Role of Crystalline Structure in Allyl Alcohol Selective Oxidation over Mo3VOx Complex Metal Oxide Catalysts

Article abstract of DOI:10.1002/cctc.201600430

The role of the crystalline phase of Mo₃VO_x in the catalytic oxidation of allyl alcohol over four kinds of crystalline (orthorhombic, trigonal, tetragonal, amorphous) Mo₃VO_x catalysts was investigated to determine the active sites for the reactions. Tetragonal Mo₃VO_x was found less active for the formation of acrylic acid from allyl alcohol, although acrolein was obtained selectively at higher temperature. For orthorhombic and trigonal Mo₃VO_x catalyst, allyl alcohol converted to acrolein and propanal competitively at the mouth of the heptagonal channel over the a–b plane of the rod-type crystalline particles, and these aldehydes were oxidized consecutively to acrylic acid. Acrylic acid was formed effectively at increased reaction temperature over orthorhombic, trigonal and amorphous Mo₃VO_x catalysts, and the maximum yields of acrylic acid were 73 % for the orthorhombic Mo₃VO_x catalyst and 72 % for the trigonal Mo₃VO_x catalyst at 350 °C.

Full text of DOI:10.1002/cctc.201600430

DOI: 10.1002/cctc.201600430
Full Papers
Role of Crystalline Structure in Allyl Alcohol Selective
Oxidation over Mo VO Complex Metal Oxide Catalysts
3
x
[
a, b]
[c, d]
[c]
[c, d]
Toru Murayama,*[ Benjamin Katryniok,
Svetlana Heyte, Marcia Araque,
a, f]
[c, e]
[c, d]
[a, f]
Satoshi Ishikawa, Franck Dumeignil,
Sꢀbastien Paul,
and Wataru Ueda
The role of the crystalline phase of Mo VO in the catalytic oxi-
propanal competitively at the mouth of the heptagonal chan-
nel over the a–b plane of the rod-type crystalline particles, and
these aldehydes were oxidized consecutively to acrylic acid.
Acrylic acid was formed effectively at increased reaction tem-
perature over orthorhombic, trigonal and amorphous Mo VO
x
3
x
dation of allyl alcohol over four kinds of crystalline (orthorhom-
bic, trigonal, tetragonal, amorphous) Mo VO catalysts was in-
3
x
vestigated to determine the active sites for the reactions. Tet-
ragonal Mo VO was found less active for the formation of
3
x
3
acrylic acid from allyl alcohol, although acrolein was obtained
selectively at higher temperature. For orthorhombic and trigo-
nal Mo VO catalyst, allyl alcohol converted to acrolein and
catalysts, and the maximum yields of acrylic acid were 73% for
the orthorhombic Mo VO catalyst and 72% for the trigonal
3
x
Mo VO catalyst at 3508C.
3
x
3
x
Introduction
[
7–12]
The use of glycerol as a starting material for obtaining com-
hol as an intermediate product.
Nowadays, allyl alcohol is
[
1–4]
modity chemicals has gained much attention.
Especially, the
conventionally obtained from acrolein by selective hydrogena-
[13]
oxidative dehydrogenation of glycerol to acrylic acid has
become into the focus, because the latter is a widely used mo-
nomer for the synthesis of resins and superabsorbents. Howev-
er, the direct synthesis of acrylic acid from glycerol is challeng-
tion or from propylene oxide by using a lithium phosphate
[14]
catalyst. Nevertheless, it can also be obtained from renewa-
[
15–17]
[18]
ble sources such as glycerol
or propanediol. Thus, the
oxidation of allyl alcohol is a promising way for a sustainable
synthesis of acrylic acid. At the current state, there are only
a few reports on the selective oxidation of allyl alcohol to
[
5,6]
ing,
whereby improvement of the synthesis route through
two-step conversion is more favourable. The first step consists
in dehydration of glycerol to acrolein and the second step in
the oxidation of acrolein to acrylic acid. In any case, allyl inter-
mediate products are important to understand the mechanism.
According to this background, we have focused on allyl alco-
[19,20]
acrylic acid.
National Distillers and Chemical Corporation
reported in 1977 a Pd–Cu/Al O catalyst giving 80% conversion
2
3
of allyl alcohol and 23% selectivity to acrylic acid. Nippon Sho-
kubai claimed a Mo–V–W–Cu–Zr complex oxide yielding 59.5%
acrylic acid from allyl alcohol.
[a] Prof. Dr. T. Murayama, Dr. S. Ishikawa, Prof. Dr. W. Ueda
Previously, we have reported a method for the synthesis of
four kinds of crystalline (orthorhombic, trigonal, tetragonal and
Institute for Catalysis
Hokkaido University
amorphous) Mo VO and their reactivity for selective oxidation
N-21 W-10, Sapporo 001-0021 (Japan)
E-mail: murayama@tmu.ac.jp
3
21]
x
[
[22,23]
of light alkanes and acrolein.
These four kinds of Mo VO
3 x
[
b] Prof. Dr. T. Murayama
materials possess similar chemical compositions with the same
layer-type structure in the c direction and a long-rod shaped
crystal (Figure 1). The overall crystal structure is determined by
the network arrangement of pentagonal {Mo O } units in the
Research Center for Gold Chemistry
Tokyo Metropolitan University
1
-1 Minami-Osawa, Hachioji, Tokyo 192-0397 (Japan)
6
21
[
c] Dr. B. Katryniok, Dr. S. Heyte, Dr. M. Araque, Prof. Dr. F. Dumeignil,
Prof. Dr. S. Paul
a-b plane. The arrangement of the a-b plane of amorphous
Unitꢀ de Catalyse et Chimie du Solide
UCCS (UMR CNRS 8181)
Citꢀ Scientifique, Villeneuve d’Ascq (France)
[d] Dr. B. Katryniok, Dr. M. Araque, Prof. Dr. S. Paul
Ecole Centrale de Lille, ECLille,
Villeneuve d’Ascq (France)
[e] Prof. Dr. F. Dumeignil
University of Lille
Villeneuve d‘Ascq (France)
[f] Dr. S. Ishikawa, Prof. Dr. W. Ueda
Kanagawa University
Rokkakubashi, Kanagawa-ku, Yokohama (Japan)
Figure 1. Structure models of a) orthorhombic, b) trigonal, c) tetragonal and
d) amorphous Mo VO . (Yellow polyhedron: M–O octahedron (M=Mo, V) lo-
3 x
Supporting information for this article can be found under http://
dx.doi.org/10.1002/cctc.201600430.
cated on the surface, blue polyhedron: M–O octahedron (M=Mo, V) and
red dot: oxygen.)
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Mo VO (Figure 1d) is an interconnection of the crystal struc-
action because of the small amount of samples. No other dif-
fraction peaks based on impurities were observed for the used
catalyst than the diffraction peaks of SiC, which was used as
a diluent. The rod-shape morphology of crystalline Mo VO cat-
3
x
ture motifs of {Mo O } units and micropore channels but with-
6
21
out long-range order. This layer-type Mo VO is denoted as
3
x
amorphous Mo VO in this report. Orthorhombic, trigonal and
3
x
3
x
amorphous Mo VO materials are classified into similar struc-
alysts was maintained after the tests (Figure 3). Characteristic
3
x
ture-type groups, but tetragonal Mo VO is excluded because
3
x
the former materials contain empty heptagonal channels,
whereas the latter does not. Among these catalysts, Mo VO
3
x
catalysts exhibiting heptagonal channels in the structure
showed good catalytic activity in acrolein oxidation, whereas
no catalytic activity was observed for catalysts without heptag-
[
24]
onal channels in the structure, indicating that the heptago-
nal channels of Mo VO are responsible for activating acrolein.
3
x
In this study, we investigated the effect of the crystalline
structure on selective oxidation of allyl alcohol to acrylic acid.
This is the first report on allyl alcohol selective oxidation using
crystalline Mo VO complex metal oxides. Furthermore the in-
3
x
fluence of the reaction conditions was examined.
Results and Discussion
Four kinds of crystalline (orthorhombic, trigonal, amorphous,
tetragonal) Mo VO catalysts were synthesized and tested for
Figure 3. STEM images of a) orthorhombic, b) trigonal, c) amorphous and
d) tetragonal Mo VO catalysts after allyl alcohol oxidation reaction.
3 x
3
x
allyl alcohol oxidation. Table S1 in the Supporting Information
summarizes the results of characterization of crystalline
Mo VO catalysts. Chemical compositions of the catalysts were
diffraction peaks corresponding to each crystalline phase were
observed at the low-angle region of less than 2q=108. Diffrac-
tion peaks at 2q=22.28 and 45.38 were observed for all sam-
ples, indicating that the materials are all of an octahedron-
based layered-type structure with a layer lattice distance of ap-
proximately 0.4 nm (Table S1). The amorphous Mo VO catalyst
3
x
found to be almost the same and the ratios of V/Mo were in
the range of 0.32–0.37. The external surface areas calculated
by the t-plot method were in the range from 2.7 to
2
À1
1
2.4 m g .
3
x
In Figure 2 the XRD patterns of the four catalysts are shown
gave a very broad peak at the low-angle region, indicating
that the material—as expected—is not well crystallized in the
before and after the reaction at 3508C for 12 h. A silicon non-
reflective sample holder was used for the catalysts after the re-
[24]
a–b plane.
The catalytic oxidation of allyl alcohol to acrylic acid was
performed over the four different Mo VO catalysts, and their
3
x
catalytic performances as a function of the reaction tempera-
ture are shown in Figure 4. The products detected were acrylic
acid, propionic acid, acetic acid, propanal, acrolein, acetalde-
hyde, acetone, CO and CO . Among these products, the yields
2
in acetaldehyde and acetone were less than 0.5% unless other-
wise noted, whereby the results for acetaldehyde and acetone
were omitted from the figures. Surprisingly, some hydrogenat-
ed products including propanal and propionic acid were found
as by-products in the case of allyl alcohol oxidation, which is
generally not the case in acrolein oxidation (Scheme 1). From
the results one can see that—as expected—the allyl alcohol
conversion increased with the reaction temperature over all
catalysts. Orthorhombic Mo VO and trigonal Mo VO catalysts
3
x
3
x
showed almost the same behaviour, reaching full conversion at
758C. Over these two catalysts, propanal and acrolein were
2
obtained as main products at low temperature (ꢀ2008C,
Table 1). The selectivity in these two products decreased grad-
ually with increase in reaction temperature giving rise to acryl-
ic acid and propionic acid yielding 66% acrylic acid at 3508C
Figure 2. XRD patterns a) orthorhombic, b) trigonal, c) amorphous and
for the orthorhombic Mo VO catalyst and 68% at 3258C for
d) tetragonal Mo
3
VO
x
catalysts before and after allyl alcohol oxidation
3
x
(
a’,b’,c’,d’). (Diffraction peaks of SiC from catalyst dilution are shown as *.)
the trigonal Mo VO catalyst. A further increase in the reaction
3 x
&
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temperature favoured the formation of CO and acetic acid.
x
The conversion of oxygen reached 100% at 4008C. Notably,
the catalysts showed stable oxidation activity (Figure S1, Sup-
porting Information) under stream (12 h).
Compared to the orthorhombic Mo VO and trigonal Mo VO
x
3
x
3
catalysts, the conversion of allyl alcohol over the tetragonal
Mo VO catalyst was far less. Furthermore, the distribution of
3
x
obtained products was totally different, and the main product
was acrolein with a selectivity of approximately 80%. These re-
sults clearly suggest that the tetragonal Mo VO catalyst con-
3
x
tains active sites for the conversion of allyl alcohol to acrolein,
but these active sites are different from those for the oxidation
of acrolein to acrylic acid. Moreover, the active sites for the
conversion of allyl alcohol to acrolein are clearly less active be-
cause the conversion of allyl alcohol was lower than that of
the other crystalline Mo VO catalyst.
3
x
Finally, the amorphous Mo VO catalyst also showed less ac-
3
x
tivity than the orthorhombic Mo VO and trigonal Mo VO cata-
3
x
3
x
lysts. Unlike these catalysts, the selectivity to acrolein was
higher than that to propanal at a lower temperature.
These results strongly suggest that the oxidation of allyl al-
cohol to acrylic acid includes the consecutive oxidation of
acrolein. Therefore space velocity is an important factor. In Fig-
ure S2, the conversion of allyl alcohol and selectivities to acrylic
Figure 4. Conversion and selectivity changes as a function of reaction tem-
perature in selective oxidation of allyl alcohol over orthorhombic Mo VO
(^,
3
x
^
), trigonal Mo VO (~, ~), tetragonal Mo VO (
&
,
&
), and amorphous
3
x
3
x
Mo
3
VO
x
(*, *) catalysts. a) Allyl alcohol conversion and selectivities to
b) acrolein (open symbols and dashed lines) and acrylic acid (filled symbols
and solid lines), c) propanal (open symbols and dashed lines) and propionic
acid (filled symbols and solid lines), and d) acetic acid (open symbols and
acid, propionic acid, acetic acid, propanal, acrolein and CO are
x
shown under the condition of various contact times and reac-
tion temperatures over the four Mo VO catalysts. The catalyst
x
dashed line) and CO (filled symbols and solid lines). Reaction conditions:
3
x
Catalyst 50 mg, 2 bar, allyl alcohol/O
2
/H
2
O/
weight was adjusted to 0.050, 0.025 and 0.100 g and total flow
À1
(N
2
+He)=0.7:1.5:29.5:8.3 mLmin
.
rates of reactant gas were adjusted to 20, 40, 60 and
À1
8
0 mLmin with the same gas composition.
As expected, the conversion of allyl alcohol over orthorhom-
bic Mo VO catalysts at 2508C increased with increase in con-
3
x
tact time (Figure S2, I–2508C)). The selectivities to propionic
acid and acrylic acid increased at the same time detrimental to
the selectivity in propanal and acrolein, suggesting that inter-
mediately formed propanal and acrolein were consecutively
oxidized to propionic acid and acrylic acid as depicted in
Scheme 1. The yield of propionic acid was 75% for a weight–
À3
À1
flow ratio (W/F) between 3.8 and 5.0ꢂ10 gcat minmL and
that of acrylic acid was 20% in the same range. Almost the
same behaviour was observed over orthorhombic Mo VO cat-
Scheme 1. Oxidation of allyl alcohol to acrylic acid.
Table 1. Allyl alcohol oxidation over crystalline Mo
3
x
alysts at 3008C (Figure S2, I–3008C). However, the selectivity to
acrylic products (acrolein and acrylic acid) was higher than at
[a]
3
VO
x
catalysts.
2
508C. At a contact time above W/F=2.5ꢂ10 gcat minmL ,
À3
À1
the acrylic acid and propionic acid yield decreased owing to
Catalyst
Reaction Conv.
Selectivity [%]
Acrylic Acrolein Propionic Propanal CO
Temp.
8C]
[%]
x
the consecutive oxidation to CO . At 3508C, the conversion of
x
À3
À1
[
acid
Acid
allyl alcohol reached 100% at W/F=0.3ꢂ10 gcat minmL and
the yield for propionic acid was much less than that at 3008C
(Figure S2, I–3008C). The maximum yield in acrylic acid (73%)
Orthorhombic 200
Mo VO
Trigonal
Mo VO
Tetragonal
Mo VO
Amorphous
Mo VO
49
46
1.0
21.7
33.6
82.1
53.9
12.9
63.3
52.2
2.2
0.9
1.3
4.0
1.9
3
x
200
200
200
1.4
0
11.4
0
À3
À1
was obtained at 0.3ꢂ10 gcat minmL . In Figure S2 (I–4008C)
the results at 4008C are shown, indicating that the yield of
acrylic acid was still obtained but that the consecutive oxida-
3
x
4.8
7.1
3
x
0
4.2
34.6
tion to CO was promoted.
x
3
x
Over the trigonal Mo VO catalyst, the trend was the same
3
x
[
a] Reaction conditions: catalyst 50 mg, 2 bar, allyl alcohol/O
2
/H
2
O/(N
2
+
as for the orthorhombic Mo VO catalyst except for the distri-
3 x
À1
He)=1:2.2:42.1:11.8 (total flow rate of 40 mLmin ), contact time=
0
bution of products (Figure S2, II). The selectivity to hydrogenat-
ed products was suppressed at a lower reaction temperature.
À1
.00125 gcat minmL
.
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The maximum yield in acrylic acid was 72% at 3508C and W/
the a–b plane, which is highly active for the selective oxida-
tion. Thus, the latter directly convert allyl alcohol to acrylic
acid. However, since orthorhombic and trigonal Mo VO cata-
À3
À1
F=0.3ꢂ10 gcat minmL over the trigonal Mo VO catalyst.
3
x
The tetragonal Mo VO catalyst was again less active than
3
x
3
x
the orthorhombic Mo VO and trigonal Mo VO catalysts for
lysts exhibit the same c plane as the tetragonal Mo VO one
3 x
3
x
3
x
the oxidation of allyl alcohol. Over the tetragonal Mo VO cata-
would expect to observe a competition between the reactions
over the side surface and the section surface at higher reaction
temperature. In Figure 5 the ratios of acrylic products (acrylic
3
x
lysts, the conversion of allyl alcohol increased with increase in
contact time, whereas the selectivity to acrolein was un-
changed (80%) regardless of the contact time at 2508C and
3
008C (Figure S2, III–2508C, –3008C)). At 3508C, the conversion
À3
À1
of allyl alcohol reached 100% (for W/F=2.5ꢂ10 gcat minmL )
and the yield of acrolein was 60% (Figure S2, III–3508C)),
whereas the yield for acrylic acid was 17% under this condi-
tion. To consecutively oxidize acrolein to acrylic acid over the
tetragonal Mo VO catalyst, the reaction temperature and the
3
x
contact time had to be increased significantly (Figure S2, III–
4008C).
The amorphous Mo VO catalyst also showed interesting be-
3
x
haviour concerning the selectivity to acrylic and hydrogenated
products (Figure S2, IV). The conversion of allyl alcohol was
Figure 5. Effects of allyl alcohol conversion on the distribution of acrylic
products at a) 250, b) 300, c) 3508C reaction temperature over orthorhombic
lower than that of the orthorhombic Mo VOx and trigonal
3
Mo
Mo
(
3
VO
VO
x
(^
), trigonal Mo VO (~), tetragonal Mo VO (
(*). Xacrylic =[Sel. (acrylic acid)+Sel. (acrolein)]/(Sel. (acrylic acid)+Sel.
acrolein)+Sel. (propionic acid)+Sel. (propanal)]ꢂ100, reaction conditions:
3
x
3
x
&
) and amorphous
Mo VO catalysts, but the selectivity to acrylic products (nota-
3
x
3
x
bly acrolein) was higher at 2508C. The yields of acrylic acid
À3
À1
were 74% at 3508C, W/F=2.5ꢂ10 gcat minmL and 77% at
4
catalyst 25, 50, 100 mg, 2 bar, allyl alcohol/O
(total flow rate of 20, 40, 60, 80 mLmin , see also Figure S2).
2
/H
2
O/(N
2
+He)=1:2.2:42.1:11.8
À3
À1
À1
008C, W/F=0.3ꢂ10 gcat minmL
over the amorphous
Mo VO catalysts.
3
x
Furthermore, the consecutive oxidation to COx over the
amorphous Mo VOx was strongly limited compared to the
acid and acrolein) and hydrogenated products (propionic acid
and propanal) over crystalline Mo VO catalysts are shown at
3
cases over the orthorhombic Mo VO and the trigonal Mo VO
3
x
3
x
3
x
catalysts. As described above, the four kinds of Mo VO cata-
several reaction temperatures. The distribution of acrylic prod-
ucts did not change regardless of the wide range of conver-
sion, indicating that both propanal and acrolein are competi-
tively formed on the active sites of the a–b plane surface from
allyl alcohol and consecutively oxidized to propionic acid and
acrylic acid, respectively (Figure 5a,b). Furthermore one can
3
x
lysts have similar chemical compositions with the same layer-
type structure in the c direction, whereas the arrangement of
pentagonal {Mo O } units in the a–b plane is different. The or-
6
21
thorhombic, trigonal and amorphous Mo VO catalysts are clas-
3
x
sified into similar structure-type groups that have heptagonal
channels. On the other hand, the tetragonal Mo VO catalyst
see that propionic acid was more easily oxidized to CO com-
3
x
2
does not have heptagonal channels. It is known that the a–
b plane of section surface and side surface of the rod-shaped
crystals provide different active sites for oxidation reactions.
We have found in a previous study that the heptagonal chan-
nel in a–b plane exposed by grinding treatment is far more
active for selective oxidation of acrolein than is the side surface
of the rod-shaped crystals by comparison with an unground
pared to acrylic acid whereby the value of Xacrylic therefore in-
creased if conversion reached 100% (Figure 5b,c). The roles of
the heptagonal channel in the a–b plane have been discussed
[21,22,25]
in our previous report.
In the case of oxidation of small
molecules such as methane and ethane, these reactants can
adsorb inside of the heptagonal channel, which function as
active sites. In contrast, the molecules such as propane, 2-
propanol, acrolein and allyl alcohol, which cannot enter the
heptagonal channel (ꢁ0.4 nm in pore diameter), adsorb and
interact with the open mouth of heptagonal channel. The
open mouth of heptagonal would function as active sites for
the oxidation.
[
23]
catalyst. The conversion of acrolein over the unground cata-
lyst was far less than that over the ground catalyst despite the
fact that the two catalysts had almost the same external sur-
face areas.
In the current study, the tetragonal Mo VO catalyst promot-
3
x
ed the oxidation dehydrogenation of allyl alcohol to acrolein,
but it was inactive for the oxidation of acrolein to acrylic acid.
The selectivity to acrolein was 80% over the tetragonal
Mo VO catalyst, implying that the section surface and/or side
In conclusion, the active sites for the formation of acrolein
from allyl alcohol on the tetragonal Mo VO are selective but
3
x
the reactivity of these active sites is not high. Therefore, acrole-
in formation over the tetragonal Mo VO catalysts is negligible
3
x
3
x
surface of the tetragonal Mo VO catalyst are selective for the
at temperatures less than approximately 2508C. The selective
oxidation to acrylic acid is ascribed to the section surface (a–
b plane). Orthorhombic and trigonal Mo VO catalysts exhibit
3
x
oxidative dehydrogenation of allyl alcohol to acrolein. Because
the arrangement in the c direction is identical for all four cata-
lysts, one can assume that the differences in the catalytic per-
formance are caused by the a–b plane. Orthorhombic and
trigonal Mo VO catalysts exhibit heptagonal arrangement in
3
x
heptagonal channel, whereby they showed almost the same
behaviour for allyl alcohol oxidation. The open mouth of the
heptagonal channel over the a–b plane acts as an active site
3
x
&
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for the allyl alcohol oxidation and possesses high activity. Thus,
the maximum yields in acrylic acid were 73% for the ortho-
rhombic Mo VO catalyst and 72% for the trigonal Mo VO cat-
The pH value of the mixed solution was adjusted to 2.2 by adding
sulfuric acid (2 moll ). The hydrothermal synthesis time was 20 h.
À1
3
x
3
x
alyst at 3508C.
Preparation of amorphous Mo VO mixed oxide
3
x
Mo VO material well-crystallized in the c direction but disordered
3
x
in the other direction was obtained by increasing the concentra-
tion of the mixed aqueous solution, which was two-fold higher. In
this paper, this material is designated as amorphous Mo VO . Other
Conclusions
Selective oxidation of allyl alcohol was performed by using
crystalline (orthorhombic, trigonal, amorphous and tetragonal)
Mo VO catalysts. These four catalysts were rod-shape particles
3
x
preparatory conditions were the same as those for orthorhombic
Mo VO .
3
x
3
x
and had similar chemical compositions with the same layer-
type structure in the c direction, but different arrangement of
pentagonal {Mo O } units in the a–b plane. The order of activi-
Preparation of tetragonal Mo VO mixed oxide
3
x
6
21
Tetragonal Mo VO was synthesized by phase transformation from
ty in the selective oxidation of allyl alcohol is: orthorhombic,
3
x
orthorhombic Mo VO by heat treatment. Dried orthorhombic
trigonal Mo VO >amorphous Mo VO >tetragonal Mo VO .
3
x
3
x
3
x
3
x
À1
Mo VO was heated in air with a heating ramp of 108Cmin to
3
x
The four kinds of rod-shaped Mo VO catalysts promote the
3
x
4
008C and kept at that temperature for 2 h before cooling to am-
formation of acrolein from allyl alcohol commonly. However,
the activity of tetragonal Mo VO was rather low whereby the
bient temperature. The heat-treated sample was again heated in
À1
À1
3
x
a nitrogen stream (50 mLmin ) with a heating ramp of 108Cmin
acrolein formation was negligible at temperatures under ap-
proximately 2508C. The high selective formation of acrylic acid
over orthorhombic, trigonal and amorphous Mo VO catalysts
to 5758C and kept at that temperature for 2 h.
3
x
Catalytic test for allyl alcohol selective oxidation
was ascribed to the heptagonal channel in the a–b plane,
whereby these three catalysts showed almost the same behav-
iour for allyl alcohol oxidation. The open mouth of the heptag-
onal channel over the a–b plane acts as an active site for the
oxidation to acrylic acid and exhibits higher activity than the
active sites in the c–plane for acrolein formation. Nevertheless,
propanal and acrolein formed competitively on the active sites
of heptagonal channel before they were consecutively oxidized
to propionic acid and acrylic acid, respectively. Thus, the maxi-
mum yields of acrylic acid were 73% for the orthorhombic
Mo VO catalyst and 72% for the trigonal Mo VO catalyst at
Allyl alcohol selective oxidation tests were performed on the REAL-
CAT platform in a Flowrence high-throughput unit (Avantium)
equipped with 16 parallel milli-fixed-bed reactors (internal diame-
ter 2.6 mm, length 300 mm). Ground and calcined catalysts sam-
ples (50 mg) (673 K for 2 h under static air) were charged in each
fixed-bed flow reactor and sandwiched between SiC powder (parti-
cle size: 0.21 mm, Prolabo) and heated up to reaction temperature
À1
under air flow (10 mLmin ). Air was switched to reaction gas with
the molar composition of allyl alcohol/O /H O/(N +He)=
2
2
2
À1
1
:2.2:42.1:11.8 (total flow rate of 40 mLmin ) under a pressure at
3
x
3
x
2 bar and the condition was kept for 20 min at reaction tempera-
ture. Then liquid products were collected every 140 min by trap-
ping at 108C. The gas phase reactants and products after the trap
system were analysed with three on-line gas chromatographs (GC)
equipped as follows: Molecular Sieve (Agilent) with TCD (for O , N
3508C.
2
2
Experimental Section
and CO), Haysep Q (Agilent) with TCD (for H O and CO ), and Pora-
2
2
Preparation of orthorhombic Mo VO mixed oxide catalyst
plot Q (Agilent) with FID (for organic compounds). The liquid
phase reactant and products in the trap were analysed with GC-
FID (ZB-WAX). The carbon balance was always more than 96%. The
catalyst weight was adjusted to 0.050, 0.025 and 0.100 g and total
3
x
Orthorhombic Mo VO materials were synthesized by a hydrother-
3
x
[24]
mal method. (NH ) Mo O ·4H O (Mo: 50 mmol, Wako) was dis-
4
6
7
24
2
solved in distilled water (120 mL). Separately, an aqueous solution
flow rates of reactant gas were adjusted to 20, 40, 60 and
of VOSO (Mitsuwa Chemicals) was prepared by dissolving hydrat-
À1
4
8
0 mLmin with the same gas composition in order to change
ed VOSO (12.5 mmol) in 120 mL distilled water. These two solu-
4
the contact time.
tions were mixed at 208C and stirred for 10 min before introducing
them into an autoclave (300 mL Teflon inner tube). After 10 min of
nitrogen bubbling to replace the residual air, hydrothermal treat-
ment was performed at 1758C for 48 h. The as-obtained grey
solids were washed with distilled water and dried at 808C over-
night. These solids were purified by treatment with oxalic acid; dry
solids were added to an aqueous solution of oxalic acid (0.4m;
Characterization
The catalysts were characterized by the following techniques. Ele-
mental compositions were determined by an inductive coupling
plasma (ICP–AES) method (ICPE-9000, Shimadzu). Samples were
2
5 mL/1 g solid) and this mixture was stirred at 608C for 30 min.
dissolved in a NH solution. Powder XRD patterns were measured
3
Solids were isolated from the suspension by filtration, washed with
with a diffractometer (RINT Ultima+, Rigaku) using CuKa radiation
distilled water and dried at 808C overnight.
(tube voltage: 40 kV, tube current: 20 mA). Diffractions were re-
corded in the range of 4–608 with 18min . Catalysts used for reac-
À1
tion were sieved (aperture: 75 mm) to separate them from SiC. The
morphology was investigated by using a scanning transmission
electron microscope (HD-2000, Hitachi) at 200 kV. The samples
were dispersed in ethanol by ultrasonic treatment for several mi-
nutes, and drops of the suspension were placed on a copper grid
Preparation of trigonal Mo VO mixed oxide
3
x
The same procedure was used for the synthesis of trigonal Mo VOx
except for pH condition and duration of hydrothermal synthesis.
3
ChemCatChem 2016, 8, 1 – 7
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5
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ

Full Papers
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perature were measured by using an auto adsorption system (BEL-
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2
catalysts were evacuated under vacuum at 3008C for 2 h. External
surface area was calculated by the t method.
[
[
[
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·
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Received: April 13, 2016
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Published online on && &&, 0000
&
ChemCatChem 2016, 8, 1 – 7
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6
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

FULL PAPERS
T. Murayama,* B. Katryniok, S. Heyte,
M. Araque, S. Ishikawa, F. Dumeignil,
S. Paul, W. Ueda
&& – &&
Role of Crystalline Structure in Allyl
Alcohol Selective Oxidation over
Mo VO Complex Metal Oxide
3
x
Catalysts
Channels required: The catalytic oxida-
tion of allyl alcohol over orthorhombic,
trigonal, tetragonal, and amorphous
Mo VO catalysts was investigated.
orthorhombic, trigonal, and amorphous
Mo VO catalysts, with conversion of
3
x
allyl alcohol to acrolein taking place at
the heptagonal channel mouths.
3
x
Acrylic acid was formed effectively over
ChemCatChem 2016, 8, 1 – 7
www.chemcatchem.org
7
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ