Catalytic Disproportionation of Formic Acid to Methanol by an Iridium Complex Immobilized on Bipyridine-Periodic Mesoporous Organosilica

Article abstract of DOI:10.1002/cctc.201900999

We report the first example of using heterogeneous Iridium (Ir) catalysts under atmospheric pressure conditions to achieve the catalytic disproportionation of formic acid to methanol. IrCp* complex (Cp=pentamethylcyclopentadienyl (?⁵-C₅Me₅)) was immobilized on the pore surface of the periodic mesoporous organosilica synthesized from a precursor mixture of ethane (Et) and 2,2′-bipyridine (BPy)-bridged organosilanes (Ir-Et-BPy-PMO). Ir-Et-BPy-PMO showed unique catalysis with higher selectivity of methanol compared to homogeneous Ir-BPy complexes. Furthermore, Ir-Et-BPy-PMO exhibited high reusability without any noticeable decrease in activity for at least five times with no leaching of Ir species during the reaction. The increase in methanol selectivity of Ir-Et-BPy-PMO would be attributed to the unique confinement effect in the mesochannels with their high aspect ratio for the retention of generated H₂/CO₂, which suppresses the competing formic acid dehydrogenation and promotes the formic acid hydrogenation.

Full text of DOI:10.1002/cctc.201900999

Accepted Article
Title: Catalytic Disproportionation of Formic Acid to Methanol by an
Iridium Complex Immobilized on Bipyridine-Periodic Mesoporous
Organosilica
Authors: Sho Yamaguchi, Yoshifumi Maegawa, Naoya Onishi, Ryoichi
Kanega, Minoru Waki Minoru Waki, Yuichiro Himeda, and
Shinji Inagaki
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ChemCatChem
10.1002/cctc.201900999
FULL PAPER
Catalytic Disproportionation of Formic Acid to Methanol by an
Iridium Complex Immobilized on Bipyridine-Periodic Mesoporous
Organosilica
[
a]
[a]
[b]
[b]
[a]
Sho Yamaguchi, Yoshifumi Maegawa, Naoya Onishi, Ryoichi Kanega, Minoru Waki, Yuichiro
[b]
[a,b]
Himeda,* and Shinji Inagaki*
Abstract: We report the first example of using heterogeneous
treatment of formate, is one of the most promising methods for
8
Iridium (Ir) catalysts under atmospheric pressure conditions to
the indirect production of MeOH from CO
formate production by hydrogenation of CO
significantly improved over the last two decades. Although the
disproportionation of FA is not good in terms of the atom
2
(Scheme 1), because
has been
achieve the catalytic disproportionation of formic acid to methanol.
2
5
9
IrCp* complex (Cp* = pentamethylcyclopentadienyl (η -C
5 5
Me )) was
immobilized on the pore surface of the periodic mesoporous
organosilica synthesized from a precursor mixture of ethane (Et) and
2
efficiency compared to the direct CO hydrogenation, the energy
2
,2′-bipyridine (BPy)-bridged organosilanes (Ir-Et-BPy-PMO). Ir-Et-
efficiency is higher because the reaction is carried out under
lower pressure and temperature. Miller and Goldberg et al.
reported the disproportionation of FA to MeOH with
BPy-PMO showed unique catalysis with higher selectivity of
methanol compared to homogeneous Ir-BPy complexes.
Furthermore, Ir-Et-BPy-PMO exhibited high reusability without any
noticeable decrease in activity for at least five times with no leaching
of Ir species during the reaction. The increase in methanol selectivity
of Ir-Et-BPy-PMO would be attributed to the unique confinement
effect in the mesochannels with their high aspect ratio for the
2 2
homogeneous [IrCp*(bpy)(H O)](OTf) (bpy = 2,2′-bipyridine) in
10
a closed system using 12 M FA (selectivity: 12.0%). Recently,
Himeda et al. achieved a significant improvement in MeOH
selectivity using [IrCp*(dmbp)(H
2,2′-bipyridine) under pressurized
pressurized H , ligand modification, and addition of H
selectivity: 47.1%). Cantat et al. reported the highly selective
MeOH generation using ruthenium catalysts and
methanesulfonic acid as an acid additive in a closed system at
2
O)](SO
4
) (dmbp = 5,5′-dimethyl-
conditions (e.g.,
SO
H
2
retention of generated H
2 2
/CO , which suppresses the competing
2
2
4
;
11
formic acid dehydrogenation and promotes the formic acid
hydrogenation.
12
1
50 ºC (selectivity: 50.2%). These studies show that a high
pressure condition in a closed system and an addition of acid
are important to improve the MeOH selectivity. It is known that
the disproportionation of FA is composed of dehydrogenation of
Introduction
Methanol (MeOH) is used as a basic ingredient of fuel and
chemicals, and research on the use of MeOH as a hydrogen
FA (Scheme 2) and hydrogenation of FA by produced H
Scheme 3). However, a reaction system under atmospheric
pressure suffered from low MeOH selectivity due to the
2
(
(
H
2
) energy carrier has attracted much attention in recent years.
The conventional hydrogenation of carbon dioxide (CO ) to
produce MeOH requires energy-intensive conditions such as
high temperature (200-250 °C) and high pressure (5-10 MPa).
Therefore, the development of an efficient system for MeOH
production under mild temperature and pressure is a challenging
issue to overcome.
2
2,11
predominance of the FA dehydrogenation (Scheme 2).
Since
reaction system under atmospheric pressure (open system)
would be more desirable for easy handling, a new approach is
needed to improve MeOH selectivity of the disproportionation of
FA under atmospheric pressure. Additionally, there are few
reports on the disproportionation of FA using heterogeneous
catalysts, which is an indispensable prerequisite for the
development of industrial MeOH production, possibly due to the
difficulties in heterogenization of Ir complexes on solid
1
Recently, the synthesis of MeOH from CO
formic acid (FA) using a homogeneous iridium (Ir) complex,
IrCp*(dhbp)(H O)](SO ) (dhbp = 4,4′-dihydroxy-2,2′-bipyridine),
2
mediated by
[
2
4
2
at a mild temperature (70 °C) in water was reported. However,
there were problems in improving the catalysis for hydrogenation
13
supports.
of CO
The hydrogenation of CO
governed by the equilibrium. Therefore, the indirect
hydrogenation of CO to MeOH has been investigated by using
CO derivatives such as carbonate , carbamate , formate , and
2
to FA and subsequent hydrogenation of FA to MeOH.
+
+
3
3HCOOH
CH
3
OH
H
2
O
2CO
2
2
to FA without base is strongly
Scheme 1. Disproportionation of formic acid.
2
4
5
6
2
7
urea . The disproportionation of FA, obtained by the acid
+
HCOOH
H
2
CO
2
[
a]
b]
Dr. S. Yamaguchi, Y. Maegawa, Dr. M. Waki, Dr. S. Inagaki
Toyota Central R&D Laboratories, Inc.,
Nagakute, Aichi 480-1192, Japan.
Scheme 2. Dehydrogenation of formic acid.
E-mail: inagaki@mosk.tytlabs.co.jp
+
+
HCOOH
2H
2
CH OH
H
O
2
3
[
Dr. N. Onishi, Dr. R. Kanega, Dr. Y. Himeda
National Institute of Advanced Industrial Science and Technology,
Tsukuba, Ibaraki 305-8565, Japan.
Scheme 3. Hydrogenation of formic acid.
E-mail: himeda.y@aist.go.jp
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ChemCatChem
10.1002/cctc.201900999
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2
+
Periodic mesoporous organosilica (PMO), which is
2+
O OH
Si
O OH
synthesized by the self-assembly and polycondensation of
organosilane precursors and a surfactant, is a functional porous
material possessing an organic-inorganic hybrid framework and
Sol.
Sol.
Ir
Si
Ir
Si
Si
O
N
O
N
O
O
N
N
Si
Si
14
N
OH
O
OH
O
a long mesochannel structure with pore diameters of 2-10 nm.
We recently synthesized BPy-PMO prepared from 100% BPy-
N
Si
O
O
Si
O
Si
O
Si
O
15
Si
Si
bridged organosilane precursors.
Since BPy groups
Si
Si
1
2
incorporated into the framework rotate freely and are exposed
on the pore surface, these BPy sites can be used as ligands for
2+
H O
1
6
2
metal complexes. Therefore, we envisaged that BPy-PMO is a
promising platform to immobilize molecular Ir-BPy complexes.
Here, we report the catalytic disproportionation of FA to MeOH
by an Ir complex immobilized on BPy-PMO. We also
synthesized Et-BPy-PMO, which is prepared by co-condensation
of Et and BPy-bridged organosilanes, as a new class of robust
BPy-containing PMO, because the co-condensation with Et-
bridged organosilane enhances the hydrothermal stability of the
PMO framework. It was revealed that Ir-Et-BPy-PMO exhibited
superior catalytic activity (MeOH yield and selectivity) and
structural stability for disproportionation of FA compared to Ir-
BPy-PMO (Figure 1). In comparison with homogeneous Ir
complexes, an increase in MeOH selectivity was achieved by
using Ir-Et-BPy-PMO under atmospheric pressure.
Ir
3: R = Me
: R = H
: R = OH
4
5
6
N
N
R
R
:
R
=
CF3
Figure 2. A lineup of Ir catalysts.
surfactant under basic conditions. While BPy-PMO has an
ordered two-dimensional (2D) hexagonal mesoporous structure
15
with crystal-like pore walls, Et-BPy-PMO has a 2D hexagonal
mesoporous structure and amorphous-like pore walls (Figure
S2). The amounts of BPy, DFT pore diameters (dDFT), and
Brunauer-Emmett-Teller (BET) surface areas (SBET) for BPy-
PMO and Et-BPy-PMO are listed in Table 1.
Immobilization of the Ir complex was carried out by mixing
[
IrCp*(H
room temperature to afford Ir-BPy-PMO (1) or Ir-Et-BPy-PMO (2)
Figure 2). The metal complexation caused a colour change in
2 3 4 3
O) ](SO ) with BPy-PMO or Et-BPy-PMO in CH CN at
(
the powder from white to yellow, thus suggesting the formation
of an Ir-BPy complex on the pore surface. From the scanning
electron microscopy (SEM) image of 2, shown in Figure S5, the
particle size was 2 – 4 µm. The amounts of Ir complexes in 1
and 2 were determined by inductively coupled plasma-optical
emission spectroscopy (ICP-OES), and are listed in Table 1. X-
ray
diffraction
patterns
(XRD)
and
nitrogen
adsorption/desorption isotherms revealed the preservation of the
ordered PMO structures and uniform mesoporosity even after
Figure 1. Disproportionation of formic acid to methanol by an iridium complex
immobilized on Et-BPy-PMO.
2
9
formation of the Ir complexes (Figure S4). The Si dipolar
decoupling magic angle spinning (DD-MAS) nuclear magnetic
resonance (NMR) spectrum of 2 showed no cleavage of Si-C
Results
1
3
bonds during the complexation (Figure S6). The C cross
polarization MAS NMR spectrum displayed the appearance of
new signals due to the Cp* ligand after the metal complexation
of Et-BPy-PMO, suggesting the formation of an IrCp* complex
Et-BPy-PMO was newly synthesized from the mixture precursors
of Et- and BPy-bridged organosilanes (9.2:1) using a cationic
(
Figure S7). X-ray absorption near-edge spectroscopy (XANES)
Table 1. Physical parameters of each sample.
and extended X-ray absorption fine structure (EXAFS) Fourier
transforms at the iridium LIII-edge for 2 showed spectral features
[
a]
[b]
[c]
DFT
[d]
Sample
BPy
mmol g ]
Ir
d
S
BET
2
corresponding
IrCp*(BPy)(H
to
O)](SO
those
of
the
model
complex
-
1
-1
-1
[
[mmol g ]
[nm]
4.3
3.8
4.9
4.9
[m g ]
[
2
4
)
(4), thus suggesting successful
formation of the desired Ir complex on the pore surface of Et-
BPy-PMO (Figures S8 and S9). The data for both catalysts, 2
and 4, are in good agreement with the fitting results (Table S1).
The disproportionation of FA to generate MeOH using
PMO catalysts 1 and 2 was investigated. FA solution containing
BPy-PMO
3.18
-
812
Ir-BPy-PMO (1)
Et-BPy-PMO
-
0.29
-
826
0.38
-
1180
802
Ir-Et-BPy-PMO (2)
0.16
2 4
5% H SO was heated at 50 °C for 24 h under atmospheric
pressure in the presence of the PMO catalysts (0.5 mol% Ir
relative to FA) (Table 2 and Figure S1). 1 showed almost no
catalytic activity (Table 2, entry 1, FA conversion: <1%), while 2
[
a] CHN analysis. [b] ICP-OES analysis. [c] Density functional theory (DFT)
pore diameter. [d] Brunauer-Emmett-Teller (BET) surface area.
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ChemCatChem
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FULL PAPER
[
a]
Table 2. Methanol generation from formic acid by several Ir catalysts.
[
b]
Entry
Catalyst
FA conv. [%]
MeOH
Yield [µmol]
Sel. [%]
-
1
2
1
2
2
2
3
4
5
6
<1
19
43
9
-
42
87
47
48
71
58
15
6.5
6.0
8.3
1.4
2.1
2.3
4.3
[
c]
d]
3
4
5
6
7
8
[
Figure 3. Time course experiments. Reaction conditions: [HCOOH] = 1.0 M,
>99
97
73
11
2 4
10 mL, 5% H SO , 0.5 mol% Ir, 50 °C.
[a] Reaction conditions: [HCOOH] = 1.0 M, 10 mL, 5% H
2 4
SO , 0.5 mol% Ir,
24 h, 50 °C. [b] The sum of MeOH and HCOOMe is used. [c] 96 h. [d]
[HCOOH] = 2.0 M, 0.5 mmol of H
2 4
SO .
was effective for disproportionation of FA to afford 42 μmol of
MeOH after 19% conversion of FA, which corresponds to 6.5%
MeOH selectivity (Table 2, entry 2). No generation of carbon
monoxide was observed. When the reaction time was increased
to 96 h, 87 μmol of MeOH was obtained with high MeOH
selectivity of 6.0% (Table 2, entry 3). In this case, the turnover
number (TON) was 1.7. At high FA concentration (2 M), MeOH
selectivity increased up to 8.3% (Table 2, entry 4).
The catalytic activity of various homogeneous catalysts for
the disproportionation of FA under identical conditions was also
examined (Table 2, entries 5-8). In order to investigate the
electronic effect of the substituents on the BPy ligand, we
prepared homogeneous Ir catalysts 3-6 based on 5,5′-
substituted BPy ligands as shown in Figure 2. When the Ir
catalysts bearing H (4) or an electron-donating Me (3) group
were applied, the conversion of FA increased dramatically
Figure 4. XRD patterns and b) nitrogen adsorption and desorption isotherms
of 1 before (black) and after (red) reaction; c) XRD patterns and d) nitrogen
adsorption and desorption isotherms of
reaction.
2 before (black) and after (red)
40 h, because the MeOH selectivity was consistently high.
Furthermore, the production rate of MeOH for 2 was faster than
that of 6. The use of 2 leads to a significant increase in the
MeOH yield and selectivity under atmospheric pressure, in
comparison with homogeneous Ir complexes possessing either
electron-donating or -withdrawing groups.
(
>97%), but the MeOH selectivity was low (1.4 – 2.1%) (Table 2,
entries 5 and 6). This means that almost all the FA was
decomposed to give H and CO as shown in Scheme 2. By
2
2
using 5 possessing the OH substituent, the conversion of FA
was also high (73%), with a MeOH selectivity of 2.3% (Table 2,
entry 7). In contrast, the introduction of the electron-withdrawing
In order to investigate the stability of the PMO catalysts,
the XRD and nitrogen adsorption/desorption isotherms were
measured after the reactions. These measurements indicated
that ordered PMO structures and uniform mesoporosity of 2
were almost completely preserved even after the reaction
CF
but an increase in the MeOH selectivity to 4.3% (Table 2, entry
).
3
group (6) led to a decrease in the FA conversion to 11%,
8
Time course experiments using catalysts 2, 3, and 6 are
2
9
shown in Figures 3 and S10. When catalyst 3 was used, the
MeOH yield increased linearly for 10 h then became saturated,
affording 48 μmol of MeOH after 96 h. The saturation of the
MeOH yield suggested the full conversion of FA due to the FA
(Figures 4c and 4d). The Si DD-MAS NMR spectrum of 2
showed the preservation of Si-C bonds during the reaction
(Figure S12). In contrast, the XRD pattern and nitrogen
adsorption/desorption isotherm of 1 after the reaction showed a
large decrease in diffraction intensity and amount of nitrogen
adsorbed, indicating a collapse of the ordered mesoporous
structure (Figures 4a and 4b). The low catalytic activity of 1 is
dehydrogenation giving H
catalyst 2 showed slow consumption of FA to give MeOH over
6 h. The MeOH yield using 2 exceeded that using 3 after 30 to
2 2
and CO . In contrast, the use of
9
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catalyst showed that the Ir loading was not changed, even after
the fifth reaction. These results indicate that the Ir complex is
immobilized strongly on the Et-BPy-PMO support and is the
active species for the disproportionation of FA. The effect of the
initial concentration of FA on the catalytic properties of 2 and 3
was investigated (Figure 6 and Table S2). For 3, the MeOH
yield increased in a linear manner with an increase in the FA
concentration, while the MeOH yield using 2 reached saturation
(
Figure 6a). The FA consumption rate was plotted against the
FA concentration (Figure 6b). Although the FA consumption rate
for 3 increased linearly, that for 2 reached saturation as the FA
concentration increased. The saturation of FA consumption rate
for 2 is attributable to the diffusion limitation of FA in the
mesochannels. It is noteworthy that the MeOH selectivity for 2
increased significantly with the FA concentration, while that for 3
only increased slightly as shown in Figure 6c. The significant
increase in MeOH selectivity for 2 strongly suggested that the
Figure 5. a) Reuse experiments using 2. Reaction conditions: [HCOOH] = 1.0
M, 10 mL, 5% H
Reaction conditions: [HCOOH] = 1.0 M, 10 mL, 5% H
0 °C.
2
SO
4
, 2 (0.5 mol% Ir), 24 h, 50 °C. b) Filtration experiment of 2.
2
SO , 2 (0.5 mol% Ir),
4
5
thus attributed to the structural collapse of PMO mesochannels
2
9
during the reaction. The Si DD-MAS NMR spectrum showed
no cleavage of Si-C bonds during the reaction (Figure S11).
These results clearly show that the co-condensation of Et- and
BPy-bridged organosilanes increased the structural stability of
PMO in FA solution.
2 2
increased amount of the generated H /CO in the mesopores
suppressed the excess FA dehydrogenation and promoted the
FA hydrogenation as discuss in the next section.
The reusability of 2 for the disproportionation of FA was
Discussion
investigated under the same reaction conditions.
2 was
recovered by filtration after the reaction and reused for the next
reaction. The experiment was repeated five times, and no
noticeable decrease of the MeOH yield or FA conversion was
observed (Figure 5a). The TON was 3.9 after the five reactions.
Furthermore, to check for leaching of the Ir species during the
reaction, the PMO catalyst was removed by filtration after 3 h
and the reaction was continued in the filtrate. No additional
MeOH generation or FA consumption was detected from the
filtered solution (Figure 5b). ICP-OES analysis of the recovered
In order to clarify the electronic effect of the substituents
on the BPy ligands, the FA conversion and MeOH selectivity for
the homogeneous and heterogeneous Ir catalysts were plotted
against the Hammett parameters (σ
m
) of the substituents on the
BPy ligands (Figure 7). The homogeneous Ir catalysts showed
a linear relationship between the σ values and both the FA
conversion and MeOH selectivity. However, the FA conversion
1
7
m
1
8
and MeOH selectivity for 2 (σ
m
= 0.09) deviated from this
relationship, with the FA conversion being lower and the MeOH
selectivity higher than those for the homogeneous catalysts.
These results indicate that the difference in catalysis between 2
and the homogeneous catalysts cannot be explained by only the
electronic effect of substituents on the BPy ligand.
Figure 7. a) FA conversion and b) MeOH selectivity versus σ
homogeneous Ir catalysts 3-6. ●: FA conversion and ♦: MeOH selectivity
using homogeneous Ir catalysts (see Table 2). ○, ◊: 2 based on σ value of
Si(OMe)
m
value for 2 and
m
3
.
Figure 6. Influence of the initial FA concentration on the a) MeOH yield, b) FA
consumption rate and c) MeOH selectivity using 2 and 3. The FA consumption
rate was estimated based on total 24 h for 2 and initial 30 min for 3. Reaction
The Laurenczy and Himeda group reported that MeOH
selectivity for homogeneous Ir catalysts largely increased when
2 4
conditions: [HCOOH] = 10 mL, 0.5 mmol of H SO , 0.5 mol% Ir, 24 h, 50 °C.
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a closed vessel was used instead of an open vessel or when
Et-BPy-PMO. The BPy-nanotubes have a pore diameter of 6.4
nm and tube lengths of 100 – 300 nm (estimated from TEM
images). The aspect ratios of the tubes were 15 – 50,
significantly smaller than the values (400 – 800) for Et-BPy-PMO.
Thus, the confinement effect in the nanotubes for the retention
2
,11
H
H
2
/CO
/CO
2
pressure was applied.
pressure suppresses the excess FA dehydrogenation
This is reasonable because the
2
2
(
Scheme 2) and promotes the FA hydrogenation to produce
MeOH (Scheme 3). Therefore, we speculated that the H /CO ,
2
2
generated by the FA dehydrogenation, would be retained in the
PMO mesochannels which suppresses the excess reaction of
FA dehydrogenation and promotes the FA hydrogenation, and
consequently improve the MeOH selectivity even under
atmospheric pressure using an open vessel. Figure 8 shows
2 2
of H /CO should be very small. This would be one of reasons
for almost no formation of MeOH in the BPy-nanotube system. A
lower Hammett parameter of the substituents for Ir-BPy-
nanotubes (σ
p
m
= –0.17) compared to Ir-Et-BPy-PMO (σ = 0.09)
also contributes to the decreasing yield of MeOH.
H
2
/CO
open systems in this study. For the homogeneous system, the
generated H /CO can be smoothly evacuated from the reaction
solution, while for the heterogeneous PMO system, the
generated H /CO would be retained to some extent in the
2
flow for the homogeneous and heterogeneous catalysis
2
2
Conclusions
2
2
The catalytic disproportionation of FA by heterogeneous Ir-BPy-
PMO catalysts and homogeneous Ir-BPy catalysts with electron-
donating and -withdrawing substituents was evaluated under
atmospheric pressure. The conventional BPy-PMO was not
suitable as a support for this reaction, because the mesoporous
structure collapsed after the reaction. The newly synthesized Ir-
Et-BPy-PMO was stable for this reaction and exhibited efficient
catalysis with higher MeOH selectivity (up to 8.3%) compared to
homogeneous Ir catalysts (1.4 – 4.3%). This catalyst gave a
high yield of MeOH (87 µmol) after 96 h, which was higher than
those for homogeneous Ir-BPy catalysts with electron-donating
mesopores due to their long and narrow mesochannel structure.
The large particle size of Et-BPy-PMO (2 – 4 µm) creates a long
mesochannel structure with a small pore diameter (4.9 nm),
yielding a very high aspect ratio (400 – 800). The characteristic
2 2
pore structure of Et-BPy-PMO could retain H /CO , similar to
when H /CO pressure is applied for the homogeneous catalyst.
2
2
The increase in MeOH selectivity with the increase in FA
concentration for 2 in Figure 6c supports the idea of the
confinement effect. In other words, the confinement effect plays
a significant role at high FA concentration due to an increase in
the generated amount of H
a great advantage in that H
2
/CO
2
. The PMO system would have
pressure can be increased
(
3
Me) and electron-withdrawing (CF ) groups (48 and 47 µmol,
2
/CO
2
respectively). Ir-Et-BPy-PMO also exhibited good reusability for
at least five times with no leaching of the Ir species during the
reactions. As one of the possible reasons for increasing MeOH
selectivity, we discussed on the confinement effect in the
locally in the mesochannels due to the confinement effect even
under atmospheric pressure using an open vessel. However,
further work is needed for proving the confinement effect of
PMO for the improvement of MeOH selectivity.
mesopores for the retention of
dehydrogenation reaction of FA. The retention of H
H
2
/CO
2
generated by the
/CO in the
2
2
mesochannels suppressed the excess reaction of FA
dehydrogenation and promoted the FA hydrogenation, and
consequently improved the MeOH selectivity. Our findings will
provide insights into new directions for improvement of MeOH
selectivity in FA disproportionation under atmospheric pressure.
Acknowledgements ((optional))
We wish to thank Dr. Masamichi Ikai (Toyota Central R&D Labs,
Inc.) for the XAFS measurements, and Mr. Satoru Kosaka
(
Toyota Central R&D Labs, Inc.) for the ICP–OES
measurements. The XAFS measurements were performed at
SPring 8 (BL14B2: 2017B1633). This work was supported in
part by the ACT-C program of the Japan Science and
Technology Agency (JST) (JPMJCR12Y1) and by a Grant-in-Aid
for Scientific Research (18K14267) from the Japan Society for
the Promotion of Science (JSPS).
2 2
Figure 8. Schematic illustrations for H /CO flow in a) homogeneous and b)
PMO systems.
Very recently, Gascon et al. reported the hydrogenation of
FA to produce MeOH using Ir-based bipyridine-functionalized
organosilica nanotubes (BPy-nanotubes), which has almost the
same framework composition to our Et-BPy-PMOs. However,
they did not observe any formation of MeOH via
disproportionation of FA when the reaction was performed in the
Keywords: heterogeneous catalysis • iridium •
disproportionation • methanol • formic acid
13
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2
absence of H , which was different result from our study using
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3
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Iridium complex immobilized on
periodic mesoporous organosilica
containing a bipyridine scaffold
exhibited higher methanol selectivity
in disproportionation of formic acid
compared to equivalent
homogeneous complexes, possibly
due to the confinement effect of
mesopores to retain the generated
Sho Yamaguchi, Yoshifumi Maegawa,
Naoya Onishi, Ryoichi Kanega, Minoru
Waki,Yuichiro Himeda*, Shinji Inagaki*
Page No. – Page No.
Catalytic Disproportionation of
Formic Acid to Methanol by an
Iridium Complex Immobilized on
Bipyridine-Periodic Mesoporous
Organosilica
2 2
H /CO which suppress the excess
formic acid dehydrogenation and
promote the formic acid
hydrogenation.
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