Hydrothermal synthesis of microporous W-V-O as an efficient catalyst for ammoxidation of 3-picoline

Article abstract of DOI:10.1016/j.apcata.2015.10.011

W-V complex metal oxide (W-V-O) was prepared by hydrothermal synthesis method. Characterization by XRD, XPS, ICP-AES, N₂ adsorption, and STEM showed that W-V-O had a layered structure with micropore. W-V-O was tested for the vapor phase ammoxid

Full text of DOI:10.1016/j.apcata.2015.10.011

Applied Catalysis A: General 509 (2016) 118–122
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Hydrothermal synthesis of microporous W–V–O as an efficient
catalyst for ammoxidation of 3-picoline
Yoshinori Goto , Ken-ichi Shimizua,b, Toru Murayamaa,c, Wataru Uedad,∗
a
a
Institute for Catalysis, Hokkaido University, N-21, W-10, Sapporo 001-0021, Japan
Elements Strategy Initiative for Catalysts and Batteries, Kyoto University, Katsura, Kyoto 615-8520, Japan
Research Center for Gold Chemistry, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji,
b
c
Tokyo 192-0397, Japan
d
Kanagawa University, Rokkakubashi 3-27-1, Yokohama 221-8686, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 August 2015
Received in revised form 7 October 2015
Accepted 7 October 2015
Available online 28 October 2015
W–V complex metal oxide (W–V–O) was prepared by hydrothermal synthesis method. Characterization
by XRD, XPS, ICP-AES, N2 adsorption, and STEM showed that W–V–O had a layered structure with micro-
pore. W–V–O was tested for the vapor phase ammoxidation of 3-picoline (PIC) to 3-cyanopyridine (CP)
and compared with VOx/WO3 catalyst prepared by impregnation method and other V-based catalysts
which were reported to be efficient for this reaction. W-added vanadium oxides, W–V–O and VOx/WO3,
showed higher CP selectivity than conventional catalysts such as VOx/TiO2. The W–V–O catalyst showed
the highest CP selectivity of 99.5% at full PIC conversion. Kinetic studies showed that CP was the primary
product and small amount of pyridine and CO2 were produced from CP. The reaction by W–V–O in low
NH3 concentration condition or without co-feeding of water was also studied to evaluate the catalytic
performance of W–V–O in industrially relevant conditions.
Keywords:
Mixed metal oxide
W–V–O
Ammoxidation of 3-picoline
3
-Cyanopyridine
High yield
High selectivity
© 2015 Elsevier B.V. All rights reserved.
1
. Introduction
Direct synthesis of nitriles via partial oxidation of hydrocarbons
studies on this reaction and related selective oxidation reaction
of picolines [20–22], methylpyradine [23] and toluene [24] sug-
gested bifunctional catalysis as a catalyst design concept, where the
VOx sites catalyze partial oxidation of hydrocarbons to oxygenate
intermediate and acid sites originated from co-catalysts, such as
in the presence of ammonia (NH ), so called ammoxidation, is an
3
industrially important reaction [1,2]. The gas-phase ammoxidation
of substituted aromatics/heteroaromatics is currently used in the
production of fine chemicals and intermediates [1–18]. Especially,
the ammoxidation of 3-methylpyridine (3-picoline) to nicotinoni-
trile (3-cyanopyridine) has been extensively studied [3–16] due to
the commercial importance of 3-cyanopyridine for the industrial
production of vitamin B3 (nicotinamide and nicotinic acid) as feed
additives [19]. These compounds are also used as a precursor for
commercial compounds such as cancer drugs, antibacterial agents,
and pesticides [2]. Various metal oxide-based catalysts have been
reported to be efficient for the ammoxidation of 3-methylpyridine
POx, act as adsorption site of basic substrate (picolines and NH ).
3
Knowing the fact that oxides of tungsten (W) are well known acidic
co-catalysts of V-based catalysts, one hypothesizes that W–V–O
oxides can be an attractive candidate of the catalyst for the ammox-
idation of picolines. To the best of our knowledge, quite a few efforts
have been devoted to the development of W–V binary oxides as an
attractive candidate of catalyst for the ammoxidation of picolines.
Our research group has focused on the hydrothermal synthesis
of single crystalline Mo–V–O based catalysts [25–27]. Particularly,
single phasic orthorhombic Mo VOx, having a microporous and
3
(
PIC) to 3-cyanopyridine (CP) [3–16]. Most of the reported cata-
layered structure, is of importance because it catalyzes selective
oxidative dehydrogenation of ethane even at around 300 C [26].
◦
lysts are vanadium (V)-based catalysts, including VOx/Nb O5 [3],
2
V O5 [4], (VO) P O7 [5,6], ꢀ-VOHPO [7], VOx/TiO [8], V–Sb–O [9],
V–Cr–O [10], VZrPO [11], VZr(Al)PON [11–13], industrial VTiSbSiOx
The single phase Mo–V–P catalyst also catalyzeds the ammoxi-
dation of propane [27]. Recently, we extended the hydrothermal
synthetic methodology to metal oxides consisted of various group
2
2
2
4
2
catalyst [14], V O5/MgF [15], and V O5/CeF3 [16]. Mechanistic
2
2
2
5
and 6 elements, and prepared a series of metal oxides with sim-
ilar microporous and layered structure as orthorhombic Mo VOx
3
[
28,29]. We hypothesized that W–V–O oxides with similar struc-
∗ Corresponding author.
E-mail address: uedaw@kanagawa-u.ac.jp (W. Ueda).
ture may show redox/acid bifunctional catalysis for ammoxidation
http://dx.doi.org/10.1016/j.apcata.2015.10.011
0
926-860X/© 2015 Elsevier B.V. All rights reserved.

Y. Goto et al. / Applied Catalysis A: General 509 (2016) 118–122
119
300
W-V-O
VO /WO
3
Fig. 1. Polyhedral model of the microporous and layered W–V–O oxide.
x
10
20
30
40
50
60
2
θ (deg.)
Table 1
Surface area and composition of the catalysts.
Fig. 2. XRD patterns of W–V–O and VOx/WO3: ꢀ = WO3 (PDF#00-033-1387),
Catalyst
S.A.a (m2
g
−1
)
Bulk W/Vb
Surface W/Vc
ꢁ
= V2O5 (PDF#00-040-1297), ♦ = VO2 (PDF#43-1051).
V2O5
VOx/WO3
W–V–O
4.8
14
16
–
–
62/38
67/33
60/40
76/24
◦
stirred for 1 h at 70 C, followed by adding 55 g of citric acid, stirring
◦
for 16 h at 70 C, evaporation to dryness using a rotating evapora-
tor, and by drying at 120 C for 16 h. After grinding, the resulting
a
Surface area determined by the BET method.
W/V atomic ratio determined by ICP-AES.
W/V atomic ratio determined by XPS.
◦
b
c
brown powder was calcined under flowing air (6 L/h) for 16 h at
◦
◦
5
00 C and for another 6 h at 600 C.
Mixed oxide of V and Cr (VCrO) was prepared as follows [10];
of 3-picoline. There are no attempts on the development of W–V
binary oxides for the ammoxidation of picolines. We report herein
the first example of ammoxidation of 3-picoline by hydrothermally
prepared W–V–O oxide with microporous and layered structure.
V O5 (5.28 mmol) and CrO (13.2 mmol) were dissolved in an aque-
2
3
◦
ous oxalic acid solution, followed by drying at 110 C for 10 h, and
◦
by calcination in air at 500 C for 6 h.
2.2. Catalyst characterization
2
. Experimental
◦
Nitrogen adsorption experiments at −196 C were carried out
2
.1. Catalyst preparation
with a BELSORP MAX (BEL Japan Inc.) sorption analyzer. Prior
to the measurement, the samples were evacuated at 200 C for
h. Specific surface area of the catalysts was estimated by BET
method. Powder X-ray diffraction (XRD) pattern of the catalysts
was recorded on RINT2200 (Rigaku) with Cu K␣ radiation (tube
voltage: 40 kV, tube current: 20 mA). Scanning transmission elec-
tron microscopy (STEM) images were obtained with a HD-2000
Hitachi High-Tech Inc.). Bulk composition of the catalysts was
determined by an inductive coupling plasma (ICP-AES) method
ICPE-9000, Shimadzu). Surface composition of the catalysts was
◦
Inorganic materials were purchased from Wako Pure Chemi-
2
cal Industries. The complex metal oxide of W and V (W–V–O) was
prepared by a hydrothermal synthesis method. An aqueous solu-
tion (40 mL) of (NH ) [H W12O40]·nH O (6.24 mmol), VOSO ·nH O
4
6
2
2
4
2
(
4.16 mmol) and oxalic acid (0.10 mmol) was introduced into a
stainless steel autoclave with a Teflon inner tube (50 mL), fol-
lowed by filling the inner space of the tube by Teflon thin sheet
(
(
50 mm × 1000 mm). The presence of the sheet is important to pre-
(
pare W–V–O. Then, N2 was fed into the solution for 10 min to
remove residual oxygen. The autoclave placed to rotating machine
was installed in an oven. The mixture underwent hydrothermal
estimated by X-ray photoelectron spectroscopy (XPS) measure-
ments using a JEOL JPS-9010MC (MgK␣ irradiation).
◦
reaction at 175 C for 24 h under mechanical rotation (1 rpm). The
formed solid was filtered, washed with ion-exchanged water, dried
◦
◦
at 80 C overnight and then heated at 500 C for 2 h under N flow.
2
V O5 and WO for catalytic studies were commercially supplied
2
3
from Wako Pure Chemical Industries. Tungsten oxide-supported
vanadia (VOx/WO ) was prepared by impregnation method. A sus-
3
pension of WO3 (8.01 mmol) in an aqueous solution (50 mL) of
◦
NH VO (4.91 mmol) was heated to 90 C for 30 min to evaporate
4
3
◦
water, followed by drying at 80 C overnight, and by heating at
00 C for 2 h under N2 flow. The bulk and surface compositions
◦
5
and surface area of the W–V–O and VOx/WO catalysts are listed in
3
Table 1. The composition and surface area of VOx/WO3 are close to
those of W–V–O.
According to the literature [8], TiO -supported vanadia
2
(
VOx/TiO ) with V loading of 5.9 wt% was prepared by impregnation
2
method. A suspension of anatase TiO2 (4 g) in aqueous oxalic acid
◦
solution (50 mL) of NH VO (4.9 mmol) was evaporated at 50 C,
4
3
◦
◦
followed by drying at 100 C, and by heating at 450 C for 6 h under
air.
Mixed oxide of VZrPO was prepared according to the literature
[
11]. To aqueous solution of ZrO(NO3)2 (8.6 mmol, 0.02 M), aque-
ous HNO solution of NH VO (17.1 mmol, 0.02 M, pH 3) was added
3
4
3
◦
under stirring at 70 C. After adding the corresponding amount
of phosphoric acid (7.7 mmol, 3 M), a gel was formed, which was
Fig. 3. STEM image of W–V–O.

1
20
Y. Goto et al. / Applied Catalysis A: General 509 (2016) 118–122
Table 2
Ammoxidation of 3-picoline.a
◦
Catalyst
Cat. wt. (g)
T ( C)
Conversion (%)
PIC
Selectivity (%)
CP
O2
NAc
NA
Pyr
CO
CO2
WO3
1.00
0.38
0.75
0.85
383
389
386
381
0.0
100
100
11.5
47.3
51.7
59.8
0.0
98.0
99.5
91.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.7
0.0
0.7
0.2
3.8
0.0
0.1
0.0
0.2
0.0
1.2
0.3
4.3
VOx/WO3
W–V–O
V2O5
100
a
Conditions: gas composition, PIC/H2O/NH3/O2/He = 1/8/6/4.4/19.6.
1
5
0
5
0
The rod-shaped crystal is due to stacking of the layers along the
c-axis by sharing the apex oxygen. The microporosity is suggested
to be due to the heptagonal channel structure of the a–b plane.
The following results of XRD, STEM, N adsorption suggest that the
2
1
present W–V–O catalyst has the same structural characteristics as
the porous and layered structure illustrated in Fig. 1. The XRD pat-
◦
tern of W–V–O (Fig. 2) showed two sharp diffraction lines at 22.7
◦
and 46.5 . The XRD pattern of VOx/WO3 showed diffraction lines
attributed to VO , V O5 and WO .
2
2
3
The STEM image of W–V–O (Fig. 3) shows rod shaped crystals.
The N -adsorption isotherm of W–V–O (Fig. 4) shows N adsorption
2
2
−
6
feature at low relative pressure (P/P < 10 ) which is characteristic
0
1
0-8
10-6
10-4
P / P0
10-2
100
to microporos materials. The micropore volume estimated by the
−3
−1
.
t-plot method is 7.7 × 10 mL g
Fig. 4. N2-adsorption isotherm of W–V–O.
3.2. Catalytic performance
2
.3. Catalytic testing
First, four catalysts (WO3, V2O5, VOx/WO3, W–V–O) were tested
◦
for the ammoxidation of PIC at 383–389 C. Table 2 lists the con-
versions of PIC and O2 and selectivities to cyanopyridine (CP),
nicotinamide (NA), nicotinic acid (NAc), pyridine (Pyr), CO, and CO2.
As previously reported [4], V2O5 showed good selectivity of CP at
high conversion level (99.2%), while WO3 showed no conversion
of CP. This indicates that vanadium is an indispensable element for
this catalytic system. The W-added vanadium oxides, VOx/WO3 and
W–V–O, were tested for the reaction under the conditions of full CP
conversion. VOx/WO3 and W–V–O show higher CP selectivities than
V2O5, which indicates that tungsten oxides as co-catalysts increase
the CP selectivity of V-based ammoxidation catalysts. Especially,
the W–V–O catalyst showed the highest CP selectivity of 99.5%.
The catalytic performances of the V-based catalysts, including
a well established VOx/TiO2 catalyst for this reaction [8], were
Ammoxidation of 3-picoline was carried out at atmospheric
pressure using a fixed-bed flow reactor (Pyrex glass tube) with an
inner diameter of 9 mm. Catalyst powders were pressed to pellets,
crushed, and sieved. Catalyst pellets (0.25–0.50 mm size), diluted
with quartz (0.2–0.4 mm) in a volumetric ratio of 1:6, were set in the
reactor. The reaction temperature was measured inside the catalyst
bed by a thermocouple. The gas stream (NH /O /He) was fed to the
reactor with mass flow controller. The aqueous solution of 11 mol%
3
from a syringe pump with a micro-feeder. The volumetric com-
position of reaction gas was PIC:H O:NH :O :He = 1:8:4:4.4:19.6
3
2
◦
-picoline (PIC) was fed continuously into the gas stream at 150 C
2
3
2
(
PIC/H O/NH /O /He = 2.7%/21.6%/10.8%/11.9%/53.0%). Total flow
2 3 2
−
1
rate was 37 mL min . CH4 gas was fed into outlet gas as exter-
nal standard. The gas phase products (CO and CO ) in the outlet gas
◦
further compared under different contact time at 380 C. From
2
were collected in a gas bag and analyzed by TCD-GC (GL science
GC-3200, 6 m SHINCARBON-ST packed column). Organic products,
trapped in ethanol at 0 C, followed by adding n-octane as exter-
the slope of the curve in the plot of CP conversion versus con-
tact time (Fig. 5), the order of the catalytic activity is as follows:
VOx/WO3 > VOx/TiO2 > W–V–O ≈ V2O5. The selectivities of the main
product (CP) and byproducts (Pyr and CO2) are plotted as a function
◦
nal standard, were analyzed with FID-GC (Shimadzu GC-14A, 30 m
0.32 mm TC-5 capillary column). Note that carbon balance and
oxygen balance for the catalytic results were 100.1 ± 0.6% and
100
9
7.5 ± 2.6%, respectively.
80
60
40
3
. Result and discussion
3.1. Catalyst characterization
Previously, we have reported a series of studies on the
hydrothermal synthesis of metal oxides consisted of group 5 and 6
elements. A group of the synthesized metal oxides have micropore
due to heptagonal channel and layered structure as illustrated in
Fig. 1, which is characterized by the common structural results as
20
◦
◦
0
0.5
1
1.5
follows: (i) two sharp diffractions around 23 and 46 along with
-
1
◦
◦
Contact time (g s mL )
broad diffraction peaks around 8 and 27 observed by XRD, (ii)
long rod-shaped crystal morphology, (iii) the presence of microp-
Fig. 5. Effects of contact time on PIC conversion for ammoxidation of PIC over
◦
◦
ore. The diffractions around 23 and 46 have been attributed to the
0 0 1) and (0 0 2) planes of the layered structure in c-axis direction.
(
ꢀ)W–V–O, (ꢁ) VOx/WO3, (᭹) V2O5, and (ꢁ) VOx/TiO2. Conditions: catalyst
◦
(
amount = 0.5 g, T = 380 C, gas composition, PIC/H2O/NH3/O2/He = 1/8/6/4.4/19.6.

Y. Goto et al. / Applied Catalysis A: General 509 (2016) 118–122
121
Fig. 6. Selectivity versus PIC conversion for ammoxidation of PIC over (ꢀ) W–V–O, (ꢁ) VOx/WO3, (ꢁ) VOx/TiO2 and (᭹) V2O5. Conditions are the same as those in Fig. 5.
of the CP conversion in Fig. 6. A possible pathway of the formation
of CP, NA, NAc, Pyr and CO2 is also included in Fig. 6. Generally, Pyr
100
9
9
9
8
and CO were the main byproducts. The selectivities to NA, NAc, and
2
CO were quite low (<0.2%) for the W–V–O and VOx/WO3 catalysts,
while NA was also produced in 0.6–1.4% selectivity for VOx/TiO2
and V O5 at high conversion levels. For all the catalysts tested, the
CP selectivity decreased with the increase of the conversion, while
2
97
96
the selectivities of the byproducts (Pyr and CO ) increased. This
2
indicates that CP is the product of the ammoxidation of PIC and Pyr
and CO2 are produced from CP probably via consecutive reactions
9
5
0
100
200
of CP → NA → NAc → Pyr + CO or via direct oxidation of CP to Pyr
Time-on-stream (min)
2
and CO . In the whole range of the conversion level, the W-added
2
Fig. 8. (᭹) PIC conversion and (ꢀ) CP selectivity as a function of reaction time
vanadium oxides (VOx/WO3 and W–V–O) showed higher CP selec-
for ammoxidation of 3-picoline over W–V–O. Conditions: catalyst amount = 0.5 g,
tivities than V O5 and VOx/TiO . Especially, the W–V–O catalyst
◦
2
2
T = 380 C, gas composition, PIC/H2O/NH3/O2/He = 1/8/6/4.4/19.6.
showed the highest CP selectivity as well as the lowest selectivities
of Pyr and CO2.
To investigate the formation pathway of the byproduct in Fig. 6,
the amide (NA), which undergoes further hydration to give the car-
we carried out hydration of CP (CP + H O reaction in the absence of
2
boxylic acid (NAc) and NH . Pyr and CO2 can be produced by the
3
O ) by the W–V–O catalyst under the conditions shown Fig. 7. As
shown in Fig. 7A, the conversion of CP increased with the reaction
temperature. With increase in the temperature, the selectivity of
2
decomposition of NAc.
Next, we tested the ammoxidation of PIC with some represen-
tative catalysts (VCrO [10] and VZrPO [11]) which were reported to
be efficient for this reaction in the literature (Table 3). The reactions
were carried out under the same conditions (contact time, gas com-
NA decreased and the selectivities of Pyr and CO the increased. The
2
result indicates that NA, NAc, Pyr and CO2 are produced by hydra-
tion of the nitrile (CP) in the absence of O . The result in Fig. 7A is
◦
2
position) except for the temperatures (365–410 C). The reaction
re-plotted in Fig. 7B where the selectivities are plotted as a function
of the CP conversion. With increase in the conversion, the selectivity
of NA decreased and the selectivities of Pyr and CO2 the increased.
The selectivity of NAc increased up to 14% conversion and then
decreased with the conversion. The result suggests that NA, NAc,
Pyr and CO2 are produced from CP via consecutive reactions of
temperature for each experiment was adopted to achieve nearly
full conversion of CP (98.9–100%). The result shows that VOx/WO3
and W–V–O exhibit higher CP selectivities than the conventional V-
based catalysts, and W–V–O showed the highest CP selectivity and
the lowest selectivities of Pyr and CO2 among the catalysts tested.
The above results demonstrate excellent catalytic performances of
the W–V–O catalyst for the ammoxidation of PIC to CP. It should be
noted that the XRD pattern of the W–V–O did not essentially change
after the reaction, suggesting no change in the catalyst structure
during the reaction.
CP → NA → NAc →nPyr + CO . The hydration of the nitrile (CP) gives
2
From a viewpoint of industrial catalysis, long time durability
and the reaction without co-feeding of water or without too much
excess of NH3 are important. The stability versus time-on-stream
of the best performing W–V–O catalyst has been investigated and
the result is shown in Fig. 8. The data show that the CP selectivity
remains essentially constant (99.4–99.6%) during 3 h of the oper-
◦
ation at 380 C. Fig. 9 shows the catalytic performance of W–V–O
under different NH3 concentration. The result shows that the NH3
partial pressure of around 12%, corresponding to 4.4 equivalent
with respect to CP, is enough to give the highest selectivity at full CP
conversion. Finally, we studied the effect of co-feeding of water on
the catalytic performance of W–V–O. The temperature dependence
Fig. 7. Hydration of CP on W–V–O (0.5 g): gas composition, CP/H2O/He = 1/10/10,
−1
flow rate = 21 mL min . (A) Temperature dependence of (+) CP conversion and selec-
tivities of (ᮀ) NA, (ꢂ) NAc, (ꢀ) Pyr, (᭹) CO2. (B) Selectivities of (ᮀ) NA, (ꢂ) NAc, (ꢀ)
Pyr, (᭹) CO2 versus CP conversion.

1
22
Y. Goto et al. / Applied Catalysis A: General 509 (2016) 118–122
Table 3
Comparison of the catalysts for the ammoxidation of 3-picoline.
a
S.A (m2
g
−1
)
T ( C)
◦
Conversion (%)
PIC
Selectivity (%)
CP
Catalyst
O2
NAc
NA
Pyr
CO
CO2
W–V–O
VOx/WO3
VCrO
16
14
23
30
407
410
365
370
99.6
100
98.9
99.0
49.2
50.0
54.3
53.7
99.4
95.8
92.0
83.4
0.0
1.6
1.0
2.7
0.0
0.6
1.1
0.8
0.2
1.0
1.6
0.7
0.0
0.0
0.9
0.0
0.4
1.0
3.3
VZrPO
12.3
a
Conditions: catalyst amount = 0.5 g; gas composition, PIC/H2O/NH3/O2/He = 1/8/6/4.4/19.6.
1
00
idation of 3-picoline, the W–V–O catalyst gave an exceptionally
high 3-cyanopyridine selectivity of 99.5% under full conversion
conditions. The selectivity of W–V–O was higher than those of
x
9
9
9
9
9
8
7
6
VO /WO3 and other catalysts reported to be efficient for this reac-
tion such as VCrO, VZrPO, and VOx/TiO . The W–V–O catalyst gave
2
high catalytic performance even in the absence of co-feeding of
water, demonstrating that the present system can be of importance
from a viewpoint of industrial production of 3-cyanopyridine from
3
-picoline. Silent finding of this study was that the VOx/WO3 cat-
alyst showed higher activity and selectivity for this reaction than
previous V-based catalysts.
5
10
15
20
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1
[
4
[
1
340
360
380
T ( C)
400
420
2
o
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Fig. 10. (᭹,ꢂ) PIC conversion and (ꢀ,ꢁ) CP selectivity as a function of temper-
ature with water-dosing (ꢂ,ꢁ) in the feed or without the water-dosing (᭹,ꢀ)
over W–V–O catalyst. Gas composition, PIC/H2O/NH3/O2/He = 1/8/6/4.4/19.6 or
PIC/NH3/O2/He = 1/6/4.4/19.6.
3
[
8
[
[
[
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this reaction have been carried out under water-dosing conditions,
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[
[
[
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4
. Conclusion
The microporous and layered W–V metal oxide, W–V–O, was
synthesized by hydrothermal method. For the vapor phase ammox-