Photocatalytic reduction of CO2 coupled with selective alcohol oxidation under ambient conditions

Article abstract of DOI:10.1039/c5cy00772k

A new method for the reduction of CO₂ to CH₃OH coupled with selective alcohol oxidation using a photocatalytic method has been developed in the present paper. CO₂ as the oxidant was reduced to methanol by photo-induced electrons, and aromatic alcohols were used as the reductants to react with photo-generated holes and were converted to aromatic aldehydes with high selectivity. The maximum conversion of aromatic alcohol to aldehyde was 91.7% with a selectivity of 98%, and the highest yield of methanol was 358.7 μmol g^-1. This study could provide a valuable method not only for carbon dioxide conversion into fuel which could remission energy shortages, but also for the selective oxidation of alcohols to produce aldehydes.

Full text of DOI:10.1039/c5cy00772k

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Photocatalytic Reduction of CO Coupling with Alcohol Selective
2
Oxidation under Ambient Conditions
Received 00th January 20xx,
Accepted 00th January 20xx
a,b
a,b
a
a
a
Liujie Wang , Xiaoliang Zhang *, Longhua Yang , Chao Wang , and Hongming Wang *
DOI: 10.1039/x0xx00000x
A new method for the reduction of CO
2
3
to CH OH coupling with alcohol selective oxidation by photocatalytic method has
been developed in the present paper. CO
2
as oxidant was reduced to methanol by photo-induced electrons. And aromatic
www.rsc.org/
alcohol was used as reductant to react with photo-generated holes, converting to aromatic aldehyde with high selectivity.
The maximum conversion of aromatic alcohol to aldehyde is 91.7 % with selectivity of 98 %, and the highest yield of
-1
methanol is 358.7 μmol g . This study would provide a valuable method not only for carbon dioxide conversion into fuel
which could remission energy shortage, but also for selective oxidation of alcohol to produce aldehyde.
In fact, the majority of these studies in the literatures are
1
. Introduction
carried out in liquid H O as the reaction medium in
2
6
-11
photocatalyzing reduction of CO
2
. It could be interesting to
The photocatalytic conversion of solar energy into
check other solvents that are more difficult to reduce than H
2
O
nonpolluting and usable chemical energy keep a great
interesting always. Since Fujishima and Honda et al. found the
production of hydrogen and oxygen by photocatalyzing water
1
2
.
In addition, alcohols also allow the presence of Brönsted
acids, which could favour the thermodynamics of the
reduction. It is possible that photocatalytic reduction of CO
1
2
slipping in 1972 , photocatalysis in various systems have been
coupled with alcohols selective oxidation in organic solvent
would be more efficient than that in the water. Actually, only
investigated. Especially, Tooru et al had demonstrated
photocatalytic synthesis formic acid, formaldehyde, methyl
1
3
a few groups studied this kind of photocatalytic reaction in
organic media.
alcohol and methane from carbon dioxide over photosensitive
2
semiconductor powders catalysts in water medium
.
The selective oxidation of alcohols to corresponding
Subsequently, many research efforts have been done to
aldehydes, in particular benzyl alcohol to benzaldehyde
14,15
address photocatalytic reduction of CO . The photocatalytic
2
conversion
, is one of the most popular organic
reduction of CO into organic small molecules also have been
2
3
-5
transformations and is of fundamental importance for
laboratory and commercial processes. Since aromatic
aldehydes are widely used in the fragrances, flavorings,
become a great intention in recent years
.
Being a cheap, stable, nontoxic, and environmentally
friendly material, titania (TiO ) is an idea semiconductor
2
pharmaceutical industries
，plastic additives, and is also highly
photocatalyst. As a versatile material, TiO2 is extensively
applied in various photocatalytic reactions. In the particular
valuable for the perfume industry. Heterogeneous
photocatalysis have also been used for performing alcohols
selective oxidation. A number of studies have been reported
case of CO photoreduction, one of the efficient photocatalysts
2
6
is metal-doped titania . Copper doping is the most efficient
-9
on the selective catalyst oxidation of alcohol into aldehyde
16-19
way to enhance selectivity towards CH OH production and
3
under O
2
using a series of photocatalysts
. Moreover, the
formation of formic acid derivatives in the photoreduction of
1
0
facile preparation method using inexpensive transition metals
with a more selective and environmentally friendly system for
the catalytic oxidation of aromatic alcohols to the
corresponding aldehydes is certainly more in demand.
CO
the sol-gel method has been reported recently for CO
reduction to CH and CH OH as main products in the
photocatalytic reduction of CO
2
2
. Silver doped crystalline titania (Ag-TiO ) prepared by
2
4
3
1
1
2
in water solution.
Photocatalytic reduction of CO
2
into organic small
molecules coupling with alcohols selective oxidation to
aldehydes in organic solvent have a certain practical value and
application prospect, and is challenging. This reaction, not only
is able to convert carbon dioxide into fuel, but also is able to
convert alcohol to aldehyde with high selectivity. However, to
the best of our knowledge, there is no report on photocatalytic
xlzhang@jxnu.edu.cn
2
reduction of CO into organic small molecules coupling with
alcohols selective oxidation to aldehydes. In this paper, a
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series of inexpensive and facile preparation photocatalysts, transmission electron microscopy (TEM) was performed with a
Ag/TiO nanocomposites were fabricated from conventional JEM 2100F transmission electron microscope equipped with
2
sol-gel together with photo assisted methods. These kinds of EDX operated voltage at 200 kV. The TEM samples were
catalysts have been used to explore the photocatalytic activity prepared by sonication the powders in absolute alcohol for 15
2
of CO reduction coupling with aromatic alcohol oxidation in minutes and subsequently dispersion on carbon coated copper
organic solvent.
grids drying at room temperature. UV-Vis diffuse reflectance
spectra (UV-Vis DSR) were recorded using a SHIMADU UV-
2
550 UV-vis spectrophotometer with an integrating sphere
attachment for their diffuse reflectance in the range of 300-
00nm and using BaSO powder as reference. The
2
. Experimental
8
4
2.1 The preparation of titanium dioxide nanoparticle.
photoluminescence (PL) spectrum was recorded using a
Perkin-Elmer LS55 fluorescence spectrometer at room
temperature. The nanocomposites were dispersed in carbon
tetrachloride and excited using D light at wave length of 265
nm.
TiO nanoparticle was prepared by modified sol-gel method.
2
In a typical synthesis procedure, a volume of 20 ml of
tetrabutyl titanate was dissolved in 80 ml of anhydrous diethyl
ether at room temperature, and then 24 ml of acetic acid was
added. After stirring this solution for 30 min, 30 ml mixture
solution of double deionized water and acetic acid with the
ratio of 2:1 (by volume) was added dropwise to the precursor
solution under vigorously stirring. And that, a great plenty of
white precipitate were formed in the solution. Subsequently
the mixture was stirring keeping for 2 hours. The suspension
was aged under airtight condition at room temperature for 24
hours. After suction filtration, the xerogel was washed several
times by deionized water to remove the residual acid, and
2
.4 Photocatalytic reduction of CO
2
coupling with aromatic alcohol
selective oxidation activity test.
2
The reactions of photocatalytic CO reduction coupling with
aromatic alcohol oxidation were carried out in a 70 ml
homemade double-jacket quartz glass reactor. 0.5g catalyst
was added to the photo-reactor, 30 ml anhydrous acetonitrile
(purified by calcium hydroxide and distilled before using) and
1mmol aromatic alcohol (purified by distilled before using) was
subsequently put into the reactor. After that, the reaction cell
was evacuated to base pressure of 10 kPa for 15 minutes to
then dried at the 100
samples were divided into several sections and calcined at
00-800 for 2 hours in a muffle furnace at 5 /minute
℃ temperature for one day. Finally, the
2
remove resolution oxygen, afterward high-purity CO was filled
4
℃
℃
into the reactor 30 minutes at a flow rate of 15 ml per minute.
To ensure remove trace amounts of oxygen fully,
such operation was repeated three times. In order to remove a
heating rate from room to setting temperature. Then, the
sample was grounded to power in an agate mortar.
2
.2 Synthesis of Ag/TiO
Ag/TiO nanoparticles were produced by photodeposition
method. By using above synthetic TiO nanoparticles as
support of catalyst, 1g TiO was dispersed in oxalic acid
aqueous solution and sonicated for 15 min, then
predetermined amount of AgNO was added to the solution
2
composites
2 2
trance amount of H O and oxygen in gas, the CO gas was
2
purified through allochroic silica gel, asbestos and activated
carbon before importing into the reactor, respectively. And
then, a balloon was connected to the reactor keeping the
reaction under 0.1Mpa pressure. Before irradiation the
suspension was kept at 500 rpm stirring for 60 minutes to
2
2
a
3
and stirring for 2 hours to form homogeneous solution. Then
these solution was irradiated on ultraviolet lam (PHILIPS TUV
2
ensure the CO adsorption and desorption equilibrium. The
ultraviolet (UV) light (high pressure mercury lamp main
wavelength is 365 nm) was irradiation from the box wall
before the reactor 10 cm. The liquid products were analyzed
by Gas Chromatograph (GC) with flame ionization detector
25 W G2578 bactericidal lamp) for 4 hours under stirring 500
rpm at room temperature. When its colour was changed from
white to reddish brown, the suspension was centrifuged at
1
0000 rpm and washed several times with deionized water.
The xerogel was transferred to electronic vacuum oven and
dried overnight at 60
.3 Catalysts characterization.
XRD measurements were performed on
(
FID). In order to analyse qualitatively the gas products, The
gas chromatography-mass spectrometer (GC-MS) (7890A-
975C Agilent Corporation equipped with a HP-5 capillary
℃.
5
2
column (Hewllett-Packard, USA, 30 m×0.25 mm × 0.25 mm)),
D8 also used to identify the component of product. And the liquid
a
diffractometer from Bruker instruments (Cu Kα radiation, products were also charactered by a Bruker vance 400MHz
=0.15406 nm) operated at 40kV and 25mA. The diffractgrams spectrometer (NMR).
were collected at 2θ range from 20 to 80° in steps of 0.02°/min
λ
with count time 20s at each point. The crystalline phase can be
determined from integration intensities of anatase and rutile 3. Results and Discussion
corresponding to (101), (110) and (120), respectively. The
The experimental details and characterization of the
average crystalline sizes were determined according to the
Debye-Scherrer equation using the full width half maximum
catalysts were showed in experimental section and supporting
information. Figure 1 and S1 present the nanoparticles
data of each phase. The nanoparticles average crystalline sizes
o
were determined according to 2θ= 25.3 (101) face.
microscopes of TiO
2 2
and Ag/TiO nanocomposites. From these
of TiO
2
representative morphologies, it can be clearly seen that TiO
2
SEM morphology of the samples was carried out using a
scanning electron microscope (Quanta 200F FEI). The
crystallite is very well and its surface is smooth. Moreover, the
2
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Cat Pa ll ey as si es dS oc ni eo nt ca ed j &u s Tt me ca hr gn i on sl ogy
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SEM and TEM image in figure 1 shows silver nanoparticles atmosphere, the highest conversion of benzyl alcohol is only
anchored on the surface of TiO nanoparticles, silver 1.7 % and 1.9 %, and there is no methanol or other products to
nanoparticles are homogeneous dispersion on the surface of be observed, catalyzed by TiO and ca.3wt % Ag/TiO catalysts,
TiO , formation a series of Ag/TiO nanocomposites. respectively. The blind test without catalyst (please see Table 1
Entry 19) shows that the conversion of benzyl alcohol is very
low (0.75 %) and there is no methanol to be observed. These
results verified that CO is able to be reduced to methanol
coupling with the selective oxidation of benzyl alcohol to
benzaldehyde and that the methanol is only produced from
CO , catalyzed by both TiO and Ag/TiO
The effects of silver loading content on TiO
activity were evaluated as well. Compared to pure TiO
2
2
2
2
2
，
2
,
2
2
2
.
2
to the catalytic
, the
2
photocatalytic activity of ca.2-6wt % Ag/TiO nanocomposites
2
exhibited a significantly increase (Table 1). Meanwhile,
conversion of benzyl alcohol and the yield of the methanol
both are drastically increased catalyzed by ca.2-6wt % Ag/TiO2.
It was found that the ca.3wt % Ag/TiO2 was optimum to
achieve the highest conversion of benzyl alcohol (24.6 %) and
-1
maximum yield of methanol (40.9 μmol g ) after reacting 18
hours. When the silver loading content is less than 3wt %, the
photocatalytic efficiency of catalyst is increased with silver
loading content. It could be explained that the Ag
nanoparticles deposited on the surface of TiO can act as
2
2
3
photo-induced carrier separation centers
. Moreover,
Figure.1. (a) SEM and (b) TEM image of ca.3wt% Ag/TiO2 nanoparticles. (c and d) HR-
TEM image of ca.3wt% Ag/TiO2 nanoparticles.
Schottky barrier was formatted between the silver and TiO2
contact region, which improved the charges separation and
2
4
enhanced the photocatalytic activity of TiO2
.
To obtain more information of the catalysts, HR-TEM was
used to observe these nanoparticles. Typical TEM micrographs
of TiO and Ag/TiO nanoparticles catalysts are shown in Figure
2
2
1. From figure 1b, the relatively dark points are ascribed to Ag
nanoparticles. The silver nanoparticles morphology is irregular
spherical particles and have narrow size distribution, while the
transparent region are assigned to TiO2 in Figure 1b.
Meanwhile, it was evident that average particle size of
nanoparticles was 40-50nm, which was in good agreement
with the XRD results calculated from Debye-Scherrer equation
(figure S2). The HR-TEM was used to investigate the interfacial
1
Figure.2. The H NMR spectrums of (a) the stand CH
3
OH and (b) the product (MeOH)
structures between Ag and TiO (Figure 1c and 1d). In Figure 1c
2
catalyzed by ca.3wt% Ag/TiO
2
under 0.1 Mpa of CO
2
after irradiation for 48 hours.
and 1d, the lattice fringes of Ag and TiO showed surface-
2
junction. The (111) lattice fringes of Ag nanoparticles was
However, when silver loading exceeds 3wt%, the
0- photocatalytic activity rapidly decreases. The conversion of
0
.236 nm, and the (101) lattice fringes of anatase was 0.356
2
nm. These results are agreement with the previous reports
2
2
benzyl alcohol and yield of methanol are decreased from
.
-1
2
4.6% to 14.9 % and from 40.9 to 14.9 μmol g with the
The photocatalytic reduction of CO
alcohol selective oxidation was carried out under ultraviolet
light irradiation at 0.1 Mpa CO pressure. The main liquid
2
coupling with benzyl
increasing of silver loading content from 3 % to 9 %,
respectively. It is maybe that exceeds silver nanoparticles
2
2
cover the surface of TiO activity sites that can absorb UV
products were determined by GC (FID detector) (Figure S3).
This result was also proved by 1H NMR spectrum (Figure 2).
photon. Therefore, absorption photon capacity of the catalyst
is reduced. And also, the exceeding silver nanoparticles can
also act as recombination centers of electron and hole, which
also results in the decreasing of the photocatalytic activity of
2 2
When the reaction was carried out in CO , the CO was
reduced to methanol, and benzaldehyde was the mainly
product of the benzyl alcohol photocatalytic selective
oxidation, along with a trace of benzoic acid and benzyl ether
Ag/TiO
probability for the hole capture increases by the large number
of negating charged silver particles on the surface of TiO at
the high silver loading, which also increases the photo-induced
2
nanocomposites. In fact, it has been reported that the
(Table 1). The highest conversion of benzyl alcohol is 10.3 %
2
and 10.7 %, the maximum yield of methanol is 21.8 and 20.5
-
1
μmol g catalyzed by TiO
2 2
and ca.1wt % Ag/TiO after reacting
2
5
electrons and holes recombination . These results are good
18 hours, respectively. However, as reacting in Ar gas
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agreement with the photoluminescence (PL) spectra intensity higher. However, when the Ag loading content exceeds ca.4wt
of the photocatalysts showed in Figure S4. Form figure S4, the %, the PL intensities is increasing. It is indicated that excess
2
PL intensities are decreased with increase of the Ag loading silver deposited on the surface of TiO can act as electron sinks
content when Ag loading content is less than 3wt %. The PL to capture the photo-induced electrons and holes pairs.
intensity signal is weaker, that photocatalytic efficiency is
Table 1. Production yields of the photocatalytic reduction of CO2 coupling with benzyl alcohol selective oxidation under UV light irradiation on TiO2 and Ag/TiO2
catalystsa.
b
Entry
Catalyst
RT
Gas
CH
3
OH
Benzyl alcohol
-
1
μmol g
Con.[ %]
Sel.[%]
1
2
3
4
5
6
7
8
9
TiO
TiO
2
2
18
18
18
18
18
18
18
18
18
18
18
18
18
24
34
48
18
18
18
18
CO
Ar
2
21.8
͞
10.3
1.7
99
99
99
99
99
99
99
99
99
99
99
99
99
98
98
98
99
99
99
͞
P25
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
Ar
2
2
2
2
2
2
2
2
2
2
2
2
2
2
20.7
20.5
24.4
40.9
30.7
23.3
23.8
20.4
23.0
24.7
24.4
11.1
10.7
15.4
24.7
21.3
14.4
14.8
12.6
14.6
14.9
16.5
46.2
57.5
70.6
1.9
1%Ag/ TiO
2%Ag/ TiO
3%Ag/ TiO
4%Ag/ TiO
5%Ag/ TiO
6%Ag/ TiO
7%Ag/ TiO
8%Ag/ TiO
9%Ag/ TiO
2
2
2
2
2
2
2
2
2
10
11
12
13
14
15
16
17
10%Ag/TiO
2
3%Ag/ TiO
3%Ag/ TiO
3%Ag/ TiO
3%Ag/ TiO
3%Ag/ TiO
͞
2
104.8
2
314.3
2
2
2
358.7
͞
c
18
CO
CO
CO
2
2
2
43.9
0.25
0.75
͞
19
͞
͞
d
20
3%Ag/ TiO
2
a
b
c
d
Reaction condition: 40 ml CH
alcohol.
3
CN, 1mmol benzyl alcohol; Reaction time; Reaction condition: 40 ml benzyl alcohol; Reaction condition: 40 ml CH
3
CN, without benzyl
-1
Furthermore, the photocatalytic reduction of CO2 to CH OH is low as well (13.6 and 79.5 μmol g ) under same
3
methanol coupled with various alcohols selectively oxidation reaction condition.
have been performed over 3wt% Ag/TiO2 under the same
In order to know the stoichiometry of this reaction, the
reaction conditions. The results are shown in Table 2. It is ratio of formation methanol and aldehyde have been
indicated that all catalyzing systems investigated were capable calculated (the last column in table 2). The result shows that
to convert CO to methanol and convert the aromatic alcohols the ratio will be increased with prolongation of the reaction
2
to corresponding aldehydes with different yield. The groups on time. It can be explained that there are some intermediates to
the aromatic ring are effect on the reaction performing. The form (such as HCOOH, HCHO) in the initial phase. And at 48
electron donating groups on the aromatic ring favors the hours, the highest ratio is 1:4 that is till smaller than the
methanol production and alcohols oxidation. For example, the reaction stoichiometry (1:3). The first reason is that there are
methoxybenzyl alcohol can convert to p-anisaldehyde with side-products, such as, H2, CH4, HCOOH, HCHO et al, was
conversions of 50.3% and 91.7%, and the yield of CH OH is formed. For the second reason, with processing the reaction,
3
-
1
4
0.9 and 309.6 μmol g after reacting 18 and 48 hours, the methanol also reacts with photo-generated holes to
respectively. However, the drawing groups on the aromatic produce H and CO . With the increasing of the concentration
2
2
ring hold
a low conversion. The conversion of p- of methanol, this reaction is more and more fast. When the
nitrobenzaldehyde to nitrobenzyl alcohol is only 8.4% and 19.8% formation rate of methanol was most equated to the its’
after reacting 18 and 48 hours, respectively. And the yield of decomposition rate, production of methanol levels off.
4
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Table 2.Photocatalytic reduction of CO
2
to methanol coupling with alcohols oxidation with 3wt% Ag/TiO
2
catalyst
b
c
d
e
f
Entry
1
Substrate
OH
Product
RT
Yield
Con.[%]
Sel.[%]
ME/Aldehyde
CHO
18
40.9
24.7
99
1/12
4
8
358.7
50.4
70.56
32.7
98
99
1/4
CHO
2
18
48
1/13
OH
Me
Me
219.4
73.3
74.6
50.3
98
99
1/6
CHO
3
OH
18
1/13
MeO
MeO
4
8
309.6
13.6
91.7
8.4
98
99
99
99
98
1/6
1/12
1/5
CHO
4
5
18
48
18
OH
OH
2
O N
O N
79.5
19.8
61.6
88.4
2
CHO
121.6
325.4
1/10
1/5
4
8
6
7
18
48
26.3
63.4
15.7
27.3
99
98
1/12
1/8
OH
CHO
CHO
O
O
OH
18
14.7
54.3
8.9
20.4
99
99
1/12
1/7
4
8
a
b
Reaction conditions: alcohols (1mmol), 3wt%Ag/TiO
2
,
stirred in 40 ml CH
3
CN, under 0.1 MPa CO
2
and ultraviolet light (main wavelength of 365 nm) irradiation; RT:
c
-1
d
e
f
reaction time; unit: [μmol g ]; conversion, of alcohol, selectivity of benzaldehyd; the ratio of formation methanol and aldehyde.
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8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
4
3
0
5
a
35
35
30
25
20
15
10
3
0
9
0
0
30
1
st
25
2 nd
3 rd
2
5
2
1
0
5
20
1
1
5
0
6
10
0
10
20
30
40
50
9
121518212427309 121518212427309 12151821242730
Irradiation time (h)
Irradiation time (h)
2
Figure. 4. Photocatalytic reduction of CO to methanol coupling with alcohols oxidation
400
with 3wt% Ag/TiO catalyst in three cycles run.
2
3
3
2
2
1
1
50
00
50
00
50
00
In order to test the stability of Ag/TiO2 nanoparticles
catalyst, the used catalysts were recovered by centrifuged and
thoroughly washed with anhydrous acetonitrile. The
photocatalyst was recycled up to three times. As shown in
Figure 4, its photocatalytic activity was only slightly
deteriorated after three consecutive photocatalytic
experiments. It can account for less silver nanoparticles leach
and aggregation after the test, leading to the photocatalytic
efficiency decrease weakly after three run times. The result
showed that the photocatalyst was stable under repeated
application with a constant conversion of benzyl alcohol to
benzaldehyde.
5
0
0
0
10
20
30
40
50
Irradiation time ( h )
Figure3. (a) The effect of irradiation time on conversion of benzyl alcohol and
-
1
selectivity of benzaldehyde. (b) The yields of methanol production(unit: μmol g ) as
function of irradiation time. (Reaction condition: 30 ml CH CN, 1mmol benzyl alcohol
0mg catalyst.).
To understand the reaction mechanism of CO
coupling with alcohols oxidation, the proposed mechanism for
photocatalytic reduction of CO to methanol coupling with
The effect of irradiation time on photocatalytic reduction alcohols oxidation is as follows:
catalyst* + econd + p+
of CO and benzyl alcohol conversion was investigated over a Catalyst + hv
period of 1-48 hours on ca.3wt % Ag/TiO nanocoposites PhCH OH(aq) + 2p+
2
to methanol
3
5
2
2
val
(1)
2
2
val
PhCHO + 2H+cond (2)
catalysts (figure 3). With the increase of irradiation time, the
conversion is clearly increased. However, the selectivity is
slightly decrease due to by-products emerged in reaction
system. The methanol yield is increased with the extension of
irradiation time (Figure 3b). When the photoirradiation time is
less than 18 hours, the increasing of yield is lowly. But when
photoirradiation time is larger than 18 hours, the yield is
obviously improving. After the photoirradiation time reaches
CO2 + 2H+cond + 2eꢀcond
HCOOH (3)
HCOOH + 2H+
+ 2eꢀ
HCHO + H O (4)
cond
cond
2
HCHO + 2H+
+ 2eꢀ
cond
cond
CH OH (5)
3
Photogenerated holes in the VB of semiconductor oxidize
+
alcohol to aldehyde and release H (equation (2)), and
photogenerated electrons in CB reduce carbon dioxide by
sequence of reaction to produce HCOOH, HCHO and CH3OH
-1
(equation (3), (2) and (5)).
to 45 hours, the yield of methanol is 344.6 μmol g (figure 3b),
and the conversion of benzyl alcohol is 70.6% with 98%
selectivity of benzaldehyde.
4
. Conclusions
2
The photocatalytic reduction of CO coupling with
alcohols selective oxidation was catalyzed by Ag/TiO2
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ARTICLE
nanocomposites under UV light irradiation at room 10 (a) M. Murdoch1, G. I. N. Waterhouse, M. A. Nadeem, J. B.
temperature and ambient pressure. CO
2
as oxidant was
Metson, M. A. Keane, R. F. Howe, J. Liorca, H. Idriss, Nature
chemistry, 2011, 3, 489-492. (b) Y. Li, W.-N. Wang, Z. Zhan,
M.-H. Woo, C.-Y. Wu, P. Biswas, Appl. Catal. B: Environ, 2010,
100, 386.
reduced to methanol by photo-induced electrons acted. And
aromatic alcohol was used as reductant to react with photo-
generated holes, converting to aromatic aldehyde with high
selectivity. The optimal catalyst was ca.3wt % Ag/TiO
2
1
1 (a) L. Li, J. Yan, T. Wang, Z.-J. Zhao, J. Zhang, J. Gong, N.
Guan, Nat. Commun.2015, 6, 5881. (b) S. Krejčíková, L.
Matějová, K. Kočí, L. Obalová, Z. Matěj, L. Čapek, O. Šolcová,
Appl. Catal. B: Environ, 2012, 111–112, 119.
nanoparticles. The maximum conversion of aromatic alcohol to
aldehyde is 91.7 % with selectivity of 98 %, and the highest
-1
yield of methanol is 358.7 μmol g under irradiation for 48
hours. Our findings may help to design more active
photocatalysis system for the reduction of carbon dioxide and
to open an environment-friendly strategy for the alcohol
selective oxidation based on photocatalysis.
1
1
1
1
1
1
2 Dhakshinamoorthy, S. Navalon, A. Corma, H. Garcia, Energy
Environ. Sci. 2012, 5, 9217–9233.
3 V. Puga , A. Forneli , H. García , A. Corma, Adv. Funct. Mater.
2
014, 24, 241-248.
4 T. Yokoyama, T. Setoyama, N. Fujita, M. Nakajima, T. Maki, K.
Fujii, Appl. Catal. A: General, 1992, 88, 149.
Acknowledgements
5 S. Higashimoto, N. Kitao, N. Yoshida, T. Sakura, M. Azuma, H.
Ohue, Y. Sakata, Journal of Catalysis, 2009,266, 279-285.
6 X. Lang, W. Ma, C. Chen, H. Ji, J. Zhao, Acc. Chem Res. 2014,
The support of the National Natural Science Foundation of
China (21363014, 21106059 and 21103082) is gratefully
acknowledged. This work was also supported by Natural
Science Foundation of Jiangxi Province of China (Grant No.
4
7, 355–363.
7 (a) S. Liang, L. Wen, S. Lin, J. Bi, P. Feng, X. Fu, L. Wu, Angew.
Chem. Int. Ed. 2014, 53, 2951-2955. (b) W. Chang, C. Sun, X.
Pang, H. Sheng, Y. Li, H. Ji, W. Song, C. Chen, W.Ma, J. Zhao,
Angew. Chem. Int. Ed. 2015, 54, 2052 –2056.
20142BCB23003 and 20143ACB21021)
Notes and references
1
1
2
2
2
2
2
2
8 A.Tanaka, K. Hashimoto, H. Kominami, J. Am. Chem. Soc.
1
2
A. Fujishima, K. Honda, Nature, 1972, 238, 37-38.
2
012, 134, 14526−14533.
T. Inoue, A. Fujishima, S. Konishi, K. Honda, Nature, 1979,
9 S. Higashimoto, N. Suetsugu, M. Azuma, H. Ohue, Y. Sakata, J.
Catal. 2010, 274, 76-83.
2
77, 637-638.
3
(a) S. N. Habisreutinger, L. Schmidt-Mende, J. K. Stolarczyk,
Angew. Chem. Int. Ed. 2013, 52, 7372-7408. (b) X. Chen, J.
Wang, C. Huang, S. Zhang, H. Zhang, Z. Li, Z. Zou, Catal. Sci.
Technol. 2015, 5, 1758–1763.
0 D. Wang, Y. Duan, Q. Luo, X. Li, J. An, L. Bao L. Shi. J.
Materi. Chem, 2012. 22. 4847-4854.
1 Z. Chen, L. Fang, W. Dong, F. Zheng, M. Shen, J. Wang. J.
Materi. Chem, A, 2014. 2. 824-832.
4
5
S. Sato, T. Arai, T. Morikawa, K. Uemura, T.M. Suzuki, H.
Tanaka, T. Kajino, J. Am. Chem. Soc. 2011,133,15240-15243.
(a) J. Tripathy, K. Lee, P. Schmuki, Angew. Chem. Int. Ed.
2 Y. Li, H. Zhang , Z. Guo, J. Han, X. Zhao, Q. Zhao, S. Kim.
Langmuir, 2008, 24, 8351-8357.
3 J. M, Herrmann, J. Disdier, P. Pichat, J. Phys. Chem., 1986,
2
014, 53, 12605-12608. (b) J. Mao, T. Peng, X. Zhang, K. Li, L.
9
0, 6028-6034.
4 Y. Ji, B. Wang, Y. Luo, J. Phys. Chem. C. 2014, 118, 21457-
1462
Ye, L. Zan, Catal. Sci. Technol. 2013, 3, 1253--1260
6
7
(a) X. Chen, L. Liu, P. Y. Yu, S. S. Mao, Science, 2011, 331,746-
2
7
2
49. (b) J. Tripathy, K. Lee, P. Schmuki, Angew. Chem. Int. Ed.
5 D. Tomova, L. Bilyarska, A. Eliyas, L. Petrov. Appl. Catal. A:
General, 2006, 63, 266-271.
014, 53, 12605-12608. (c) K. Varghese, M. Paulose, T. J.
Latempa, C. A. Grimes, Nano Lett. 2009, 9, 731-737.
(a) Q. Kang, T. Wang, P. Li, L. Liu, K. Chang, M. Li, J. Ye,
Angew. Chem. Int. Ed. 2015, 54, 841-845. (b) C. Wang, R. L.
Thompson, J. Baltrus, C. Matranga, J. Phys. Chem. Lett., 2010,
1
2
, 48. (c) M. Xing, F. Shen, B. Qiu, J. Zhang, Science Reports,
014, 4, 6341. (d) Y. Yang, T. Zhang, L. Le, X. Ruan, P. Fang, C.
Pan, R. Xiong, J. Shi, J. Wei, Science Reports, 2014, 4, 7045.
(a)J. Pan, X. Wu, L. Wang, G. Liu, G. Q. Lu and H.-M. Cheng,
Chem. Commun., 2011, 47, 8361. (b) L-. L. Tan, S-.P. Chai, A.
R. Mohamed, ChemSusChem 2012, 5, 1868-1882.(c) L. Liu, C.
Zhao, D.Pitts, H. Zhao, Y. Li, Catal. Sci. Technol., 2014, 4,
8
9
1
539–1546
(a) H. Li , X. Zhang, D. R. MacFarlane, Adv. Energy Mater.
015, 5, 1401077. (b) Y. T. Liang, B. K. Vijayan, K. A. Gray, M.
C. Hersam, Nano Lett., 2011, 11, 2865.
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