Isostructural metal-carboxylates MIL-100(M) and MIL-53(M) (M: V, Al, Fe and Cr) as catalysts for condensation of glycerol with acetone

Article abstract of DOI:10.1016/j.apcata.2016.11.006

The synthesis of solketal from acetone and glycerol (I) was investigated in the presence of the isostructural MOFs of the families MIL-100(M) and MIL-53(M) (M = V, Al, Fe and Cr) and mixed MIL-53(Al,V) (Al/V – 100/0, 75/25, 50/50, 25/75 and 0/100 atom/atom). The main products were a five-membered solketal (2,2-dimethyl-1,3-dioxane-4-methanol, (II)) and a six-membered acetal (2,2-dimethyl-dioxane-5-ol, (III)). It was demonstrated that the reaction rate and isomer selectivity depend on different parameters such as the type of metal ion, the length of the M-O bond, the rate constant for the exchange of the water molecules from the first coordination sphere of a metal ion and the value of the zero point of the surface charge (pH_PZC). Investigation of mixed MIL-53(Al,V) shows that the reaction rate and selectivity towards (II) increase with increasing V³⁺ content in MIL-53(Al,V). V-containing MOFs possess a high activity and selectivity at 25 °C. The efficiencies of MIL-100(V) and MIL-47(V) were higher than those of H₂SO₄, SnCl₂ and p-toluenesulfonic acid at 25 °C. The MIL-100(V) catalyst showed good reusability for 4 catalyst recycles.

Full text of DOI:10.1016/j.apcata.2016.11.006

Accepted Manuscript
Title: Isostructural metal-carboxylates MIL-100(M) and
MIL-53(M) (M: V, Al, Fe and Cr) as catalysts for
condensation of glycerol with acetone
Author: Maria N. Timofeeva Valentina N. Panchenko Nazmul
Abedin Khan Zubair Hasan Igor P. Prosvirin Sergey V.
Tsybulya Sung Hwa Jhung
PII:
S0926-860X(16)30545-2
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2016.11.006
APCATA 16054
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
11-7-2016
4-11-2016
7-11-2016
Please cite this article as: Maria N.Timofeeva, Valentina N.Panchenko, Nazmul
Abedin Khan, Zubair Hasan, Igor P.Prosvirin, Sergey V.Tsybulya, Sung Hwa Jhung,
Isostructural metal-carboxylates MIL-100(M) and MIL-53(M) (M: V, Al, Fe and Cr)
as catalysts for condensation of glycerol with acetone, Applied Catalysis A, General
http://dx.doi.org/10.1016/j.apcata.2016.11.006
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Isostructural metal-carboxylates MIL-100(M) and MIL-53(M) (M: V, Al,
Fe and Cr) as catalysts for condensation of glycerol with acetone
Maria N. Timofeeva1*, Valentina N. Panchenko1, Nazmul Abedin Khan2,
Zubair Hasan2, Igor P. Prosvirin1, Sergey V. Tsybulya1, Sung Hwa Jhung2*
1
Boreskov Institute of Catalysis SB RAS, Prospekt Akad. Lavrentieva 5, 630090, Novosibirsk,
Russian Federation
2
Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National
University, Sankyuck-Dong, Buk-Ku, Daegu 702-701, Republic of Korea
*Corresponding authors
M.N. Timofeeva
Tel.: +7-383-330-7284
Fax: +7-383-330-8056
E-mail: timofeeva@catalysis.ru
Address: Boreskov Institute of Catalysis SB RAS, Prospekt Akad. Lavrentieva 5, 630090,
Novosibirsk, Russian Federation
S.H. Jhung
Tel: +82-53-950-5341
Fax: +82-53-950-6330
e-mail: sung@knu.ac.kr
Address: Department of Chemistry and Green-Nano Materials Research Center, Kyungpook
National University, Sankyuck-Dong, Buk-Ku, Daegu, 702-701, Republic of Korea

Graphical abstract
Research highlights
 Synthesis of solketal from glycerol and acetone was studied over MIL-100(M) and MIL-
53(M) (M = V, Al, Fe, Cr).

Reaction was studied at acetone/glycerol 4.5 mol/mol ratio in acetonitrile as reaction
media and 700C
 The yield of solketal depends on the type of metal and decreases as follows: V3+ > Al3+ >
Fe3+ > Cr3+
 The increase in V3+ content in mixed MIL-53(Al,V) leads to rise reaction rate and selectivity
reaction.
 Activities of MIL-47(V) and MIL-100(V) were higher in compared with H2SO4, SnCl2 and
p-toluenesulfonic acid at 25oC.

Abstract
The synthesis of solketal from acetone and glycerol (I) was investigated in the presence
of the isostructural MOFs of the families MIL-100(M) and MIL-53(M) (M = V, Al, Fe and Cr) and
mixed MIL-53(Al,V) (Al/V – 100/0, 75/25, 50/50, 25/75 and 0/100 atom/atom). The main
products were a five-membered solketal (2,2-dimethyl-1,3-dioxane-4-methanol, (II)) and a six-
membered acetal (2,2-dimethyl-dioxane-5-ol, (III)). It was demonstrated that the reaction rate and
isomer selectivity depend on different parameters such as the type of metal ion, the length of the M-
O bond, the rate constant for the exchange of the water molecules from the first coordination sphere
of a metal ion and the value of the zero point of the surface charge (pHPZC). Investigation of mixed
MIL-53(Al,V) shows that the reaction rate and selectivity towards (II) increase with increasing V3+
content in MIL-53(Al,V). V-containing MOFs possess a high activity and selectivity at 25 °C. The
efficiencies of MIL-100(V) and MIL-47(V) were higher than those of H2SO4, SnCl2 and p-
toluenesulfonic acid at 25 °C. The MIL-100(V) catalyst showed good reusability for 4 catalyst
recycles.
Keywords: Metal-organic frameworks; MIL-53; MIL-100; Glycerol; Acetone; Solketal
1. Introduction
The field of glycerol use as a raw material for the production of various chemicals is
currently advancing actively. One of the directions of this field is the synthesis of cyclic acetals and
ketals from glycerol with aldehydes and ketones that can be used as chemical
intermediates/additives for fuels and biofuels. Condensation of glycerol with acetone (Scheme 1)
leads to the formation of a solketal (II) that can be used as a fuel additive for improving cold flow,
ignition properties and the cetane number of fuels [1-3]. Traditionally, the reaction of glycerol with
acetone has been carried out in the presence of Brønsted and Lewis acids [4]. p-Toluenesulfonic

acid [5], H2SO4 [5], Amberlyst-15 and Amberlyst-36 [6-7], silica supported heteropoly acids [8],
mesoporous silicates containing arylsulfonate groups [9] and zeolite [10-11] have been used as
Brønsted type catalysts. At the same time, Ni-Zr supported on a mesoporous activated carbon
catalyst [12], M-AlPO4 (M – Co, Ni, Cu and Zn) [13] and M-TUD-1 (M: Zr, Hf and Sn) [14] were
suggested for use as Lewis-type catalysts. The high activity of these systems was explained by the
simultaneous presence of both Lewis and Brønsted acid sites[14]. We note that the synthesis of
glycerol cyclic acetals from glycerol and ketones was carried out over SnCl2 [5] and ZnCl2 [15] at
room temperature. Here, we would like to demonstrate the potential application of porous
metal-carboxylates in this reaction.
Currently, metal-organic frameworks (MOFs) are widely used as catalysts in acid catalysis
[16-19]. The presence of coordinatively unsaturated metal sites (CUS) gives rise to the Lewis acidity
of MOFs. The ability to vary both textural and structural properties allows variation in the amount
and dispersion of CUS in the framework. At the same time, a change in the nature of the metals and
organic ligands permits the adjustment of Lewis acidity [18].
Moreover, several MOFs possess original Brønsted acid sites (BAS) [18, 21]. Thus, the
original BAS are present in the rod-like 1D inorganic network MIL-53 family of materials
[M3+(OH)(BDC)], where BDC is 1,4-benzenedicarboxylate, and M is Al3+, Cr3+, Fe3+, In3+, Ga3+
(also called IM-19) and V3+ (also called MIL-47(V)) [22-24]. Their BAS are formed by the bridging
H
O
H
O
M
M
Si
Al
2-OH-groups in the
groups that are similar to the
groups in the H-
form of zeolites. We note that after thermal activation at 300 °C, MIL-47(V3+) transforms into MIL-
47(V4+) (V4+(O)(BDC)), which possesses corner-sharing oxo-groups instead of μ2-OH groups
linking the metal atoms [24]. All of these unique features provide researchers with ample
opportunity to control the catalytic behaviour of these complexes. According to Ravon et al. [23],

the activity of MIL-53 depends on the nature of the metal. For example, in the tert-butylation of
biphenyl, MIL-53(Al) was nearly inactive in contrast to MIL-53(Ga). Brønsted sites were also found
in the structure of MIL-100(M). Thus, the existence of structural M-OH groups and -OH groups of
М···H2O complexes in MIL-100(Al) and MIL-100(Cr) was confirmed by IR spectroscopy using CO
as the probe molecule [25-26]. The effect of Brønsted acid sites on the catalytic activity of MIL-
101(Cr) was demonstrated in the condensation reaction of aldehydes with alcohols [27].
In our investigation, we used the isostructural MOFs such as the MIL-100(M) and MIL-
53(M) (M - V, Al, Fe and Cr) materials. First, we suggested that the reaction of glycerol with
acetone should depend on the type of metal ions in the MOFs. Recently, the effect of the nature of
the metal on the catalytic activity of MOF-74(Co, Cu, Mg, Ni) and MIL-100(Al, Cr, Sc, V) was
demonstrated in the reaction of 3,4-dihydro-2H-pyran with alcohols [28]. Moreover, these materials
are good candidates for our investigation because their textural properties are different, which can be
important for the access of the reactants to the active sites.
Mixed MIL-53(Al,V) (Al/V – 100/0, 75/25, 50/50, 25/75 and 0/100) were another objectives
of our investigation. The change in chemical composition should change their structural, textural
and acidic properties. These expectations follow from the work of Dhakshinamoorthy, Asiri, and
Garcia [29-30]. They demonstrated that Fe-doping into the framework of MFM-300(Ga2), (MFM =
Manchester Framework Material) allows for an increase in the reaction rate in the acetylation of
benzaldehyde by methanol and epoxide ring-opening of different organic substrates due to the
appearance of acid sites. Therefore, the main purpose of our study was to establish a correlation
between the nature of the metal ions and the catalytic behaviour of these samples. A combination of
spectroscopic and catalytic methods was used for the analysis of the main factors that can affect the
reaction rate and isomer selectivity.
2. Experimental

2.1. Materials
Terephthalic acid (H2BDC) was purchased from Sigma-Aldrich. Glycerol and acetone were
purchased from Aldrich. Al(NO3)3 9H2O (98 wt.%, Junsei), 1,3,5-benzenetricarboxylic acid
(H3BTC), 1,3,5-trimethyl-benzenetricarboxylate (Me3-BTC, 98%, Aldrich), ortho-phosphoric acid
H3PO4 (85 wt%, Merck), sodium hydroxide (NaOH, 4 M), nitric acid (HNO3, 60 wt.%), CrO3 (98%,
Junsei), and hydrofluoric acid (HF, 48%, OCI Company Ltd.) were used without any further
purification.
Samples of MIL-53(Al), MIL-47(V), MIL-53(Cr), MIL-100(Al), MIL-53(Fe) and MIL-
53(Al/V) were prepared by the procedures previously described in the literature [31-34]. The MIL-
53 samples were crystallized through microwave heating to take advantage of rapid syntheses [32].
The obtained samples were purified to remove the unreacted H2BDC from the as-synthesized
samples. The purification was carried out at 70 °C using an ultrasonic generator (VC × 750, max.
power 750 W, Sonic & Materials, Inc.) in the presence of DMF according to the previously reported
purification method [35]. Additionally, the as-synthesized MIL-100 samples were treated with hot
water/ethanol mixture to remove the unreacted H3BTC. Textural properties and XRD patterns of
MOFs are shown in Table 1 and Figs. S1-S6 (supporting information), respectively. The chemical
composition of the samples is shown in Table 2.
2.2. Instrumental measurements
The porous structure of the materials was determined from the of N2 adsorption isotherm at -
196 °C using a Micrometrics ASAP 2400 instrument. The Brunauer-Emmett-Teller specific surface
area (SBET) was calculated from the adsorption data over the relative pressure range between 0.05
and 0.20. The total pore volume (V) was calculated from the amount of nitrogen adsorbed at a
relative pressure of 0.99. The X-ray diffraction patterns were measured using аn X-ray
diffractometer (ThermoARL) with Cu-K ( = 1.5418 Å) radiation. The POLYCRYSTAL program

was used to refine the unit cell parameters using the least squares method [36]. Chemical analyses
were performed by inductively coupled plasma-atomic emission spectrometry (ICP-AES) using a
PERKIN-ELMER instrument OPTIMA 4300.
The oxidation state of the metal ions in MIL-53(V, Al, Fe and Cr) was investigated by IR
spectroscopy using PhCN as probe molecule. The samples were pre-treated within the cell by
heating under vacuum for 3 h at 200 °С prior to the adsorption experiments. Then, the samples were
exposed to saturated PhCN vapours at room temperature. The sample was then transferred from the
cell to a DRIRT cuvette under argon. FT-IR spectra were recorded using a Shimadzu FTIR-8300
spectrometer in the 400-6000 cm-1 range with a resolution of 4 cm-1.
XPS spectra were recorded using a SPECS spectrometer with PHOIBOS-150-MCD-9
hemispherical energy analyser and an X-ray monochromator FOCUS-500 (AlK irradiation, h =
1486.74 eV, 100 W). The binding energy scale was preliminarily calibrated using the positions of
the peaks of the Au4f7/2 (84.0 eV) and Cu2p3/2 (932.67 eV) core levels. The samples were supported
onto a double-sided conducting copper scotch tape. For the wide scan and narrow spectral regions,
the pass energy values of the analyser were 50 eV and 10 eV, respectively.
The point of zero charge of a MIL-100(M) suspension (pHPZC) was determined by mass
titration as described in the literature [37]. A pH meter was calibrated using pH 1.68 and 6.86
buffers. All measurements were carried out using distilled-deionized water.
2.3. Catalytic tests
The reaction of glycerol with acetone was carried out at 70 °C in a glass vial (15 cm3)
equipped with a magnetic stirrer. Prior to the reaction, the MOFs were treated at 200 °C for 2 h
under vacuum to remove the residual water in the samples. The standard procedure was as follows:
2.17 mmol of glycerol, 10.19 mmol of acetone in 5 ml of acetonitrile and 0.04 g of catalyst were
introduced into the reactor. At different time intervals, aliquots were taken from the reaction mixture
and analysed after separation by centrifugation of the catalysts. The products were analysed using

gas chromatography (Agilent 7820) with a flame ionization detector on a capillary column (HP-5).
Dodecane was used as the internal standard.
3. Results and discussion
3.1. Catalytic properties of MIL-100(M) and MIL-53(M)
The reaction of glycerol with acetone in the presence of the isostructural families MIL-
100(M) and MIL-53(M) (M: V3+, Al3+, Fe3+ and Cr3+) was investigated at 70 °C at a
glycerol/acetone molar ratio of 4.7 using acetonitrile as the solvent. The results of the catalytic
performance of the MOFs are presented in Table 3. Examination of these data shows that five-
membered solketal (II) and six-membered acetal (III) are the main products (Scheme 1). The
heterogeneous character of the reactions was confirmed experimentally. An illustration of a typical
experiment in the presence of MIL-100(Al) is shown in Fig. 1. The MIL-100(Al) sample was
filtered off after 35 min of reaction, when the conversion of glycerol was approximately 33.7%.
Then, the filtrate without the catalyst was stirred at 70 °C. The reaction could not proceed in the
absence of a catalyst.
According to the experimental data, the nature of the metal ion in the SBUs affects the
catalytic behaviour of the MOFs. The highest conversion of glycerol is observed in the presence of
MIL-100(V) (85.4%) and MIL-47(V) (75.9%), while in the presence of MIL-100(Cr) and MIL-
53(Cr), the conversion of glycerol was the lowest (4.2 and 1.6%, respectively) (Table 3). Note that
the low reaction rate is also observed in the presence of MIL-101(Cr). In general, the conversion of
glycerol decreases in the following order:
V3+ > Al3+ > Fe3+ > Cr3+.
We can assume that this trend is related to the difference in the surface acidities of the samples that
generally play an important role in determining their catalytic properties. The surface acidities of the
MOFs can be estimated from the values of the isoelectric point or zero point of the charge of the
surface (pHPZC). We estimated the pHPZC values for MIL-100(M) in an aqueous solution using the

method of mass titration. This method was suggested by Noh and Schwarz for the determination of
the point of zero charge of oxides and carbons modified by HNO3 [37-38]. Plots of pH versus the
mass percentage of MIL-100(M) in an aqueous solution are shown in Fig. 7S (Supporting
information). The plateau in the mass titration curve is the pH corresponding to pHPZC. The pHPZC
values indicate the presence of Brønsted acidity that can arise both from the coordinated hydroxyl
groups in the framework (M-OH) and water molecules adsorbed on the metal sites. We note that the
change in the selectivity towards (II) in the course of the reaction in the presence of MIL-47(V3+)
also indicates the formation of Brønsted acid sites due to the water formation (Fig. 1). Thus, the
pHPZC values are evidence that the acidity of MIL-100(M) decreases in the following order:
MIL-100(V) > MIL-100(Al) > MIL-100(Fe) > MIL-100(Cr).
This order is in accordance with the variation of their catalytic activities (Fig. 2). It is noteworthy
that MIL-100(V) exhibits a high activity at 25 °C (Table 4) due to the high pHPZC value.
However, water can also have a negative effect on the activity of MIL-100(M) and MIL-
53(M). According to Helm et al. [39] and Xu et al. [40], the rate constants for the exchange of the
water molecules from the first coordination sphere of a given metal ion are different and decrease in
the order:
V3+ > Fe3+ > Al3+ >> Cr3+
According to spectroscopic investigations, the interaction of the water molecules with Cr3+ is much
stronger than that with Fe3+ [41-43]. This result is also in agreement with DFT calculations. The
binding energy for the water adsorption on MIL-100(Cr) was higher (94.7 kJ/mol) than that on MIL-
100(Fe) (75.5-80 kJ/mol) [44-45]. Based on this phenomenon, we can suggest that the exchange of
the adsorbed water molecules by the reactants can affect the activity of MIL-53(M) and MIL-
100(M). Therefore, we can assume that the rate of the exchange of the water molecules by the
reactants also determines the catalytic activity of MIL-53(M) and MIL-100(M) (Table 3). Moreover,

according to a previous study [46], adsorption of organic molecules on MIL-100(Al, Fe, Cr)
depends on the nature of the metal ions and is correlated with the charge of the surface (pHPZC).
Isomer selectivity also depends on the nature of the metal and decreases in the following
order: V3+ > Al3+ > Fe3+ > Cr3+. Analysis of the literature allows us to suggest that isomer
selectivity depends on the length of the M-O bond in SBU of MIL-53(M) and MIL-100(M). The
lengths of the M-O bond in MIL-53(M) and MIL-100(M) change in the following orders (Å):
MIL-53(Cr) (2.08 [22]) > MIL-53(Al) (1.82-2.00 [47]) > MIL-47(V) (1.946-1.998 [48])
MIL-100(Cr) (2.18 [49]) > MIL-100(Fe) (2.065 [50]) > MIL-100(Al) (1.831-1.995 [51])
As shown in Fig. 3, the larger the length of the M-O bond is, the higher is the selectivity towards the
six-membered acetal (III). Based on our experimental data, the reaction mechanism in the presence
of Brønsted acids [4], and theoretical calculations [52-53], we can suggest that the length of the M-
O bond is an important parameter for the rearrangement of the intermediates to the products with
five- and six-membered rings. Initially, the acetone carbonyl group is activated by the acid sites of
the catalyst, and then the glycerol terminal -OH group attacks the carbonyl carbon with formation of
a hemiacetal intermediate, which then undergoes cyclization with elimination of water. We can
assume that the short the M-O bond favours the attack of the secondary glycerol -OH group to the
carbonyl carbon of the intermediate and the interaction between the MOF oxygen atom and the
glycerol terminal -OH group that should lead to the formation of a five-membered ring. At the same
time, the long M-O bond favours the attack of the glycerol primary -OH group to the carbonyl
carbon of the intermediate that should lead to the formation of a six-membered ring. This assertion
is in agreement with our experimental data (Table 3, Fig. 3).
It is interesting to compare the effect of the textural properties of MIL-100(M) and MIL-
53(M) on the reaction rate and isomer selectivity. According to the experimental data (Table 3),
glycerol conversion depends strongly on the porosity of the MOFs. In the presence of all
mesoporous MIL-100(M) samples, glycerol conversion is higher than that for the microporous MIL-

53(M). Thus, in the presence of MIL-100(Al)/MIL-53(Al) and MIL-100(V)/MIL-53(V), glycerol
conversion values are 44.2%/12.5% and 84.4%/75.9%, respectively, at 70 °C. However, the
differences in the selectivity towards (II) are negligible. The effect of the porosity on isomer
selectivity and, therefore, the accessibility of the reactants can be revealed at 25 °C (Table 4). In the
presence of mesoporous MIL-100(V), the selectivity towards (II) is higher (98%) than that for
microporous MIL-53(V) (87%).
3.2. Investigation of mixed MIL-53(Al,V)
Hereinafter, our main attention was focused on the investigation of the catalytic behaviour of
isostructural MIL-53(Al,V) samples with mixed metal-oxide clusters in SBUs. These samples were
synthesized using a modified procedure reported by Mitchell et al. [34]. Purification of the as-
synthesized samples from the unreacted H2BDC was carried out by washing with DMF. The Al/V
molar ratios in the precursors for the syntheses were 100/0, 75/25, 50/50, 25/75 and 0/100. The
chemical composition and textural data of MIL-53(Al,V) samples are shown in Tables 2 and 3. The
data in Table 3 show that the Al/V molar ratios for the synthesized MIL-53(Al,V) materials are
slightly different from the expected ratios, but a general tendency is observed. All materials are
microporous and exhibit high nitrogen adsorption (Fig. 1S, supporting information). Based on the
XRD analysis, the framework topology of all samples is identical to the MIL-53 structure, and the
lattice parameters depend on the Al/V molar ratios (Fig. S6, supporting information). X-ray
photoelectron spectroscopy (XPS) data indicate that the vanadium oxidation state in MIL-53(Al,V)
samples is 3+ (Fig. 8S, supporting information). DR-UV-vis spectroscopy (Fig S9, supporting
information) and IR spectroscopy using PhCN as the probe molecule (Fig. S10, supporting
information) also indicate that the vanadium oxidation state is 3+. Moreover, IR spectroscopy data
indicate the presence of -OH groups in the MIL-53(Al,V) samples (Fig. S11, supporting
information). In the spectra of the samples, bands at 512 and 901 cm-1 that may be attributed to the
γ(V-OH) deformation mode and δ(OH) [54], respectively, are observed. Thus, the removal of the

unreacted H2BDC from the samples by washing with DMF allows the preservation of the V3+
oxidation state and, therefore, chains of µ-OH corner-sharing MO6-octahedra ([M3+O4(OH)2]) that
can act as acid sites.
The reaction of glycerol with acetone in the presence of MIL-53(Al,V) was investigated at
25 and 70 °C at a glycerol/acetone molar ratio of 4.7 using acetonitrile as the solvent. The reaction
also has the heterogeneous character that was confirmed in special experiments in the presence of
MIL-47(V) (Fig. 1). The MIL-47(V) sample was filtered off after 20 min of reaction, when the
conversion of glycerol was approximately 43.5%. Then, the filtrate without the catalyst was stirred
at 25 °C for 65 min. The reaction could not proceed in the absence of a catalyst.
It is reasonable to suggest that the Al/V molar ratio affects the catalytic properties of the
MIL-53(Al,V) samples. According to the experimental data shown in Table 3 and Fig. 4A, glycerol
conversion and selectivity towards (II) linearly increase from 12.5 to 75.9% and from 90.1 to 97.5%,
respectively, as the vanadium content increases from 0 (MIL-53(Al)) to 100% (MIL-47(V)),
respectively. These changes are in agreement with the IR spectroscopy data obtained using PhCN as
the probe molecule. Experimentally, the increasing V content in MIL-53(Al,V) leads to an increase
in the ratio of SV2275/SAl2282 integral intensities of the bands assigned to the interaction between the
nonbonding electrons of PhCN and electron-deficient V3+ and Al3+ ions, respectively (Fig. 4B). At
the same time, glycerol conversion also increases steadily as the ratio of SV2275/SAl2282 increases (Fig.
4B). It is important to observe that the dependence of glycerol conversion and selectivity towards
(II) on the V3+ content can also be explained by the variation of the integral intensity of the band at
25250 cm-1, characterizing the V3+ ion in the SBU framework in the DR-UV-vis spectra of MIL-
53(Al,V) samples (Fig. S9, supporting information).
It is noteworthy that the catalytic properties of MIL-47(V) depend on the oxidation state of
the vanadium ions. Table 4 demonstrates the catalytic properties of MIL-47(V3+) obtained by
calcination at 200 °C in air for 2 h and of MIL-47(V4+) obtained by calcination at 300 °C for 9 h in

air. As is evident from these data, their activities are close, while the selectivity towards (II) in the
presence of MIL-47(V4+) is lower (70%) than that in the presence of MIL-47(V3+) (87%). The
activity of MIL-47(V4+) is an unexpected result at first sight because the coordination sphere around
the vanadyl [V=O]2+ does not allow the activation of carbonyl oxygen of the acetone in accordance
with the reaction mechanism. The high glycerol conversion and selectivity towards (II) in the
presence of MIL-47(V4+) can be related to the formation of structural defects due to the interaction
of V4+ sites with H2O [55-56].
3.3. The comparison of efficiencies of V-containing MOFs
It is interesting to compare the efficiency of the most active MIL-100(V) and MIL-47(V3+)
samples with those of H2SO4, SnCl2 and p-toluenesulfonic acid reported in the literature [57]. Their
efficiencies were compared using the TON numbers (eq. (1)):
glycerol
TON 
, (mol/mol)
(1),
mcatalyst
where glycerol is the amount of consumed glycerol (mol) and mcatalyst is the amount of catalyst in the
reaction mixture (mol). The main results are shown in Table 4. The results indicate that the
efficiency of MIL-100(V) is higher than that of MIL-47(V) and other samples. The catalytic
properties of MIL-100(V) are comparable to those of SnCl2.
It was equally important to investigate the stability of MIL-100(V) in the reaction mixture.
Fig. 5 demonstrates the stability and activity of MIL-100(V) in recycling tests. After each operation
cycle, the catalyst was separated, washed with acetone, dried at room temperature, then dried at
70 °C for 1 h and 200 °C for 2 h and used in the next run. It was found that this sample can be used
repeatedly without a significant loss of the catalytic activity during at least 4 catalytic cycles.
4. Conclusions

In this work, the catalytic properties of metal-organic frameworks (MOFs) such as the
isostructural MOFs of the families MIL-100(V, Al, Fe and Cr), MIL-53(V, Al, Fe and Cr)) and
mixed MIL-53(Al,V) (Al/V – 100, 75, 50, 25 and 0), were studied in the synthesis of solketal from
glycerol and acetone at 70 °C, with the acetone/glycerol mol/mol ratio of 4.7 in acetonitrile as
the reaction media. The main products were a five-membered solketal (II) and a six-membered
acetal (III). It was shown that the reaction rate and isomer selectivity depended on the type of metal
ion in MIL-100(M) and MIL-53(M). Glycerol conversion decreases in the following order V3+ >
Al3+ > Fe3+ > Cr3+. This order is in agreement with the value of the zero point of charge of the
surface (pHPZC). Another reason for the differences in the catalytic activity was related to the
exchange of the water molecules from the first coordination sphere of the metal ion. Isomer
selectivity was suggested to depend on the length of the M-O bond in the framework of the MOFs.
The decrease in the length of the M-O bond favours increased formation of (II). The high activity
and selectivity towards (II) were observed in the presence of the V-containing MOFs.
Catalytic properties of mixed MIL-53(Al,V) were also investigated in reaction of glycerol
with acetone. According to the experimental data, glycerol conversion and selectivity towards (II)
rise with the increasing V3+ content. It is important to observe that both MIL-47(V) and MIL-100(V)
can be used as catalysts at 25 °C. The efficiency of MIL-100(V) was higher than that of H2SO4,
SnCl2 and p-toluenesulfonic acid.
Justification for publication
Results of our investigation provides broadening knowledge and insights towards catalytic behavior
of the isostructural MOFs of the families MIL-100(M) and MIL-53(M) (M = V, Al, Fe and Cr) and
mixed MIL-53(Al,V) (Al/V – 100/0, 75/25, 50/50, 25/75 and 0/100 at./at.). For the first time in this
article we investigated catalytic behaviour of these materials in synthesis of solketal from glycerol
and acetone which can be used as fuel additive. Experimental data point that catalytic activity of
MIL-100(M) and MIL-53(M) depend on acidity, the differences in the rate constant for the
exchange of water molecules from the first coordination sphere of a given metal ion and the length
of the M-O bond.

Acknowledgements
This work was supported by SB RAS project V.44.2.12 and funded by a grant from the Korea
government (NRF, MSIP) (№ 2015R1A2A1A15055291).

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Figure caption
Figure 1. Reaction of glycerol with acetone in the presence of MIl-100(Al) and MIL-47(V)
(Experimental conditions: (A) 2.17 mmol of glycerol, 10.19 mmol of acetone in 5 ml of
acetonitrile, 0.040 g of MIL-100(Al), 70 oC; (B) Experimental conditions: 4.79 mmol of
glycerol, 19.64 mmol of acetone in 15 ml of acetonitrile, 0.011 g of MIL-47(V), 25 oC).
Figure 2. Correlations between the point of zero charge (pHpzc) of MIL-100(M) and conversion of
glycerol.
Figure 3. Correlations between length of M-O bond selectivity in reaction of glycerol with acetone
in the presence of isostructural MIL-100(M) and MIL-53(M) (Reaction conditions: 5 ml
of glycerol/acetone solution (Experimental conditions: 0.43 mmol of glycerol, 1.96 mmol
of acetone in 5 ml of acetonitrile, 0.040 g of catalyst, 70 oC, 75 min).
Figure 4. (A) Correlations between amount of V in MIL-53((Al,V), conversion of glycerol and
selectivity towards (II) in reaction of glycerol with acetone in the presence of MIL-
53(Al,V). (B) Correlations between amount of V in MIL-53(Al,V) and ratio of integral
Al
intensities of SV2275/SAl
S
2282 (Inside: Correlation between molar ratio of Al/V and
2282
ratio of integral intensities of SV2275/SAl2282). (Experimental conditions: 2.17 mmol of
glycerol, 10.19 mmol of acetone in 5 ml of acetonitrile, 0.040 g of catalyst, 70 oC, 75
min).
Figure 5. MIL-100(V) recycling in reaction of glycerol with acetone. (Experimental conditions:
4.79 mmol of glycerol, 19.64 mmol of acetone and 11 mg MIL-100(V) in 15 ml of
CH3CN, 25 oC, 90 min. Amount of reactants was corrected based on reaction conditions).
Scheme 1. Main reaction products in the glycerol acetalization with acetone.

MIL-47(V)
MIL-100(Al)
60
40
20
0
100
75
50
25
0
100
75
50
25
0
catalyst was filtered off
catalyst was filtered off
0
20
40
60
80
0
20
40
60
80
Time, min
Time, min
Figure 1. Reaction of glycerol with acetone in the presence of MIl-100(Al) and MIL-47(V)
(Experimental conditions: (A) 2.17 mmol of glycerol, 10.19 mmol of acetone in 5 ml
of acetonitrile, 0.040 g of MIL-100(Al), 70 oC; (B) Experimental conditions: 4.79
mmol of glycerol, 19.64 mmol of acetone in 15 ml of acetonitrile, 0.011 g of MIL-
47(V), 25 oC).

100
75
50
25
0
MIL-100(V)
MIL-100(Al)
MIL-100(Fe)
MIL-100(Cr)
3.0
3.3
3.6
3.9
4.2
4.5
pHPZC
Figure 2. Correlations between the point of zero charge (pHpzc) of MIL-100(M) and conversion of
glycerol.

100
90
100
90
MIL-47(V)
MIL-100(Al)
MIL-100(Fe)
MIL-53(Al)
CH3
O
CH3
O
CH3
CH3
MIL-53(Cr)
MIL-53(Cr)
MIL-100(Cr)
MIL-100(Cr)
O
O
80
80
CH2OH
CH2OH
CH3
O
CH3
O
CH3
O
CH3
O
20
10
0
20
10
0
OH
MIL-100(Fe)
MIL-100(Al)
OH
MIL-53(Al)
MIL-47(V)
2.00
2.05
2.10
2.15
2.20
1.95
2.00
2.05
2.10
Length of M-O, A
Length of M-O, A
Figure 3. Correlations between length of M-O bond selectivity in reaction of glycerol with
acetone in the presence of isostructural MIL-100(M) and MIL-53(M) (Reaction
conditions: 5 ml of glycerol/acetone solution (Experimental conditions: 0.43 mmol of
glycerol, 1.96 mmol of acetone in 5 ml of acetonitrile, 0.040 g of catalyst, 70 oC, 75
min).

90
60
30
0
100
75
50
25
0
100
95
B
A
1.00
0.75
0.50
0.25
0.00
90
correlation coefficient 0.96
mean square deviation 0.13
0
25
50
75
100
85
Amount of V in MIL-53, at.%
0.0
0.4
V
2275
0.8
1.2
0.00
0.25
0.50
0.75
1.00
Al
/S
Ratio of S
, a.e.
2282
Amount of V in MIL-53, at.%
Figure 4. (A) Correlations between amount of V in MIL-53((Al,V), conversion of glycerol and
selectivity towards (II) in reaction of glycerol with acetone in the presence of MIL-
53(Al,V). (B) Correlations between amount of V in MIL-53(Al,V) and ratio of integral
intensities of SV2275/SAl2282 (Inside: Correlation between molar ratio of Al/V and ratio
of integral intensities of SV2275/SAl2282). (Experimental conditions: 2.17 mmol of
glycerol, 10.19 mmol of acetone in 5 ml of acetonitrile, 0.040 g of catalyst, 70 oC, 75
min).

Figure 5. MIL-100(V) recycling in reaction of glycerol with acetone. (Experimental conditions:
4.79 mmol of glycerol, 19.64 mmol of acetone and 11 mg MIL-100(V) in 15 ml of
CH3CN, 25 oC, 90 min. Amount of reactants was corrected based on reaction conditions).

CH3
O
CH3
O
CH3
O
CH3
H2C OH
H-C OH
H2C OH
O
O
+
+
CH3CCH3
CH2OH
OH
(I)
(II)
(III)
Scheme 1. Main reaction products in the glycerol acetalization with acetone.

Table 1. Textural properties of isostructural MIL-53(V, Al, Fe, Cr)
Textural data
Sample
ABET
V
V
(m2/g)
(cm3/g)
(cm3/g)
MIL-53
1157
1
2
3
4
5
6
7
MIL-53(Al)
0.58
0.60
0.62
0.56
0.47
0.49
-
0.47
0.50
0.51
0.46
0.41
0.44
-
MIL-53(Al:V)/(75:25)
MIL-53(Al:V)/(50:50)
MIL-53(Al:V)/(25:75)
MIL-47(V)
1115
1102
1057
810
MIL-53(Cr)
1025
MIL-53(Fe)
Non porous
MIL-100
1450
8
MIL-100(Al)
MIL-100(V)
MIL-100(Fe)
MIL-100(Cr)
MIL-101(Cr)
0.68
0.75
0.79
0.64
1.57
0.37
0.43
0.38
0.40
0.36
9
1525
10
11
12
1714
1377
3116

Table 2
Chemical composition of MIL-53 samples
Experimental
Theoretical
Chemical composition
(wt%)
XRF-analysis (wt%)
CH-analysis (wt%)
Al/V
Formula
MW
(mol/mol)
Al
V
C
H
Al
V
C
H
MIL-53(Al)
12.60±0.21
0.0
100/0
81/19
42/58
26/74
0/100
12.90 0.0
46.04 1.92 [(AlOH)(C8H4O4)]
208.5
40.620.13 2.760.09
43.620.13 2.060.09
40.750.23 1.760.09
39.850.13 2.100.03
41.100.01 2.110.05
MIL-53(Al:V)/(75:25) 11.05±0.11
MIL-53(Al:V)/(50:50) 5.75±0.08
MIL-53(Al:V)/(25:75) 3.43±0.15
4.81±0.21
14.84±0.24
18.05±0.23
19.96±0.20
10.28 4.47 44.96 1.87 [(AlOH)0.81(VOH)0.19(C8H4O4)] 213.5
5.12 13.25 43.16 1.18 [(AlOH)0.42(VOH)0.58(C8H4O4)] 222.4
3.15 16.60 42.45 1.71 [(AlOH)0.26(VOH)0.74(C8H4O4)] 226.1
MIL-47(V)
0.0
0.0
21.94 41.29 1.72 [(VOH)(C8H4O4)]
232.5
M
C
H
M
C
H
MIL-53(Cr)
MIL-53(Fe)
19.55±0.16
18.29±0.18
23.58
22.27
[(FeOH)(C8H4O4)]
237.5
233.5
40.42 1.68
43.520.13 2.660.19
37.950.04 2.460.06
41.11 1.71 [(CrOH)(C8H4O4)]

Table 3. Catalytic activity of MOFs in reaction of glycerol with acetone a
Selectivity (%)
Conversion of (I)
(%)
(II)
(III)
MIL-100 and MIL-101
MIL-100(V)
MIL-100(Al)
MIL-100(Fe)
MIL-100(Cr)
MIL-101(Cr)
85.4
44.2
19.5
4.2
97.7
94.3
86.1
77.5
85.5
2.3
5.7
13.9
22.5
14.5
2.2
MIL-53
75.9
MIL-47(V)
97.5
95.1
93.2
91.4
90.1
86.7
80.5
2.5
4.9
MIL-53(Al:V)/(25:75)
MIL-53(Al:V)/(50:50)
MIL-53(Al:V)/(75:25)
MIL-53(Al)
57.7
38.9
19.2
12.5
3.1
6.8
8.6
9.1
MIL-53(Fe)
13.3
19.5
MIL-53(Cr)
1.6
a Experimental conditions: 2.17 mmol of glycerol, 10.19 mmol of acetone in 5 ml of acetonitrile,
0.040 g of catalyst, 70 oC, 75 min.

Table 4. Catalytic activity of different catalysts in reaction of glycerol with acetone in
acetonitrile a
Catalyst
TON c
Conversion of (I) Selectivity of (II)
Ref.
(mol/mol)
(mg) (wt.%) b
(%)
(%)
SnCl2
8.2
4.7
9.1
11
1.86 c
1.07 c
2.07 c
2.50
81
51
65
73
78
83
98
97
98
87
70
98
89.6
50.9
58.9
81.4
87.0
106.1
[57]
[57]
H2SO4
PTSA
[57]
MIL-47(V) d
MIL-47(V4+) e
MIL-100(V) f
This work
This work
This work
11
2.50
11
2.5
a 4.79 mmol of glycerol and 19.64 mmol of acetone, 1 mol % of catalyst in 15 ml of CH3CN,
25 oC, 90 min; b Weight amount of catalyst based on weight of glycerol; c 1 mol% based on
glycerol
c TON 
glycerol.
; d Catalyst was activated at 200 oC in air for 2 h, amount of V in sample
mcatalyst
is 19.96±0.20; e catalyst was activated at 300 oC in air for 9 h; f Catalyst was activated at 200 oC
in air for 2 h, amount of V in sample is 17.28±0.23.
29