Catalysis
Science &
Technology
PAPER
Cite this: Catal. Sci. Technol., 2017,
7, 293
Received 7th October 2016,
Accepted 4th December 2016
DOI: 10.1039/c6cy02121b
www.rsc.org/catalysis
Water oxidation mediated by ruthenium oxide
nanoparticles supported on siliceous mesocellular
foam†
Karl P. J. Gustafson,‡a Andrey Shatskiy,‡a Oscar Verho,§¶a Markus D. Kärkäs,‖a
Bastian Schluschass,**a Cheuk-Wai Tai,b Björn Åkermark,*a
Jan-Erling Bäckvall*a and Eric V. Johnston*a
Artificial photosynthesis is an attractive strategy for converting solar energy into fuel. In this context, devel-
opment of catalysts for oxidation of water to molecular oxygen remains a critical bottleneck. Herein, we
describe the preparation of a well-defined nanostructured RuO2 catalyst, which is able to carry out the oxi-
dation of water both chemically and photochemically. The developed heterogeneous RuO2 nanocatalyst
was found to be highly active, exceeding the performance of most known heterogeneous water oxidation
catalysts when driven by chemical or photogenerated oxidants.
Introduction
Today's society is strongly dependent on fossil fuels as the
main source of energy. Considering the fact that fossil fuel re-
serves are being depleted, it is clear that they need to be re-
placed with sustainable alternatives to ensure the continued
growth and development of our society.1 In order to ascertain
a continuous supply of renewable energy that is economically
feasible, the raw materials must be abundant and inexpen-
sive. An attractive solution is to use solar energy for produc-
tion of storable fuels by, e.g. splitting of water into molecular
oxygen and hydrogen. At present, we do not possess the tech-
nology to carry out this intricate process on a commercial
scale. One promising approach to achieve this could be to
mimic Nature's photosynthetic machinery and employ solar
energy for the oxidation of water to molecular oxygen, which
can deliver protons and reducing equivalents. In an artificial
system, these water-derived reducing equivalents can in turn
be utilized to produce the solar fuel of choice. Unfortunately,
the design of such artificial photosynthetic systems consti-
tutes a major challenge from an engineering perspective, as it
requires the orchestration of several complicated processes,
including light absorption, electron transfer from the gener-
ated excited state, charge separation, and electron transfer ac-
tivation of catalysts at physically separated half-reactions. In
such artificial schemes, water oxidation (eqn (1)) is consid-
ered to be the most critical obstacle since the reaction is
highly endergonic and proceeds via a highly intricate mecha-
nism. The overall process requires the collective removal of
four electrons, coupled with the cleavage of multiple bonds
and finally the creation of the O–O bond. These features pose
considerable challenges from a chemical perspective and may
require interfacing several chemical disciplines in the pursuit
of viable water oxidation catalysts (WOCs).2
2H2O → O2 + 4H
+ + 4e− (1)
Extensive research during the past decades has therefore
focused on the design of robust and efficient WOCs.3 This
has resulted in the construction of a wide array of molecular
WOCs based on the metals Ru4 and Ir,5 and the more earth-
abundant metals Mn,6 Fe,7 Co8 and Cu.9 However, these mo-
lecular WOCs suffer from decomposition and/or deactivation
under the highly oxidizing environment required for the wa-
ter oxidation.10 An alternative and more attractive approach
would be to produce robust heterogeneous catalysts for effi-
cient splitting of water. Since heterogeneous catalysts are not
Catal. Sci. Technol., 2017, 7, 293–299 | 293This journal is © The Royal Society of Chemistry 2017
aDepartment of Organic Chemistry, Arrhenius Laboratory, Stockholm University,
SE-106 91, Stockholm, Sweden. E-mail: bjorn.akermark@su.se,
jan.e.backvall@su.se, eric.johnston@su.se
bDepartment of Materials and Environmental Chemistry, Arrhenius Laboratory,
Stockholm University, SE-106 91, Stockholm, Sweden
† Electronic supplementary information (ESI) available: Nitrogen absorption/
desorption isotherm analysis, XPS spectra, HAADF-STEM characterization of the
RuO2 nanocatalyst, and NMR spectra. See DOI: 10.1039/c6cy02121b
‡ These authors contributed equally.
§ Present address: Center for the Science of Therapeutics, Broad Institute, 415
Main Street, Cambridge, Massachusetts 02142, USA.
¶ Present address: Howard Hughes Medical Institute, Department of Chemistry
and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massa-
chusetts 02138, USA.
‖ Present address: Department of Chemistry, University of Michigan, Ann Arbor,
Michigan 48109, USA.
** Present address: Institut für Anorganische Chemie, Georg-August-Universität,
Tammannstraße 4, 37077 Göttingen, Germany.
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294 | Catal. Sci. Technol., 2017, 7, 293–299 This journal is © The Royal Society of Chemistry 2017
associated with oxidative degradation to the same extent as
their molecular counterparts, they have been extensively stud-
ied during the past decades.11–17 Among these heterogeneous
catalysts, nanoparticle-based catalysts have attracted particu-
lar attention because of their higher surface-to-volume ratio,
which ensures that the majority of the catalytic centers reside
on the particle surface and are thus available to participate in
catalysis.18 Today, stabilization of such nanoparticle-based
species is possible by immobilization onto, for example,
mesoporous materials19 or metal–organic frameworks
(MOFs).20
Recently, we reported on a well-characterized heteroge-
neous catalyst comprised of Pd nanoparticles immobilized
on siliceous amino-functionalized mesocellular foam (MCF)
for both chemically- and photochemically-induced oxidation
of water.21 Interestingly, this catalyst was found to efficiently
catalyze water oxidation at rates comparable to those of state-
of-the-art heterogeneous metal-based WOCs,22,23 while
displaying high stability under the reaction conditions
employed. In perspective of these results, it was of interest to
synthesize and test related Ru-based nanocatalysts given the
fact that Ru has proved to be one of the most effective metals
for promoting water oxidation.24–26
Herein, we report the preparation of a RuO2 nanocatalyst
supported on pyridine-functionalized MCF that is capable of
mediating both chemical and photochemical water oxidation.
The developed catalyst is a promising candidate for incorpora-
tion in a complete photoelectrochemical water splitting cell.27
Results and discussion
Synthesis and characterization
It was envisioned that RuO2 nanoparticles could be firmly an-
chored to the MCF support surface through a pyridine-based
linker. For this purpose, 1-(pyridin-3-yl)-3-(3-(triethoxysilyl)-
propyl)urea (PPU) was synthesized as the linker, which can be
conveniently grafted onto the MCF through condensation of
the alkoxysilane groups of the linker to the silanol groups on
the support surface. The synthesis of the RuO2 nanocatalyst
is outlined in Fig. 1 (see Experimental section for further de-
tails). Briefly, the PPU linker was synthesized by reacting
3-aminopyridine with triethoxyIJ3-isocyanatopropyl)-silane in
CH2Cl2 at room temperature to afford the desired linker in
quantitative yield. The MCF material was subsequently grafted
with the PPU linker by refluxing a toluene solution of the linker
together with MCF for 48 h. The pyridine-functionalized MCF
(PPU-MCF) was then impregnated with RuCl3 in water (pH 9)
at room temperature to give the RuIII-PPU-MCF precursor. Fi-
nally, the MCF-supported RuIII species was reduced by NaBH4,
and after exposure to air the RuO2 nanocatalyst was generated.
The RuO2 nanocatalyst was characterized by several tech-
niques: N2 adsorption/desorption measurements, infrared
spectroscopy (IR), high-angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM), inductively
coupled plasma-optical emission spectroscopy (ICP-OES), and
X-ray photoelectron spectroscopy (XPS). The anchoring of the
linker to the support was confirmed by IR, which showed the
presence of a characteristic peak around 1640 cm−1 (CO
stretch) belonging to the urea moiety. From ICP-OES analysis,
the nitrogen loading of the pristine PPU-MCF support was
measured to be 4.55 wt%, which corresponds to a pyridine
content of 1.08 mmol g−1. The Ru nanocatalyst was also ana-
lyzed by ICP-OES, which measured the Ru and nitrogen load-
ings to be 7.26 wt% and 2.56 wt%, respectively. Isotherm
analysis was conducted on both pristine PPU-MCF and the
RuO2 nanocatalyst (see Table S1†). For the Ru catalyst, the av-
erage pore size and window size were determined to be 19.6
nm and 12.4 nm, respectively, and BET surface area analysis
Fig. 1 Synthesis of the RuO2 nanocatalyst.
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Catal. Sci. Technol., 2017, 7, 293–299 | 295This journal is © The Royal Society of Chemistry 2017
showed a specific pore volume and surface area of 1.55
cm3 g−1 and 341.15 m2 g−1, respectively. To assess the size
and distribution of the RuO2 nanoparticles, the catalyst was
analyzed by HAADF-STEM. This analysis revealed that the cat-
alyst was primarily comprised of subnanometer sized nano-
particles that were well-dispersed on the support surface
(Fig. 2). By comparing to previously reported heterogeneous
Ru WOCs on mesoporous silica,24,26 it appears that the ex-
tremely small particle size observed for this RuO2 nano-
catalyst is unique and may be promising for achieving high
catalytic efficiency. XPS was used to establish the oxidation
state of the catalyst. After adjusting the XPS spectrum to the
C 1s peak at 285.0 eV as the reference, it was found that the
strongest peak of Ru corresponding to the 3d orbital unfortu-
nately overlapped with the 1s signal of C. Therefore the sec-
ond strongest Ru peak, Ru 3p3/2, had to be used for determi-
nation of the oxidation state. The main Ru 3p3/2 peak was
found at ∼463 eV, which is indicative of RuO2.28 Oxidation of
the reduced catalyst to RuIV most likely occurs spontaneously
once the reduced Ru nanocatalyst is exposed to air, resulting
in a more stable RuO2.
Catalytic activity
The catalytic activity of the developed RuO2 nanocatalyst was
initially evaluated using ceric ammonium nitrate (CAN, CeIV),
which is a strong oxidant that is widely used for screening of
WOCs. Upon addition of degassed water to a solid mixture of
CAN and the RuO2 nanocatalyst, O2 evolution could be ob-
served by real-time mass spectrometry (Fig. 3). Evolution of
O2 was followed for 24 h. The rate of O2 evolution was found
to decrease during the first three hours, after which it be-
came relatively constant. When employing CAN as oxidant, a
turnover number (TON; defined as moles of produced O2 per
mole of Ru) of 10 after 24 h and an initial turnover frequency
(TOF; defined as moles produced O2 per mole Ru per unit
time) of 24 h−1 were obtained for the RuO2 nanocatalyst.
30
The catalyst subjected to the abovementioned water oxida-
tion conditions was also recovered and analyzed by XPS,
showing an XPS spectrum which is essentially identical to
that of the unused catalyst (Fig. S1†). Possible leaching from
the catalyst was also tested, but only trace amounts of ruthe-
nium (close to the detection limit, less than 5% of the total
amount of used ruthenium) could be observed.
To be practical on the commercial scale, water oxidation
ultimately has to be driven by photogenerated oxidants
formed by oxidative quenching of the corresponding photo-
sensitizers. Currently, [RuIJbpy)3]
2+-complexes (bpy = 2,2′-
bipyridine) are the most extensively studied and commonly
used photosensitizers for evaluation of WOCs.31 In this per-
spective, we were interested to see whether the developed
RuO2 nanocatalyst could promote light-driven water oxida-
tion with a [RuIJbpy)3]
2+-type photosensitizer as the light-
absorbing component and sodium persulfate (Na2S2O8) as
the sacrificial electron acceptor. This photodriven system is
well-studied32 and proceeds via oxidative quenching of the
photoexcited [RuIJbpy)3]
2+* state by S2O8
2−, to generate
[RuIJbpy)3]
3+, a sulfate ion and a sulfate radical (SO4˙
−). The
chemistry of this system is described in eqn (2)–(4), with the
overall reaction shown in eqn (5).
[Ru(bpy)3]
2+ + hv → [Ru(bpy)3]
2+* (2)
[Ru(bpy)3]
2+* + S2O8
2− → [Ru(bpy)3]
3+ + SO4˙
− + SO4
2− (3)
Fig. 2 Structure and particle-size distribution of the RuO2 nano-
catalyst. (Upper) Representative HAADF-STEM image of the RuO2
nanocatalyst. (Lower) Particle-size distribution for the RuO2 nano-
catalyst with a number-average particle size of 1.1 nm.
Fig. 3 Background-subtracted O2 evolution catalyzed by the RuO2
nanocatalyst using CAN as the chemical oxidant. Conditions:
deaerated water (1.0 mL) was added to a solid mixture of RuO2
nanocatalyst (0.25 mg of the nanocatalyst, containing 0.18 μmol Ru)
and CAN (60 mg, 109 μmol). The resulting solution had a pH of ∼1.0
(see ref. 29).
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296 | Catal. Sci. Technol., 2017, 7, 293–299 This journal is © The Royal Society of Chemistry 2017
[Ru(bpy)3]
2+ + SO4˙
− → [Ru(bpy)3]
3+ + SO4
2− (4)
2[Ru(bpy)3]
2+ + S2O8
2− + hv → 2[Ru(bpy)3]
3+ + 2SO4
2− (5)
Gratifyingly, when a solution containing the RuO2 nano-
catalyst, persulfate and photosensitizer was irradiated with
light (blue LEDs, λ = 420–450 nm), O2 evolution was triggered
and resulted in a TON of 4 with [RuIJbpy)3]
2+ as the photosen-
sitizer (Fig. 4). In contrast, control experiments conducted
under the same reaction conditions, where either persulfate
or light were omitted resulted in negligible oxygen evolution.
Moreover, the recovered catalyst displayed an almost
unchanged morphology and particle size distribution
according to the TEM analysis (Fig. S3 and S4†).33
By comparing the catalytic activity of the developed RuO2
nanocatalyst with other heterogeneous catalysts it is evident
that our catalytic system compares well with the current
state-of-the-art heterogeneous WOCs (Table 1). Replacing the
[RuIJbpy)3]
2+ photosensitizer (E1/2IJRu
III/II) = 1.26 V vs. NHE)
with [RuIJbpy)2IJdeeb)]
2+ (deeb = diethyl-2,2′-bipyridine-4,4′-
dicarboxylate), which has a higher redox potential (E1/2IJRu
III/II)
= 1.40 V vs. NHE) resulted in decreased activity and a TON of
1. This trend was observed previously for a related Pd-MCF
catalyst;21 however, the trend is opposite compared to what
has been observed for homogeneous WOCs,4j,6c,36–38 indicat-
ing that the decreased activity could be due to the heteroge-
neous and/or porous nature of the catalyst. It is likely that
the more polar carboxy-substituted photosensitizers are
strongly absorbed on the MCF walls, precluding diffusion of
the photogenerated oxidant to the RuO2 particles.
Conclusions
Herein, we have reported the synthesis of a heterogeneous
catalyst consisting of RuO2 nanoparticles with an average par-
ticle size of 1.1 nm. The catalyst was obtained by
immobilizing the Ru nanoparticles on pyridine-
functionalized MCF. The synthesized RuO2 nanocatalyst was
evaluated in water oxidation catalysis and was found to medi-
ate both chemical and photochemical water oxidation. In the
CeIV-catalyzed water oxidation, the nanocatalyst reached a
TON of 10. Photochemical water oxidation could also be real-
ized, using [RuIJbpy)3]
2+-type photosensitizers. The developed
nanocatalyst exhibits a higher catalytic performance com-
pared to the majority of the previously reported heteroge-
neous WOCs. The high activity of the RuO2 nanocatalyst is
ascribed to the high surface-to-volume ratio granted by the
small particle size, which makes the majority of the metal
centers accessible for catalysis. The results disclosed herein
illustrate a non-conventional approach to the design of
heterogeneous water oxidation catalysts, where small organic
molecules are used to facilitate the synthesis of the
supported heterogeneous nanocatalyst. Systematic investiga-
tion of the influence of the organic linker on the catalyst
structure and performance is currently under investigation.
Experimental section
Materials and methods
The mesocellular foam (MCF),39 [RuIJbpy)3]IJPF6)2,
40 and
[RuIJbpy)2IJdeeb)]IJPF6)2
41 were prepared according to previously
reported procedures. All other reagents including solvents
were obtained from commercial suppliers and used directly
without further purification. All solvents were dried by standard
methods when needed. Deionized water was used in all experi-
ments. FTIR spectra were recorded on a Perkin-Elmer Spectrum
One spectrometer, using samples prepared as KBr discs.
The physical properties of the mesoporous materials were
determined from N2 adsorption/desorption isotherms using
an ASAP 2010 instrument. For TEM analyses, small amounts
of grinded RuO2 nanocatalyst were added to EtOH,
ultrasonicated, and a few drops of the resulting slurry were
deposited onto a Cu TEM grid with amorphous carbon
supporting films (SPI Supplies Inc.). Samples were dried
Fig. 4 Photochemical H2O oxidation catalyzed by the RuO2
nanocatalyst using [RuIJbpy)3]IJPF6)2 (orange line) and
[RuIJbpy)2IJdeeb)]IJPF6)2 (red line) as photosensitizers. Conditions: an
aqueous deaerated phosphate buffer solution (1.0 mL, 0.1 M, pH 7.2)
was added to a solid mixture of photosensitizer (5.8 μmol), sodium
persulfate (11.6 mg, 49 μmol) and the RuO2 nanocatalyst (0.50 mg of
the nanocatalyst, containing 0.36 μmol Ru).
Table 1 Comparison of water oxidation activity for various heteroge-
neous catalystsa
Catalyst TONb TOFc Ref.
RuO2-PPU-MCF ∼4.0 2.2 × 10−3 s−1 This work
Pd-MCF ∼5.0 2.2 × 10−3 s−1 Ref. 21
RuO2-SBA-15 ∼4.0 6.7 × 10−3 s−1 Ref. 34
Mesoporous Mg-Co3O4 >0.30 1.6 × 10
−4 s−1 Ref. 35
LaCoO3 ∼0.70 1.4 × 10−3 s−1 Ref. 23
LiCoMnO4 ∼0.055 8.3 × 10−5 s−1 Ref. 23
Li1.1Co2O4 ∼0.10 1.6 × 10−4 s−1 Ref. 23
Li2Co2O4 ∼0.50 9.0 × 10−4 s−1 Ref. 23
LaMnO3 ∼0.20 4.8 × 10−4 s−1 Ref. 23
Mn2O3 ∼0.23 5.0 × 10−4 s−1 Ref. 23
MgMn2O4 ∼0.060 8.2 × 10−5 s−1 Ref. 23
a Photochemical oxidation using [RuIJbpy)3]
2+ as photosensitizer and
Na2S2O8 as sacrificial electron acceptor.
b Turnover number (TON) =
amount of evolved O2/total amount of metal.
c Turnover frequency
(TOF) = turnover per unit time (amount of evolved O2/{total amount
of metal × s}).
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thoroughly before insertion into the microscope column. For
the particle analysis, high-angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM) was
performed in a 200 kV electron microscope with a Schottky
field-emission gun (JEOL JEM-2100). The HAADF-STEM im-
ages were recorded using a JEOL ADF detector. The camera
length was 8 cm and the incident beam probe size was ∼0.2
nm. The gain of the detector was kept constant throughout
the experiments of all samples. Since the contrast of RuO2 in
HAADF-STEM images is apparently stronger than that of the
MCF support, particle size measurements were possible by
careful adjustment of the background threshold. Imaging
and particles size analysis were carried out by Gatan Digital
Micrograph (Gatan Inc.). X-ray photoelectron spectroscopy
(XPS) was used to determine the structure and oxidation
states of the Ru nanoparticles on the PPU-MCF material.
Gas analysis by mass spectrometry
Oxygen evolution was measured by MS, where the mass
spectrometer consisted of three separate parts connected by
gas valves; a reaction chamber, a gas handling system (GHS),
and a residual gas analyzer (MKS Spectra Products, Micro-
vision Plus RGA, 0–100 mass units) in ultra-high vacuum (base
pressure 2 × 10−10 mbar). A rough pump is used to evacuate the
GHS, so the pressure can be regulated within 0.1–1000 mbar.
The enclosed volume in the reaction chamber is continuously
probed by the mass spectrometer by an inlet through the leak
valve. A ca. 1 cm thick rubber gasket has been added to the sys-
tem and permits injection of solutions containing reactants
into the reaction chamber, essentially without any leakage of
the external atmosphere. Any air leakage is continuously
followed by the mass spectrometer (by increase of both O2 and
N2). In order to avoid splashing when injecting the solution, a
pressure of ∼40 mbar is needed and in this study the enclosed
volume was filled with He to obtain the desired pressure.
The change over time of the measured signal of masses
0–100 in the mass spectrometer is thus converted to the
amount in the enclosed volume in two steps. The first step is
to convert the signal from the mass spectrometer to pressure
in the enclosed volume. This conversion is done by calibra-
tion of the system, i.e. measuring the response in the MS to
different pressures in the enclosed volume. In the second
step the pressures in the enclosed volume are converted to
the amounts of the different gases by using the gas law,
which makes it possible to determine the production of gases
with masses 1–100 quantitatively.
Chemical oxidation with CeIV
In a typical run, the Ru nanocatalyst (0.25 mg RuO2 nano-
catalyst, 7.26 wt% Ru, 0.18 μmol Ru) and (NH4)2ijCeIJNO3)6]
(60.0 mg, 0.11 mmol) were placed in the reaction chamber
and the reaction chamber was evacuated with a rough pump.
∼40 mbar He was then introduced into the system. After an
additional 5 min, deoxygenated water (1.0 mL, MilliQ) purged
with N2 for at least 10 min, was injected into the reaction
chamber. The generated oxygen gas was then measured and
recorded versus time by MS.
Photochemical oxidation using [RuIJbpy)3]
2+-type
photosensitizers
In a typical run, [RuIJbpy)3]
2+-type photosensitizer (5.8 μmol),
sodium persulfate (11.6 mg, 49 μmol) and Ru nanocatalyst
(0.50 mg RuO2 nanocatalyst, 7.26 wt% Ru, 0.36 μmol Ru)
were placed in the reaction chamber. ∼40 mbar He was then
introduced into the system. After an additional 5 min deoxy-
genated aqueous phosphate buffer solution (0.1 M, pH 7.2,
1.0 mL) purged with N2 for at least 10 min, was injected into
the reaction chamber and the reaction was irradiated by blue
LED light. To avoid heating of the reaction by the light
source, the reaction vessel was placed in a water bath and
cooled with a small flow of water. The generated oxygen gas
was measured and recorded versus time by MS.
Procedure for recovering of the RuO2 nanocatalyst after
catalytic water oxidation experiments
After having scaled up the catalytic experiments (×4) with CAN
(5 h reaction time), the reaction solution was transferred to a
Falcon tube (15 mL), suspended in water (10.0 mL, MilliQ) and
centrifuged (4100 rpm, 5 min). The supernatant was removed
and the RuO2 nanocatalyst was resuspended in water (10 mL)
and centrifuged (4100 rpm, 5 min). This was repeated 3 times
and the resulting solid was dried under vacuum overnight.
Synthesis of 1-(pyridin-3-yl)-3-(3-(triethoxysilyl)propyl)urea
(PPU)
3-Aminopyridine (1.90 g, 20.2 mmol) dissolved in CH2Cl2 (4.0
mL) was added dropwise to a solution of triethoxyIJ3-
isocyanatopropyl)silane (5.00 g, 20.2 mmol) in CH2Cl2 (5.0
mL). The reaction was stirred at room temperature for 48 h.
The solution was evaporated to afford the title compound as
pale yellow crystals in quantitative yield without the need of
any further purification. 1H NMR (400 MHz, CDCl3): δ = 8.32
(m, 1H), 8.18 (m, 1H), 8.03 (m, 1H), 7.90 (s, 1H), 7.19 (m,
1H), 5.62 (m, 1H), 3.79 (q, J = 7.1 Hz, 6H), 3.23 (m, 2H), 1.62
(m, 2H), 1.19 (t, J = 7.1, 9H), 0.63 (m, 2H); 13C NMR (101
MHz, CDCl3): δ = 156.1, 143.5, 140.6, 137.0, 126.8, 124.2,
58.8, 42.9, 23.8, 18.6, 7.9; HRMS (ESI) calcd. for
C15H28N3O4SiNa [M + Na
+]+: 364.1669; found: 364.1663.
Functionalization of MCF with 1-(pyridin-3-yl)-3-(3-
(triethoxysilyl)propyl)urea
MCF (500 mg) and 1-(pyridin-3-yl)-3-(3-(triethoxysilyl)propyl)-
urea (PPU, 3.40 g, 9.95 mmol) were placed under vacuum for
1 h. The flask was filled with argon gas upon addition of tolu-
ene (12.0 mL) and the reaction mixture was refluxed for 48 h.
The reaction was then cooled to room temperature and the
solid was washed with toluene (200 mL), CH2Cl2 (200 mL)
and EtOH (200 mL). The functionalized MCF was
resuspended in EtOH and heated overnight at 60 °C, after
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298 | Catal. Sci. Technol., 2017, 7, 293–299 This journal is © The Royal Society of Chemistry 2017
which the suspension was filtered and washed with addi-
tional EtOH (200 mL) and CH2Cl2 (200 mL). The amine load-
ing was determined to be 4.55 wt% using ICP-OES. FTIR λ
(cm−1): 3450, 1642, 1557, 1400, 1385, 1088, 802.
Preparation of the RuO2 nanocatalyst
Functionalized MCF (100 mg) was suspended in pH-adjusted
deionized water (7.5 mL, adjusted to pH 9.0 using 0.1 M
LiOH) solution in a Falcon tube and stirred for 10 min. RuCl3
(36 mg, 0.175 mmol) was suspended in pH-adjusted deion-
ized water (7.5 mL) and added to the suspension of PPU-
MCF. The mixture was stirred at room temperature overnight,
deionized water was subsequently added, and the mixture
was centrifuged (4100 rpm, 8 min). The dark solid was subse-
quently washed with water (8 × 45 mL). The solid was
resuspended in water (7.5 mL) and reduced by slow addition
of a solution of NaBH4 (67.0 mg, 1.77 mmol) in water (2.5
mL), and the mixture was stirred for 30 min. Centrifugation
of the mixture was followed by washing of the suspension
with water (3 × 45 mL) and acetone (3 × 45 mL). Before use
the catalyst was dried under vacuum overnight, and the cata-
lyst was stored under air at room temperature. The amine
and ruthenium loadings were determined using ICP-OES to
be 2.56 and 7.26 wt%, respectively. FTIR λ (cm−1): 3456, 1640,
1553, 1487, 1401, 1385, 1089, 802.
Acknowledgements
Financial support from the Swedish Research Council (621-
2010-4737, 621-2013-4653 and 621-2013-4872), the Berzelii
Centre EXSELENT, the European Research Council (ERC AdG
247014), and the Knut and Alice Wallenberg Foundation are
gratefully acknowledged.
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