The effect of TiO2 particle size on the characteristics of Au-Pd/TiO2 catalysts

Article abstract of DOI:10.1016/j.catcom.2014.07.030

The nanocrystalline TiO₂ materials with average crystallite sizes of 9 and 15 nm were synthesized by the solvothermal method and employed as the supports for preparation of bimetallic Au/Pd/TiO₂ catalysts. The average size of Au-Pd alloy particles increased slightly from sub-nano (< 1 nm) to 2-3 nm with increasing TiO₂ crystallite size from 9 to 15 nm. The catalyst performances were evaluated in the liquid-phase selective hydrogenation of 1-heptyne under mild reaction conditions (H₂ 1 bar, 30 °C). The exertion of electronic modification of Pd by Au-Pd alloy formation depended on the TiO₂ crystallite size in which it was more pronounced for Au/Pd on the larger TiO₂ (15 nm) than on the smaller one (9 nm), resulting in higher hydrogenation activity and lower selectivity to 1-heptene on the former catalyst.

Full text of DOI:10.1016/j.catcom.2014.07.030

The effect of TiO2 particle size on the characteristics of Au-Pd/TiO2 catalysts
Prathan Kittisakmontree, Hiroshi Yoshida, Shin-ichiro Fujita, Masahiko
Arai, Joongjai Panpranot
PII:
DOI:
Reference:
S1566-7367(14)00292-1
doi: 10.1016/j.catcom.2014.07.030
CATCOM 3987
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
21 May 2014
17 July 2014
21 July 2014
Please cite this article as: Prathan Kittisakmontree, Hiroshi Yoshida, Shin-ichiro
Fujita, Masahiko Arai, Joongjai Panpranot, The effect of TiO2 particle size on
the characteristics of Au-Pd/TiO2 catalysts, Catalysis Communications (2014), doi:
1
0.1016/j.catcom.2014.07.030
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ACCEPTED MANUSCRIPT
REVISED
The effect of TiO particle size on the characteristics of Au-Pd/TiO catalysts
2
2
a
b
b
b
Prathan Kittisakmontree , Hiroshi Yoshida , Shin-ichiro Fujita , Masahiko Arai , and
a,*
Joongjai Panpranot
a
Center of Excellence on Catalysis and Catalytic Reaction Engineering, Department of
Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok
1
0330, Thailand
b
Division of Chemical Process Engineering, Faculty of Engineering, Hokkaido
University, Sapporo 060-8628, Japan
Date: July 17, 2014
Submitted to: Catalysis Communications
*
To whom all correspondence should be addressed.
Tel.: 66-2218-6869 Fax: 66-2218-6877 E-mail: joongjai.p@chula.ac.th
1

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Abstract
The nanocrystalline TiO materials with average crystallite sizes of 9 and 15 nm
2
were synthesized by the solvothermal method and employed as the supports for
preparation of bimetallic Au/Pd/TiO catalysts. The average size of Au-Pd alloy
2
particles increased slightly from sub-nano (< 1 nm) to 2-3 nm with increasing TiO2
crystallite size from 9 to 15 nm. The catalyst performances were evaluated in the
liquid-phase selective hydrogenation of 1-heptyne under mild reaction conditions (H 1
2
o
bar, 30 C). The exertion of electronic modification of Pd by Au-Pd alloy formation
depended on the TiO crystallite size in which it was more pronounced for Au/Pd on
2
the larger TiO (15 nm) than on the smaller one (9 nm), resulting in higher
2
hydrogenation activity and lower selectivity to 1-heptene on the former catalyst.
Keywords: 1-heptyne, selective hydrogenation, TiO , Pd-Au bimetallic catalysts
2
2

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1
. Introduction
Bimetallic catalysts have attracted much attention because of their markedly
different properties from either of the constituent metals, and their enhanced catalytic
stabilities, activities and/or selectivities. Important examples are AuPd catalysts which
have been found to be effective in many catalytic reactions such as CO oxidation, vinyl
chloride synthesis, hydrodesulfurization, selective oxidation of alcohols to aldehydes or
ketones and alkenes to epoxides, oxidation of hydrogen to hydrogen peroxide, and
selective hydrogenation [1]. The selective hydrogenation of alkyne to the
corresponding alkene is a very valuable reaction in synthetic organic chemistry. The
alkyne hydrogenation over Pd–Au bimetallic catalysts focused on the gas-phase
selective hydrogenation of low molecular weight substrates, mostly acetylene. In the
present research, 1-heptyne a relatively long chain alkyne is used as the model reactant.
The promotional effect of Au in Au–Pd catalysts has been attributed to the
synergistic effects arisen from both ligand effect and ensemble effect of the Au–Pd
alloy [2, 3]. In hydrogenation reactions, a number of studies showed that electron
transfer between Pd and Au species resulted in the modification of catalyst activity and
selectivity [4-7]. However, it appears that the exertion of electronic interaction between
Pd and Au species depend on several factors such as the molar ratio of Au to Pd, the
preparation method, the particle morphology, and/or the particle size of Au–Pd alloys
[
8-11]. In our previous study, the formation of small size Au-Pd bimetallic particle (<
0 nm) could enhance the second step hydrogenation of 1-heptyne in the liquid-phase
1
selective hydrogenation of 1-heptyne [12].
Despite the variety of supports being used for preparation of supported Au-Pd
catalysts such as γ-Al O [4], SiO [5], TiO [6, 13], SiO -Al O [14], zeolite [15],
2
3
2
2
2
2
3
CeO [16], α-Fe O [17], and carbon [18, 19], only a few studies systematically
2
2
3
3

ACCEPTED MANUSCRIPT
reported the influence of support nature on the interaction of Au-Pd species and their
corresponding catalytic behavior. Smolentseva et al. [16] showed that Pd-Au/Al O3
2
exerted more pronounced interaction between gold and palladium species than Pd-
Au/CeO but the Pd–Au/CeO manifested higher activity and selectivity in the selective
2
2
oxidation of arabinose to arabinonic acid. The interaction of Au and Pd with reducible
ceria coexisted with the mutual interaction between these metals.
TiO is one of reducible metal oxides that have received considerable attention
2
as catalyst supports. In the liquid-phase selective hydrogenation of alkyne to alkene,
Pd/TiO exhibited the strong metal-support interaction (SMSI) effect, resulting in an
2
improvement of the catalytic performances [20]. However, the SMSI effect in Pd/TiO2
depended on the properties of the TiO such as the crystalline phase composition and
2
the crystallite size [21, 22]. The TiO supports used for preparation of Au–Pd catalysts
2
in many research works were mostly the commercially available Degussa P25. For
example, Enache and co-workers [7] studied the effect of Au–Pd ratio on the Au–
Pd/TiO catalyst performance in the oxidation of benzyl alcohol.
2
In the present study, the solvothemal method was employed to synthesize the
nanocrystalline anatase TiO . Solvothemal method is an alternative route for direct
2
(
one step) synthesis of pure anatase TiO . Particle morphology, crystalline phase, and
2
surface chemistry of the solvothemal-derived TiO can be controlled by regulating
2
precursor composition, reaction temperature, pressure, solvent property, and aging time
[
20]. The effect of TiO crystallite size on the catalytic behavior of Au–Pd/TiO2
2
catalysts was investigated in the selective hydrogenation of 1-heptyne to 1-heptene
under mild reaction conditions. The catalysts were also characterized using X-ray
diffraction (XRD), transmission electron microscopy (TEM), Fourier transformed
4

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infrared spectroscopy of adsorbed CO (CO-IR), and X-ray photoelectron spectroscopy
(XPS).
2
. Experimental
2
.1 Catalyst preparation
The TiO support used in this work was synthesized by the solvothemal method
2
as described in Ref. [20] using titanium (IV) tert-butoxide (97%TNB) and 1,4-
butanediol (Aldrich) as titanium precursor and solvent, respectively. Twenty five g of
TNB was suspended in 100 ml of 1,4-butanediol. After the autoclave was completely
o
o
purged with nitrogen, it was heated to 300 C at a rate of 2.5 C/min and held at this
temperature for 30 min and for 6 h to prepare TiO _of 9 nm and 15 nm, respectively.
2
After the reaction, the autoclave was cooled to room temperature. The resulting powder
that collected from the test tube was centrifuged in methanol five times and then dried
in air at room temperature overnight. The final product obtained were TiO powders,
2
which were denoted as TiO _9 and TiO _15.
2
2
The monometallic catalysts (ca. 0.5 wt% of Pd) were prepared by the incipient
wetness impregnation technique using 1 M HCl solution of PdCl (Aldrich). The
2
o
o
catalysts were dried overnight at 110 C and calcined in air at 500 C for 2 h. The
monometallic catalysts supported on solvothermal-derived TiO2 with average
crystallite sizes of 9 and 15 nm are denoted as Pd/TiO _9 and Pd/TiO _15,
2
2
respectively. The bimetallic (ca. 0.5 wt% of Pd and 1.0 wt% of Au) catalysts were
prepared by the combination of impregnation of Pd and deposition-precipitation of Au
according to Ref. [23]. Firstly, HAuCl .3H O, which was used as gold precursor, was
4
2
3
dissolved in 100 cm of deionized water. The pH was adjusted to 7 by using 0.1 M of
NaOH. The Pd/TiO catalyst was dispersed in the solution and the pH was adjusted
2
5

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o
again to 7 with 0.1 M NaOH. The suspension was vigorously stirred for 2 h at 80 C.
After that the suspension was cooled and centrifuged five times with deionized water in
o
order to remove chloride and then dried at 110 C. The bimetallic catalysts supported on
the solvothermal-derived TiO with average crystallite sizes of 9 and 15 nm were
2
denoted as Au/Pd/TiO _9 and Au/Pd/TiO _15, respectively.
2
2
2
.2 Catalyst characterization
The physisorption of nitrogen was performed using a Micromeritics ASAP
020 automated system to evaluate the BET specific surface area, pore volume, and
2
average pore diameter. The XRD patterns of the catalysts were measured from 10 to
o
8
0 2θ using a SIEMENS D5000 X-ray diffractometer and Cu K radiation with a Ni
α
filter. TEM was carried out using a JEOL JEM 2010 transmission electron microscope
that employed a LaB electron gun in the voltage range of 80–200 kV with an optical
6
point to point resolution of 0.23 nm. The XPS measurement was carried out using an
AMICUS photoelectron spectrometer equipped with an Mg K X-ray as a primary

excitation and KRATOS VISION2 software. XPS elemental spectra were acquired with
0
.1 eV energy step at a pass energy of 75 eV. All the binding energies were referenced
to the C 1s peak at 285.0 eV of the surface adventitious carbon. The CO species
adsorbed on the Pd/TiO catalysts were measured using FTIR-620 spectrometer
2
-1
(
JASCO) with a MCT detector at a wavenumber resolution of 2 cm . He gas was
introduced into the sample cell in order to remove the remaining air. The system was
o
switched to hydrogen and heated to 150 C. The temperature was kept constant for 30
min and then cooled to the room temperature with He gas. After that, carbon monoxide
was passed to the system for 15 min. The IR spectrum of CO adsorbed onto the catalyst
6

ACCEPTED MANUSCRIPT
−
1
was recorded in the 600–4000 cm range after the gaseous CO was removed from the
cell by He flow.
2
.3 Reaction study in the liquid-phase hydrogenation of 1-heptyne
The liquid-phase hydrogenation of 1-heptyne (98%, Aldrich) was carried out in
3
a magnetically stirred 50-cm Teflon-lined stainless steel autoclave reactor. Prior to the
reaction testing, the catalyst sample was reduced by hydrogen gas at a flow rate of
3
o
3
5
0cm /min at 40 C for 2 h. Then, 0.01 g of the sample was dispersed in 10 cm of
toluene (99.9%, Merck) containing 2 vol. % 1-heptyne. The effect of mass transfer on
the reaction rate was negligible by using a high stirring rate (1000 rpm). The reaction
o
was carried out under flowing hydrogen at 1 bar and 30 C for 10-120 min. The liquid
reactants and products were analyzed by a gas chromatograph equipped with an FID
detector (Shimadzu GC-14A and TC-WAX column).
3
. Results and discussion
3
.1 Catalyst characterization
The XRD patterns of the TiO supports and TiO supported Au–Pd catalysts are
2
2
shown in Figure 1. All the samples showed the characteristic peaks of pure anatase
o
o
o
o
o
o
o
o
phase titania at 2 degrees = 25 (major), 37 , 48 , 55 , 56 , 62 , 71 , and 75 without
contamination of the other phases such as rutile and brookite [24]. The average
crystallite sizes of TiO were calculated from the full width at half maximum of the
2
o
XRD peak at 2 = 25 using the Scherrer equation. As shown in Table 1, the
solvothermal-derived TiO had average crystallite sizes of 9 and 15 nm with specific
2
2
surface area 145 and 79 m /g, respectively. The XRD characteristic peaks
7

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corresponding to palladium and gold species were not detected for all the catalysts
probably due to the low amount of metals present.
Typical TEM images the monometallic Pd and the bimetallic Au–Pd catalysts
are shown in Figure 2. The TiO _9 and TiO _15 supports obtained from the
2
2
solvothermal method showed uniform particle size of average size of 9 and 15 nm,
respectively. The metal dispersion on the catalysts can be observed from the TEM
images. The average Pd particles size on the monometallic Pd/TiO _9 catalyst was in
2
the range of sub-nano particles (< 1 nm) whereas that of Pd/TiO _15 catalyst was larger
2
(
 2 nm). Similarly, for the bimetallic Au–Pd catalysts much smaller Au–Pd particles
were seen on the Au/Pd/TiO _9 than on the Au/Pd/TiO _15. The metal particles on the
2
2
Au/Pd/TiO _9 and Au/Pd/TiO _15 had a uniform particle size distribution in the range
2
2
of sub-nano particles (< 1 nm) and 2-3 nm, respectively. It is suggested that the size of
Au–Pd particles depend on the original size of the Pd particles, which is itself a
function of the TiO crystallite size.
2
The surface properties and the chemical states of Pd and Au on the different
catalysts were investigated by XPS. The binding energies and atomic concentrations of
Pd and Au determined by XPS are given in Table 2. The Pd 3d spectra of the
monometallic and bimetallic catalysts are shown in Figure 3(a) and 3(b), respectively.
For the Pd/TiO _9 and Pd/TiO _15 catalysts, the binding energies (B.E.) of Pd 3d
5/2
2
2
were detected at 336.5-337.1 eV which could be attributed to the presence of palladium
in the form of PdO. On the other hand, the Pd 3d spectra of the Au/Pd/TiO _9 and
2
Au/Pd/TiO _15 catalysts were fitted by two peaks at higher and lower binding energies
2
of 336.0-336.2 eV and 334.8-335.2 eV, which were attributed to Pd–Au alloy and
0
metallic Pd , respectively [25, 26]. It has been reported that Pd particles in the
bimetallic catalysts were highly resistant to oxidation, compared to those of the
8

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monometallic catalysts [27]. The atomic percent of the species at 336.0-336.2 eV (Au–
Pd alloy) for Au/Pd/TiO _9 and Au/Pd/TiO _15 catalysts were determined by peak
2
2
fitting to be 19% and 18%, respectively. The percentages of Au–Pd alloy formation
were not significantly different on the different bimetallic Au–Pd catalysts. The Au 4f
spectra of the bimetallic catalysts are shown in Figure 3(c). The Au 4f peaks were
detected at the binding energy of 83.0-83.2 eV, which were shifted from the typical
metallic gold (B.E. 84.0 ± 0.1). A small shift of binding energies could be attributed to
charge transfer from Pd to Au on the grounds of the bulk electronegativity differences
and could also be indicative of alloy formation [27].
o
The infrared spectra obtained after CO adsorption at 30 C on the Pd
monometallic and Au–Pd bimetallic catalysts are shown in Figure 4. The spectral
envelopes were deconvoluted into individual vibrational bands in order to identify the
specific adsorbed species. The CO adsorption on Pd-based catalysts generally reveals
-1
two main regions: a first one between 2100 and 2030 cm and a larger second one in
-1
2
000–1800 cm range. The IR spectra for Pd monometallic and Au–Pd bimetallic
-1
catalysts represent four adsorption modes of CO, linear (2100-2030 cm ), compressed
-1
-1
bridged (1995-1975 cm ), isolated bridged (1960-1925 cm ), and tricoordinated
-1
(
1890-1870 cm ) bonds, as described in Ref. [28]. Compared to the monometallic Pd
catalysts, the peaks corresponding to linear CO adsorbed species were shifted to lower
wavenumbers after Au addition for all the Au–Pd bimetallic catalysts, suggesting the
Pd–Au alloy formation [28, 29].
9

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3
.2 Hydrogenation of 1-heptyne
The catalytic behavior of the mono and bimetallic catalysts was evaluated in the
liquid-phase semihydrogenation of 1-heptyne to 1-heptene under mild conditions. The
conversion of 1-heptyne and the selectivity to 1-heptene as a function of reaction time
are shown in Figure 5(a) and 5(b), respectively. The hydrogenation rates of the
bimetallic Au–Pd catalysts were higher than those of the monometallic Pd ones and
were found to be in the order: Au/Pd/TiO _15 > Au/Pd/TiO _9 > Pd/TiO _15 >
2
2
2
Pd/TiO _9. The conversion of 1-heptyne was completed in 30 min for all the catalysts,
2
except the Pd/TiO _9 in which complete conversion was achieved after 40 min reaction
2
time under the conditions used. The dependence of hydrogenation activity of supported
Pd catalysts on Pd particle size has been investigated extensively. Typically, specific
activity of Pd in the liquid-phase selective hydrogenation decreases as Pd particle size
decreases especially when the average Pd size is very small (≤ 3-5 nm) [30].
Diminishing activity of small metal particles was probably due to the different band
structure characteristics of nano-sized metal compared to bulk metals, through which
the nano-sized metal particles are electron deficient [31]. The results were consistent to
the previous study on the comparison of Pd catalysts supported on micron- and
solvothermal-derived nanocrystalline TiO in the liquid-phase selective hydrogenation
2
of phenylacetylene. The activity for hydrogenation of phenylacetylene of Pd supported
TiO with large crystallite size was higher than that of supported TiO with small
2
2
crystallite size, due to the smaller Pd particle size deposited on the smaller TiO2
crystallite size. However, the selectivity of catalyst supported on the small TiO2
crystallites was still higher than that of catalyst supported on the larger ones. Moreover,
the nanocrystalline TiO exhibited strong metal–support interaction (SMSI) when
2
reduced at 500 ◦C [20, 21].
1
0

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All the present catalysts exhibited high selectivity to 1-heptene (> 97%) up to
nearly full conversion of 1-heptyne. During 120 min, the selectivity of 1-heptene
decreased further after complete conversion of 1-heptyne due to the hydrogenation of
1
-heptene to heptane. Nonetheless, the selectivities to 1-heptene of the monometallic
catalysts were higher than those of the bimetallic catalysts. The selectivity to 1-heptene
for the bimetallic catalysts at 120 min was in the order: Au/Pd/TiO _9 (54 %) >
2
Au/Pd/TiO _15 (41 %) whereas the selectivity was not much different among the
2
monometallic catalysts (70%).
Unlike the alkyne hydrogenation activity, the selectivity to alkene formation
was irrespective of Pd particle diameter for most reactants in the selective alkyne
hydrogenation [32-34]. It is rather affected by electronic modification of Pd metal (i.e.,
alloy formation and presence of the strong metal-support interaction effect). In our
recent papers [12], the rate of 1-heptene hydrogenation in the second step was greatly
enhanced as the Pd species became electron-rich in the Au–Pd alloy particles. In other
words, the Au species acted as an electronic promoter for Pd and greatly promoted the
second step of hydrogenation of 1-heptene to heptane. In our previous studies, the
formation of Au–Pd alloy was found to be dependent on the loading sequence [12] and
the preparation method used [35]. The results in the present work emphasized that the
formation of Au–Pd alloy was responsible for the increased hydrogenation activity of
1
-heptene to heptane in the selective hydrogenation of 1-heptyne and this suggests the
dependence of alkene hydrogenation rate on the Au–Pd particle size. The exertion of
electronic modification of Pd by Au-Pd alloy formation was more pronounced for
Au/Pd on the larger TiO (15 nm) than on the smaller one (9 nm), resulting in higher
2
hydrogenation activity and lower selectivity to 1-heptene on the former catalyst.
1
1

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The catalyst performance plots in terms of 1-heptene selectivity versus
conversion of 1-heptyne are shown in Figure 5(c). Both high conversion of 1-heptyne
(
95%) and high selectivity for 1-heptene (97%) can be obtained from the bimetallic
Au/Pd/TiO -15 nm catalysts under the reaction conditions used at 20 min, giving the
2
highest yield of 1-heptene among all the catalysts used in this study (92.15%). The
highest yield of 1-heptene over monometallic Pd/TiO was ca. 80% at 40 min reaction
2
time. Such results suggest the advantages of the bimetallic AuPd catalysts over the
monometallic Pd in the selective alkyne hydrogenation.
4
. Conclusions
Smaller Pd metal and/or Pd-Au alloy (< 1 nm) were obtained on the TiO _9
2
than on TiO _15 (2-3 nm). In the bimetallic Au-Pd alloy, the Au species acted as an
2
electronic promoter for Pd and greatly promoted the second step of hydrogenation of 1-
heptene to heptane. The catalytic behavior of Au/Pd/TiO strongly depended on the
2
crystallite size of TiO and Au-Pd alloy particle size. The smaller particles size of Pd
2
and/or Pd-Au alloy provided a higher selectivity to 1-heptene in the selective
hydrogenation of 1-heptyne under mild reaction conditions.
Acknowledgements
We gratefully thank the Dusadeepipat scholarship from Chulalongkorn
University, the Thailand Research Fund (TRF) for the financial supports. The authors
also acknowledge support from the National Research Council of Thailand (NRCT)
and Japan Society for the Promotion of Science (JSPS) under the Joint Research
Program.
1
2

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Table 1 Properties of TiO support
2
Crystallite size
BET surface area
Pore volume
Average pore diameter
(nm)
TiO support
Phase
2
2
3
(nm)
(m /g)
(cm /g)
TiO _9
Anatase
Anatase
9
145
79
0.42
0.40
8.1
2
TiO _15
15
14.9
2
1
3

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Table 2 XPS results of TiO supported Pd and Au/Pd catalysts
2
Pd 3d5/2
FWHM (eV)
Au 4f7/2
FWHM (eV)
Atomic concentration
Sample
B.E. (eV)
336.7
B.E. (eV)
n/a
Pd (%)
0.12
Au (%)
n/a
Pd/TiO _9
0.924
n/a
1.173
n/a
2
(
1) 334.9
2) 336.0
1.336
1.372
(1) 0.69
(2) 0.16
Au/Pd/TiO _9
83.2
n/a
0.50
n/a
2
(
Pd/TiO _15
337.1
0.775
0.07
2
(
1) 334.8
2) 336.2
1.365
1.452
(1) 0.46
(2) 0.10
Au/Pd/TiO _15
83.0
1.226
0.43
2
(
1
4

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Figure Captions
Figure 1
XRD patterns of TiO _9, Pd/TiO _9, Au/Pd/TiO _9, TiO _15,
2
2
2
2
Pd/TiO _15 and Au/Pd/TiO _15.
2
2
Figure 2
TEM images of Pd/TiO _9, Au/Pd/TiO _9, Pd/TiO _15 and
2 2 2
Au/Pd/TiO _15.
2
Figure 3(a)
XPS Pd 3d core level spectra of Pd/TiO _9 and Pd/TiO _15.
2 2
Figure 3(b) XPS Pd 3d core level spectra of Au/Pd/TiO _9 and Au/Pd/TiO _15.
2
2
Figure 3(c)
Figure 4
XPS Au 4f core level spectra of Au/Pd/TiO _9 and Au/Pd/TiO _15.
2 2
FTIR spectra of adsorbed CO at room temperature on Pd/TiO _9,
2
Au/Pd/TiO _9, Pd/TiO _15 and Au/Pd/TiO _15.
2
2
2
Figure 5
Hydrogenation of 1-heptyne on Pd/TiO _9, Au/Pd/TiO _9, Pd/TiO _15
2 2 2
and Au/Pd/TiO _15 carried out under flowing hydrogen at 1 bar and
2
o
3
0 C for 10-120 min: % 1-heptyne conversion (a) and %1-heptene
selectivity (b).
1
5

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Fig1
1
6

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Figure 2
1
7

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1
8

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Fig3
Fig 4
1
9

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2
0

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Fig 5
2
1

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ACCEPTED MANUSCRIPT
Effects of TiO crystallite size on the solvothermal-derived nanocrystalline TiO2
2
supported Au-Pd catalysts in the liquid-phase hydrogenation of 1-heptyne
a
b
b
b
Prathan Kittisakmontree , Hiroshi Yoshida , Shin-ichiro Fujita , Masahiko Arai , and
Joongjai Panpranot
a,*
a
Center of Excellence on Catalysis and Catalytic Reaction Engineering, Department of
Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok
1
0330, Thailand
b
Division of Chemical Process Engineering, Faculty of Engineering, Hokkaido
University, Sapporo 060-8628, Japan
.
Au-Pd catalysts were prepared on TiO with average crystallite sizes 9 and 15
2
nm.
.
.
The size of Au-Pd alloy depended on the TiO crystallite size.
Electronic effect by Au-Pd alloy formation was more pronounced on the larger
2
TiO2.
.
Au acted as an electronic promoter for Pd, which promoted 1-heptene
hydrogenation.
2
5