catalytic performance for the
hydroxylation of benzene to phenol.
for 24 h to remove the water. Elemental analysis calcd (%) for
60H48N12O49SiMo2V2W12 (4249.15): C 16.95, H 1.13, N 3.95.
C
Found (%): C 16.94, H 1.17, N 3.93.
2. Experimental
2.2.4. Preparation of [(CH3)4N]4[PMo11VO40] (3)
3 was prepared [24,25] by adding four equivalents of (CH3)4NOH
into the H4[PMo11VO40] solution and was identified by IR spectra
(Fig. S1b).
2.1. Materials
Disodium hydrogen phosphate (Na2HPO4·12H2O, 99% purity)
from Tianjin Kermel Chemical Reagent Co., Ltd., sodium molyb-
date (Na2MoO4·2H2O, 99% purity) from Tianjin Kermel Chemical
Reagent Co., Ltd., sodium metavanadate (NaVO3·2H2O, 98% purity)
from Tianjin Kermel Chemical Reagent Co., Ltd., tetramethy-
lammonium hydroxide ((CH3)4NOH, 97% purity) from Aladdin
Chemistry Co., Ltd., molybdenum trioxide (MoO3, 99.5% purity)
from Shanghai Colloid Chemical Plant, vanadium pentoxide (V2O5,
99% purity) from Tianjin Guangfu Fine Chemical Research Institute,
2,2ꢀ-bipyridine (bpy, C10H8N2, 99% purity) from Sigma–Aldrich
(Shanghai) Trading Co., Ltd., silicotungstic acid (H4[SiW12O40], A.
R.) from Tianjin Damao Chemical Reagent Factory were all used
as received without further purification to produce catalysts. Ben-
zene (C6H6, 99.5% purity) from Beijing Chemical Works was used
as substrate. Acetic acid (CH3COOH, 99.5% purity) from Guangdong
Guanghua Chemical Factury Co., Ltd., acetonitrile (CH3CN, 99.5%
purity) from Beijing Chemical Works, methanol (CH3OH, 99.8%
purity) from Sinopharm Chemical Reagent Beijing Co., Ltd., ethanol
(CH3CH2OH, 99.8% purity) from Sinopharm Chemical Reagent Bei-
jing Co., Ltd., sulfolane (C4H8O2S, G. R.) from Aladdin Chemistry
Co., Ltd., dimethyl sulfoxide ((CH3)2SO, A. R.) from Aladdin Chem-
istry Co., Ltd. were used as solvents. Hydrogen peroxide (H2O2, 35%
purity) from Shanghai Yuanda Peroxide Co., Ltd. was used as the
oxidant.
2.2.5. Synthesis of [(CH3)4N]4[SiW12O40] (4)
4 was prepared by adding four equivalents of (CH3)4NOH to the
H4[SiW12O40] solution and was identified by IR spectra (Fig. S1c).
2.3. Catalyst characterization
The IR spectra of the catalysts were performed in the range
4000–400 cm−1 at the resolution of 4 cm−1 on a FT-IR Bruker
NEXUS470 spectrometer with pressed KBr disks. The TG/DTA data
of the catalysts were recorded on a Pyris Diamond TG/DTA instru-
ment with a heating rate of 10 ◦C min−1 under immobile airflow.
Crystal data of 1 were collected on a SMART APEX II-CCD X-
ray single crystal diffractometer with graphite-monochromatic Mo
˚
Ka radiation (ꢀ = 0.71073 A). The elemental analyses of catalysts
(C/H/N) were analyzed on a Perkin-Elmer 2400 CHN Elemental
Analyzer.
2.4. Catalytic testing
The hydroxylation of benzene was carried out in a 25 mL
flask equipped with a condenser. In a typical reaction, 0.0788 g
(0.025 mmol) of 1, 0.78 g (10 mmol) of benzene and 2.83 g
(30 mmol) of 35% H2O2 were added into 6.8 mL of acetonitrile. The
flask was put into a water bath at 80 ◦C for 2 h. After reaction, 0.2 g
of toluene was added as the internal standard. The GC analysis
of the samples were recorded on a GC-Agilent 7890 series instru-
ment equipped with an Agilent SE-30 capillary column and a flame
ionization detector.
2.2. Catalyst preparation
2.2.1. Preparation of H4[PMo11VO40
]
H4[PMo11VO40] was prepared according to reference [23]. 7.16 g
(20 mmol) of Na2HPO4·12H2O, 3.16 g (20 mmol) of NaVO3·2H2O
were added in 80 mL of water at 25 ◦C. 2 mL of 98% H2SO4 was added
to the mixture above, 53.2 g (220 mmol) of Na2MoO4·2H2O was dis-
solved in 80 mL of water then mixed the two solutions. Another
34 mL of 98% H2SO4 was added into the solution. 160 mL of ethyl
phenol
initial benzene
Yield of phenol(%) =
× 100%.
phenol
Selectivity to phenol(%) =
×
phenol+benzoquinone+catechol+hydroquinone+maleic anhydride
100%.
ether was added to the mixture. H4[PMo11VO40] was separated
from the middle layer of the mixture then was characterized by
IR spectra (Fig. S1a).
3. Results and discussion
3.1. Catalyst characterization
3.1.1. FT-IR spectral studies
2.2.2. Preparation of [Mo2V2O9(bpy)6][PMo11VO40] (1)
1
was prepared by the hydrothermal method. 0.21 g of
When a mixture of MoO3, V2O5, bpy and H4PMo11VO40 has
been heated to 180 ◦C for 2 days under the hydrothermal condition,
orange crystals can be achieved. These crystals were washed by
water for several times, then were dried and characterized by FT-IR.
The FT-IR spectra of 1 (Fig. 1) with the peaks at 951 cm−1, 868 cm−1
and as(Mo–Oc–Mo) for the Keggin structure, while the peaks at
1071 cm−1 and 1055 cm−1 were attributed to the (P–O) [26]. Peaks
at 1606 cm−1 and 759 cm−1 were caused by the (C–C) and (C–C)
of bpy ligand, while the ring breathing of bpy ligand caused the
peak at 994 cm−1 [27].
H4[PMo11VO40]·19H2O, 0.073 g of MoO3, 0.018 g of V2O5, 0.062 g of
2,2ꢀ-bpy and 10 mL distilled water were mixed and stirred, then the
pH of the solution was adjusted to 4.8 with 2 M NaOH. The suspen-
sion was transferred into a 30 mL Teflon-lined autoclave and kept
at 160 ◦C for 48 h. After the temperature was cooled slowly to 25 ◦C,
orange crystals were obtained. The yield was 31% (based on Keggin
anion). The catalyst was dried in vacuum at 80 ◦C for 24 h to remove
the water. Elemental analysis calcd (%) for C60H48N12O49PMo13V3
(3152.09): C 22.86, H 1.53, N 5.33. Found (%): C 22.80, H 1.57, N
5.30.
2.2.3. Preparation of [Mo2V2O9(bpy)6][SiW12O40] (2)
2
was prepared as
1
but added 0.28 g (0.1 mmol)
3.1.2. Thermal analysis
of H4[SiW12O40]·xH2O instead of 0.21 g (0.1 mmol) of
H4[PMo11VO40]·19H2O [22]. Based on W, 43% yield of crys-
tals was obtained. The catalyst was dried in vacuum at 80 ◦C
The TG/DTA analysis was carried out to investigate the thermal
stability of 1. As shown in Fig. 2, the crystal water of 1 led to the
weight loss (2.50%) below 400 ◦C. The weight loss in the range of