Insights into Redox Dynamics of Vanadium Species Impregnated in Layered Siliceous Zeolitic Structures during Methanol Oxidation Reactions

Article abstract of DOI:10.1002/cctc.201901567

Supported transition metal catalysts have been extensively applied to oxidative and reductive processes. The understanding of surface speciation and active site-support interactions in these materials play a substantial role in developing improved heterogeneous catalysts. Herein, a series of impregnated 3D ferrierite and 2D ITQ-6 siliceous supports with variable loading of vanadium oxide was prepared. Chemical and structural properties of the materials were studied by X-ray diffraction, N₂ physisorption, inductively coupled plasma – optical emission spectrometry, X-ray absorption, Fourier transform infrared and diffuse reflectance UV-vis spectroscopies, and temperature-programmed reduction with H₂. Reactivity of the catalyst surface, associated with the incidence of isolated silanol groups, was found to be more effective when vanadium oxides were better dispersed and stabilized than increases in surface area. Differences in activation and the oxidation state dynamic behavior of active sites were then probed by methanol oxidation as a model reaction monitored by in situ FTIR spectroscopy and XANES/MS. By applying isothermal periods of reaction under non-oxidizing atmosphere and regeneration of catalysts by O₂, it was found that, even at distinct rates, all types of sites are accessible during reaction, since a complete reduction to V⁴⁺ was observed. However, reoxidation of sites to V⁵⁺ is limited and sensitive to the different vanadium species on the surface, and probably, the determinant factor of the distinct V⁵⁺/V⁴⁺ equilibrium reached for the catalysts when the reaction is carried out under constant oxidizing atmosphere.

Full text of DOI:10.1002/cctc.201901567

DOI: 10.1002/cctc.201901567
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Insights into Redox Dynamics of Vanadium Species
Impregnated in Layered Siliceous Zeolitic Structures during
Methanol Oxidation Reactions
[a, b]
[a]
[a]
[b]
[b]
Luiz H. Vieira,
Christopher W. Jones, and Leandro Martins*
Luiz G. Possato, Thiago F. Chaves, Jason J. Lee, Taylor P. Sulmonetti,
[b]
[a]
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Supported transition metal catalysts have been extensively
applied to oxidative and reductive processes. The understand-
ing of surface speciation and active site-support interactions in
these materials play a substantial role in developing improved
heterogeneous catalysts. Herein, a series of impregnated 3D
Ferrierite and 2D ITQ-6 siliceous supports with variable loading
of vanadium oxide were prepared. Chemical and structural
properties of the materials were studied by X-ray diffraction, N2
physisorption, inductively coupled plasma - optical emission
spectrometry, X-ray absorption, Fourier transform infrared and
diffuse reflectance UV-vis spectroscopies, and temperature-
with the incidence of isolated silanol groups, was found to be
more effective to better disperse and stabilize vanadium oxides
than increase in surface area. Differences in activation and the
oxidation state dynamics behavior of active sites were then
probed by methanol oxidation as a model reaction monitored
by in situ FTIR and XANES/MS. Keeping isothermal steps of
reaction (in absence of oxidant) and regeneration by O it was
2
found that, even at distinct rates, all species of vanadium oxides
on surface are able to oxide methanol but reoxidation of
reduced sites is limited and, probably, a determinant step to
5
+
4+
V
/V equilibrium when reaction is carried in the presence of
programmed reduction with H . Reactivity of surface, associated
oxidant.
2
1
. Introduction
of dioxymethylene intermediates with adsorbed methoxy or
methanol, and methyl formate production requires two oxygen
atoms from catalyst structure, making them favorable in
adjacent vanadium sites, increasing activity per site with the
surface coverage, with a maximum productivity in a complete
monolayer. In contrast, for propane oxidative dehydrogenation
systems, the presence of monomeric, polymeric or a complete
monolayer of vanadium species on the surface of the same
Vanadium-based materials play an important role in heteroge-
neous catalysis. Redox properties present in vanadium oxides
are very useful to promote significant chemical processes, like
[1,2]
[3,4]
[5,6]
oxidations,
ammoxidations
and reductions.
An impor-
tant parameter that induces catalytic properties in vanadium-
based materials is the support surface coverage. In some
specific cases, like oxidation of methanol, formation of different
products is favored according to vanadium species formed on
the active surface. In the submonolayer range, where only
monomeric and polymeric vanadium oxide species are present,
formaldehyde is preferentially formed, and activity per site is
independent of polymer/monomer ratio, since one oxygen
support did not influence the activity, but the presence of V O5
2
nanoparticles with sizes in the range of 1–3 nm, above the
monolayer coverage, considerably increased the activity of the
[9]
catalyst.
To guide the production of specific compounds by catalytic
processes involving vanadium as the active sites, determining
the choice of supports, the selection of precursor salts and
preparation methods need to be finely tuned during catalyst
development to minimize the occurrence of undesirable types
of active species on the surface. Impregnation is the simplest
and most often employed method to prepare vanadium oxide
catalysts, but it presents a very low control when dispersion of
atom and, consequently, one VO site, is involved in the
4
[7]
reaction mechanism. When monolayer coverage is reached,
formation of methyl formate and dimethoxymethane are
favored under mild conditions, as reported in the VO /TiO
X
2
[8]
catalysts. Formation of dimethoxymethane involves reaction
[10]
surface species is determinant. To improve dispersion and
[
11]
[a] Dr. L. H. Vieira, Dr. L. G. Possato, Dr. T. F. Chaves, Prof. L. Martins
Instituto de Química
avoid formation of isopoly-vanadates in solution,
which
facilitates agglomeration in vanadium pentoxide nanoparticles,
even at low metal loadings, a series of bulky organic precursors
Universidade Estadual Paulista – UNESP
R. Prof. Francisco Degni, 55
Quitandinha SP 14800-900 (Brazil)
E-mail: leandro.martins@unesp.br
[
12–15]
and solvents that lead to a higher solubility were studied.
[16]
[17]
Alternatively, grafting,
flame spray pyrolysis
and ion
[
b] Dr. L. H. Vieira, Dr. J. J. Lee, Dr. T. P. Sulmonetti, Prof. C. W. Jones
School of Chemical & Biomolecular Engineering
Georgia Institute of Technology
[18]
exchange methods have been employed too and they offer
better control of vanadium speciation. Unfortunately, scaling
the application of these compounds and methods can consid-
erably increase costs related to catalyst production.
311 Ferst Drive NW
Atlanta GA 30332 (USA)
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/cctc.201901567
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In addition to metal oxide dispersion, the nature of oxide
support plays a determining role in the uniform creation of
precursor PreFER on the dispersion of vanadium oxide species
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prepared by a wet impregnation method using VOSO as a
4
[12]
surface vanadia species.
It can be assumed that when a
precursor. By applying in situ spectroscopic techniques and
methanol as a model molecule, we monitored the activation
over the vanadium surface and the dynamic behavior of the
active sites during reaction and regeneration steps.
strong interaction between vanadium oxide and the support
occurs (e.g. TiO ), a monolayer of surface species can be
2
[19]
reached without the formation of nanoparticles. However,
when the reactivity of the support surface is low (e.g. SiO ),
2
[20]
nanoparticles are also present below monolayer coverage.
Some strategies to improve dispersion over silica-based sup-
ports involve the preparation of highly ordered mesoporous
2. Results and Discussion
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[21]
[16]
silicas, like MCM-41, or thermally treated commercial silicas,
Structural properties and vanadium speciation. Figure 1A
shows the X-ray diffraction patterns for the lamellar precursor
Si-PreFER, supports Si-FER and Si-ITQ-6, and impregnated
catalysts with different vanadium loadings. The presence of four
methyl groups in 4-amino-2,2,6,6-tetramethylpiperidine, used as
the organic structure-directing agent instead of piperidine,
prevented the stacking of the Si-PreFER layers into a condensed
or by generation of surface reactive isolated silanol groups.
Increasing the surface area and surface hydroxyl density can
directly affect electrostatic interactions between the precursor
and support during impregnation, and the stability of sites
during thermal post-treatments like drying and calcination is
[11]
also important.
Despite the improvement in the activity
[24]
generated by applying these types of supported materials in
relation to bulk metal oxides, when high vanadium contents are
employed, problems are often encountered. Commercial silicas
generally have a limited surface area available and the surface
area of MCM-41 tends to drastically drop upon vanadium
3D structure. The separation of layers in Si-PreFER can be
noted by the displacement of the (h00) diffraction planes to
lower 2θ values, as observed in the first peak of the diffracto-
[24]
gram, corresponding to the (200) plane. Comparison of unit
cell parameters (Figure S1) revealed a retraction of parameter a
from 26.444 Å in Si-PreFER to 18.746 Å in 3D Si-FER. Starting
from a lamellar precursor it was an important step in this study,
since it enabled different post-synthesis treatments that led to a
3D structure of Si-FER and to a 2D structure of Si-ITQ-6. The
long-range structural disorganization, generated in Si-ITQ-6 by
[22]
loading, caused by a collapse in the mesoporous structure. In
this regard, more robust zeolitic structures appear as an
alternative, combining high surface area and structural stability.
The microporous character of zeolites can limit access of metal
precursors and reactants during preparation and application in
[23]
[37]
catalysis.
However, the discovery of lamellar structures
the delamination process suppressed diffraction peaks. Fur-
opened new opportunities to application of zeolitic and related
structures, based on precursors where the layers are not
thermore, the ratio between the intensities of (h00) and (0kl)
planes decreased, as given in Table 1, indicating a favored
disorder along axis a. A detailed view of Si-FER and Si-ITQ-6
after different vanadium loadings is shown in Figure 1B.
Although no structural changes were observed in the supports
after impregnation, in the [5 V]Si-FER, [10 V]Si-FER and [10 V]Si-
ITQ-6 catalysts it is possible to observe the presence of the
[24]
completely condensed.
These materials have allowed the
development of micro/mesoporous structures, in the form of
[25]
delaminated zeolites. The structural disorganization exposes
an elevated and hydroxyl rich area of siliceous zeolitic
[26]
structures associated with the rigid and well-ordered micro-
porous structure of individual layers, making them promising
supports for metal oxide domains.
Another important factor to be considered in combination
with speciation-driven reactivity is the dynamic behavior of the
active sites under reducing and oxidizing environments.
Operando XANES/EXAFS studies allowed the identification of
differences in vanadium site dynamics during redox cycles in V-
[
27]
based mixed oxides and binary V O /CeO and ternary V O /
2
5
2
2
5
[
28]
[29]
CeO /SiO systems. Recently Ek et al. explored the facet-
2
2
dependent reactivity of VO species on TiO previously observed
x
2
30]
[
in the selective reduction of NO to NH3 by visualizing redox
dynamic processes over (001) and (101) facets of the oxide
applying combined atomic-resolution TEM and electron energy
loss spectroscopy (EELS) under alternated oxidizing and reduc-
[
31–33]
ing environments. By applying in situ spectroscopic
atomic-resolution imaging
and
[34–36]
techniques to monitor redox
properties under a reaction environment, new ways are opened
to move towards a more complete understanding of the
reactivity in oxide-catalyzed processes.
In this study, we investigated the influence of the texture
and surface composition of siliceous supports with 3D Ferrierite
and 2D ITQ-6 zeolitic structures derived from the lamellar
Figure 1. (A) X-ray diffraction patterns of lamellar precursor, supports and
catalysts. (B) Detailed view of Si-ITQ-6-based (green) and Si-FER-based (blue)
catalysts, and identification of crystalline V O phase diffraction peaks.
2 5
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Table 1. Chemical and textural properties of catalysts.
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Catalyst
V
V-density
N
N
V2O5
/
I
I
(200)
(011)
/
V
micro
3
V
meso
3
H
2
consumption
molH2/
[h]
[a]
À 2 [b]
[c]
[d]
À 1 [e]
À 1 [f]
À 1 [g]
[
% w/w]
[VO
x
.nm
]
total [%]
[cm g
]
[cm g
]
[mmolg
]
mol
V
[1 V]Si-FER
0.8
4.5
7.9
1.0
4.7
9.7
0.15
0.86
1.51
0.02
0.11
0.23
0
48.2
39.1
34.8
8.4
4.0
2.9
0.105
0.103
0.085
0.030
0.030
0.029
–
–
–
1.90
1.33
1.04
0.12
0.92
1.40
0.17
0.97
1.44
0.78
1.03
0.90
0.90
1.04
0.76
[
[
[
5 V]Si-FER
10 V]Si-FER
1 V]Si-ITQ-6
82.2
92.4
0
0
35.0
[5 V]Si-ITQ-6
10 V]Si-ITQ-6
[
[a] Determined by ICP-OES, [b] Calculated from molecules of VO in the catalyst and external surface area (ESA) of supports (molecules of VO were estimated
x
x
2
À 1
À 1
from ICP-OES results; ESASi-FER =62 m g and ESASi-ITQ-6 =496 m
2
g
), [c] Ratio between the number of vanadium atoms in V
2
O
5
form (identified by XRD
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refinement) and number of total vanadium impregnated (identified by ICP-OES), [d] Ratio between peak intensity referent to X-ray diffraction in planes (200)
and (011) of siliceous FER structure, [e] Micropore volume, [f] Mesopore volume, [g] Determined by temperature-programmed reduction, [h] 1 mol of H to
reduce 1 mol of V to V ; 2 mol of H to reduce 1 mol of V to V . Stoichiometry was based on following equations: V O +H !V O +H O and V O +
2
5
+
4+
5+
3+
2
2
5
2
2
4
2
2
5
2
2
H !V
2 3 2
O +2H O.
main diffraction peaks related to a V O5 crystalline phase
2
(Figure S2). The quantification of phases for these three
catalysts (Figure S3) revealed that 3.7 wt.% of the vanadium
atoms impregnated in [5 V]Si-FER are composed by V O
2
5
crystallites, and in the catalyst [10 V]Si-FER the amount of
crystalline V O increased to 7.3wt.%. These values represent
2
5
8
2% and 92% of the total vanadium present in the samples,
respectively (Table 1). On the other hand, the catalyst [10 V]Si-
ITQ-6 presented only 3.4wt.% vanadium in the V O crystallite
form and suggests that most of the vanadium oxides are
dispersed on the surface of catalyst.
2
5
More accurate information regarding vanadium species was
obtained by X-ray absorption and UV-Vis spectroscopies. Fig-
ure 2A shows diffuse reflectance UV-Vis spectra of the sup-
ported catalysts and of pure vanadium pentoxide. In vanadium-
based materials, the energy of bands related to oxygen to
vanadium charge transfer (CT) provides essential information
about the coordination of the vanadium center, where an
increase in coordination number displaces CT bands to higher
[38]
wavelengths/lower energies.
In this study, two bands can
immediately be identified in the supported-vanadium catalysts,
centered at around 250–300 and 350–400 nm. The first one is
related to the presence of monomeric VO4 species and the
second one to chain-growth by polymerization of these units to
Figure 2. (A) Diffuse reflectance UV-vis spectroscopy analyses of the catalysts
and vanadium pentoxide. (B) X-ray absorption spectra (XAS) in the XANES
region at the V K-edge for catalysts and vanadium pentoxide. (C) Room-
temperature FT[χ(k)k ]-EXAFS spectra in R space for catalysts and vanadium
pentoxide.
2
[39]
form (VO4)n species. In Si-FER-supported catalysts, an extra
shoulder appears at around 450–500 nm. This grows gradually
with an increase in vanadium loading and it is related to oxygen
[
40]
to vanadium CT in vanadium pentoxide clusters, as observed
at 475 nm for the reference V O sample. In Si-ITQ-6-supported
The X-ray absorption near vanadium K-edge spectra
(XANES) of supported catalysts and vanadium pentoxide are
shown in Figure 2B. The main information obtained from these
spectra arise from electronic transitions of 1s to 3d orbitals (due
to 2p and 3d hybridization), responsible for the appearance of a
pre-edge peak around 5470 eV, and 1s to 4p orbitals, respon-
2
5
catalysts only discrete changes were observed. By increasing
vanadium loadings, a short displacement can be noted in the
band of monomeric VO4 species to higher wavelengths,
suggesting a minor short-chain polymerization of these species.
In the [10 V]Si-ITQ-6 catalyst an additional displacement in the
band of polymerized species is observed, probably associated
with the initial development of V O clusters as perceived in the
[42]
sible for post-edge oscillations in the spectra.
Post-edge
oscillations are commonly seen when clusters are formed, and
these have their intensity increase as these species become
more abundant, as observed in the bulk V O sample. In
supported catalysts, these oscillations are more pronounced in
[5 V]Si-FER and [10 V]Si-FER materials, and a discrete oscillation
in the [10 V]Si-ITQ-6 is also noted. The Fourier-transformed (FT)
2
5
X-ray diffraction pattern. The absence of d-d CT in the region of
2
5
[
4+] 41
6
00–800 nm for all samples is due to the absence of V,
because vanadium was fully oxidized to valence 5+ during the
calcination of samples in air.
2
k -weighted Extended X-ray Absorption Fine Structure (EXAFS)
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profile of the supported catalysts and vanadium pentoxide are
shown in Figure 2C. For V O , the first coordination sphere is
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5
composed of a vanadium atom penta-coordinated by oxygen in
a tetragonal pyramid geometry, with distances of vanadium
and oxygen atoms varying between 1.58 and 2.02 Å. The
distance to the oxygen at the apex of the pyramid, forming a
double-bond, is 1.58 Å, while the distances of the four single
bonds at the base of the pyramid are 1.78, 1.78, 1.88 and
[42,43]
2
.02 Å.
The impregnated samples clearly showed a lower
intensity in the region of the first coordination sphere,
suggesting that a fraction of these bonds is absent. The
quantitative structural parameters of V atoms in the first
coordination shell of V O , [5 V]Si-FER and [5 V]Si-ITQ-6 catalysts
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
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3
3
3
3
3
4
4
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4
4
4
5
5
5
5
5
5
5
5
2
5
(Table S1) extracted from fitted EXAFS curves (Figure S4),
confirmed the decrease in the average coordination number,
representative of formation of fewer vanadium oxide agglomer-
ates and improved dispersion of sites. A less pronounced
decrease in the region of the second coordination shell was
observed, likely associated with the abundant presence of
polymeric chains of vanadium, as observed by UV-Vis spectro-
scopy (Figure 2A).
The assemblage of the results of XRD, XAS and DR-UV-Vis
spectroscopies correspondingly identified the major vanadium
species in each catalyst. The dispersion of vanadium on Si-ITQ-6
surface was straightforwardly enabled, with no evidence of
formation of V O clusters in [1 V]Si-ITQ-6 and [5 V]Si-ITQ-6 and
2
5
a predominance of monomeric and polymeric species in
relation to oxide clusters in [10 V]Si-ITQ-6. In Si-FER, a high
incidence of V O clusters on surface was identified, with most
Figure 3. (A) Nitrogen adsorption isotherms and (B) pore size distribution of
Si-FER and Si-ITQ-6 supports. (C) Nitrogen adsorption/desorption isotherms
and (D) pore size distribution of catalysts. Isotherms were displaced in Graph
C for a better visualization. A scale bar and starting point corresponding to a
2
5
of the vanadium in the [5 V]Si-FER and [10 V]Si-FER catalysts
present in this form.
Influence of surface texture and composition on vana-
dium speciation. The textural properties of the catalysts were
3
À 1
P/P =0 and volume=0 cm g was added on each isotherm for guidance.
0
evaluated by N adsorption/desorption isotherms and the data
micropore volumes remaining practically unchanged until the
[5 V]Si-FER sample. In the [10 V]Si-FER sample, a decrease of the
micropore volume is observed and is probably associated with
the obstruction of some pore entrances. By increasing the
vanadium loading in the Si-ITQ-6 catalysts, a gradual decrease
in the mesopore volume is observed, with the micropore
volume remaining unchanged. Observing the pore size distribu-
tion of these catalysts, a gradual filling of the mesopores in the
range of 2 to 10 nm can be observed. Interestingly, despite the
fact that all the catalysts presented a surface coverage of
2
are shown in Figure 3 and Table 1. The type I isotherm profile
for Si-FER support and related catalysts confirms the purely
microporous nature of these materials, and the combination of
[44]
type I and type IV isotherm profiles
for Si-ITQ-6-based
materials are consistent with the mesoporosity generated by
structural disorganization along with remaining microporosity
in the individual layers of these materials. Figure 3A and
Figure 3B show the isotherms and pore size distributions,
respectively, for the siliceous supports, Si-FER and Si-ITQ-6.
Comparing the two supports, it is noted that for Si-ITQ-6 the N
vanadium below those calculated for a monolayer of polymeric
2
À 5
À 2 [45]
adsorption shoulder at around 10 P/P and the pore family
species (10 VO nm ), as presented in the Table 1, the Si-FER
0
x
centered at around 0.8 nm disappears. The micropores in Si-FER
catalysts showed a high incidence of V O clusters, indicating a
2
5
support arise from N adsorption in the 10-membered ring (10-
random deposition of vanadium species on the Si-FER surface,
and suggesting that the modification of the textural properties
of the support is not the only parameter to be considered to
obtain a good dispersion of vanadium oxides.
2
MR) cavities formed by the condensation of FER layers (Fig-
ure S5), and the considerable decrease of this pore family is
consistent with the high degree of disorganization in Si-ITQ 6.
The remaining microporosity in Si-ITQ-6 is associated to the
presence of micropores in the detached 2D layers and to
residual condensed layers, confirmed by transmission electron
microscopy (TEM) images (Figure S6). Figure 3C and Figure 3D
show the isotherms and pore size distributions for the
vanadium supported catalysts. As observed in Table 1, increas-
ing the vanadium loading in the Si-FER catalysts results in
The surface composition of the supports and the changes
caused by vanadium deposition were monitored by in situ
Fourier-transform infrared spectroscopy of dehydrated samples
and the spectra are shown in Figure 4A. The spectra were
normalized by the band intensity appearing between 1550 and
À 1
[16]
2100 cm , regarding Si-OÀ Si vibrations. In the Si-ITQ-6-based
materials, two signals are observed in the hydroxyl region at
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increasing the probability of agglomeration of vanadium in
V O clusters.
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After the identification of the physicochemical properties of
the supports that lead to different forms of vanadium
deposition on the surface of Si-FER and Si-ITQ-6, the varied
redox activity of these materials was investigated in methanol
oxidation by in situ techniques.
Redox properties of the catalysts. Temperature-pro-
grammed reduction (TPR) profiles for catalysts and pure
vanadium pentoxide in a temperature range of 100 to 700°C
are shown in Figure 5. Profiles are normalized for a better
comparison and H2 consumption is depicted in Table 1. All
impregnated catalysts had a single reduction peak, associated
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+
4+
to reduction of V to V , as calculated by the stoichiometry of
the reaction (Table 1). Comparing the reduction peaks of
catalysts [1 V]Si-FER and [1 V]Si-ITQ-6, a very close profile with a
maximum around 445°C is perceived for both materials and,
therefore, for low vanadium loadings the dispersion is not
dependent on support texture or composition, with the redox
properties unaffected. However, by increasing the vanadium
loading, a displacement of the reduction peak to higher
temperatures is noted as vanadium polymeric chains grow and
clusters of vanadium oxide are formed. In Si-FER, the reduction
peak is gradually displaced to higher temperatures; 490°C for
[
5 V]Si-FER and 515°C for [10 V]Si-FER, approaching the first
reduction peak of bulk V O .
2
5
Methanol oxidation was used as a probe reaction for
assessing the redox properties of the catalysts. [5 V]Si-FER and
[5 V]Si-ITQ-6 catalysts were selected for the in situ Fourier-
transform infrared (FTIR) analysis during reaction, because both
had the most pronounced differences in surface species,
considering the same vanadium loading. The application of
catalytic systems involving methanol oxidation are both
fundamentally and practically interesting, because it can
generate a wide range of products, and the direct formation of
each one strongly depends on reaction conditions and catalyst
active sites. Figure 6A shows the main reaction pathways that
can occur during methanol oxidation. Basically, three different
intermediate species can be formed: methoxy groups, that lead
to formaldehyde production, dioxymethylene groups, leading
Figure 4. (A) Fourier-transform infrared spectra of dehydrated samples for
supports and catalysts. (B) Evolution of band intensity related to isolated and
H-bonded silanol groups in the supports and catalysts.
À 1
~
3740 cm , related to OÀ H vibrations of isolated silanol
[46]
groups
generated from the exfoliation of the lamellar
À 1
precursor, and a broad band at ~3665 cm related to OÀ H
[46]
vibrations on H-bonded silanol groups.
After vanadium
impregnation in Si-ITQ-6, a gradual decrease in the intensity of
bands related to these silanol groups is noted with increasing
vanadium loading, with a more pronounced decrease in the
band related to isolated silanols, as depicted in Figure 4B. In
this support, the presence of reactive isolated silanols and H-
bonded silanol groups facilitated the interaction with the
vanadium precursor during impregnation. The interaction of
metal precursors with lone pairs of electrons on the oxygen of
[47]
the silanol favors the organization of vanadium in monomeric
VO species on the surface of Si-ITQ-6, avoiding the formation
4
of V O clusters. The Si-FER-based materials presented only the
2
5
band related to vibrations of H-bonded silanol groups. The
intensity of this band remained constant with increasing
vanadium loading until the [5 V]Si-FER catalyst, and showed a
significant decrease in [10 V]Si-FER, as represented in Figure 4B,
probably associated with the interference in the signal caused
by the high predominance of V O on the surface. The results
2
5
suggest that the surface of Si-FER is composed of non-reactive
siloxane groups and the H-bonded silanol groups are inside the
micropores, poorly accessible for vanadium precursors during
impregnation, causing a random deposition on the surface,
Figure 5. H
2
temperature-programmed reduction profiles of catalysts.
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Figure 6. (A) Schematic representation of pathways during methanol oxidation over vanadium sites. Fourier-transform infrared spectra collected in situ during
methanol oxidation over (B) [5 V]Si-FER and (C) [5 V]SI-ITQ-6 catalysts. (full lines: collected under oxidant atmosphere; dotted lines: collected under inert
À 1
À 1
atmosphere). (D) Evolution observed in the intensity of bands in 2933 cm (methoxy species) and 2958 cm (methanol adsorbed) during methanol oxidation
À 1
À 1
over [5 V]Si-FER and [5 V]SI-ITQ-6 catalysts. (gray circles: methoxy at 2933 cm ; black circles: methanol at 2958 cm ; open circles: reaction at inert
atmosphere; filled circles: reaction at oxidant atmosphere). (E) Derivative curves of absorbance profiles under oxidant atmosphere observed in (D) as a
À 1
À 1
function of time-on-stream (TOS). (full lines: methoxy at 2933 cm ; dashed lines: methanol at 2958 cm ; black lines: [5 V]Si-ITQ-6; red lines: [5 V]Si-FER).
[
49]
À 1
to dimethoxymethane, or formate groups, intermediate of
methoxy species, and at 1745 cm related to C=O stretching
[8]
[50]
methyl formate, CO or formic acid production. Figure 6B and
of molecularly adsorbed formaldehyde, confirmed the obser-
2
Figure6 C show the FTIR spectra for [5 V]Si-FER and [5 V]Si-ITQ-6
catalysts, respectively, acquired during 1 h of reaction under
different temperatures in both inert and oxidizing atmospheres.
In the range of temperatures studied, the most abundant
intermediates identified were methoxy species adsorbed at
vations of high wavenumber spectra. Considering that inten-
sities are proportional to the concentration of species adsorbed
[51]
on surface, the evolution of adsorbed methanol on the silica
surface and methoxy species on V sites were monitored by
À 1
band intensities at 2958 and 2933 cm , respectively, during
vanadium sites (CH OÀ V), marked by characteristic bands at
methanol flow for 30 min, and the results are shown in
Figure 6D. In the presence of the [5 V]Si-ITQ-6 catalyst, methoxy
intermediates (gray circles) are preferentially formed when the
reaction starts, and a fast saturation of these species on active
sites is observed. After that, the remaining surface is saturated
by adsorption of molecular methanol (black circles) on silica. A
decrease of methoxy surface species is observed by increasing
the temperature of reaction, associated to the increase in the
formation of formaldehyde from methoxy, as observed by
characteristic bands of molecularly adsorbed formaldehyde
3
À 1
2
933, 2980 and 2832 cm
associated to symmetric and
asymmetric stretching, and Fermi resonance modes of CÀ H on
À
[48]
CH O , respectively. Additional bands observed at 2958 and
2
3
À 1
855 cm are related to the symmetric stretching and Fermi
resonance modes of CÀ H in adsorbed molecular CH OH on the
3
[
48]
silica surface, confirmed by the observations in the spectra of
pristine supports under the same reaction conditions (Fig-
À 1
ure S7). At 250°C, a small band at 2896 cm appears and it is
probably associated to symmetrical CÀ H stretching of surface
À
À 1
À 1
formate species (HCOO ) generated by the re-adsorption of the
(1745 cm ) and formate (2896 cm ) due to re-adsorption of
product. Under a non-oxidizing atmosphere (open circles) a
more pronounced decrease in the incidence of methoxy species
[49]
formaldehyde produced during the reaction.
In the low
À 1
wavenumber region (Figure S8), bands at 1434 and 1451 cm ,
related to symmetric and asymmetric deformation modes of
is noted, probably associated with
a
combination of
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5
+
formaldehyde formation and irreversible reduction of active
observed. Since only V sites are present in the fresh catalysts,
as observed by UV-vis spectroscopy (Figure 2A), the change in
the pre-edge intensities are probably associated to changes in
coordination of hydrated distorted sites to tetracoordinated VO4
sites. As the incidence of these sites are more pronounced in
[5 V]Si-ITQ-6, a more significant increase in the peak is
observed. During the reaction steps, the decrease in the
intensity of pre-edge peak and the displacement of the main
absorption edge and post-edge peak to lower energies, related
to a 1s to 4p transition, are indications of a decrease in the
oxidation states, as observed by some standard compounds
(Figure S10) and previously reported for vanadium-based
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sites to V in the absence of molecular oxygen. In the presence
of the [5 V]Si-FER catalyst, methanol adsorbed on silica prefer-
entially saturates the surface of the catalyst in relation to the
formation of methoxy species on vanadium, and for the same
reaction conditions the fraction of these intermediates on the
surface considerably decreases compared to the [5 V]Si-ITQ-6
catalyst. As observed by the TPR profile of [5 V]Si-FER (Figure 5),
the development of vanadium oxide agglomerates may make
inner V sites inaccessible to activate the target molecules.
Differences in reactivity of methanol become clear when
derivative curves of the absorbance for methoxy species on V
sites and methanol adsorbed on the silica surface are observed
1
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[42]
materials. At the end of the regeneration steps an intermedi-
ate profile of spectra are observed, suggesting the presence of
mixed oxidation states in the catalysts. The speciation of
vanadium in Figure 7B, determined by linear combination of
XANES spectra, revealed a nearly complete reduction of active
(Figure 6E), confirming the concurrent formation of two species
on [5 V]Si-FER, and the predominance of activation over V sites
on [5 V]Si-ITQ-6 to convert methanol to formaldehyde (Route
A).
4
+
Results of in situ XANES experiments performed during
methanol oxidation under inert atmosphere are shown in
Figure 7A. After the initial pre-treatment, the catalysts V O ,
sites to V in all catalysts studied, after approximately 15 min
of reaction in inert atmosphere. In the first minutes of reaction
5
+
(5 min), reduction of V sites were more evident in [5 V]Si-ITQ-
6 (Table S2 and Figure S11A), as a result of its effectiveness in
activating methanol to form methoxy intermediates, as
observed by FTIR spectroscopy (Figure 6). After the first cycle of
reoxidation, approximately 77% of the reduced sites are
2
5
[5 V]Si-FER and [5 V]Si-ITQ-6 were submitted to two reaction
cycles, comprising isothermal steps of reaction (30 min) and
reoxidation (30 min). During the pre-treatment (Figure S9), a
discrete increase in the intensity of the pre-edge peak of [5 V]Si-
FER and a more pronounced increase in [5 V]Si-ITQ-6, were
5
+
regenerated to V in the [5 V]Si-ITQ-6 catalyst, 58% in [5 V]Si-
Figure 7. (A) In situ XANES of V
2
O
5
, [5 V]Si-FER and [5 V]Si-ITQ-6 catalysts during methanol oxidation at 350°C under He flow and catalyst reoxidation at 350°C
st
st
under He/O flow. Four steps alternating between reaction (in black) and reoxidation (in red) of 30 min each are applied (1 R and 1 Ox are the first reaction
2
nd
nd
and reoxidation and 2 R and 2 Ox are the second reaction and reoxidation, respectively). (B) Time on stream-dependent abundance of vanadium species
on V O , [5 V]Si-FER and [5 V]Si-ITQ-6 catalysts determined by linear combination of XANES spectra during methanol oxidation under He flow and catalyst
2 5
4+ 5+
reoxidation at 350°C under He/O
flow (dark blue circles: V ; orange circles: V ).
2
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FER and 33% in V O . Most of the reduced sites (60%) in [5 V]Si-
2
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ITQ-6 were regenerated in the very first 5 min (Table S2 and
Figure S11B), and [5 V]Si-FER showed an intermediate behavior
between this catalyst and V O . Even with a high occurrence of
2
5
V O crystallites on the surface of [5 V]Si-FER a more efficient
2
5
redox cycle was evidenced when compared to bulk V O ,
2
5
probably associated with the formation of smaller crystallites.
When the reaction was carried out under an oxidizing
4
+
5+
atmosphere, a balance between V /V should be reached due
to simultaneous reduction of sites by oxidation of methanol
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[52]
and reoxidation by activation of molecular oxygen. For V O
2
5
and the [5 V]Si-FER catalyst, only small changes are observed in
the XANES spectra during methanol reactions under an
oxidizing atmosphere (Figure S12A) and after a few minutes of
4
+
5+
reaction a V /V equilibrium seems to be formed, keeping
approximately 70% of the vanadium sites in the 5+ oxidation
state in V O and, approximately 80% in [5 V]Si-FER (Figure S12B
2
5
and Table S3). Comparing the regeneration steps in these
catalysts, after reaction at different atmosphere compositions
5
+
(
Table S1 and S2) it may be noted that as V sites become
more abundant, the effectiveness of reoxidation decreases.
During reaction steps using the [5 V]Si-ITQ-6 catalyst a very fast
Figure 8. MS signal ratio of carbon monoxide and formaldehyde formed
st
during first reaction (1 R) for [5 V]Si-ITQ-6, [5 V]Si-FER and V
under (a) oxidant and (b) inert atmosphere.
2 5
O catalysts
activation of O and regeneration of reduced sites occurs, since
2
4
+
no contribution of V
species were observed in the total
spectra. By monitoring the gases exiting the XANES cell during
the reaction steps (Figure S13), formaldehyde and carbon 3. Conclusions
monoxide were identified as major products, with small
amounts of dimethyl ether, due to the low acidity present in
Vanadium-based catalysts were prepared by impregnation of
vanadyl sulfate solution on siliceous supports derived from
Ferrierite and ITQ-6 structures. By applying structural and
spectroscopic techniques, differences between the distributions
of vanadium species on the surface were observed, with a
predominance of dispersed monomeric and polymeric groups
on Si-ITQ-6 support and a tendency to agglomerate as oxide
nanoparticles on Si-FER. High surface area provided by addi-
tional mesoporosity generated on Si-ITQ-6 proved not to be the
main factor in providing a better dispersion of active species.
High incidence of isolated hydroxyl groups on the surface
facilitated an ordered anchoring of vanadium precursor species
on the support as well as stability after calcination. In the
presence of methanol this catalyst showed a fast and predom-
inant formation of methoxy intermediates until surface satu-
ration, while the [V]Si-FER catalyst showed concurrent adsorp-
tion of non-reacted methanol. Using isothermal periods at
350°C during contact with methanol under a non-oxidizing
atmosphere followed by regeneration with oxygen, we ob-
served that, even with different rates, all type of sites are able
[53–55]
the vanadium sites.
Under the oxidizing atmosphere,
formaldehyde formation is predominant in relation to carbon
monoxide. This is explained by the use of a limited O /CH OH
2
3
ratio (0.71), since oxidation to CO and CO2 are favored in
oxygen rich conditions (Table S4). Comparing the CO/H CO
2
signal ratio (Figure 8a), it can be seen that the signal tends to
stabilize around a ratio of 0.2 in all catalysts, but at different
rates. For the [5 V]Si-ITQ-6 and [5 V]Si-FER catalysts,
formaldehyde formation rapidly increases in relation to CO
formation and the ratio between the two products stabilizes
after a few minutes, while for V O signal stabilization occurred
2
5
after 20 min of reaction. The stabilization of the ratio of CO to
formaldehyde formation seems to be related with a transition
of a clean surface, where methanol is instantly activated and
converted, to a saturated surface, where concurrently vacancy
filling and methanol activation are occurring at the vanadium
sites. Under an inert atmosphere, the CO/H CO signal ratio
2
(Figure 8b) decreases, suggesting an initial increase in the rate
of formation of formaldehyde in relation to CO, followed by an
inversion point where formation of CO is growing, until a
stabilization point at a ratio around 0.85. This inversion is
probably associated with the complete consumption of oxygen
4
+
to react, since a complete reduction to V was observed and
reoxidation was limited, being sensitive to the different
vanadium species. Fundamentally, this study shows that
separately monitoring the processes of oxidation reactions in
absence of oxidant (reduction of V sites) and regeneration of
sites by molecular oxygen can aid the understanding of the
5
+
4+
atoms bound to V sites, converting them to V sites that
cannot be regenerated in the absence of molecular oxygen.
Therefore, under these reaction conditions, methanol molecules
5
+
4+
keep being converted to H CO and subsequently to CO by a
differences in the V /V
equilibrium formed during the
2
[56]
tandem dehydrogenation or by a catalytic decomposition.
combined process (reaction under oxidant atmosphere). From a
practical perspective, Si-ITQ-6 proved to be a promising sili-
ceous support to obtain a good dispersion of vanadium by
Thermal decomposition of methanol is unprobable, since the
[57]
alcohol just decomposes at temperatures above 600°C.
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applying a simple impregnation method and a low-cost salt
precursor. Herein, we based our study on the classical method-
acquisition. Phases were quantified by the Rietveld refinement
method using TOPAS® 4.2 software. The occupancy and temper-
ature factors of all atoms were fixed, and the unit cell parameters,
scale factor and atomic positions (except for special positions: 0,
1/4, 1/3, 1/2 etc.) were refined. Sample displacement, zero error and
intensity corrections were refined as well. The background was
fitted using a fifth-order Chebyshev polynomial function. Funda-
mental parameters profile fitting (FPPF) was used for the peak
profile refinements. For the [10 V]Si-ITQ-6 sample, a split-type
pseudo-Voigt (SPV) peak was used for modelling the amorphous
profile generated in the diffraction pattern due to structural
disorder. Diffuse reflectance UV-vis spectra were obtained in the
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[58]
ology for synthesis of these supports, however recent studies
have been developed to simplify the exfoliation methods in
[59–64]
lamellar zeolitic structures,
providing a good perspective
on expanding the application of these materials in catalytic
processes.
Experimental Section
Synthesis of the lamellar precursor (Si-PreFER). Approximately
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
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5
5
5
5
5
5
À 1
range from 190 to 800 cm , using a dual-beam PerkinElmer
Lambda 1050 UV/Vis/NIR spectrophotometer equipped with an
integrating sphere. The reflectance was converted using the
Kubelka-Munk equation and was plotted as a function of the
wavelength. In addition to the catalysts, the UV-Vis spectrum of
6
0 g of an aqueous solution containing 1.0 g of hydrofluoric acid
(Sigma-Aldrich, 48 wt.% in H O, purity >99.9%), 7.5 g of
2
ammonium fluoride (Sigma-Aldrich, purity >98.0%), 19.8 g of 4-
amino-2,2,6,6-tetramethylpiperidine (TMPP, TCI Chemicals, purity
2
vanadium pentoxide (V O ), prepared from calcination of VOSO ,
>
98.0%) and 7.8 g of fumed silica (Sigma-Aldrich, 200 m /g) was
2
5
4
was recorded for reference. X-ray absorption spectroscopy (XAS)
measurements were recorded at the V K-edge, in transmission
mode, at the XAFS1 beamline of Brazilian Synchrotron Light
Laboratory (LNLS). For vanadium analyses, the XAFS1 beamline was
equipped with a Si(111) monochromator, operated in Bragg mode,
for selection of the desired range of X-ray wavelengths. The
monochromator was calibrated by setting the first inflection point
at the K-edge spectrum of the corresponding metallic foil standard
prepared and kept under stirring for 3 h at 30°C. The molar
composition was: 25 SiO : 10 HF: 40 NH F: 25 TMPP: 250 H O. After
2
4
2
preparation and stirring, the solution was heat treated in a
stainless-steel autoclave at 150°C for 120 h. The solid product was
separated by filtration, washed with distilled water and dried at
8
0°C for 24 h. Preparation of supports. The microporous 3D
support, Si-FER, was prepared by calcination of Si-PreFER in air at
620°C for 6 h. A micro/mesoporous 2D support, Si-ITQ-6, was
prepared by refluxing a solution containing 190 g of distilled water,
approximately 10 g of Si-PreFER, 55 g of hexadecyltrimeth-
ylammonium bromide (Sigma-Aldrich, purity �98.0%), and 120 g
of tetrapropylammonium hydroxide (Sigma-Aldrich, 1.0 mol/L in
(5465 eV for vanadium). The powdered samples, diluted with boron
nitride, were pressed into wafers whose thickness was chosen so
that the normalized absorption jump at the edge was close to 1.
Analysis of the XAS data employed Athena and Artemis graphical
interface software, using three merged spectra to improve the
H O) at 80°C for 22 h. The resulting suspension was placed in an
2
signal-to-noise ratio. To fit the EXAFS data, the initial values of E ,
ultrasonic bath at 50°C for 2 h, and concentrated hydrochloric acid
(Sigma-Aldrich, 36.5–38.0 wt.%) was then added to the solution,
until it reached pH 2, to re-precipitate the layered material. The
solid product was separated by filtration, washed with distilled
water, dried at 80°C for 24 h, and calcined in air at 620°C for 6 h.
0
2
used for k-scaling, and S , the amplitude reduction factor, were
0
2
obtained by fitting the EXAFS results for the crystalline V O5
reference, with the number of nearest neighbor atoms (CN) and
their distance (R) fixed at their expected crystallographic values.
2
The obtained E and S values were used for modelling the EXAFS
0
0
Preparation of impregnated catalysts. The [nV]Si-FER and [nV]Si-
ITQ-6 catalysts (where n stands for 1, 5, or 10 wt.% of vanadium)
were prepared by the wet impregnation method. Typically, 1 g of
the support was added to a solution containing 50 mL of distilled
water and vanadium(IV) oxide sulfate hydrate (Sigma-Aldrich, purity
signals of impregnated catalysts. Nitrogen physisorption isotherms
of supports were performed on a MicrotracBEL BELSORP-max
instrument at liquid nitrogen temperature (196 C), with a relative
°
À 6
pressure P/P0 interval between 1×10 and 0.997. Prior to the
measurements, the samples were evacuated on a BELPREP-vac II at
200°C for 12 h. Nitrogen physisorption isotherms of vanadium
oxide supported catalysts were performed on a Micromeritics
Tristar II instrument at liquid nitrogen temperature (196 C), with a
97%, VOSO ×4H O), followed by rotary evaporation at 60°C under
4
2
vacuum until complete dryness. The samples were then calcined in
air at 500°C for 6 h. The quantity of VOSO in solution varied
4
°
À 3
according to the final wt.% of vanadium in the catalyst. A reference
sample of bulk vanadium pentoxide (V O ) was prepared from
relative pressure interval of between 1×10 and 0.998. Prior to the
2
5
measurements, the samples were evacuated at 200 C for 12 h.
Micropore volumes of all samples were determined by using the t-
plot method. Mesopore volumes were determined by difference
°
calcination of VOSO in air at 500°C for 6 h.
4
Ex situ characterization of catalysts. The vanadium content in the
catalysts was determined by Inductively Coupled Plasma-Optical
Emission Spectrometry (ICP-OES) of digested samples using an
Optima 8000 spectrometer. Acid digestion was performed by
suspending 100 mg of sample in 1 mL of distilled water, followed
by the addition of 0.1 mL of sulfuric acid (Sigma-Aldrich, nominally
between total pore volume at P/P =0.95 and the micropore
0
volumes. Pore size distributions were determined by applying the
Barrett-Joyner-Halenda (BJH) method. Transmission electron micro-
graph (TEM) images were obtained on a FEI Tecnai F30 at 300 kV.
The samples were suspended in ethanol and dispersed over a holey
carbon film grid for subsequent imaging. Temperature-pro-
grammed reduction (TPR) profiles were recorded in a Micromeritics
AutoChem II 2920. Approximately 50 mg of sample was placed on a
small bed of quartz wool in a quartz U-tube. The catalyst was
pretreated under a flow of 20 mL/min of He at 200°C for 2 h, and
9
4
1
5–98% H SO ) and 1 mL of hydrofluoric acid (Sigma-Aldrich,
2 4
8 wt.% in H O, purity >99.9%). The suspension was heated to
2
00°C during 2 h, and the resulting volume was diluted in 100 mL
of deionized water. X-ray diffraction patterns were obtained at the
XPD beamline of the Brazilian Synchrotron Light Laboratory (LNLS).
The XPD beamline was equipped with a Huber 4+2 circle
diffractometer and a Eulerian cradle (model 513) positioned ca.
then cooled to 50°C. After pretreatment, 20 mL/min of 10% H /Ar
2
was flown through the U-tube, and the sample was heated up to
7
00°C at 5°C/min. The outlet gas passed through a trap, kept
1
3 m from
a double-bounce Si (111) monochromator (λ=
cooled with acetone/liquid nitrogen, and the H consumption was
recorded by a thermal conductivity detector. Finally, the reduction
2
0.1377 nm). The data were collected in high resolution mode,
employing a Si(111) analyzer crystal and a Mythen detector. The
measurements were performed at room temperature, in the
2θ range from 7 to 40°, with, approximately, 8 min for each
profile of the reference V
O was recorded under the same
2
5
conditions applied to the supported catalysts.
ChemCatChem 2019, 11, 1–12
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In situ characterization of catalysts. In situ Fourier-Transform
Infrared (FTIR) spectroscopy experiments were recorded using a
Thermo Scientific Nicolet iS10 with a mercury cadmium telluride
(MCT) detector. Catalysts were pressed into self-supported wafers,
placed into a high temperature Harrick transmission cell equipped
with CaF2 windows, and pretreated at 400°C for 30 min under
Keywords: lamellar material · zeolite structure · vanadium ·
methanol · oxidation
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[1] V. V. Kaichev, Y. A. Chesalov, A. A. Saraev, A. Y. Klyushin, A. Knop-
5
0 mL/min of N . For surface hydroxyl monitoring, spectra were
Gericke, T. V. Andrushkevich, V. I. Bukhtiyarov, J. Catal. 2016, 338, 82–93.
2] K. Otake, Y. Cui, C. T. Buru, Z. Li, J. T. Hupp, O. K. Farha, J. Am. Chem. Soc.
2018, 140, 8652–8656.
3] F. Folco, J. Velasquez Ochoa, F. Cavani, L. Ott, M. Janssen, Catal. Sci.
Technol. 2017, 7, 200–212.
4] Q. He, J. Woo, A. Belianinov, V. V. Guliants, A. Y. Borisevich, ACS Nano
2015, 9, 3470–3478.
2
[
[
[
collected immediately after pretreatment. For methanol reaction
studies, the samples were cooled to reaction temperature (150, 250
or 350°C) and a background spectrum was collected under 50 mL/
min of N (reaction in inert atmosphere) or synthetic air (reaction in
2
oxidant atmosphere). Methanol was continuously flowed through
the cell for 1 h, by passing inlet gas through a saturator containing
1
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3
4
4
4
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4
4
4
4
4
4
5
5
5
5
5
5
5
5
[5] A. Marberger, D. Ferri, M. Elsener, O. Kröcher, Angew. Chem. Int. Ed.
2016, 55, 11989–11994; Angew. Chem. 2016, 128, 12168–12173.
the alcohol. Spectra were collected with 64 scans at a resolution of
À 1
[
6] S. S. R. Putluru, L. Schill, A. Godiksen, R. Poreddy, S. Mossin, A. D. Jensen,
R. Fehrmann, Appl. Catal. B 2016, 183, 282–290.
4
cm every 1 min. To avoid interference of bands from non-
adsorbed species on the surface, background spectra of methanol
vapor and, N2 or synthetic air flowing through the cell, without
catalyst, were collected and subtracted from results. After each
reaction, catalyst wafer was cut with a circular stamp and weighted
to determine its mass, used to normalize the spectra. In situ XANES
measurements were recorded in the XAFS1 beamline described
before. Catalyst wafers were placed into beamline reactor cell and
[
[
7] I.E. Wachs, Catal. Today 2005, 100, 79–94.
8] V. V. Kaichev, G. Y. Popova, Y. A. Chesalov, A. A. Saraev, D. Y. Zemlyanov,
S. A. Beloshapkin, A. Knop-Gericke, R. Schlögl, T. V. Andrushkevich, V. I.
Bukhtiyarov, J. Catal. 2014, 311, 59–70.
[9] C. A. Carrero, C. J. Keturakis, A. Orrego, R. Schomäcker, I.E. Wachs,
Dalton Trans. 2013, 42, 12644–12653.
[10] G. C. Bond, S. F. Tahir, Appl. Catal. 1991, 71, 1–31.
[11] C. A. Carrero, R. Schloegl, I.E. Wachs, R. Schomaecker, ACS Catal. 2014, 4,
pretreated under 50 mL/min of 40% O /He at 400°C for 30 min.
2
3
357–3380.
After pretreatment, the inlet gas was flowed through a saturator
[
[
12] H. Tian, E. I. Ross, I.E. Wachs, J. Phys. Chem. B 2006, 110, 9593–9600.
13] S. Yang, E. Iglesia, A. T. Bell, J. Phys. Chem. B 2005, 109, 8987–9000.
containing methanol at 50
°
C. Four steps alternating between
reaction and catalyst regeneration of 30 min each were applied.
The temperature was kept at 350°C during all steps. During the
reactions, the oxidant atmosphere that flowed through the
[14] A. Dinse, B. Frank, C. Hess, D. Habel, R. Schomäcker, J. Mol. Catal. A
2
008, 289, 28–37.
[15] E. V. Kondratenko, M. Cherian, M. Baerns, Catal. Today 2006, 112, 60–63.
[16] A. M. Love, C. A. Carrero, A. Chieregato, J. T. Grant, S. Conrad, R. Verel, I.
Hermans, Chem. Mater. 2016, 28, 5495–5504.
saturator containing methanol was 40% O /He, and for inert
2
atmosphere pure He was used. For the regeneration steps, the inlet
[
[
17] M. Høj, A. D. Jensen, J. D. Grunwaldt, Appl. Catal. A 2013, 451, 207–215.
18] L. Bai, K. Li, Y. Yan, X. Jia, J. M. Lee, Y. Yang, ACS Sustainable Chem. Eng.
gas bypassing the saturator was composed by 40% O /He in both
2
cases. The composition of the outlet gas was followed by mass
spectrometry. The following gases were monitored and measured
as an intensity of m/z signal: formaldehyde (m/z=30), carbon
monoxide (m/z=28), carbon dioxide (m/z=44), dimethyl ether
2
016, 4, 437–444.
[19] B. M. Reddy, I. Ganesh, E. P. Reddy, J. Phys. Chem. B 1997, 101, 1769–
774.
1
[20] R. Chlosta, G. Tzolova-Müller, R. Schlögl, C. Hess, Catal. Sci. Technol.
2011, 1, 1175–1181.
[21] A. Jentys, K. Kleestorfer, H. Vinek, Microporous Mesoporous Mater. 1999,
(
m/z=45) and methyl formate (m/z=60). Vanadium speciation
were calculated by means of linear combinations (LC) of the spectra
using the Athena graphical interface software. The standards used
2
7, 321–328.
[
22] B. Solsona, T. Blasco, J. M. López Nieto, M. L. Peña, F. Rey, A. Vidal-Moya,
for the spectra treatment were VOSO , NH VO , VO , VO , VO and
4
4
3
3/2
2
5/2
J. Catal. 2001, 203, 443–452.
metallic vanadium foil. Total species with formal charge 5+ were
calculated by sum of contributions from tetrahedrally and penta-
[23] M. Hartmann, Angew. Chem. Int. Ed. 2004, 43, 5880–5882; Angew. Chem.
004, 116, 6004–6006.
2
coordinated sites using NH VO and VO as standards, total species
4
3
5/2
[24] L. Schreyeck, P. Caullet, J. C. Mougenel, J. L. Guth, B. Marler, Microporous
Mater. 1996, 6, 259–271.
[25] F. S. O. Ramos, M. K. De Pietre, H. O. Pastore, RSC Adv. 2013, 3, 2084–
with formal charge 4+ by sum of contributions from VOSO and
4
VO2 standards and species with formal charge 3+ from VO3/2
standard.
2
111.
26] B. Solsona, J. M. Lopez Nieto, U. Díaz, Microporous Mesoporous Mater.
006, 94, 339–347.
[
2
[27] M. O. Guerrero-Pérez, R. López-Medina, E. Rojas-Garcia, M. A. Bañares,
Catal. Today 2017, 336, 210–215.
[28] A. Iglesias-Juez, M. V. Martínez-Huerta, E. Rojas-García, J. M. Jehng, M. A.
Banares, J. Phys. Chem. C 2018, 122, 1197–1205.
[29] M. Ek, Q. M. Ramasse, L. Arnarson, P. Georg Moses, S. Helveg, Nat.
Commun. 2017, 8, 305–313.
[30] Q. Shi, Y. Li, Y. Zhou, S. Miao, N. Ta, E. Zhan, J. Liu, W. Shen, J. Mater.
Chem. A 2015, 3, 14409–14415.
Acknowledgements
This research was supported by Sao Paulo Research Foundation,
FAPESP (grants #2014/20116-6, #2017/00860-0 and #2018/01258-
5
). The authors wish to thank the Brazilian Synchrotron Light
Laboratory (LNLS) in Campinas for use of the XPD (proposal XPD-
0150244) and XAFS1 (proposal 20150135) beamlines. Authors
[31] O. A. Bulavchenko, Z. S. Vinokurov, A. A. Saraev, A. M. Tsapina, A. L.
Trigub, E. Y. Gerasimov, A. Y. Gladky, A. V. Fedorov, V. A. Yakovlev, V. V.
Kaichev, Inorg. Chem. 2019, 58, 4842–4850.
2
[
[
[
32] A. Iglesias-Juez, A. Martínez-Arias, M. A. Newton, S. G. Fiddy, M.
Fernández-García, Chem. Commun. 2005, 32, 4092–4094.
33] O. Ovsitser, M. Cherian, A. Brückner, E. V. Kondratenko, J. Catal. 2009,
also acknowledge Dr. Simon H. Pang for N2 physisorption
measurements and Byung Hyun Min for TEM images.
265, 8–18.
34] J. R. Jinschek, Chem. Commun. 2014, 50, 2696–2706.
[35] Y. A. Wu, L. Li, Z. Li, A. Kinaci, M. K. Y. Chan, Y. Sun, J. R. Guest, I.
Conflict of Interest
McNulty, T. Rajh, Y. Liu, ACS Nano 2016, 10, 3738–3746.
[
[
36] P. A. Crozier, R. Wang, R. Sharma, Ultramicroscopy 2008, 108, 1432–1440.
37] A. Corma, U. Diaz, M. E. Domine, V. Fornés, Angew. Chem. Int. Ed. 2000,
39, 1499–1501; Angew. Chem. 2000, 112, 1559–1561.
The authors declare no conflict of interest.
[
38] R. Bulánek, L. Čapek, M. Setnička, P. Čičmanec, J. Phys. Chem. C 2011,
115, 12430–12438.
ChemCatChem 2019, 11, 1–12
www.chemcatchem.org
10
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
��
These are not the final page numbers!

Full Papers
[
39] F. Gao, Y. Zhang, H. Wan, Y. Kong, X. Wu, L. Dong, B. Li, Y. Chen,
[55] Z. Liu, R. Zhang, S. Wang, N. Li, R. Sima, G. Liu, P. Wu, G. Zeng, S. Li, Y.
Sun, J. Phys. Chem. C, 2016, 120, 6591–6600.
[56] P. González-Navarrete, J. Andrés, M. Calatayud, J. Phys. Chem. A 2018,
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
Microporous Mesoporous Mater. 2008, 110, 508–516.
[40] Y. M. Liu, Y. Cao, N. Yi, W. L. Feng, W. L. Dai, S. R. Yan, H. Y. He, K. N. Fan,
J. Catal. 2004, 224, 417–428.
41] A. E. Lewandowska, M. A. Banares, F. Tielens, M. Che, S. Dzwigaj, J. Phys.
122, 1104–1113.
[
[57] C. J. M. F. Fletcher, Proc. R. Soc. London 1934, A147, 119–128.
[58] A. Corma, U. Diaz, M. E. Domine, V. Fornés, J. Am. Chem. Soc. 2000, 122,
2804–2809.
[59] X. Ouyang, Y. J. Wanglee, S. J. Hwang, D. Xie, T. Rea, S. I. Zones, A. Katz,
Dalton Trans. 2014, 43, 10417–10429.
[60] I. Ogino, E. A. Eilertsen, S. J. Hwang, T. Rea, D. Xie, X. Ouyang, S. I. Zones,
A. Katz, Chem. Mater. 2013, 25, 1502–1509.
[61] X. Ouyang, S. J. Hwang, R. C. Runnebaum, D. Xie, Y. J. Wanglee, T. Rea,
S. I. Zones, A. Katz, J. Am. Chem. Soc. 2014, 136, 1449–1461.
[62] E. A. Eilertsen, I. Ogino, S. J. Hwang, T. Rea, S. Yeh, S. I. Zones, A. Katz,
Chem. Mater. 2011, 23, 5404–5408.
Chem. C 2010, 114, 19771–19776.
[42] J. Wong, F. W. Lytle, R. P. Messmer, D. H. Maylotte, Phys. Rev. B 1984, 30,
596–5610.
43] K. Lie Bøyesen, F. Meneau, K. Mathisen, Phase Transitions 2011, 84, 675–
86.
[44] P. Schneider, Appl. Catal. A 1995, 129, 157–165.
5
[
6
[
45] D. A. Bulushev, F. Rainone, L. Kiwi-Minsker, A. Renken, Langmuir 2001,
7, 5276–5282.
46] P. Hoffmann, E. Knözinger, Surf. Sci. 1987, 188, 181–198.
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
[
[47] S. Srinivasan, A. K. Datye, M. H. Smith, C. H. F. Peden, J. Catal. 1994, 145,
5
65–573.
[63] I. Ogino, M. M. Nigra, S. J. Hwang, J. M. Ha, T. Rea, S. I. Zones, A. Katz, J.
Am. Chem. Soc. 2011, 133, 3288–3291.
[64] H. Y. Luo, V. K. Michaelis, S. Hodges, R. G. Griffin, Y. Román-Leshkov,
Chem. Sci. 2015, 6, 6320–6324.
[
[
48] L. J. Burcham, M. Badlani, I.E. Wachs, J. Catal. 2001, 203, 104–121.
49] L. J. Burcham, I.E. Wachs, Catal. Today 1999, 49, 467–484.
[50] B. Kortewille, I.E. Wachs, N. Cibura, O. Pfingsten, G. Bacher, M. Muhler, J.
Strunk, Eur. J. Inorg. Chem. 2018, 2018, 3725–3735.
[
[
51] E. Garrone, C. O. Areán, Chem. Soc. Rev. 2005, 34, 846–857.
52] G. I. Panov, A. K. Uriarte, M. A. Rodkin, V. I. Sobolev, Catal. Today 1998,
41, 365–385.
[
[
53] X. L. Xue, W. Z. Lang, X. Yan, Y. J. Guo, ACS Appl. Mater. Interfaces 2017,
Manuscript received: August 23, 2019
9
, 15408–15423.
Revised manuscript received: September 20, 2019
Accepted manuscript online: September 25, 2019
Version of record online: ■■■, ■■■■
54] F. Roozeboom, P. D. Cordingley, P. J. Gellings, J. Catal. 1981, 68, 464–
472.
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FULL PAPERS
Redox Dynamics in Zeolites: Reoxi-
Dr. L. H. Vieira, Dr. L. G. Possato,
Dr. T. F. Chaves, Dr. J. J. Lee, Dr. T. P.
Sulmonetti, Prof. C. W. Jones, Prof. L.
Martins*
4
+
5+
dation of V to V was found to be
5
+
4+
the determining step to V /V
equilibrium during methanol
oxidation.
1
– 12
Insights into Redox Dynamics of
Vanadium Species Impregnated in
Layered Siliceous Zeolitic Structures
during Methanol Oxidation
Reactions
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