High dimensionally structured W-V oxides as highly effective catalysts for selective oxidation of toluene

Article abstract of DOI:10.1016/j.cattod.2019.08.023

High dimensionally structured W-V-O catalysts (HDS-WVO) were synthesized by hydrothermal method and catalyst structures were investigated by HAADF-STEM analysis. HDS-WVO were rod-shaped crystals and the cross-sections were constituted by W₆O₂₁ pentagonal units and MO₆ octahedra (M = V, W), forming heptagonal and hexagonal channels. HDS-WVO catalysts showed excellent catalytic performance for selective oxidation of toluene to benzoic acid, and the activity and the selectivity to benzoic acid were superior to those of state-of-the-art catalysts. After the ion exchange using Cs⁺, the catalytic activity over HDS-WVO was significantly decreased. Since HAADF-STEM analysis and N₂ adsorption revealed that Cs⁺ was located mainly at the heptagonal channel of HDS-WVO, it can be concluded that toluene oxidation takes place at the heptagonal channel site of HDS-WVO.

Full text of DOI:10.1016/j.cattod.2019.08.023

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Catalysis Today
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High dimensionally structured W-V oxides as highly effective catalysts for
selective oxidation of toluene
Toru Murayamaa,1, Satoshi Ishikawab,1, Norihito Hiyoshic, Yoshinori Gotod, Zhenxin Zhangb,
Takashi Toyaod, Ken-ichi Shimizud, Shutoku Leeb, Wataru Uedab,⁎
a Research Center for Gold Chemistry, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1-F203 Minami-Osawa, Hachioji, Tokyo,
Japan
b Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University, 3-27, Rokkakubashi, Kanagawa-ku, Yokohama, Japan
c Research Institute for Chemical Process Technology, National Institute of Advanced Industrial Science and Technology (AIST), 4-2-1 Nigatake, Miyagino, Sendai, Japan
d Institute of catalysis, Hokkaido University, N-21, W-10, Sapporo, Hokkaido, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords:
High dimensionally structured W-V-O catalysts (HDS-WVO) were synthesized by hydrothermal method and
catalyst structures were investigated by HAADF-STEM analysis. HDS-WVO were rod-shaped crystals and the
cross-sections were constituted by W6O21 pentagonal units and MO6 octahedra (M = V, W), forming heptagonal
and hexagonal channels. HDS-WVO catalysts showed excellent catalytic performance for selective oxidation of
toluene to benzoic acid, and the activity and the selectivity to benzoic acid were superior to those of state-of-the-
art catalysts. After the ion exchange using Cs+, the catalytic activity over HDS-WVO was significantly decreased.
Since HAADF-STEM analysis and N2 adsorption revealed that Cs+ was located mainly at the heptagonal channel
of HDS-WVO, it can be concluded that toluene oxidation takes place at the heptagonal channel site of HDS-WVO.
Complex metal oxide
Selective oxidation of toluene
Site isolation
1. Introduction
pentagonal units and MO6 (M = Mo, V) octahedra to form the hex-
agonal and heptagonal channel in the a–b plane which is stacked to
Investigation of active sites in heterogeneous catalysts has been of
scientific and industrial importance because it offers an idea for the
rational design of new catalysts. Particularly, active sites of V-based
complex metal oxides for selective oxidations have long been discussed.
However, due to the complexity of their structure, identification of
catalytically active site can be partially achieved only for a few mate-
rials such as Mo-V based mixed metal oxides [1–16]. Historically,
highly effective Mo-V based mixed metal oxide catalysts for selective
oxidation of ethane were firstly revealed to have a X-ray diffraction
peak (2θ = 22°; Cu-Kα) due to the stacking of MO6 (M = Mo, V, and
third metal) octahedra along with c-direction [2]. In 90′s, Ushikubo
et al. [1] developed Mo-V-Te-Nb oxide catalysts active for selective
oxidation of C3 hydrocarbons, and the active phase, so-called “M1
phase” was then assigned to the orthorhombic phase (space group=
Pba2). Later, a group of Ueda reported the first example of crystalline
orthorhombic Mo3VOx having identical crystal structure with M1 phase
[17]. The atomic-level structure of orthorhombic Mo3VOx was clarified
by single crystalline X-ray diffraction analysis and HAADF-STEM
technique [7,9,11]. The orthorhombic Mo3VOx is composed by Mo6O21
each other along with c-direction. It is proposed that the local catalyst
structure around the heptagonal channel of the orthorhombic Mo3VOx
is responsible for the catalysis for selective oxidation of lower hydro-
carbons [8,9,12–14].
Selective catalytic oxidation of toluene to benzoic acid by molecular
oxygen is of great economical and industrial importance. Currently, the
commercial production of benzoic acid is achieved by the liquid-phase
oxidation of toluene in a solution of toluene, cobalt acetate and bromide
promoter in acetic acid at 250 °C under pressured O2 [18]. Although
complete conversion is achieved, the use of acidic solvents and bromide
promoter results in serious problems such as difficulties in the pur-
ification of the products, co-production of toxic wastes, and equipment
corrosion. From economic and environmental points of view, the pro-
cess should be replaced by the gas-phase oxidation of toluene. Various
catalysts, mostly V-based oxides, were reported for the gas-phase se-
lective oxidation of toluene, but the yields of benzoic acid reported so
far (30–72%) are lower than the commercially acceptable level
[19–24].
Herein, we report the synthesis and characterizations of high
⁎ Corresponding Author.
E-mail address: uedaw@kanagawa-u.ac.jp (W. Ueda).
1 These authors contributed equally.
https://doi.org/10.1016/j.cattod.2019.08.023
Received 21 February 2019; Received in revised form 26 July 2019; Accepted 15 August 2019
0920-5861/©2019ElsevierB.V.Allrightsreserved.
Pleasecitethisarticleas:ToruMurayama,etal.,CatalysisToday,https://doi.org/10.1016/j.cattod.2019.08.023

T. Murayama, et al.
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dimensionally structured W-V oxide (HDS-WVO) catalysts with the
same structural motif as orthorhombic Mo3VOx. HAADF-STEM analysis
revealed that HDS-WVO are rod shaped crystals constituted by W6O21
pentagonal units and MO6 (M = V or W) octahedra and form hexagonal
and heptagonal channels in the crystal structure. HDS-WVO catalysts
showed higher yields of benzoic acid than the catalyst in the literature
for the selective oxidation of toluene. Role of catalyst structure of HDS-
WVO for selective oxidation of toluene will be discussed.
Table 1
Catalytic results for selective oxidation of toluenea.
Catalyst
Conv. of toluene [%]
Selectivity [%]
PhCOOH
PhCHO
benzene
COx
W83V17OX
W64V36OXb
Cs-W83V17OX
VOx/WO3
V2O5
91
92
9
93
92
6
82
80
84
58
33
83
0
0
14
4
0
11
8
1
16
25
8
7
12
1
22
42
9
2. Experimental
WO3
0
a
Reaction conditions: toluene/O2/He = 1/5/34, flow rate =39 mL min−1
;
2.1. Catalyst preparation
catalyst weight =1.5 g; T =400 °C.
b
Inorganic precursors were purchased from Wako Pure Chemical
Industries. According to our previous reports [25,26], the complex
metal oxide of W and V with W/V molar ratio of 83/17, named
catalyst weight =1.25 g.
W
83V17Ox, was prepared by hydrothermal synthesis method as follows.
An aqueous solution (40 mL) of (NH4)6[H2W12O40]·nH2O (W:
10.4 mmol), VOSO4·nH2O (V: 4.16 mmol) and oxalic acid (0.10 mmol)
was introduced into a stainless steel autoclave with a Teflon inner tube
(50 mL), followed by filling the inner space of the tube by Teflon thin
sheet (50 mm × 1000 mm). Then, N2 was fed into the solution for
10 min to remove residual oxygen. The autoclave attached to a rotating
machine was installed in an oven, and the mixture underwent hydro-
thermal reaction at 175 °C for 24 h under mechanical rotation (1 rpm).
The solid formed was filtered, washed with ion-exchanged water, dried
at 80 °C overnight and then heated at 400 °C for 2 h under N2 flow.
W
64V36Ox with W/V molar ratio of 64/36 was prepared according to
the method in the same manner. Bulk composition of the catalysts was
determined by an inductively coupled plasma (ICP-AES) method (ICPE-
9000, Shimadzu). Cs+-exchanged W83V17Ox (designated as Cs-
W
83V17Ox) was prepared by mixing W83V17Ox (2.0 g) with 40 mL of
aqueous solution of Cs2CO3 (8.2 mmol) for 0.5 h at room temperature,
followed by centrifuging and washing with ion-exchanged water four
times, drying at 80 °C overnight and by heating at 400 °C for 2 h under
N2 flow. The Cs content in Cs-W83V17Ox (0.24 mmol g−1) was de-
termined by ICP-AES analysis. WO3-supported vanadia (VOx/WO3)
with W/V molar ratio of 85/15 was prepared by impregnation method;
a suspension of WO3 (20.0 mmol) in an aqueous solution (50 mL) of
NH4VO3 (3.5 mmol) was heated to 90 °C for 30 min to evaporate water,
followed by drying at 80 °C overnight, and by heating at 400 °C for 2 h
under N2 flow. V2O5 and WO3 were supplied from Wako Pure Chemical
Industries.
Fig. 1. XRD patterns of W83V17Ox, W64V36Ox and Cs-W83V17Ox.
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 ther-
mocouple. The gas stream (O2/He) was fed to the reactor with mass
flow controllers. Toluene was fed continuously into the gas stream at
150 °C from a syringe pump with a micro-feeder. The reactor was fed
with toluene/O2/He mixture in the molar ratio of 1/4/34 with total
flow rate (F) of 49 mL min−1. The gas phase products (CO, CO2) in the
outlet gas were analyzed by GC-TCD (GL Sciences GC-3200, 6 m SHI-
NCARBON-ST packed column). Organic products, trapped in ethanol at
0 °C, followed by adding n-octane as an external standard, were ana-
lyzed with GC-FID (Shimadzu GC-14B with TC-5 capillary column). The
carbon balance values for all the catalytic results were in a range of
95.9–99.9%, so that the selectivity listed in Table 1 was calculated on
the basis of the product.
2.2. Catalyst characterization
Powder X-ray diffraction (XRD) pattern of the catalysts was re-
corded on a Rigaku MiniFlex II/AP diffractometer with Cu-Kα radia-
tion. FT-IR analysis was carried out using a spectrometer (FT/IR-4700,
JASCO). IR spectra were obtained by integration of 64 scans with a
resolution of 4 cm−1. N2 adsorption isotherms at liq. N2 temperature
were obtained using an auto-adsorption system (BELSORP MAX,
Nippon BELL). Prior to the N2 adsorption, a catalyst was pre-treated
under a vacuumed condition at 200 °C for 2 h. Aberration-corrected
STEM images were obtained using ARM-200 F (JEOL Ltd, Japan)
equipped with a cold field emission gun at an acceleration voltage of
200 kV. The convergence semi-angle of the probe was 24 mrad. The
collection semi-angle for the high angle annular dark field (HAADF)
imaging was adjusted in the range of 68–175 mrad. Images were treated
with a light low-pass filter using 3 × 3 kernel (Digital Micrograph,
Gatan Inc., USA) to remove high-frequency noise.
3. Results and discussion
3.1. Characterization of high dimensionally structured WVO
High dimensionally structured WeVOe catalysts (HDS-WVO) were
prepared by hydrothermal method and were abbreviated as W83V17Ox
and W64V36Ox [25,26]. Ion exchange with Cs+ was conducted on
2.3. Catalytic reactions
Vapor phase oxidation of toluene was carried out at atmospheric
W
83V17Ox and the obtained material is abbreviated as Cs-W83V17Ox.
pressure using a fixed-bed flow reactor (Pyrex glass tube) with an inner
Fig. S1 shows IR spectra of W83V17Ox and Cs-W83V17Ox. Almost no
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Fig. 2. HAADF-STEM images of W83V17Ox. (a) Side surface of the rod-type particle. (b), (c) Basal plane of the rod-type particle. The image of (c) is magnified from the
yellow region of (b). Yellow region in (c) represents the orthorhombic Mo3VOx like structure. Structural model of the orthorhombic Mo3VOx like structure is shown in
(d). Structural model in top plane is shown by pink and pentagonal M6O21 unit is highlighted by light green circle. (For interpretation of the references to colour in
this figure legend, the reader is referred to the web version of this article).
Fig. 3. HAADF intensities of the W83V17Ox and W64V36Ox in the orthorhombic Mo3VOx like structure observed in HAADF-STEM images (W83V17Ox, Fig. 2; W64V36Ox,
Fig. S1).
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Fig. 4. Atomic-resolution HAADF-STEM images of Cs-W83V17Ox: (a) original and (b) 6- and 7-membered rings are highlighted. Insert in (a) is expanded image and
red allow shows Cs+. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
Fig. 5. Nitrogen adsorption isotherms of W83V17Ox and Cs-W83V17Ox. (a) normal P/P0 range, (b) low pressure P/P0 range.
changes were observed under 1000 cm−1, indicating that structural
framework of W83V17Ox is unchanged by the ion exchange. However,
the IR band intensity at 1401 cm−1 attributable to the deformation
the crystal structure (dark spots). This situation is very similar with that
of the crystalline Mo3VOx materials as reported previously [30,31].
Interestingly, an expanded image (Fig. 2 (c)) shows that orthorhombic
Mo3VOx like crystal structure (Fig. 2 (d)) was partially formed in
+
vibration of NH4 was significantly decreased after the ion exchange,
indicating that NH4+, counter cation of W83V17Ox, was replaced with
Cs+ by the ion exchange. XRD patterns of the obtained catalysts (Fig. 1)
shows intense and sharp peaks at 22.8° and 46.6° due to (001) and
(002) planes deriving from the stacking of octahedral to form rod
shaped material [27–29]. Almost no changes in the XRD patterns were
observed by the ion exchange with Cs+. HAADF-STEM images of
W83V17Ox. HAADF-STEM image of W64V36Ox shown in Fig. S2 was si-
milar to that of W83W17Ox and was constituted by the arrangement of
the M6O21 pentagonal units and MO6 octahedra. For the orthorhombic
Mo3VOx like crystal structure, HAADF intensity analysis was carried out
to distinguish the position of W and V, since it is well known that the
HAADF intensity of the white spot is roughly proportional to the square
of the atomic number (Z) and provides an enhanced Z-constant image.
The position of the elements and its HAADF intensity are shown in
Fig. 3. For both W83V17Ox and W64V36Ox samples, the averaged HAADF
intensity of the M6O21 pentagonal unit (S5-6, S8-11 sites) and the
central MO6 of pentamer unit (S2 site) were higher than those of the
MO6 units (S1, S3, S4 and S7 sites) linked to the pentagonal units. The
observed difference in the HAADF intensity suggests that W is pre-
ferentially located at the M6O21 pentagonal unit and the S2 site, while V
is preferentially located at the MO6 linker units.
W
83V17Ox are shown in Fig. 2. The HAADF-STEM image showed that
W
83V17Ox is a rod-like crystallite showing the lattice fringe along with
rod direction with an interlayer distance of 3.90 Å (Fig. 2 (a)), which is
consistent with the interlayer distance of (001) planes in the XRD
pattern (3.90 Å).
HAADF-STEM images of the cross-section of the W83V17Ox rod–type
particles are shown in Fig. 2 (b,c). The white spots correspond to the
MO6 octahedra stacked vertically to the image, and the dark spots are
empty channels. In the images, M6O21 pentagonal units (highlighted by
light green) and the MO6 octahedra were observed and the arrange-
ment of these units forms empty hexagonal and heptagonal channels in
HAADF-STEM measurement was also conducted on Cs-W83V17Ox for
observing the location site of Cs+ in W83V17Ox (Fig. 4). Unit
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Fig. 6. Conversion of toluene (+), selectivities of benzoic acid (○), benzaldehyde (△), benzene (▼), and COx (⬤) versus temperature for selective oxidation of
toluene by W83V17Ox (a), VOx/WO3 (b), Cs-W83V17Ox (c), and V2O5 (d) under the conditions shown in Table 1.
arrangement of Cs-W83V17Ox was similar to that containing no Cs+, and
the M6O21 pentagonal units and the MO6 octahedra were observed in
the image. Different from W83V17Ox, white spots were observed in the
micropore channels of Cs-W83V17Ox possibly due to the introduction of
Cs+. For 7- and 6-membered rings in the crystal, white spots are ob-
served in almost all of the 7-membered rings, suggesting that almost all
of the 7-membered rings were occupied by Cs+ after the ion exchange
(Fig. 4 (b), closed yellow circles). In contrast, while white spots were
observed in 18% of the 6-membered rings (Fig. 4 (b), closed red circles),
82% of the 6-membered rings were empty (Fig. 4 (b), open red circle).
This fact suggests that Cs+ is hardly introduced into the hexagonal
channel. It has been reported that counter cations are occluded into the
heptagonal channel of the orthorhombic Mo3VOx during the crystal
formation process and almost no counter cations are located at the
hexagonal channel [31]. In consideration of the structural similarity
between the orthorhombic Mo3VOx and W83V17Ox, it can be speculated
that NH4+, counter cation of W83V17Ox (Fig. S1), is mainly located at
relative pressure (P/P0 < 10−6), which is characteristic to microporous
materials. On the other hand, no such the micropore adsorption was
observed in Cs-W83V17Ox. This fact suggested that Cs+ is located at the
micropore channel and prevent N2 from entering micropore. In the case
of the orthorhombic Mo3VOx, it was reported that the empty hepta-
gonal channel works as a micropore to adsorb small molecules [30,31].
Taking into account the similarity in the crystal structure between the
orthorhombic Mo3VOx and W83V17Ox, the heptagonal channel of
W
83V17Ox is considered to work as a micropore to adsorb N2. Based on
the above results, we concluded that Cs+ is mainly located at the
heptagonal channel and blocks the access of N2 into the heptagonal
channel micropore. However, Cs+ was located at the 18% of the hex-
agonal channel. It has been reported that the hexagonal channel in the
hexagonal WO3 structure (Hex-WO3) can accommodate H+ and the H+
is replaceable with other alkali cation like as K+ [32]. Therefore, we
considered that W83V17Ox contains the Hex-WO3 moiety in its crystal
structure and the H+ in the hexagonal channel of the Hex-WO3 moiety
was replaced by Cs+ after the ion exchange.
the heptagonal channel and the NH4 is exchanged with Cs+ during
+
the cation exchange process. N2 adsorption experiment supported this
observation fact. The N2 adsorption isotherms of W83V17Ox and Cs-
The amount of Cs+ measured by ICP was 0.24 mmol g−1. If we
considered that W83V17Ox has the similar crystal structure with the
+
W
83V17Ox are shown in Fig. 5. W83V17Ox showed N2 adsorption at low
orthorhombic Mo3VOx, the amount of NH4 locating at the micropore
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for designing the catalyst, that is, site isolation concept. He pointed out
that over-oxidation of desired products can be suppressed if catalyti-
cally active site is spatially isolated from each other in crystal structure
level [8,33–37,]. Taking into account that V site is mainly responsible
for the toluene oxidation, site isolation of VO6 site by W6O21 pentagonal
unit in HDS-WVO catalysts is considered to suppress the over-oxidation
of PhCOOH. Nano scale catalyst structure is considered to be crucial for
the selective oxidation of toluene for the PhCOOH selectivity and its
sequential oxidation.
Interestingly, catalytic activity over Cs-W83V17Ox (SBET = 12.0
m2 g−1) was an order of magnitude lower than that of W83V17Ox and
the toluene conversion at 400 °C was 9%. As discussed above, Cs+ is
considered to be located mainly at the heptagonal channel site near the
catalyst surface. Taking into account this fact, we speculated that to-
luene oxidation preferentially occurred over the heptagonal channel
site, including the side- and the cross-section of the rod-shaped crystal
of HDS-WVO catalysts. It is interesting to note that the reason of the
catalytic activity loss could be evaluated based on the nano-scale cat-
alyst structure by using HAADF-STEM analysis.
Finally, catalyst durability was evaluated over W83V17Ox. Fig. 7
shows the toluene conversion and product selectivity as a function of
reaction time over W83V17Ox at 450 °C in the presence of steam. The
toluene conversion slightly decreased from 99% to 95% during the 90 h
of the continuous reaction. However, the catalytic activity was re-
covered by the calcination under O2/H2O/He at 500 °C for 1 h and the
conversion recovered to 98%. The same treatment at 180 h made the
conversion recovered again to 98%. On the other hand, the selectivity
to benzoic acid was nearly constant (80–81%) for entire reaction time
of 190 h. It is notable that the yield of benzoic acid in a range 75–79% is
higher than those of previously reported catalytic systems for the gas-
phase oxidation of toluene.
Fig. 7. Time course of toluene oxidation on W83V17Ox at 450 °C: conversion of
toluene (+), selectivities to benzoic acid (○), benzene (▼), and COx (●), to-
luene/O2/H2O/He = 1/4.5/26/8. After 90 h and 180 h, the catalyst was heated
at 500 °C for 1 h under flowing O2/H2O/He ( = 4.5/26/8) followed by re-
starting the catalytic reaction. Selectivity to benzaldehyde was lower than
0.1%.
channel can be assumed to be 0.77 mmol g-1 [31]. Therefore, ca. 1/3 of
the amount of NH4+ in W83V17Ox is considered to be replaced with Cs+
by the ion exchange. Since the amount of the Cs+ introduced by the ion
exchange was enough lower than that of the theoretical value, Cs+ is
considered to be not deeply introduced into the bulk of the channel and
Cs+ might be located near the catalyst surface.
4. Conclusion
3.2. Selective oxidation of toluene over high dimensionally structured WVO
High dimensionally structured W-V-O catalysts (HDS-WVO) were
synthesized by the hydrothermal method and the catalyst structure was
investigated by HAADF-STEM analysis. HDS-WVO catalysts are com-
prised of W6O21 pentagonal units and MO6 octahedra (M = W, V),
forming heptagonal and hexagonal channels in the catalyst structure.
HDS-WVO showed excellent catalytic performance for selective oxida-
tion of toluene and the selectivity to benzoic acid was considerably
higher than those of other W-V based catalysts. The high selectivity to
PhCOOH over HDS-WVO is considered to be the result of the nano-level
structural vicinity of W and V site in the crystal structure. Interestingly,
almost no decrease in benzoic acid selectivity was observed over HDS-
WVO catalysts by the increase of reaction temperature different from
other W-V based catalysts. Since VO6 site over HDS-WVO catalysts was
well isolated for each other by the W6O21 pentagonal units as observed
by HAADF-STEM images, sequential oxidation of benzoic acid would be
suppressed even at high reaction temperature range. After the ion ex-
change with Cs+, Cs+ was introduced mainly at the heptagonal channel
of HDS-WVO. Based on the fact that the catalytic activity over HDS-
WVO was significantly decreased after the ion exchange with Cs+, we
concluded that the local catalyst structure around the heptagonal
channel site in HDS-WVO is strongly related to the catalytic activity for
toluene oxidation.
In our previous studies [30,31], it has been concluded that the
heptagonal channels and/or their entrance (the surface 7-membered
ring) play an essential role in the selective oxidation of light alkanes
over Mo3VOx catalysts. Here, we carried out the selective oxidation of
toluene at 400 °C using various W- and/or V-containing oxides in-
cluding HDS-WVO catalysts. Results are shown in Fig. 6 and the com-
parisons of the catalytic activity over various catalysts at 400 °C are
summarized in Table 1. Under the same reaction conditions, WO3
(SBET = 16.8 m2 g−1) shows an order of magnitude lower conversion of
toluene than V2O5 (SBET = 4.8 m2 g−1) and WO3-supported VOx, VOx/
WO3 (V/W = 15/85, SBET = 14.2 m2 g−1). This indicates that V is an
essential element for this reaction. The higher benzoic acid (PhCOOH)
selectivity of VOx/WO3 (58%) than that of V2O5 (33%) suggests that the
addition of W improves the selectivity to PhCOOH. Under similar to-
luene conversion levels (91–93%), W83V17Ox (SBET = 42.0 m2 g−1
)
shows higher selectivity to PhCOOH (80–82%) than those of other (W)-
V-based catalysts, V2O5 (33%) and VOx/WO3 (58%). A similar activity
result with W83V17O was obtained over W64V36Ox. The high selectivity
to PhCOOH over HDS-WVO is considered to be brought in the structural
vicinity of W and V site at nano-level as were seen in HAADF-STEM
analysis. Interestingly, the selectivity to PhCOOH over W83V17O was
almost constant by the change of the reaction temperature, while the
selectivity to PhCOOH was decreased over V2O5 and VOx/WO3 with the
increase of reaction temperature. The observed fact suggests that se-
quential oxidation of PhCOOH is suppressed over W83V17Ox while in-
creasing reaction temperature. As has been seen in HAADF-STEM
images, W83V17Ox is comprised of the network arrangement of W6O21
pentagonal units and MO6 (M = V, W) octahedra, and the MO6 moities
are structurally isolated by W6O21 pentagonal unit as a result of its
arrangement. Grasselli has long been proposing an important concept
Funding sources
This work was supported by JSPS KAKENHI Grant Number 2324-
6135.
Declaration of Competing Interest
The authors declare no competing financial interest.
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Appendix A. Supplementary data
M.G. Willinger, R. Schlögl, T. Lunkenbein, J. Phys. Chem. C 121 (2017)
24093–24103.
[17] T. Katou, D. Vitry, W. Ueda, Chem. Lett. 32 (2003) 1028–1029.
[18] T.W. Bastock, J.H. Clark, K. Martin, B.W. Trenbirth, Green Chem. 4 (2002)
615–617.
[19] J. Miki, Y. Osada, Y. Tachibana, T. Shikada, Catal. Lett. 30 (1995) 263–268.
[20] J. Miki, Y. Osada, T. Konishi, Y. Tachibana, T. Shikada, Sekiyu Gakkaishi 39 (1996)
34–40.
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.cattod.2019.08.023.
References
[21] J. Miki, Y. Osada, T. Konoshi, Y. Tachibana, T. Shikada, Appl. Catal. A Gen. 137
(1996) 93–104.
[1] T. Ushikubo, O. Kazynori, A. Kayo, T. Umezawa, K. Kiyono, I. Sawaki, United States
Patent, 1994, 5281745.
[2] W. Ueda, N.F. Chen, K. Oshihara, Chem. Commun. (Camb.) (1999) 517–518.
[3] P. Desanto, D.J. Buttrey, R.K. Grasselli, C.G. Lugmair, A.F. Volpe, B.H. Toby,
T. Vogt, Top. Catal. 23 (2003) 23–38.
[22] H. Ge, G. Chen, Q. Yuan, H. Li, Catal. Today 110 (2005) 171–178.
[23] H. Ge, G. Chen, Q. Yuan, H. Li, Chem. Eng. J. 127 (2007) 39–46.
[24] F.M. Bautista, J.M. Campelo, D. Luna, J. Luque, J.M. Marinas, Catal. Today 128
(2007) 183–190.
[25] Y. Goto, K. Shimizu, T. Murayama, W. Ueda, Appl. Catal. A Gen. 509 (2016)
118–122.
[26] Y. Goto, K. Shimizu, K. Kon, T. Toyao, T. Murayama, W. Ueda, J. Catal. 344 (2016)
346–353.
[27] T. Murayama, N. Kuramata, S. Takatama, K. Nakatani, S. Izumi, X. Yi, W. Ueda,
Catal. Today 185 (2012) 224–229.
[4] M. Sadakane, N. Watanabe, T. Katou, Y. Nodasaka, W. Ueda, Angew. Chem. Int. Ed.
46 (2007) 1493–1496.
[5] M. Sadakane, K. Kodato, T. Kuranishi, Y. Nodasaka, K. Sugawara, N. Sakaguchi,
T. Nagai, Y. Matsui, W. Ueda, Angew. Chem. Int. Ed. 47 (2008) 2493–2496.
[6] M. Sadakane, K. Yamagata, K. Kodato, K. Endo, K. Toriumi, Y. Ozawa, T. Ozeki,
T. Nagai, Y. Matsui, N. Sakaguchi, W.D. Pryz, D.J. Buttrey, D.A. Blom, T. Vogt,
W. Ueda, Angew. Chem. Int. Ed. 48 (2009) 3782–3786.
[28] T. Murayama, N. Kuramata, W. Ueda, J. Catal. 339 (2016) 143–152.
[29] T. Murayama, J. Chen, J. Hirata, K. Matsumoto, W. Ueda, Catal. Sci. Technol. 4
(2014) 4250–4257.
[7] W.D. Pyrz, D.A. Blom, M. Sadakane, K. Kodato, W. Ueda, T. Vogt, D.J. Buttrey,
Chem. Mater. 22 (2010) 2033–2040.
[30] S. Ishikawa, X. Yi, T. Murayama, W. Ueda, Catal. Today 238 (2014) 35–40.
[31] S. Ishikawa, X. Yi, T. Murayama, W. Ueda, Appl. Catal. A Gen. 474 (2014) 10–17.
[32] Z. Huang, H. Li, J. Gao, X. Gu, L. Zheng, P. Hu, Y. Xin, J. Chen, Y. Chen, Z. Zhang,
J. Chen, X. Tang, Environ. Sci. Technol. 49 (2015) 14460–14465.
[33] R.K. Grasselli, Top. Catal. 15 (2001) 93–101.
[34] R.K. Grasselli, Catal. Today 238 (2014) 10–27.
[35] L. Whittaker, T.-L. Wu, A. Stabile, G. Sambandamurthy, S. Banerjee, ACS Nano 5
(2011) 8861–8867.
[36] A. Trunschke, J. Noack, S. Trojanov, F. Girgsdies, T. Lunkenbein, V. Pfeifer,
M. Hävecker, P. Kube, C. Sprung, F. Rosowski, R. Schlӧgl, ACS Catal. 7 (2017)
3061–3071.
[37] X. Li, T. Lunkenbein, V. Pfeifer, M. Jastak, P.K. Nielsen, F. Girgsdies, A. Knop-
Gericke, F. Rosowski, R. Schlögl, A. Trunschke, Angew. Chem. Int. Ed. 55 (2016)
4092–4096.
[8] R.K. Grasselli, J.D. Burrington, D.J. Buttrey, P. DeSanto, C.G. Lugmair, A.F. Volpe,
T. Weingand, Top. Catal. 23 (2003) 5–22.
[9] T. Konya, T. Katou, T. Murayama, S. Ishikawa, M. Sadakane, D. Buttrey, W. Ueda,
Catal. Sci. Technol. 3 (2013) 380–387.
[10] D.A. Blom, T. Vogt, L.F. Allard, D.J. Buttrey, Top. Catal. 57 (2014) 1138–1144.
[11] T. Lunkenbein, F. Girgsdies, A. Wernbacher, J. Noack, G. Auffermann, A. Yasuhara,
A. Klein-Hoffmann, W. Ueda, M. Eichelbaum, A. Trunschke, R. Schlӧgl,
M.G. Willinger, Angew. Chem. Int. Ed. 54 (2015) 6828–6831.
[12] J. Woo, A. Borisevich, C. Koch, V.V. Guliants, ChemCatChem 7 (2015) 3731–3737.
[13] M. Aouine, T. Epicier, J.M.M. Millet, ACS Catal. 6 (2016) 4775–4781.
[14] D. Melzer, P. Xu, D. Hartmann, Y. Zhu, N.D. Browning, M. Sanchez-Sanchez,
J.A. Lercher, Angew. Chem. Int. Ed. 55 (2016) 8873–8877.
[15] T. Vogt, D.A. Blom, L. Jones, D.J. Buttrey, Top. Catal. 59 (2016) 1489–1495.
[16] L. Masliuk, M. Heggen, J. Noack, F. Girgsdies, A. Trunschke, K.E. Hermann,
7