Y. Zeng, et al.
Chemical Physics Letters 730 (2019) 95–99
−1
H
2
reduction at high temperature [17]. Wong and his co–workers
60 mL·min and 0.3 g sample was used. The TDP experimental began
with pre-treating sample with 3 vol%O /N at 50 °C for 60 min, and
then the gas was switched to He for 30 min. Subsequently, O –TPD was
to 800 °C in He
pointed that photo–deposition method can also induce high degree
SMSI in PtTi catalyst and lead to the high performance in oxygen re-
duction reaction in acid medium [18].
2
2
2
−1
performed by ramping the temperature at 10 °C·min
The most used preparation method of PtTi mainly included wet
flow.
impregnation with H
cing agent (such as NaBH
2
reduction, deposition–precipitation with redu-
, N ·H O and HCHO) reduction and pho-
4
2
H
4
2
2
.3. Catalytic activity test
Total oxidation of toluene was carried out at 130–190 °C in a quartz
to–deposition. The comparation study of two preparation method had
been widely reported. As our best known, except for the study [19]
reported by Leung groups that investigating the effect of three reduc-
fixed-bed reactor (i,d, 5 mm) using 0.3 g catalyst with 40–80 mesh
under atmospheric pressure. The typical reactant gas composition was
as follows: 500 ppm toluene, 20 vol% O and N as the balance gas.
2 2
Total flow rate was 250 mL·min , corresponding to a space velocity of
about 40,000 h . The concentration of toluene in the inlet and outlet
gas was measured by on-line gas chromatography equipped with a TCD
and two FID (one for analysis of organics and another for determine of
2 2 2
CO and CO via methanation reactor) detectors. CO and H O could be
detected as the only products, so the toluene conversion was calculated
by follow equation:
4 2
tion processes (NaBH , H and photo-deposition reduction) on im-
pregnation of PtTi catalyst for HCHO oxidation at room temperature,
little study had been done to analyse the effect of these three pre-
paration method on the catalytic activity of PtTi catalyst.
In this study, we compared the PtTi (PtTi–I, PtTi–D and PtTi–P)
catalysts prepared by impregnation (PtTi–I), deposition precipitation
−1
−1
(
PtTi–D) and photo–deposition (PtTi–P) from the catalyst formation
process and catalytic activity in toluene oxidation. Combined with the
results of TEM, BET, XRD, XPS, UV–vis, O –TPD and EPR, it was re-
2
vealed that preparation method naturally affected the structural char-
acteristics, surface properties of PtTi catalysts. These features domi-
nated the oxygen activation process, which plays a key role in toluene
total oxidation. We expected this study could provide some inspiration
in the design of noble metal based catalysts.
Toluene conversion (%) =
(
noutlet CO − nintlet CO2)/7ntoluene × 100%
2
where nCO2 is the molar flow of CO
molar flow of toluene at the inlet.
2
at the outlet and ntoluene is the
2. Experimental
3. Results and discussion
2
.1. Catalyst preparation
The TEM images and particles size distribution of PtTi sample are
presented in Fig. 1. The size of 100 TiO nanoparticles and 50 Pt na-
noparticles were counted for obtaining the histogram of particle size
distribution for each sample. It can be noted that the TiO particles size
in PtTi–I was greater than that in PtTi–D and PtTi–P, inferring that TiO
support was prone to sintering during hydrogen reduction process in
comparison with photodeposition and mild solution reduction process.
For Pt particles over PtTi–I, their size located at a small range of
1.6–2.4 nm. And it was worth noting that Pt nanoparticles could only be
2
TiO
chemicals were purchased from Aladdin and used without any treat-
ment. 1 wt%Pt/TiO catalysts were prepared by impregnation, deposi-
tion precipitation and photo-deposition methods, respectively. In a ty-
pical impregnation process, 2 g TiO (P25, Degussa) was added into
0 mL stoichiometric H PtCl solution under stirring, and then the
2
was purchased from Degussa (P25) and other analytical pure
2
2
2
2
6
2
6
solvent was removed by evaporation at 100 °C. Finally, PtTi–I (im-
pregnation) was obtained after drying at 80 °C and reducing at 450 °C
2
found on a portion of the TiO particles, which suggested that Pt na-
(
To avoid phase transformation from anatase TiO
for 2 h in 10 vol%H /Ar atmosphere. For light deposition reduction
process, 2 M NaOH solution was dropped into the mixture of 2 g TiO
and H PtCl solution under vigorous stirring until the pH = 12, then
0 mL 50 wt% hydrated hydrazine solution was added. After reduction
2
into rutile TiO
2
[15])
noparticles were tended to agglomeration at high temperature hy-
drogen reduction process. Moreover, from the HRTEM images shown in
2
2
Fig. S1, the lattice line of TiO
particles. This well consistent with the reported phenomenon that high
temperature reducing atmosphere can lead to the transfer of TiO onto
2
could be observed next to Pt nano-
2
6
1
2
for 2 h, the solid was washed by filtration for three times, and then
PtTi–D (deposition precipitation) catalyst was obtained after dried at
the surface of Pt0 particles and then encapsulate them [16,20]. For
PtTi–D sample, there no obvious Pt particles could be seen. The Pt
content obtained from ICP-MS for PtTi–I, PtTi–D and PtTi–P respec-
tively were 1.02 wt%, 0.95 wt% and 0.92 wt%, which close to the
theoretical value. Thus, the Pt particle on PtTi–D was too small to de-
tect. As to PtTi–P, its displayed the largest Pt particles with a size of
2.8–5.7 nm.
8
0 °C for 6 h in vacuum oven. As to photo-deposition process, it was
performed in a quartz glass reactor under N atmosphere. Generally, 2 g
TiO and 20 mL methanol was added into 180 mL stoichiometric
PtCl solution under stirring, then mixture was irradiated by UV light
CEL-HXUV 300, wavelength < 300 nm) for 2 h. Finally, PtTi–P (pho-
2
2
H
2
6
(
to–deposition) was got via filtration, washing for three times and dried
Fig. 2 displays the XRD patterns of catalysts. All catalysts displayed
at 80 °C for 6 h in vacuum oven.
a typical P25 TiO
PDF#21–1272) and few rutile (PDF#21–1276). No diffraction peaks of
Pt could be observed, inferring that Pt species were well dispersed on
TiO or the Pt species were too small to be detected by XRD. Notably,
all peaks of PtTi catalysts presented the same intensity, which were
lower than that of TiO supported. This result showed that the inter-
action between Pt nanoparticles and TiO affected the near surface
structure of TiO . To investigate the influence of Pt loading on the
specific surface area, the BET was carried out. As listed in Table 1,
PtTi–I had the smallest specific surface area, while TiO , PtTi–D and
2
diffraction peaks, which composed with anatase
(
2.2. Characterization
2
The catalysts were characterized by X–ray diffraction measurements
(
XRD Purkinje General Instrument Cu, Ltd, China, XD–3), Inductively
2
coupled plasma (ICP, Varian ICP 720), Brunauer–Emmett–Teller (BET
Quadrasorb-S1, Quantachrome, USA), High–resolution transmission
electron microscope (HRTEM, JEOL JEM2100, 100 kV), UV–vis spec-
trophotometer (UV–2550 Shimadzu), X–ray photoelectron spectroscopy
2
2
2
−1
2
(
XPS, PHI–5000C, ESCA) and Electron paramagnetic resonance (EPR
PtTi–P exhibited a specific surface area of 54 ± 1 m ·g , indicating
that Pt loading had no obvious effect on the specific surface area via
mild preparation method. The smallest specific surface area of PtTi–I
EMX–10/12–type, Bruker).
2
Oxygen temperature-programmed desorption (O –TPD) experiment
was performed on an automated chemisorption analyzer
Quantachrome Instruments), equipped with thermal conductivity de-
tector (TCD). During experiment, all gaseous flow rates were
2
could be ascribed to the agglomeration of TiO support, which was
consistent with the results observed in TEM images.
(
Fig. 3a shows the Pt 4f XPS spectra. Clearly, the binding energy of Pt
96
Zeng, Yiqing
