Catalytic Semi-Water–Gas Shift Reaction: A Simple Green Path to Formic Acid Fuel

Article abstract of DOI:10.1002/cssc.201903417

Formic acid (FA) is a promising CO and hydrogen energy carrier, and currently its generation is mainly centered on the hydrogenation of CO₂. However, it can also be obtained by the hydrothermal conversion of CO with H₂O at very high pressures (>100 bar) and temperatures (>200 °C), which requires days to complete. Herein, it is demonstrated that by using a nano-Ru/Fe alloy embedded in an ionic liquid (IL)-hybrid silica in the presence of the appropriate IL in water, CO can be catalytically converted into free FA (0.73 m) under very mild reactions conditions (10 bar at 80 °C) with a turnover number of up to 1269. The catalyst was prepared by simple reduction/decomposition of Ru and Fe complexes in the IL, and it was then embedded into an IL-hybrid silica {1-n-butyl-3-(3-trimethoxysilylpropyl)-imidazolium cations associated with hydrophilic (acetate, SILP-OAc) and hydrophobic [bis((trifluoromethyl)sulfonyl)amide, SILP-NTf₂] anions}. The location of the alloy nanoparticles on the support is strongly related to the nature of the anion, that is, in the case of hydrophilic SILP-OAc, RuFe nanoparticles are more exposed to the support surface than in the case of the hydrophobic SILP-NTf₂, as determined by Rutherford backscattering spectrometry. This catalytic membrane in the presence of H₂O/CO and an appropriate IL, namely, 1,2-dimethyl-3-n-butylimidazolium 2-methyl imidazolate (BMMIm?MeIm), is stable and recyclable for at least five runs, yielding a total of 4.34 m of free FA.

Full text of DOI:10.1002/cssc.201903417

Accepted Article
Title: Catalytic Semi-Water Gas Shift Reaction: A Simple Green Path to
Formic Acid Fuel
Authors: Jairton Dupont, Muhammed Irfan Qadir, Marcus V
Castegnaro, Felipe F, Mario Samperi, Jesum A Fernandes,
and Jonder Morais
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemSusChem 10.1002/cssc.201903417
Link to VoR: http://dx.doi.org/10.1002/cssc.201903417
A Journal of
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ChemSusChem
10.1002/cssc.201903417
FULL PAPER
Catalytic Semi-Water Gas Shift Reaction: A Simple Green Path to
Formic Acid Fuel
[
a]
[b]
[b]
[c]
[c]
MuhammadꢀI.ꢀQadir, ꢀMarcusꢀV.ꢀCastegnaro, ꢀFelipeꢀF.ꢀSelau, ꢀMarioꢀSamperi, ꢀJesumꢀA.ꢀFernandes, ꢀ
[
b]
[a]
JonderꢀMorais ꢀandꢀJairtonꢀDupont*
Abstract: Formic acid (FA) is a promising CO and hydrogen energy
generated from water electrolysis, most hydrogen is still
produced by the water gas shift reaction (WGSR), which is not a
carrier and currently its generation is mainly centred on the
1
1-15
hydrogenation of CO
hydrothermal conversion of CO with H
>100 bar) and temperatures (>200°C) and requiring days to
2
. However, it can also be obtained by the
green process.
The WGSR is typically operated at high
2
O at very high pressures
pressure (1–6 MPa) and temperature (>200°C) to overcome the
reaction kinetics, though the reaction is mildly exothermic (~41
(
–
1
16, 17
complete. Herein, we demonstrate that use of a nano-Ru/Fe alloy
embedded in an ionic liquid (IL)-hybrid silica in the presence of the
appropriate IL in water, CO can be catalytically converted into free
FA (0.73 M) under very mild reactions conditions (10 bar at 80°C)
with TON up to 1269. The catalyst was prepared by simple
reduction/decomposition of Ru and Fe complexes in the IL, and it
was then embedded into an IL-hybrid silica [1-n-butyl-3-(3-
kJ mol ).
However, carbon monoxide (CO) can also be
used for the input energy since it can be generated by the partial
combustion of carbonaceous waste materials, which can then be
hydrothermally converted into FA. This strategy is akin to the
fixation of solar energy since the biomass used is grown by
sunlight.
The growth of plant life is the most efficient and cheapest
method in the first step of the solar energy. However, the direct
conversion of CO and water to FA (semi-water gas shift reaction,
SWGSR) has received little attention and the reported results
indicate that this process occurs at very high pressures (100–
trimethoxysilylpropyl)-imidazolium
hydrophilic (acetate, SILP-OAc)
2
bis((trifluoromethyl)sulfonyl)amide, (SILP-NTf )
cations
associated
and hydrophobic
anions]. The
with
(
location of the alloy NPs on the support is strongly related with the
nature of the anion, i.e., in the case of hydrophilic SILP-OAc, RuFe
NPs are more exposed to the support surface than in the case of the
1
8-20
200 bar) and temperatures (100–200°C).
Note that the first
step in the classical WGSR is generally assumed to follow
primarily via the formation of formiates. Therefore, if FA can be
generated directly from CO and water under mild reaction
conditions, the process will constitute a real green alternative to
current classical processes involving WGSR (to generate
hydrophobic SILP-NTf
backscattering spectrometry). This catalytic membrane in the
presence of H O/CO and an appropriate IL, namely, 1,2-dimethyl-3-
2
,
as determined by RBS (Rutherford
2
n-butylimidazolium 2-methyl imidazolate (BMMIm.MeIm), is stable
and recyclable for at least 5 runs, yielding a total of 4.34 M of free
FA.
2
hydrogen), followed by CO reduction, which is an energetically-
demanding approach. We envisaged that by using WGSR nano-
catalysts in the presence of FA “scavengers” (buffer-like
solution) and working at lower temperatures, FA could be
produced without decomposition into hydrogen (Scheme 1).
Introduction
The generation of formic acid (FA) from water can be a potential
man-made fuel alternative to present conventional fuels since it
1
, 2
can be relatively easily decarboxylated to produce hydrogen.
Currently, the most investigated process for the generation of FA
is mainly centred on the hydrogenation of carbon dioxide,
3
-5
employing several types of catalysts.
In fact, there is a
plethora of both homogeneous and heterogeneous catalysts that
can perform this reduction under different conditions with high
–
6-9
conversions, but they generally lead to formiate (HCO
2
). One
of the major drawbacks of this approach is the need of
1
0
hydrogen. Although hydrogen can be, in principle, sustainable,
[a]
Dr. M. I. Qadir, Prof. Dr. J. Dupont
Scheme 1. Reaction pathways for the generation of formic acid (FA) fuel.
Institute of chemistry
Universidade Federal do Rio Grande do Sul
Av. Bento Gonçalves, 9500 Porto Alegre 91501-970 RS (Brazil)
E-mail: jairton.dupont@ufrgs.br
Dr. M. V. Castegnaro, Dr. F. F. Selau, Prof. Dr. J. Morais
Institute of Physics, Federal University of Rio Grande do Sul,
Campus Agronomia, Porto Alegre, 90650-001 Brazil
M. Sampri, Dr. J. Alves Fernandes
Herein, we report that indeed free FA can be efficiently
generated by catalytic “water carbonylation” (SWGSR) by
employing supported bimetallic (Ru/Fe) nanoparticles (NPs) in
ionic liquid (IL) buffer-like solutions (Scheme 2) under very mild
[
b]
c]
[
School of Chemistry, University of Nottingham, University Park,
Nottingham, NG7 2RD United Kingdom
Supporting information for this article is given via a link at the end of
the document.
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ChemSusChem
10.1002/cssc.201903417
FULL PAPER
Figure 1. Transmission electron microscopy (TEM) image of RuFe NPs embedded in SILP-NTf
2
and (b) SILP-OAc supports and their size distribution with an
EDS map. Overlay of Ru-L and Fe-K of RuFe NPs.
reaction conditions (from 30 to 100°C) and pressures from 1 to
0 bar of CO. This represents a huge breakthrough in the
hydrophilic
[bis((trifluoromethyl)sulfonyl)amide, SILP-NTf
have already been shown to efficiency catalyse the WGSR in
the presence of ruthenium (Ru/SILP-NTf ). It is assumed that
formiate species are the primary intermediates of this reaction.
(acetate,
SILP-OAc)
and
hydrophobic
2
1
1
2
] anions, which
production of FA from biomass waste, opening new windows of
opportunity for the development of green and sustainable
processes of one the most promising chemical hydrogen energy
reservoirs.
2
2
2-
2
6
Hence, monometallic Ru and Fe, as well as alloyed bimetallic
RuFe nanoparticles, were prepared in the BMIm.NTf [1-n-butyl-
-methyl-1H-imidazol-3-ium bis((trifluoromethyl)sulfonyl)amide]
IL, employing chemical decomposition of Fe(CO) and
Ru(methylallyl) (cod) complexes under a H atmosphere using
similarly reported procedures (see the supporting information).
These NPs where embedded in prepared hybrid organosilicas
SILP-NTf and SILP-OAc) by simple impregnation and
characterized by transmission electron microscopy (TEM), X-ray
photoelectron spectroscopy (XPS), and Rutherford
backscattering spectrometry (RBS) analyses.
HR-TEM (Figures 1a and 1b) revealed the presence of regularly-
shaped ultrafine RuFe NPs with high dispersion in SILP-NTf
and a mean diameter of 1.0 ± 0.6 nm, where relatively large
.1±0.6 nm sized NPs were observed in SILP-OAc. The smaller
size NPs in SILP-NTf support is because of its hydrophobic
nature and has week cation−anion interaction strength (Im-NTf ),
2
3
5
2
2
2
7
(
2
2
2
Scheme 2. Schematic representation of the SWGSR driven by RuFe/SILP-
2
2
NTf in an aqueous solution of ionic liquids (ILs).
2
which does not allow the aggregation of NPs. While the
hydrophilic effect and strong cation−anion interaction strength
Results and Discussion
(
Im-OAc) in SILP-OAc support may cause the aggregation of
NPs to relatively large RuFe NPs (2.1±0.6 nm). EDX elemental
mapping of Fe and Ru (Figure 2), with their overlay, provided a
direct view of the metal atom distribution, confirming the alloyed
state of the NPs.
Preparation and characterization of catalysts
The first approach was to prepare supported ionic phase (SILP)
nanocatalysts by sol-gel processes using 1-n-butyl-3-(3-ꢀ
trimethoxysilylpropyl)-imidazolium cations associated with
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ChemSusChem
10.1002/cssc.201903417
FULL PAPER
summarizes the surface and the bulk, or global, metal loadings
and the stoichiometries obtained for the catalysts.
The NP stoichiometries obtained by XPS are close to those
obtained by RBS (see Table 1). The comparison of XPS and
RBS results for the catalysts´ metal loadings corroborates the
fact that the RuFe/SILP-OAc catalyst has a higher amount of
metal NPs anchored at the SILP surface (Table 1, entries 1).
Figure 2. Structures and abbreviations of the ILs and SILPs used in this study
2
The RBS spectrum of sample RuFe/SILP-NTf is shown as a
solid black line in Fig. 3(a). It presents regular plateaus for each
metal and silicon, indicating a uniform distribution of Fe and Ru
on the SILP. The PowerMEIS program was used to provide the
RBS simulation (red line) considering a simple sample structure
consisting of the superposition of uniform layers (silica and metal
alloy) with different heights and compositions in order to find the
best fit. The result indicates that iron and ruthenium form an
alloy with stoichiometries of 0.6 and 0.4, respectively. Figure
3
2
(b) compares the RBS spectra of both RuFe/SILP-NTf and
RuFe/SILP-OAc samples. It is clearly distinguishable that
RuFe/SILP-OAc shows prominent peaks in rising of the
corresponding Fe and Ru plateaus, which suggests a high
concentration of these metals on the catalyst surface. The inset
shows a schematic illustration of the sample structure used for
the RBS simulation of RuFe/SILP-OAc [solid red line in Figure
3
(b) inset]. The best structure case consisted of a spherical SILP
core (size of 150 nm) with a 1-nm thick Ru0.4Fe0.6 shell covering
0% of the SILP surface. The RBS simulations also indicated a
3
Figure 3. (a) RBS spectra obtained with 1.2 MEV He+ beam impinging on the
metal loading of 5% for both samples. Powder XRD analysis of
the catalysts (Figure S9) did not showed the RuFe phase
because of the low metal amount (2%).
RuFe/SILP-NTf
simulation (solid red line) provided by the PowerMEIS program.
2
sample (solid black line) along with the best fit RBS
(b)
Comparison between the RBS measurements of both RuFe/SILP-NTf2 and
RuFe/SILP-OAc samples. The inset shows the best fit RBS simulation
considering a spherical core-shell model consisting of a SILP core and a
Ru0.4Fe0.6 shell with 30% coverage. XPS data (circles) and chemical
components (colored lines) used in the analysis of Fe 2p (c) and Ru 3p (d)
regions
Table 1. Metal loadings and stoichiometries obtained by RBS (bulk) and XPS
(
surface).
Metal (%) location
Surface Bulk (by
Stoichiometry
Cat
Surface
Bulk (by
RBS)
(
by XPS)
RBS)
(by XPS)
Moreover, in the case of the NTf
the alloy NPs are located preferentially away from the surface
Table 1, entries 1). This is probably related to the
2 2
-containing support (SILP-NTf ),
RuFe/SILP-OAc
RuFe/SILP-NTf
20.7
5
Ru0.5Fe0.5
Ru0.4Fe0.6
2
7.3
5
Ru0.5Fe0.5
Ru0.4Fe0.6
(
hydrophobicity of the IL and their preferential interaction with the
hybrid silica and the alloy. The alloy is mainly composed of
oxidized metals (Figure 3) and has the tendency to be
accommodated close to more ionic regions of the material
XPS measurements were performed in the same conditions for
both RuFe/SILP-NTf and RuFe/SILP-OAc catalysts, as well as
for the supports (SILP-NTf and SILP-OAc) without the RuFe
2
2
(
surface of the hybrid silica) rather than to the IL contact ion pair
NPs used in their preparation (Figure 3c,d). Figure S1 shows the
XPS survey scan data of the four samples. The spectra
collected for the catalysts and their respective supports are very
similar, despite the presence of Ru and Fe peaks, whose low
intensities are due to the low metal-loadings of catalysts. The
presence of N and F are due the presence of the IL at the
sample surfaces. The main emission peaks of Ru, Fe, and Si
were used in quantifying the surface compositions. Table 1
2
8
regions. This behaviour is opposite, as expected, to that what
was observed for Pd(0) and Au(0) nanoparticles imprinted in
2
9, 30
similar hybrid silica supports.
It is important to note that XPS
analysis was used to study the location of metal only at the
surface region of the supports (Table), since XPS is a surface
sensitive technique. Such difference also corroborates the RBS
results, which indicated that RuFe/SILP-OAc sample presents a
much higher NPs concentration at the surface region as
2
compared to the RuFe@SILP-NTf . The chemical environments
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ChemSusChem
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of the Ru and Fe surface atoms were investigated by high
resolution XPS data of Ru 3p (Fig 3d) and Fe 2p (Figure 3c)
regions. The results obtained from the data deconvolution are
presented in Table S1. The Ru 3p doublet was deconvoluted
Interestingly, no FA was observed when the reaction was
performed with CO
conditions, which confirmed that the generated HCO
result from the hydrogenation of CO (Table 2, entry 8).
Remarkably, a high TONs (1452) was found with 0.84 M FA at
100°C, without the detection of H and CO gaseous products.
This showed that this catalytic system is not only active and
selective for the production of FA from CO and H O, but it also
does not decompose the formed FA. The Fe(CO) catalyst
2
/H
2
(1:1, 30 bar) under our standard
2
H did not
2
0
4+ 27, 31
into two chemical components related to Ru and Ru .
0
Table S1 indicates that the Ru component accounts for almost
2
2
7
0% of the Ru 3p photoemission region. The analysis of Fe 2p
region proved to be much more complicated due to the presence
of Fe atoms in different chemical environments. At the lower
2
5
0
binding energy part of Figure 3c, a small contribution of Fe can
showed very low activity for the FA (TON=0.4) under our
standard conditions (Table 2, entry 11).
be observed; however, the spectra are dominated by the
3
+
27, 32
contribution of Fe in tetrahedral and octahedral sites.
It is important to note that the type of IL has a strong effect on
both the catalytic activity and selectivity (Table 2, entries 5–7).
The best performance was obtained when employing the 1-n-
2
+
Additionally, a relevant contribution of Fe was observed for the
sample RuFe/SILP-NTf
2
.
butyl-2,3-dimethylimidazolium
2-methylimidazolate
Catalytic generation of formic acid from CO and H
The embedded bimetallic RuFe NPs in the supported ionic liquid
phase (SILP-NTf ) were found to be very active for the selective
generation of base-free FA (HCO H) in an aqueous solution of
imidazolium-based ILs at 80°C under 10 bar of CO gas (Table 2). buffer-like solution. Our catalytic systems representing higher
2
O
(BMMIm.MeIm) IL, which is known to activate water and
3
4, 35
generate a latent nucleophilic OH anion
CO surface species to generate formiates (akin to the classical
that can attack the
2
3
6-38
2
WGSR paths)
that are protonated to stabilized free FA in this
3
9
–
No HCO
However, a significant amount of HCO
was observed when utilizing the Ru/SILP-NTf
By incorporating the Ru with Fe, RuFe/SILP-NTf
2
H
was detected when Fe/SILP-NTf
H, with a TON of 174,
(Table 1, entry 3).
catalyst
2
was used.
2
catalytic effeciencies than the reported [Ru-EDTA(H O)]
4
0
2
catalyst that has only 1.5 TON, using inorganic bases.
2
2
represented significant activity with the generation of 0.73 M
FA/IL with the dominance of SWGSR (Table 2, entry 4), which
3
3
displays a positive metal dilution effect.
a
2 2
Table 2. Catalytic systems for the production of FA (HCO H) from CO/H O
b
Entry
Cat
–
IL
FA/M
–
TON/TOF
1
2
3
4
5
6
BMMIm.MeIm
BMMIm.MeIm
BMMIm.MeIm
BMMIm.MeIm
BMMIm.Im
–
–
Fe/SILP-NTf
2
–
2
Figure 4. Graphical representation of the IL-cage effect of hydrophobic (NTf )
and hydrophilic (OAc) anions in SILPs containing RuFe NPs
Ru/SILP-NTf
2
0.20
0.73
0.34
0.02
0.84
–
174/9.6
RuFe/SILP-NTf
RuFe/SILP-NTf
RuFe/SILP-NTf
RuFe/SILP-NTf
RuFe/SILP-NTf
RuFe/SILP-NTf
RuFe/SILP-NTf
2
2
2
2
2
2
2
1269/70.5
591/32.8
27.8/1.54
1452/80.6
–
Indeed, imidazolium-based ILs form a cage around the NPs,
akin to an ionic nano-container environment that allows for
controlling the diffusion of reactants, intermediates, and products
3
(But) EP.MeIm
(
mainly via hydrophobicity and contact ion pairs) to the catalytic
c
active sites. It was found that BMMIm.MeIm showed remarkable
activity for the generation of FA (0.73 M, Table 2, entry 4) as
7
BMMIm.MeIm
BMMIm.MeIm
BMMIm.OAc
d
8
compared
to
the
tri-n-butyl(ethyl)phosphonium
2-
methylimidazolate (0.02 M FA/IL, Table 2, entry 6). This reflects
the vital role of the imidazolium moiety in BMMIm.MeIm ILs on
its buffering properties and stabilization of weak carbonic acid
9
–
–
1
0
BMIm.BF
4
–
–
3
4
species.
e
1
1
Fe(CO)
RuFe/SILP-OAc
RuFe/SiO
5
BMMIm.MeIm
BMMIm.MeIm
BMMIm.MeIm
0.20
0.55
0.59
0.4/0.02
1026/57.0
956/53.1
The geometric and electronic properties of NPs supported in ILs
can be tuned by the proper choice of the IL cations and anions,
along with NPs that strongly influence the residence
time/diffusion of the reactants, intermediates, and products in
1
1
2
3
2
2
9, 30
the nano-environment.
hydrophilic nature of the SILP represented
influence on the conversion of CO and H O to FA. SILP having a
hydrophobic anion (NTf ) showed higher activity (TOF 80.6 h )
Interestingly, the hydrophobic and
[
a] Reaction conditions: Cat. (RuFe/SILP.NTf
bar), H O (3.8 mL, 211 mmol), IL (1.07 mmol), time (18 h) and temp. (80 °C).
b] TON/TOF were calculated on the basis of presence of active atoms of Ru
2
, 2 wt% RuFe, 25 mg), CO (10
a
remarkable
2
2
[
(
4
1
–1
chemcatchem). [c] Reaction at 100°C. [d] In the presence of CO
2
/H
2
(1:1, 60
2
bar). [e] Fe(CO) (100 mg).
5
as compared to the RuFe NPs having hydrophilic SILP with the
acetate (OAc) anion (Figure 4). This may be correlated with the
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ChemSusChem
10.1002/cssc.201903417
FULL PAPER
–
hydrophobicity of the NTf
2
anion of RuFe/SILP-NTf
2
) in which
are provided in the SI (Table S1). The calculated Ea for the
–
1
RuFe NPs are presented deep into the IL, region (as shown by
the XPS analysis). It generates the “IL-cage” around the NPs
that act as a catalytic membrane-like device, which not only
repels the water from the catalytic active surface species but
also allows reactive intermediate to follow the SWGS pathway.
The opposite phenomena were observed in RuFe/SILP-OAc, in
which the RuFe NPs were presented at the surface of the IL
region (as shown by the XPS analysis). The recyclability of the
WGSR range from 33 to 80 KJ mol , which is obtained when
employing Ir, Pd, Pt, and Au supported catalysts for the water
2 2
carbonylation that leads to H and CO . In these cases, formiate
is the most abundant experimentally observed intermediate
because its formation barrier is lower than its dissociation barrier.
4
4-49
But it is hard to be desorbed from the catalyst surface.
Ruthenium complexes supported in SILPs have also
–
1
represented higher activation energies (41–84 KJ mol ) in
2
4, 25, 50
RuFe/SILP-NTf
2
catalyst under our standard condition was also
WGSR.
Of note, neither of these catalytic systems were
examined that represented the stability of the catalysts without
able to yield FA.
th
losing the catalytic activity until 5 cycle (Figure S2). The final
FA concentration of 4.34 M (1.05 wt%) is similar to that obtained
2
by the hydrothermal transformation of CO/H O in presence of
4
2
bases at 217.9°C and 69.5 bar of CO. Hence, this system is a
potential substitute for the currently used hydrothermal method
of the catalytic generation of free FA.
2
Figure 6. Arrhenius plot: Cat. (RuFe/SILP.NTf , 2 wt% RuFe, 25 mg), CO (10
2
bar), H O (3.8 mL, 211 mmol), BMMIm.MeIm IL (1.07 mmol) and time (18 h).
InTOF (molFA/mol of presence of active atoms of Ru per second).
Figure 5. Reaction conditions: (a) Cat. (RuFe/SILP.NTf
CO (10 bar), H O (3.8 mL, 211 mmol), BMMIm.MeIm IL (1.07 mmol), time (18
h) and temp. (100°C). (b) Cat. (RuFe/SILP.NTf , 2 wt% RuFe, 25 mg), CO (10
bar), H O (3.8 mL, 211 mmol), IL (1.07 mmol) and time (18 h).
2
, 2 wt% RuFe, 25 mg),
2
Of note, the BMMIm.MeIm IL plays an important role not only in
the formation of reactive active species but also in the
stabilization of FA. A linear relationship between the amount of
IL and the amount of FA on a double logarithmic scale (Fig. 7a)
provides evidence that the IL acts as a buffer during the
2
2
The effect of CO concentration was investigated at different
pressures (Fig. 5a). It is important to note that a significant
carbonylation of CO with H
2
O to FA. This behaviour is explained
5
1,
–
1
by the Henderrson-Hasselbach equation for buffering systems
amount of FA (0.60 M) was generated, with TOF of 61.3 h , just
at 1 bar of CO. The rate of reaction increased with the CO
5
2
and is consistent with the formation of free FA (not formates).
–
1
Moreover, the activity of the catalyst was also evaluated as a
function of time (Figure 7b), which increased with increasing
reaction time.
pressure from 1 bar to 10 bar at 100°C reaching TOF of 80.6 h .
Unfortunately, the concentration of formed FA decreased when
increasing the CO pressure (>10 bar). At 20 bars, a small
amount of FA (0.41 M) was obtained, which may be due to the
poisoning of the catalyst at very high concentration of CO.
Furthermore, the influence of reaction temperature, ranging from
3
0 to 100°C, was also examined, and increases in the TOF of
the reaction at fixed pressure were observed (Fig. 5b). Of note,
–
1
a turnover frequency (3.2 h ) was obtained at low temperature
–
1
(
30°C), reaching a value of 80.6 h , which may be because of
the increase in the sorption of CO in ILs with the increase in
temperature, which may be kinetically controlled owing to the
4
3
high activation energy. An Increase in temperature could
reduce the kinetic barrier and promote this reaction efficiently.
Unfortunately, the rate of reaction decreased significantly at
1
20°C, which is due to the decomposition of HCO
2
H into CO
2
Figure 7. (a) Reaction conditions: Cat. (RuFe/SILP.NTf
CO (10 bar), H O (3.8 mL, 211 mmol), BMMIm.MeIm IL, time (18 h) and temp.
100°C). (b) TON vs time; Cat. (RuFe/SILP.NTf , 2 wt% RuFe, 25 mg), CO (10
O (3.8 mL, 211 mmol), BMMIm.MeIm IL and temp. (100°C).
2
, 2 wt% RuFe, 25 mg),
and H , as observed by GC of the gaseous phase.
2
2
(
2
Arrhenius plot were obtained based on the linear fitting of lnTOF
vs. 1000/T from from 30 to 100°C, which lead to an apparent
bar), H
2
–
1
activation energy Ea= 31.04±0.6 KJ mol (Figure 6). The details
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The turnover number was 695 with 0.4 M FA after 1 h of reaction, Keywords: Semi-water gas shift • RuFe NPs • ionic liquids •
which reached 1,452 with 0.84 M FA after 18 h, indicating a first
carbon monoxide • formic acid
4
order reaction. Of note, no CH and other higher hydrocarbons
were detected in gas phase during our reactions.
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We demonstrate a simple method for
the production of formic acid by the
simple catalytic carbonylation of water
under very mild reaction conditions
employing supported bimetallic Ru/Fe
nanoparticles in the presence of ionic
liquids.
Muhammad I. Qadir,ꢀMarcus V.
Castegnaro, Felipe F. Selau, Mario
Samperi, Jesum A. Fernandes, Jonder
Morais and Jairton Dupont*
Page No. – Page No.
Catalytic Semi-Water Gas Shift
Reaction: A Simple Green Path to
Formic Acid Fuel
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