High performance Pd catalyst using silica modified titanate nanotubes (STNT) as support and its catalysis toward hydrogenation of cinnamaldehyde at ambient temperature

Article abstract of DOI:10.1039/c4ra12488j

Titanate nanotubes (TNTs) were coupled with amino-propyl-triethoxy silane (KH550) and calcinated at 400 °C, then the silica modified titanate nanotubes (STNTs) were prepared and used as the support of a Pd catalyst by the method of wet-impregnation. The catalyst was characterized with XRD, Raman spectra, TEM, XPS, and H₂-TPR/TPD. The silica modification could effectively resist morphology collapse and crystallization of TNT during calcination, and preserve the high surface area of the TNT support, which contribute to the high metal dispersion of loaded Pd. Moreover, the introduced silica could strengthen the metal-support interaction, causing an electronic effect that facilitates the reduction of Pd ions. The Pd/STNT showed 3 times and 2.5 times higher activity than those of commercial Pd/C and unmodified Pd/TNT catalysts towards the selective hydrogenation of cinnamaldehyde at room temperature, respectively, indicating the enhanced catalytic activity by the addition of silica.

Full text of DOI:10.1039/c4ra12488j

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PAPER
High performance Pd catalyst using silica modified
titanate nanotubes (STNT) as support and its
catalysis toward hydrogenation of cinnamaldehyde
at ambient temperature
Cite this: RSC Adv., 2014, 4, 63062
Xu Yang,a Liangpeng Wu,a Li Du,b Lizhen Long,a Tiejun Wang,a Longlong Ma,a
a
b
*
*
Xinjun Li and Shijun Liao
Titanate nanotubes (TNTs) were coupled with amino-propyl-triethoxy silane (KH550) and calcinated at
400 ꢀC, then the silica modified titanate nanotubes (STNTs) were prepared and used as the support of a
Pd catalyst by the method of wet-impregnation. The catalyst was characterized with XRD, Raman
spectra, TEM, XPS, and H2-TPR/TPD. The silica modification could effectively resist morphology collapse
and crystallization of TNT during calcination, and preserve the high surface area of the TNT support,
which contribute to the high metal dispersion of loaded Pd. Moreover, the introduced silica could
strengthen the metal–support interaction, causing an electronic effect that facilitates the reduction of Pd
ions. The Pd/STNT showed 3 times and 2.5 times higher activity than those of commercial Pd/C and
unmodified Pd/TNT catalysts towards the selective hydrogenation of cinnamaldehyde at room
temperature, respectively, indicating the enhanced catalytic activity by the addition of silica.
Received 16th October 2014
Accepted 14th November 2014
DOI: 10.1039/c4ra12488j
www.rsc.org/advances
regarded as an effective method to modulate the catalytic
performance of heterogeneous catalysts.
1. Introduction
The discovery15 of titanate nanotubes (TNTs) has attracted
Growing concern about energy availability and related envi-
ronmental impacts has in recent years led many scientists to
investigate green catalysis, which requires chemical trans-
formations to be catalyzed using clean, efficient methods and
materials.1–7 One effective strategy to achieve this target is to
develop high-performance heterogeneous catalysts for use at
room temperature.
To date, many investigations in the eld of heterogeneous
catalysis have revealed that the microstructure/composition of
the loaded active components is closely related to the physico-
chemical properties of the supports (surface chemistry,
surface area, crystallinity, morphology, etc.). The interaction
between metal and support, an important factor inuencing the
catalysis process, is also strongly associated with the support's
surface physico-chemical properties. Considerable work on
various support modications has been done to ne-tune the
general properties of the support. For example, multiple inor-
ganic oxide composites, such as NiO–TiO2,8,9 carbon–titania,10
TiO2–SiO2,11,12 and Al2O3–TiO2,11,13,14 have been used as supports
for metal catalysts to obtain a variety of catalytic properties.
Adjusting the physico-chemical properties of the support is
signicant attention because of their many advantages,
including their tubular morphology, and modest cost. TNT is an
excellent support material for heterogeneous catalysis because
it can effectively improve the dispersion of the loaded metal, a
feature attributable to its tubular structure and large surface
area.16–18 Furthermore, the abundant –OH groups on the surface
of TNT facilitate the introduction of inorganic/organic molecule
to modify that surface with various structure and composition.
Recently, researchers have demonstrated that TiO2 surface
structure and properties, such as surface potential,19 and crys-
talline degree,20 can be tuned effectively by the addition of silica,
which could change the TNT's surface composition, inuence
the interface interaction between the TNT and the loaded
components and yield various catalytic properties. More
importantly, the deposited silica could act as “isolated layer”, a
feature widely applied in constructing metal core–silica shell
nanocomposites.21–24 Thus, supposed that it may protect the
TNT's multiple wall from damage, which oen occurres at
calcination larger than 400 ꢀC and would limit its practical
application in the heterogeneous catalysis.
Herein, we described a novel preparation of silica-modied
Pd/TNT catalysts by modifying the TNT surface with amino-
propyl-triethoxy silane (KH550), then using the silane/silica-
modied TNT as the catalyst support. To the best of our
knowledge, there is no literature involving with silica modied
aKey Laboratory of Renewable Energy, Guangzhou Institute of Energy Conversion,
Chinese Academy of Sciences, Guangzhou 510640, China
bSchool of Chemistry and Chemical Engineering, South China University of
Technology, Guangzhou 510641, China. E-mail: chsjliao@scut.edu.cn
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TNT as support of Pd catalyst via route of silane modication. of the laser was 10 mW, and the laser excitation was 488 nm.
This modied catalyst exhibited greatly enhanced performance Scans were taken over an extended range (100–1000 cmꢁ1), and
towards the selective hydrogenation of cinnamaldehyde. We the exposure time was 20 s.
also characterized the catalysts using XRD, XPS, and other
N2 adsorption–desorption isotherms were measured with a
techniques, and attempted to discover the promotion mecha- Tristar 3010 isothermal nitrogen sorption analyzer (Micro-
nism of silica.
meritics, USA) using a continuous adsorption procedure.
Transmission electron microscopy (TEM) was carried out on
a JEM-2010 microscope (JEOL, Japan) using an accelerating
voltage of 200 kV.
X-ray photoelectron spectroscopy (XPS) was performed with
an AXIS Ultra DLD (Kratos, Britain) to examine the catalysts'
electronic properties. The C 1s line was taken as an internal
standard at 284.8 eV.
2. Experimental
2.1 Catalyst preparation
Synthesis of support materials. Titanate nanotubes (TNTs)
were synthesized by a route described in ref. 15. As-received
TiO2 (Hualisen Corp., China) was mixed with 100 mL concen-
trated NaOH solution (10 M) and placed in a Teon-lined
autoclave under mild stirring at 140 ꢀC for 24 h, then the
resultant white precipitate was separated from the mixture and
washed with deionized water several times until the conduc-
Hydrogen temperature-programmed reduction/desorption
(H2-TPR/TPD) was performed on an Autosorb-iQ-C automated
system (Quantachrome, USA). Approximately 50 mg of as-
prepared catalyst was placed in a quartz tube within a
temperature-controlled oven. H2-TPR was conducted using a
heating rate of ca. 10 ꢀC minꢁ1 from 35 to 800 ꢀC. For H2-TPD,
the catalyst was rst reduced in H2 ow at 100 cm3 minꢁ1 for 1 h
tivity of the solution remained below 100 ms cmꢁ1
.
Modication of TNT with silica. Amino-propyl-triethoxy
silane (KH550) was used as silane coupler (see Scheme 1 for
their molecular structures). Modication of TNT was conducted
as follows: in a mass ratio of 2 : 1, pristine TNT and KH550 were
added to a water–ethanol mixed solution under vigorous stir-
ring at 50 ꢀC for 5 h. The resulting white precipitate was ltered,
washed with ethanol to eliminate the extra KH550, and dried at
ꢀ
at 400 C and then cooled to room temperature. TPD was per-
ꢁ1
ꢀ
formed using a constant heating rate of ca. 10 C min from
35 to 600 ꢀC.
ꢀ
60 C for overnight. Finally, the silane modied TNT was cal-
2.3 Catalyst evaluation
cinated in the oven at 400 ꢀC for 3 h to transform into silica
modied TNT. We denote the silica modied TNT as STNT.
Preparation of catalyst. TNT-supported palladium catalysts
were prepared by the following procedures. First, the support
was impregnated via the incipient wetness impregnation tech-
nique, using an aqueous solution containing a calculated
amount of PdCl2; the mixture was then vacuum dried overnight
at 40 ꢀC, followed by calcination in air at 400 ꢀC for 2 h. The Pd
loading was xed at ca. 2.5 wt%. These preparation procedures
are presented in Scheme 1.
The selective hydrogenation of cinnamaldehyde was used to
evaluate the catalysts. The reaction mixture—composed of 0.2 g
cinnamaldehyde (CALD), 20 mg catalyst, and 10 mL hexane—
was introduced into a stainless steel autoclave under stirring at
1200 rpm, a value chosen to eliminate the mass transfer limi-
tation. Air in the autoclave was purged by hydrogen for 20 min,
and then the reaction proceeded at room temperature (25 C)
and 0.5 MPa of 99.99% hydrogen.
The products were analyzed by a gas chromatograph (Agilent
6840N, USA) equipped with a ame ionization detector. Gas
chromatography-mass spectrometry (GC-MS) analysis was
carried out using a Shimadzu GCMS-QP5050A (Japan) equipped
ꢀ
2.2 Catalyst characterization
X-ray diffraction (XRD) patterns were obtained with an X'Pert with a 0.25 mm ꢂ 30 m DB-WAX capillary column, to identify
Pro MPD X-ray diffractometer (PANalytical, Netherlands) using the product. The column oven temperature was programmꢁe1d
Cu Ka radiation.
from 120 ꢀC (held for 1 min) to 280 ꢀC at a rate of 20 ꢀC min
.
Raman measurement was carried out using a Raman spec-
The mass reaction rate, r, was determine using the equation
troscope (HORIBA Jobin Yvon LabRAM HR, France). The power below:
Scheme 1 Preparation route of silica modified TNT (STNT) and Pd/STNT catalyst.
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mCALD
r ¼
mPd ꢂ treact
where mCALD, mPd, and treact stand for the mass of CALD
converted, the total mass of Pd used, and the reaction time
(typically xed at an initial 30 min).
3. Results and analysis
3.1 XRD analysis
As shown in Fig. 1, the as-prepared TNT material exhibits a
typical titanate phase, which can be assigned to trititanate,
(H, Na)2Ti3O7.15 Aer calcination at 400 ꢀC, all of the catalysts—
with either unmodied Pd/TNT or silica modied Pd/STNT—
exhibited a typical anatase TiO2 structure with space group
I41/amd (JCPDS card no. 21-1272).25 However, the diffraction
intensity of the Pd/STNT is clearly much weaker than that of the
Pd/TNT, revealing that silica modication obstructed modi-
cation to the crystallization of the TNT support. By applying the
Scherrer equation to the (101) peak of each support, the crys-
tallite sizes of TNT, and STNT particles were estimated to be 7.9
and 4.5 nm, respectively, further conrming that the presence
of silica may have affected the crystalline degree of TNT during
calcination. This result is quite consistent with that reported by
Okada et al.26 who found that the crystallinity of anatase
decreased and the crystallization temperature increased upon
the addition of silica. It should be pointed out that no obvious
diffraction peaks indexed to metallic Pd could be observed in
the XRD patterns. There may be two reasons for this: a low
supporting amount of Pd (2.5%), and high dispersion of Pd on
the TNT supports.27,28
Fig. 2 Raman spectra of various catalysts.
perspective of molecular bonding. The pattern of the as-
prepared TNT (with 2ꢂ magnication) shows four well-
dened active mode at 275, 385, 450, and 705 cmꢁ1, similar to
the spectrum of titanate reported by Gao29 and Li.15 Aer
calcination, the Pd/TNT shows spectrum with ve sharp
contributions at 146, 199, 398, 515, and 641 cmꢁ1, in good
agreement with the theoretical analysis and the published
data,30 indicating that the as-prepared TNT were transformed
into an anatase-phase TiO2. The modied Pd/STNT, show peaks
(with 2ꢂ magnication) similar to but much weaker than those
of Pd/TNT. This is a good demonstration that the introduced
silica effectively weakened the crystallinity of TNT undergoing
calcination, a nding that is consistent with the XRD results.
3.2 Raman spectra analysis
The corresponding Raman spectra of the catalysts are given in
Fig. 2. The Raman spectra provide a way to measure the
percentage of anatase TiO2 exposed facets from the micro
3.3 Nitrogen sorption analysis
Table 1 gives the surface areas and porosity parameters of
various samples. The as-prepared TNT shows high surface area
of 302 m2 gꢁ1 with mesopores of 8.0 nm. Undergoing calcina-
tion, the surface area of Pd/TNT decreased sharply, with ca. 50%
decline, in accordance with previous observation reported by
E. Morgado et al.31 While for the Pd/STNT, the surface area and
the pore size decreased (by 10% for surface area and ꢃ10% for
pore size). These results state that the silica modication could
effectively preserve TNT's high surface area undergoing
calcination.
3.4 TEM observation
Fig. 3 presents TEM images of the samples. The tubular
morphology can be seen clearly for the as-prepared TNT, and
the inner cavity is 6–8 nm, consistent with the BET results. For
the Pd/TNT calcined at 400 ꢀC, it's revealed that in spite of
maintaining an elongated feature, some part of the tubular
structure collapsed and aggregated to form irregular bulk
particles. Similar results have also been reported in documents
Fig. 1 XRD patterns of various catalysts and support.
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Table 1 Specification of various support and catalysts
Sample
SBET (m2 gꢁ1
)
Dinner pore (nm)
TiO2 Crystal. size (nm)
Pd wt%
Pd crystal. size (nm)
As-prepared TNT
Pd/TNT
Pd/STNT
302
145
270
8.0
3.3
7.0
—
8.5
7.1
—
2.5
2.4
—
6.2
4.5
silica modication can improve the Pd dispersion. A similar
nding has been also reported in Binder's work,34 they have
ascribed this to the increased surface roughness of support by
the addition of silica.
3.5 XPS analysis
Fig. 4 shows the XPS spectra of the catalysts. The Pd 3d spectra
can be deconvoluted into two doublets, attributable to the
higher Pd 3d energy value of PdIIO and the lower energy value of
metallic Pd0.35 A shi of ca. 0.4 eV and 0.8 eV toward high
binding energy with respect to the silica-supported mono-Pd
catalyst (335.1 eV)36 can be observed for Pd/TNT and Pd/STNT,
respectively, indicating that charge transfer occurred between
the Pd and the support. The binding energies centered at ca.
458.6 eV and 102.8 eV correspond to the oxide states of Ti and
Si, respectively, conrming the co-presence of titania and silica.
Table 2 gives the Pd0/PdII ratios; Pd/STNT presents higher value
than that of Pd/TNT. This means that the Pd/STNT have higher
proportions of metallic Pd than the Pd/TNT, which can be
regarded as a result of the electronic effect.
3.6 H2-TPR/TPD analysis
The characteristics of the surface active sites of the catalysts
were studied by means of the temperature-programmed
reduction/desorption of H2 (H2-TPR/TPD) from 50 to 700 ꢀC.
No obvious reduction peaks are observable in the TPR patterns
of Pd/TNT and Pd/STNT (not shown for simplicity), implying
that most of the Pd2+ ions on the support were fully reduced
aer the H2/Ar ow was switched into the system at ambient
temperature.37 The H2-TPD proles of the reduced catalysts are
shown in Fig. 5, in which the Pd/TNT and Pd/STNT have two
well-dened desorption peaks. Generally, a TPD pattern reveals
the various interactions between the adsorbed H2 species and
the Pd particles.38 By calculating the integrated areas of the H2
desorption peaks for each catalyst, the H2 adsorption capacities
of Pd/STNT was nearly 2.3 times higher than that of the Pd/TNT.
It means that the Pd/STNT possess more active sites than that of
the Pd/TNT at ambient temperature.
Fig. 3 TEM images of as-prepared TNT (a and b), Pd/TNT (c and d),
and Pd/STNT (e and f).
elsewhere.32,33 This result explains well the shrink of surface
area for the calcinated TNT. The Pd/STNT treated at 400 ꢀC still
exhibited nanotubes features which did not differ from those
observed from as-prepared TNT. This result strongly states that
the silica modication could improve the thermal stability of
TNT, and preserve well its tubular morphology and high surface
area.
3.7 Catalysis towards selective hydrogenation of
cinnamaldehyde
As shown in these gures, the Pd dispersion varies. The
Pd/TNT presents non-uniform metal dispersion and has a size
range of 4–8 nm; some irregular aggregates as large as 10 nm
can be observed as well. The average size of the Pd particles is
ca. 7.2 nm. The Pd/STNT catalyst shows a uniform particle size
distribution centered at 4.5 nm. This result indicates that the
The reaction scheme of cinnamaldehyde hydrogenation
proceeds via parallel and consecutive pathway that involve with
hydrogenation of C]O and C]C groups forming cinnamal
alcohol (CALC), hydro-cinnamaldehyde (HALD) and hydro-
cinnamal alcohol (HALC), seeing Fig. 6. The catalysis of the
catalysts towards the hydrogenation of cinnamaldehyde (CALD)
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Fig. 4 XPS spectra of catalysts.
Table 2 XPS data: binding energy and atomic ratio of various Pd
catalysts
Binding energy (eV)
Pd0 PdII
Atomic ratio
Catalyst
Ti2p3
Pd/Ti
Pd0/PdII
3d5
3d5
aPd/C
Pd/TNT
Pd/STNT
335.1
335.5
335.9
336.5
336.9
337.2
—
458.4
458.6
—
0.06
0.05
—
0.54
0.81
a
Data in our previous reported document.37
was tested under mild reaction conditions (30 ꢀC and 0.5 MPa of
hydrogen pressure).
As shown in Fig. 7, the introduction of silica seems to have
had little effect on the catalysts' product selectivity, which is
almost the same for the two catalysts (seeing Table 3). These are
common results for Pd catalytic systems, showing that hydro-
genation occurs mainly on the C]C bond,36,39 instead of the Pt
catalyzed reaction in which the C]O is preferentially hydro-
genated.40 It is worth noting that the silica modication
signicantly improved the hydrogenation activity of the affected
Fig. 5 H2-TPD pattern of various catalysts.
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Table 3 Hydrogenation of CALD over various catalysts: mass reaction
rate and product selectivity
Selectivityb (%)
r
Catalyst
(gCALD gPd hꢁ1
)
HALD
HALC
CALC
ꢁ1
aPd/C
48
65
151
137
87
85
84
82
12
14
15
16
<1
1
1
Pd/TNT
Pd/STNT1st
Pd/STNT3rd
2
a
Fig. 6 Reaction pathway for the hydrogenation of CALD over Pd
catalyst.
Commercial Pd/C catalysts bought from Aladin agent company
b
(Shanghai, China).
Selectivity was determined at 80% CALD
conversion; no other product was found in the GC-mass spectra.
Pd/STNT showed ꢃ10% decrease in reaction rate (seeing
Table 3), suggesting the good recycling stability.
4. Discussion
Based on the above results, we conclude that the introduced
silane were transformed into silica, underwent the calcination
ꢀ
at 400 C, and then were deposited on the surface of TNT (see
Scheme 1). The effect of silica modication on the TNT can be
seen as: resist crystallization (justied by the XRD and Raman
spectra) and morphology collapse (justied by the TEM obser-
vation) during calcination. The decreased crystalline can be
explained as that the SiO2 lattice locked the Ti–O species at the
interface with the TiO2 domains and prevented the nucleation
that was necessary for the crystallization and phase trans-
formation.41 The lower crystalline degree means larger content
of amorphous bulk for the STNT, which could strengthen the
metal–support interaction.42 With respect to the morphology
collapse the deposited silica can act as “isolation wall” to retard
the condensation of hydroxyl groups during calcination. There
is a common agreement that the interlayer hydroxyl groups and
water in the multi-walled structure of TNT act as support to
maintain the tubular morphology.31 As the tubular morphology
is maintained intact, high surface area are well preserved, as
shown by N2 sorption in Table 1. In addition, the amorphous
silica layer deposited on the surface of TNT could contribute to
the high surface area as well.
When the Pd NPs were loaded on the modied STNT
support, the metal dispersion (seeing TEM images of Fig. 3) and
composition (atomic ratio of Pd0/PdII, seeing XPS result of Table
2) of Pd NPs was greatly modulated. The improved metal
dispersion can be ascribed to the high surface area of STNT.
Plus, the strengthened Pd–support interaction, indicating by
the shi of binding energy of Pd and Ti (seeing Fig. 4), could
effectively hind the metal sintering, and decrease the particle
Fig. 7 Course of hydrogenation of CALD over (a) Pd/TNT and (b) Pd/
STNT.
catalysts. Blank tests carried out over the supports alone showed size. Moreover, the charge transfer induced by the intensied
no catalytic activity. Reaction catalyzed by the Pd/STNT pro- Pd–support interaction can facilitate the reduction of Pd species
ceeded to a conversion of ꢃ80% in 150 min, while merely 40% and produce more metallic Pd phase. Some studies13,14 have
of conversion is obtained for the Pd/TNT in the same period. proven that compositing TiO2 with other metal oxides (e.g.,
The mass reaction rate (r) of catalysts calculated at the initial 30 SiO2, Al2O3) can effectively modify the metal–support interac-
min reaction, exhibited that the Pd/STNT presents 3 time and tions. The improved H2 adsorption capacities for the Pd/STNT
2.5 times higher activity than that of commercial Pd/C and catalysts (justied by the H2-TPD) could be related to metal
Pd/TNT, respectively. Aer 3 times of recycle utilization, the dispersion/composition strongly: (i) high metal dispersion
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creates more active sites for hydrogen adsorption; (ii) high
metallic Pd content also facilitates H2 adsorption. Much more
active sites were produced, when silica-modied TNT was used
as the support; one would expect this to result in enhanced
catalyst performance.
2 P. T. Anastas, L. B. Bartlett, M. M. Kirchhoff and
T. C. Williamson, Catal. Today, 2000, 55, 11–22.
3 V. Polshettiwar and R. S. Varma, Green Chem., 2010, 12, 743–
754.
4 J. Mao, G. Zhao, D. Wang and Y. Li, RSC Adv., 2014, 4, 25384–
25388.
5 X. Peng, W. Ye, Y. Ding, S. Jiang, M. Hanif, X. Liao and
H. Hou, RSC Adv., 2014, 4, 42732–42736.
6 S. Rostamnia and E. Doustkhah, RSC Adv., 2014, 4, 28238–
28248.
7 J. Safari and S. Gandomi-Ravandi, RSC Adv., 2014, 4, 11486–
11492.
Clearly, the catalytic performance of catalysts towards the
hydrogenation of CALD (presented in Fig. 7) veried the above
assumption. The great enhanced hydrogenation activity of Pd/
STNT can be obviously ascribed to its high Pd dispersion, in
one respect. Plus, the large surface of STNT could contribute to
the improved activity due to the high external surface area could
facilitate mass transfer. In another respect, it should be
noticeably that the greater improvement shown by silica
modication is associated with its ratio of Pd0/PdII, indicating
the important role of metallic Pd phase In Winterbottom's early
work,43 it has revealed that pre-reduced PdO gave rise to better
8 M. Yadav, D. K. Mishra and J.-S. Hwang, Appl. Catal., A, 2012,
425, 110–116.
9 A. Villa, G. M. Veith, D. Ferri, A. Weidenkaff, K. A. Perry,
S. Campisi and L. Prati, Catal. Sci. Technol., 2013, 3, 394–399.
activity for the liquid-phase hydrogenation of 1-octyne at 30 ꢀC, 10 J. Zhu, M. Li, M. Lu and J. Zhu, Catal. Sci. Technol., 2013, 3,
indicating that metallic Pd could accelerate the hydrogenation
rate. Agostini's group44 recently has declared that the metallic 11 N. Jagtap, S. B. Umbarkar, P. Miquel, P. Granger and
phase of Pd can shorten the induction period for the debenzy- M. K. Dongare, Appl. Catal., B, 2009, 90, 416–425.
lation process catalyzed by Pd/Al2O3. Thus, we hypothesize that 12 Z. Zhang, Y. Zhou, Y. Zhang, X. Sheng, S. Zhou and S. Xiang,
the metallic phase can also preferentially promote hydrogena- RSC Adv., 2014, 4, 40078–40084.
737–744.
tion activity, overwhelming the PdO phase at low temperatures 13 G. Wan, A. Duan, Z. Zhao, G. Jiang, D. Zhang, R. Li, T. Dou
ꢀ
(<30 C). This can come about in two ways: metallic Pd can (i)
and K. H. Chung, Energy Fuels, 2008, 23, 81–85.
facilitate hydrogen dissociative adsorption and (ii) accelerate 14 W. Yan, S. M. Mahurin, Z. Pan, S. H. Overbury and S. Dai, J.
the induction period of hydrogenation. In a word, silica modi- Am. Chem. Soc., 2005, 127, 10480–10481.
cation can change the Pd–TiO2 interaction, yielding much 15 X. Sun and Y. Li, Chem.–Eur. J., 2003, 9, 2229–2238.
more of the metallic Pd phase, increasing the active center sites 16 L. Torrente-Murciano, A. A. Lapkin, D. V. Bavykin,
for hydrogenation, and consequently improving the catalytic
activity at low reaction temperatures.
F. C. Walsh and K. Wilson, J. Catal., 2007, 245, 272–278.
17 M. Wang, D.-j. Guo and H.-l. Li, J. Solid State Chem., 2005,
178, 1996–2000.
18 V. Idakiev, Z.-Y. Yuan, T. Tabakova and B.-L. Su, Appl. Catal.,
A, 2005, 281, 149–155.
5. Conclusions
We report high-performance Pd catalysts with silica modied 19 D. V. Bavykin, A. A. Lapkin, P. K. Plucinski, L. Torrente-
TNT (STNT) as supports. The catalysts show improved perfor-
mance towards the hydrogenation of cinnamaldehyde at
Murciano, J. M. Friedrich and F. C. Walsh, Top. Catal.,
2006, 39, 151–160.
ambient temperature. The effect of silica modication on the 20 H.-H. Ou and S.-L. Lo, Sep. Purif. Technol., 2007, 58, 179–191.
TNT support can be regard as resist crystallization and 21 S. H. Joo, J. Y. Park, C.-K. Tsung, Y. Yamada, P. Yang and
morphology collapse during calcination, change the interface
structure and properties of TNT. The modied surface further 22 A. C. S. Sekhar, C. J. Meera, K. V. Ziyad, C. S. Gopinath and
modulates the Pd–support interaction strongly and cause high C. P. Vinod, Catal. Sci. Technol., 2013, 3, 1190–1193.
metal dispersion and metallic Pd content, both of which could 23 B. Zeng, B. Hou, L. Jia, J. Wang, C. Chen, D. Li and Y. Sun,
enhance its hydrogenation activity signicantly. Pd/STNT in Catal. Sci. Technol., 2013, 3, 3250–3255.
particular may shed light on the design of promising catalysts 24 L. Mo, K. K. M. Leong and S. Kawi, Catal. Sci. Technol., 2014,
G. A. Somorjai, Nat. Mater., 2009, 8, 126–131.
for hydrogenation in green catalysis applications.
4, 2107–2114.
25 D. Li, D. Shi, Z. Liu, H. Liu and Z. Guo, J. Nanopart. Res.,
2013, 15, 1–10.
26 K. Okada, N. Yamamoto, Y. Kameshima, A. Yasumori and
K. J. MacKenzie, J. Am. Ceram. Soc., 2001, 84, 1591–1596.
Acknowledgements
This work was supported by the National Scientic Foundation
of China (project no. 21303210), the National 973 Project of 27 S. Tauster, S. Fung and R. Garten, J. Am. Chem. Soc., 1978,
China (project no. 2009CB220002), and the Postdoctoral Foun-
100, 170–175.
dation of China (project no. 2013M531881), the Fundamental 28 H. Chen, Y. Shao, Z. Xu, H. Wan, Y. Wan, S. Zheng and
Research Funds for the Central Universities, SCUT.
D. Zhu, Appl. Catal., B, 2011, 105, 255–262.
˚
29 T. Gao, H. Fjellvag and P. Norby, Inorg. Chem., 2009, 48,
1423–1432.
References
30 F. Tian, Y. Zhang, J. Zhang and C. Pan, J. Phys. Chem. C, 2012,
116, 7515–7519.
1 A. Fukuoka and P. L. Dhepe, Chem. Rec., 2009, 9, 224–235.
63068 | RSC Adv., 2014, 4, 63062–63069
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
31 E. Morgado Jr, M. A. S. de Abreu, O. R. C. Pravia, 38 D. Xu, W. Li, H. Duan, Q. Ge and H. Xu, Catal. Lett., 2005,
B. A. Marinkovic, P. M. Jardim, F. C. Rizzo and
102, 229–235.
´
A. S. Araujo, Solid State Sci., 2006, 8, 888–900.
39 A. Mehri, H. Kochkar, S. Daniele, V. Mendez, A. Ghorbel and
G. Berhault, J. Colloid Interface Sci., 2012, 369, 309–316.
40 Y. J. Zhu and F. Zaera, Catal. Sci. Technol., 2014, 4, 955–962.
32 R. Yoshida, Y. Suzuki and S. Yoshikawa, Mater. Chem. Phys.,
2005, 91, 409–416.
33 J. Yu, H. Yu, B. Cheng and C. Trapalis, J. Mol. Catal. A: Chem., 41 Z. Li, B. Hou, Y. Xu, D. Wu and Y. Sun, J. Colloid Interface Sci.,
2006, 249, 135–142. 2005, 288, 149–154.
34 A. Binder, M. Seipenbusch and G. Kasper, J. Phys. Chem. C, 42 J. Panpranot, K. Kontapakdee and P. Praserthdam, J. Phys.
2010, 114, 7816–7821. Chem. B, 2006, 110, 8019–8024.
35 G. Zhang, Y. Wang, X. Wang, Y. Chen, Y. Zhou, Y. Tang, 43 I. Caga, E. Shutt and J. Winterbottom, J. Catal., 1976, 44,
L. Lu, J. Bao and T. Lu, Appl. Catal., B, 2011, 102, 614–619. 271–280.
36 X. Yang, D. Chen, S. Liao, H. Song, Y. Li, Z. Fu and Y. Su, J. 44 E. Groppo, G. Agostini, A. Piovano, N. B. Muddada,
Catal., 2012, 291, 36–43.
G. Leofanti, R. Pellegrini, G. Portale, A. Longo and
37 H. Zhu, Z. Qin, W. Shan, W. Shen and J. Wang, J. Catal.,
2004, 225, 267–277.
C. Lamberti, J. Catal., 2012, 287, 44–54.
This journal is © The Royal Society of Chemistry 2014
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