Visible light promoted hydrochlorination of olefin over Pt, Au and Pd supported on zirconia

Article abstract of DOI:10.1007/s10562-013-1154-8

The Pt, Au and Pd catalysts supported on zirconia were prepared by the colloid deposition method. The catalytic activities of the catalysts for the hydrochlorination of 4-phenyl-1-butene were investigated under the irradiation of visible light, taking hyd

Full text of DOI:10.1007/s10562-013-1154-8

Catal Lett (2014) 144:81–86
DOI 10.1007/s10562-013-1154-8
Visible Light Promoted Hydrochlorination of Olefin Over Pt, Au
and Pd Supported on Zirconia
Xuzhuang Yang
•
•
Huaiyong Zhu
•
•
Guanjun Gao
•
•
Chenhui Han
Huailiang Lu
Jie Wang
Min Tong
Jie Liu
Xiaoyuan Liang
•
•
Received: 13 October 2013 / Accepted: 23 October 2013 / Published online: 5 November 2013
Ó Springer Science+Business Media New York 2013
Abstract The Pt, Au and Pd catalysts supported on zir-
conia were prepared by the colloid deposition method. The
catalytic activities of the catalysts for the hydrochlorination
of 4-phenyl-1-butene were investigated under the irradia-
tion of visible light, taking hydrochloric acid as the sources
of chloride and hydrogen. The catalysts exhibited superior
activities under the irradiation, giving rise to 4-phenylbutyl
chloride and 4-phenyl-2-butenol, but they were almost
inactive without the irradiation. Ethanol was unfavorable to
the reaction. In addition to 4-phenylbutyl chloride, 2,3-
dimethylstyrene was the by-product on the Pt and Au
catalysts, and the isomerization from 4-phenyl-1-butene to
benzene-1-butenyl occurred on the Pd/ZrO2 catalyst in
ethanol solution.
to olefins, only occurs at a useful rate to strained, highly
substituted or part of a styryl system [2–4]. Gaspar and
Carreira [1] have studied a series of hydrochlorination
reactions using the Co catalyst at the room temperature in
the ethanol solution. The sources of hydrogen and chloride
are from PhSiH and para-toluenesulfonyl chloride (TsCl),
3
respectively. Taking hydrochloric acid as the sources of
hydrogen and chloride and promoting the hydrochlorina-
tion process by visible light on supported noble metal
catalysts has seldom been studied.
Zirconia is a semiconductor, and the energy of its band
gap is about 5.0 eV [5], much larger than the energies of
the photons of visible light. Zirconia is widely used as a
photocatalyst in the production of hydrogen from water [6],
the oxidation of 2-propanol to acetone [7], the oxidation of
propene [8], oxidations of methanol and hexane [9] etc.
Supported Pt, Au and Pd nanoparticles have usually been
used in the photocatalytic processes such as the degrada-
tion of pollutants [10, 11], the hydrogen production from
water or methanol [12–15], and the selective oxidations
Keywords Alkenes Á Photocatalysis Á
Hydrochlorination Á Noble metal
1
Introduction
[
16, 17] in recent years due to their good photocatalytic
The addition of hydrogen halide to olefins is one of the
fundamental reactions in organic chemistry [1, 2]. But the
hydrochlorination of olefins, especially the addition of HCl
performance and chemical inertness towards the photo
oxidation [18]. Noble metal nanoparticles supported on a
semiconductor do not form a part of the framework of the
support, but are in a separate phase in the interfacial con-
tact with the support. The electron transfer occurs between
the noble metal nanoparticles and the semiconductor under
irradiation [17, 18], which enhances the redox capabilities
of the active sites on the semiconductor or on the noble
metal nanoparticles and thus improves the photocatalytic
performance. Electrons are supposed to transfer from noble
metal to the conduction band of the semiconductor under
the irradiation of visible light, by which oxidative sites
form on the noble metal nanoparticles and reductive sites
form on the surface of the semiconductor [17, 18]. But they
X. Yang (&) Á G. Gao Á C. Han Á J. Wang Á J. Liu Á H. Lu Á
M. Tong Á X. Liang
School of Chemistry and Chemical Engineering, Inner Mongolia
University, Hohhot, Inner Mongolia 010021, People’s Republic
of China
e-mail: xzyang2007@yahoo.com
H. Zhu
School of Physical and Chemical Sciences, Queensland
University of Technology, Brisbane, QLD 4001, Australia
e-mail: hy.zhu@qut.edu.au
123

8
2
X. Yang et al.
transfer reversely under the irradiation of UV light,
reducing the recombination of the photoexcited electrons
and holes on the surface of the semiconductor [10, 12, 14,
Pt/ZrO2
Pt
Au
Pd
Au/ZrO2
1
9]. The surface plasmon resonance (SPR) often occurs on
Pd/ZrO2
supported noble metal nanoparticles under the irradiation
of light, which is believed to be capable of inducing or
promoting some reactions [16, 18, 20].
In this study, the catalysts of gold, platinum and palla-
dium nanoparticles supported on zirconia were prepared by
the metal colloid deposition method. The photocatalytic
activities of the catalysts for the hydrochlorination of
4
-phenyl-1-butene were investigated under the irradiation
of visible light. The aims are to study the influence of
visible light on the activities of the catalysts and the
product distribution of the reaction.
20
25 30 35 40 45 50 55 60 65 70 75 80
2
Theta, °
Fig. 1 XRD patterns of supported noble metal catalysts
2
Experimental
3
Results
In a general procedure, 2.5 g of zirconia powder was dis-
persed in 100 ml of the HAuCl Á3H O, H PtCl ÁxH O or
Figure 1 shows the XRD patterns of the catalysts. The dif-
fraction intensity of the peaks from the noble metal in each
sample is weak due to its high dispersion and low content
(about 1.5 wt%). The weak diffraction peaks at 2h = 39.7°
4
2
2
6
2
PdCl solution with a specific concentration, followed by
2
adding 20 ml of the 0.53 M lysine solution in the suspen-
sion with vigorous stirring for 30 min. Then, 10 ml of the
0
.35 M sodium borohydride solution was added portion-
and 81.2° in the pattern of the Pt/ZrO catalyst are attributed
2
wise followed by adding 10 ml of the 0.3 M hydrochloric
acid solution, and continuously stirring for 24 h. The cat-
alysts of noble metals supported on zirconia were then
obtained by filtration, washing with deionized water and
ethanol, and finally drying at 60 °C, labeled as Pt/ZrO2,
Au/ZrO and Pd/ZrO . The nominal metal content in each
to the diffractions of metallic Pt in the cubic phase. The
shoulder at 2h = 38.1° and the weak peak at 2h = 81.7° in
the pattern of the Au/ZrO catalyst are attributed to gold in
2
the cubic phase, and the weak peaks at 2h = 39.9° and 81.6°
in the pattern of the Pd/ZrO catalyst are attributed to
2
2
2
metallic Pd in the cubic phase. The diffractions from zirconia
indicate that zirconia is in the monoclinic phase. The average
crystal size of zirconia calculated by Scherrer’s equation is
about 20 nm, using the diffraction peak of the (-111) crystal
faces of zirconia at 2h = 28.2°.
The TEM images of the catalysts are shown in Fig. 2. The
sizes of the Pt, Au, and Pd nanoparticles on the surface of
zirconia are almost similar and distribute in a very narrow
range, with a diameter of about 5–6 nm. The TEM images of
the three catalysts at a higher magnification indicate that no
other noble metal species other than metallic nanoparticles in
the three catalysts. The sizes of zirconia nanoparticles
observed by TEM are about 20–30 nm, which is in consistent
with the calculation from XRD.
catalyst was 1.5 wt%.
X-ray diffraction (XRD) measurements were performed
using a Philips PANalytical X’Pert PRO diffractometer
operating at 40 kV and 40 mA. The morphology of the
catalyst was investigated by a Philips CM200 transmission
electron microscope (TEM) employing an accelerating
voltage of 200 kV. X-ray photoelectron spectroscopy
(
XPS) analysis was performed on a Kratos Analytical Axis
Ultra X-ray photoelectron spectrometer. The diffuse
reflectance UV–visible spectra (UV–Vis) of the samples
were recorded on a Cary 5000 spectrometer.
The hydrochlorination reaction was conducted in a
5
0 ml round bottom flask connected with a reflux con-
denser at the atmospheric pressure at 60 °C. The outlet of
the condenser was connected with a pressure balancing
bag. In a general procedure, 2.5 ml of the pure 4-phenyl-1-
butene and 10 ml of the hydrochloric acid solution
The XPS results are shown in Fig. 3. The peaks of the
binding energy at 83.9 and 87.7 eV in the pattern of Au are
assigned to Au4f7/2 and Au4f5/2 of metallic gold,
respectively; those at 71.2 and 74.4 eV in the pattern of Pt
are assigned to Pt4f7/2 and Pt4f5/2 of metallic platinum,
respectively; those at 335.5 and 341.0 eV in the pattern of
Pd are assigned to Pd3d5/2 and Pd3d3/2 of metallic pal-
ladium, respectively. The peak at 332.5 eV in the pattern of
(
36.5 wt%) together with 100 mg of the catalyst were
added in the flask with stirring, irradiating by incandes-
cence light during the reaction. The products were qualified
by a GC–MS and quantified by a GC-FID.
1
23

Visible Light Promoted Hydrochlorination
83
Fig. 2 TEM images of supported noble metal catalysts
8
7
6
5
4
00
00
00
00
00
1
0000
Pt
1600
Au
9
8
7
6
5
4
000 Pd
1
1
1
400
200
000
000
000
000
000
000
8
6
4
00
00
00
3000
2000
1
000
351 348 345 342 339 336 333 330 327
7
7
76 75 74 73 72 71 70 69
90 89 88 87 86 85 84 83 82 81
Binding Energy, eV
Binding Energy, eV
Bingding Energy, eV
Fig. 3 XPS spectra of supported noble metal catalysts
Pd is attributed to Zr3p3/2 of zirconia, which is overlap-
ping with that of Pd3d5/2 of metallic palladium. The XPS
results indicate that noble metal species on zirconia are in
metallic phases.
250 nm, attributed to the electron transition from defect to
conduction band, and a strong absorption band from 250 to
190 nm, corresponding to the transition of electrons from
valance band to conduction band. Thus the band gap of this
zirconia is 4.96 eV. All the three catalysts exhibit strong
absorption bands from visible to UV regions, which can be
Figure 4 shows the UV–Vis spectra of the catalysts.
Zirconia exhibits a weak absorption band from 400 to
123

8
4
X. Yang et al.
1
1
1
0
0
0
0
0
.4
.2
.0
.8
.6
.4
.2
.0
100
80
100
80
60
40
20
Pt/ZrO2
Au/ZrO2
4
-phenylbutyl chloride
Pd/ZrO2
Zirconia
6
4
2
0
0
0
0
4
-phenyl-1-butene
Square --Pd
Circle --Au
Triangle --Pt
4-phenyl-2-butenol
0
0
1
2
3
4
5
2
00
300
400
500
600
700
800
Time, h
Wavelength, nm
Fig. 5 Conversions and selectivities of Pt, Au and Pd catalysts
Fig. 4 UV–Vis spectra of supported noble metal catalysts
2
Table 1 Results of addition on noble metal supported catalysts (3 h, 60 °C, light strength, 1 w/cm )
Catalyst
Irradiation
No irradiation
Irradiation in ethanol
Conversion (%) Selectivity (%)
Conversion (%)
Selectivity (%)
Conversion (%)
Selectivity (%)
A
B
A
B
A
B
Blank
1.2
1.5
100
100
82.3
85.3
96.1
–
–
–
–
–
–
–
Zirconia
–
–
–
–
–
–
–
b
b
Pt/ZrO
Au/ZrO
Pd/ZrO
2
60.5
57.2
52.3
17.7
14.7
3.9
2.0
4.5
3.1
93.8
92.6
93.7
6.2
7.4
6.3
5.0
1.2
15.8
78.8
55.0
11.2
45.0
0
2
a
2
100
A 4-phenylbutyl chloride, B 4-phenyl-2-butenol
a
Benzene, -1-butenyl
b
Benzene-4-ethenyl-1,2-dimethyl-
attributed to the interband and intraband transition of
electrons in noble metal nanoparticles. The broad band
visible light. The selectivity of 4-phenylbutyl chloride
decreased from about 93 to 82.3 % and 85.3 % for Pt/ZrO2
peaking at 520 nm in the pattern of the Au/ZrO catalyst is
2
and Au/ZrO , respectively, but increased from 93.7 to
2
attributed to the SPR absorption of gold nanoparticles.
The addition results of 4-phenyl-1-butene in different
conditions are listed in Table 1. The addition of 4-phenyl-
96.1 % for Pd/ZrO , compared with the results of the
2
thermal reaction.
The reaction was also investigated in an ethanol solution
(Table 1). The reaction rates were dramatically retarded on
all catalysts when ethanol was added in the reactor. The
conversions of 4-phenyl-1-butene on Pt/ZrO , Au/ZrO and
1
-butene occurred at a very slow rate, with a conversion of
about 1.2 % in 3 h, only by irradiation at 60 °C (blank
reaction). Zirconia was not active to this reaction under
irradiation at 60 °C because the conversion on it was only
2
2
Pd/ZrO decreased to 5.0, 1.2 and 15.8 %, respectively. The
2
1
.5 % which was comparative to that of the blank reaction.
main products are 4-phenylbutyl chloride and 2,3-dimeth-
The product of the blank reaction and that on zirconia was
solely 4-phenylbutyl chloride. The conversion on the noble
metal supported catalysts increased slightly, from 2 to
ylstyrene (benzene, 4-ethenyl-1,2-dimethyl-) onPt/ZrO and
2
Au/ZrO . However, the isomerization from 4-phenyl-1-
2
butene to benzene, -1-butenyl- occurred on Pd/ZrO in the
2
4
6
.5 % in 3 h, when the reaction was proceeded in dark at
ethanol solution, instead of the addition reaction. Benzene, -
1-butenyl- was the only product of the isomerization reac-
tion. The conversions of 4-phenyl-1-butene on the recovered
catalysts decreased by about 20 %.
0 °C, indicating these supported noble metal catalysts
were not active in the thermal condition. The products in
this condition were mainly 4-phenylbutyl chloride and a
small amount of 4-phenyl-2-butenol. The conversion of
The results of time-on-stream of the three catalysts are
shown in Fig. 5. The conversions of 4-phenyl-1-butene
increased with time on the three catalysts. The Pt/ZrO2
4
5
-phenyl-1-butene in 3 h dramatically increased to
2.3–60.5 % for the three catalysts under the irradiation of
1
23

Visible Light Promoted Hydrochlorination
85
hν
a
Cl
Cl
C
H
H
H
H
photoexcited electron
noble metal nanoparticle
OH
HO
H
H
C
H
H
hν
H
H
b
H
C
H
H
C
H
C
H
ethanol molecule
C
H
C H
H
H
C
C
C
C
CH
C H
H
C H
H
H
H
H
H
H
H
hν
hν
hν
intramolecular
hydrogen transfer
hν
H atom absorbed on Pd
bonding with terminal carbon
charge transfer
hydrogen bond breaking
Fig. 6 Mechanisms of addition and isomerization on supported noble metal catalysts under irradiation of visible light
catalyst exhibited the best conversion but the poorest
selectivity of 4-phenylbutyl chloride in 5 h. The Pd/ZrO2
catalyst has the best selectivity of 4-phenylbutyl chloride
during the reaction. The selectivity of 4-phenylbutyl
positively charged carbon to form the final products
4-phenylbutyl chloride or 4-phenyl-2-butenol. The addition
mechanisms under irradiation of visible light on noble
metal supported catalysts are shown in Fig. 6a.
chloride on the Au/ZrO catalyst was lower than that on the
2
Ethanol molecules surrounding the noble metal nano-
particles blocks most of the protons from reaching and
being absorbed by the noble metal nanoparticles, making
the reaction rate decrease dramatically. On the hand, some
of the transition molecules containing positively charged
carbon absorbed on noble metal nanoparticles cannot
capture chloride ions or hydroxyls timely due to the
blocking of ethanol molecules, as a result, they break into
fragments under the attack of radicals in the solution or
Pd/ZrO catalyst in 3 h but they are comparable in 5 h.
2
4
Discussion
The results above indicate that visible light promotes the
addition reactions of an olefin on supported noble metal
catalysts. The activities of the catalysts exhibit strong
relations with the absorption of visible light by the noble
metal nanoparticles on zirconia. The strong absorption
bands from the visible region to the UV region by the Pt,
Au and Pd nanoparticles indicate that electrons in the noble
metal nanoparticles are excited by visible light and the
interband and intraband transitions occur. The SPR can
also occur on Au nanoparticles under irradiation in addition
to the interband and intraband transitions. The electron
transitions and the SPR result in active electrons on the
surface of the noble metal nanoparticles. The active elec-
trons on the surface of noble metals attract protons in the
solution. The hydrogen atom absorbed on the surface of
noble metal is readily to be added to the terminal carbon of
the C=C group in the molecule of 4-phenyl-1-butene
according to the Markovnikov rule [21]. A chloride anion
or hydroxyl in the solution can be attracted by the
light. 2,3-dimethylstyrene is formed on Pt/ZrO and Au/
2
ZrO in this condition. The photoexcited electrons on the
2
surface of Pd nanoparticles might be less active than those
on the surface of the Au or Pt nanoparticles, which cannot
generate radicals to attack the transition molecules and thus
the isomerization from 4-phenyl-1-butene to benzene, -1-
butenyl- occurs due to the intramolecular hydrogen transfer
[21]. The mechanism proposed is shown in Fig. 6b.
5 Conclusion
The catalysts of noble metal nanoparticles supported on
zirconia exhibit superior activities for the hydrochlorina-
tion of 4-phenyl-1-butene using hydrochloric acid as the
sources of chloride and hydrogen, which is regarded as a
123

8
6
X. Yang et al.
reaction that is difficult to occur under usual thermal con-
ditions, under the irradiation of visible light. The main
products are 4-phenylbutyl chloride and 4-phenyl-2-bute-
nol. The supported noble metal catalysts are almost inac-
tive for the hydrochlorination reaction at 60 °C without
irradiation. The activity of the catalyst is associated with
the photoexcited electrons on the surfaces of the noble
metal nanoparticles. Ethanol in the reaction system is
unfavorable to the reaction because the ethanol molecules
surrounding the noble metal nanoparticles block the
hydrogen ions from reaching to their surfaces. In addition
to 4-phenylbutyl chloride, another product is 2,3-dimeth-
ylstyrene on Pt/ZrO and Au/ZrO , and the isomerization
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Acknowledgments The work was financially supported by the key
project of Inner Mongolia Education Department (NJZZ13002), the
project of Grassland Talent of Inner Mongolia and the project of the
western light from the ODPC of Inner Mongolia, and the Endeavour
Australia Cheung Kong Research Fellowships.
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