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solution. After rectification of the pH to 9 by adding ammonia
(Carlo Erba, 30% aqueous solution), the solution was left under ag-
itation at room temperature until a dry paste was obtained. The re-
sulting powder was further dried and finally calcined at 5008C in
static air for 3 h with a heating rate of 58Cminꢀ1 to form the Ca-
TiO2 supports. A reference TiO2 support was synthesized according
to a similar sol–gel method in the absence of any calcium nitrate,
and the resulting material after calcination at 5008C was labelled
as T500.
mitted to H2/Ar (5:95 v/v) flow at a weight hourly space velocity
(WHSV) of 0.161 hꢀ1 and a heating rate of 108Cminꢀ1. For studying
the catalyst reducibility, the TPR profiles were recorded after per-
forming an in situ oxidative treatment in air (2008C for 30 min) on
the impregnated supports after a drying step, allowing the decom-
position of the chloride precursor.
CO adsorption and desorption measurements were performed
with a Nicolet 6700 FTIR spectrometer equipped with an MCT de-
tector made by Thermo Scientific, using a transmission cell. The
number of scans was 64 and the spectral resolution was set as
4 cmꢀ1. Before the measurements, the samples were first reduced
in H2 flow at 2008C for 1 h, before they were cooled down to 408C
in argon. Then, carbon monoxide sorption was performed for
20 min and during this process spectra were collected every 5 min.
After that time, CO desorption was performed for 20 min in Ar
flow. During desorption, spectra was collected every 2 min. Gas
Incipient wet impregnation: Ruthenium catalysts were prepared
by incipient wet impregnation from aqueous RuCl3 (Sigma–Aldrich,
minimum 40% Ru content) solutions on commercial TiO2 (Aero-
xideꢀ P25, Evonik), TiO2 prepared by a sol–gel method (T500), and
Ca-modified TiO2 supports to obtain 5 wt% of Ru loading. The cat-
alysts were then reduced for 1 h in a hydrogen flow at 2008C and
labelled as 5%Ru/P25-I, 5%Ru/T500-I, and 5%Ru/Ca-T500-I.
flow was set every time as 20 mLminꢀ1
.
Photodeposition: Ruthenium(III) chloride hydrate (RuCl3·xH2O, min
40% Ru content, Sigma–Aldrich) was used as a ruthenium precur-
sor salt for the catalyst preparation by photodeposition method.
RuCl3 was dissolved under stirring in 100 mL of methanol for 12 h,
prior to the addition of 900 mL of distilled water to give a metha-
nol/water ratio of 1:9 v/v. Subsequently, the TiO2 support was dis-
persed under stirring in 1 L of ruthenium solution in a beaker-type
glass reactor at a 1 gLꢀ1 TiO2 concentration, and with a ruthenium
precursor concentration corresponding to 5 wt% of Ru relative to
TiO2. After stirring for 1 h in the dark, the pH was adjusted with
NaOH to pH 8 before the suspension was stirred in the dark for an-
other 1 h to ensure the establishment of the adsorption–desorp-
tion equilibrium prior to irradiation. The TiO2 suspension was fur-
ther exposed to a 500 Wmꢀ2 solar light irradiation under stirring
within an ATLAS Suntest XLS+ reaction chamber equipped with a
Xenon arc lamp NXE 2201. At each time interval, 1 mL of solution
was sampled and filtrated through a 0.20 mm porosity filter (Aireka
Cells) to remove the TiO2 powder if any. The deposition was fol-
lowed by UV/Vis spectrophotometry using a Cary 100 Scan Varian
spectrophotometer to monitor the disappearance of the main ab-
sorption peak at l=324 nm assigned to the RuCl3 precursor. After
completion of the process, the catalysts were recovered by filtra-
tion and dried at 1008C for 1 h. The catalysts were labelled as
5%Ru/P25-P, 5%Ru/T500-P and 5%Ru/Ca-T500-P.
The Ru nanoparticle size distribution of the Ru/TiO2 samples was
determined by TEM, which was performed using a JEOL 2100F
with a point resolution of 0.2 nm. The samples were sonically dis-
persed in an ethanol solution before a drop of the solution was de-
posited onto a copper grid covered by a holey carbon membrane
for observation. The size distributions were calculated for each
nanoparticle sample by averaging 300 particles from the TEM
images using ImageJ software. They were also characterized by the
FWHM.
ToF-SIMS measurements were performed using ION-TOF GmbH in-
strument (ToF-SIMS IV) equipped with a 25 kV pulsed Bi+ primary
ion gun in static mode. The samples were pressed into pellets
before the measurements and attached to the sample holder
using double-sided tape. The analyzed area corresponded to a
500ꢂ500 mm size square. For each sample, three spectra were col-
lected. A pulsed electron flood gun was used for the charge com-
pensation. Depth of the analysis did not exceed 1 nm, mass resolu-
tion at m/z=29 was in the range of 4000–7000. The samples were
stored and transported in disposable containers to avoid any con-
tamination.
Atomic absorption spectroscopy (AAS) was used to determine the
Ru concentration in the post-reaction mixtures using SOLAAR M6
Unicam atomic absorption spectrometer.
Material characterization
Catalytic tests
The surface area measurements were performed on a Micrometrics
Tristar 3000 using N2 as adsorbent at ꢀ1968C with prior outgassing
at 2008C overnight to desorb the impurities or moisture. The BET
specific surface area and the total pore volume were calculated
from the N2 adsorption isotherm. Zeta potential measurements
were conducted on a Malvern Zetasizer NanoZS system with irradi-
ation from a 632.8 nm He-Ne laser. The zeta-potential was deter-
mined from the measured electrophoretic mobility using the Smo-
luchowski approximation. X-ray diffraction (XRD) patterns were re-
corded on a D8 Advance Bruker diffractometer in q/q mode and
using the Ka1 radiation of a Cu anticathode (l=1.5406 ꢁ). The ana-
tase mean crystallite size was calculated with the Scherrer equation
applied with the usual assumption of spherical crystallites. Anatase
cell parameters and cell volume were calculated using FullProf soft-
ware. SEM and elemental mapping was performed in secondary
electron mode on a JEOL JSM-6700 F FEG microscope.
Levulinic acid hydrogenation: In a typical LA hydrogenation ex-
periment, LA (1 g), catalyst (0.15 g), and water (30 mL) were mixed
in a stainless steel autoclave (Berghof, Germany), equipped with a
Teflon insert allowing a reaction volume of 45 mL. The reactor was
pressurized with H2 to 5 bar and the temperature was maintained
at 1908C for 30 min. At the end of the reaction, the reactor was
cooled down, the remaining pressure was released, and the reac-
tion mixture was centrifuged to separate the solid catalyst and the
product solution.
Formic acid decomposition: In a typical experiment, FA (0.4 mL),
reduced catalyst (0.15 g), and distilled water (30 mL) were mixed in
a stainless steel autoclave (Berghof) equipped with a Teflon insert
allowing a reaction volume of 45 mL. The reactor was flushed with
H2 for 30 s and Ar for 15 s. The reactor was then heated to 1908C
for 2 h.
TPR was performed on AMI1 system (Altamira Instruments)
equipped with a thermal conductivity detector (TCD) and was
used for examining the catalyst reducibility. The catalysts were sub-
LA hydrogenation with formic acid as a hydrogen source (FALA):
In a typical LA hydrogenation experiment, LA (1 g), FA (0.4 mL), a
catalyst (0.6 g), and water (30 mL) were mixed in a stainless steel
ChemSusChem 2019, 12, 1 – 13
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