4
158
K. Sahiro et al. / Materials Research Bulletin 48 (2013) 4157–4162
P/W 0.2. Elemental analysis for (NH
.91; W, 72.50; O, 24.00; H, 0.77; N, 1.52; total 99.70%; calcd: P,
.02; W, 72.59; O, 24.22; H, 0.80; N, 1.38; total 100.01%. IR
4
)
3
PW12
O
40ꢁ6H
2
O, found: P,
Instruments) thermogravimetric analyzer. The sample (ca. 20 mg)
ꢀ1 ꢀ1
0
1
was heated in a flow of N (50 ml min ) at 10 K min from room
2
temperature to 973 K. Temperature-programed desorption (TPD)
measurements were performed with a TPD-1-AT (BEL Japan).
Helium was used as a carrier gas. The temperature range was from
ꢀ1
+
spectrum (
nmax/cm ): 1635 (m, H
2
O), 1401 (m, NH
4
bending),
1
080 (s, P–O stretching), 984 (s, W 55 O stretching), 888 (s, W–O–W
stretching), 802 (vs, W–O–W stretching).
P/W 0.4. Elemental analysis for (NH
ꢀ
1
303 K to 973 K with heating rate of 10 K min after pretreatment at
ꢀ
1
4
)
3
PW12
O
40ꢁ6H
2
O, found: P,
303 K under He flow (50 ml min ) for 30 min.
0
.87; W, 72.50; O, 24.30; H, 0.83; N, 1.47; total 99.70%; calcd: P,
.02; W, 72.59; O, 24.22; H, 0.80; N, 1.38; total 100.01%. IR
1
2.5. Hydrolysis of alkyl acetate
ꢀ
1
+
spectrum (
n
max/cm ): 1631 (m, H
2
O), 1403 (m, NH
4
bending),
1
080 (s, P–O stretching), 983 (s, W 55 O stretching), 888 (s, W–O–W
stretching), 800 (vs, W–O–W stretching).
Hydrolysis of ethyl acetate was carried out at 333 K with 5 wt%
ethyl acetate in D
(1.7 mmol)) for 2 h. The weight of the catalyst used was 0.075 g
(24.7 mol) [10].
2
O (total volume: 3.0 ml, ethyl acetate: 0.15 g
ꢀ
1
P/W 1.0. IR spectrum (
n
max/cm ): 1630 (m, H
bending), 1080 (s, P–O stretching), 983 (s, W 55 O stretching),
88 (s, W–O–W stretching), 798 (vs, W–O–W stretching).
P/W 2.0. Elemental analysis for (NH O, found: P,
2
O), 1402 (m,
+
NH
8
4
m
1
1
Conversion and yield were estimated using H NMR. In the H
NMR spectra, peaks corresponding to ethyl acetate, ethyl alcohol,
and acetic acid were observed. No other peak was observed.
Therefore, we assumed that selectivity of this hydrolysis was 100%.
4
)
3
PW12O
40ꢁ6H
2
0
1
.94; W, 72.40; O, 24.90; H, 0.83; N, 1.53; total 100.60%; calcd: P,
.01; W, 72.16; O, 24.60; H, 0.86; N, 1.37; total 100.00%. IR
ꢀ
1
+
spectrum (
n
max/cm ): 1631 (m, H
2
O), 1402 (m, NH
4
bending),
2
Since peaks of methylene (CH O) for ethyl acetate (4.03 ppm) and
1
080 (s, P–O stretching), 983 (s, W 55 O stretching), 888 (s, W–O–W
ethyl alcohol (3.52 ppm) were well separated, the conversion of
ethyl acetate was calculated using the integration ratio of these
two peaks as follows:
stretching), 800 (vs, W–O–W stretching).
ꢀ1
P/W 3.0. IR spectrum (
n
max/cm ): 1633 (m, H
bending), 1080 (s, P–O stretching), 983 (s, W 55 O stretching),
90 (s, W–O–W stretching), 801 (vs, W–O–W stretching).
2
O), 1401 (m,
+
NH
8
4
Conversionð%Þ ¼ ðintegrationofCH
ðintegrationofCH
þ integrationofCH
2
OofethylalcoholÞ=
Oofethylacetate
OofethylalcoholÞ ꢂ 100:
2
.3. Synthesis of (NH
4
)
3
PW12
O
40 by reaction of H
3
PW12O40 with
2
NH
4
HCO
3
(neutralization method)
2
H
3
PW12
O
40ꢁ6H
2
O (2.99 g, 1 mmol) was dissolved in 40 mL
The calculated conversion and yield of hydrolysis of ethyl
acetate in the presence of Keggin-type phosphotungstic acid were
consistent with data obtained by the GC method, indicating that
our analytical method using NMR is appropriate.
water, and then the solution was heated in an oil bath at 368 K.
After the temperature of the solution had become constant, a
stoichiometric amount of NH
dropwise to the solution of H
stirring. The produced suspension was stirred at 368 K for
0 min and dried at 328 K by a rotary evaporator to obtain a
white solid of (NH 40 (ca. 2.8 g).
IR spectrum ( max/cm ): 1633 (m, H
84 (s), 889 (s), 816 (vs).
4
HCO
3
solution (0.055 M) was added
3
PW12
O
40ꢁ6H O with vigorous
2
3
. Results and discussion
.1. Synthesis and characterization
4 6 2 12 40
NH 40 was produced by reaction of (NH ) H W O
9
4 3
) PW12O
3
ꢀ1
n
2
O), 1404 (m), 1080 (s),
9
(
4
)
3
PW12O
and phosphoric acid with various phosphorus/tungsten molar
ratios (P/W ratios). Samples obtained from solutions with P/W
ratios of 0.2, 0.4, 1.0, 2.0, and 3.0 were designated as P/W 0.2, P/W
2
.4. Characterizations
FT-IR spectra were recorded on a Nicolet 6700 FT-IR spectrom-
0.4, P/W 1.0, P/W 2.0, and P/W 3.0, respectively. Yields based on
ꢀ1
eter with 2 cm
resolution. Powder X-ray diffraction (XRD)
tungsten (W), pore volumes, crystallite sizes, and BET surface areas
of the obtained samples are summarized in Table 1.
patterns were measured with a diffractometer (Rigaku, Mini Flex)
equipped with a graphite monochromator using Cu Ka radiation
(tube voltage: 40 kV, tube current: 30 mA). Diffraction line widths
were obtained after subtraction of the instrumental width
determined by the line width of an NaCl sample, and crystallite
sizes were calculated from the width of the (2 2 2) line using
Scherrer’s equation. Scanning electron microscopy (SEM, Hitachi,
S-4800) observations were made using samples dusted on
adhesive conductive carbon paper attached to a brass sample
mount. Nitrogen adsorption measurements were performed using
a sorption analyzer (Bel Japan, BELSORP max). Samples (ca. 0.1 g)
were degassed under vacuum at 423 K for 3 h prior to measure-
ment. Surface areas were estimated by the BET method. Micropore
volume (Vmicro) was estimated using the t-plot method, and
mesopore volume (Vmeso) was calculated from BJH desorption
(a)
(
(
b)
c)
(
d)
31
0
cumulative volume of pores (P/P between 0.39–0.99). P-NMR
spectra were recorded on a Varian System 500 (500 MHz)
spectrometer (P resonance frequency of 202.333 MHz) using an
1
externalH PO
3 4
reference. HNMRspectra wererecordedona Varian
700
1
900
1600
1300
1000
System 500 (500 MHz) spectrometer (H resonance frequency of
99.828 MHz). Complete elemental analyses were carried out by
Wavenumber/cm-1
4
Mikroanalytisches Labor Pascher (Remagen, Germany). TG-DTA
measurements were performed with an SSC/5200 (Seiko
Fig. 1. FT-IR spectra of samples P/W 0.2 (a), P/W 3.0 (b) and (NH
4 3 40
) PW12O
prepared by the neutralization method (c), and H PW12 40 (d).
3
O