Preparation and characterization of lamellar vanadyl alkylphosphates as catalyst precursors for the selective oxidation of butane

Article abstract of DOI:10.1246/bcsj.76.837

Vanadyl alkylphosphates consisting of V⁴⁺ and P⁵⁺ were synthesized by the reaction of a solid mixture of V₂O₅ and V₄O₉ (2:3 in mol) with P₂O₅ in primary aliphatic (from C₁ to C₈), secondary aliphatic (C₃ and C₄), and alicyclic (C₅) alcohols, and were characterized by means of elemental analysis, thermogravimetric analysis, X-ray diffraction, IR spectroscopy, and magnetic susceptibility. The chemical formulae of the products were determined to be VO(RO)_x(HO)_1-xPO₃·(ROH)_y (x = 0.5-0.7, y = 0.3-0.5 for primary aliphatic alcohols; x = 0.1-0.2, y = 0.4-0.9 for secondary aliphatic and alicyclic alcohols; and R = organic group). X-ray diffraction revealed that the compounds had a lamellar structure, where the organic groups existed as double layers with a tilt of about 56° against the basal plane. Magnetism and IR spectroscopy demonstrated that the construction of the basal planes in the vanadyl alkylphosphates was similar to that of VOHPO₄ · 0.5H₂O, which consists of V⁴⁺ dimers linked with PO₄, except for vanadyl sec-butylphosphate, consisting of isolated V⁴⁺ monomers. Calcination of vanadyl methylphosphate and vanadyl cyclopentylphosphate brought about crystallites of (VO)₂P₂O₇. These (VO)₂P₂O₇ exhibited high selectivities to maleic anhydride (65-68%) for the selective oxidation of butane under a high concentration of butane (5.0%).

Full text of DOI:10.1246/bcsj.76.837

Ó 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 837–846 (2003)
837
Preparation and Characterization of Lamellar Vanadyl Alkylphosphates
as Catalyst Precursors for the Selective Oxidation of Butane
ꢀ
y
yy
Yuichi Kamiya, Eiichiro Nishikawa, Atsushi Satsuma, and Toshio Okuhara
Research and Development Center, Tonen Chemical Corporation, 3-1 Chidori-cho, Kawasaki-ku, Kawasaki 210-0865
yDepartment of Applied Chemistry, Graduate School of Engineering, Nagoya University, Nagoya 464-8603
yyGraduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810
(
Received August 7, 2002)
4þ
5þ
Vanadyl alkylphosphates consisting of V and P were synthesized by the reaction of a solid mixture of V
2 5
O and
V
4
O
9
(2:3 in mol) with P in primary aliphatic (from C to C ), secondary aliphatic (C and C ), and alicyclic (C ) alcohols,
5
2
O
5
1
8
3
4
and were characterized by means of elemental analysis, thermogravimetric analysis, X-ray diffraction, IR spectroscopy, and
magnetic susceptibility. The chemical formulae of the products were determined to be VO(RO) (ROH)
x
(HO)1ꢁxPO
3
ꢂ
y
(
x ¼ 0:5{0:7, y ¼ 0:3{0:5 for primary aliphatic alcohols; x ¼ 0:1{0:2, y ¼ 0:4{0:9 for secondary aliphatic and alicyclic
alcohols; and R = organic group). X-ray diffraction revealed that the compounds had a lamellar structure, where the organic
ꢃ
groups existed as double layers with a tilt of about 56 against the basal plane. Magnetism and IR spectroscopy demonstrated
thattheconstructionofthebasalplanesinthevanadylalkylphosphateswassimilartothatofVOHPO
4
0.5H
2
O,whichconsists
, except for vanadyl sec-butylphosphate, consisting of isolated V monomers. Calcination of
vanadyl methylphosphate and vanadyl cyclopentylphosphate brought about crystallites of (VO) . These (VO)
ꢂ
4þ
4þ
of V dimers linked with PO
4
2
P
2
O
7
2 2 7
P O
exhibited high selectivities to maleic anhydride (65–68%) for the selective oxidation of butane under a high concentration of
butane (5.0%).
The selective oxidation of butane to maleic anhydride
abbreviatedasMA) isanimportantcommercialprocess, because
2 2 7
that vanadyl methylphosphonate was transformed to (VO) P O
by calcination.
11
(
MA is a useful raw material for agricultural chemicals, food
additives, and unsaturated polymer resins. Furthermore, this
reaction presently has only a few commercialized applications in
the gas-solid catalytic oxidations of lower alkanes with molecular
1
On the contrary, there are only few reports about vanadyl
alkylphosphates, in which ester bonds of (O=)P–O–C are
included, and V and P are 4þ and 5þ, respectively. Researchers
of DuPont described vanadyl alkylphosphates synthesized by the
10
oxygen. Vanadylpyrophosphate,(VO)
2
P
2
O
7
, isclaimedtobean
efficient phase for this reaction, and is a main component of the
2 5 2 5
reaction of V O with P O in alcohol. However, the incor-
porated alkylphosphates are limited to only those obtained from
primary aliphatic alcohols. In addition, the structure has been
insufficiently characterized.
We reported in a previous communication that vanadyl
alkylphosphates incorporating various alkylphosphates can be
2
{4
commercial catalyst.
formed by a topotactic transformation of VOHPO
2 2 7
The (VO) P O catalyst is usually
5
;6
4
ꢂ
2
0.5H O,
which is a prevailing precursor. So far, there have been many
reports on the preparation methods, preparation conditions, and
7
{9
activation processes.
However, since the yields are limited to
synthesized by the reaction of partially reduced V
in alcohols including secondary aliphatic and alicyclic alcohols.
2
O
5
with P
2
O
5
5
2
about 55%, further improvement of the yield is still desired. A
newprecursorisindispensableforthedevelopmentofaneffective
catalyst.
A seriesofvanadiumphosphorus(V–P) oxideshaveattracted a
great deal of attention, because of their structural diversity and
unique catalytic property. So far, there are many reports on the
The catalyst obtained by the calcination of vanadyl methyl-
phosphate showed a high catalytic performance for the selective
25
oxidation of butane, demonstrating that these vanadyl alkyl-
phosphates are promising starting materials for the catalysts.
In the present study, the vanadyl alkylphosphates were synthe-
sized, and were systematically characterized by means of
elemental analysis, X-ray diffraction, IR spectroscopy, thermo-
gravimetric analysis, and magnetic susceptibility. The catalytic
properties of the V–P oxides obtained from these vanadyl
alkylphosphates were investigated for the selective oxidation of
butane. Their catalytic performance is discussed in relation to
microstructure of the catalyst crystallites.
10{16
various V–P oxides, such as lamellar compounds,
large
and thin-layer
Lamellar compounds are demonstrated by
17
18{21
crystallites,
compounds.
mesostructured materials,
2{24
2
vanadyl alkylphosphonates and alkylphosphates consisting of
alternating inorganic V–P–O layers and organic group ones.
Vanadyl alkylphosphonates are shown by VO(RPO
3
) nH
2
O, in
ꢂ
which the oxidation numbers of V and P are þ4 and þ3,
respectively, and R is an alkyl group. These compounds contain
P–C bonds. Johnson et al. synthesized a number of vanadyl
Experimental
2
5
alkylphosphonates from V
alkylphosphonic acid, RPO(OH)
2
O
5
and a variety of corresponding
1
Materials. Vanadyl alkylphosphates were prepared as follows.
2 5
V O (29.2 g (0.16 mol), Koso Chemical Co., Ltd.) was reduced with
2{14;16
2
.
Guliants et al. claimed

8
38 Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
Preparation of Vanadyl Alkylphosphates
3
3
ꢁ1
a mixture of isobutyl alcohol (180 cm , Koso Chemical Co., Ltd.),
3
pretreated in a flow of dried air (10 cm min ) at 323 K for 24 h. The
ꢁ1
and benzyl alcohol (120 cm , Koso Chemical Co., Ltd.) at the
refluxing temperature (387 K) for 3 h. The obtained black solid was
separated by filtration. The powder XRD pattern revealed that this
temperature was raised from 323 K to 493 K at a rate of 5 K min
,
and molecules desorbed from the sample were collected in a U-
shaped tube at 77 K. The trapped molecules were then analyzed by a
gas chromatograph (TCD (GL science, GC-380)) equipped with a
Chromosorb 105 column.
Catalytic Oxidation of Butane. The catalytic oxidation of
butanewascarriedoutinafixed-bedreactor(Stainlesstube, 10mmof
inside diameter) under atmospheric pressure at 703 K. Prior to the
reaction, vanadyl alkylphosphates were calcined in a flow of a
solid was a mixture of V
number of V was determined by a titration method to be þ4:73,
indicating that V and V coexisted at a molar ratio of 2:3. The
obtained V 4:73 (20 g) was added to 300 cm of each alcohol. The
2 5 4 9
O and V O . The average oxidation
26
2
O
5
4
O
9
3
2
O
followingprimaryaliphatic alcoholswereused:methanol, ethanol, 1-
propanol, 1-butanol (Koso Chemical Co., Ltd.), 1-hexanol, and 1-
octanol (Tokyo Kasei Kogyo Co., Ltd.). The secondary alcohols
were: aliphatic alcohol; 2-propanol and 2-butanol (Koso Chemical
Co., Ltd.), and alicyclic alcohol; cyclopentanol (Tokyo Kasei Kogyo
2 2
mixture of O (10%) and N (90%) for 2 h. The calcination
temperature was adjusted to 703 K for VAP–methanol, VAP–
2-propanol, and VAP–2-butanol, and 803 K for VAP–1-butanol,
VAP–1-octanol, and VAP–cyclopentanol. These calcination tem-
peratures approximately correspond to the end temperatures of the
weight decrease on the TG profiles. The obtained catalysts are
2 5
Co., Ltd.). A mixtureof P O (29.6g (0.21 mol), KosoChemicalCo.,
3
Ltd.) and toluene (70 cm , Koso Chemical Co., Ltd.) was slowly
added to an alcoholic suspension with stirring at room temperature.
The mixture was then refluxed until the color of the suspension
changedtolightblue,e.g., methanol(80h), ethanol(30h),1-propanol
18 h), 1-butanol (3 h), 1-hexanol (2 h), 1-octanol (2 h), 2-propanol
40 h), and cyclopentanol (20 h). In the case of 2-butanol, the mixture
was refluxed for 100 h, and a greenish-brown suspension was
obtained instead of a light-blue suspension. The resulting vanadyl
alkylphosphates were separated by filtration, washed with acetone
and dried at room temperature for 16 h. Hereafter, these vanadyl
alkylphosphates will be denoted as VAP–alcohol name, e.g., VAP–
methanol.
4 2
denoted by VPO(alcohol name). VOHPO 0.5H O was treated in a
ꢂ
2
flow of N at 823 K for 2 h.
(
(
A reaction mixture consisting of 5.0% butane, 20% O
3
2
, and N
ꢁ1
2
(balance) was fed to the catalyst (1.5 g) at a rate of 30 cm min , and
the temperature of the reactor was raised from room temperature to
ꢁ1
703 K at a rate of 5 K min . Since the stationary activity and
selectivity were obtained after about 25 h of the reaction at 703 K, the
data were collected at 30 h of the reaction. The products were
analyzed with on-line gas chromatographs (FID (Shimadzu 14A or
Shimadzu 9A) and TCD (Shimadzu 9A)). For butane and MA, a
Porapak QS column (inside diameter 2.2 mm, length 1 m) was used.
A Molecular Sieve 13X column (inside diameter 2.2 mm, length 4 m)
As a reference, vanadyl hydrogen phosphate hemihydrate,
2
7
VOHPO
(
4
0.5H
2
O, was prepared according to the literature.
3
14.7 g (0.08 mol)) was added to a mixture of 90 cm of isobutyl
2 5
V O
ꢂ
was utilized for O
2
, N
2
and CO and a Porapak N column (inside
. CO and CO were converted
3
alcohol and 60 cm ofbenzylalcohol. The suspension was refluxedat
87 K for 3 h, and cooled to room temperature. 99% H PO (15.8 g
0.16 mol), MERCK Ltd.) was added to the suspension, followed by
diameter 2.2 mm, length 2 m) for CO
2
2
3
3
4
to methane using a Methanizer (Shimadzu MTN-1) for an FID
analysis.
(
refluxing at 387 K for 3 h. The resulting solid was filtered, washed
with acetone and dried at room temperature for 16 h. The XRD
pattern of this material was in good agreement with that of
Results
2
7;28
Vanadyl Alkylphosphates Obtained from Primary Ali-
phatic Alcohols. Table 1 summarizestheresults ofanelemental
chemical analysis for the vanadyl alkylphosphates from primary
aliphatic alcohols (abbreviated as VAPs–Pri). The P/V ratios of
all compounds were 1:00 ꢄ 0:03. Expectedly, the C/P ratio
increased as the carbon number of the starting alcohol increased.
The R/P ratios calculated from the C/P ratios were 1:00 ꢄ 0:11,
where R shows an alkyl group. The oxidation numbers of V in
these compounds were determined to be 4:00 ꢄ 0:02.
4 2
VOHPO 0.5H O reported in the literature.
ꢂ
Characterization. XRD patterns were recorded on an X-ray
diffractometer (Rigaku RINT-1400) with CuKꢀ radiation (ꢁ ¼
0:154 nm) at room temperature. Infrared spectra were obtained with
an IR spectrometer (Perkin Elmer model 1600) at room temperature
using a pressed disk composed of a mixture of the samples and KBr.
ThemagneticsusceptibilitywascollectedonaSQUIDmagnetometer
(
Quantum Design MPMS-5) with a magnetic field (H) of 1 kG. After
the sample was evacuated at 323 K for 1 h, the temperature of the
sample was swept from 300 K to 2 K.
The IR spectra of VAPs–Pri are shown in Fig. 1. The IR bands
at around 900–1300 cm are due to the lattice vibration of the
V–P–O layers of these compounds. The bands of 1192, 1095, and
Elemental analysis of the compound was performed by Mikro-
analytisches Labor Pascher (Germany) for V, P, C, and H. The
oxygen content in the sample was calculated by subtracting the sum
of the weights of V, P, C, and H. Prior to the analysis, the sample
was evacuated at 323 K for 24 h. The average oxidation number of V
ꢁ1
ꢁ1
ꢁ1
1
054 cm are assigned to ꢂ(PO
3
), and that at 981 cm is due to
29
ꢂ(V=O). The vibrations of the P–O–C bond were detected at
around 1161 cm as shoulder peaks. The C–H vibration of the
alkyl groups appeared at 2850–3000 cm , where the intensities
of these bands greatly depended on the kinds of alkyl groups.
Furthermore, two bands at 3528 and 3581 cm are assignable to
free OH stretching.
ꢁ
1
30
was determined by a redox titration method using KMnO
2
4
and
FeSO (NH ) SO 6H O according to the literature. The surface
ꢁ
1
6
4 4 2 4 2
ꢂ
area was measured by a BET method with an automatic adsorption
system (BELSORP 28SA, BEL Japan Inc.). SEM images were taken
with a scanning electron microscope (HITACHI S-2100).
ꢁ
1
31
TG/DTA profiles of VAPs–Pri are illustrated in Fig. 2. As
shown in Fig. 2a, the weight decreased in two steps for VAP–
methanol. The first weight loss was observed below 490 K with a
slight endothermic, and the second one, above 570 K, was
exothermic. The molecules desorbed from VAP–methanol,
measured by the temperature-programmed decomposition, were
mostly methanol (97 mol%) and a small amount of water. As
A thermogravimetric analysis (TG/DTA) was performed using a
TG/DTA 200 of Seiko Instruments. After the sample was pretreated
3
ꢁ1
ina flow ofdried air (50 cm min ) at323K for 24h, the temperature
ꢁ
1
of the sample was raised to 853 K at a rate of 5 K min
.
The temperature-programmed decomposition of VAP–methanol
was carried out using a flow system. Sample powder (10 mg) was
placed in a flow reactor (Pyrex-tube, 6 mm of inside diameter) and

Y. Kamiya et al.
Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
839
Table 1. Elemental Chemical Analysis for Vanadyl Alkylphosphates Synthesized from Primary Aliphatic Alcohols
a)
Elemental analysis/wt%
Atomic ratio Atomic ratio
Alcohol
Formula
b)
V
P
C
H
O
of P/V
1.02
of C/P
0.96
Methanol
28.1
17.4
6.5
2.0
46.1
VO{(CH
VO{(C
3
)
0:5/H0:5gPO
4
(CH
3
OH)0:5
ꢂ
(
(
27.4) (16.7) (6.5) (2.2) (47.3)
24.8 15.1 12.8 3.1 44.2
25.4) (15.4) (13.2) (3.1) (43.0)
15.0 15.6 3.3 41.1
24.8) (15.1) (15.8) (3.2) (41.2)
23.3 14.3 21.1 4.2 37.2
22.7) (13.8) (21.4) (4.3) (37.8)
19.3 12.0 30.5 6.0 32.2
19.3) (11.7) (30.0) (5.7) (33.3)
17.3 10.2 34.4 6.8 31.3
17.3) (10.5) (35.8) (6.6) (29.8)
Ethanol
1.00
0.99
1.01
1.02
0.97
2.19
2.68
3.81
6.56
8.71
2
H
5
)
0:7/H0:3gPO
4
2 5
(C H OH)0:4
ꢂ
1
1
1
1
-Propanol 25.0
VO{(n-C
VO{(n-C
VO{(n-C
VO{(n-C
3
4
6
8
H
H
H
H
7
)
0:6/H0:4gPO
4
(n-C
(n-C
3
4
H
H
7
9
OH)0:3
ꢂ
ꢂ
4
(
(
(
(
-Butanol
-Hexanol
-Octanol
9
)
0:7/H0:3gPO
4
OH)0:3
13
17
)
)
0:6/H0:4gPO
0:6/H0:4gPO
ꢂ
ꢂ
(n-C
(n-C
6
8
H
13OH)0:5
17OH)0:5
4
H
a) The figures in parentheses are the values calculated from the formulae. b) The oxygen content was estimated by subtracting the
sum of weights of V, P, C, and H.
Fig. 1. Infrared spectra of vanadyl alkylphosphate obtained from (a) methanol, (b) 1-propanol, and (c) 1-octanol.
discussed below, the first and second weight losses correspond to
the desorption of intercalated methanol and the combustion of the
methylgroupconnectedbyacovalentbond, respectively. TheTG
profiles of other VAPs–Pri showed loose changes (Fig. 2b–d).
Sharp exothermic peaks were detected above 500 K for all of the
compounds, and the magnitudes of the peaks increased with an
increase in the carbon number of the alcohol.
ethanol),1.23nm(VAP–1-propanol),1.54nm(VAP–1-butanol),
1.93 nm (VAP–1-hexanol), and 2.37 nm (VAP–1-octanol),
respectively. The d(001) value increased as the carbon number
of the starting alcohol increased.
Figure 4 provides a correlation between the d(001) value and
the molecular length of the startingalcohol. The molecular length
represents the distance between the H atom of OH (H-OH) and the
remotest H atom from H-OH, and was estimated based on the
covalent bond lengths with MOPAC (FUJITSU, WinMOPAC
Version 1.0). It was found that the d(001) values increased in
Figure 3 presents the XRD patterns of VAPs–Pri. All of the
ꢃ
compounds gave intense diffraction lines at less than 10 of 2ꢃ.
Thecompoundsfromsmalleralcohols, such asmethanol, ethanol,
and 1-propanol, showed similar XRD patterns (Figs. 3a–c). On
the other hand, VAP–1-butanol, VAP–1-hexanol and VAP–1-
octanol gave typical patterns due to lamellar compounds (Figs.
25
proportion to the length of the alcohol.
Figure 5 shows the dependencies of the magnetic susceptibility
on the temperature of the samples for VAP–methanol (Fig. 5a)
and VAP–1-octanol (Fig. 5b). The existence of exchange-
3
2
1
d–f). For example, VAP–1-octanol (Fig. 3f) has reflections at
ꢃ
ꢃ
ꢃ
4þ
ꢃ ¼ 3:72 (2.37 nm), 7.38 (1.20 nm), 11.00 (0.80 nm), and
coupled V dimers in various V–P oxides was confirmed from
5;11;32
ꢃ
4.68 (0.60 nm), which were assignable to the (001), (002),
the magnetic susceptibility.
When the temperature de-
(003), and (004) reflections of the lamellar phase, respectively.
creased from 300 K, ꢄ gradually increased, and then decreased
g
The basal spacings (d(001)) were estimated from 2ꢃ of the (001)
reflections to be 0.91 nm (VAP–methanol), 1.04 nm (VAP–
through a maximum at around 45 K. These changes were similar
5
32
to those of VOHPO
4
0.5H
2
O and VOHPO
3
1.5H
2
O
in the
ꢂ
ꢂ

8
40 Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
Preparation of Vanadyl Alkylphosphates
Fig. 3. XRD patterns of vanadyl alkylphosphates obtained from
(a) methanol, (b) ethanol, (c) 1-propanol, (d) 1-butanol, (e) 1-
hexanol, and (f) 1-octanol.
Fig. 2. TG/DTA profiles of vanadyl alkylphosphates measured in
air. The vanadyl alkylphosphates were obtained from (a)
methanol, (b) 1-propanol, and (c) 1-octanol.
4þ
literature, which have V dimers. These results indicate the
4
þ
presence of the V dimers in the vanadyl alkylphosphates. The
data can be analyzed by the Bleaney–Bowers expression (Eq. 1)
for an isolated dimer model in which each cation has 1/2 spin, and
33
the g tensors of the cations are isotopic:
ꢄ ¼ ꢄ þ C =ðT ꢁ ꢃÞ þ 4Cd=ðTð3 þ exp ðꢁ2J=kBTÞÞÞ; ð1Þ
where ꢄ is a temperature-independent parameter; C and ꢃ are
the constants associated with the magnetic impurities (i.e. the
0
i
0
i
4
þ
residual isolated paramagnetic V
temperature; Cd is a Curie constant associated with the V
monomers); T is the
Fig. 4. Correlation between the d(001) values of vanadyl alkyl-
phosphates and length of the starting alcohol. The vanadyl
alkylphosphates were obtained from primary aliphatic alcohol
4þ
4þ
dimer; J is a coupling constant within the V dimer; and kB is
Boltzman’s constant. The results of a least-squares fit over the
whole temperature range are shown in Fig. 5 (solid line), and the
parameters are listed in Table 2 along with the data for
(
) (1) methanol, (2) ethanol, (3) 1-propanol, (4) 1-butanol, (5)
1-hexanol, (6) 1-octanol; secondary aliphatic alcohol ( ) (7) 2-
propanol, (8) 2-butanol; and alicyclic alcohol ( ) (9) cyclo-
pentanol.
4 2
VOHPO 0.5H O.
ꢂ

Y. Kamiya et al.
Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
841
listed in Table 3. The P/V ratios were close to unity in all of the
compounds. The R/P ratios of VAP–2-butanol and VAP–
2
-propanol were 0.98 and 0.88, respectively. On the other hand,
the ratio of VAP–cyclopentanol was 0.55. The oxidation number
of V for these vanadyl alkylphosphates was 4:00 ꢄ 0:04.
Figure 6 shows the XRD patterns of VAP–2-propanol, VAP–
2
-butanol, and VAP–cyclopentanol. These compounds gave
ꢃ
intense lines at less than 2ꢃ ¼ 10 . For VAP–2-propanol (Fig.
ꢃ
6
a), a weak diffraction line (2ꢃ ¼ 6:7 ) at a slightly lower 2ꢃ
ꢃ
angle of the intense one (2ꢃ ¼ 7:6 ) was observed. Since the
ꢃ
diffraction line assigned to the (200) was observed at 13.8 , this
phase is probably a contaminant lamellar phase. The d(001)
values were 1.16 nm (VAP–2-propanol), 1.37 nm (VAP–2-
butanol), and 1.23 nm (VAP–cyclopentanol), respectively. The
correlation between the d(001) value and the molecular length of
the starting alcohol was in good accordance with that for VAPs–
Pri (Fig. 4).
The magnetic susceptibility of VAP–2-propanol and VAP–
cyclopentanol(notshown)gaveamaximumofꢄ ofaround45K,
g
4þ
as well showing the presence of the V dimers in these
compounds. The data could be well fitted to the Bleaney–Bowers
expression (Eq. 1). The obtained parameters are listed in Table 2.
As shown in Fig. 7, VAP–2-butanol showed a distinctly different
profile of magnetic susceptibility. When the temperature
decreased from 300 K, ꢄ monotonously increased. The data
were well fitted to the Curie–Weiss expression,
g
Fig. 5. Magnetic susceptibility of vanadyl alkylphosphates ob-
tained from (a) methanol and (b) 1-octanol. Solid lines represent
the result simulated by using the Bleaney–Bowers expression.
ꢄ ¼ ꢄ þ C=ðT ꢁ ꢃÞ;
ð2Þ
g
0
for the whole temperature range, as listed in Table 2 and Fig. 7
(solid line). As discussed below, VAP–2-butanol has isolated
Vanadyl Alkylphosphates Obtained from Secondary
Aliphatic and Alicyclic Alcohols. The compositions of
VAP–2-propanol, VAP–2-butanol, and VAP–cyclopentanol are
4þ
V
monomers.
As shown in Fig. 8, the IR spectra of VAP–2-propanol (Fig.
Table 2. Parameters Used to Fit the Magnetic Susceptibility of Vanadyl Alkylphosphates Synthesized from Various Alcohols and
O
VOHPO
4
0.5H
2
ꢂ
ꢄ0
C
i
ꢃ
Cd
C
3
J
ꢅeff
ꢅB
Alcohol
ꢁ7
3
ꢁ1
ꢁ5
3
ꢁ1
ꢁ3
3
ꢁ1
ꢁ3
ꢁ1
ꢁ1
1
0
cm K g
10 cm K g
deg
10 cm K g
10 cm K g
cm
a)
VOHPO
Methanol
4
0.5H
2
O
2.5
0.8
5.6
3.2
15.3
9.9
3.0
5.6
8.1
—
ꢁ0:6
ꢁ3:4
ꢁ2:4
ꢁ1:3
ꢁ0:9
ꢁ9:1
1.99
1.69
1.31
1.59
1.70
—
—
—
—
—
—
1.86
ꢁ30:6
ꢁ26:1
ꢁ27:5
ꢁ29:5
ꢁ28:8
—
1.72
1.63
1.77
1.66
1.69
1.90
ꢂ
1
2
-Octanol
-Propanol
Cyclopentanol
-Butanol
0.5
ꢁ15:4
2
2
7
4 2
a) VOHPO 0.5H O which was prepared by the so-called organic solvent method.
ꢂ
Table 3. Elemental Analysis for Vanadyl Alkylphosphates Synthesized from Secondary Aliphatic and Alicyclic Alcohols
a)
Elemental analysis/wt%
Atomic ratio Atomic ratio
Alcohol
Formula
b)
V
P
C
H
O
of P/V
1.07
of C/P
2.64
2
-Propanol
-Butanol
24.3 15.9 16.2 3.5 40.1
23.9) (14.5) (15.2) (3.7) (42.7)
21.0 13.7 20.7 4.8 39.8
22.0) (13.4) (22.5) (4.7) (37.4)
VO{(sec-C
3
4
H
H
7
9
)
)
0:2/H0:8gPO
0:1/H0:9gPO
4
(sec-C
3
4
H
H
7
9
OH)0:7
OH)0:9
ꢂ
ꢂ
(
(
2
1.07
1.02
3.90
2.74
VO{(sec-C
4
(sec-C
Cyclopentanol 25.4 15.7 16.7 2.8 39.4
24.2) (14.7) (17.1) (3.1) (40.9)
VO{(C
5
H
9
)
0:2/H0:8gPO
4
(C
5
H
9
OH)0:4
ꢂ
(
a) The figures in parentheses are theoretical values calculated from formulae. b) The oxygen content was estimated by subtracting
the sum of weight of V, P, C, and H.

8
42 Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
Preparation of Vanadyl Alkylphosphates
8a) and VAP–cyclopentanol (Fig. 8c) were similar to those of
VAPs–Pri. Onthe other hand, VAP–2-butanol gave a broad band
ꢁ1
ꢁ1
around 1040 cm together with a broad band around 3380 cm
Fig. 8b).
TG/DTA profiles of VAP–2-propanol, VAP–2-butanol, and
(
VAP–cyclopentanol are given in Fig. 9. VAP–2-propanol and
VAP–cyclopentanol gave loose changes of weight in the TG
profiles (Figs. 9a and c) and indistinct exothermic peaks were
observed. On the other hand, the TG profile of VAP–2-butanol
(
Fig. 9b) showed a very sharp weight loss with endothermic peaks
at 440 K.
Catalytic Oxidation of Butane. The surface area and the
catalytic data are summarized in Table 4. As a reference, the data
of a typical (VO) catalyst (abbreviated as VPO–org)
2 2 7
P O
Table 4. Activity and Selectivity of VP Oxide Catalysts for
Oxidation of Butanea)
SAc) Conversiond) Selectivityd),e)/%
b)
Fig. 6. XRD patterns of vanadyl alkylphosphates obtained from
a) 2-propanol, (b) 2-butanol, and (c) cyclopentanol.
Catalyst
2
ꢁ1
/
m g
/%
MA CO
2
CO
(
VPO(methanol)
VPO(1-butanol)
VPO(1-octanol)
VPO(2-propanol)
VPO(2-butanol)
37.6
6.4
3.8
11.5
3.1
59.0
21.7
15.5
34.3
16.7
58.9
13.2
65.3 14.7 20.0
59.3 16.2 23.5
56.7 15.7 27.6
61.6 13.8 24.6
31.0 20.1 48.9
68.0 13.4 18.6
43.2 21.6 35.2
VPO(cyclopentanol) 21.2
VPO(isobutanol)
5.2
VPO–orgf)
43.5
68.9
66.0 15.8 18.3
a) The reaction wasperformedat703K withthemixture of 5.0%
butane, 20% O , and N (balance). W=F (catalyst weight/flow
rate) was 373 g h (mol of butane) . b) The precursors were
previously calcined in a flow of a mixture of 10% O and N
balance) for 2 h at 703 K (VAP–methanol, VAP–2-propanol,
2
2
ꢁ1
2
2
(
VAP–2-butanol), 803 K (VAP–1-butanol, VAP–1-octanol,
VAP–cyclopentanol). c) Surface area after the reaction. d)
Stationary values obtained after 30 h of the reaction. e)
Selectivity based onbutane. f) VPO–org which was prepared by
Fig. 7. Magnetic susceptibility of vanadyl alkylphosphate ob-
tained from 2-butanol. Solid line represents the result simulated
by using the Curie–Weiss expression.
2
7
the so-called organic solvent method.
Fig. 8. Infrared spectra of vanadyl alkylphosphate obtained from (a) 2-propanol, (b) 2-butanol, and (c) cyclopentanol.

Y. Kamiya et al.
Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
843
Fig. 10. XRD patterns of vanadium phosphorus oxide catalysts
after the oxidation of butane. (a) VPO(methanol), (b) VPO(1-
butanol), (c) VPO(1-octanol), (d) VPO(2-propanol), (e) VPO(2-
butanol), (f) VPO(cyclopentanol), and (g) VP oxide obtained
from VOHPO
phase, and ( ) ꢀ-VOPO
4
0.5H
2
O. ( ) (VO)
.
2
P
2
O
7
, ( ) ꢆ-VOPO
4
, (ꢅ) X
1
ꢂ
4
2 2 7
showedweakdiffractionlinesof(VO) P O andverybroadpeaks
ꢃ
around 2ꢃ ¼ 20 , indicating the presence of an amorphous phase.
VPO(2-propanol) gave weak diffraction lines of ꢆ-VOPO
besides medium intense lines of (VO)
VPO(2-butanol) showed only diffraction lines due to ꢀ-VOPO
4
,
2 2 7
P O . On the other hand,
4
34
1
and the X phase.
Fig. 9. TG/DTA profiles of vanadyl alkylphosphates measured in
air. The vanadyl alkylphosphates were obtained from (a) 2-
propanol, (b) 2-butanol, and (c) cyclopentanol.
SEM images of the catalysts are given in Fig. 11. It was found
that the morphology of these compounds changed significantly.
VPO(methanol) displayed sponge-like shapes consisting of
microcrystallites of thin flakes (Fig. 11a). VPO(1-butanol)
showed bunches of grapes (Fig. 11b). VPO(cyclopentanol)
displayeda rose-petal morphology, which was showninq catalyst
4 2
obtained from VOHPO 0.5H O are shown. The catalytic
ꢂ
activitydifferedsignificantlydependingonthekindofprecursors.
VPO(methanol) and VPO(cyclopentanol) were highly active
2
ꢁ1
27
because of the high surface areas, e.g., 37.6 and 21.2 m g ,
respectively. VPO(1-octanol) and VPO(2-butanol), having
prepared by the so-called organic solvent method.
2
ꢁ1
Discussion
surface areas less than 4 m g , showed low activities for the
reaction. VPO(methanol) and VPO(cyclopentanol) exhibited
selectivities comparable to that of VPO–org. VPO(1-butanol),
VPO(1-octanol), and VPO(2-propanol) are slightly less selective
than VPO(methanol) and VPO(cyclopentanol). On the other
hand, VPO(2-butanol) gave low selectivity (31.0% at 16.7%
conversion).
Structure of Vanadyl Alkylphosphates Synthesized from
Primary Aliphatic Alcohols.
VAPs–Pri have a lamellar
structure, because these compounds exhibited a typical XRD
pattern of the lamellar phase, as shown in Fig. 3. The linear
correlation of the d(001) values with the molecular length of the
starting alcohol (Fig. 4) indicates that these alkyl groups are
present in the interlayer space of these compounds. In other
words, VAPs–Pri consists of alternating V–P–O layers and
organic group ones. In Fig. 4, the value of the intercept, 0.40 nm,
Powder XRD patterns of the catalysts after the reactions are
given in Fig. 10. These samples gave basically the patterns of
(
VO)
nol), VPO(cyclopentanol), and VPO–org were assigned to highly
crystallized (VO) . VPO(1-butanol) and VPO(1-octanol)
2 2 7
P O , except for VPO(2-butanol) (Fig. 10e). VPO(metha-
35
of the vertical axis is close to that of VOPO
4
(0.411 nm). If the
2 2 7
P O
alkyl groups existed as a single or double layer perpendicularly

8
44 Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
Preparation of Vanadyl Alkylphosphates
Fig. 11. SEM images of the catalysts after the oxidation of butane. (a) VPO(methanol), (b) VPO(1-butanol), and (c)
VPO(cyclopentanol).
Fig. 12. Proposed model for structure of vanadyl methylphosphate as a typical sample of vanadyl alkylphosphates. The V–P–O layer
4 3 3 3
consists of edge-shared VO dimers connected through corners by (HO)PO or (CH O)PO tetrahedra.
against the V–P–O layer, the slope of the line in Fig. 4 would be
.0 or 2.0, respectively. Since the observed slope is 1.65, it is
deduced that the alkyl groups are present as a double layer with a
tilt of about 56 in the interlayer space.
The P/V atomic ratios of VAPs–Pri were nearly unity, and the
average oxidation numbers of V were very close to þ4:0. The
second weight loss is due to the combustion of methyl group.
From these results, the chemical formula of VAP–methanol is
1
described asVO(CH
P ratio of VAP–methanol was almost unity (0.96), the chemical
formula of VAP–methanol was determined to be
3
O)
x
3 3
(HO)1ꢁxPO (CH OH)1ꢁx. Since the C/
ꢂ
ꢃ
3 3 3
VO(CH O)0:5(HO)0:5PO (CH OH)0:5. The composition calcu-
ꢂ
absorption bands ofꢂ(PO
the same positions as that for VOHPO 0.5H O. The magnetic
4 2
3
) and ꢂ(V= O)wereobservedatalmost
lated from this chemical formula is in good agreement with the
experimental values, as listed in Table 1. The two weight losses
on the TG profile (8.7 wt% and 8.9 wt%) are also consistent with
the calculated values (8.4 wt% and 8.7 wt%).
5
ꢂ
4þ
susceptibility (Fig. 5) indicates the existence of V dimers in
thesecompounds. Inaddition, thecouplingconstants(J)ofVAP–
ꢁ1
ꢁ1
methanol (ꢁ26:1 cm ) and VAP–1-octanol (ꢁ27:5 cm ) were
Next, we estimate the chemical formulae of the other VAPs–
Pri. Similarly to the case of VAP–methanol, it was deduced that
the exothermic weight losses are due to the combustion of the
alkyl group on alkyl phosphate, and that the other weight losses
are due to the intercalated alcohol. From this assumption, the
chemical formulae of these VAPs–Pri were proposed, as listed in
Table 1. These formulae are well consistent with the experi-
mental data.
Based on these results, the schematic structure of VAP–
methanol as a typical sample of VAPs–Pri is depicted in Fig. 12.
VAPs–PriarelamellarcompoundsconsistingofalternatingofV–
P–O layers with a thickness of 0.40 nm and alkyl group layers. In
this structure, the V–P–O layer is similar to the layer in
ꢁ
1
almost the same as that of VOHPO
4
0.5H
2
O (ꢁ30:6 cm ). The
O consists of alternating VOHPO layers
O ones. The VOHPO layer is made up of edge-shared
ꢂ
layeredVOHPO
4
0.5H
2
4
ꢂ
and H
VO
PO
2
4
4þ
6
octahedras, V dimers, connected through the corners by
5
4
tetrahedras. These results demonstratethatthe V–P–O layer
of the VAPs–Pri is similar to that of VOHPO
4
0.5H
2
O.
The formula of VAP–methanol will be discussed first. The IR
ꢂ
ꢁ1
spectrum showed the vibration of P–O–C (1161 cm ) for VAP–
methanol (Fig. 1). Thus, the methyl group would exist as methyl
phosphate (P–O–CH
3
). Alkyl phosphate is known to be formed
36
by a reaction of P O with the corresponding alcohol, support-
5
2
ing the existence of methyl phosphate in this compound. As
shown in Fig. 2a, the TG profile showed two-step weight
decreases, 8.7 wt% and 8.9 wt%. Since the first decrease was the
desorption of methanol and a small amount of water, this weight
losswasduetotheremovalofintercalatedmethanol. Considering
the exothermic behavior at the relatively high temperature, the
4
þ
VOHPO
PO
4
0.5H
2
O, in which the V dimers are connected by
4
tetrahedra. About half of the total phosphorus is present as
ꢂ
alkyl phosphate and the others as hydrogen phosphate (H–O–P–).
The alkyl groups of alcohol and alkyl phosphate exist as a double
layer with a tilt of about 56 . Since the XRD pattern of VAP–
ꢃ

Y. Kamiya et al.
Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
845
methanol was not almost unchangedupon a pretreatment at 450 K
in air flow, it is presumed that the methyl groups of the methyl
phosphate in the adjoining layers are stable and face each other.
Two bands due to the free OH vibration observed in the IR spectra
2 7
P O phases were obtained from VAP–methanol and VAP–
cyclopentanol by calcination, followed by activation under the
reaction conditions for 30 h. These vanadyl alkylphosphates with
4
þ
a structure containing V
(VO) . On the other hand, only VAP–2-butanol having
isolatedV monomerschanged toa mixture ofꢀ-VOPO
phases instead of (VO) . Such a difference in the resulting
dimers were transformed to
(Fig. 1) indicate that the interaction between alcohol and
hydrogenphosphate is weak. Probably, the alcohol is located on
2 2 7
P O
4þ
4
and X
1
4þ
the V dimer and, consequently, apart from the hydrogen
phosphates.
2 2 7
P O
phases would be caused by the difference in the structures of the
V–P–O layers of the vanadyl alkylphosphates. VAP–1-butanol
and VAP–1-octanol were transformed to less-crystalline
Structure of Vanadyl Alkylphosphates Synthesized from
Secondary Aliphatic and Alicyclic Alcohols. The P/V ratios
and oxidation numbers of V for VAP–2-propanol, VAP–2-
butanol (abbreviated as VAPs–sec), and VAP–cyclopentanol
2 2 7
(VO) P O with amorphous V–P oxides. VAP–1-butanol and
VAP–1-octanol gave large exothermic peaks above 500 K in TG/
DTA, as compared with that for VAP–methanol and VAP–
cyclopentanol (Fig. 2). Therefore, the amorphous V–P oxides
would arise from local temperature excursions resulting from the
exothermic combustion of these alkyl phosphates.
The concentrations of butane used for commercial processes
are usually about 1.5 vol% and 4.0 vol% for fixed-bed and
fluidized-bed reactor, respectively. From an industrial viewpoint,
operation under higher concentrations of butane is preferred for a
higher space-time yield of MA. Thus, catalytic oxidation was
performed at 5.0 vol% of butane.
(abbreviated as VAP–cycl) are 1.02–1.07 and 3.99–4.04, respec-
tively, which are very close to those of VAPs–Pri. The linear
correlation of the d(001) value with the length of the alcohol was
also observed (Fig. 4), indicating that the branched-alkyl and
alicyclic groups in these vanadyl alkylphosphates exist in the
same configuration as the straight alkyl groups.
The IR spectra of VAP–2-propanol and VAP–cyclopentanol
were similar to those of VAPs–Pri, and the magnetic suscept-
4þ
ibility was in accordance with the presence of the V dimers
Table 2). It is thus considered that the structure of the V–P–O
(
layer is analogous to those of VAPs–Pri. The chemical formulae
of these compounds were estimated in a similar manner to VAPs–
Pri (Table 3). Only 10–20% of phosphorus exists as alkyl
phosphate (R–O–P–) in these compounds, while 50–70% of
phosphorus was alkyl phosphate in VAPs–Pri. Hiyama et al.
reported that secondary aliphatic alcohol was readily dehydrated
VPO(methanol) and VPO(cyclopentanol) showed high cata-
lytic activities and selectivities to MA (Table 4). The catalytic
performances of these catalysts were comparable to that of VPO–
org (66% of selectivity), which was reported to be selective at 5%
41
of butane.
On the other hand, the selectivities of VPO(1-
butanol), VPO(1-octanol), and VPO(2-propanol) were not high
(about 60%) and that of VPO(2-butanol) was low (31% at 16.7%
conversion).
37
under the presence of P
2
O
5
.
Since P
, most of the added P was probably converted to
. Consequently, the concentrations of alkyl phosphate
2 5 2
O reacts withH O toform
H
H
3
PO
PO
4
2 5
O
5
þ
3
4
Shimoda et al. reported that the VOPO
ꢀ-VOPO and ꢇ-VOPO , as well as the amorphous and X
phases, were less selective than (VO)
4
phases of V , such as
formed from the secondary alcohols would be low. It is thus
deduced that the incorporation of these alkyl phosphates into
VAPs–sec and VAP–cycl is limited.
Contrary to the above compounds, the structure of the V–P–O
layers for VAP–2-butanol was different from that of the other
vanadyl alkylphosphates. As shown in Fig. 7, the magnetic
susceptibility of VAP–2-butanol obeyed the Curie–Weiss ex-
pression (Eq. 2). Magnetism like this was observed for vanadyl
4
4
1
3
4
2
P
2
O
7
.
Therefore, the low
selectivity of VPO(2-butanol) is due to the presence of X
VOPO , predominantly. It is also considered that the presence of
amorphous V–P oxides or ꢆ-VOPO is responsible for the
1
and ꢀ-
4
4
relatively low selectivities of VPO(1-butanol), VPO(1-octanol),
and VPO(2-propanol). Onthe otherhand, the highselectivities of
VPO(methanol) and VPO(cyclopentanol) are due to the single
1
2
13
benzylphosphonate and vanadyl n-pentylphosphonate with
isolated V monomers. The IR spectra of VAP–2-butanol,
2 2 7
phase of (VO) P O .
4þ
It is known that the catalytic performance greatly depends on
the morphology of the catalyst as well. Catalysts consisting of
microcrystallites of thinner plates showed high selectivities to
ꢁ
1
having a broad band around 1040 cm in the V–P–O lattice
vibration region (Fig. 8), was also different from that of other
compounds. These broad bands were observed in intercalated
42
MA, because of a preferential exposure of the (100) plane of
(VO) . The relatively high selectivities of VPO(methanol)
VOPO
VOPO
4
compounds having isolated VO
–aniline,
6
39
octahedra, e.g.,
and VOPO –4-
2 2 7
P O
38
4
VOPO
4
–anilinoaniline,
These results indicate that the isolated V
4
and VPO(cyclopentanol) would be due to their thinner plate-like
shapes (Fig. 11a,c).
40
4þ
butylaniline.
monomers exist in VAP–2-butanol. Furthermore, VAP–2-
butanol gave a broad band of around 3380 cm in the IR spectra,
suggesting that hydrogenphosphate (POH) of the V–P–O layer
interacts with the OH of intercalated 2-butanol.
ꢁ
1
Conclusion
The present study clarified the structure of the vanadyl
alkylphosphates by using various characterization techniques.
The vanadyl alkylphosphates have a lamellar structure and the
In summary, the structure of VAP–2-propanol and VAP–
cyclopentanol is the same as those of VAPs–Pri, while the
ROPO /HOPO ratios are smaller than those in VAPs–Pri. On
ꢃ
alkyl groups exist as a doublelayerswitha tilt of about 56 against
the V–P–O layer. The structure of the V–P–O layers is similar to
3
3
4
þ
the other hand, VAP–2-butanol has a different structure from that
that of VOHPO
PO
4
4
0.5H
2
O, having the V dimers connected by
tetrahedra, except for vanadyl sec-butylphosphate. In
vanadyl sec-butylphosphate, isolated VO monomers exist. The
(ROPO )/(total P) ratios were 0.5–0.7 for the vanadyl alkyl-
phosphates obtained from primary aliphatic alcohols and 0.1–0.2
ꢂ
4þ
of the above compounds, and has isolated V monomers linked
with PO tetrahedra.
Selective Oxidation of Butane with the Catalysts Obtained
from Vanadyl Alkylphosphates. Highly crystalline (VO)
4
6
3
2
-

8
46 Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
Preparation of Vanadyl Alkylphosphates
for that from secondary aliphatic and alicyclic alcohols. Well-
crystallized (VO) catalysts were obtained from vanadyl
methylphosphate and vanadyl cyclopentylphosphate. These
catalystsshowedbothhighcatalyticactivityandselectivitytoMA
under a high concentration of butane, which was comparable to
that of catalysts preparedbythe so-calledorganic solvent method.
1635.
19 T. Abe, A. Taguchi, and M. Iwamoto, Chem. Mater., 7, 1429
(1995).
M. Roca, J. E. Haskouri, S. Cabrera, A. B. Porter, J. Alamo,
D. B. Porter, M. D. Marcos, and P. Amor o´ s, Chem. Commun.
Cambridge), 1998, 1883.
H. Hatayama, M. Misono, A. Taguchi, and N. Mizuno,
Chem. Lett., 2000, 884.
N. Hiyoshi, N. Yamamoto, N. Terao, T. Nakato, and T.
Okuhara, Stud. Surf. Sci. Catal., 130, 1715 (2000).
N. Hiyoshi, N. Yamamoto, and T. Okuhara, Chem. Lett.,
001, 484.
2 2 7
P O
2
0
(
2
1
This work was supported by the New Energy and Industrial
Technology Development Organization (NEDO) and Japan
Chemical Industry Association (JCIA). We thank Dr. H. Sato
(TokyoInstituteofTechnology)forthemeasurementandanalysis
of the magnetic susceptibility.
2
2
2
3
2
2
11.
4
T. Nakato, Y. Furumi, and T. Okuhara, Chem. Lett., 1998,
6
2
5
Y. Kamiya, E. Nishikawa, A. Satsuma, N. Mizuno, and T.
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