Selective oxidation of methane to methanol with H2O2 over an Fe-MFI zeolite catalyst using sulfolane solvent

Article abstract of DOI:10.1039/c8cc10026h

The effect of reaction conditions for direct oxidation of methane to methanol over Fe-MFI zeolite with H₂O₂ has been investigated. Sulfolane has been proved to be an efficient solvent for liquid-phase methane oxidation. A sulfolane/water mixture with an appropriate proportion led to an extremely high methanol production with a high selectivity.

Full text of DOI:10.1039/c8cc10026h

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DOI: 10.1039/C8CC10026H
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Selective oxidation of methane to methanol with H O over Fe-MFI
2
2
zeolite catalyst using sulfolane solvent
a
a
a
a
a, b
Peipei Xiao, Yong Wang, Toshiki Nishitoba, Junko N. Kondo, Toshiyuki Yokoi *
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
The effect of reaction conditions for direct oxidation of methane to medium with H
methanol over Fe-MFI zeolite with H has been investigated. heterogeneous catalysts, including Cu and/or Fe-ZSM-5,
Sulfolane has been proved to be an efficient solvent for liquid- Pd/TiO
phase methane oxidation. Sulfolane/water mixture with an catalysts, the highest 0.5% of CH
appropriate proportion led to an extremely high methanol to CH OH was achieved by using Fe-Cu/ZSM-5 as catalyst in the
production with a high selectivity. continuous flow fixed bed reactor, even so the highest total
2 2
O under low temperature on various kinds of
1
4-17
2
O
2
Au-
and Au-Pd colloids . Among of these
conversion with 92% of selectivity
18,19
20
21
2
,
AuPdCu/TiO
2
4
3
−
1
−1 15
productivity was only 0.08 mol kgcat h . Chadwick et al. found the
generation of CH (OH) in the liquid phase and H in the gas phase
for selective oxidation of methane using Fe-ZSM-5 and H in
4
Methane (CH ), as the main component of natural gas, is a highly
2
2
2
abundant and inexpensive source of fuel and chemicals.1, 2 The
synthetic path for direct conversion of methane to methanol
2 2
O
−1 −1
aqueous medium. The productivity was high to 26.7 mol kgcat h ,
(
CH
building block for the generation of many chemical goods.
The approaches of direct conversion of methane to methanol
3
OH) is a hot topic since methanol is useful as a fuel and a good
22
but the yield and selectivity of MeOH were only 14.9 µmol and 30%.
Recently, Shan and co-workers used O and CO as co-oxidants, Rh-
3, 4
2
ZSM-5 as catalyst to oxidize methane at 423 K in aqueous medium.
The highest yield of MeOH and total liquid products were up to 1.2
5, 6
7, 8
9
mainly include gas phase using O
under high temperature, liquid phase using homogenous catalysts in
highly concentrated acids, and liquid phase using H or O as
oxidant on heterogeneous catalysts. Direct oxidation of CH in gas
phase requires high temperatures (473 to 773 K) to activate the
2
,
2
N O
or H
2
O
as oxidants
−1 −1
and 13.9 mol kgcat h , but the selectivity of methanol was less than
2
O
2
2
23
9
%. Very recently, Ohkubo’ s group successfully produced
methanol from methane using perfluorohexane as solvent and
NaClO as oxidant without catalyst, achieving 99% CH conversion
with 14% methanol selectivity.
The inertia C-H bond of CH
solubility of CH result in the low CH
phase system. CH is a kind of non-polar molecule with very
symmetrical tetrahedron structure, and only 1.9 mg CH dissolves in
00 g water at 303 K and 0.1 Mpa. Besides, the solubility of CH is
highly dependent on the temperature and pressure of CH . It is
increased to 87.5 mg at 5 Mpa and 303 K. We have focused on the
use of organic solvents to enhance the solubility of CH . Among the
4
2
4
2
, 9, 10
reactants,
oxidize to CO
but the oxidation products are prone to further
. Recently, Bokhoven and co-workers developed a
24
2
molecule and the extremely low
conversion under the liquid-
4
4
direct stepwise method for converting of CH
4
to CH
3
OH over Cu-MOR
4
4
with water under 473 K and 7 bars of CH
4
; they achieved the
4
production of 0.2 molMeOH molCu-1.9 The homogeneous liquid phase
system achieves high methane conversion and methanol selectivity,
but it usually accompanies by high acid and high pollution, and
4
25
1
4
4
2, 11,12
methanol is not the direct product.
Periana et al. described the
25
oxidation of methane through methyl bisulfate catalyzed by mercuric
bisulfate. An unprecedented 85% selectivity of methyl bisulfate at
4
variety kinds of organic solvents, sulfolane is a very stable aprotic
polar solvent. Furthermore, it is water-soluble with strong affinity for
13
5
0% methane conversion was reported. Liquid phase using H
2 2
O or
O
2
as environmentally benign oxidants and heterogeneous
26, 27
CH
4
.
4
The solubility of CH reaches 1.4 g/100 g sulfolane at 313 K
substances as catalysts is the trend of development. Hutchings and
co-workers have made outstanding contributions in aqueous
28
and 3.7 Mpa, almost 100 times higher than that in water.
Here, the Fe-MFI zeolite catalyst, which was synthesized by
direct hydrothermal method, was applied as catalyst for methane
oxidation in liquid phase. The details of the synthesis and
characterization are described in ESI (Fig. S1 and Table S1).
a.Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta,
Midori-ku, Yokohama 226-8503, Japan.
b.
PRESTO, JST, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
†
Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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(
a)
(b)
MeOH
HCOOH
HCOH
Total liquid products
H
2
O
2
V
coienv
w
ers
A
io
r
n
ticle Online
2
1
1
1
000
800
600
400
DOI: 10.1039/C8CC10010
26H
0
(
a)
(b)
90
80
70
60
50
40
30
20
10
0
Sulfolane
Sulfolane
H O
2
CH OH
3
1200
TMS
1000
H O
2
TMS
800
Mesitylene
6
4
2
00
00
00
0
Mesitylene
HCOOH
HCOH
9
8
7
6
5
4
3
2
1
0
-1
9
8
7
6
5
4
3
2
1
0
-1
303
323
353
0.5
(d)
1.5
3.0
ppm
ppm
Temperature (K)
CH4 pressure (Mpa)
2000
100
90
80
70
60
50
40
30
20
10
0
(
c)
1
1800
Fig. 1 H-NMR spectra of the liquid phase after (a) blank test
1600
1400
1200
(
without CH
mesitylene as internal standard and CD
shift calibrator. Reaction conditions: (a) 323 K, 10 ml
sulfolane, 50 mg Fe-MFI, 27 mmol H , 2 h. (a) 323 K, 10 ml
sulfolane, 50 mg Fe-MFI, 27 mmol H , PCH4=3 Mpa, 2 h.
4
as reactant) and (b) with CH
4
as reactant, using
CN/ TMS as chemical
3
1000
800
2 2
O
O
2 2
6
4
2
00
00
00
0
0.5
2.0
4.0
10
25
50
100
Prior to the effects of various reaction parameters, the stability
of different organic solvents under the typical reaction conditions
was investigated. Figs. S2 and S3 show the H-NMR spectra of the
liquid phase after blank test (without CH as reactant) of acetonitrile
4
and ethanol, respectively. The peaks at around 4.9 and 8.1 ppm are
assigned to the hydrogen of formaldehyde (HCOH) and formic acid
Reaction Time (h)
Catalyst amount (mg)
Fig. 2 Liquid product amount and H O conversion over Fe-
2
2
1
MFI catalyst under different (a) temperatures, (b) CH4
pressures, (c) reaction times and (d) catalyst amounts.
Reaction conditions: (a) 10 ml sulfolane, 50 mg catalyst, 27
mmol H
mg catalyst, 27 mmol H
mg catalyst, 27 mmol H O , PCH4=3 Mpa. (d) 323 K, 10 ml
2
O
2
, 2 h, PCH4=3 Mpa. (b) 323 K, 10 ml sulfolane, 50
2 2
O
2
, 2 h. (c) 323 K, 10 ml sulfolane, 50
(
HCOOH), respectively, which could be produced from the reaction
2
of the solvents with H . As a result, acetonitrile and ethanol were
2
O
2
2 2
sulfolane, 27 mmol H O , 2 h, PCH4=3 Mpa.
not stable in the reaction conditions. When sulfolane was employed
as solvent, the peaks ascribed to the products were not observed
after the blank test in the H-NMR spectrum (Fig. 1(a)), indicating
and the selectivity of every liquid product was relatively stable under
different CH pressures (Fig. S4(b)). In addition, H conversion
enlarged from 4 to 14 % with CH pressure growing from 0.5 to 3
Mpa. It is clear that the CH pressure mainly influences the solubility
of methane, i.e. the reactant amount. The solubility of CH in
1
4
2 2
O
that sulfolane was stable under this reaction condition. Actually,
sulfolane is a widely used polar aprotic, stable and water-soluble
4
4
27
industrial solvent. However, to the best of our knowledge, it has not
2 2
been applied as solvent in direct oxidation of methane with H O .
4
sulfolane was enhanced from 917 mg/ 100 g sulfolane at 2.37 Mpa
Thus, the direct oxidation of methane in sulfolane/H
solution over Fe-MFI was carried out at 323 K. The H-NMR spectrum
of the liquid-phase after the reaction is presented in Fig. 1(b),
2
O
2
aqueous
29
and 313 K to 2460 mg/ 100 g sulfolane at 7.44 Mpa and 313 K.
1
4
Obviously, high CH pressure under the maximum pressure of the
instrument is beneficial to the reaction. The effect of reaction time
was depicted in Fig. 2(c). The yields of the products in liquid phase
were increased over time, especially the production of HCOH, which
was improved from 314.4 to 864.4 µmol by extending reaction time
showing the hydrogens of CH
HCOOH (8.9 ppm). These products resulted from the reaction
between CH and H in sulfolane.
3
OH (3.4 ppm), HCOH (4.9 ppm) and
4
2 2
O
The effects of various reaction parameters were investigated.
First the temperature was changed from 303 to 353 K to study the
influence on the reaction performance, as shown in Fig. 2(a). The
amount of total liquid products and HCOOH increased with
temperature. The yields of MeOH and HCOH were increased with
temperature raising from 303 to 323 K. Further increase in the
temperature to 353 K led to the decrease in the productions. This is
probably caused by the successive oxidation of MeOH and HCOH to
from 2 to 4 h. The H
2 2
O conversion was relatively stable at around
12% against reaction time. HCOOH as the oxidation production of
14, 16
HCOH presented lower selectivity than the results of Hutchings
22
and Chadwick , probably due to the solvent effect (Fig. S4(c)). Fig.
2
(d) shows the relationship between the amount of the products in
the liquid-phase and the catalyst mass. When the catalyst mass was
increased from 10 to 100 mg, the yields of the products and the H O
2
2
conversion were increased but the selectivity to MeOH was
decreased.
Sulfolane is rarely used alone but in admixture with another
solutions.28 The use of mixed solvents is an attractive alternative to
HCOOH. The H
temperature. Because the liquid phase boiled at 3 Mpa and 353 K,
leading to the dissociation of H . The solubility of CH in sulfolane
is decreased by increasing the temperature. Based on the literature,
the solubility of CH in sulfolane was decreased from 1229 mg/ 100 g
sulfolane at 298 K and 3.36 Mpa to 1137 mg/ 100 g sulfolane at 343
2 2
O conversion increased from 3 to 100% along with
2
O
2
4
either the solvent effect or the economic benefit and environment
protection. Sulfolane-water mixed solvent is extensively applied in
4
31
the lithium batteries and as extraction agent in the petrochemical
29
K and 3.04 Mpa. However, high temperature could improve the
reaction activity for both catalysts and reactants.30 Thus,
temperature is a “double-edged sword”. The reaction performance
32
industry. Thus, the reaction performance in aqueous sulfolane with
the volume content ranging from 0 to 100 vol.% were investigated,
the results are presented in Figs. 3 and S5. When distilled water (0
vol.% of sulfoalne) was used as solvent, the minimum amount of
MeOH (12.2 µmol) and HCOH (0 µmol), but the maximum amount of
HCOOH (462.5 µmol) were obtained in the liquid phase. Meanwhile
was investigated over a range of CH
expected, the yields in the liquid-phase were enhanced along with
CH pressure, as shown in Fig. 2(b). MeOH gave the highest selectivity
4
pressure from 0.5 to 3 Mpa. As
4
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In conclusion, we have successfully found that sulfolane was a
stable and effective organic solvent in the direct oxidation of
methane with H O . The dramatic improvement for the yield of
2 2
MeOH reported herein could have a significant impact on the
methane conversion.
View Article Online
DOI: 10.1039/C8CC10026H
2
1
1
1
1
1
000
800
600
400
200
000
100
90
80
70
60
50
40
30
20
10
0
MeOH
HCOOH
HCOH
H O conversion
2
2
Total liquid products
CO2
ACKNOWLEDGMENT
This work was partially supported by Grant-in-Aid for Scientific
Research (B) (No. 16H04566) of Education, Culture, Sports, Science
and Technology of Japan (MEXT). A part of this work was also
supported by JST PRESTO Grant Number, JPMJPR15S8, Japan.
8
6
4
2
00
00
00
00
0
0
25
50
75
100
Notes and references
Sulfolane content (vol.%)
1.
C. Hammond, N. Dimitratos, R. L. Jenkins, J. A. Lopez-Sanchez, S.
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2 2
Fig. 3 The amount of products and H O conversion under
different proportions of sulfolane content. Reaction
conditions: 323 K, 10 ml solvent, 50 mg catalyst, 27 mmol
2 2
H O , PCH4=3 Mpa, 2 h.
2
.
M. Ravi, M. Ranocchiari and J. A. van Bokhoven, Angew. Chem.
Int. Ed., 2017, 56, 16464-16483.
it was worth pointing out that large amount of CO
2
(825.5 µmol) was 3. P. G. Lustemberg, R. M. Palomino, R. A. Gutierrez, D. C. Grinter,
detected in the gas phase (Fig. S6(a)). The H conversion in water
2
O
2
M. Vorokhta, Z. Liu, P. J. Ramirez, V. Matolin, M. V. Ganduglia-
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2
018, 140, 7681-7687.
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4, 15
22
4. P. Schwach, X. Pan, X. Bao, Chem. Rev., 2017, 117, 8497-8520.
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.
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to 50 vol.%, the yields of the products, MeOH and HCOH, were
increased, but the HCOOH yield and the H conversion were
0
2 2
O
6
K. Yoshizawa and Y. Shiota, J. Am. Chem. Soc., 2006, 128, 9873-
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9881.
7
8
.
.
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O
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−
1
−1
on the catalyst was reached up to 11.2 mol kgcat h . It was
necessary to mention that no CO was detected in the gas-phase (Fig.
S6(b)). Continuing to increase the proportion of sulfolane to 100
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2
11. R. A. Periana, D. J. Taube, S. Gamble, H. Taube, T. Satoh and H.
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O
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1
1
3. R. A. Periana, D. J. Taube and E. R. Evitt, Science, 1993, 259, 15.
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2 2 2
was not discovered in the gas phase (Fig. S6(c)). The H O
conversion was decreased to 14%.
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1
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26
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O
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