Q. Yuan et al. / Applied Catalysis A: General 507 (2015) 26–33
27
2
. Experimental
(25 mL/min) for 1 h at the adsorption temperature. NH desorption
3
◦
was carried out in the temperature range of 100–400 C at ramp
◦
2.1. Preparation of catalysts
rate of 10 C/min.
Fourier transform infrared (FT-IR) spectroscopy of pyridine
adsorption measurements were performed on a Nicolet iS50 spec-
trometer equipped with a vacuum cell. Catalyst samples were
pressed into self-supported disks (12–22 mg with diameter of
Titanate nanotubes (TNT) were prepared according to the refer-
ence [18]. Typically, commercial anatase-type TiO (2 g) was added
2
to 100 mL of NaOH aqueous solution (10 M). After being stirred for
−
3
◦
1
0 min, the mixture was transferred into a Teflon-lined (120 mL)
13 mm) and activated under vacuum (1 × 10 Pa) at 350 C. After
activation the samples were cooled to room temperature. A spec-
troscopy of the activated sample was recorded as background.
Adsorption of pyridine was conducted at room temperature.
Thermo gravimetric analysis (TG) was performed using a NET2SCH
◦
stainless steel autoclave and statically heated in an oven at 130 C
for 72 h. The white product was filtered and washed with large
amount of deionized water until the pH was 7. The final products
◦
◦
were subsequently dried at 110 C overnight, calcined at various
◦
temperatures (400, 600 and 800 C) for 3 h and labeled as TNT-T
STA449F3 TGA analyzer with ramp rate of 10 C/min from 25 to
◦
(
400, 600 and 800, respectively).
800 C in N2 flow.
For comparison, we also prepared the proton-exchanged TNT
X-ray photoelectron spectroscopy (XPS) spectra were recorded
DLD
with 0.1 M HCl solution to investigate the acid-base properties of
TNT samples. After that, the mixture was filtered, washed thor-
with a Kratos AXIS Ultra
multi-technique X-ray photoelectron
spectrometer, equipped with a monochromated Al K˛ radiation
(E = 1486.6 eV). The C 1 s peak with binding energy of 284.6 eV was
taken as energy reference.
◦
oughly with deionized water and dried at 110 C and labeled as
TNT-H.
Pd supported on commercial anatase-type TiO2 or TNTs were
prepared using a deposition-reduction method. The support (0.5 g)
2.3. Catalytic tests
was dispersed in H O (60 mL) with stirring. A specified amount of
2
H PdCl aqueous solution (21.512 gPd/L) was added to the mixture
and stirred for 3 h. The final pH value of the suspension was adjusted
A two-necked round-bottom flask was used to carry out the liq-
uid phase hydrogenation of FA. No pretreatment on the catalyst
was conducted prior to reaction. The reactor was charged with FA
(0.2 mL), solvent (4 mL) and catalyst (50 mg), and the mixture was
2
4
to 10 by adding NaOH solution (1 M). Then, NaBH aqueous solution
4
(
NaBH /Pd = 10, molar ratio) was added into the suspension and
4
◦
the mixture was stirred for another 30 min allowing for the full
stirred under ambient hydrogen pressure (balloon) at 25 C for 1 h.
2
+
◦
reduction of Pd species. Thus obtained catalyst was dried at 110 C
overnight.
The products were analyzed with flame ionization detector (FID)
and capillary column DB-FFAP (30 m length and 0.25 mm internal
diameter).
2
.2. Catalyst characterization
The spent catalyst was recovered by centrifugation washing
with ethanol for three times, and then drying in vacuum. The activ-
ity of the recovered catalyst was tested under the same conditions
as that applied for the fresh sample.
◦
Nitrogen adsorption–desorption isotherms at −196 C were
obtained on a BELSORP-Max equipment. Prior to the measure-
ment, the samples were first degassed at 150 C under vacuum for
◦
6
h. Specific surface areas (SSA) were calculated according to the
3. Results and discussion
Brunauer–Emmett–Teller (BET) method using five relative pressure
points in the interval of 0.05–0.30. The pore size distribution was
obtained by the BJH model applied to the adsorption isotherm.
Pulse CO chemisorption was performed on a Micromeritics
AutoChem 2910 to determine the metal dispersion of the reduced
catalysts. Prior to measurement, the catalyst was reduced in a flow
3
.1. Characterization of TNTs
Fig. 1 shows the XRD patterns of the commercial anatase-type
TiO and the TNTs. Diffraction peaks positioned at 9.8, 24 and
2
are noticed on TNT (Fig. 1c) [18]. Upon calcination at 600 C,
2
◦
8
assigned to the titanates such as Na Ti O5·H O and Na Ti O7
2
2
2
2
3
◦
of 80 mL/min 10 vol.% H2 in Ar at 80 C for 2 h and then cooled
◦
◦
to 30 C by flushing He for 2 h. Afterwards, CO gas pluses (5 vol.%
in He) were introduced in a flow of 110 mL/min. The gas phase
CO concentration was followed by thermal conductivity detector
(
TCD).
The Pd loading was quantified by inductively coupled plasma
ICP) on a Thermo IRIS Intrepid II XSP atomic emission spectrome-
(
ter. About 5 mg catalysts were digested using 10 mL of aqua regia.
The obtained solutions were diluted with deionized water before
test.
The power X-ray diffraction (XRD) patterns were collected on
a Rigaku Ultima IV X-ray diffractometer using Cu K˛ radiation
(
ꢀ = 1.5405 Å) operated at 35 kV and 25 mA. Scanning electron
microscopy (SEM) was performed on a Hitachi S-4800 microscope.
Transmission electron microscopy (TEM) images were taken on a
2
FEI Tecnai G F30 microscope operating at 300 kV. The average Pd
particle size was calculated by dTEM = (ꢁnidi )/(ꢁnidi2) by measur-
ing at least 100 particles. Temperature-programmed desorption of
NH (NH -TPD) testing was performed using a TP-5080 chemisorp-
3
3
3
tion instrument (Xianquan Co., Ltd., Tianjin, China) with a thermal
◦
conductivity detector (TCD). After pretreatment at 400 C under
flowing He (25 mL/min) for 1 h, each sample (100 mg) was cooled
◦
to 100 C, and then adsorbed to saturation by NH3 for 30 min. The
Fig. 1. XRD patterns of pristine anatase and different titanates (TNTs): (a) anatase;
physisorbed NH3 was removed by flushing the sample with He
(b) TNT-H; (c) TNT; (d) TNT-400; (e) TNT-600; (f) TNT-800.