Efficient oxidative dehydrogenation of ethanol by VOx@MIL-101: On par with VOx/ZrO2 and much better than MIL-47(V)

Article abstract of DOI:10.1016/j.cattod.2018.07.034

The possibility to apply metal organic framework (MOF) based catalysts for oxidation reaction in gas phase was explored. Catalytic activity of the vanadium oxide catalyst incorporated in MIL-101(Cr) as support was investigated in gas phase ethanol oxidative dehydrogenation (EtOH-ODH) and compared to that of MIL-47(V) metal organic framework material containing vanadium as central metal in the framework structure and to a classical VO_x/ZrO₂ supported vanadium oxide catalyst. It was found that vanadium species, incorporated in MIL-101(Cr) support by a variant of vapor deposition method, are stabilized in the form of well dispersed VO_x species (no vanadium pentoxide clusters was detected in the catalyst). The obtained VO_x@MIL-101(Cr) catalyst exhibited high selectivity towards acetaldehyde (up to 99%) at reaction temperatures not exceeding 200 °C. The catalytic activity of VO_x@MIL-101(Cr) catalyst reached an activity level comparable to that of the classical VO_x/ZrO₂ catalyst, but the specific productivity of acetaldehyde (3 kg_AA kg_cat^?1 h^?1) was higher by 75% compared with productivity on VO_x/ZrO₂ due to much higher content of vanadium species, which could be hosted by the MOF. On the other hand, MIL-47(V) catalyst exhibited negligible activity seemingly due to coordinatively saturated character of the vanadium centers and/or too high stability of the V^IV oxidation state. This proof-of-concept study proved that application of MOF materials as host matrices for heterogeneous catalysts aiming oxidation reaction in gas phase could be efficient as demonstrated on the example of oxidative dehydrogenation of ethanol.

Full text of DOI:10.1016/j.cattod.2018.07.034

Catalysis Today xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Efficient oxidative dehydrogenation of ethanol by VO @MIL-101: On par
x
with VO /ZrO and much better than MIL-47(V)
x
2
⁎
⁎
Roman Bulánek , Pavel Čičmanec, Jiří Kotera, Ishtvan Boldog
University of Pardubice, Faculty of Chemical Technology, Department of Physical Chemistry, Studentská 573, CZ 532 10, Pardubice, Czech Republic
A R T I C L E I N F O
A B S T R A C T
Keywords:
Oxidative dehydrogenation
Vanadium
Ethanol
Acetaldehyde
MIL-101
The possibility to apply metal organic framework (MOF) based catalysts for oxidation reaction in gas phase was
explored. Catalytic activity of the vanadium oxide catalyst incorporated in MIL-101(Cr) as support was in-
vestigated in gas phase ethanol oxidative dehydrogenation (EtOH-ODH) and compared to that of MIL-47(V)
metal organic framework material containing vanadium as central metal in the framework structure and to a
classical VO
01(Cr) support by a variant of vapor deposition method, are stabilized in the form of well dispersed VO
no vanadium pentoxide clusters was detected in the catalyst). The obtained VO @MIL-101(Cr) catalyst ex-
hibited high selectivity towards acetaldehyde (up to 99%) at reaction temperatures not exceeding 200 °C. The
catalytic activity of VO @MIL-101(Cr) catalyst reached an activity level comparable to that of the classical VO
ZrO catalyst, but the specific productivity of acetaldehyde (3 kgAA kgcat
with productivity on VO /ZrO due to much higher content of vanadium species, which could be hosted by the
x
/ZrO
2
supported vanadium oxide catalyst. It was found that vanadium species, incorporated in MIL-
1
x
species
MOF
(
x
x
x
/
−
1
−1
2
h
) was higher by 75% compared
x
2
MOF. On the other hand, MIL-47(V) catalyst exhibited negligible activity seemingly due to coordinatively sa-
IV
turated character of the vanadium centers and/or too high stability of the V oxidation state. This proof-of-
concept study proved that application of MOF materials as host matrices for heterogeneous catalysts aiming
oxidation reaction in gas phase could be efficient as demonstrated on the example of oxidative dehydrogenation
of ethanol.
1. Introduction
chemical and thermal stability (up to 280 °C) to be a promising candi-
date for a multi-purpose catalyst. The higher stability of MIL-47(V) is
Metal-organic frameworks (MOFs), also known as Porous
explained by the fact that high temperature activation causes internal
III
IV
Coordination Polymers (PCPs), are crystalline coordination compounds
consisting of inorganic entities connected by means of organic bridging
ligands [1]. They feature record holding surface areas, nearing the
oxidation of V in the as-synthesized form to V , which undergoes
IV
with minor structural reorganization [20]. The structure V does not
feature explicitly opened metal sites and the capacity towards easy
4
2 −1
theoretical limits of porosity for any material at 10 m g [2], which
creates significant prospects for their practical use [3–6]. Due to rela-
tively low stability there are still no large scale uses of them, but op-
portunities for such industrial applications as small molecule storage
charge flipping decreases due to increased structural stabilization.
III
Some other MOFs like MIL-88(V) and MIL101(V) featuring V with
opened metal sites would be much better candidates for catalytic ma-
terials, but unfortunately they convert at high temperatures to MIL-
47(V) [21]. Vanadium based MOFs were demonstrated to have some
catalytic effect [22] for such reaction as epoxidation of cyclohexene
[23–25] and oxidative desulfurization [26] (however excesses of such
agents as tertbuthylperoxide tend to degrade even the most robust MIL-
47(V) or its derivatives [27]). MOFs based on mixed-metal clusters
containing vanadium were occasionally synthesized, using chiefly alu-
[
7–9], separation [10,11], heterogeneous catalysis [12–16], an recently
also for electrical accumulator technologies [17,18] are significant.
There are two principal ways in incorporating the catalytic metal in
the MOFs structure. The first one is the use of it as a part of the structure
and the second is to load and subsequently immobilize the species in
the pores of the matrix-material. Approximately a dozen of conven-
tional vanadium-only based MOFs are known [19]. Among these only
MIL-47(V) (MIL means Matérial Institut Lavoisier) with surface area up
n
minium-based prototypes, like [Al(OH)L] , where L= p-benzenedi-
carboxylate or p-naphtalenedicarboxylate [28] or MIL-53(Al) [29],
which are essentially close to vanadium analogues, but testing of such
2
−1
to 900 m g [20] and pore sizes up to 10.5 × 11 Å possesses sufficient
⁎
Corresponding authors.
E-mail addresses: roman.bulanek@upce.cz (R. Bulánek), ishtvan.boldog@gmail.com (I. Boldog).
https://doi.org/10.1016/j.cattod.2018.07.034
Received 29 March 2018; Received in revised form 1 June 2018; Accepted 13 July 2018
0920-5861/ © 2018 Elsevier B.V. All rights reserved.
Please cite this article as: Bulanek, R., Catalysis Today (2018), https://doi.org/10.1016/j.cattod.2018.07.034

R. Bulánek et al.
Catalysis Today xxx (xxxx) xxx–xxx
materials in catalysis is still in its infancy. According to some re-
searchers, until now there are practically no examples, where the me-
tals incorporated in the clusters (‘constitutional’ metal ion) would ex-
press pronounced catalytic effect [30]. While this statement is
disputable―the actual catalytic sites are associated with defects, which
are inevitably generated at elevated temperatures even in co-
ordinatively saturated MOFs like MIL-47(V) by disruption of some of
the inherently labile coordination bonds―the approach targeting the
use of the relatively non-numerous and not really modifiable SBUs as
catalytic species has limited prospects. Somewhat broader possibilities
exist, when the metal is incorporated in the organic linkers. Despite this
group of compounds is still highly exotic due to additional synthetic
steps necessary, examples of vanadium containing MOFs based on di-
pyridyl struts for oxidation of tetralin [31] or on salen-struts for
asymmetric cyanosylilation do exists [32], even if the result are far
from being breakthrough, due to the simplicity of the chosen reactions.
The second approach, namely the loading of the vanadium species
in the pores of the MOFs provides much more opportunities regarding
the choice of the catalytic species. The evident drawback is the decrease
of the internal surface area and problems with different localization and
non-uniform concentration of the species, and the material could be
viewed rather as a heterogeneous catalytic mixture than an individual
material. MOFs themselves are relatively labile compounds, while the
ODH reaction conditions often demands temperatures over 200 °C as
well as presence of oxygen and water as reaction products. MOFs with
high hydrolytic stability are relatively rare, with main classes available
being the carboxylate and azolate MOFs [33] (very recently the phos-
phonate class with appreciable porosities starts to emerge [34]). The
azolate MOFs, with the exception of the more labile tetrazolates [35],
possess inherently low oxidative stability, while among carboxylate
x 2 x 2
vanadyls play crucial role; VO /TiO and VO /ZrO catalysts exhibit
significantly higher activity than vanadyls dispersed on silica and alu-
mina supports [48,50,52,56]. To the best of our knowledge, no study on
vanadium containing MOF catalysts for ODH of ethanol in gas phase
was conducted. However, an obvious interest towards the related va-
nadium catalyzed ODH reaction of (cyclo)alkanes to respective (cyclo)
x 2
alkenes as in the Ni-doped CoO @Nu-1000(Zr) [57] and VO(acac) @
UiO-66(Zr) [58] functioning below 300 °C is emerging recently. These
compounds feature well-defined anchoring of the catalytic species to
the SBUs, which facilitates the interpretation of the catalytic test re-
sults. Unfortunately the Zr-based MOFs are not solvo-/hydrolytically
stabile enough at elevated temperatures to be used for ODH of alcohols.
In any case the elucidation of the anchoring mode and mechanism of
catalysis of the encapsulated metal species in MOFs is of a great im-
portance [59], and is topical for potential vanadium catalysts.
Proper, uniform deposition of the vanadium species in the pores of
MOFs is an evident problem. In the case of metal oxide supports the
high temperature ‘annealing’ (> 350 °C), which allows the vanadium
species to redistribute uniformly on the surface makes the differences
between deposition method not very pronounced. The widely used wet-
impregnation method, which is particularly not uniform in general
case, still ensures good results. MOFs are different from metal-oxide
matrixes in regard of much lower thermal stabilities and low affinity of
the organic moieties towards vanadium oxides, which is a hindrance for
uniform distribution of the catalyst within a surface monolayer.
Methods of low-temperature decomposition of species introduced by
wet-impregnation without harsh calcination, i.e. ‘burning’ out the or-
4 3
ganic species, do exist, namely the decomposition of NH VO
(Tdecomp > 180–220 °C [60], even if > 400 °C are typically used), which
was successfully used for the deposition of vanadium species in the
pores of MIL-101(Cr) [47]. However there is a dual-sided problem of
vanadium loading optimization dealing with uniform distribution and
low-processing temperatures in order to preserve maximally the MOF
matrix.
MOFs one of the highest hydrolytic stability belongs to MIL-101(Cr)
+
[
36,37] due to kinetic inertness of the Cr3 regarding ligand exchange
[
38]. The latter also possess very large pores, compared to an average
2
−1
MOF, excellent porosity (SBET up to 4000 m g , ∼29 Å largest ac-
cessible pore diameter as well as ∼11 and 15 Å vdW (van der Waals
dimensions) free pore opening in the pentagonal and hexagonal win-
dows respectively [39–41]) and good thermal stability (up to
Based on the above mentioned facts, we report here VO @MIL-
x
101(Cr) catalytic system using a loading method related to vapor de-
position with subsequent hydrolysis and activity testing of such catalyst
in oxidative dehydrogenation of ethanol to acetaldehyde. Catalytic
300–350 °C). Hence MIL-101 is a natural choice as a matrix material for
general purpose catalysis. A special attention is drawn by encapsulated
polyoxometallate species, POM@MIL-101 [42,43] (and refs. herein)
particularly for oxidative catalysis, including vanadium containing [Co
performance of the VO @MIL-101(Cr) material is compared to that of
MIL-47(V) MOF, where vanadium is part of MOF structure, and VOx/
ZrO2 catalysts, representing one of the most active and selective cata-
lytic system among the classical metal-oxide supported materials.
x
(
H
2
O)
2
(PW
9
O
34
)
2
]@MIL-101 investigated for photocatalytic water
[PMo 40]@MIL-101(Cr)@SBA-15 for liquid
oxidation [44], and H
6
9 3
V O
phase benzene hydroxylation by oxygen gas at 80 °C [45]. Embedded
catalysts of other types are less frequent, however the incorporation of
metal-oxides in the receives growing attention [46]. There is only one
report featuring catalytic vanadium containing materials of this type,
2. Experimental part
2.1. Materials
the VO
x
@MIL-101(Cr), demonstrated to catalyze high yield oxidations
2.1.1. Synthesis of MIL-47(V)
of sulfides to the respective sulfoxides/sulfones in polar media at room
temperature [47].
The material was synthesized using a slight modification of the
original procedure [20,61]. 1.10 g (7.00 mmol) of VCl3 and 1.16 g
(7.00 mmol) of terephtalic acid were dissolved and thoroughly homo-
genized in 25.2 ml deionized water in a 50 ml Teflon lined autoclave.
The sealed vessel was heated at 200 °C for three days. The solid product
was filtered by gravity filtration through a filter paper. The dried pro-
duct was transferred in an Erlenmeyer flask containing 40 ml of DMF
and heated under slow stirring at 80 °C for 1 h. The solid was filtered
out and washed with a small amount of DMF. The purification proce-
dure, employing heating at 80 °C, was repeated once with DMF fol-
lowed by one treatment with EtOH. After thorough final washing with
EtOH the product was dried in air at 80 °C during 16 h. Yield of the
yellow solid was 0.50 g (a few syntheses were worked up together and
the given amounts of solvents and yield correspond to a single synth-
esis. Note also that even the relatively low temperature treatment in
A promising catalytic process employing vanadium species in MOFs
is the oxidative dehydrogenation (ODH) of ethanol to acetaldehyde in
the gas phase, which can be realized at temperatures as low as 200 °C.
In addition, ethanol ODH can be also used as alternative process to the
Wacker production of acetaldehyde from ethylene [48–50]. The benefit
of using oxidative dehydrogenation is in possible implementation of the
biomass-derived bio-ethanol, reduction of ethylene demand and im-
proving the environmental friendliness by suppressing the production
of toxic chlorinated by-products, typical for the Wacker process. Va-
nadium based catalysts belong to the most investigated and promising
catalytic systems for the ODH of ethanol. Previous studies demonstrated
that catalytic activity of the catalyst depends on nature of the support
and speciation of vanadium complexes [50–54]. Regarding the activity
and selectivity pair of parameters, the tetrahedral oligomeric vanadate
species seem to be the most appropriate catalytic entities
IV
DMF was sufficient to oxidize the vanadium to V state, so the obtained
product is the conventional MIL-47(V) and not the MIL-47(V)-as pre-
cursor form).
[
50,52,55,56]. Nature of the support and its interaction with surface
2

R. Bulánek et al.
Catalysis Today xxx (xxxx) xxx–xxx
2.1.2. Synthesis of MIL-101(Cr)
2.3. Catalytic tests
The material was synthesized using a modification of a fluoride-free
method of preparation using nitric acid as an additive [62]. 2.00 g
5.00 mmol) of chromium(III) nitrate nonahydrate (Cr(NO ·9H O)
Catalytic performances of the materials were measured by a Micro-
activity Effi microreactor (PID Eng&Tech, Spain). Catalyst weight used
(
3
)
3
2
and 0.83 g of terephtalic acid (5.00 mmol) in a solution of 0.347 ml of
concentrated nitric acid (60%) in 25 ml of deionized water were thor-
oughly homogenized in a 50 ml Teflon lined autoclave. The sealed
vessel was heated for 8 h at 220 °C and cooled to room temperature
in tests was 25, 50 mg (and 75 mg for the VO
total flow rate of reaction mixture was 6 l/h STP with the O
x
/ZrO
2
-10 sample) and
/EtOH/
2
He = 2.5/5/92.5 M ratio. Reaction was investigated at the temperature
range 150–250 °C to avoid thermal decomposition of catalyst. The ob-
tained products were monitored by on-line GC instrument (Agilent
7890B). Independent blank test with empty reactor proved negligible
ethanol conversion (bellow 1%) under tested reaction conditions.
−1
(
−40 °C h
gradient). The product was filtered by gravity filtration
through a paper filter, washed thoroughly by multiple large portions of
hot (∼70-80 °C) deionized water. The same sequence of 2 × DMF and
1× EtOH washings (30 ml in each case) as described in the synthesis of
i
Conversion of ethanol (X) and selectivity values (S ) towards to the
MIL-47(V) were applied (see above). The product, after final filtration
and washing with a copious amount of EtOH was dried in air at 80 °C
during 16 h yielding 904 mg of the product in a form a fine green
powder (similarly to the previous compound, multiple syntheses were
worked up together).
main reaction products were calculated according to Sachtler et al. [63]
and supporting info (SI). For calculation of turn-over-frequency (TOF)
and productivity (P) following equations have been utilized:
0
n˙
XEtOH MV
EtOH
TOF =
mcat wV
(1)
(2)
2
.1.3. Synthesis of VO
Before the loading, the MIL-101(Cr) material was degassed at 120 °C
and 2 Torr in a Schlenk tube. The tube was cooled down and an excess
of vanadium(V) oxytriisopropoxide (VO(OiPr) ) is added (approx. 4 ml
of VO(OiPr) to 1 g of the MOF). The stirred slurry in 2 Torr vacuum
was slowly heated up avoiding bumping until slow reflux started
∼50–60 °C). The refluxing was continued for 2 h, followed by rising
the temperature to 100 °C and slow distilling off the excess of VO(OiPr)
x
@MIL-101(Cr)
0
n˙
X
EtOH
AA AA
S M
EtOH
P =
m
cat
0
3
where n˙
denotes the inlet molar flow of ethanol, XEtOH is the ethanol
EtOH
3
conversion (conversion degree equal to 15% was used), SAA is the se-
lectivity towards acetaldehyde, mcat denotes the weight of catalyst
(interpolated value for XEtOH = 15% from plot X ∼ mcat), wV is the
(
3
mass fraction of vanadium, M is the atomic weight of vanadium
V
−
1
(
the vacuum during distillation was precisely in the range of 1–2 Torr;
(50.94 g mol ) and MAA is the molar weight of acetaldehyde (44.05 g
−
1
the VO(OiPr)
loadings). After fast removal of VO(OiPr)
3
recovered by distillation was reused for subsequent
the formed powder was ad-
mol ).
3
Values of E factor for tested catalysts were calculated based on
f
ditionally left under the same temperature and pressure for 1 h and then
cooled to r.t. The loaded sample was quickly transferred in air to a
atomic balances from stoichiometric equations using all detected pro-
ducts in reaction mixture. The final expression using selectivity values
Si and molar masses of detected compounds was:
storage vial and hermetically sealed (1.95 g of VO(OiPr)
3
@MIL-101(Cr)
in a form of a light green solid was isolated, which quickly turns yellow
upon contact with moist air). Finally, the material loaded with vana-
dium species was controllably hydrolyzed by steaming in the flow of
wetted nitrogen (flow rate 25 ml/min of gas containing 0.6 vol.% of
water vapor) at 120 °C for 8 h.
M(C H ) O + MH
2
O
2
5 2
2
SC2H4 (MC2H4 + MH2O) + S(C2H5)2O
+ SAAMH2O
Ef =
SAAMAA
(3)
It must be noted that derived E
f
represents theoretical value as-
suming nearly complete consumption of ethanol via its recycling and
hence only products of the reaction are involved in the Eq. (3). Such
2.2. Materials characterization
f
definition was adopted to be comparable with E of the Wacker process
operated also with 100% conversion of utilized ethene.
Chemical analysis was performed on the ICP-OES Optima 8000
Optical Emission Spectrometer (PerkinElmer) equipped with CCD de-
tector. Meinhard and Scott-type mist chamber was used to measure the
samples. Particles size and morphology of the synthesized materials was
measured by scanning electron microscope JEOL JSM-7500 F with cold
cathode-field emission at voltage of 5 kV in secondary electron imaging
mode. Crystallinity of the samples was measured by D8-advance dif-
fractometer (Bruker AXE, Germany) with Cu Kα radiation
3. Results and discussion
3.1. Characterization of the catalysts
Content of vanadium in the as-prepared MOF catalysts was 20.1 wt.
% and 12.5 wt.% for MIL-47(V) and VO
Chromium content in VO @MIL-101(Cr) catalyst was 9.3 wt.%. SEM
micrographs of both MOFs are shown in Fig. 1. VO @MIL-101(Cr)
x
@MIL-101(Cr), respectively.
(
λ = 1.5406 Å). The diffractometer was equipped by LynxEye detector,
x
each diffractogram was measured with the step of 0.01° and integration
time of 15 s per step. Specific surface area and porosity of the materials
were estimated by N adsorption/desorption isotherms measurement
2
performed on ASAP 2020 volumetric apparatus (Micromeritics, USA).
Prior to measurement, all samples were thoroughly degassed by slow
heating (heating rate 0.5 °C/min) under turbomolecular pump vacuum
up to 220 °C and degassed at target temperature for 12 h. Surface area
was calculated according to both BET methodology for fixed 0.02 – 0.1
x
material (Fig.1A) exhibits octahedral crystallites with average 300 nm
long edge sizes, whereas MIL-47(V) catalyst has particles of cuboidal
shape with the sizes in the range from 0.5 to several micrometer.
Fig. 2 shows the powder X-ray diffraction (PXRD) patterns of both
types of MOF materials. The XRD pattern of the as-prepared MIL-
101(Cr) agrees very well with theoretical simulated pattern (shown in
x
the figure also). The diffraction pattern of the VO @MIL-101(Cr) cat-
relative pressure (p/p
0
) interval and Langmuir approach. Pore size
alyst is almost the same as that of the original MIL-101(Cr) support
evidencing that introduction of the vanadium oxocomplexes into MIL-
101(Cr) preserves the crystallinity of the matrix. The near perfect match
also proves that there are no large crystallites outside of the pores are
present (the possible nanocrystallites within the pores are not supposed
to give appreciable diffraction signals due to different species and dif-
ferent possible localizations, which precludes long-range order). How-
distribution was calculated from adsorption branch by the nonlocal
density functional theory approach by using the “N2@77 K” model for
cylindrical pores and oxide surface (Microactive data reduction soft-
ware, Micromeritics). Raman spectra were collected by Nicolet DXR2
Raman microscope (Thermo Scientific, USA) equipped by Smart ex-
citation laser with wavelength of 785 nm. Spectra were recorded by
−1
accumulation of 180 scans (scan time was 20 s, resolution of 2 cm
laser power was 2 mW).
,
ever, the XRD pattern of the VO
x
@MIL-101(Cr) catalyst after catalytic
test in ethanol ODH at 250 °C for 3 h reveals significant loss of
3

R. Bulánek et al.
Catalysis Today xxx (xxxx) xxx–xxx
x
Fig. 1. SEM micrographs of VO @MIL-101(Cr) catalyst (A) and MIL-47(V) catalyst (B).
crystallinity, with only a fraction of long-range order retained (see
pattern d in the left panel of the Fig. 2). The powder X-ray diffraction
pattern (PXRD) of the as-synthesized MIL-47(V) exhibits intense and
sharp diffraction peaks evidencing high quality of the crystals. Com-
exhibited by microporous materials and features a distinct sub-step
around relative pressure 0.15 demonstrating presence of pores on the
border between micro- and mesoporosity. It is also clearly seen from
pore size distribution (PSD) curve of this sample (Fig. 3 curve a in right
panel) exhibiting three distinct peak at 1.9, 2.1 and 2.8 nm. BET-spe-
cific surface area and total pore volume of the MIL-101(Cr) sample is
III
parison with simulated patterns of MIL-47 with the presence of V and
IV
V
clearly shown that the position of the diffraction peaks in the ob-
2
−1
3 −1
tained MIL-47(V) sample fit well with the simulated PXRD pattern of
2439 m g
and 1.21 cm g
in good agreement with the textural
IV
the conventional MIL-47(V ). It means that complete conversion of
data previously published in the literature for MIL-101(Cr) materials
[40,62], (note, that the fluoride-free MIL-101(Cr) is characterized with
slightly lower surface areas compared to the conventional synthesis, in
which HF is used as additive). Introduction of the vanadium ox-
ocomplexes significantly reduce surface area and pore volume of the
material (by 50 rel.%) as is evident from adsorption isotherm of the
III
IV
MIL-47(V ), known as MIL-47(V)-as, to MIL-47(V ) took place during
the low temperature treatment of the solid in dimethylformamide. In
addition, it is noteworthy that the after-catalysis MIL-47(V) catalysts is
x
deteriorated in much lesser extent compared to VO @MIL-101(Cr). It
exhibits still sharp diffraction lines, slightly broader than as-synthesized
one. There are a few weak broad additional peaks, which are localized
quite close to the peaks of the MIL-47(V ) form, which suggests that
reduction of vanadium could take place (the slight differences in peak
x
VO @MIL-101(Cr) sample (Fig. 3b). Interestingly, presence of the guest
III
vanadium species influences pore volumes unequally; pores at 2.1 nm
almost complete disappeared, whereas the largest pores became nar-
rower (PSD peak shifted from 2.8 to 2.6 nm) and their volume de-
creased. On the other hand, the smallest pores (with diameter 1.9 nm)
positions for these observed additional peaks and the peaks of the si-
III
mulated MIL-47(V ) could be explained by the fact that MIL-47(V) still
possess some very minor flexibility, so characteristic to MIL-53(Al)
analogue [64]).
were virtually unaffected by the presence of VO
x x
species. VO @MIL-
101(Cr) sample after catalytic tests conducted up to 250 °C exhibits low
2
−1
The nitrogen adsorption/desorption isotherms of investigated ma-
terials and calculated pore size distribution curves are presented in
Fig. 3 and textural parameters (i.e. BET and Langmuir surface areas and
total pore volumes) are summarized in Table 1. The isotherm of as-
synthesized MIL-101(Cr) sample has a shape close to type I isotherm
porosity with surface area of only 138 m g
and total pore volume
3
−1
0.08 cm g . The latter observation indicates that in current form the
catalyst is not stabile for prolonged use at 250 °C, which is consistent
with the drop of selectivity and productivity at temperatures over
200 °C. It might happen due to redistribution/leaching of vanadium
Fig. 2. PXRD patterns of the investigated MOFs. Left panel: a – simulated pattern of the MIL-101(Cr), followed by the experimental patterns of b – MIL-101(Cr), c –
III
VO
7(V)-as’ [20], b - simulated pattern of the MIL-47(V ) material, followed by the experimental patterns of the MIL-47(V) catalyst and d - MIL-47(V) catalyst after
ethanol ODH reaction at 250 °C for 3 h.
x x
@MIL-101(Cr), d - VO @MIL-101(Cr) after ethanol ODH reaction at 250 °C for 3 h. Right panel: a – simulated pattern of the MIL-47(V ) material known as ‘MIL-
IV
4
4

R. Bulánek et al.
Catalysis Today xxx (xxxx) xxx–xxx
2
Fig. 3. N adsorption/desorption isotherms of the investigated samples (left panel) and pore size distribution curves calculated by NLDFT methodology (right panel).
a – MIL-101(Cr), b – VO @MIL-101(Cr), c - VO @MIL-101(Cr)-r, d – MIL-47(V), e - MIL-47(V)-r (the suffix ‘–r’ stands for ‘after catalytic tests, i.e. reactions’).
x x
−
1
Table 1
vibrations of the terephtalate linkers and band at 867 cm
usually to the benzene ring−COO group bending vibration mode
65,66]. Besides these characteristic bands of terephtalate linker, the
spectra also exhibit bands related to presence of vanadium. Intense
assigned
Textural properties of the catalysts.
[
c
V
S
m
BET
2
S
Lang
2
V
p
g−1
m
g−1
cm g−1
3
wt.%
−1
band at 902 cm observed in the Raman spectrum of the MIL-47(V) is
caused by V =O group’s stretching vibration [67]. The Raman spec-
@MIL-101(Cr) exhibits intense
band at 910 cm accompanied by a few poorly distinguished bands in
MIL-101(Cr)
–
2439
1258
138
681
730
2720
1530
221
762
856
1.21
0.61
0.08
0.30
0.33
IV
VOx@MIL-101(Cr)
12.5
12.4
20.1
20.1
VOx@MIL-101(Cr)-ra
trum of the intermediary VO(OiPr)
3
−1
MIL-47(V)
MIL-47(V)-ra
−1
1030-920 cm
most likely caused by O = V(eOe)
spectrum of the VO @MIL-101(Cr) sample after hydrolysis reveals that
region originating from the triisopropoxide moieties
(
n
vibration [68]. The Raman
a
r denotes sample after reaction test.
x
typical Raman bands of the MIL-101(Cr) support are preserved while
the spectral features of the triisopropoxide moiety disappeared and new
bands located at 1021 and 934 cm , which are assigned to terminal
V]O and bridging VeOeV vibrations [69] respectively, showed up in
the spectrum. This observation proves that the structure of the MIL-
species obturating the pores. Adsorption isotherms recorded on MIL-
7(V) samples resemble type I shape of the isotherm according to
IUPAC nomenclature typical for ultra-microporous solids (Fig. 3, line d
4
−1
and e). As-prepared MIL-47(V) sample exhibits BET-specific surface
2
−1
3 −1
area of 681 m g
and total pore volume 0.30 cm g . Sample after
101(Cr) matrix is not damaged and complete hydrolysis of the iso-
2
−1
reaction exhibits slightly larger BET-specific surface area (730 m g
)
propoxides took place. Vanadium species are incorporated in the pores
of the MIL-101(Cr) in the form of dispersed vanadate species, no bulk
3
−1
and pore volume (0.33 cm g ). The increase of the surface area is
associated with complete removal of the residual adsorbed terephtalic
acid from the pores during the catalytic tests.
vanadium pentoxide clusters are present as proven by absence of its
−1
characteristic band at 995 cm
.2. Catalytic tests
.
The Raman spectra (Fig. 4) provide additional information about
the structure and the state of vanadium species in the composite ma-
terials. All Raman spectra exhibit intense bands at 1615 and ca.
3
−1
1450 cm
ascribed to asymmetric and symmetric −COO stretching
Vanadium species anchored on the surface of MIL-101(Cr) support
catalyzes the oxidative dehydrogenation at temperature as low as
75 °C. The effect of reaction temperature on conversion of reactant and
1
product selectivity is reported in the Fig. 5A. According to the data, at
temperatures up to 200 °C the reaction produces almost exclusively
acetaldehyde (more than 98% of selectivity) with traces of diethylether.
At higher reaction temperature, reactant conversion steeply increases
and other products, like ethene and carbon dioxide, occur with ag-
gregate selectivity not exceeding 15% at the highest temperature
(
250 °C). At this temperature, oxygen is almost completely consumed
and ethanol conversion reaches 78%. It is important to note that con-
version of ethanol at 250 °C is changing in time-on-stream, which is
attributed to the partial collapse of the MOF framework as documented
by PXRD and N adsorption isotherm measurements (see Figs. 2 and 3).
2
However, sample deactivation was not observed at 200 °C, as is illu-
strated in the Fig. 5B, where ethanol conversion and product selectivity
is shown as a function of time on stream at 200 °C. It means that VO
MIL-101(Cr) catalyst is able to activate ethanol at temperature as low as
00 °C and convert it to acetaldehyde with reasonable high rate and
x
@
2
excellent selectivity. On the other hand, despite high concentration of
vanadium in MIL-47(V) MOF, its catalytic activity was negligible.
Conversion of ethanol over 25 mg of sample did not exceed 2% even at
Fig. 4. Raman spectra of the synthesized samples. a – MIL-47(V), b - MIL-
01(Cr), c - VO(OiPr) @MIL-101(Cr), d - VO @MIL-101(Cr).
1
n
x
5

R. Bulánek et al.
Catalysis Today xxx (xxxx) xxx–xxx
Fig. 5. Catalytic performance of the 25 mg MOF catalysts in ethanol ODH. (A) Conversion of the reactant (open symbols, square – ethanol, circle - oxygen) and
selectivity toward individual products (full symbols, diamond – acetaldehyde, circle −CO , up triangle – ethene, down triangle – diethylether, square −CO) over
VO @MIL-101(Cr) as a function of the reaction temperature. (B) Ethanol conversion and product selectivities as function of the time-on-stream at 200 °C over VO
MIL-101(Cr). (C) Conversion of the reactant and selectivity toward individual products over MIL-47 as a function of the reaction temperature.
2
x
x
@
2
50 °C. The reason for such low activity is most probably the in-
Table 2
Results of catalytic tests at 200 °C compared at iso-conversion degree
iso = 15%.
IV
accessibility of active centers and/or too high stability of the V oxi-
dation state. Selectivity to acetaldehyde was also slightly lower com-
X
pared to VO
x
@MIL-101(Cr) catalyst (no higher than 96%) and ethylene
TOFb
Pc
d
Selectivity
E
f
was produced with selectivity around 4%, probably due to presence of
acidic VeOH sites on the MIL-47(V) surface [66]. Selectivity to ethene
start to grow at temperature above 200 °C, but the values did not exceed
C
%
2
H
4
(C
%
2
H
5
2
) O
CH
%
3
CHO
−
1
h
kgAA/kgcat
h
/
kg/kgAA
8%. Gobara et al. reported significant activity of MIL-101(Cr) catalyst in
a
dehydration of ethanol to ethene with 26% yield at 300 °C and im-
proved yields in the case of M@MIL-101(Cr) composites (where
M = Ni, Pt) [70].
VO /ZrO -5
0.3
0.5
0.6
1.2
2.5
1.1
98.5
97.0
98.3
55
22
29
1.7
1.2
3.0
0.425
0.441
0.427
x
2
VO
x
/ZrO
2
-10a
VOx@MIL-101
Cr)
(
x
For proper evaluation of functioning of the VO @MIL-101(Cr) cat-
alyst, it is worth to compare it with well-known benchmarks. However,
direct comparison of performances of various catalytic systems is not
straightforward due to application of different reaction conditions,
which have strong effect on the overall performance. Thus, we are
a
the detailed characterization and catalytic performance is described in Ref.
71].
[
b
the calculated specific activity is based on Eq. (1).
the calculated productivity is based on Eq. (2).
the E-factor value is calculated on the basis of Eq. (3).
c
d
going to compare and discuss the catalytic performance of the VO
x
@
MIL-101(Cr) primarily with the VO /ZrO catalytic system, which ex-
x
2
hibited very good performance at the 200 °C, investigated in our group
recently under precisely the same conditions. Comparative results of
catalytic tests in ODH of ethanol at 200 °C together with corresponding
x
The specific activity of vanadium oxide species in the VO @MIL-
101(Cr) catalyst expressed by the TOF value is roughly half in com-
parison to best performing zirconia supported VO catalyst VO /ZrO -5.
x
x
2
catalytic data for the best performing VO
x
/ZrO
2
-5 and VO
x
/ZrO
2
-10
Nevertheless this material was close to its optimal vanadium con-
centration and further increase of vanadia content led to decrease of
activity for this type of material due to formation of more polymerized
catalyst references of similar vanadium concentration, which were re-
ported in our recent article [71], are summarized in Table 2. All re-
ported data corresponds to the same conversion degree 15% obtained
by varying the weight of the catalyst samples in the reactor.
bulk V
VO /ZrO
precisely value of the specific activity) than the MIL-101 supported VO
catalyst in this contribution. It can note that similar or slightly higher
activity can be expected for VO /TiO systems, while VO /SiO and
VO /Al usually exhibit significantly lower activity (5-20-times)
[72].
2
O
5
-like species [71] as it can be demonstrated on the example of
x
2
-10 catalyst which has even lower value of TOF (or more
The main reaction product formed over the VO
00 °C was acetaldehyde, while minor amounts of ethene and diethy-
lether were also formed, but no carbon oxides or acetic acid formation
x
@MIL-101(Cr) at
x
2
x
2
x
2
were detected. The composition of the products formed over VO
catalysts under the same conditions is very close.
x
/ZrO
2
x
2 3
O
6

R. Bulánek et al.
Catalysis Today xxx (xxxx) xxx–xxx
The productivity of catalyst P (in kg of product per kg of catalyst
observed high activity of VO
x
@MIL-101(Cr) is very interesting as the
and time unit) belongs to most frequently used characteristics for the
comparison of the applicability of the catalysts in industry. The values
of calculated productivity for our set of catalysts clearly indicate that
absolute majority of vanadium catalysts used for similar reactions are
strongly bound by a metal-oxide support, while the involvement of the
latter is viewed as crucial for activation, rationalized e.g. through its
involvement in the Mars-van Krevelen mechanism. The anchorage of
the productivity of the VO
x
@MIL-101(Cr) catalyst is at value ca. 3 kgAA
and higher than productivity of both zirconia supported
samples due to its significantly higher content of VO catalytic species.
Furthermore, the calculated VO surface density for our MIL-101 sup-
−1
−1
kgcat
h
VO
tained by coordination bonding with the chromium oxo/hydroxy car-
boxylate clusters. It was suggested before that individual VO species,
x
species to the MOF support is much weaker and should be sus-
x
x
x
2
ported sample is ca. 0.65 V atoms per nm area and this is below theirs
monolayer capacity for the most supporting materials (but it must be
stressed that monolayer capacity for MOFs makes not much physical
sense, because the organic linkers, associated with a large part of the
surface area, only weakly interact with vanadium oxides and could not
be viewed as a proper support) [50,52,54]. Therefore we believe there
is still a room for the improvement of the productivity of this type of
catalysts.
though completely impractical due to considerable solubility in water,
might be as effective catalysts as their metal-oxide supported forms.
The presented case opens up an interesting opportunity for investiga-
tion of quasi-isolated VO species in relatively neutral matrices, their
x
mode of anchorage and alternative immobilization methods in a range
of modified forms.
Acknowledgements
The selectivity of catalytic process towards desired product is
practically a more important factor than the activity of catalyst. All
tested catalysts exhibit very high selectivity to acetaldehyde higher
A financial support of the Czech Science Foundation under the
project Center of Excellence No. 106/12/G015 and grant LM2015082
Center of Materials and Nanotechnologies from the Ministry of
Education, Youth and Sports of the Czech Republic is highly acknowl-
edged.
than 98% for both VO
by-products formed in the reaction are yielded by parallel reactions
catalyzed concurrently on acid sites as already documented for VO
ZrO -10 [71]. The impact of the formation of unwanted compounds in
x x 2
@MIL-101(Cr) and VO /ZrO -5. Both observed
x
/
2
the reaction is another classification criterion, which should be con-
sidered during the catalysts or catalytic processes evaluation. The so
called E-factor, representing the “weight of waste formed per one kilogram
of desired product produced”, is frequently used for the characterization
and evaluation of this aspect of catalytic processes. The values of E-
factor calculated for tested set of catalysts using Eq. 3 are presented in
the Table 2. The theoretical lower limit of the E-factor for the ethanol
oxidative dehydrogenation assuming 100% selectivity towards acet-
References
[1] B. Li, H.-M. Wen, Y. Cui, W. Zhou, G. Qian, B. Chen, Emerging multifunctional
metal-organic framework materials, Adv. Mater. 28 (2016) 8819–8860, https://doi.
org/10.1002/adma.201601133.
[
2] O.K. Farha, I. Eryazici, N.C. Jeong, B.G. Hauser, C.E. Wilmer, A.A. Sarjeant,
R.Q. Snurr, S.T. Nguyen, A.Ö. Yazaydın, J.T. Hupp, Metal–organic framework
materials with ultrahigh surface areas: is the sky the limit? J. Am. Chem. Soc. 134
(2012) 15016–15021, https://doi.org/10.1021/ja3055639.
[
3] P. Silva, S.M.F. Vilela, J.P.C. Tomé, F.A. Almeida Paz, Multifunctional metal–or-
ganic frameworks: from academia to industrial applications, Chem. Soc. Rev. 44
(2015) 6774–6803, https://doi.org/10.1039/C5CS00307E.
aldehyde is
M
H O/MAA = 0.409 kg of waste per kg of acetaldehyde for a
2
stoichiometric reaction. All tested catalysts deviate only in the order of
few percent from this theoretical limit due to their high selectivity
[
4] X.-Y. Yang, L.-H. Chen, Y. Li, J.C. Rooke, C. Sanchez, B.-L. Su, Hierarchically porous
materials: synthesis strategies and structure design, Chem. Soc. Rev. 46 (2017)
481–558, https://doi.org/10.1039/C6CS00829A.
discussed in the paragraph above. VO
value of the E-factor approximately the same as the VO
x
@MIL-101(Cr) catalyst has the
/ZrO -5 cata-
[5] B. Li, M. Chrzanowski, Y. Zhang, S. Ma, Applications of metal-organic frameworks
featuring multi-functional sites, Coord. Chem. Rev. 307 (2016) 106–129, https://
doi.org/10.1016/j.ccr.2015.05.005.
x
2
lysts, but in the same time demonstrating approx. 75% higher pro-
ductivity. It must be noted that simple comparison of the E-factor va-
lues for completely different processes can be misleading. According to
[
[
[
6] Y. Cui, B. Li, H. He, W. Zhou, B. Chen, G. Qian, Metal–organic frameworks as
platforms for functional materials, Acc. Chem. Res. 49 (2016) 483–493, https://doi.
org/10.1021/acs.accounts.5b00530.
7] W. Lu, D. Yuan, T.A. Makal, Z. Wei, J.-R. Li, H.-C. Zhou, Highly porous metal-
organic framework sustained with 12-connected nanoscopic octahedra, Dalton
Trans. 42 (2013) 1708–1714, https://doi.org/10.1039/c2dt32479b.
8] B. Li, H.-M. Wen, W. Zhou, B. Chen, Porous metal–organic frameworks for gas
storage and separation: what, how, and why? J. Phys. Chem. Lett. 5 (2014)
[
0
73], the E-factor for a two stage Wacker process is approximately
.07 kg of waste per kg of acetaldehyde, nevertheless at least 60% of
this waste is represented by chlorinated aldehydes and alkanes. From
this point of view water (more than 95%), ethene and diethylether
produced in the oxidative dehydrogenation of ethanol offer a much
cleaner process.
3
468–3479, https://doi.org/10.1021/jz501586e.
[9] J. Sculley, D. Yuan, H.-C. Zhou, The current status of hydrogen storage in meta-
l–organic frameworks—updated, Energy Environ. Sci. 4 (2011) 2721, https://doi.
org/10.1039/c1ee01240a.
4. Conclusions
[
[
10] Y. Wang, D. Zhao, Beyond equilibrium: metal–organic frameworks for molecular
sieving and kinetic gas separation, Cryst. Growth Des. 17 (2017) 2291–2308,
https://doi.org/10.1021/acs.cgd.7b00287.
11] J.-R. Li, R.J. Kuppler, H.-C. Zhou, Selective gas adsorption and separation in metal-
organic frameworks, Chem. Soc. Rev. 38 (2009) 1477–1504, https://doi.org/10.
In summary, a proof-of-concept study of a MIL-101(Cr) matrix
hosting VO
the pores as well as distinct stability of the host among other MOF
material peers, was conducted. VO @MIL-101(Cr) catalyst represents
x
species, inspired by high surface area, volume- and sizes of
1
039/b802426j.
[12] Y.-B. Huang, J. Liang, X.-S. Wang, R. Cao, Multifunctional metal–organic frame-
x
work catalysts: synergistic catalysis and tandem reactions, Chem. Soc. Rev. 46
promising and interesting catalytic system for ethanol conversion to
value-added acetaldehyde and is able to compete with vanadium cat-
(2017) 126–157, https://doi.org/10.1039/C6CS00250A.
[
[
[
13] J. Liu, L. Chen, H. Cui, J. Zhang, L. Zhang, C.-Y. Su, Applications of metal–organic
alysts deposited on traditional inorganic supports. At 200 °C, VO
x
@MIL-
frameworks in heterogeneous supramolecular catalysis, Chem. Soc. Rev. 43 (2014)
6
011–6061, https://doi.org/10.1039/C4CS00094C.
1
01(Cr) exhibited noteworthy catalytic activity and very high se-
14] T. Zhang, W. Lin, Metal–organic frameworks for artificial photosynthesis and
photocatalysis, Chem. Soc. Rev. 43 (2014) 5982–5993, https://doi.org/10.1039/
C4CS00103F.
15] A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Commercial metal–organic frame-
works as heterogeneous catalysts, Chem. Commun. (Camb.) 48 (2012) 11275,
https://doi.org/10.1039/c2cc34329k.
−
1
-1
lectivity to the desired acetaldehyde resulting in 3 kgAA kgcat
productivity, which is 75% higher compared to VO /ZrO . Raman
spectra revealed that inner surface of the structural pores of the MIL-
01(Cr) MOF is suitable for anchoring and stabilization of the vanadyl
species. Contrary to VO @MIL-101(Cr), MIL-47(V) metal organic fra-
h
x
2
1
x
[16] J. Lee, O.K. Farha, J. Roberts, K. a Scheidt, S.T. Nguyen, J.T. Hupp, Metal-organic
framework materials as catalysts, Chem. Soc. Rev. 38 (2009) 1450–1459, https://
doi.org/10.1039/b807080f.
mework material, having ‘constitutional’ vanadium ions in the struc-
ture, exhibited very poor catalytic activity, which might reflect gen-
erally low prospects for precisely this type of materials. Most probably
the low activity is associated with inaccessibility of active (vanadium)
[
17] X. Cao, C. Tan, M. Sindoro, H. Zhang, Hybrid micro-/nano-structures derived from
metal–organic frameworks: preparation and applications in energy storage and
conversion, Chem. Soc. Rev. 46 (2017) 2660–2677, https://doi.org/10.1039/
C6CS00426A.
IV
centers and/or too high stability of the V oxidation state. The
7

R. Bulánek et al.
Catalysis Today xxx (xxxx) xxx–xxx
chemistry, simulation, and powder diffraction, Angew. Chem. Int. Ed. Engl. 43
(2004) 6296–6301, https://doi.org/10.1002/anie.200460592.
[
18] H. Wang, Q.-L. Zhu, R. Zou, Q. Xu, Metal-organic frameworks for energy applica-
tions, Chem 2 (2017) 52–80, https://doi.org/10.1016/j.chempr.2016.12.002.
19] P. der Voort, K. Leus, Y.-Y. Liu, M. Vandichel, V. Van Speybroeck, M. Waroquier,
S. Biswas, Vanadium metal-organic frameworks: structures and applications, New J.
Chem. 38 (2014) 1853–1867, https://doi.org/10.1039/c3nj01130e.
[
[40] D.-Y. Hong, Y.K. Hwang, C. Serre, G. Férey, J.-S. Chang, Porous chromium ter-
ephthalate MIL-101 with coordinatively unsaturated sites: surface functionaliza-
tion, encapsulation, sorption and catalysis, Adv. Funct. Mater. 19 (2009)
1537–1552, https://doi.org/10.1002/adfm.200801130.
[41] G. Férey, C. Mellot-Draznieks, C. Serre, F. Millange, J. Dutour, S. Surblé,
I. Margiolaki, A chromium terephthalate-based solid with unusually large pore
volumes and surface area, Science (80-) 80 (309) (2005) 2040–2042, https://doi.
org/10.1126/science.1116275.
[42] D.-Y. Du, J.-S. Qin, S.-L. Li, Z.-M. Su, Y.-Q. Lan, Recent advances in porous poly-
oxometalate-based metal–organic framework materials, Chem. Soc. Rev. 43 (2014)
4615–4632, https://doi.org/10.1039/C3CS60404G.
[43] J.-W. Sun, P.-F. Yan, G.-H. An, J.-Q. Sha, G.-M. Li, G.-Y. Yang, Immobilization of
polyoxometalate in the metal-organic framework rht-MOF-1: towards a highly ef-
fective heterogeneous catalyst and dye scavenger, Sci. Rep. 6 (2016) 25595,
https://doi.org/10.1038/srep25595.
[
20] K. Barthelet, J. Marrot, D. Riou, G. Férey, A breathing hybrid organic–inorganic
solid with very large pores and high magnetic characteristics, Angew. Chemie Int.
Ed. 41 (2002) 281, https://doi.org/10.1002/1521-3773(20020118)
4
1:2<281::AID-ANIE281>3.0.CO;2-Y.
[
21] F. Carson, J. Su, A.E. Platero-Prats, W. Wan, Y. Yun, L. Samain, X. Zou, Framework
isomerism in vanadium metal-organic frameworks: MIL-88B(V) and MIL-101(V),
Cryst. Growth Des. 13 (2013) 5036–5044, https://doi.org/10.1021/cg4012058.
22] M. Vandichel, S. Biswas, K. Leus, J. Paier, J. Sauer, T. Verstraelen, P. der Voort,
M. Waroquier, V. Van Speybroeck, Catalytic performance of vanadium MIL-47 and
linker-substituted variants in the oxidation of cyclohexene: a combined theoretical
and experimental approach, Chempluschem 79 (2014) 1183–1197, https://doi.org/
[
1
0.1002/cplu.201402007.
[
23] K. Leus, I. Muylaert, M. Vandichel, G.B. Marin, M. Waroquier, V. Van Speybroeck,
P. Van Der Voort, The remarkable catalytic activity of the saturated metal organic
framework V-MIL-47 in the cyclohexene oxidation, Chem. Commun. (Camb.) 46
[44] J. Han, D. Wang, Y. Du, S. Xi, Z. Chen, S. Yin, T. Zhou, R. Xu, Polyoxometalate
immobilized in MIL-101(Cr) as an efficient catalyst for water oxidation, Appl. Catal.
A Gen. 521 (2016) 83–89, https://doi.org/10.1016/j.apcata.2015.10.015.
[45] H. Yang, J. Li, H. Zhang, Y. Lv, S. Gao, Facile synthesis of POM@MOF embedded in
SBA-15 as a steady catalyst for the hydroxylation of benzene, Microporous
Mesoporous Mater. 195 (2014) 87–91, https://doi.org/10.1016/j.micromeso.2014.
04.023.
(2010) 5085, https://doi.org/10.1039/c0cc01506g.
[
24] K. Leus, M. Vandichel, Y.-Y. Liu, I. Muylaert, J. Musschoot, S. Pyl, H. Vrielinck,
F. Callens, G.B. Marin, C. Detavernier, P.V. Wiper, Y.Z. Khimyak, M. Waroquier,
V. Van Speybroeck, P. Van Der, Voort, The coordinatively saturated vanadium MIL-
4
7 as a low leaching heterogeneous catalyst in the oxidation of cyclohexene, J.
[46] P. Falcaro, R. Ricco, A. Yazdi, I. Imaz, S. Furukawa, D. Maspoch, R. Ameloot,
J.D. Evans, C.J. Doonan, Application of metal and metal oxide nanoparticles@
MOFs, Coord. Chem. Rev. 307 (2016) 237–254, https://doi.org/10.1016/j.ccr.
2015.08.002.
[47] R. Fazaeli, H. Aliyan, M. Moghadam, M. Masoudinia, Nano-rod catalysts: building
MOF bottles (MIL-101 family as heterogeneous single-site catalysts) around vana-
dium oxide ships, J. Mol. Catal. A Chem. 374–375 (2013) 46–52, https://doi.org/
10.1016/j.molcata.2013.03.020.
[48] I. Boldog, P. Čičmanec, Y. Ganjkhanlou, R. Bulánek, Surfactant templated synthesis
of porous VO x -ZrO 2 catalysts for ethanol conversion to acetaldehyde, Catal.
Today 304 (2018) 64–71, https://doi.org/10.1016/j.cattod.2017.08.034.
[49] I.E. Wachs, B.M. Weckhuysen, Structure and reactivity of surface vanadium oxide
species on oxide supports, Appl. Catal. A Gen. 157 (1997) 67–90, https://doi.org/
10.1016/S0926-860X(97)00021-5.
[50] T.V. Andrushkevich, V.V. Kaichev, Y.A. Chesalov, A.A. Saraev, V.I. Buktiyarov,
Selective oxidation of ethanol over vanadia-based catalysts: the influence of support
material and reaction mechanism, Catal. Today 279 (2017) 95–106, https://doi.
org/10.1016/j.cattod.2016.04.042.
[51] C.A. Carrero, R. Schloegl, I.E. Wachs, R. Schomaecker, Critical literature review of
the kinetics for the oxidative dehydrogenation of propane over well-defined sup-
ported vanadium oxide catalysts, ACS Catal. 4 (2014) 3357–3380, https://doi.org/
10.1021/cs5003417.
[52] B. Beck, M. Harth, N.G. Hamilton, C. Carrero, J.J. Uhlrich, A. Trunschke,
S. Shaikhutdinov, H. Schubert, H.-J. Freund, R. Schlögl, J. Sauer, R. Schomäcker,
Partial oxidation of ethanol on vanadia catalysts on supporting oxides with different
redox properties compared to propane, J. Catal. 296 (2012) 120–131, https://doi.
org/10.1016/j.jcat.2012.09.008.
Catal. 285 (2012) 196–207, https://doi.org/10.1016/j.jcat.2011.09.014.
25] Y.-Y. Liu, K. Leus, M. Grzywa, D. Weinberger, K. Strubbe, H. Vrielinck, R. Van Deun,
D. Volkmer, V. Van Speybroeck, P. Van Der Voort, Synthesis, structural char-
acterization, and catalytic performance of a vanadium-based metal-organic frame-
work (COMOC-3), Eur. J. Inorg. Chem. (2012) 2819–2827, https://doi.org/10.
[
1
002/ejic.201101099 2012.
[
[
[
26] N.D. McNamara, G.T. Neumann, E.T. Masko, J.A. Urban, J.C. Hicks, Catalytic
performance and stability of (V) MIL-47 and (Ti) MIL-125 in the oxidative de-
sulfurization of heterocyclic aromatic sulfur compounds, J. Catal. 305 (2013)
2
17–226, https://doi.org/10.1016/j.jcat.2013.05.021.
27] K. Leus, G. Vanhaelewyn, T. Bogaerts, Y.Y. Liu, D. Esquivel, F. Callens, G.B. Marin,
V. Van Speybroeck, H. Vrielinck, P. Van Der Voort, Ti-functionalized NH2-MIL-47:
an effective and stable epoxidation catalyst, Catal. Today 208 (2013) 97–105,
https://doi.org/10.1016/j.cattod.2012.09.037.
28] O. Kozachuk, M. Meilikhov, K. Yusenko, A. Schneemann, B. Jee, A.V. Kuttatheyil,
M. Bertmer, C. Sternemann, A. Pöppl, R.A. Fischer, A solid-solution approach to
mixed-metal metal-organic frameworks - detailed characterization of local struc-
tures, defects and breathing behaviour of Al/V frameworks, Eur. J. Inorg. Chem.
(2013) 4546–4557, https://doi.org/10.1002/ejic.201300591 2013.
[
29] I. Nevjestić, H. Depauw, K. Leus, G. Rampelberg, C.A. Murray, C. Detavernier,
P. Van Der Voort, F. Callens, H. Vrielinck, In situ electron paramagnetic resonance
and X-ray diffraction monitoring of temperature-induced breathing and related
structural transformations in activated V-Doped MIL-53(Al), J. Phys. Chem. C. 120
(2016) 17400–17407, https://doi.org/10.1021/acs.jpcc.6b04402.
[
30] A. Dhakshinamoorthy, A.M. Asiri, H. Garcia, Metal-organic frameworks as catalysts
for oxidation reactions, Chem. –A Eur. J. 22 (2016) 8012–8024, https://doi.org/10.
1
002/chem.201505141.
[53] L.J. Lakshmi, Z. Ju, E.C. Alyea, Synthesis, characterization, and activity studies of
vanadia supported on zirconia and phosphorus-modified zirconia, Langmuir 15
(1999) 3521–3528, https://doi.org/10.1021/la981103m.
[54] I.E. Wachs, Raman and IR studies of surface metal oxide species on oxide supports:
supported metal oxide catalysts, Catal. Today 27 (1996) 437–455, https://doi.org/
10.1016/0920-5861(95)00203-0.
[
31] H.G.T. Nguyen, M.H. Weston, A.A. Sarjeant, D.M. Gardner, Z. An, R. Carmieli,
M.R. Wasielewski, O.K. Farha, J.T. Hupp, S.T. Nguyen, Design, synthesis, char-
acterization, and catalytic properties of a large-pore metal-organic framework
possessing single-site Vanadyl(monocatecholate) Moieties, Cryst. Growth Des. 13
(2013) 3528–3534, https://doi.org/10.1021/cg400500t.
[
32] A. Bhunia, S. Dey, J.M. Moreno, U. Diaz, P. Concepcion, K. Van Hecke, C. Janiak,
P. Van Der Voort, A homochiral vanadium–salen based cadmium bpdc MOF with
permanent porosity as an asymmetric catalyst in solvent-free cyanosilylation,
Chem. Commun. (Camb.) 52 (2016) 1401–1404, https://doi.org/10.1039/
C5CC09459C.
[55] B. Kilos, A.T. Bell, E. Iglesia, Mechanism and site requirements for ethanol oxidation
on vanadium oxide domains, J. Phys. Chem. C. 113 (2009) 2830–2836, https://doi.
org/10.1021/jp8078056.
[56] P. Čičmanec, K. Raabová, J.M. Hidalgo, D. Kubička, R. Bulánek, Conversion of
ethanol to acetaldehyde over VOX-SiO2 catalysts: the effects of support texture and
vanadium speciation, React. Kinet. Mech. Catal. 121 (2017) 353–369, https://doi.
org/10.1007/s11144-017-1169-z.
[33] C. Wang, X. Liu, N. Keser Demir, J.P. Chen, K. Li, Applications of water stable
metal–organic frameworks, Chem. Soc. Rev. 45 (2016) 5107–5134, https://doi.org/
1
0.1039/C6CS00362A.
[57] Z. Li, A.W. Peters, A.E. Platero-Prats, J. Liu, C.-W. Kung, H. Noh, M.R. DeStefano,
N.M. Schweitzer, K.W. Chapman, J.T. Hupp, O.K. Farha, Fine-tuning the activity of
metal–organic framework-supported cobalt catalysts for the oxidative dehy-
drogenation of propane, J. Am. Chem. Soc. 139 (2017) 15251–15258, https://doi.
org/10.1021/jacs.7b09365.
[58] H.G.T. Nguyen, N.M. Schweitzer, C.Y. Chang, T.L. Drake, M.C. So, P.C. Stair,
O.K. Farha, J.T. Hupp, S.T. Nguyen, Vanadium-node-functionalized UiO-66: a
thermally stable MOF-supported catalyst for the gas-phase oxidative dehy-
drogenation of cyclohexene, ACS Catal. 4 (2014) 2496–2500, https://doi.org/10.
1021/cs5001448.
[
34] T. Zheng, Z. Yang, D. Gui, Z. Liu, X. Wang, X. Dai, S. Liu, L. Zhang, Y. Gao, L. Chen,
D. Sheng, Y. Wang, J. Diwu, J. Wang, R. Zhou, Z. Chai, T.E. Albrecht-Schmitt,
S. Wang, Overcoming the crystallization and designability issues in the ultrastable
zirconium phosphonate framework system, Nat. Commun. 8 (2017) 15369, https://
doi.org/10.1038/ncomms15369.
35] V. Colombo, S. Galli, H.J. Choi, G.D. Han, A. Maspero, G. Palmisano, N. Masciocchi,
J.R. Long, High thermal and chemical stability in pyrazolate-bridged metal–organic
frameworks with exposed metal sites, Chem. Sci. 2 (2011) 1311, https://doi.org/
[
1
0.1039/c1sc00136a.
[
36] J.J. Low, A.I. Benin, P. Jakubczak, J.F. Abrahamian, S.A. Faheem, R.R. Willis,
Virtual high throughput screening confirmed experimentally: porous coordination
polymer hydration, J. Am. Chem. Soc. 131 (2009) 15834–15842, https://doi.org/
[59] C.-D. Wu, M. Zhao, Incorporation of molecular catalysts in metal-organic frame-
works for highly efficient heterogeneous catalysis, Adv. Mater. 29 (2017) 1605446,
, https://doi.org/10.1002/adma.201605446.
1
0.1021/ja9061344.
[60] A. Arya, P.K. Tripathy, D.K. Bose, Thermal decomposition of ammonium metava-
nadate in a fluidized bed reactor, Thermochim. Acta 244 (1994) 257–265, https://
doi.org/10.1016/0040-6031(94)80225-4.
[
[
[
37] A.J. Howarth, Y. Liu, P. Li, Z. Li, T.C. Wang, J.T. Hupp, O.K. Farha, Chemical,
thermal and mechanical stabilities of metal–organic frameworks, Nat. Rev. Mater. 1
(
2016) 15018, https://doi.org/10.1038/natrevmats.2015.18.
[61] S. Devautour-Vinot, G. Maurin, F. Henn, C. Serre, T. Devic, G. Férey, Estimation of
the breathing energy of flexible MOFs by combining TGA and DSC techniques,
Chem. Commun. (Camb.) 37 (2009) 2733, https://doi.org/10.1039/b822834e.
[62] T. Zhao, F. Jeremias, I. Boldog, B. Nguyen, S.K. Henninger, C. Janiak, High-yield,
fluoride-free and large-scale synthesis of MIL-101(Cr), Dalton Trans. 44 (2015)
16791–16801, https://doi.org/10.1039/C5DT02625C.
38] N.C. Burtch, H. Jasuja, K.S. Walton, Water Stability and adsorption in metal–or-
ganic frameworks, Chem. Rev. 114 (2014) 10575–10612, https://doi.org/10.1021/
cr5002589.
39] G. Férey, C. Serre, C. Mellot-Draznieks, F. Millange, S. Surblé, J. Dutour,
I. Margiolaki, A hybrid solid with giant pores prepared by a combination of targeted
8

R. Bulánek et al.
Catalysis Today xxx (xxxx) xxx–xxx
vanadium(V) oxo compounds, J. Phys. Chem. 100 (1996) 18357–18362, https://
doi.org/10.1021/jp961923c.
[63] W.M.H. Sachtler, N.H.D. de Boer, North-Holland Publishing Company, Amsterdam,
Proceedings, 3-rd International Congress on Catalysis (1964).
[
64] P. Van Der Voort, K. Leus, Y.-Y. Liu, M. Vandichel, V. Van Speybroeck,
M. Waroquier, S. Biswas, Vanadium metal–organic frameworks: structures and
applications, New J. Chem. 38 (2014) 1853–1867, https://doi.org/10.1039/
C3NJ01130E.
65] B. Civalleri, F. Napoli, Y. Noël, C. Roetti, R. Dovesi, Ab-initio prediction of materials
properties with CRYSTAL: MOF-5 as a case study, CrystEngComm 8 (2006)
[69] L.J. Burcham, X. Gao, G. Deo, I.E. Wachs, In situ IR, Raman, and UV-Vis DRS
spectroscopy of supported vanadium oxide catalysts during methanol oxidation,
Top. Catal. 11/12 (2000) 85–100, https://doi.org/10.1023/A:1027275225668.
[70] H.M. Gobara, R.S. Mohamed, S.A. Hassan, F.H. Khalil, M.S. El-Sall, Pt and Ni na-
noparticles anchored into metal–organic frameworks MIL-101 (Cr) as swift catalysts
for ethanol dehydration, Catal. Lett. 146 (2016) 1875–1885, https://doi.org/10.
1007/s10562-016-1826-2.
[
3
64–371, https://doi.org/10.1039/B603150C.
[
66] H. Leclerc, T. Devic, S. Devautour-Vinot, P. Bazin, N. Audebrand, G. Férey,
M. Daturi, A. Vimont, G. Clet, Influence of the oxidation state of the metal center on
the flexibility and adsorption properties of a porous metal organic framework: MIL-
[71] P. Čičmanec, Y. Ganjkhanlou, J. Kotera, J.M. Hidalgo, Z. Tišler, R. Bulánek, The
x 2
effect of vanadium content and speciation on the activity of VO /ZrO catalysts in
the conversion of ethanol to acetaldehyde, Appl. Catal. A Gen. (2018), https://doi.
org/10.1016/j.apcata.2018.07.040.
4
7(V), J. Phys. Chem. C. 115 (2011) 19828–19840, https://doi.org/10.1021/
jp206655y.
[72] J.-H. Lee, S.J. Schmieg, S.H. Oh, Catalytic reforming of ethanol to acetaldehyde for
Lean-NO x emission control, Ind. Eng. Chem. Res. 43 (2004) 6343–6348, https://
doi.org/10.1021/ie049680v.
[73] M. Eckert, G. Fleischmann, R. Jira, H.M. Bolt, K. Golka, Acetaldehyde, Ullmann’s
Encycl. Ind. Chem. Wiley-VCH Verlag GmbH & Co., KGaA, Weinheim, Germany,
2006, https://doi.org/10.1002/14356007.a01_031.pub2.
[
67] S. Biswas, D.E.P. Vanpoucke, T. Verstraelen, M. Vandichel, S. Couck, K. Leus, Y.-
Y. Liu, M. Waroquier, V. Van Speybroeck, J.F.M. Denayer, P. Van Der Voort, New
functionalized metal–organic frameworks MIL-47-X (X = −Cl, −Br, −CH3, −CF3,
−
OH, −OCH3) synthesis, characterization, and CO2 adsorption properties.pdf, J.
Phys. Chem. C 117 (2013) 22784–22796, https://doi.org/10.1021/jp406835n.
[68] J.-C. Panitz, A. Wokaun, Effects of excitation wavelength on the Raman Spectra of
9