Efficient UV-vis-IR photothermocatalytic selective ethanol oxidation on MnO: X/TiO2 nanocomposites significantly enhanced by a novel photoactivation

Article abstract of DOI:10.1039/c9ta12531k

MnO_x/TiO₂ nanocomposites of amorphous manganese oxide supported on TiO₂ with Mn/(Mn + Ti) molar ratios of 0.1, 0.2, 0.3, and 0.4 were prepared and characterized. Based on these nanocomposites, a novel strategy of photothermocatalytic selective ethanol oxidation to acetaldehyde was developed. The MnO_x/TiO₂ nanocomposites with a Mn/(Mn + Ti) molar ratio of 0.3 exhibit efficient catalytic activity, high acetaldehyde selectivity, and excellent catalytic durability under UV-vis-IR irradiation. They also exhibit good catalytic activity and more than 92% acetaldehyde selectivity under vis-IR irradiation of λ > 420, 560, and 690 nm. Even under λ > 830 nm IR irradiation, they exhibit catalytic activity and 98.8% acetaldehyde selectivity. Selective ethanol oxidation on the MnO_x/TiO₂ nanocomposites follows a mechanism of light-driven thermocatalysis. A novel photoactivation is found to occur on amorphous manganese oxide in the MnO_x/TiO₂ nanocomposites: At the same reaction temperature, both UV-vis-IR and λ > 420 nm vis-IR irradiation significantly enhance the ethanol reaction rate (r_ethanol) and the acetaldehyde production rate (r_acetaldehyde) as compared to the corresponding rates in the dark. For example, at 150 °C, the r_ethanol and r_acetaldehyde values under UV-vis-IR are enhanced by 19.2 and 19.6 times as compared to the corresponding values in the dark, respectively. This catalytic enhancement upon UV-vis-IR and λ > 420 nm vis-IR irradiation is ascribed to the activation energy of selective ethanol oxidation being significantly reduced from 85.8 kJ mol^-1 in the dark to 14.2 and 13.5 kJ mol^-1, respectively. It is found that the novel photoactivation arises from the activity of oxygen of amorphous manganese oxide in MnO_x/TiO₂ being significantly promoted upon irradiation.

Full text of DOI:10.1039/c9ta12531k

Journal of
Materials Chemistry A
View Article Online
View Journal
PAPER
Efficient UV-vis-IR photothermocatalytic selective
ethanol oxidation on MnOx/TiO2 nanocomposites
significantly enhanced by a novel photoactivation†
Cite this: DOI: 10.1039/c9ta12531k
a
a
Yi Yang,ab Shaowen Wu,a Yuanzhi Li,
Qian Zhanga and Xiujian Zhao
*
MnOx/TiO2 nanocomposites of amorphous manganese oxide supported on TiO2 with Mn/(Mn + Ti) molar
ratios of 0.1, 0.2, 0.3, and 0.4 were prepared and characterized. Based on these nanocomposites, a novel
strategy of photothermocatalytic selective ethanol oxidation to acetaldehyde was developed. The MnOx/
TiO2 nanocomposites with a Mn/(Mn + Ti) molar ratio of 0.3 exhibit efficient catalytic activity, high
acetaldehyde selectivity, and excellent catalytic durability under UV-vis-IR irradiation. They also exhibit
good catalytic activity and more than 92% acetaldehyde selectivity under vis-IR irradiation of l > 420,
560, and 690 nm. Even under l > 830 nm IR irradiation, they exhibit catalytic activity and 98.8%
acetaldehyde selectivity. Selective ethanol oxidation on the MnOx/TiO2 nanocomposites follows
a mechanism of light-driven thermocatalysis. A novel photoactivation is found to occur on amorphous
manganese oxide in the MnOx/TiO2 nanocomposites: at the same reaction temperature, both UV-vis-IR
and l > 420 nm vis-IR irradiation significantly enhance the ethanol reaction rate (rethanol) and the
acetaldehyde production rate (racetaldehyde) as compared to the corresponding rates in the dark. For
example, at 150 ꢀC, the rethanol and racetaldehyde values under UV-vis-IR are enhanced by 19.2 and 19.6
times as compared to the corresponding values in the dark, respectively. This catalytic enhancement
upon UV-vis-IR and l > 420 nm vis-IR irradiation is ascribed to the activation energy of selective ethanol
Received 14th November 2019
Accepted 10th December 2019
oxidation being significantly reduced from 85.8 kJ molꢁ1 in the dark to 14.2 and 13.5 kJ molꢁ1
,
DOI: 10.1039/c9ta12531k
respectively. It is found that the novel photoactivation arises from the activity of oxygen of amorphous
rsc.li/materials-a
manganese oxide in MnOx/TiO2 being significantly promoted upon irradiation.
attracting extensive interest. Persistent studies have been
carried out to search for efficient catalysts for selective ethanol
1. Introduction
oxidation to acetaldehyde. The reported catalysts mainly
include Au nanoparticles supported on various supports such as
Au/SiO2,7 Au/TiO2,8–10 Au/MoO3,11–13 Au/MgCuCr2O4,1,14 Au/
CuSiO3,15 Au–Ir/SiO2,16 Au–Cu/BN17 etc. There are two challenges
to be addressed for supported Au catalysts. One challenge is the
scarce resource and expensiveness of precious Au metal cata-
lysts. To address this challenge, some researchers have devel-
oped non-precious metal catalysts for selective ethanol
oxidation to acetaldehyde such as V2O5/TiO2 or VOx/TiO2,18–20
VOx/ZrO2,21 VxMe1ꢁxSbO4 (Me ¼ Fe, Al, and Ga)22 etc. Another
challenge is high energy consumption as selective ethanol
Utilization of abundant biomasses and their derivatives for
synthesizing chemicals provides an important route for allevi-
ating strong dependence on depleting fossil fuels.1–3 As the
target, ethanol is very attractive as it can be produced on a large
scale with low cost by biomass fermentation. It can be used to
synthesize acetaldehyde, acetic acid, ethyl acetate, and so on by
selective oxidation. Among the products, acetaldehyde is an
important industrial chemical that is used for synthesizing
diverse chemicals such as pentaerythritol, peracetic acid,
butylene glycol, chloral, and so on.1–4 Currently, acetaldehyde is
mainly produced in industry by ethylene oxidation using PdCl2–
CuCl2 as a catalyst.5,6 Selective oxidation of renewable ethanol to
acetaldehyde is a green and sustainable approach alternative to
the present ethylene oxidation based on petroleum, thus
ꢀ
oxidation usually occurs above 200 Cꢁa1t a high space velocity
(e.g. more than 10 000 mL hꢁ1 gcatal ).1,6–17 Therefore, it is
highly anticipated and a great challenge to develop a low energy-
consumption strategy for selective ethanol oxidation using non-
precious metal catalysts.
aState Key Laboratory of Silicate Materials for Architectures, Wuhan University of
Technology, 122 Luoshi Road, Wuhan 430070, P. R. China. E-mail: liyuanzhi66@
hotmail.com
bCollege of Science, Huazhong Agricultural University, Wuhan 430070, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c9ta12531k
Photocatalytic selective ethanol oxidation to acetaldehyde is
a green approach with low energy consumption as it can use
renewable solar energy. Several photocatalysts such as VOx/
TiO2,23 Pt/TiO,24 CdS,25 CdS/TiO2,26 and so on have been re-
ported to exhibit catalytic activity for photocatalytic selective
This journal is © The Royal Society of Chemistry 2019
J. Mater. Chem. A

View Article Online
Journal of Materials Chemistry A
Paper
ethanol oxidation. There are two challenges for the photo-
catalytic approach. One is its low efficiency23–26 as the majority of
photogenerated charge carriers rapidly recombine.27,28 Another
is the difficulty in the utilization of infrared energy, which
accounts for about 50% of solar energy. Actually, the reported
photocatalysts for selective ethanol oxidation to acetaldehyde
could only use UV and a portion of visible light.23–26 Until now,
no infrared photocatalysts for selective ethanol oxidation have
been reported.
Recently, a very efficient photothermocatalytic approach has
been developed. It combines the advantages of high efficiency
of thermocatalysis18–22,29,30 and low energy consumption of
photocatalysis.23–26,31–33 UV, visible, and infrared energy in solar
light can be efficiently utilized. It has been proved to be very
efficient for photothermocatalytic abatement of air pollut-
ants34–45 and photothermocatalytic CO2 reduction.46–53
Herein, we develop a novel strategy of photothermocatalytic
selective ethanol oxidation to acetaldehyde. MnOx/TiO2 nano-
composites of amorphous manganese oxide supported on TiO2
with different Mn/(Mn + Ti) molar ratios are prepared. The
MnOx/TiO2 nanocomposites with a Mn/(Mn + Ti) molar ratio of
0.3 demonstrate very good catalytic activity, high acetaldehyde
selectivity, and excellent durability for selective ethanol oxida-
tion to acetaldehyde under UV-vis-IR irradiation. They also
exhibit good catalytic activity and high acetaldehyde selectivity
under vis-IR irradiation, even under l > 830 nm IR irradiation. It
is found that selective ethanol oxidation on the MnOx/TiO2
nanocomposites follows light-driven thermocatalysis, which is
signicantly promoted by a novel photoactivation. Based on
a number of experimental evidence, we provide insight into the
novel photoactivation. To the best of our knowledge, such
photothermocatalytic selective ethanol oxidation and photo-
activation have not been reported.
Fig. 1 TEM images of the samples: MnOx/TiO2-A (A), MnOx/TiO2-B
(B), MnOx/TiO2-C (C), and MnOx/TiO2-D (D).
50 wt% Mn(NO3)2 for MnOx/TiO2-D are 0.4399 and 1.9926 g,
respectively.
2.2 Characterization
XRD patterns of the MnOx/TiO2 samples were acquired on an X-
ray diffractometer (Rigaku Dmax). Their TEM images were
acquired on an electron microscope (JEM-2100F). Their surface
area values were measured using N2 adsorption on ASAP2020.
2. Experimental
2.1 Preparation
Nanocomposites of amorphous manganese oxide loaded on
TiO2 were prepared in accordance with the following procedure.
0.0733 g KMnO4 and 1.0 g TiO2(P25) (Degussa) were added into
50 mL deionized water in a 200 mL beaker, and magnetically
stirred for 30 min. Aqueous Mn(NO3)2 solution, obtained by
adding 0.3321 g of 50 wt% Mn(NO3)2 in 50 mL deionized water,
was added to the obtained suspension of KMnO4 and TiO2. Aer
magnetically stirring for several minutes, the resulting slurry
ꢀ
was ltered, washed with deionized water, and dried at 120 C
for 4 h. The molar ratio of Mn/(Mn + Ti) is 0.1. The obtained
sample is labeled as MnOx/TiO2-A.
The other samples with Mn/(Mn + Ti) molar ratios of 0.2, 0.3,
and 0.4 were prepared in accordance with the procedure, the
same as that used for MnOx/TiO2-A except for changing the
amounts of KMnO4 and 50 wt% Mn(NO3)2. The samples are
labeled as MnOx/TiO2-B, MnOx/TiO2-C, and MnOx/TiO2-D,
respectively. The amounts of KMnO4 and 50 wt% Mn(NO3)2 for
MnOx/TiO2-B are 0.1650 and 0.7472 g, respectively. The
amounts of KMnO4 and 50 wt% Mn(NO3)2 for MnOx/TiO2-C are
Fig. 2 HRTEM images of the samples: MnOx/TiO2-A (A), MnOx/TiO2-B
0.2828 and 1.2809 g, respectively. The amounts KMnO4 and (B), MnOx/TiO2-C (C), and MnOx/TiO2-D (D).
J. Mater. Chem. A
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
Journal of Materials Chemistry A
Table 1 BET surface area, pore volume, Mn3+/Mn4+ atomic ratio of the MnOx/TiO2 samples
N2 adsorption/desorption
XPS
Mn/(Ti + Mn) molar
ratio in reactant
Pore volume
Mn3+/Mn4+ by
Mn2p
Sample
Surface area (m2 gꢁ1
)
(cm3 gꢁ1
)
AOS by Mn3+/Mn4+
AOS by Mn3s
MnOx/TiO2-A
MnOx/TiO2-B
MnOx/TiO2-C
MnOx/TiO2-D
10%
20%
30%
40%
94.1
104.0
149.8
181.9
0.48
0.43
0.52
0.45
1.98
2.22
2.64
3.07
3.34
3.31
3.27
3.25
3.39
3.36
3.30
3.28
Their XPS spectra were acquired on an X-ray photoelectron bers of aluminum silicate. The diameter of the sample
spectrometer (ESCALAB 250Xi). Their optical absorption spectra dispersed area was 2 cm. A stream of 0.78 vol% O2/N2 with
were acquired on a spectrophotometer (Lambda 750 S).
30 g mꢁ3 ethanol was continuously fed into the reactor at 40
O2 temperature programmed oxidation (O2-TPO) of the pre- mL minꢁ1. The reactants and products were analyzed on a gas
reduced MnOx/TiO2 sample was performed on a multifunc- chromatograph (GC9560) equipped with a ame ionization
tional adsorption apparatus (TP-5080) in a ow of 5 vol% O2/He. detector (FID), a methane converter, a Porapak Q Column, and
Before O2-TPO, the MnOx/TiO2 sample was pre-reduced at a TDX-01 column. To measure photothermocatalytic activity
170 ꢀC in a ow of 5 vol% CO/He for 30 min. The O2-TPO under visible-infrared (vis-IR) and infrared (IR) irradiation,
procedure is detailed in the reported work.54
a corresponding long wave pass lter of l > 420, 560, 690, or
830 nm was used. The light intensity values of UV-vis-IR l > 420,
560, 690, and 830 nm were 555.30, 507.36, 483.97, 454.65, and
434.51 mW cmꢁ2, respectively.
2.3 Photothermocatalytic and photocatalytic activity
For conducting the photocatalytic tests, 0.0500 g of the
MnOx/TiO2–C sample was dispersed at the bottom of the
stainless steel reactor, and the reactor was placed in an ice-
water bath to keep the surface temperature of the sample
under UV-vis-IR irradiation at near room temperature. The
Photothermocatalytic selective oxidation of ethanol on the
samples was conducted in a cylindrical stainless steel reactor
(volume 107 mL) with a quartz window (5.5 cm in diameter)
under 500 W Xe lamp irradiation as illustrated in Scheme S1.†
0.0500 g of the sample was dispersed on thermal insulation
Fig. 3 Ti2p, O1s, Mn2p, and Mn3s spectra of MnOx/TiO2-A (a), MnOx/TiO2-B (b), MnOx/TiO2-C (c), and MnOx/TiO2-D (d).
This journal is © The Royal Society of Chemistry 2019
J. Mater. Chem. A

View Article Online
Journal of Materials Chemistry A
Paper
Fig. 4 The ethanol conversion (A), selectivity of acetaldehyde, CO, and CO2 (B), and acetaldehyde production rate (C) for selective ethanol
oxidation on the samples under UV-vis-IR irradiation: MnOx/TiO2-A (a), MnOx/TiO2-B (b), MnOx/TiO2-C (c), MnOx/TiO2-D (d), and TiO2 (P25) (e).
Time course of ethanol conversion and acetaldehyde selectivity for photothermocatalytic selꢁe1ctive ethanol oxidation on MnOx/TiO2-C under
UV-vis-IR irradiation (light intensity, 543.9 mW cmꢁ2) (D). The space velocity is 48 L hꢁ1 gcatal
.
other procedure was the same as that used for the photo- in previous studies.41,44 For measuring thermocatalytic activity
thermocatalytic test.
of all the samples in the dark, the sample amount used was
0.050 g. A stream of 0.78 vol% O2/N2 with 30.0 g mꢁ3 ethanol
was continuously fed into the reactor at 40 mL minꢁ1. For
measuring catalytic activity of the MnOx/TiO2-C sample in the
dark and under irradiation, the sample amount used was
0.0080 g. The ow rate of a stream of 0.78 vol% O2/N2 with
30.0 g mꢁ3 ethanol was 20 mL minꢁ1. The light intensity values
of UV-vis-IR and l > 420 nm vis-IR irradiation were 561.3 and
471.0 mW cmꢁ2, respectively.
2.4 Catalytic activity in the dark and under irradiation
Catalytic activity of the samples for selective oxidation of
ethanol in the dark and under irradiation was measured in
a tubular quartz reactor linked to a quartz window. The
temperature of the samples in the reactor, monitored using
a thermocouple inserted in the reactor, was controlled using an
electric tubular furnace. The details of the reactor were reported
Table 2 Catalytic activity comparison between the reported photocatalytic approach and the present photothermocatalytic approacha
Irradiation wavelength Aldehyde production Aldehyde selectivity
Approach
Catalyst
Alcohol
(nm)
rate (mmol gꢁ1 minꢁ1
)
(%)
Ref. no.
Photocatalysis
Photocatalysis
Photocatalysis
Photocatalysis
Pt/TiO2
CdS
CdS/TiO2
Au/TiO2
Ethanol
Ethanol
Ethanol
Ethanol
375
>410
>420
350–400
428–780
60.0
0.7
2.5
79.1
100.0
24
25
26
60
2.1*
2.0*
9.8
103.1
89.1
640.2
313.8
273.1
108.9
99.0*
99.0*
99.0
99.0
99
Photocatalysis
Photocatalysis
Photocatalysis
Bi2MoO6
Pd/BiOCl
Benzyl alcohol >400
Benzyl alcohol 360–780
61
62
63
Bi24O31Br10(OH)d Ethanol
Benzyl alcohol 450
Ethanol 240–2400
450
99
Photothermocatalysis
89.7
92.1
98.8
Present work
l > 420
l > 830
a
The aldehyde production rates in Table 2 are calculated according to the data reported in the literature. * denotes the acetic acid production rate
and selectivity.
J. Mater. Chem. A
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
Journal of Materials Chemistry A
suggests that increasing the Mn/(Mn + Ti) molar ratio leads to
an enhancement in the Mn3+/Mn4+ atomic ratio. In accordance
with the Mn3+/Mn4+ atomic ratio, the average oxidation states
(AOSs) of Mn in amorphous manganese oxide of MnOx/TiO2-A,
MnOx/TiO2-B, MnOx/TiO2-C, and MnOx/TiO2-D are calculated to
be 3.34, 3.31, 3.27, and 3.25, respectively (Table 1). The AOS
value is further obtained by determining the magnitude of
2.5 Temperature programmed ethanol oxidation (TPEO) in
the dark and under irradiation
TPEO on the MnOx/TiO2-C sample in the absence of O2 in the
dark and under irradiation was performed in a tubular quartz
reactor (with a quartz window) linked to an FTIR cell in an
infrared spectrometer (Nicolet-6700) as illustrated in Scheme
S2.† 0.0050 g of the MnOx/TiO2-C sample was kept in the
reactor. Before TPEO, the MnOx/TiO2-C sample was pre-treated
with a ow of 5 vol% O2/N2 at 200 ꢀC for 1 h to remove the
absorbed organic compounds. Aer cooling to ambient
temperature, the reactor and the system were purged with a ow
of high purity N2. Then, the system was closed. 4.0 mL of ethanol
was injected into the gas bag. The micꢁro1 pump was turned on.
The reactor was heated at 2 ꢀC min to 200 ꢀC. The FTIR
spectra of the reactants and products were recorded at known
time.
3. Results and discussion
3.1 Characterization
MnOx/TiO2 nanocomposites with Mn/(Mn + Ti) molar ratios of
0.1, 0.2, 0.3, and 0.4 were prepared by depositing manganese
oxide on TiO2 through the reaction between KMnO4 and
Mn(NO3)2 at ambient temperature. The corresponding nano-
composites are labeled as MnOx/TiO2-A, MnOx/TiO2-B, MnOx/
TiO2-C, and MnOx/TiO2-D, respectively. XRD patterns show that
there are only peaks of anatase (JCPDF 86-1157) and rutile
(JCPDF 21-1276) of TiO2(P25) as a support (Fig. S1†). No peaks of
any crystalline manganese oxides are observed. TEM images
show that there are short ber aggregates around nanoparticles
of TiO2. With the increase of the Mn/(Mn + Ti) molar ratio, the
amount of short ber aggregates increases (Fig. 1). HRTEM
images show that thin amorphous layers closely contact TiO2
nanocrystals for MnOx/TiO2-A (Fig. 2). With the increase of the
Mn/(Mn + Ti) molar ratio from 0.1 to 0.2, 0.3, and 0.4, the
thickness of the amorphous layer around TiO2 nanocrystals
increases. The results of XRD and HRTEM indicate that
manganese oxide exists in the amorphous state in all the MnOx/
TiO2 samples. EDX maps of the elements in MnOx/TiO2-C are
shown in Fig. S2.† It can be seen from Fig. S2† that Mn, Ti, and
O are generally well distributed. This shows that manganese
oxide is well distributed on TiO2 nanoparticles.
N2 adsorption measurement shows that BET surface area
values of MnOx/TiO2-A, MnOx/TiO2-B, MnOx/TiO2-C, and MnOx/
TiO2-D are 94.1, 104.0, 149.8, and 181.9 m2 gꢁ1, respectively
(Fig. S3 and S4,† Table 1). Their BJH adsorption pore volume
values are 0.48, 0.43, 0.52, and 0.45 cm3 gꢁ1, respectively.
The valence states of Ti, O, and Mn in the MnOx/TiO2
samples are analyzed by XPS (Fig. 3). For all the MnOx/TiO2
samples, Ti has a peak around 458.5 eV, which is assigned to
Ti4+. O has a peak around 529.7 eV, which is assigned to O2ꢁ
.
55,56
For Mn, the two peaks around 641.8 and 653.3 eV are assigned
to Mn3+, while the two peaks around 643.6 and 654.5 eV are
assigned to Mn4+.54,57 The Mn3+/Mn4+ atomic ratios in MnOx/
TiO2-A, MnOx/TiO2-B, MnOx/TiO2-C, and MnOx/TiO2-D are
Fig. 5 The ethanol conversion (A), selectivity of acetaldehyde, CO, and
CO2 (B), and acetaldehyde production rate (C) for selective ethanol
calculated to be 1.98, 2.22, 2.64, and 3.07, respectively. This oxidation on MnOx/TiO2-C under vis-IR irradiation.
This journal is © The Royal Society of Chemistry 2019
J. Mater. Chem. A

View Article Online
Journal of Materials Chemistry A
Paper
Fig. 6 Reflectance diffusive absorption spectra of the samples (A). Photocatalytic activity of MnOx/TiO2-C for selective ethanol oxidation to
acetaldehyde at near room temperature under UV-vis-IR irradiation (B). Equilibrium temperature values of MnOx/TiO2-A (a), MnOx/TiO2-B (b),
MnOx/TiO2-C (c), and MnOx/TiO2-D (d) under the UV-vis-IR irradiation (C). Equilibrium temperature values of MnOx/TiO2-C under vis-IR or IR
irradiation (D).
Mn3s multiplet splitting (DEs, eV) in accordance with the MnOx/TiO2-C is enhanced by 11.7 times. Further increasing the
following equation:57–59
Mn/(Mn + Ti) molar ratio to 0.4 leads to a slight change in its
catalytic activity. The ethanol conversion and acetaldehyde
production rate of MnOx/TiO2-D slightly change to 53.9% and
331.1 mmol gꢁ1 minꢁ1, respectively.
Photocatalytic selective oxidation of renewable ethanol using
inexhaustible solar energy is a green, sustainable, and prom-
ising approach to synthesize valuable chemicals alternative to
the present approach of thermocatalytic ethylene oxidation
based on petroleum. Several photocatalysts such as Pt/TiO2,
CdS, CdS/TiO2, Au/TiO2 etc. have been reported to exhibit
AOS ¼ 8.95 ꢁ 1.13DEs
The AOS values of Mn in MnOx/TiO2-A, MnOx/TiO2-B, MnOx/
TiO2-C, and MnOx/TiO2-D are 3.39, 3.36, 3.30, and 3.28,
respectively (Table 1). They are in general agreement with the
corresponding values obtained by tting the Mn2p spectra.
3.2 Photothermocatalytic performance
3.2.1. Photothermocatalytic activity. Selective ethanol
oxidation on TiO2(P25) and the MnOx/TiO2 samples under UV-
vis-IR irradiation was conducted (see Experimental). As shown
in Fig. 4, TiO2(P25) shows very low catalytic activity. Its ethanol
conversion is only 5.1%. Its selectivity of acetaldehyde and CO2
is 98.3% and 1.7%, respectively. Its acetaldehyde production
rate is only 26.9 mmol gꢁ1 minꢁ1. Remarkably, loading amor-
phous manganese oxide on TiO2(P25) tremendously promotes
catalytic activity. The ethanol conversion of MnOx/TiO2-A
signicantly increases to 48.1%. Although its acetaldehyde
selectivity decreases to 89.4%, its acetaldehyde production rate
signicantly increases to 246.5 mmol gꢁ1 minꢁ1. With the
increase of the Mn/(Mn + Ti) molar ratio to 0.2 (MnOx/TiO2-B),
ethanol conversion and the acetaldehyde production rate
increase to 54.2% and 312.7 mmol gꢁ1 minꢁ1, respectively. With
the increase of the Mn/(Mn + Ti) molar ratio to 0.3 (MnOx/TiO2-
C), ethanol conversion and the acetaldehyde production rate
increase to 59.1% and 313.8 mmol gꢁ1 minꢁ1, respectively.
Scheme
1 Schematic illustration of light-driven thermocatalytic
Compared to TiO2(P25), the acetaldehyde production rate of ethanol oxidation enhanced by a photoactivation on MnOx/TiO2.
J. Mater. Chem. A
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
Journal of Materials Chemistry A
photocatalytic activity for selective ethanol oxidation to acetal-
dehyde or acetic acid (Table 2). Pt/TiO2 exhibited a high acet-
aldehyde production rate of 60.0 mmol gꢁ1 minꢁ1 and
acetaldehyde selectivity of 79.1% under UV irradiation.25
However, visible and infrared energy in solar light could not be
utilized by Pt/TiO2. The photocatalysts of CdS, CdS/TiO2, and
Au/TiO2 exhibited very high selectivity of acetaldehyde or acetic
acid (99–100%) under visible light irradiation. But their
production rate of acetaldehyde or acetic acid is low (0.7–2.5
mmol gꢁ1 minꢁ1).26,60 Recently, photocatalytic selective oxida-
tion of other alcohols to aldehydes has attracted interest. For
example, Jing et al. reported that hierarchical Bi2MoO6 spheres
exhibited phototocatalytic activity for selective benzyl alcohol
oxidation with a benzaldehyde production rate of 9.8 mmol
gꢁ1 minꢁ1 and a benzaldehyde selectivity of 99% under l >
400 nm visible light irradiation.61 Li et al. achieved a very high
benzaldehyde production rate of 103.1 mmol gꢁ1 minꢁ1 and
a benzaldehyde selectivity of 99% using Pd/BiOCl as a photo-
catalyst for selective benzyl alcohol oxidation under 360–780 nm
irradiation.62 Very recently, Dai et al. investigated photocatalytic
selective oxidation of a series of alcohols including aliphatic
alcohols and aromatic alcohols on Bi24O31Br10(OH)d under
visible light irradiation (e.g. 450 nm LED).63 They found that
oxidation of aromatic alcohols was much faster than that of
aliphatic alcohols. For example, Bi24O31Br10(OH)d had an acet-
aldehyde production rate of 89.1 mmol gꢁ1 minꢁ1 for selective
ethanol oxidation. For selective benzyl alcohol oxidation, its
benzaldehyde production rate signicantly increased to 640.2
mmol gꢁ1 minꢁ1. However, Bi24O31Br10(OH)d exhibited no pho-
tocatalytic activity under l > ꢂ580 nm vis-IR irradiation due to
its larger band gap (ꢂ2.5 eV).63 Compared to the reported
photocatalytic approach, the present approach of photo-
thermocatalytic selective ethanol oxidation on MnOx/TiO2
nanocomposites provides a very high acetaldehyde production
rate of 313.8 mmol gꢁ1 minꢁ1 under UV-vis-IR irradiation. Even
under l > 830 nm IR irradiation, MnOx/TiO2 has a high acetal-
3.3 Role of light
3.3.1. Light-driven thermocatalysis. Why does the irradia-
tion lead to efficient selective ethanol oxidation on the MnOx/
TiO2 nanocomposites? To address this, the optical absorption
spectra of the MnOx/TiO2 nanocomposites were acquired. As
shown in Fig. 6A, all the MnOx/TiO2 nanocomposites show
strong absorption across the region of 240–2400 nm. The
absorption below 420 nm is mainly due to the absorption of
dehyde production rate of 108.9 mmol gꢁ1 minꢁ1
.
Catalytic stability of a catalyst is very crucial for its potential
applications. Therefore, long-term photothermocatalytic selec-
tive ethanol oxidation on the MnOx/TiO2-C sample under UV-
vis-IR irradiation was conducted. As shown in Fig. 4D, aer
reacting for 30 h, its ethanol conversion and acetaldehyde
selectivity generally remain unaltered. This indicates that
MnOx/TiO2-C has excellent photothermocatalytic durability.
The photothermocatalytic selective ethanol oxidation on the
MnOx/TiO2-C sample under vis-IR and IR irradiation was also
conducted. As shown in Fig. 5, MnOx/TiO2-C shows good pho-
tothermocatalytic activity and high acetaldehyde selectivity under
vis-IR irradiation. Under vis-IR irradiation of l > 420, 560, and
690 nm, its ethanol conversion values are 52.2%, 43.4%, and
33.8%, respectively. Its acetaldehyde selectivity values are 92.1%,
95.4%, and 97.4%, respectively. Its acetaldehyde production rate
values are 273.1, 244.1, and 187.7 mmol gꢁ1 minꢁ1, respectively.
Even under l > 830 nm IR irradiation, MnOx/TiO2-C shows good
photothermocatalytic activity. Its ethanol conversion, acetalde-
hyde selectivity, and acetaldehyde production rate are 19.1%,
98.8%, and 108.9 mmol gꢁ1 minꢁ1, respectively.
Fig. 7 The ethanol conversion (A), acetaldehyde selectivity (B), and
acetaldehyde yield (C) for thermocatalytic selective ethanol oxidation
on the samples at different temperatures in the dark: MnOx/TiO2-A (a),
MnOx/TiO2-B (b), MnOx/ꢁT1iO2-C (c), and MnOx/TiO2-D (d). The space
ꢁ1
velocity is 48 L h
g
.
catal
This journal is © The Royal Society of Chemistry 2019
J. Mater. Chem. A

View Article Online
Journal of Materials Chemistry A
Paper
TiO2, while the absorption above 420 nm is attributed to the IR irradiation. As can be seen from Fig. 7, among the MnOx/TiO2
absorption of manganese oxide due to the d–d transitions of Mn samples, MnOx/TiO2-A with the lowest Mn/(Mn + Ti) molar ratio
ions.41,64 However, the test of photocatalytic selective ethanol (0.1) shows the lowest thermocatalytic activity. With the
oxidation on MnOx/TiO2-C shows that its photocatalytic activity increase of the Mn/(Mn + Ti) molar ratio to 0.2 (MnOx/TiO2-B)
is quite low (Fig. 6B). Its ethanol conversion is only 1.65%, 35.8 and 0.3 (MnOx/TiO2-C), thermocatalytic activity gradually
times less than its photothermocatalytic conversion (59.1%, increases. Further increasing the Mn/(Mn + Ti) molar ratio to
Fig. 4). This means that the very high catalytic activity of the 0.4 (MnOx/TiO2-D) does not promote thermocatalytic activity.
MnOx/TiO2 nanocomposites under irradiation (Fig. 4 and 5) is The thermocatalytic activity order of MnOx/TiO2-D z MnOx/
mainly attributed to light-driven thermocatalytic selective TiO2-C > MnOx/TiO2-B > MnOx/TiO2-A is generally in agreement
ethanol oxidation as illustrated in Scheme 1.
with the photothermocatalytic activity order (Fig. 4).
Upon irradiation, the surface temperature of the MnOx/TiO2
3.3.2. Photoactivation. Is the high photothermocatalytic
sample increases to an equilibrium temperature (Teq) due to activity of the MnOx/TiO2 samples merely attributed to light-
photothermal conversion induced by its strong absorption driven thermocatalysis? To address this, we conducted cata-
(Fig. 6A). Once the Teq value exceeds the light-off temperature lytic selective ethanol oxidation on MnOx/TiO2-C at different
(Tlight-off) of thermocatalytic selective ethanol oxidation on the temperatures in the dark and under irradꢀiation. As shown in
sample, the thermocatalytic reaction proceeds.
Fig. 8, at the same temperature above 120 C, compared to the
This mechanism is veried by measuring both the Teq and ethanol reaction rate (rethanol) and the acetaldehyde production
Tlight-off values of the MnOx/TiO2 samples. Under UV-vis-IR rate (racetaldehyde) in the dark, UV-vis-IR irradiation signicantly
irradiation, the Teq values of MnOx/TiO2-A, MnOx/TiO2-B, enhances the rethanol and racetaldehyde values (Fig. 8A and B). For
ꢀ
MnOx/TiO2-C, and MnOx/TiO2-D are 199, 204, 206, and 207 C, example, at 150 ꢀC, the rethanol and racetaldehyde values under UV-
respectively (Fig. 6C). Under vis-IR and IR irradiation of l > 420, vis-IR are 759.6 and 740.7 mmol gꢁ1 minꢁ1, respectively. They
560, 690, and 830 ꢀnm, the Teq values of MnOx/TiO2-C are 198, are enhanced by 19.2 and 19.6 times as compared to the cor-
183, 171, and 156 C, respectively (Fig. 6D). The Tlight-off values responding values (39.53 and 37.8 mmol gꢁ1 minꢁ1) in the dark,
are determined by performing thermocatalytic selective ethanol respectively. However, UV-vis-IR irradiation only causes a slight
oxidation on the MnOx/TiO2 samples in the dark at different reduction in acetaldehyde selectivity (Fig. 8C). As the photo-
temperatures. As shown in Fig. 7, once the temperature is catalytic activity of MnOx/TiO2-C is very low (Fig. 6B), the
increased above 100 ꢀC or so, thermocatalytic selective ethanol signicant enhancement in catalytic activity upon irradiation
oxidation starts to proceed (Tlight-off ¼ ꢂ100 ꢀC). All the Teq clearly indicates the presence of a novel photoactivation.
values exceed the Tlight-off values, thus the light-driven thermo-
We also conducted catalytic selective ethanol oxidation on
catalytic reaction is able to proceed under UV-vis-IR, vis-IR, and MnOx/TiO2-C at different temperatures under l > 420 nm vis-IR
Fig. 8 The ethanol reaction rate (A), acetaldehyde production rate (B), acetaldehyde selectivity (C), and ln(rethanol) vs. 1000/T (D) for selective
ethanol oxidationꢁo1n MnOx/TiO2-C at different temperatures in the dark and under UV-vis-IR and l > 420 nm vis-IR irradiation. The space
ꢁ1
velocity is 150 L h gcatal
.
J. Mater. Chem. A
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
Journal of Materials Chemistry A
irradiation. In this case, a little photocatalytic contribution of
TiO2 in MnOx/TiO2-C is completely ruled out as TiO2(P25) could
not be excited by l > 420 nm vis-IR irradiation due to its large
band gap (3.2 eV of anatase, 3.0 eV of rutile). Similar to the
observation under UV-vis-IR irradiation, l > 420 nm vis-IR
irradiation signicantly enhances the rethanol and racetaldehyde
values as compared to the corresponding values in the dark. The
rethanol and racetaldehyde values under l > 420 nm vis-IR irradia-
tion less than the corresponding values under UV-vis-IR irra-
diation are due to the light intensity of the former being less
than that of the latter (see Experimental). This undoubtedly
reveals that the novel photoactivation occurs on amorphous
manganese oxide in MnOx/TiO2-C, resulting in the signicant
catalytic enhancement upon irradiation.
Based on the rethanol values at different temperatures,
proles of ln(rethanol) vs. 1/T are plotted. There is a very good
linear relationship between ln(rethanol) and 1/T in the dark and
under irradiation (Fig. 8D). Therefore, we calculated apparent
activation energy (Ea) in accordance with the Arrhenius equa-
tion (k ¼ AeꢁE /RT). The Ea value in the dark is 85.8 kJ molꢁ1
.
a
Upon UV-vis-IR irradiation and l > 420 nm vis-IR irradiation,
the Ea values are signicantly reduced to 14.2 and 13.5 kJ molꢁ1
,
respectively. The Ea reduction upon l > 420 nm vis-IR irradia-
tion, similar to that upon UV-vis-IR irradiation, further conrms
that the novel photoactivation occurs on amorphous manga-
nese oxide in MnOx/TiO2–C rather than on TiO2.
It is well known that the oxidation of organic compounds on
manganese oxides follows a redox mechanism of Mars–van
Krevelen.54,57 Organic compound is oxidized by oxygen of
manganese oxide. The resulting oxygen vacancies in manganese
oxide are relled by O2. The former step is the rate-determining
step as it is much sluggish than the latter.54,57 This means that
the activity of oxygen in manganese oxide plays a decisive role in
the catalytic oxidation. Therefore, to gain insight into the pho-
toactivation, we investigated the effect of UV-vis-IR irradiation
on ethanol oxidation by oxygen of amorphous manganese oxide
in MnOx/TiO2-C and in the absence of O2 by temperature pro-
grammed ethanol oxidation (TPEO, see Experimental). The
reactants and products of TPEO were monitored by FTIR. In the
dark, when the temperature is increased above 120 ꢀC, the peak
around 1066 cmꢁ1 due to C–O stretching of ethanol65 gradually
decreases, while the peak around 1760 cmꢁ1 due to C–O
stretching of acetaldehyde65 gradually increases (Fig. 9A). As
there is no O2 existed in the reactants, the formation of acet-
Fig. 9 Time course of the FTIR spectra of reactants and products
produced by ethanol oxidation on the MnOx/TiO2-C sample in the
absence of O2 in the dark (A) and under UV-vis-IR irradiation (B). O2-
TPO profile of the pre-reduced MnOx/TiO2-C sample (C).
increased above 80 ꢀC (Fig. 9B), the C–O stretching peak of
ethanol around 1066 cmꢁ1 gradually decreases, while the C–O
stretching peak of acetaldehyde around 1760 cmꢁ1 gradually
increases. This indicates that UV-vis-IR irradiation signicantly
promotes the activity of oxygen of amorphous manganese oxide
in MnOx/TiO2-C as illustrated in Scheme 1, thus signicantly
enhancing the catalytic activity of selective ethanol oxidation on
MnOx/TiO2-C.
ꢀ
aldehyde at a temperature above 120 C is ascribed to ethanol
oxidation by oxygen of amorphous manganese oxide in MnOx/
TiO2-C. The temperature (120 ꢀC) is generally similar to that of
ethanol oxidation by O2 on MnOx/TiO2-C in the presence of O2
(Fig. 7). This conrms that selective ethanol oxidation on MnOx/
TiO2-C actually follows the Mars–van Krevelen mechanism. This
is further proved by temperature programmed oxidation of the
pre-reduced MnOx/TiO2-C sample by O2 (O2-TPO) (see Experi-
4. Conclusion
mental). O2-TPO shows that the oxidation of the pre-reduced In summary, the MnOx/TiO2 nanocomposites exhibited good
ꢀ
MnOx/TiO2-C sample occurs around 73 C (Fig. 9C), much less catalytic activity, high acetaldehyde selectivity, and excellent
than the temperature (120 ꢀC) of ethanol oxidation by oxygen of durability for selective ethanol oxidation under UV-vis-IR irra-
amorphous manganese oxide in MnOx/TiO2-C. Very interest- diation. They also exhibited good catalytic activity and high
ingly, under UV-vis-IR irradiation, when the temperature is only acetaldehyde selectivity under vis-IR irradiation, even under l >
This journal is © The Royal Society of Chemistry 2019
J. Mater. Chem. A

View Article Online
Journal of Materials Chemistry A
Paper
830 nm IR irradiation. Selective ethanol oxidation on the MnOx/ 17 Y. Wang, L. Shi, W. Lu, Q. Sun, Z. Wang, C. Zhi and A.-H. Lu,
TiO2 nanocomposites follows a mechanism of light-driven ChemCatChem, 2017, 9, 1363–1367.
thermocatalysis. A novel photoactivation is found to occur on 18 V. V. Kaichev, Y. A. Chesalov, A. A. Saraev, A. Y. Klyushin,
amorphous manganese oxide in the MnOx/TiO2 nano-
A.
Knop-Gericke,
T.
V.
Andrushkevich
and
composites: the irradiation signicantly reduces the activation
V. I. Bukhtiyarov, J. Catal., 2016, 338, 82–93.
energy of selective ethanol oxidation, thus enhancing the 19 D. M. Yun and J. E. Herrera, J. Catal., 2017, 350, 72–85.
ethanol reaction rate and the acetaldehyde production rate. 20 D. M. Yun, Y. Wang and J. E. Herrera, ACS Catal., 2018, 8,
This is ascribed to the fact that the irradiation signicantly 4681–4693.
promotes the activity of oxygen of amorphous manganese oxide 21 I. Boldog, P. Cicmanec, Y. Ganjkhanlou and R. Bulanek,
in the MnOx/TiO2 nanocomposites. The present strategy Catal. Today, 2018, 304, 64–71.
provides an effective approach to synthesize valuable organic 22 B. Mehlomakulu, T. T. N. Nguyen, P. Delichere, E. van Steen
´
chemicals using renewable solar energy.
and J. M. M. Millet, J. Catal., 2012, 289, 1–10.
23 D. Sannino, V. Vaiano and P. Ciambelli, Catal. Today, 2013,
205, 159–167.
24 B. D. Fraters, R. Amrollahi and G. Mul, J. Catal., 2015, 324,
119–126.
Conflicts of interest
There are no conicts to declare.
25 M. A. Nasalevich, E. A. Kozlova, T. P. Lyubina and
A. V. Vorontsov, J. Catal., 2012, 287, 138–148.
Acknowledgements
26 E. A. Kozlova, N. S. Kozhevnikovac, S. V. Cherepanova,
T. P. Lyubinaa, E. Y. Gerasimova, V. V. Kaichev,
A. V. Vorontsov, S. V. Tsybulya, A. A. Rempelc and
V. N. Parmon, J. Photochem. Photobiol., A, 2012, 250, 103–109.
27 J. W. Tang, J. R. Durrant and D. R. Klug, J. Am. Chem. Soc.,
2008, 130, 13885–13891.
This work was supported by the National Natural Science
Foundation of China (21673168 and 21473127). Dr Yi Yang and
Mr Shaowen Wu contributed equally to this work.
28 M. Kong, Y. Z. Li, X. Chen, T. T. Tian, P. F. Fang, F. Zheng
and X. J. Zhao, J. Am. Chem. Soc., 2011, 133, 16414–16417.
References
1 P. Liu and E. J. M. Hensen, J. Am. Chem. Soc., 2013, 135, 29 C. H. Zhang, H. Huang, G. Q. Li, L. Wang, L. Song and
14032–14035.
X. B. Li, Catal. Today, 2019, 327, 374–381.
2 D. M. Alonso, J. Q. Bond and J. A. Dumesic, Green Chem., 30 Z. Wang, Q. Sun, D. Wang, Z. Hong, Z. P. Qu and X. B. Lia,
2010, 12, 1493–1513.
Sep. Purif. Technol., 2019, 209, 1016–1026.
31 X. J. Zou, C. Y. Yuan, Y. Y. Dong, H. Ge, J. Ke and Y. B. Cui,
Chem. Eng. J., 2020, 379, 122380.
32 X. D. Zhang, Y. Yang, W. Y. Huang, Y. Q. Yang, Y. X. Wang,
C. He, N. Liu, M. H. Wu and L. Tang, Mater. Res. Bull., 2018,
99, 349–358.
33 X. D. Zhang, Y. X. Wang, F. L. Hou, H. X. Li, Y. Yang,
X. X. Zhang, Y. Q. Yang and Y. Wang, Appl. Surf. Sci., 2017,
391, 476–483.
3 P. Gallezot, Chem. Soc. Rev., 2012, 41, 1538–1558.
4 C. Caro, K. Thirunavukkarasu, M. Anilkumar, N. R. Shiju and
G. Rothenberg, Adv. Synth. Catal., 2012, 354, 1327–1336.
5 R. Jira, Angew. Chem., Int. Ed., 2009, 48, 9034–9037.
6 J. A. Keith and P. M. Henry, Angew. Chem., Int. Ed., 2009, 48,
9038–9049.
7 N. Zheng and G. D. Stucky, J. Am. Chem. Soc., 2006, 128,
14278–14280.
8 O. A. Simakova, V. I. Sobolev, K. Y. Koltunov, B. Campo, 34 Y. Yang, Y. Z. Li, Q. Zhang, M. Zeng, S. W. Wu, L. Lan and
´
A.-R. Leino, K. Kordas and D. Y. Murzin, ChemCatChem,
2010, 2, 1535–1538.
X. J. Zhao, J. Mater. Chem. A, 2018, 6, 14195–14206.
35 L. Lan, Z. K. Shi, Q. Zhang, Y. Z. Li, Y. Yang, S. W. Wu and
X. J. Zhao, J. Mater. Chem. A, 2018, 6, 7194–7205.
36 Y. L. Zheng, W. Z. Wang, D. Jiang, L. Zhang, X. M. Li and
Z. Wang, J. Mater. Chem. A, 2016, 4, 105–112.
9 V. I. Sobolev, K. Y. Koltunov, O. A. Simakova, A.-R. Leino and
D. Y. Murzin, Appl. Catal., A, 2012, 433–434, 88–95.
10 S. Mostrou, A. Nagl, M. Ranocchiari, K. Fottinger and
¨
J. A. van Bokhoven, Chem. Commun., 2019, 55, 11833–11836. 37 Y. Yang, Y. Z. Li, M. Zeng, M. Y. Mao, L. Lan, H. H. Liu,
11 T. Takei, N. Iguchi and M. Haruta, New J. Chem., 2011, 35,
2227–2233.
12 J. C. Bauer, G. M. Veith, L. F. Allard, Y. Oyola, S. H. Overbury
and S. Dai, ACS Catal., 2012, 2, 2537–2546.
13 E. A. Redina, A. A. Greish, I. V. Mishin, G. I. Kapustin,
O. P. Tkachenko, O. A. Kirichenko and L. M. Kustov, Catal.
Today, 2015, 241, 246–254.
14 P. Liu, X. C. Zhu, S. B. Yang, T. Li and E. J. M. Hensen, J.
Catal., 2015, 331, 138–146.
J. Chen and X. J. Zhao, Appl. Catal., B, 2018, 224, 751–760.
38 M. Zeng, Y. Z. Li, F. Liu, Y. Yang, M. Y. Mao and X. J. Zhao,
Appl. Catal., B, 2017, 200, 521–529.
39 L. Lan, Y. Z. Li, M. Zeng, M. Y. Mao, L. Ren, Y. Yang,
H. H. Liu, L. Yun and X. J. Zhao, Appl. Catal., B, 2017, 203,
494–504.
40 Y. Yang, Y. Z. Li, M. Y. Mao, M. Zeng and X. J. Zhao, ACS Appl.
Mater. Interfaces, 2017, 9, 2350–2357.
41 F. Liu, M. Zeng, Y. Z. Li, Y. Yang, M. Y. Mao and X. J. Zhao,
Adv. Funct. Mater., 2016, 26, 4518–4526.
15 X. J. Du, N. H. Fu, S. L. Zhang, C. Chen, D. S. Wang and
Y. D. Li, Nano Res., 2016, 9, 2681–2686.
16 Y. J. Guan and E. J. M. Hensen, J. Catal., 2013, 305, 135–145.
42 Z. R. Lou, D. C. Yuan, F. Y. Zhang, Y. C. Wang, Y. G. Li and
L. P. Zhu, Nano Energy, 2019, 62, 653–659.
J. Mater. Chem. A
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
Journal of Materials Chemistry A
43 M. Zeng, Y. Z. Li, M. Y. Mao, J. L. Bai, L. Ren and X. J. Zhao, 55 C. D. Wagner, W. M. Riggs, L. E. Davis, Handbook of X-Ray
ACS Catal., 2015, 5, 3278–3286.
44 M. Y. Mao, Y. Z. Li, J. T. Hou, M. Zeng and X. J. Zhao, Appl.
Catal., B, 2015, 174, 496–503.
45 J. J. Kong, G. Y. Li, M. C. Wen, J. Y. Chen, H. L. Liu and
T. C. An, J. Catal., 2019, 370, 88–96.
Photoelectron Spectroscopy, PerkinElmer, Waltham, MA,
1979.
56 C. H. Zhang, K. Zeng, C. Wang, X. H. Liu, G. L. Wu, Z. Wang
and D. Wang, Ceram. Int., 2019, DOI: 10.1016/
j.ceramint.2019.11.153.
46 M. Y. Mao, Q. Zhang, Y. Yang, Y. Z. Li, H. Huang, Z. K. Jiang, 57 J. T. Hou, Y. Z. i. Li, M. Y. Mao, L. Ren and X. J. Zhao, ACS
Q. Q. Hu and X. J. Zhao, Green Chem., 2018, 20, 2857–2869. Appl. Mater. Interfaces, 2014, 6, 14981–14987.
47 Q. Zhang, M. Y. Mao, Y. Z. Li, Y. Yang, H. Huang, Z. K. Jiang, 58 V. P. Santos, O. S. G. P. Soares, J. J. W. Bakker,
Q. Q. Hu, S. W. Wu and X. J. Zhao, Appl. Catal., B, 2018, 239,
555–564.
M. F. R. Pereira, J. J. M. Orfao, J. Gascon, F. Kapteijn and
J. L. Figueiredo, J. Catal., 2012, 293, 165–174.
48 S. W. Wu, Y. Z. Li, Q. Zhang, Z. K. Jiang, Y. Yang, J. C. Wu and 59 X. D. Zhang, X. T. Lv, F. K. Bi, G. Lu and Y. X. Wang, Mol.
X. J. Zhao, Energy Environ. Sci., 2019, 12, 2581–2590. Catal., 2019, DOI: 10.1016/j.mcat.2019.110701.
49 H. Huang, M. Y. Mao, Q. Zhang, Y. Z. Li, J. L. Bai, Y. Yang, 60 B. W. Zhou, J. L. Song, Z. R. Zhang, Z. W. Jiang, P. Zhang and
M. Zeng and X. J. Zhao, Adv. Energy Mater., 2018, 201702472. B. X. Han, Green Chem., 2017, 19, 1075–1081.
50 Z. K. Jiang, Y. Z. Li, Q. Zhang, Y. Yang, S. W. Wu, J. C. Wu and 61 K. Q. Jing, W. Ma, Y. H. Ren, J. H. Xiong, B. B. Guo, Y. J. Song,
X. J. Zhao, J. Mater. Chem. A, 2019, 7, 4881–4892. S. J. Lianga and L. Wu, Appl. Catal., B, 2019, 243, 10–18.
51 Q. Zhang, Y. Z. Li, S. W. Wu, J. C. Wu, Z. K. Jiang, Y. Yang, 62 B. X. Li, L. Z. Shao, R. S. Wang, X. P. Dong, F. G. Zhao, P. Gao
L. Ren and X. J. Zhao, J. Mater. Chem. A, 2019, 7, 19800–
19810.
52 Y. Y. Li, C. H. Wang, M. Song, D. S. Li, X. T. Zhang and
Y. C. Liu, Appl. Catal., B, 2019, 243, 760–770.
53 M. N. Ha, G. Z. Lu, Z. F. Liu, L. C. Wang and Z. Zhao, J. Mater.
Chem. A, 2016, 4, 13155–13165.
and Z. Q. Li, J. Mater. Chem. A, 2018, 6, 6344–6355.
63 Y. Dai, P. J. Ren, Y. R. Li, D. D. Lv, Y. B. Shen, Y. W. Li,
H. Niemantsverdriet, F. Besenbacher, H. W. Xiang,
W. C. Hao, N. N. Lock, X. D. Wen, J. P. Lewis and R. Su,
Angew. Chem., Int. Ed., 2019, 58, 6265–6270.
64 Y. K. Hsu, Y. C. Chen, Y. G. Lin, L. C. Chen and K. H. Chen, J.
Mater. Chem., 2012, 22, 2733–2739.
65 C. Eaton, Laboratory Investigations in Organic Chemistry,
McGraw-Hill, Inc., 1989, pp. 653–655.
54 J. T. Hou, Y. Z. Li, L. L. Liu, L. Ren and X. J. Zhao, J. Mater.
Chem. A, 2013, 1, 6736–6741.
This journal is © The Royal Society of Chemistry 2019
J. Mater. Chem. A