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REDINA et al.
to room temperature (RT), and the solid was isolated erence. The spectra were recorded for powdered TiO
2
by centrifugation. The parent solution was checked for and the 1Fe/TiO catalyst placed in a quartz chamber.
2
3
+
the presence of Fe ions by adding KSCN to an ali-
quot amount of the parent solution. The test showed
complete Fe deposition on the support. The solid was
then washed three times with DI water (30 mL), dried
under a vacuum at 40°C, and calcined at 400°C for
The oxidation of glycerol was performed in a liquid
phase in a lab-constructed finger-type autoclave
(
inner volume 10 mL) at 90°C and an O pressure of
2
5
bar. In the experiment, the weighed amount of the
catalyst (11 mg) was placed in the inner glass insert and
then an aqueous solution of glycerol (0.5 mL, 0.3 M)
was added to the catalyst. The reaction was performed
in water under alkaline conditions with NaOH to glyc-
erol ratio 1.7. The glass inner part was inserted in the
autoclave. The reactor was closed, flushed with nitro-
gen and O for 3 times. After adjusting O pressure
4
h. The catalyst was marked as 1Fe/TiO .
2
The monometallic parent catalyst was then modi-
fied with gold by a redox reaction [16]. The 1Fe/TiO
2
catalyst was first reduced in an H flow (10 mL/min)
2
at 450°C for 4 h in a U-shaped quartz reactor. After
2
2
that, the reactor was cooled down to RT and a proper
(
5 bar), the reactor was placed on an oil bath heated to
amount of an aqueous HAuCl solution (1.2 mM) was
4
the desired temperature. The reaction was carried out
for 2 h under stirring at 800 rpm at 90°C. After that,
the reactor was cooled down to RT. The catalyst was
isolated by centrifugation and the clear solution of the
reaction products was collected.
added to obtain the gold loading equal to 0.5, 0.1, or
0
.025 wt %. The obtained suspension was kept for 2 h,
and then the solid was separated by centrifugation.
The parent solution was checked for the presence of
3+
Au ions by reverse iodometric titration [16], and the
test showed complete gold deposition on the parent
The analysis of the products was performed using
1
NMR spectroscopy. H Spectra of the reaction mix-
catalyst 1Fe/TiO . The solid was then washed with DI
2
ture were recorded on a Bruker AV300 spectrometer
using a mixture of H O and D O (from 75 to 25%) as a
water (three times with 30 mL of DI water) and dried
at 40°C under a vacuum.
2
2
solvent and benzoic acid as an external standard. The
The morphology of the samples was studied by presaturation technique was used to suppress the water
scanning electron microscopy (SEM) and transmis- signal; yields and molar ratios of the products were
sion electron microscopy (TEM). A target-oriented
approach was utilized for the optimization of the ana-
lytic measurements [23]. Before SEM measurements
the samples were mounted on a 25 mm aluminum
specimen stub, fixed by conductive carbon paint and
coated with a thin film (15 nm) of carbon. The obser-
vations were carried out using a Hitachi SU8000 field-
emission scanning electron microscope (FE-SEM).
Images were acquired in a secondary electron mode at
the 2 kV accelerating voltage and at the working dis-
tance 4–5 mm. Morphology of the samples was stud-
ied taking into account a possible influence of carbon
coating on the surface. To obtain TEM images, before
measurements the samples were deposited on 3 mm
carbon-coated copper grids from an isopropanol sus-
pension. Samples morphology was studied using a
1
calculated by integration of the signals in H NMR
spectra on the basis of 3H. Assignments of proton sig-
1
nals: H NMR (300 MHz, H O + D O) glycerol: δ
2
2
3
.45–3.67 (4H, m, CH (OH)), 3.70–3.80 (1H, m,
2
CH(OH)); lactic acid: δ 1.31 (3 H, d, J = 6.9 Hz,
CH ), 4.09 (1H, q, J = 6.9 Hz, CH(OH)); acetic acid:
3
δ 1.90 (3 H, s, CH ); glyceric acid: δ 3.65–3.83 (2 H,
3
m, CH (OH)), 4.05–4.07 (1H, m, CHOH), glycolic
2
acid: δ 3.92 (2 H, s, CH (OH)); tartronic acid: δ 4.32
2
(
1H, s, CH(OH)); formic acid: δ 8.42 (1H, s,
CH(O)OH).
RESULTS AND DISCUSSION
The DRIFT-CO spectrum of the monometallic
Hitachi HT7700 transmission electron microscope. 1Fe/TiO (Fig. 1, curve a) catalyst reveals the presence
2
Images were acquired in a bright-field TEM mode at
the 100 kV accelerating voltage.
3+
–1
of Fe cations as a band observed at 2362 cm that
2+
can be assigned to Fe –CO complexes formed by
2
oxidation of CO with Fe O [24, 25]. The intense band
DRIFT spectra were recorded using a Nicolet
2
3
–
1
4+
Protégé 460 spectrometer in the interval of 6000– at 2177 cm is attributed to Ti –CO linear carbonyl
−1
−1
[24, 25]. The UV–Vis spectra of 1Fe/TiO and TiO
2
4
00 cm at a resolution of 4 cm (500 scans). The
2
adsorption of CO was performed at RT and a CO equi- are presented in Fig. 2. The subtraction of the TiO
2
librium pressure of 20 Torr. Before the experiments, spectrum from the 1Fe/TiO spectrum gives the final
2
the monometallic samples were treated at 400°C in a spectrum with a maximum at 398 nm and a shoulder
vacuum for 2 h. The bimetallic samples were evacu- at 478 nm (Fig. 2). The band at 398 nm can be
3+
ated for 2 h at 90°C.
attributed to octahedral Fe in small oligomeric
Fe O clusters, while the band at 478 nm presumably
x
y
Diffuse-reflectance spectra in the UV–Vis range
corresponds to bulk Fe O oxide [26, 27].
2
3
(
200–850 nm, UV–Vis DRS) were recorded with a
Hitachi M-340 spectrometer supplied with an inte-
After redox deposition of the extra-low amount of
, the band attributed
grating sphere attachment using a MgO pellet as a ref- gold (0.025 wt %) onto 1Fe/TiO
2
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 92
No. 11
2018
Redina
