Novel Mo-V Oxide Catalysts with Nanospheres as Templates for the Selective Oxidation of Acrolein to Acrylic Acid

Article abstract of DOI:10.1007/s10562-020-03457-9

Abstract: Novel Mo-V-PMMA and Mo-V-PS catalysts are prepared by addition of hard polymethyl methacrylate (PMMA) and polystyrene (PS) nanospheres into Mo/V compounds in the preparation process, respectively. The catalytic tests in selective oxidation of acrolein reveal that Mo-V-PMMA catalyst shows very high acrolein conversion (99.1%) and the yield of acrylic acid (90.7%). The BET, DLS, SAXS, XRD, XPS, H₂-TPR and NH₃-TPD measurements reveal that the addition of PMMA and PS nanospheres causes the obvious changes of porous structure, crystal phases composition and chemical properties of catalysts. These differences between Mo-V-PMMA and Mo-V-PS catalysts are attributed to the totally different “real” nano–environment during heat treatment in the high–concentration component mixture. PS nanospheres are in a state of adhesion or agglomeration or not uniformly distributed in the active component solution, while PMMA nanospheres with much better hydrophilicity and monodispersed state promote Mo and V ions more easily and uniformly dispersed in the mixture. Graphic abstract: Novel Mo-V catalysts are prepared by addition of hard polymethyl methacrylate (PMMA) and polystyrene (PS) nanospheres into Mo/V mixture. Obvious changes of porous structure, crystal phases and chemical properties of catalysts are caused by the nanospheres introduction, showing very high acrolein conversion (99.1%) and the yield of acrylic acid (90.7%) in selective oxidation of acrolein.[Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-020-03457-9

Catalysis Letters
https://doi.org/10.1007/s10562-020-03457-9
Novel Mo‑V Oxide Catalysts with Nanospheres as Templates
for the Selective Oxidation of Acrolein to Acrylic Acid
1
1
1
1
2
2
1
1
Weihua Wang · Wenjie Xu · Weilin Song · Bin Yang · Li Li · Xuhong Guo · Lianghua Wu · Hongxing Liu
Received: 20 August 2020 / Accepted: 4 November 2020
©
Springer Science+Business Media, LLC, part of Springer Nature 2021
Abstract
Novel Mo-V-PMMA and Mo-V-PS catalysts are prepared by addition of hard polymethyl methacrylate (PMMA) and poly-
styrene (PS) nanospheres into Mo/V compounds in the preparation process, respectively. The catalytic tests in selective
oxidation of acrolein reveal that Mo-V-PMMA catalyst shows very high acrolein conversion (99.1%) and the yield of acrylic
acid (90.7%). The BET, DLS, SAXS, XRD, XPS, H -TPR and NH -TPD measurements reveal that the addition of PMMA
2
3
and PS nanospheres causes the obvious changes of porous structure, crystal phases composition and chemical properties
of catalysts. These diꢀerences between Mo-V-PMMA and Mo-V-PS catalysts are attributed to the totally diꢀerent “real”
nano–environment during heat treatment in the high–concentration component mixture. PS nanospheres are in a state of adhe-
sion or agglomeration or not uniformly distributed in the active component solution, while PMMA nanospheres with much
better hydrophilicity and monodispersed state promote Mo and V ions more easily and uniformly dispersed in the mixture.
Graphic abstract
Novel Mo-V catalysts are prepared by addition of hard polymethyl methacrylate (PMMA) and polystyrene (PS) nanospheres
into Mo/V mixture. Obvious changes of porous structure, crystal phases and chemical properties of catalysts are caused
by the nanospheres introduction, showing very high acrolein conversion (99.1%) and the yield of acrylic acid (90.7%) in
selective oxidation of acrolein.
Keywords Polymethyl methacrylate · Polystyrene · Mo-V-PMMA catalyst · Mo-V-PS catalyst · Acrolein · Acrylic acid
*
Weihua Wang
wangwh.sshy@sinopec.com
1
Introduction
1
2
Sinopec Shanghai Research Institute of Petrochemical
Technology, Shanghai 201208, People’s Republic of China
Acrylic acid is an important chemical raw material, which
is mainly used to manufacture acrylate, superabsorbent
resin, water treatment agent and detergent aid. Acrylic
State-Key Laboratory of Chemical Engineering, East China
University of Science and Technology, Shanghai 200237,
People’s Republic of China
Vol.:(0
1
123456789)
3

W. Wang et al.
acid provides very important intermediate for the synthesis
and preparation of various ꢁne chemicals due to its excel-
lent polymerization and esteriꢁcation ability. Acrylic acid
catalysts play a very important and irreplaceable role in
meeting the increasing demand of acrylic acid in the world-
wide. One–step oxidation process of propane or propene to
acrylic acid is well–developed [1, 2]. However, at present,
a well–developed two–step production process of propene
selective oxidation to acrylic acid is mainly used in the
industry due to better catalytic activity and higher selectiv-
ity of acrylic acid. In the reactions, propene is oxidized with
acrolein as the major product and acetone as the main by-
product in the ꢁrst step. Then acrolein is further re-oxidized
to yield acrylic acid and over–oxidized directly to CO and
In the preparation of catalyst, pore forming agents are
often used to change the pore size distribution of catalysts.
Most of the pore forming agents are of soft structure, which
may cause hole collapse during the calcination of the cata-
lyst, so it is diꢂcult to eꢀectively control the speciꢁc pore
size. Therefore, selection of a good proppant is beneꢁcial to
the formation of speciꢁc pore size and even to the improve-
ment of the catalyst performance. The nanospheres of poly-
methyl methacrylate (PMMA) and polystyrene (PS) are
prepared by emulsion polymerization from their respective
monomers. The nanospheres can be further used to prepare
spherical polyelectrolyte brushes with many functions, such
as speciꢁc adsorption of proteins [19–21] and nanoreactors
for synthesis of magnetic particles [22–24] and metal nano-
particles [25–27]. Therefore, hard nanospheres may be very
suitable for pore forming of catalyst.
CO . Further oxidation of acetone will yield aldehyde, acetic
2
acid and formaldehyde which could be further oxidized to
CO and CO in the second step [3]. Direct conversion of pro-
In this paper, novel acrylic acid catalysts are successfully
prepared through employing PMMA and PS nanospheres in
the mixture of metal components. Combined with a variety
of characterization technologies, we present a comparative
investigation on porous structure, crystalline phases and
chemical properties of catalysts. The proportion of speciꢁc
nanopore (50–100 nm) in catalyst is innovatively changed
and optimized which shows better catalytic activity under
the condition of high loading propene. Small angle X–ray
scattering (SAXS) is a powerful tool to analyze the nanopar-
ticles, including metal oxide particles or nano–nanospheres
[28–31]. Here, SAXS is used for the ꢁrst time to “see” the
invisible role of nanospheres in the pore size distribution
of catalysts.
2
pene to acrolein, then to acrylic acid in high eꢂciency is of
great scientiꢁc and industrial importance, especially in the
current circumstance of cost reduction. The production of
acrylic acid at high propene airspeed is an easy and eꢀective
method to increase production capacity, but the requirement
for catalyst performance also increases signiꢁcantly.
Over the past several decades, many eꢀorts have been
devoted to develop highly active catalysts used for selec-
tive oxidation reaction. Composite industrial catalysts
with diꢀerent elements show great diꢀerences in catalytic
properties. Metallic oxides are the most widely studied and
eꢀective catalysts. Mo-V based catalysts for the two–step
oxidation reactions have been an active topic of research in
recent years [4–18]. Mo and/or V is usually considered to
be the basic redox element [4, 5]. In addition, other metal
elements, including transition metals (Fe, Co, Ni, Cu) and
lone–pair elements (Te, Sb, Bi) play stimulative roles in oxi-
dation–reduction reaction. A series of metal ions participate
in the active sites for oxidation reactions, not isolated ions
2 Experimental
2.1 Catalysts Preparation
2.1.1 Materials
[
6]. Mo-V based catalysts added other metal ions have been
proposed as eꢂcient catalysts in the oxidation reactions of
propane or propene to acrylic acid [7–12]. It is generally
believed that Te added to Mo/V based catalyst can better
promote the formation of selective partial oxidation cata-
All the chemicals and solvents are commercially avail-
able and are used without further puriꢁcation or modiꢁca-
tion. Ammonium metavanadate (NH VO , A111822) and
4
3
6+
4+
lysts because of the existence of redox couple Te /Te [13,
4]. Addition of Sb shows the similar role with Te by the
ammonium molybdate ((NH ) Mo O .4H O, A116375) are
4 6 7 24 2
1
obtained from Sigma–Aldrich Reagent. Styrene and methyl
methacrylate are available from J&K Chemical Ltd. Sodium
dodecyl sulfonate (SDS) and potassium persulfate (KPS) are
purchased from Shanghai reagent company. The water used
in all experiments is puriꢁed by reverse osmosis (Shanghai
RO Micro Q).
5
+
3+
redox couple Sb /Sb which forms the α-Sb O phase as
2
4
an oxygen inserting element at the surface of the catalysts
[
15]. Some transition metals such as Fe can decrease the
loss of lone–pair elements and stable the catalysts [16]. The
presence of Nb improves the selective oxidation reactions
which is the result of moderate acid sites and better stability
of acrylic acid [17, 18]. A better investigation of the element
composition, pore structure and chemical properties of the
catalyst is quite necessary for improvement of an eꢂcient
catalyst for the oxidation reactions.
2.1.2 Mo‑V Catalyst
50 mmol ammonium metavanadate (NH VO ) are dissolved
4
3
in 100 ml of distilled water. Varying amounts of ammonium
1
3

Novel Mo-V Oxide Catalysts with Nanospheres as Templates for the Selective Oxidation of Acrolein…
molybdate ((NH ) Mo O .4H O) from 14.3 mmol to
detector corrections and azimuthally averaged, two–dimen-
4
6
7
24
2
5
1
7.4 mmol (changing Mo/V) are completed dissolved in
sional scattering patterns are converted to one–dimensional
scattering curves and normalized to an absolute scale. The
absolute scattering intensity I(q) of sample is obtained after
subtracting the normalized background.
00 ml water. Under vigorous stirring (500 rpm) all the
above solutions are mixed in a certain order at room tem-
perature. After stirring for 30 min, the mixed liquids are
dried at 100 °C for 24 h. The obtained solids are calcined
for 4 h at 410 °C.
X–ray diꢀraction patterns (XRD) are collected using a
Broker ADVANCED 8X diꢀractometer. CuKα radiation
obtained at 40 kV and 40 mA is employed as the X–ray
source.
2.1.3 Mo‑V‑PMMA Catalyst/Mo‑V‑PS Catalyst
X–ray photoelectron spectroscopy (XPS) analysis is
performed using a Shimadzu Kratos Ultra DLD instrument
with AlKα radiation (5 mA, 15 kV, 1486.6 eV) as the X–ray
source. The photoelectronic signals of C 1 s, O 1 s, Mo 3d
and V 2p are analyzed with a multi-channel detector. The
samples are submitted to electrons from a W–ꢁlament to
reduce sample charging eꢀects. The binding energy value of
C 1 s is adjusted to 284.8 eV as energy reference.
H temperature programmed reduction (H -TPR) experi-
Hard nanospheres of PMMA (polymethyl methacrylate) and
PS (polystyrene) are applicated in the catalyst preparation
process. PMMA and PS nanospheres are prepared by emul-
sion polymerization. First, 0.5 g sodium dodecyl sulfonate
(
SDS) are dissolved in 150 ml of water and mixed with 26 g
styrene/12 g methyl methacrylate under a constant stirring
rate (300 r/min). 1.4 g potassium persulfate (KPS) are dis-
solved in 50 ml of water and added into the reactor. The
polymerization lasts for 2 h at 80 °C under nitrogen atmos-
phere, and PMMA and PS nanospheres are synthesized.
NH VO and (NH ) Mo O .4H O are separately dis-
2
2
ments are carried out on a Micromeritics AutoChem II 2950
apparatus. 50 mg of sample is pre-treated in a mixed ꢃow of
O and Ar (50 ml/min, 5% O ) at 450 °C for 30 min. After
4
3
4 6
7
24
2
2
2
solved in distilled water and mixed which is the same step as
the above preparation method of Mo-V catalyst. Under vig-
orous stirring (500 rpm), PMMA/PS nanospheres are added
into the above mixture at room temperature. After stirring
for 0.5 h the mixed liquids are dried for 24 h at 100 °C and
the obtained solids are calcined for 4 h at 410 °C in air, for-
matting Mo-V-PMMA and Mo-V-PS catalysts, respectively.
cooling to room temperature, the samples are ꢃuxed with
a mixed ꢃow of H and Ar (50 ml/min, 5% H ) for 15 min.
2
2
Then the temperature is increased to 600 °C at a heating rate
of 10 °C/min.
NH temperature programmed desorption (NH -TPD)
3
3
experiments are carried out on a PX200 apparatus. 200 mg
of sample is pre-treated in a mixed ꢃow of He at 400 °C
for 2 h. After cooling to room temperature, the samples are
2.2 Catalysts Characterization
ꢃuxed with a ꢃow of NH for 30 min. Then the temperature
3
is increased to 400 °C at a heating rate of 10 °C/min.
The BET speciꢁc surface areas of the catalysts are measured
on a Micromeritics Tristar 3000 instrument by N physisorp-
2
tion at −196 °C. The pore size and pore volume of the cata-
lysts are calculated by BJH adsorption curve. The samples
are degassed for 3 h at 220 °C.
2.3 Catalytic Reaction
The catalytic performance test is carried out at atmospheric
pressure in a ꢁxed bed reactor which includes two stainless
steel tubular reactors (I.D. 15 mm; length 330 mm) in series.
The acrolein as the main product in the ꢁrst reactor enters
the second reactor to provide the feed gas. Commercial cata-
lyst is used in the ꢁrst reactor, and the studied catalysts with
the constant amounts are put into the second reactor. A mix-
ture of C H /air/H O with volume ratio of 1/7.3/1.7 passes
Thermogravimetric analyzer (TGA) experiments are car-
ried out on a TA Instruments SDT Q600 apparatus. The
temperature of 20 mg sample is increased to 600 °C at a
heating rate of 10 °C/min.
Dynamic light scattering (DLS) is used to collect particle
size and distribution analysis of nanospheres which is per-
formed on a Malvern Zetasizer Nano ZS 90 instrument with
the high resolution of 5 mV and measuring range of particle
size 0.6 nm~6 nm.
3
6
2
through the catalyst bed in the ꢁrst reactor. The amount of
air and water added in the second reactor is one–third that
in the ꢁrst reactor. The temperature of the second reactor is
controlled in 240 ~ 280 °C. The products are analyzed by
an online gas chromatograph (Agilent 7890B) with a HP-
FFAP column (50 m) connected to an FID to analyze the
organic oxygenates in the products. The other components
are separated by Unibeads 1 s 60/80 UM (2 ft), Unibeads 1 s
60/80 UM (4 ft), and HP-A1/S (25 m) columns and analyzed
by a TCD.
Transmission electron microscopy images (TEM) are
obtained on a JEOL 2100F instrument operating at 200 kV.
Small angle X–ray scattering (SAXS) measurements are
performed at BL16B1 beamline (Shanghai Synchrotron
Radiation Facility, SSRF, China). The sample–to–detector
distance is 10 m with MAR 165 CCD detector. Each scat-
tering curve for every sample is an average of 10 measure-
ments to reach better signal–to–noise ratio. After applying
1
3

W. Wang et al.
3
Theory
3.1 Theory Of SAXS Measurement
The measured scattering intensity I(q) of nanospheres as a
function of scattering vector (q) contains three independ-
ent contributions [29–33]:
I(q) = I (q) + I (q) + I (q)
cs
fluct
ps
(1)
In Eq. 1, I (q) is the major contribution to the scat-
cs
tering intensity which is determined by the structure of
2
nanospheres in solution. I (q) equals to B (q) for the sym-
cs
metric sphere with radius R, B(q) is the scattering ampli-
tude which is described by Eq. 2 [29–33]:
R
e
[ꢁ (r) − ꢁ ]
e
m
sin(qr) 2
B(q)=4ꢀ
r dr
(2)
ꢀ
qr
0
Fig. 1 Distribution model of excessive electron density of nanosphere
vs radius r
e
e
m
Here, ꢀ (r) is the electron density of nanosphere, ꢀ
e
e
m
is the electron density of solvent. And ꢀ (r) − ꢀ is the
electron density difference between nanosphere and the
4 Results and Discussion
solvent.
The I (q) is caused by the thermal fluctuations of
4.1 Catalyst Activity
fluct
environment in solution which is calculated by Eq. 3
[
29–33].
The commercial catalyst is used in the oxidation of pro-
pylene of the ꢁrst reactor. The Table 1 shows that the yield
to acrylic acid and acrolein from the ꢁrst reactor is 13.3%
and 80.9%, respectively. The products from the ꢁrst reac-
tor enter the second reactor as feed gas. The activities of
the Mo-V catalyst, Mo-V-PMMA catalyst and Mo-V-PS
catalyst in oxidation of acrolein to acrylic acid are shown
in Table 2. Acrylic acid, acrolein, aldehyde, acetic acid
and carbon oxides are the main reaction products. The
acrolein conversion is 94.9% and the yield to acrylic acid
is 88.2% in Mo-V catalyst. Obvious diꢀerences in catalytic
performance have been observed between Mo-V-PMMA
and Mo-V-PS catalysts obtained by introduction of two
kinds of diꢀerent nanospheres. Mo-V-PMMA5% catalyst
presents the highest activity in acrolein oxidation, giv-
ing a high acrolein conversion of about 99.1% and acrylic
acid yield of 90.7%. However, Mo-V-PS5% catalyst has
I
fluct(0)
Ifluct(q)=
(3)
2
+ ꢀ q
2
1
where ꢀ is the correlation length determined by the
spatial environment fluctuations. The I (q) plays an
fluct
important role at high q values.
The I (q) is resulted from the density differences in
ps
nanospheres which is usually neglected.
The fitting scattering intensity of nanospheres is
obtained by Eq. 4:
R
Ifluct(0)
e
Δꢁ (r)
sin(qr) 2
2
r dr] +
I(q)= [4ꢀ
(4)
2
1 + ꢂ q
2
ꢀ
qr
0
e
e
e
m
e
In Eq. 4, Δꢀ (r) = ꢀ (r) − ꢀ . The Δꢀ (r) is a critical
parameter for fitting the SAXS curve shown in Fig. 1.
ꢀ
ꢁ
e
3
3
Δꢀ r ≤ r = 49.6 e/mn (for PMMA) or 6.4 e/mn (for PS)
1
0
ꢀ
ꢁ
e
Δꢀ (r) = ꢀ (r) − ꢀ =
e
e
e
Δꢀ r < r ≤ r
(5)
m
1 ꢀ0
ꢁ
r > r
1
1
0
e
0
Where, Δꢀ is a constant for PMMA and PS nanospheres in
a relatively poor catalytic performance with only 86.3%
yield to acrylic acid (acrolein conversion ~ 92.0%) among
the studied catalysts. In addition, higher concentration
of nanospheres (5%) is slightly beneꢁcial to improve the
activity of the catalyst than lower concentration (3%). In
e
Eq. 5. Δꢀ is caused by the adhesion of something else to
1
the surface of nanospheres in solution which is calculated
through the ꢁtting curve.
1
3

Novel Mo-V Oxide Catalysts with Nanospheres as Templates for the Selective Oxidation of Acrolein…
the following, the mass percentage of added nanospheres
is 5% in studied Mo-V-PMMA and Mo-V-PS catalysts.
The difference of catalytic performance is directly
attributed to the addition of nanospheres. At the condi-
tion of thermo–treatment, part of the groups -CH C(CH )
(
6)
2
3
(
-
COOCH ) on the surface of PMMA nanospheres form
3
CH C(CH )COOH and CH OH by the hydrolytic reaction
4.2 Pore Structure Measurement (BET)
2
3
3
in the acidic environment (as seen in Eq. 6) while there
is no hydrolysis reaction on the -CH CH(C H )- groups
The BET surface area, total pore volume, and average pore
size of Mo-V, Mo-V-PMMA and Mo-V-PS catalysts are
summarized in Table 3. Compared with Mo-V catalyst,
the pore volume of Mo-V-PMMA catalyst increases from
2
6
5
of the PS nanospheres surface. This is one of the most
obvious diꢀerences between PMMA and PS nanospheres
in the preparation process of catalysts. The activity dif-
ferences in Mo-V-PMMA and Mo-V-PS catalysts may be
mainly attributed to porous structure [34], crystal phase
composition [35], and chemical property of surface [36].
In the following part, BET, XRD, XPS, TPR and TPD are
employed to explore the apparent diꢀerences caused by
addition of two kinds of nanospheres.
3
3
0.019 cm /g to 0.028 cm /g, and the proportion of nanopo-
res more than 50 nm increases signiꢁcantly from 36.5% to
57.2%, especially in the range of pore size 50–100 nm. The
speciꢁc area and pore size also increase in varying degrees.
While the addition of PS nanospheres leads to the decrease
in speciꢁc area, pore volume and pore size of Mo-V-PS
catalyst. The proportion of nanopores of Mo-V-PS catalyst
more than 50 nm slightly increases from 36.5% to 38.8%,
Table 1 Oxidation of propylene in the ꢁrst reactor
Catalyst no
Propylene conversion (%)
Yield to products (%)
Acrylic acid
13.3%
Acrolein
80.9%
Aldehyde
1.5%
Acetic acid
0.6%
CO
CO2
Commercial catalyst
99.3%
1.3%
1.6%
Reaction conditions: 2.5 ml of catalyst; gas composition: propene/air/H O=1:7.3:1.7(v/v); C H ꢃow: 3.3 ml/min, reaction temperature: 360 °C
2
3
8
Table 2 Activity of the catalysts
in oxidation of acrolein to
acrylic acid in the second
reactor
Acrolein con- Yield to products (%)b
Catalyst no
version (%)a
Acrylic acid Acrolein Aldehyde Acetic acid CO
CO
2
(%)
(%)
(%)
(%)
(%)
(%)
Mo-V
94.9
98.8
99.1
91.8
92.0
88.2
90.2
90.7
86.0
86.3
4.1
1.0
0.7
6.6
6.5
0.4
0.3
0.1
0.3
0.3
1.9
2.3
2.3
1.9
1.8
1.7
2.0
2.1
1.5
1.5
2.9
3.4
3.2
2.8
2.5
c
Mo-V-PMMA2%
Mo-V-PMMA5%
Mo-V-PS2%
Mo-V-PS5%
Reaction conditions: 1 ml of catalyst; raw gas: the products from the ꢁrst reactor, combining with the
added air and H O (one–third of the ꢁrst reactor); reaction temperature: 270 °C
2
a
Acrolein conversion calculated by deducting the acrolein from the ꢁrst reactor
The data of yield to products from the second reactor
The mass percentage of added nanospheres
b
c
Table 3 Analysis of physical properties of the catalysts
3
Catalyst
Speciꢁc area
Pore volume(cm /g) Pore size (nm)
Pore size distribution (adsorption branch, %)
2
(
m /g)
BJH
BJH
<
20 nm
20–50 nm
50–100 nm
>100 nm
BET
Mo-V
Mo-V-PMMA
Mo-V-PS
5.3
6.5
4.1
0.019
0.028
0.015
16.8
18.6
16.3
22.5
23.2
23.5
40.8
19.6
37.7
27.6
41.3
23.3
8.9
15.9
15.5
1
3

W. Wang et al.
but reduces in the range of 50–100 nm. According to ref-
erences [2, 4, 5, 37], the ratio of pore size in the range of
5
0–100 nm may be an important factor because it is directly
related to the activity of the catalyst. Therefore, it is of great
signiꢁcance to study the eꢀect of the addition of two kinds
of nanospheres on the pore size of the catalyst.
4.3 Nanospheres Characterization
In order to study the eꢀect of nanosphere on the pore size
of catalyst, the two kinds of nanospheres should satisfy two
basic conditions: (1) be completely removed at calcination
temperature; (2) be consistent in particle size.
Figure 2 shows the thermogravimetric analyzer (TGA)
analysis of PMMA and PS nanospheres. PMMA and PS
nanospheres start to decompose at about 310 °C, and com-
pletely ꢁnish decomposition at about 390 °C. This means
that the two nanospheres can be completely removed at cal-
cination temperature (410 °C).
Fig. 3 The particle size distribution of PMMA and PS nanospheres
and TEM micrographs of nanospheres in the inset. The distribution is
based on volume distributions
Particle size and distribution analysis of PMMA and PS
nanospheres by dynamic light scattering (DLS) are shown in
Fig. 3. Both PMMA and PS nanospheres exhibit one narrow
and intense peak which means the good dispersion in very
diluted condition. The average particle sizes of PMMA and
PS nanospheres are both about 75 nm. As shown in the inset
of Fig. 3, TEM nano–graphs conꢁrm the regular spherical
states with good dispersion in very dilute solution.
PS nanospheres with the same size (75 nm) doesn’t achieve
the purpose of pore formation in the range of 50–100 nm,
because the nanopores proportion of Mo-V-PS catalyst from
50 nm to 100 nm is only 23.3% which is even smaller than
that of Mo-V catalyst.
In the preparation process of catalysts, PMMA and PS
nanospheres are added separately to the mixture of Mo/V
compound at very high concentration. The aggregation state
of nanospheres at high concentration determines the inꢃu-
ence on the structure and performance of catalysts. Small
angle X–ray scattering (SAXS) is used to study the “real”
aggregation state of nanospheres at high concentration dur-
ing the preparation process of catalysts.
The measured particle size of two nanospheres are basi-
cally the same (both about 75 nm) from DLS measurement.
Combined with the pore size distribution of catalysts in
Table 3, the nanopores proportion of Mo-V-PMMA catalyst
in the range of 50–100 nm is 41.3% which is much more
than 27.6% of Mo-V catalyst. This means that the addition of
hard PMMA nanospheres (75 nm) indeed plays an important
role in forming precision pore (50~100 nm). However, the
The scattering intensity curves and excess electron den-
sity (Δꢀ) distribution of PMMA and PS nanospheres at dif-
ferent concentration are shown in Fig. 4a, b, c, d. The ꢁtting
curves are based on the nanospheres at inꢁnitely low con-
centrations. The diꢀerence between SAXS curve of sample
and the ꢁtting line represents the interaction of sample. The
greater the diꢀerence, the greater the interaction between the
particles in sample. SAXS curves of PMMA nanospheres at
diꢀerent concentrations can almost coincide at very small
q (scattering vector) range after concentration normaliza-
tion, while the PS nanosphere curves don’t overlap at low
q values. This indicates that there is no obvious interaction
among PMMA nanospheres, but intense interaction in PS
solution. In other words, PMMA nanospheres are in almost
independent and monodispersed state, while PS nanospheres
may be in a state of adhesion or agglomeration in high con-
centration solution.
Further structure and chemical formula analysis of
PMAA and PS nanosphere, the side–chain group -C H
6
5
Fig. 2 The TGA analysis of PMMA and PS nanospheres
in PS is completely insoluble in water, and the formed
1
3

Novel Mo-V Oxide Catalysts with Nanospheres as Templates for the Selective Oxidation of Acrolein…
Fig. 4 SAXS curves of PMMA (a) and PS (c) nanospheres as a func-
tion of concentration; SAXS curves of PMMA (b) and PS (d) nano-
spheres after concentration normalization and the radial distribution
of excess electron density of PMMA (b) and PS (d) nanosphere in the
inset. Solid lines represent ꢁtting curves
hydrophilic groups of -CH C(CH )COOH and CH OH in
2
3
3
hydrolytic reaction on the PMMA nanospheres surface are
very soluble in water. The hydrophilic groups are beneꢁcial
to make PMMA nanospheres distributed more evenly in the
mixture of component. Therefore, combining with the aggre-
gation state of nanospheres at high concentration, we may
draw a conclusion that PS nanospheres are precipitated or
not uniformly distributed in the active component solution in
the catalyst preparation, and PMMA nanospheres with much
better hydrophilicity and monodispersed state are more eas-
ily and evenly dispersed in the active component solution.
4.4 XRD analysis
The X–ray diꢀractograms of Mo-V catalyst, Mo-V-PMMA
catalyst and Mo-V-PS catalyst are presented in Fig. 5. From
the detailed comparison of XRD pattern of a, b and c, it
can be concluded that the appearance of small reꢃections
at 2θ = 12.8, 23.3, 25.7, 27.3, 33.7, 38.9, 45.7 shows the
Fig. 5 XRD patterns of Mo-V based catalysts: (a) Mo-V catalyst;
(
b) Mo-V-PMMA catalyst; (c) Mo-V-PS catalyst. (●) MoO ; (■)
3
(V Mo ) O
0.93 5 14
0
.07
1
3

W. Wang et al.
existence Mo–oxide–phase MoO [JCPDS, 05–0508].
the addition of PMMA and PS nanospheres doesn’t lead to
the change of crystal types ((V Mo ) O and MoO ),
3
Similarly, the appearance of peaks at 2θ=12.3, 16.5, 22.3,
0
.07
0.93 5 14
3
2
3.3, 24.9, 28.2, 31.5, 33.7, 38.9 could be related to the
because no additional diꢀraction peaks have been obvi-
ously observed in the XRD patterns of these catalysts. In
other words, (V Mo ) O and MoO phases co-exist
presence of crystalline phase of (V Mo ) O [JCPDS,
0
.07
0.93 5 14
31–1437] in catalysts. The (V Mo ) O phase has been
0.07 0.93 5 14
0.07
0.93 5 14
3
reported in the Mo/V based oxide catalysts in some litera-
tures [38–40]. Orthorhombic M1 phase and hexagonal M2
phase are not observed, probably because the two phases
have been destroyed after calcination in air. This is consist-
ent with the current reports [17, 40, 41].
in the Mo-V, Mo-V-PMMA and Mo-V-PS catalysts. From
the displayed XRD data of Fig. 5, compared with Mo-V
catalyst, the peak height of XRD pattern in Mo-V-PMMA
and Mo-V-PS catalyst has changed which means the appar-
ent transformation of crystalline phases between MoO and
3
In the literature, (V Mo ) O phase is active
(V Mo ) O .
0
.07
0.93 5 14
0.07
0.93 5 14
and helpful to convert the isobutene intermediate to pro-
The XRD patterns of Mo-V based catalyst at diꢀerent
duce methacrolein in the selective oxidation of isobutane
amount of MoO to (V Mo ) O crystalline phase
3
0.07
0.93 5 14
[
40]. In the oxidation of propane and propene to acrylic
are shown in Fig. 6. The crystalline phases in these cata-
acid, (V Mo ) O phase and MoO phase coexist in
lysts are all mainly MoO and (V Mo ) O but their
0
.07
0.93 5 14
3
3
0.07
0.93 5 14
the active phases of the catalysts which shows the excel-
lent catalytic performance, however, the catalyst with only
a crystal phase of (V Mo ) O without MoO phase
relative values change obviously. Here, the ratio of the peak
intensity of MoO (A, at 2θ≈27.2°) to the peak intensity of
3
(V Mo ) O (B, at 2θ≈22.2°) is calculated to study the
0
.07
0.93 5 14
3
0.07
0.93 5 14
represents relatively poor catalytic activity [39]. In our case,
relationship between crystal phase composition and catalyst
activity. Figure 7 shows the dependence of acrolein conver-
sion (Fig. 7a) and selectivity of acrylic acid (Fig. 7b) with
the ratio of A to B. Figure 7a shows that with the increase of
A/B from 0.32 to 0.80, the conversion rate of acrolein ꢁrst
gradually increases, reaching the maximum above 99.0%
at about A/B=0.7, and then decreases. It appears an obvi-
ous asymmetric peak between 0.68 and 0.75 (A/B) which
means the excellent conversion of acrolein in this range.
While the selectivity of acrylic acid changes little, keep-
ing about 96.5% to 98% (Fig. 7b). Therefore, the A/B of
the catalyst with excellent performance should be in the
range of 0.68–0.75, most preferred 0.69 to 0.72. According
to the XRD data of Mo-V catalyst, Mo-V-PMMA catalyst
and Mo-V-PS catalyst, their A/B values are 0.67, 0.69 and
0
.37, respectively. The A/B of Mo-V-PMMA catalyst is in
the best range (0.69~0.72) corresponding to excellent cata-
lytic activity.
In the catalyst preparation process, the component com-
pounds are mixed and dried at 100 °C, and then calcined
at 410 °C to form the active components of Mo-V oxide
Fig. 6 XRD patterns of Mo-V based catalysts at diꢀerent ratio of A to
B. A and B represent the highest peak intensity height of MoO (A)
3
and (V0 Mo ) O (B) crystalline phase
.07
0.93 5 14
Fig. 7 Dependence of acrolein
conversion (a) and acrylic acid
selectivity (b) on the ratio of
A to B
1
00
100
95
90
85
80
75
70
95
9
8
8
7
7
0
5
0
5
0
0.3
0.4
0.5
0.6
0.7
0.8
0.3
0.4
0.5
0.6
0.7
0.8
A/B
A/B
(
b)
(
a)
1
3

Novel Mo-V Oxide Catalysts with Nanospheres as Templates for the Selective Oxidation of Acrolein…
catalyst. During the thermo–treatment process, the type of
medium in solution is very important for the formation of
crystal phases. The addition of PMMA and PS nanospheres
in the component mixture causes the change of the ratio
of MoO and (V Mo ) O which is largely because of
3
0.07
0.93 5 14
the interaction between the nanospheres and the metal com-
pounds. The generated water–soluble -COOH and -OH can
form complex ions with vanadium and molybdenum com-
pound which greatly enhances their interaction, and also
changes the ratio and distribution of vanadium and molyb-
denum components, causing the transform between MoO
3
and (V Mo ) O phases.
0
.07
0.93 5 14
4.5 XPS Analysis
Small structure transformation can aꢀect the catalytic activ-
ity, especially the important modiꢁcations on the surface of
catalyst. In order to observe the diꢀerences in detail among
the diꢀerent catalysts, the chemical composition and the
surface electronic state are characterized by X–ray photo-
electron spectroscopy (XPS). The deconvolution results
of V2p XPS spectra are shown with short dashed lines
3
/2
in Fig. 8a and the corresponding parameters are listed in
Table 4. The high–resolution XPS spectra for V2p can
3
/2
be deconvoluted into three peaks at 517.6 eV, 516.6 eV and
5
14.5 eV which are assigned to the reported binding energy
5
+
4+
3+
for V , V and V , respectively [42–44]. As shown in
Table 4, the valence state of vanadium in Mo-V catalyst
is basically close to 5 with the only high binding energy
(
517.6 eV). For the Mo-V-PMMA catalyst, the ratio of
5
+
4+
V : V is estimated to be 85.6: 14.4, giving an average
+
V valence state of 4.86 . A small amount of low valence
4
+
state V in catalysts are necessary served as the centers for
stabilization of the intermediate compound (acrylate) which
may balance the net charge in the crystal structure and facili-
tate the intercalation and deintercalation of acrylic acid from
5+
reactive sites [42–44]. The percentage of V species in total
vanadium of Mo-V-PS catalyst (28.2%) is signiꢁcantly less
than that in Mo-V-PMMA catalyst (85.6%). In Mo-V-PS
catalyst, a new lower V species is formed with the binding
3
+
energy of 514.5 eV which is undoubtedly ascribable to V .
The introduction of nanosphere in the catalyst preparation
is more likely to cause the coexistence of multiple valence
states of vanadium. The most likely reason is that part of
5
+
vanadium is reduced from V to low state by the reduc-
tive atmosphere caused by the nanosphere’s addition. The
PMMA and PS nanospheres are all removed (see Fig. 2) pro-
ducing CO, CO and H O in the calcination stage. The redox
2
2
reaction occurs between CO and part of the high valence
vanadium which causes the reduction in vanadium valence.
Figure 8b shows typical spectra in the Mo3d region for the
three catalysts. The binding energies at 233.0 eV, 231.9 eV
Fig. 8 XPS spectra (solid lines) and their deconvolution results (short
dashed lines) for Mo-V catalyst, Mo-V-PMMA catalyst and Mo-V-PS cat-
alyst. (a) V2p; (b) Mo 3d; (c) O1s
6+
and 229.9 eV for Mo3d signal have been reported in Mo ,
5/2
1
3

W. Wang et al.
Table 4 XPS analysis results of
V5+/Vtotal (%)
Catalysts
Binding energy of V2P3/2 (eV)
catalysts
V5+
V4+
V3+
Mo-V
Mo-V-PMMA
Mo-V-PS
517.6 (100%)
517.6 (85.6%)
517.6 (28.2%)
–
–
–
≈100.0
85.6
28.2
516.6 (14.4%)
516.6 (62.2%)
514.5 (9.6%)
5+
4+
Mo , Mo , respectively [45, 46]. In the case of Mo-V, Mo-
V-PMMA and Mo-V-PS catalysts, the Mo3d core level
5
/2
signal appears at 233.4 eV, 233.2 eV and 233.0 eV and the
chemical shift between Mo3d and Mo3d keeps the same
5/2
3/2
value (3.1 eV) shown in Fig. 8b. This implies that the highest
6
+
oxidation state of molybdenum (Mo ) is the main valence
state present in all studied catalysts. The binding energy shift
of main peak from Mo-V catalyst to Mo-V-nanospheres cata-
lyst is also due to the redox reaction with carbon monoxide.
Because the amount of molybdenum is relatively high, the
surface chemical valence of these catalysts remains above 6.
The XPS spectra of our samples in the O1s region is
shown in Fig. 8c. The binding energy of O1s in metal oxides
is considered in the range of 528–531 eV [47]. Compared
with Mo-V catalyst (531.2 eV), the O1s binding energy of
peak position in Mo-V-PMMA (531.0 eV) and Mo-V-PS
catalyst (530.8 eV) variates in the direction of lower value
which means the reduction in oxygen valence on the catalyst
surface. The partial vanadium and molybdenum converted to
lower valence also lowers the valence of oxygen in the oxide
catalyst which also causes the reduction in the interaction.
A good catalyst should have the property of weak binding
ability with acrolein and acrylate [47]. But too weak adsorp-
tion may cause acrolein to stay only for a short time or not
stay, which is not conducive to the improvement of acrolein
conversion. In general, the addition of nanospheres causes
the valence change of all elements on the catalyst surface.
Fig. 9 H -TPR spectra of diꢀerently Mo-V catalyst, Mo-V-PMMA
2
catalyst and Mo-V-PS catalyst
starting temperature (298 °C) which means a low rate of H
2
consumption up to much higher temperature. Overall, the
addition of PMMA nanospheres lowers the reduction tem-
perature of the catalyst and increases the amounts of reduc-
ible components which is as opposed to the PS nanospheres.
4.7 NH ‑TPD Analysis
3
The NH -TPD profiles of catalysts in the range of
3
4
.6 H ‑TPR Analysis
100–380 °C are shown in Fig. 10. The sample Mo-V-PMMA
presents the highest number of acid sites, while the fewest
number of acid sites appears in the Mo-V-PS catalyst. The
centered desorption temperature of Mo-V-PMMA catalyst
achieving maximum desorption value is basically consistent
with Mo-V catalyst (210 °C) which is much higher than that
in Mo-V-PS catalyst (190 °C). This means that the PMMA
addition favors a remarkable increase of acid sites on the
surface of the catalyst which is probably as a consequence
of the interaction between the formed -CH C(CH )COOH,
2
Further comparation of the reduction property of the Mo-V
series catalysts, H -TPR experiments are performed as
2
shown in Fig. 9. The TPR pattern is generally considered
to be aꢀected by operating conditions, such as heating rate
and pre-calcination temperature [48]. In our case, the Mo-V
catalyst exhibits one main narrow and intense reduction peak
around 393 °C, starting at 271 °C which may account for the
5
+
6+
stoichiometric reduction of V and Mo to low valence
state [49–53]. The addition of PMMA nanosphere doesn’t
lead to the obvious shift of reduction peak position (392 °C),
but marked change of starting temperature to 232 °C which
illustrates the concomitant enhancement of reduction kinet-
ics at lower temperature. On the contrary, the introduction
of PS nanosphere in the catalyst causes its position of peak
maximum shifted to higher temperature (425 °C) with higher
2
3
CH OH and the hydroxyl in catalyst, causing the exposure
3
of more acid sites and promote the acid–base properties
of center in catalyst. The introduction of PS nanosphere
causes not only a drastic elimination of acid sites amount
in Mo-V-PS catalyst, but also an obvious decrease in the
strength of acid sites. The -CH CH(C H )- groups on the
2
6
5
PS nanospheres surface have an obvious steric hindrance
1
3

Novel Mo-V Oxide Catalysts with Nanospheres as Templates for the Selective Oxidation of Acrolein…
could be regarded as an independent unit. The active cent-
ers with larger pore channels are favorable for the adsorption
of acrolein (I–II) and the desorption of acrylate (IV–V). The
PMMA nanospheres introduction clearly raises of weak or
medium strong acid sites on the catalyst surface, contribut-
ing to the adsorption of acrolein to the catalyst surface (I–II).
The (V Mo ) O and MoO phases are the main crys-
0
.07
0.93 5 14
3
talline phases in all studied catalysts and their optimum ratio
probably speed up the transfer the lone electron pair of car-
bonyl oxygen to the vacant orbital of highly electronegative
4+
cation in the oxide catalyst (II–IV). The small amount of V
formed in Mo-V-PMMA catalyst could stabilize the inter-
mediate produce acrylate and facilitate the intercalation and
deintercalation of acrylic acid from reactive sites and pro-
motes the formation rate of acrylic acid (IV–V). The lower
valence of oxygen in catalyst also reduces the interaction
between the catalyst surface and the intermediate product
acrylate, promoting the desorption rate of acrylate (IV–V).
In a word, the addition of nanospheres aꢀects the porous
structure, crystal phase composition, and chemical prop-
erty of surface. Furthermore, the eꢂciency of each step
is aꢀected in the production process of acrylic acid from
acrolein. Novel Mo-V catalyst with PMMA nanospheres as
template obviously improves the catalytic activity for the
selective oxidation of acrolein to acrylic acid. More impor-
tantly, the hard nanospheres can be extended to the prepara-
tion of other similar metal oxide catalysts such as acryloni-
trile catalyst.
Fig. 10 NH -TPD proꢁles of catalysts Mo-V, Mo-V-PMMA and Mo-
3
V-PS
eꢀect and repulsion with hydroxyl groups which may inhibit
the formation of acid sites in Mo-V-PS catalyst. In addi-
tion, there is an obvious medium strong acid site around 325
℃
in Mo-V-PMMA catalyst. More acidic sites of weak or
medium strong acids contribute to the conversion of acrylate
to acrylic acid [47]. The highest amount and strength of acid
sites in Mo-V-PMMA catalyst are much higher than Mo-V
and Mo-V-PS catalyst.
4.8 Reaction Mechanism
It is generally accepted that the acrylic acid is produced from
acrolein by stepwise redox mechanism [54–56]. The mecha-
nism of acrylic acid formation with Mo-V series as catalysts
is shown in previous reports [54–56]. Firstly, acrolein inter-
act with molybdenum in a highly charged state due to the
existence of the long electron pair in carbonyl oxygen (I–II).
5 Conclusions
Novel Mo-V-PMMA and Mo-V-PS catalysts with nano-
spheres as templates are prepared by respectively introduc-
ing PMMA and PS nanospheres into Mo/V mixture in the
preparation process. The Mo-V-PMMA catalyst shows the
very high acrolein conversion 99.1% and acrylic acid yield
90.7% in the selective oxidation of acrolein. Based on the
characterization results, the addition of PMMA and PS
nanospheres does signiꢁcantly inꢃuence the porous struc-
ture, crystalline phases, chemical composition on surface,
reduction property and the amount and strength of acid
sites. The introduction of PMMA nanospheres obviously
increases the proportion of nanopores in the range of pore
size 50–100 nm. The ratio of MoO to (V Mo ) O
Then the electron pair is transferred to the vacant orbital
−
of Mo-V oxide catalyst (II–III) and CH =CH-C=O frag-
2
ment is rapidly produced. The fragment causes the forma-
+
tion of electrophilic CH=CH-C=O by collectivization of
carbonyl group electrons (III–IV). At last stage, the acrylic
acid is produced from the acrylate decomposition on the
surface (IV–V) which is the most time consuming and
closely related to the strength of acid anion binding with
4
+
corresponding stabilization center (V ). Lattice oxygen is
involved in the reaction and the properties of oxygen in the
oxide catalyst have great inꢃuence on the activity and selec-
tivity of the catalyst.
3
0.07
0.93 5 14
phase in Mo-V-PMMA catalyst is just in the optimal range of
0.69–0.72 corresponding to excellent catalytic activity. The
addition of PMMA nanosphere causes appearance of a small
4
+
The addition of PMMA nanospheres results to more
uniform distribution of vanadium and molybdenum com-
pounds, and does play a role in pore formation in the range
of 50–100 nm. This leads to the existence of more active
centers in the Mo-V-PMMA catalyst. Each active center
amount of stabilization center V , decrease in reduction
temperature and remarkable increase of weak or medium
strong acid sites on the catalyst surface, contributing to the
conversion of acrylate to acrylic acid.
1
3

W. Wang et al.
The obvious diꢀerence in activity of Mo-V-PMMA and
Mo-V-PS catalysts is ultimately attributed to the “real”
micro–environment during heat treatment. On the one hand,
the groups of -COOH and -OH can form complex ions with
vanadium and molybdenum ions, leading to the ions’ dis-
tribution more uniform on the surface of Mo-V-PMMA
catalyst. On the other hand, PMMA nanospheres in good
monodispersed state are more easily and evenly dispersed
in the active component solution, while PS nanospheres are
in a state of adhesion or agglomeration or not uniformly
distributed in the active component solution resulting in the
reduction of the catalyst activity.
24. Henzler K, Haupt B, Rosenfeldt S, Harnau L, Narayanan T, Ballauꢀ
M (2011) Phys Chem Chem Phys 13:17599–17605
25. Schrinner M, Ballauꢀ M, Talmon Y, Kauꢀmann Y, Thun J, Moller
M, Breu J (2009) Science 323:617–620
26. Wu S, Kaiser J, Guo XH, Li L, Lu Y, Ballauꢀ M (2012) Ind Eng
Chem Res 51:5608–5614
2
7. Wunder S, Polzer F, Lu Y, Mei Y, Ballauꢀ M (2010) J Phys Chem
C 114:8814–8820
2
8. Wang WH, Li L, Han HY, Tian YC, Zhou Z, Guo XH (2015) Col-
loid Polym Sci 293:2789–2798
29. Rosenfeldt S, Wittemann A, Ballauꢀ M, Breininger E, Bolze J,
Dingenouts N (2004) Phys Rev E 70:0614031–0614039
30. Guinier A, Fournet G (1955) Small-angle scattering of X-rays. John
Wiley and Sons, New York
31. Wang WH, Chu FF, Li L, Han HY, Tian YC, Wang YW, Yuan
ZY, Zhou ZM, Guo XH (2016) J Polym Sci Part B Polym Phys
54:405–413
References
3
2. Robillard Q, Guo XH, Ballauꢀ M, Narayanan T (2000) Macromol-
ecules 33:9109–9114
1
.
.
Chen LQ, Liang J, Lin H, Weng WZ, Wan HL, Vedrine JC (2005)
Appl Catal A 293:49–55
33. Wang WH, Li L, Henzler K, Lu Y, Wang JY, Han HY, Tian YC,
Wang YW, Zhou ZM, Lotze G, Narayanan T, Ballauꢀ M, Guo XH
2
S.A. Schunk, in: Handbook of Heterogeneous Catalysis, vol. 2, eds.
G. Ertl, H. Knoezinger, F. Schuth, and J. Weitkamp (Wiley-VCH
Verlag Gmbh & Co. KGaA, Weinheim, 2008) ch 7.
(2017) Biomacromol 18:1574–1581
3
4. Yakubovich MN, Simonstev VI, Vytnov GF, Luiksar LS, Lasareva
NP, Yaremenko EI, Telipko VA, Kholyavenko KM (1984) Appl
Catal 10:297–302
3
.
.
Liu JW, Mohamed F, Sauer J (2014) J Catal 317:75–82
Centi G, Cavani F, Triꢁro F (2001) Selective oxidation by heteroge-
neous catalysis. Kluwer Academic/ Plenum Publishers, New York
B.K. Hodnett, Heterogeneous Catalytic Oxidation (Wiley, New
York, 2000.)
4
3
3
3
3
5. Zhai Z, Wütschert M, Licht RB, Bell AT (2015) Catal Today
261:146–153
5.
6. Cremer UD, Raichle AD, Rosowski FD, Hammon UD, Müller-
Engel KJD (2008) German Patent, 2008, DE 102007010422.
7. Kaposi M, Cokoja M, Hutterer CH, Hauser SA, Kaposi T, Klap-
penberger F (2015) Kühn FE 44:15976–15983
6
.
.
Vedrine JC, Coudurier G, Millet JMM (1997) Catal Today 33:3–13
Korovchenko P, Shiju NR, Dozier AK, Graham UM, Guerrero-Pérez
MO, Guliants VV (2008) Top Catal 50:43–51
7
8. Popova GY, Andrushkevich TV, Dovlitova LS, Aleshina GA, Che-
salov YA, Ishenko AV, Ishenko EV, Plyasova LM, Malakhov VV,
Khramov MI (2009) Appl Catal A 353(249):257
8
.
.
Ueda W, Endo Y, Watanabe N (2006) Top Catal 38:261–268
Baca M, Aouine M, Dubois JL, Millet JMM (2005) J Catal
9
233:234–241
3
4
4
9. Botella P, López Nieto JM, Solsona B, Mifsud A, Márquez F (2002)
1
1
1
1
1
1
1
0. Al-Saeedi JN, Guliants VV, Guerrero-Perez O, Banares MA (2003)
J Catal 209:445–455
J Catal 215:108–115
0. Guan J, Xu H, Song K, Liu B, Shang F, Yu X, Kan Q (2008) Catal
Lett 126:293–300
1. Blasco T, Botella P, Concepcion P, Lopez Nieto JM, Martinez-Arias
A, Prieto C (2004) J Catal 228:362–373
1. Guliants VV, Bhandari R, Swaminathan B, Vasudevan VK,
Brongersma HH, Knoester A, Gaꢀney AM (2005) J Phys Chem B
2. Wagner JB, Timpe O, Hamid FA, Trunschke A, Wild U, Su DS,
Widi RK, Abd Hamid SB, Schlogl R (2006) Top Catal 38:51–58
3. Huynh Q, Schuurman Y, Delichere P, Loridant S, Millet JMM
109:24046–24055
4
2. Plyasova LM, Solovyeva LP, Kryukova GN, Andrushkevich TV
1990) Kinet Katal 32:1430
3. Plyasova LM, Solovyeva LP, Tsybulya SV (1991) Zh Strukt Khim
(2009) J Catal 261:166–176
(
4. Tauꢁq-Yap YH, Asrina SN, Hutchings GJ, Dummer NF, Bartley JK
4
(2011) J Natural Gas Chem 20:635–638
32:110
5. Nilsson J, Landa-Canovas A, Hansen S, Andersson A (1977) Catal
Today 33:97–108
4
4. Wu QH, Thißen A, Jaegermann W (2004) Surf Sci 236:473–478
5. Patterson TA, Carver JC, Leyden DE, Hercules DM (1976) J Phys
Chem 80:1700–1708
4
6. Getsoian A, Shapovalov V, Bell AT (2013) J Phys Chem C
117:7123–7137
4
4
4
4
5
6. Okamoto Y, Oh-Hiraki K, Imanaka T, Teranishi S (1981) J Catal
1
7. Ueda W, Vitry D, Katou T (2005) Catal Today 99:43–49
71:99–110
1
8. Baca M, Pigamo A, Dubois JL, Millet JMM (2005) Catal Commun
7. Moulder JF, Stickle WF, Sobol PE, Bomben KD (1992) Handbook
of X-ray photoelectron spectroscopy. Perkin-Elmer, Eden Prairie
8. Arnoldy P, de Jonge JCM, Moulijin JA (1985) J Phys Chem
6:215–220
1
2
2
2
2
9. Wang SY, Chen KM, Li L, Guo XH (2013) Biomacromol
4:818–827
0. Henzler K, Wittemann A, Breininger E, Ballauꢀ M, Rosenfeldt S
1
89:4517–4527
9. Nguyen LD, Loridant S, Launay H, Pigamo A, Dubois JL, Millet
JMM (2006) J Catal 237:38–48
(2007) Biomacromol 8:3674–3681
1. Wang SY, Chen KM, Kayitmazer AB, Li L, Guo X (2013) Colloids
Surf B 107:251–256
0. Grasselli RK, Oyama ST, Gaꢀney AM, Lyons JE (1997) Proceeding
of the 3rd world congress on oxidation catalysis. Studies in Surface
Science and Catalysis, San Diego
2. Wang WH, Li L, Yu XJ, Han HY, Guo XH (2014) J Polym Sci Part
B Polym Phys 52:1681–1688
51. Jiang HC, Lu WM, Wan HL (2004) Chin Chem Lett 15:977–980
52. Arena F, Parmaliana A (1996) J Phys Chem 100:19994–20005
53. Parmaliana A, Arena F, Frusteri F (1997) Stud Surf Sci Catal
3. Zhu Y, Chen KM, Wang X, Guo XH (2012) Nanotechnology
23:2656011–2656019
110:347–356
1
3

Novel Mo-V Oxide Catalysts with Nanospheres as Templates for the Selective Oxidation of Acrolein…
5
4. Bonareva VM, Andrushkevich TV, Paukshtis EA (1986) React Kinet
Publisher’s Note Springer Nature remains neutral with regard to
Catal Lett 32:371–376
jurisdictional claims in published maps and institutional aꢂliations.
55. Ruiz P, Delmon B (1991) Stud Surf Sci Catal 72:91–100
6. Andrushkevich TV (1993) Catalysis Reviews 35:213–259
5
1
3