Quantitative aqueous phase formic acid dehydrogenation using iron(II) based catalysts

Article abstract of DOI:10.1016/j.jcat.2015.11.012

We present here the results of our investigation on aqueous phase formic acid (FA) dehydrogenation using non-noble metal based pre-catalysts. This required the synthesis of m-trisulfonated-tris[2-(diphenylphosphino)ethyl]phosphine sodium salt (PP₃TS) as a water soluble polydentate ligand. New catalysts, particularly those with iron(II), were formed in situ and produced H₂ and CO₂ from aqueous FA solutions, requiring no organic co-solvents, bases or any additives. Manometry, multinuclear NMR and FT-IR techniques were used to follow the dehydrogenation reactions, calculate kinetic parameters, and analyze the gas mixtures for purity. The catalysts are entirely selective and the gaseous products are free from CO contamination. To the best of our knowledge, these represent the first examples of first row transition metal based catalysts that dehydrogenate quantitatively formic acid in aqueous solution.

Full text of DOI:10.1016/j.jcat.2015.11.012

Journal of Catalysis xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Quantitative aqueous phase formic acid dehydrogenation using iron(II)
based catalysts
⇑
Mickael Montandon-Clerc, Andrew F. Dalebrook, Gábor Laurenczy
Institut des Sciences et Ingénierie Chimiques, LCOM, GCEE, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
We present here the results of our investigation on aqueous phase formic acid (FA) dehydrogenation
using non-noble metal based pre-catalysts. This required the synthesis of m-trisulfonated-tris[2-(diphe
nylphosphino)ethyl]phosphine sodium salt (PP3TS) as a water soluble polydentate ligand. New catalysts,
particularly those with iron(II), were formed in situ and produced H2 and CO2 from aqueous FA solutions,
requiring no organic co-solvents, bases or any additives. Manometry, multinuclear NMR and FT-IR tech-
niques were used to follow the dehydrogenation reactions, calculate kinetic parameters, and analyze the
gas mixtures for purity. The catalysts are entirely selective and the gaseous products are free from CO
contamination. To the best of our knowledge, these represent the first examples of first row transition
metal based catalysts that dehydrogenate quantitatively formic acid in aqueous solution.
Ó 2015 Elsevier Inc. All rights reserved.
Received 2 October 2015
Revised 13 November 2015
Accepted 18 November 2015
Available online xxxx
Keywords:
Hydrogen generation
Catalysis
Formic acid
Iron(II) complex
Aqueous solution
Non-precious metal
Phosphine ligands
1. Introduction
candidates for the chemical storage and controlled release of
hydrogen, but they present selectivity and safety issues, and this
A large proportion of our energy infrastructure is fossil fuel
based, and as energy demand continues to grow in parallel with
society [1], we consume more and more of this limited resource.
The problem is twofold; as supply dwindles prices fluctuate, while
at the same time extraction and utilization of gas, coal and oil exac-
erbate terrestrial and atmospheric pollution. Society must there-
fore shift toward less wasteful lifestyles, and new technologies
such as wind and solar electricity should be pursued as alternative
energy sources.
Hydrogen will play an important role as a future energy carrier
due to its high gravimetric energy density and clean combustion
pathways. However, current storage methods using pressurized
vessels or very low temperature liquid H2 present safety hazards
and are inconvenient to handle. For example, a 300 bar cylinder
with 200 L capacity typically weighs around 100 kg, with an effec-
tive gravimetric storage density of only 5.4 wt.% [2,3]. An impor-
tant challenge for the scientific community is thus the
development of new hydrogen storage materials [4]. These could
include physical storage media such as carbon nanostructures [5]
and metal–organic frameworks (MOFs), which often require low
adsorption temperatures [6,7]. Alcohols [8–10] are likely
latter is due to their flammability, volatility and toxicity. Sodium
borohydride and ammonia borane [11] are alternatives with mod-
erate storage capacities, however NaBH4 is costly, while ammonia
borane regeneration is difficult in practice. Formic acid (FA) is also
a promising hydrogen storage material with distinct advantages. It
is liquid at r.t. with a gravimetric storage capacity of 4.4 wt.%. FA is
somewhat corrosive, has a low toxicity and is non-flammable
below 85 vol.% concentration. In 2008, our group presented a novel
approach to hydrogen generation using FA, where hydrogen was
released on demand using a robust and effective ruthenium cata-
lyst under mild conditions [12]. We have contributed further in
this area over the past years [13–17].
FA has two potential decomposition pathways. These are
dehydrogenation,
HCOOH ? H2 + CO2,
and
dehydration,
HCOOH ? H2O + CO. As the main objective of this work is to
directly use the produced H2 in fuel cells, the latter reaction is
undesirable due to the poisoning effects of CO on the catalysts that
are on the polymer membrane of the fuel cells.
An ideal energy storage cycle would combine carbon dioxide
with H2 from renewable resources, or reduce CO2 electrochemi-
cally with solar/wind-powered electricity to generate formic acid.
FA production is even possible in acidic media, under base-free
conditions, as our group demonstrated recently [18,19]. Stocks of
FA then would be used as transportable fuels for on-demand
⇑
Corresponding author. Fax: +41 21 693 9780.
E-mail address: gabor.laurenczy@epfl.ch (G. Laurenczy).
http://dx.doi.org/10.1016/j.jcat.2015.11.012
0021-9517/Ó 2015 Elsevier Inc. All rights reserved.
Please cite this article in press as: M. Montandon-Clerc et al., Quantitative aqueous phase formic acid dehydrogenation using iron(II) based catalysts, J.
Catal. (2015), http://dx.doi.org/10.1016/j.jcat.2015.11.012

2
M. Montandon-Clerc et al. / Journal of Catalysis xxx (2015) xxx–xxx
remote power generation or even for mobile applications. Other
research groups have also investigated the formic acid/CO2 couple
using different metal salts as pre-catalysts, such as ruthenium
[20–23], iridium [24–26], or even their combination in bimetallic
systems [27]. Usually homogeneous catalysts offer greater selectiv-
ity toward the dehydrogenation reaction, although progress is
being made with certain gold or palladium nanoparticles sup-
ported on various media [28–31], or the use of non-metal catalysts
such as boron [32]. With the intent to combine the advantages of
both homogeneous and heterogeneous catalysts, immobilization
of the highly active and stable Ru(II)-mTPPTS catalyst on ion
exchange resins, in polymers, on silica and zeolites was carried
out in our group [33].
It is notable that most of the current catalysts for formic acid
dehydrogenation based on noble metals operate in organic media
or require additives for an efficient reaction. The utility of these
processes will thus be diminished by dwindling metal resources,
the hazardous nature of solvents and/or the overall costs. While
several examples of non-noble iron and cobalt metal containing
catalysts are active for the selective cleavage of FA or for the
reverse reaction of CO2 hydrogenation in basic media [34–42],
none of them operate in aqueous solution. In this paper we
describe the synthesis of a new water soluble phosphine ligand,
its in situ complexation with various first row transition metals
and the results of catalytic investigations for formic acid dehydro-
genation reaction.
with respect to the metal salts. The tubes were capped and perfo-
rated with a small plastic tube to maintain 1 bar pressure, and then
subsequently heated to the desired temperature. The first catalytic
reactions of the FA dehydrogenation were followed by 1H NMR via
monitoring the formyl peak integrals versus an internal standard
(Table 1 and Fig. 2).
In light of successful studies utilizing Co–PP3 complexes for FA
decomposition [38], we similarly tested cobalt, manganese and
zinc salts in combination with PP3TS (Table 1, entries 1–4). In each
case a color change indicating complexation was observed upon
mixing the reagents, however none were active for FA
dehydrogenation.
A similar color change to deep purple occurred upon mixing
PP3TS and various iron(II) salts. As a difference to the other metals,
an 1 mM iron(II)–PP3TS solution exhibited slight activity for FA
decomposition (Table 1, entry 5), while with a 5 mM precatalyst
concentration (entry 6), 100% conversion was reached after 7.5 h
with a turnover number (TON) of 1000. Considering entries 5–9,
the reaction rates correlated with pre-catalyst concentration, i.e.
at 25 mM the reaction completed in 3 h, while doubling this to
50 mM required only about 1 h. It is notable that the reaction rate
was not increased further at 100 mM, where it is likely that a sol-
ubility limit was reached and/or inactive particles formed and a
precipitate was observed. Entries 16 and 17 reveal that anion
effects could also be significant, as an Fe(BF4)2 precursor displayed
higher TOF (turnover frequency) values than the chloride salts. Pre-
vious works by Beller’s group for a similar iron(II) system indicated
that chloride ions have inhibiting effect due to the chloro-complex
formation [37]. We should note that with no special precautions
against oxidation (air), 25 mM aqueous precatalyst solutions do
not lose activity even after 30 dehydrogenation cycles at 80 °C
and 8 weeks in solution (total TONs of over 13 000, see experimen-
tal part for detailed procedure and conditions). Additionally, sepa-
rate blank tests were performed with only Fe(BF4)2 or PP3TS. At
80 °C no reaction was observed in either case, indicating that the
in situ-formed complex is solely responsible for formic acid
dehydrogenation.
2. Results and discussion
2.1. Synthesis of PP3TS
Recently Boddien et al. developed a highly active iron(II) catalyst
with the tris[2-(diphenylphosphino)ethyl]phosphine (PP3) ligand
[37]. We have decided to replace the applied propylene carbonate
solvent with water, as a greener and cheaper environmentally
benign alternative reaction media. Like the triphenylphosphine
(PPh3), PP3 is a fairly hydrophobic compound, but we have realized
that its phenyl rings were amenable toward aromatic sulfonation.
We developed a route for the sulfonation of PP3. PP3 was dis-
solved in concentrated sulfuric acid under an inert atmosphere,
oleum was carefully added and the reaction mixture was stirred
for 4 days. It was neutralized and worked up to afford PP3TS as a
purple crystalline powder (see Section 4). The purity of PP3TS
was confirmed by 31P NMR, 1H NMR, mass spectroscopy and ele-
mental analysis. Although we have no direct structural evidence,
it is obvious that sulfonation took place at the meta position of
three phenyl rings [43] where the functional groups should not
sterically interfere with metal binding (see Fig. 1).
The effect of the temperature was also investigated by running
reactions directly in the NMR at different temperatures and moni-
toring the disappearance of the FA proton and 13C signals. We
selected a catalyst concentration of 25 mM and varied the probe
temperature from 40 to 80 °C (Table 1, entries 12–14, 8).
As an example, a kinetic run at 60 °C is depicted in the SI along
with the exponential fit according to the (pseudo-) first order inte-
grated rate law.
½Aꢀ ¼ A0eꢁkt
ð1Þ
Table 2 collects the experimental (pseudo-) first order rate con-
stants at different temperatures. These results are reproducible
within 5% error.
2.2. Catalytic studies
From the Arrhenius equation, plotting the natural logarithm
values of k versus reciprocal temperature yields an estimation for
activation energy of the reaction (see figure in the SI). The fitted
line has a slope of ꢁ9147 ( 893), corresponding to an activation
energy of +76.05 7 kJ molꢁ1, which is in good agreement with
the Fe2+ꢂPP3/propylene carbonate system of Beller et al.
(+77 0.4 kJ molꢁ1) [37]. The catalytic activity of Fe2+ꢂPP3TS is sim-
ilar to the PP3 system (TON of 8117) [44], and to the Ru2+ꢂTPPTS
catalyst in water (TON of 715) [45].
We have prepared PP3TS complexes of various metal salts in situ
in 10 mm NMR tubes and tested all in FA dehydrogenation reac-
tions. PP3TS was used as a ligand in D2O solution with a 1:1 ratio
As the ligand to metal ratio influences the catalyst activity,
experiments were conducted to test this parameter (Table 3). At
a ligand to metal ratio of 2:1 (entry 2) TOFs were increased, relative
to the 1:1 experiment (entry 1). No further rate increases were
observed with higher ratios (entries 3–5) for the first cycle and
the formation of new iron complexes was observed as
Fig. 1. Ligands: tris[2-(diphenylphosphino)ethyl]phosphine (PP3) -left- and the
water soluble PP3TS -right-.
Please cite this article in press as: M. Montandon-Clerc et al., Quantitative aqueous phase formic acid dehydrogenation using iron(II) based catalysts, J.
Catal. (2015), http://dx.doi.org/10.1016/j.jcat.2015.11.012

M. Montandon-Clerc et al. / Journal of Catalysis xxx (2015) xxx–xxx
3
Table 1
Catalytic activity of different metal salts with PP3TS ligand in formic acid dehydrogenation reaction.
Entry
Metal precursor
[cat] (mM)
Temperature (°C)
Conversiona (%)
Time (h)
TON
TOF (hꢁ1
)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Co(BF4)2
CoCl2
MnSO4
ZnSO4
FeCl2
FeCl2
FeCl2
FeCl2
FeCl2
FeCl2
FeCl2
FeCl2
FeCl2
FeCl2
FeCl2
Fe(BF4)2
Fe(BF4)2
25
25
25
25
1
80
80
80
80
80
80
80
80
80
80
40
50
60
70
90
60
80
<1
<1
<1
<1
700
700
700
700
56
7.5
5.66
3
–
–
–
–
–
–
–
–
12
133
89
66
100
66
7
13
650
1000
500
200
100
50
116
190
200
200
200
200
200
5
100
100
100
100
100
58
10
25
50
100
25
25
25
25
25
25
25
1
0.75
16.5
22
15
3.75
3
95
8
100
100
100
100
100
13
53
66
23
109
8.66
1.83
a
Initial formic acid concentration 5 M, V = 2 mL water. Reproducibility 5%.
Fig. 2. 1H NMR spectra of a 5 M formic acid solution at 80 °C, c(Fe) = c(PP3TS) = 0.025 M, (data from Table 1, entry 17), monitoring FA dehydrogenation as a function time
(time difference between two successive spectra is 150 s). The small shoulders adjacent to the FA are CH peaks of the ligand phenyl groups.
Table 3
Table 2
Effect of the ligand to metal ratio on the catalytic activity.
Rate constant values at different temperatures (see Table 1 for details).
Entry (–)
[PP3TS]:[Fe2+] (–)
Conversion (%)
Time (min)
TOF (hꢁ1
)
Entry (–)
T (°C)
k (⁄10ꢁ2 (sꢁ1))
1
2
3
4
5
1:1
2:1
3:1
4:1
5:1
100
100
100
100
100
180
50
50
50
50
66
240
240
240
240
1
2
3
4
80
70
60
50
2.01
1.30
0.44
0.20
Average values of several kinetic runs, reproducibility is 5%.
Temperature = 80 °C; iron(II) concentration = 25 mM; reproducibility 5%.
Please cite this article in press as: M. Montandon-Clerc et al., Quantitative aqueous phase formic acid dehydrogenation using iron(II) based catalysts, J.
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4
M. Montandon-Clerc et al. / Journal of Catalysis xxx (2015) xxx–xxx
Table 4
demonstrated by significant color changes, shifting the color of the
solution from purple to orange. So the further studies were carried
out with 1:1 and 1:2 metal to ligand ratios.
Pressure increase in the reaction vessel during consecutive dehydrogenation cycles
under isochoric condition.
Entry (–)
FA added (g)
Pestimate (bar)
pfinal (bar)
1
2
3
4
0.2074
0.2030
0.2035
0.1998
72
70
71
69
54
50
51
52
2.3. Kinetic studies
The previously investigated Fe2+ꢂPP3 complex is known to toler-
ate CO2 pressure but shows a decrease in activity under as little as
20 bar hydrogen pressure, during formic acid dehydrogenation
[37]. These effects were examined using medium pressure sap-
phire NMR tubes, as reaction vessels, in the current study for the
aqueous iron complex Fe2+ꢂPP3TS. The pressure evolution at 80 °C
was monitored over time using 25 mM pre-catalysts with a 1:1
metal to ligand ratio and at 2.2 M initial formic acid concentra-
tions. After the maximum pressure was reached, the tube was
carefully vented and recharged with 0.2 g FA. This process was
repeated several times (Fig. 3 and Table 4).
Temperature = 80 °C; iron(II)-PP3TS concentration = 25 mM; reproducibility 5%.
Table 5
FA decomposition in sealed sapphire NMR tubes with initial CO2 or H2 pressure.
Entry (–)
FA added (g)
pini (bar)
Pestimate (bar)
pfinal (bar)
1
2
0.2068
0.2065
50 (CO2)
50 (H2)
115
115
99
99
Temperature = 80 °C; iron(II)-PP3TS concentration = 25 mM; reproducibility 5%.
The pressure increase was faster during the first kinetic run
compared to the subsequent recycling experiments where the
kinetic curves were similar. This could indicate that an initial acti-
vation period takes place, in which the transient intermediates are
more active than the species which finally form. We noted a simi-
lar effect for one Ru2+ꢂTPPTS system [13] but interestingly the
opposite was found for the Fe2+ꢂPP3 complex, where the catalyst
required an induction period of 1–2 h in propylene carbonate
before reaching maximum efficacy [37].
The observed maximum pressures are below the approximate
values of 69–72 bar for closed sapphire NMR tubes (estimated
from the HCOOH quantity) and could be explained by the fact that
this approximation doesn’t account for the solubility of the gases in
water (mainly CO2), and the fact that CO2 does not follow the ideal
gas law under these conditions. The conversion yields were
checked by 1H and 13C NMR.
The individual effects of carbon dioxide or hydrogen pressures
were then tested. Sapphire NMR tubes were charged with 25 mM
precatalyst and 2.2 M FA, and were initially pressurized with
50 bar CO2 or H2 and the reaction mixtures were thermostatized
at 80 °C temperature. Table 5 indicates that neither H2, nor CO2
gas pressure has influence on the catalytic reaction.
2.4. Gas analysis for carbon monoxide impurities
Carbon monoxide is a fuel cell catalyst poison, so the generated
hydrogen/CO2 mixture cannot contain CO impurities for this appli-
cation. We monitored the FA dehydrogenation reactions in sealed
sapphire NMR tubes by 13C NMR, too, where a peak at 125.2 ppm
was detected corresponding to the dissolved CO2. CO would have
been observed at 181.3 ppm but no peak was visible indicating
an absence of carbon monoxide [46]. However, the solubility of
CO2 is much greater than that of the CO, so it has a higher detection
Fig. 4. Analysis of CO impurities using FT-IR spectroscopy for (a) sample gas
generated by FA dehydrogenation (conditions: entry 4, Table 4); (b) 5 ppm CO in a
50% H2–50% CO2 gas mixture; and (c) 10 ppm CO in a 50% H2–50% CO2 gas mixture.
limit in 13C NMR [47,48]. To get a better limit for CO impurities, the
gas samples from the sapphire NMR tube were then transferred
into an IR gas cell and analyzed by FT-IR spectroscopy (Fig. 4).
Spectra were then compared to the standards having known CO
concentrations (measured previously in our laboratory) [12] to
determine carbon monoxide levels. The sample appeared to con-
tain less than 5 ppm of CO, as there is no indication of absorption
at 2140 cmꢁ1, showing that the FA decomposition reaction is selec-
tive toward dehydrogenation, so the hydrogen could potentially be
used in a PEM fuel cell without any risk of contamination.
3. Conclusions
Fig. 3. Successive cycles of the Fe2+ꢂPP3TS system under isochoric conditions
(sealed sapphire NMR tube) using 25 mM Fe2+ꢂPP3TS and 2.2 M formic acid,
t = 80 °C.
We have demonstrated that iron(II) salts together with the
hydrophilic multi-dentate PP3TS ligand are active in FA
Please cite this article in press as: M. Montandon-Clerc et al., Quantitative aqueous phase formic acid dehydrogenation using iron(II) based catalysts, J.
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M. Montandon-Clerc et al. / Journal of Catalysis xxx (2015) xxx–xxx
5
dehydrogenation reactions in aqueous solutions. The produced 50%
H2–50% CO2 are CO free (less than 5 ppm CO contamination). The
catalyst remains active after a large number of cycles, even in the
presence of oxygen (air exposure). Key kinetic parameters, includ-
ing rate constants and the activation energy, were determined. It
was shown that the Fe2+ꢂPP3TS catalyst system can tolerate H2
and CO2 pressures without any inhibition effects, and prior pres-
surization had no effect on the system, proving that neither CO2
nor H2 has an influence on the reaction rate and equilibrium
position, showing that these systems are good candidates for
high-pressure H2 generation.
m/z = 302.98 for [M]3ꢁ and 465.72 for [M+Na]2ꢁ. Elemental analy-
ses were concordant with trisulfonation, considering the expected
composition of C = 51.64% and H = 4.02% for C42H39Na3O9P4S3 and
the obtained values of C = 51.64% and H = 4.01%.
Elemental analysis calculated for C42H39Na3O9P4S3: C = 51.64%
and H = 4.02%. Found: C = 51.64% and H = 4.01%. MS (ESIꢁ) calcu-
lated for C42H39O9P4S3 [M]3ꢁ: m/z 302.61. Found: m/z 302.98. 1H
NMR (400 MHz, D2O) d 8.44–6.22 (m, 27H), 1.67 (m, 6H, CH2),
1.19 (m, 6H, CH2). 31P NMR (162 MHz, D2O) d ꢁ10.51 to ꢁ16.20
(m), ꢁ17.26 to ꢁ23.12 (m).
4.5. Kinetic studies at 1 bar pressure
4. Experimental section
In a typical experiment, PP3TS (0.049 g, 0.05 mmol) was dis-
solved in D2O (2 mL) in a standard 10 mm NMR tube. One mol-
equivalent of metal salt was added and the solution was mixed.
An immediate color change indicated the complex formation. Then
FA (0.46 g, 0.01 mol) was added to the tube, which was closed with
a perforated cap and heated to the desired temperature either in an
aluminum block or directly in the NMR. Reactions were followed
by monitoring the formic acid peaks, relative to DSS standard.
4.1. General
All air-sensitive compounds were manipulated under nitrogen
atmosphere using standard Schlenk techniques. PP3 (97%) was pur-
chased from Acros. All other reagents were commercially available
and used as received.
4.2. NMR spectroscopy
4.6. Recycling experiments
1H, 13C and 31P NMR spectra were recorded on Bruker DRX-400
(5 mm) and Avance DRX-400 (10 mm) instruments. 3-(Trimethylsi
lyl)-1-propanesulfonic acid sodium salt (DSS) was used as an inter-
nal standard for 1H and 13C NMR experiments. The spectra were
processed with XWin NMR, TopSpin, MestReNova and Igor Pro
softwares.
0.049 g (0.05 mmol) PP3TS was dissolved in D2O (2 mL) in a
standard 10 mm NMR tube. One mol-equivalent of metal salt
was added and the solution was mixed (color change indicated
the complex formation). Then FA (0.46 g, 0.01 mol) was added to
the tube, which was closed with a perforated cap and heated to
the desired temperature either in an aluminum block or directly
in the NMR. NMR spectra were taken after a determined period
of time to check for the absence of FA. If no more formic acid
was present, 0.46 g was added again and the procedure was
repeated.
To study the catalyst stability in a long experiment, always
0.92 g of FA was added every day into the NMR tube for recycling
(10 M FA). Before the next addition, the following day, 13C and 1H
NMR spectra were taken to check the absence of FA (complete con-
version), it has been repeated 32.
4.3. FT-IR spectroscopy
FT-IR experiments were performed on a Perkin Elmer FT-IR
Spectrum GX system using a 100 mm long gas cell. The gas mix-
tures were transferred from the sapphire NMR tubes to the gas
sample cell and the taken spectra were processed with Igor Pro
software.
4.4. PP3TS synthesis
A 3 L three-neck flask was equipped with a magnetic stirrer and
charged with H2SO4 (98%, 56 mL, 1.05 mol), cooled to ꢁ10 °C by an
ice–salt bath. PP3 (5 g, 7.45 mmol) was slowly added over a 1 h
period. After complete dissolution of the solid phosphine, oleum
(65% SO3, 30 mL, 0.33 mol) was carefully added to the reaction
mixture. The reaction mixture was allowed to slowly warm to
room temperature and stirred for 4 days. After this time the reac-
tion was quenched with ice (100 g) and the mixture was neutral-
ized over a 4 h period by adding NaOH (7 M) through a dropping
funnel. The water was removed under vacuum and MeOH (alto-
gether 1 L) added to extract the sulfonated phosphine salt. The
mixture was filtered under nitrogen and the filtrate reduced to
dry, to afford 4.2 g (58%) of pure PP3TS as purple crystals.
4.7. Isochoric experiments
PP3TS (0.049 g, 0.05 mmol) was dissolved in 2 mL D2O in a
10 mm NMR sapphire tube, after one equivalent of metal salt
was added and dissolved. FA (0.20 g, 0.004 mol) was added to the
tube, which was sealed and thermostatted at 80 °C using an elec-
tric heating jacket. Reactions were followed by monitoring pres-
sure as a function of time with a transducer connected to the
tube via a high-pressure capillary and/or directly by NMR [49].
Data acquisition was performed over a NI USB 6008 interface and
recorded with homemade LabView 8.2 software.
The 31P NMR spectrum of PP3TS displays one broad signal from
ꢁ22.07 ppm to ꢁ18.26 ppm for the bridgehead phosphorous, while
the diphenylphosphino groups gave rise to a broad signal from
ꢁ15.52 to ꢁ11.54 ppm. Oxidation at phosphorous did not occur
during the synthesis, as no peaks attributable to P@O groups were
present in the usual region in 31P NMR (30–80 ppm). The 1H NMR
spectrum contains a broad resonance centered at 1.43 ppm for the
three equivalent ethylene groups and several broad peaks between
6.22 and 8.44 ppm for the phenyl rings. The respective integral
ratio was 12:27, indicating that three positions were sulfonated.
The negative mode ESI (electrospray ionization) mass spectrum
also agrees with a trisulfonated salt, which contained peaks at
Acknowledgments
We thank the Swiss Competence Center for Energy Research
(SCCER), the Commission for Technology and Innovation
(CTI) – Switzerland and the École Polytechnique Fédérale de
Lausanne – Switzerland for their financial support.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jcat.2015.11.012.
Please cite this article in press as: M. Montandon-Clerc et al., Quantitative aqueous phase formic acid dehydrogenation using iron(II) based catalysts, J.
Catal. (2015), http://dx.doi.org/10.1016/j.jcat.2015.11.012

6
M. Montandon-Clerc et al. / Journal of Catalysis xxx (2015) xxx–xxx
[27] S. Fukuzumi, T. Kobayashi, T. Suenobu, Efficient catalytic decomposition of
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Please cite this article in press as: M. Montandon-Clerc et al., Quantitative aqueous phase formic acid dehydrogenation using iron(II) based catalysts, J.
Catal. (2015), http://dx.doi.org/10.1016/j.jcat.2015.11.012