Ionic liquid protected heteropoly acids for methanol dehydration

Article abstract of DOI:10.1016/j.cattod.2011.03.077

We report herein the synthesis of an organic-inorganic hybrid composed by the ionic liquid protected Keggin structure, as a precursor for acid catalyst and its subsequent application in the methanol dehydration reaction. Special attention was paid to the thermal stability of the resulted hybrids as a function of the Keggin anion. The catalytic behaviour of these new materials are also studied and compared to the metal salt Cs₂HPW ₁₂O₄₀. The prepared hybrids are less thermally stable than the metal salt, but their partial decomposition results in very active and selective catalysts for the dehydration of methanol to dimethyl ether.

Full text of DOI:10.1016/j.cattod.2011.03.077

Catalysis Today 171 (2011) 236–241
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Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Ionic liquid protected heteropoly acids for methanol dehydration
Svetlana Ivanovaa,∗ , Xavier Nitschb , Francisca Romero-Sarriaa , Benoît Louisb , Miguel Angel Centenoa ,
Anne Cecile Rogerb, Jose Antonio Odriozolaa
a Departamento de Química Inorgánica and Instituto de Ciencias de Materiales de Sevilla, CSIC-US, Avda. Américo Vespucio 49, 41092, Sevilla, Spain
b Laboratoire des Matériaux, Surfaces et Procédés pour la Catalyse, 25, rue Becquerel, 67087 Strasbourg, France
a r t i c l e i n f o
a b s t r a c t
Article history:
We report herein the synthesis of an organic-inorganic hybrid composed by the ionic liquid protected
Keggin structure, as a precursor for acid catalyst and its subsequent application in the methanol dehy-
dration reaction. Special attention was paid to the thermal stability of the resulted hybrids as a function
of the Keggin anion. The catalytic behaviour of these new materials are also studied and compared to
the metal salt Cs2HPW12O40. The prepared hybrids are less thermally stable than the metal salt, but their
partial decomposition results in very active and selective catalysts for the dehydration of methanol to
dimethyl ether.
Received 29 October 2010
Received in revised form 22 March 2011
Accepted 29 March 2011
Available online 31 May 2011
Keywords:
Ionic liquid
Organic–inorganic hybrid
Keggin anion
© 2011 Elsevier B.V. All rights reserved.
Thermal stability
Selective methanol dehydration
1. Introduction
an extensive and continuous leaching during the reaction on sup-
ported HPAs catalysts.
The popularity of the ionic liquids (IL) has attached a significant
scientific interest in the last decade due to their unique proper-
ties; relatively wide electrochemically stable window, good electric
conductivity, high ionic mobility, broad range of room tempera-
ture liquid compositions, negligible vapour pressure and excellent
chemical and thermal stability [1,2]. Many of these materials have
been applied in different fields of the material chemistry such as
electrochemistry [3,4], organic synthesis [5], catalysis [2,5–10] and
synthesis of nanostructured materials [11]. However, the use of the
ionic liquid as an integral part of material is slightly studied.
The heteropoly acids (HPAs) and related polyoxymetalate com-
pounds still provoke a huge interest in the scientific community.
They are powerful acid and oxidizing catalysts but possess a fairly
high thermal stability ranging from 350 to 450 ◦C depending on the
type of the Keggin structure, being W- containing HPAs more sta-
ble than Mo containing acids [12]. Despite their valuable properties
as catalysts for liquid-phase processes, their use as heterogeneous
catalysts still needs improvement. Firstly, the HPAs have to be sup-
ported on mineral oxide in order to develop their specific surface
and, depending on the application, their thermal stability. In addi-
tion, the application of the supported HPAs remains limited due
to their sensitivity to the presence of water, which can produce
Here comes the idea of trying to improve the stability and to
increase the lifetime of the Keggin structure by its protection with
organic cation instead of supporting it on the mineral carrier [13].
Combining heteropoly acids with room temperature ionic liquids
(RTILs) should ease the design of some interesting materials.
In addition, the acidity of the new materials, if exists, can be
easily tested in the reaction of dehydration of methanol to dimethyl
ether (DME), known to occur on acid type catalysts [14–16].
2CH3OH → CH3OCH3 + H2O
This study presents the preparation and characterization of
ionic liquid protected phosphomolybdic (PMo12O403−) and phos-
3−
photungstic (PW12O40
) Keggin structure. For this purpose
1-butyl-3-methyl imidazolium methanesulfonate (Bmim) ionic liq-
uid was used as a protecting cation. The resulted materials possess
the known molecular structure of IL3PA type. In this paper, the
thermal stability and phase transformation under heating of such
materials will be discussed.
2. Experimental
2.1. Synthesis
The halide free ionic liquid 1-butyl-3-methylimidazolium
methanesulfonate was prepared by the method proposed by Cassol
et al. [17]. The used reactants were methanesulfonyl chloride (Alfa
∗
Corresponding author.
E-mail address: svetlana@icmse.csic.es (S. Ivanova).
0920-5861/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2011.03.077

S. Ivanova et al. / Catalysis Today 171 (2011) 236–241
237
70
-0,010
-0,015
-0,020
-0,025
-0,030
-0,035
Aesar), triethylamine (Alfa Aesar), 1-methylimidazole (Aldrich), n-
A
butanol, dichloromethane, acetone and distilled water. The method
goes first through the synthesis of the butyl methanesulfonate, as
described below;
60
50
40
30
20
10
0
2.1.1. Preparation of butyl methanesulfonate
Methanesulfonyl chloride (61.1 g, 0.53 mol) was added slowly,
under vigorous stirring, to a solution of n-butanol (39.4 g, 0.53 mol)
and triethylamine (53.9 g, 0.53 mol) in dichloromethane (0.5 L). An
external water–ice bath was used to control the reaction mixture
temperature between 10 and 20 ◦C. After addition, stirring was con-
tinued for further 2 h at room temperature. Then, 200 mL of water
was added and the aqueous phase containing the triethylammo-
nium chloride by-product was separated. The organic phase was
washed with water (200 mL) and dried with sodium carbonate.
Finally, the solvent was evaporated and, after reduced pressure dis-
tillation, 55.14 g of a colorless liquid butyl methanesulfonate was
obtained (73% yield).
-10
-20
-30
0
200
400
600
800
Temperature, ºC
10
8
6
4
2
0
-2
-4
-6
0,006
0,005
0,004
0,003
0,002
0,001
0,000
-0,001
-0,002
B
2.1.2. Preparation of 1-butyl-3-methylimidazolium
methanesulfonate
Butyl methanesulfonate (55.14 g, 0.36 mol) was mixed with 1-
methylimidazole (29.74 g, 0.36 mol) and the reaction mixture was
kept at room temperature by means of an external water bath.
After 24 h, one crystal of 1-butyl-3-methyl imidazolium methane-
sulfonate (Fluka) was added and the crystallization reaction was
allowed to proceed at room temperature for 120 h. Recrystal-
lization was performed twice using acetone as solvent (120 mL;
from reflux temperature to freezer temperature overnight). After
vacuum drying, 77.4 g of colorless and very hygroscopic crystals
of 1-butyl-3-methylimidazolium methanesulfonate were obtained
(95% yield).
-8
-10
-12
-14
-16
-18
-20
-22
-24
-26
-28
The HPAs were synthesized as proposed by Wu [18], by mix-
ing in appropriate amounts Na2MoO4 or Na2WO4 respectively with
H3PO4 in the presence of HCl. The hybrid salt with IL3PA molecular
structure was synthesized according to Ranga Rao et al. [19]. In a
typical synthesis, an aqueous solution of the IL in slight excess was
added dropwise to heteropoly acid aqueous solution and the rapid
formation of precipitate was observed. The obtained salt was then
filtered and dried at room temperature.
0
100
200
300
400
500
600
700
800
900
Temperature, ºC
Fig. 1. TGA curves of A) Bmim3PMo12O40 and B) Bmim3PW12O40
.
of 0.234 mL min−1, vaporized and fed in air flow (21.5 mL min−1).
The products were monitored by an on-line GC equipped with FID
detector and DB-1 column.
2.2. Characterizations
TGA experiments were performed on SDTQ60 thermobalance
from 30 to 900 ◦C with heating rate of 10 ◦C min−1 in constant air
3. Results
flow of 50 mL min−1
.
3.1. Thermogravimetric analysis (TGA)
X-ray diffraction (XRD) analysis was performed in a high tem-
perature camera Anton Paar HTK 1200 coupled with an X’Pert Pro
Philips diffractometer, equipped with X’Celerator detector with an
opening of 2.18◦ step of 0.05◦ and an equivalent time acquisition
of 30 s. The diffractograms were taken every 50 ◦C in the range of
25–500◦ C, from 5◦ to 50◦ in flow of synthetic air.
TPO was performed in a U-shaped quartz reactor under oxy-
gen flow (21% in He) from 25 ◦C to 400 ◦C with heating rate of
10 ◦C min−1. All the products were followed by mass spectrometry
in Balzers Omnistar Bentchop equipment.
The thermal stability of the obtained hybrids has been studied
by thermogravimetric analysis (TGA) in the presence of O2. The
results are presented in Fig. 1.
The hybrid material based on phosphomolybdic acid (Fig. 1A)
exhibits low thermal stability and starts to decompose at 300 ◦C
in air. The organic part is lost by 3 successive steps up to 450 ◦C,
indicated by the DTG curve accompanied by a heat release visi-
ble in the DTA curves. In the 450–700 ◦C temperature range, the
obtained phase remains stable. At 730 ◦C the hybrid exhibits a sin-
gle mass loss and heat consumption due to the sublimation of the
molybdenum oxide in the presence of oxygen [20].
2.3. Catalytic reaction
Prior the reaction, activation was carried out at 400 ◦C for 1 h in
the reaction flow (methanol and air). After the activation procedure
the temperature was decreased to the temperature of dehydration
reaction (275 ◦C). Both, activation and reaction were carried out
in a vertical tubular quartz reactor housed in an electrical oven
at atmospheric pressure using 50 mg of sample for every experi-
ment. Methanol was supplied with a syringe pusher at a flow rate
It is well known, that the thermal stability of the HPAs fol-
lows the trend W > Mo and P > Si [21]. One could expect that the
phosphotungstic based hybrid will decompose at higher tempera-
tures compared to the phosphomolybdic one, which was confirmed
by TGA experiments. The W-based hybrid starts to decompose at
400 ◦C in only two delayed steps of organics combustion resulting
in a final weight loss of around 15 wt.% (Fig. 1B).

238
S. Ivanova et al. / Catalysis Today 171 (2011) 236–241
MoO3
MoP2O7
H3PMo12O40
H3PMo12O40,13H2O
MoO3
MoP2O7
H3PMo12O40
H3PMo12O40,13H2O
500º
400º
350º
400º
350º
250º
150º
RT
300º
50
10
20
30
40
10
20
30
40
50
2 Θ
2Θ
A
H P W
WO
Bmim PW
O
500º
400º
350º
500º
400º
350º
250º
250º
150º
RT
150º
RT
5
10
15
20
25
30
35
40
45
50
5
6
7
8
9
10
11
12
2 Θ
2 Θ
B
Fig. 2. XRDiffractograms as a function of temperature of A) Bmim3PMo12O40 (first line) and B) Bmim3PW12O40 (second line).
3.2. X-ray diffraction study
The hybrid originated from H3PW12O40 maintained the original
structure up to 200 ◦C and then starts to change. Probably, a part
of the ionic liquid is removed and the hybrid converts to a new
structure very similar to the initial one (Fig. 2. right hand image),
In order to study in more details the phase formation and
distribution in both hybrids, a XRD study as a function of the
temperature was undertaken. The XRD patterns of the materials,
Bmim3PMo12O40 and Bmim3PW12O40 were measured in situ in
flowing air from room temperature to 500 ◦C at every 50 ◦C (Fig. 2).
At room temperature, both samples exhibit the typical
structure of HPAs organic hybrids with molecular structure
proposed by Ranga Rao et al. [19,22]. However, at high tem-
perature in the presence of air, the stability of the hybrids
strongly depends on the nature of the parent acid. At tem-
peratures higher than 250 ◦C, the structure of Bmim3PMo12O40
is no longer available and products from the decomposition
of the phosphomolybdic acid start to appear in the follow-
ing order; H3PMo12O40·13H2O (JCPDS# 01-075-1588) completely
dehydrated H3PMo12O40 (JCPDS# 01-070-1705), molybdenum
phosphate MoP2O7 (JCPDS# 00-039-0026) and molybdenum oxide
MoO3 (JCPDS# 00-001-0706). At 500 ◦C, MoO3 was the only phase
detected. In the 250–300 ◦C temperature range the diffraction pat-
tern shows a slightly amorphous character caused by the presence
of the dehydrated phosphomolybdic acid [23]. The detailed distri-
bution of all obtained phases as a function of the temperature for
both hybrids is presented in Table 1.
denoted in the table as an organic deficient hybrid, BmimxPW12O40
.
This structure is stable till 400 ◦C where the material structure
Table 1
Detected crystal phases at different temperatures.
Temperature Phases (Bmim3 PMo12O40
(◦C)
)
Phases (Bmim3
PW12O40
)
RT
50
100
150
200
250
Bmim3 PMo12O40
Bmim3 PMo12O40
Bmim3 PMo12O40
Bmim3 PMo12O40
Bmim3 PMo12O40
H3PMo12O40 + 10MoO3·H3PO4·24H2O
H3PMo12O40 + 10MoO3·H3PO4·24H2O
H3PMo12O40 + 10MoO3·H3PO4·24H2O
Bmim3 PW12O40
Bmim3 PW12O40
Bmim3 PW12O40
Bmim3 PW12O40
Bmimx PW12O40
Bmimx PW12O40
300
350
Bmimx PW12O40
Bmimx PW12O40
400
450
500
550
600
+MoP2O7
MoP2O7 + MoO3
MoO3
MoO3
MoO3
amorphous*
amorphous*
+WO3
WO3
WO3

S. Ivanova et al. / Catalysis Today 171 (2011) 236–241
239
Bmim3PMo12O40
Bmim3PW12O40
Cs2HPW12O40
100
A
90
m/z 68
400
80
300
70
200
60
m/z 57
100
50
0
40
400
30
300
m/z 18
20
m/z 44
200
10
100
m/z 28
0
0
0
5
10
15
20
25
30
0
2000
4000
6000
8000
Time, h
Time, s
Fig. 4. DME yield for the prepared samples.
the presence of acid centres able to break the butyl–imidazolium
bond. However, the presence of only the butyl signals in the
Bmim3PW12O40 case suggests strong bonding between the imida-
zolium cation and the Keggin structure at this temperature in this
solid. This was further confirmed by the lower quantity of oxida-
tion products (CO, CO2 and H2O) detected when compared to the
amounts obtained from the phosphomolybdic hybrid.
B
400
300
200
100
0
m/z 57
m/z 68
3.4. Methanol dehydration
400
300
200
100
0
m/z 18
The results for methanol dehydration are presented in Fig. 4 as
dimethyl ether yield versus time.
m/z 28
m/z 44
6000
The selectivity to dimethyl ether (DME) is close to 100% at 275 ◦C
for both hybrids. However, the hybrid based on phosphomolybdic
acid presents higher activity. By comparing the catalytic activity
of the different hybrids with the one achieved over water insolu-
ble Cs2HPW12O40 acidic metal salt of HPAs, the effect of the ionic
liquid on the catalytic activity is studied. The acid metal salt of
the phosphotungstic acid (Cs2HPW12O40) presents low activity to
methanol dehydration, which confirms that the obtained hybrids
could be very interesting for further investigation as acid catalyst
precursors.
0
2000
4000
8000
Time, s
Fig. 3. Temperature programmed oxidation of A) Bmim3PMo12O40 and B)
Bmim3PW12O40
.
reorganizes through hydrated phosphotungstic acid (JCPDS# 00-
050-0654) and then becomes amorphous. It has been reported
elsewhere, that the HPAs could become amorphous when anhy-
drous acid is obtained at temperatures close to 400 ◦C [14]. The
WO3 (JCPDS# 00-032-1395) appears at 500 ◦C as a minor phase
and remains the only one present at 600 ◦C.
Another interesting fact is that at the temperature of activation
(400 ◦C) in the reaction flow, methanol is fully converted to CO2
over both hybrids. The hybrids become oxidizing catalysts in the
reaction
CH3OH + 3/2O2 → CO2 + H2O
3.3. Temperature programmed oxidation (TPO)
4. Discussion
In order to find out what happened with the ionic liquid during
the activation period prior the reaction a TPO study coupled with
qualitative MS analysis was carried out. The results are presented
in Fig. 3.
4.1. Bmim3PMo12O40
From the TGA results, it can be deduced that the presence of
oxygen promotes the combustion of the ionic liquid. However,
the stability of the material in a broad range of temperatures
(450–700 ◦C) suggests that a stationary phase is rapidly obtained.
The fast transformation of the mixed oxide products of the sec-
ondary Keggin structure decomposition takes place, thus leading
to the formation of stable ␣-MoO3 phase, which, in the presence of
oxygen, suffers sublimation at high temperatures. It can be con-
cluded that the presence of oxygen promotes the formation of
MoO3 and once formed, it starts to catalyze the organic part oxi-
dation. The ionic liquid removal occurs in three successive steps,
The phosphomolybdic acid based hybrid starts to decompose
at temperatures close to 300 ◦C showing a lower thermal stability
than the Bmim3PW12O40. The later appears to be stable at the acti-
vation temperature for 30 min and then starts to decompose. It is
interesting to emphasize, that the two hybrids do not lead to the
same oxidation products. In addition to the signals corresponding
to CO, CO2 and H2O (m/z 28, 44 and 18, respectively) the signals
of unsubstituted imidazolium (m/z 68) and butyl radical (m/z 57)
are observed in the MS spectra of the evolved products. The pres-
ence of both m/z signals at 57 and 68 for Bmim3PMo12O40 suggests

240
S. Ivanova et al. / Catalysis Today 171 (2011) 236–241
MoO3
BmimxPW12O40
WO3
C
C
B
B
A
A
10
20
30
40
50
10
20
30
40
50
2 Θ
2 Θ
Fig. 6. XRD patterns of the Bmim3 PW12O40 A) before B) after the reaction and C) of
the parent acid after the oxidation treatment.
Fig. 5. XRD patterns of the Bmim3 PMo12O40 A) before B) after the reaction and C)
of the parent acid after the oxidation treatment.
hybrid is able to break only the butyl–imidazolium bond. At the
temperature of the activation, the obtained products appear to be
amorphous caused by the presence of free dehydrated phospho-
tungstic acid.
starting by butyl–imidazolium bond breaking suggesting the pres-
ence of acidic active centres able to break the C–N bond. All the
characterization methods confirm that the only phase originated
from this hybrid is MoO3. Hence, in the conditions of activation
(400 ◦C), when only the MoO3 is present, the hybrid give rise oxi-
dizing catalyst converting methanol to CO2, but at the temperature
of the dehydration reaction (275 ◦C) becomes acidic. At the tem-
perature of the dehydration reaction, the phase composition could
be influenced by the water formation. It was reported [15] that in
the presence of water the phosphomolybdic acid treated at 400 ◦C
transforms from the mixture of phosphorus oxide, ␣ and ␤ MoO3
into a mixture of PMo12H and ␣-MoO3. Hence, the presence of
water limits the collapse of the Keggin structure thus leading to
quasi equilibrium and acid catalyst able to dehydrate methanol.
That fact could explain the high activity of this hybrid in the dehy-
dration reaction, which if only MoO3 is present should convert to
an oxidizing reaction and it is not the case. In addition a change
of the catalyst colour is observed going from yellowish (colour of
the initial hybrid) through blue (oxide/hydroxide species of mixed
valence known as molybdenum blues) to greenish at the end of
the reaction (probably of the mixture of MoO3 and PMo12H units).
However, the diffraction pattern of the catalyst after reaction shows
only the presence of MoO3 (Fig. 5).
However, as reported by Rocchiccioli-Deltcheff et al. [24], the
production of water during the reaction can play an essential role
on the reactivity. In the temperature range where the thermal pre-
treatment produces an anhydrous acid, the water produced during
the catalytic reaction allows a steady state where the anhydrous
HPA and the 13-hydrate coexist. The resulted phase is probably
responsible of the acidic character and activity in the dehydration
reaction. Kozhevnikov et al. [25] also reports that the proton sites
in solid HPAs are strongly dependent on the hydration degree: the
less hydrated the compounds, the more trapped the protons. How-
ever, the phosphotungstic hybrid shows lower catalytic activity
compared to the phosphomolybdic hybrid despite of the fact that
the phosphotungstic acid should present higher acid strength [21].
The XRD patterns (Fig. 6) of the hybrid after the reaction show the
presence of the organic deficient hybrid, which could explain the
lower activity due to the presence of the ionic liquid protection
layer.
A comparison of the catalytic activity of the both hybrids to
the Cs2HPW12O40 in the same conditions was made. However, the
metal salt, thermally more stable, presents low catalytic activity
for the dehydration of methanol, which helps us to conclude that
probably the intact Keggin anions are not the active species for this
reaction.
The key parameter for this hybrid is probably its tendency to
form the ␤-form MoO3 which hinders the textural evolution, and
its capability to react with the water vapour in the presence of phos-
phoric oxide, as reported elsewhere [24]. This renders this hybrid a
very good precursor for the highly active catalyst in the dehydration
of methanol.
4.3. Comparison of the thermal stability of the hybrids to the
parent acids
4.2. Bmim3 PW12O40
In order to compare the stability of the hybrids to those of the
original acids, the later were submitted to the oxidation treat-
ment, in the same conditions (from RT to 400 ◦C, heating rate of
10◦ min−1). For H3PMo12O40 only the signals corresponding to H2O
(m/z = 18) were observed. Two water loss processes can be distin-
guished in the temperature range between 50–200 ◦C, one major
loss corresponding to the physicsorbed water and the loss of the
H2O molecules of the primary acid structure, and the second at
around 370 ◦C corresponding to the Keggin structure decomposi-
tion (Fig. 3A inset). For the H3PW12O40 acid, again two H2O losses
are detected, one major at higher temperature compared to the
H3PMo12O40 in the 150–200 ◦C temperature range and the second
one observed during the isotherm period at 400 ◦C (Fig. 3 inset B).
The TGA curves for the phosphotungstic acid originated hybrid
show two steps of organics removal from the hybrid, the second one
at high temperature (600 ◦C), which suggests that in the reaction
conditions, the organic part still exists as an intermediate phase.
The initial temperature of the decomposition is 100 ◦C higher than
that of the phosphomolybdic hybrid. In addition, the diffraction
patterns study as a function of the temperature reveals that the
hybrid looses part of the ionic liquid protection converting itself
into an organic deficient hybrid. Based on the TPO results, one
could suggest that the organic deficient hybrid consists of the Keg-
gin anion and methyl-imidazolium cation which suggests that this

S. Ivanova et al. / Catalysis Today 171 (2011) 236–241
241
The XRD patterns of the solids, after the oxidation treatment
show that the H3PMo12O40 acid loses a part of Keggin structure
water molecules and turns into a mixture of dehydrated acid and
MoP2O7 (Fig. 5C). In the case of the corresponding hybrid, low or
inexistent protection was observed. However, the presence of the
organic part forces in first place the combustion of the organic
molecule and then the acid loses water at temperatures around
300 ◦C, as shown from the TPO experiments. It should be noted that
the combustion of the organic part for this hybrid is accelerated by
the first appearence of MoO3.
gin structure shows a very different results which are now object
of detailed study.
Acknowledgements
Financial support for this work has been obtained from Junta
de Andalucía (Plan Andaluz de Investigación, grupo TEP106). S.
Ivanova and F. Romero-Sarria acknowledge MEC for their contract
Ramón y Cajal.
The H3PW12O40 seems to present better thermal stability com-
pared to the H3PMo12O40. The XRD pattern after the treatment
shows the presence of a mixture of the original dehydrated acid and
WO3 (figure 6 C). The corresponding hybrid however shows better
stability and in the conditions of the reaction, does not convert into
WO3 or other oxidation products of the H3PW12O40. The hybrid oxi-
dation goes through organic part partial oxidation resulting directly
into catalyst - organic deficient hybrid.
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In summary, as shown above the thermal stability of the hybrids
do not differ a lot from the stability of the initial acids, except in
the order of water removal and Keggin structure decomposition.
Even if many catalytic reactions are performed at relatively high
temperatures (often > 350 ◦C) and it is necessary to use a catalyst
that is stable under these thermal conditions, the partial decom-
position of the hybrids in the activation procedure could conduct
to precursor of catalytically active species. However the conditions
of the activation have to be optimized in order to reveal the truly
potential of the hybrids.
The partial decomposition of the hybrids results in an active
and more important very selective catalyst for the dehydration of
methanol to dimethyl ether.
It should be noted that the nature of the ionic liquids plays as
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