Mesoporous Metal Oxide Encapsulated Gold Nanocatalysts: Enhanced Activity for Catalyst Application to Solvent-Free Aerobic Oxidation of Hydrocarbons

Article abstract of DOI:10.1021/acs.inorgchem.8b02197

Here, we present a series of experimental studies to encapsulate ultrasmall gold nanoparticles into mesoporous metal oxide via an in situ self-assembly method. Notably, the 2.0Au@mZnO catalyst (～2.0 nm gold nanoparticles loading on mesoporous ZnO nanospheres) shows excellent catalytic activity for indane oxidation (120 °C, conversion 88.5%) and affords much high turnover frequencies (9521 h^-1). The catalytic activity of these gold-based catalysts was found to be correlated with the size of gold nanoparticles and the types of metal oxide supports. With a decrease in gold nanoparticle size, the catalytic conversion efficiency of indane oxidation increased. In addition, such catalysts possessed high thermal and chemical stability and could be reused more than 10 times without a remarkable loss of catalytic activity.

Full text of DOI:10.1021/acs.inorgchem.8b02197

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Mesoporous Metal Oxide Encapsulated Gold Nanocatalysts:
Enhanced Activity for Catalyst Application to Solvent-Free Aerobic
Oxidation of Hydrocarbons
Yali Liu, Tu-Nan Gao, Xi Chen, Kaiqian Li, Yali Ma, Hailong Xiong, and Zhen-An Qiao*
State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun, Jilin
130012, People’s Republic of China
S
* Supporting Information
ABSTRACT: Here, we present a series of experimental studies to encapsulate ultrasmall gold nanoparticles into mesoporous
metal oxide via an in situ self-assembly method. Notably, the 2.0Au@mZnO catalyst (∼2.0 nm gold nanoparticles loading on
mesoporous ZnO nanospheres) shows excellent catalytic activity for indane oxidation (120 °C, conversion 88.5%) and affords
much high turnover frequencies (9521 h−1). The catalytic activity of these gold-based catalysts was found to be correlated with
the size of gold nanoparticles and the types of metal oxide supports. With a decrease in gold nanoparticle size, the catalytic
conversion efficiency of indane oxidation increased. In addition, such catalysts possessed high thermal and chemical stability and
could be reused more than 10 times without a remarkable loss of catalytic activity.
reported that Au nanoparticles (Au NPs) with sizes in the
range of 2−5 nm show unusually excellent catalytic activities.18
However, Au NPs tend to grow or aggregate into larger
particles under high-temperature treatment, which is a critical
issue in stabilizing ultrasmall Au NPs.19 In addition, as many
important catalytic processes require high reaction temper-
atures, the poor thermal stability of gold-based catalysts
obstructs their use in real-world catalysis; therefore, improving
their thermal stability is also urgent.20−22
Loading small Au NPs on oxide supports by an
impregnation method to stabilize the size of metal particles
has been the most commonly used method.23−31 Among
various oxide supports, mesoporous metal oxides have been
found to be the most helpful promoters in the catalytic
reactions, because of fast mass transfer and confinement effect
for loading particles.32−36 Unfortunately, this simple loading of
Au nanoparticles makes gold easily aggregate because of strong
Brownian motion, leading to a serious decrease in catalytic
activity.19,37 So far, there is an urgent need to find an efficient
and simple approach to stabilize ultrasmall gold nanoparticles.
INTRODUCTION
■
Metal-catalyzed C−H activation reactions are strategies for
achieving highly valuable and structurally complex products
from cheap, simple, and readily available organic substrates.1−3
The selective oxidation of C−H bonds is a primary
transformation in organic chemistry.2−6 In general, various
oxidants, such as halides,7 tert-butyl hydroperoxide,8 hydrogen
peroxide,9,10 and O22 or ozone,11 have been used for oxidation
of C−H reactions. There is no doubt that O2 is one of the
most universal and environmentally friendly oxidants among
those oxidants. However, the high C−H bond dissociation
energies of hydrocarbons make it is difficult for oxygen
molecules to oxidize the C−H bonds of hydrocarbons.
Therefore, the development of selective oxidation of C−H
bonds with O2 as oxidant is still the greatest challenge in this
field.
During the past few decades, various metal-based catalysts
(such palladium-based catalysis,12 Au−Pd alloy catalysis13,14
)
have been studied for aerobic oxidation. Among those
materials, nanosized gold-based materials are considered as
being the most promising for C−H activation reactions, due to
their extraordinary catalytic activity and resistance to poisoning
by chemical groups and oxygen.15−17 Haruta and co-workers
Received: August 2, 2018
© XXXX American Chemical Society
A
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Figure 1. TEM images of different sizes of Au NPs (2.0 0.3 nm (a), 2.5 0.3 nm (b), 3.0 0.3 nm (c)) and the corresponding UV/vis spectra
(d).The insets in (a)−(c) in each image are the size distributions of Au NPs.
Scheme 1. Schematic Illustration of the Synthetic Procedure for Au NPs@mMOx Nanospheres
0.023 M Zn(NO3)2, and 18 mL of a 0.047 M hexamethylenetetramine
(HMT) solution. Then the mixture solution was reacted at 85 °C for
8 h. The as-synthesized products were separated by centrifugation at
10000 rpm. The obtained products were washed with ethanol and
distilled water several times and then dried at 70 °C overnight. The
as-synthesized samples were calcined in air at 300 °C for 2 h at a
heating rate of 2 °C min−1. The obtained samples with different gold
sizes were denoted 2.0Au@mZnO, 2.5Au@mZnO, and 3.0Au@
mZnO, respectively. 2.0Au@mCeO2 and 2.0Au@mCuO catalysts
were synthesized in the same way (cerium nitrate or copper nitrate
was used as a precursor).
In this work, we develop a series of high-performance
heterogeneous catalysts by encapsulating ultrasmall Au NPs on
mesoporous metal oxides via an in situ self-assembly method.
The separated Au NPs were tightly anchored on the inner
walls of the mesoporous metal oxides and were successfully
stabilized by interface and space confinement effects. In
comparison with the impregnation approach, the encapsulated
Au NPs via the self-assembly method exhibited much higher
activity and stability. In particular, the obtained 2.0Au@mZnO
(2.0 nm Au NPs loaded on mesoporous ZnO) turned out to
be highly active in the oxidation of indane (conversion 88.5%,
TOF 9521) with molecular oxygen as the oxidant. Moreover,
these catalysts present excellent thermal stability and can be
subjected to long-term high-temperature treatment at temper-
atures up to 500 °C. In addition, we further investigate the
effect of the gold nanoparticle size and the support species on
catalytic activity.
RESULTS AND DISCUSSION
■
In the first phase of our work, Au NPs with different sizes were
synthesized according to the literature.38,39 Figure 1a−c shows
transmission electron microscopy (TEM) images of the 2.0 nm
(Figure 1a), 2.5 nm (Figure 1b), and 3.0 nm (Figure 1c) Au
NPs synthesized in this work. UV/vis spectra of the Au NPs
with different sizes dispersed in chloroform all exhibit the
characteristic Au absorption between 520 and 530 nm (Figure
1d). Then Au NPs were assembled within mesoporous ZnO
nanospheres by an in situ self-assembly method. The synthetic
protocol is represented in Scheme 1. First, organic-ligand-
protected Au NPs were encapsulated in the hydrophobic core
of hexadecyl trimethylammonium bromide (CTAB) micelles.
Then CTAB serves as a bridge for the in situ formation of
EXPERIMENTAL SECTION
■
Au NPs were dispersed in 5 mL of chloroform with a concentration of
6.7 mg/mL. Then 0.1 mL of the gold solution in chloroform was
added to 20 mL of CTAB aqueous solution (0.055 M) with vigorous
stirring. Then the solution was aged at 60 °C for 10 min with stirring
to remove the chloroform, giving a clear black Au@CTAB solution.
The resulting mixture was mixed with a solution of 270 mL of water,
18 mL of 0.025 M ascorbic acid, 36 mL of 0.023 M CTAB, 36 mL of
B
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Figure 2. TEM images of 2.0Au@mZnO before calcination (a) and after calcination at 300 °C (b). Mapping and EDX of 2.0Au@mZnO after
calcination at 300 °C (c, d). XRD patterns (e) and TG analysis in air (f) of 2.0Au@mZnO after calcination at 300 °C (0.3 wt % loading rate of Au
NPs).
Figure 3. TEM images (a, b) and XRD patterns (c) of 2.0 Au@mZnO after calcination at 400 and 500 °C. N2 adsorption−desorption isotherms
(d) of a 2.0Au@mZnO sample after calcination at different temperatures (inset in (d) is the corresponding pore size distribution of samples; 0.3 wt
% loading rate of Au NPs).
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mesoporous ZnO around Au-CTAB. As shown in Figure 2a, a
TEM image of the representative 2.0Au@mZnO reveals that
the individual Au NPs are homogeneously distributed
throughout the zinc oxide nanosphere. As we all know, thiolate
ligands negatively affect the catalytic activity of gold due to a
simple site-blocking effect of the ligands between the reactant
molecules and active gold atoms.37 In this study, the organic
ligands and surfactant in the sample were removed by
calcination at 300 °C in air. Figure 2b shows that the size of
Au NPs has a slight range of 2.0−3.1 nm after removal of the
ligands. Energy dispersive X-ray (EDX) and element mapping
measurements of the 2.0Au@mZnO sample shows the
coexistence of Au, Zn, and O signals throughout the
nanospheres (Figure 2c,d). No characteristic peaks of gold
were observed in the X-ray diffraction (XRD) patterns, which
further confirmed that gold still maintains a small size (Figure
2e). Thermogravimetric analysis (TGA) in air performed on a
calcined sample indicates that the organic molecules were
burned completely (Figure 2f). These analyses clearly indicate
that gold nanoparticles were successfully stabilized by the
mesoporous ZnO nanospheres after removal of the protective
organic group through thermal treatment.
Furthermore, a series of tests for the 2.0Au@mZnO sample
after calcination at different temperatures were undertaken to
verify the thermal stability. The TEM images directly indicate
the evolution of 2.0Au@mZnO at different treatment temper-
atures (Figure 3a,b). As the calcination temperature increases
from 300 to 500 °C in air, the loaded Au NPs still maintained a
small size, which confirmed by the XRD patterns (Figure 3c),
HRTEM images, and corresponding Au NPs size distributions
(Figure S1). The slight pore expansion of zinc oxide
nanospheres might be due in part to the channel collapse
with the gradual growth of nanocrystals. On calcination of
2.0Au@mZnO nanospheres at 800 °C, the size of the gold
nanoparticles increased to 10−15 nm (Figure S2a), and sharp
gold diffraction peaks were observed in the corresponding
XRD pattern (Figure S2b). Figure 3d and Figure S2c.d present
the N2 adsorption−desorption isotherms and corresponding
pore size distribution curves for 2.0Au@mZnO nanospheres
with different calcination temperatures. The isotherm of these
samples shows a type IV curve with distinct capillary
condensation steps, indicating the presence of uniform
mesopores. At relatively low pressures (0.2−0.4) the
adsorption curves of these samples exhibit an apparent
capillary step, suggesting the presence of a pore size of about
2.2 nm. The isotherm has a hysteresis loop at a relative
pressure of 0.5−0.8, which indicates the existence of larger
mesopores (6.1 nm) as calculated by the Barrett−Joyner−
Halenda (BJH) method. With an increase in the calcination
temperature, the surface areas of samples calculated by the
Brunauer−Emmett−Teller (BET) decreased gradually from
159 to 27 m2 g−1, and the corresponding pore volumes
decreased from 0.6 to 0.083 cm3 g−1.
in Figure S5. The N2 sorption isotherms of 2.0Au@mCeO2
and 2.0Au@mCuO samples show type IV isotherms,
suggesting the presence of mesopores (Figure S6). The surface
areas of 2.0Au@mCeO2, and 2.0Au@mCuO after calcination
are 110 and 20 m2 g−1, respectively. Regrettably, the
calcination temperature had a dramatic effect upon the surface
areas of mesoporous CuO (decreased from 119 to 20 m2 g−1),
which may affect the mass transfer rate during the catalytic
process.
We chose solvent-free oxidation of indane as a model
reaction to investigate the catalytic activity of 2.0Au@mZnO
using molecular oxygen as an oxidant under atmospheric
pressure. Catalytic performances of samples are given in Table
1. No products were obtained when the reaction was run for
Table 1. Oxidation of Indane Catalyzed by Gold-Based
a
Catalysts
product selectivity
(%)
1-
1-
TOF
(h−1
conversion
(%)
catalyst
mZnO
indanol indanone T (°C)
)
1
2
3
80
80
2.0Au@
mZnO
63
31
80
453
6.2
4
5
6
76
73
64
21
26
35
100
100
100
5.7
8.2
62.6
mZnO
2.0Au@
mZnO
2.0Au@
mZnO
2.0Au@
mZnO
8582
9521
7
8
9
10
60
120
120
120
120
120
120
88.5
b
2.5Au@
mZnO
66
60
17
9
32
31
64
56
7820
7574
4157
6302
78.3
67.8
45.6
76.4
10 3.0Au@
mZnO
11 2.0Au@
mCuO
12 2.0Au@
mCeO2
a
The accurate amount of substrate was calculated by weight. TOF =
[reacted mol of substrate]/ [(total mol of metal) × (reaction time)].
The TOFs were measured after the first 2 h of reaction. Reaction
conditions unless specified otherwise: indane 5 mL, catalyst 10 mg
(all the catalyst after 300 °C calcined), O2 1 bar, reaction time 20 h.
b
Under a nitrogen atmosphere (0.3 wt % loading rate of Au NPs).
20 h at 80 °C without addition of any catalyst, giving evidence
that the auto-oxidation of indane by O2 cannot proceed
spontaneously (entry 1, Table 1). When it was catalyzed by the
mZnO sample alone, the oxidation reaction of indane at 80 °C
also did not produce any product (entry 2, Table 1). On
catalysis by 2.0Au@mZnO, 6.2% indane conversion was
afforded, and the main product was 1-indanone (entry 3,
Table 1). The above results show that 2.0Au@mZnO as a
heterogeneous catalyst indeed promoted the air oxidation of
indane. Notably, the conversion of indane was markedly
improved to 62.6% in 20 h when the reaction temperature was
increased to 100 °C (entry 6, Table 1). However, the blank
(entry 4, Table 1) and pure mZnO (entry 5, Table 1)
oxidationd only gave 5.7% and 8% indane conversion,
respectively, at 100 °C due to noncatalytic oxidation. It is
significant that the 2.0Au@mZnO catalyst reached a high
indane conversion value of 88.5% when the reaction
In order to prove the broad applicablility of this method,
mesoporous ZnO nanospheres as support to load gold
nanoparticles with the size of 2.5 and 3.0 nm have been
successfully prepared (the corresponding TEM images are
shown in Figure S3). The N2 sorption isotherms of mZnO,
2.5Au@mZnO, and 3.0Au@mZnO samples shows the
characteristic of type IV curves with similar capillary
condensation steps (Figure S4). In addition, we also
synthesized 2.0Au@mCeO2 and 2.0Au@mCuO nanospheres
by this method, and the corresponding TEM images are shown
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temperature was increased further to 120 °C (entry 7, Table
1). This conversion value of indane is noticeably higher than
that for other catalysts under the same reaction conditions
(Table S1). All of these results suggested that the reaction
temperature had a significant influence on indane oxidation. In
addition, no product was obtained when the indane oxidation
reaction was carried out under an N2 atmosphere, indicating
that O2 is actually important in the reaction (entry 8, Table 1).
In order to study the surface chemical composition and the
oxidation state of the catalysts, X-ray photoelectron spectros-
copy (XPS) spectra for the Au 4f and O 1s core levels of the
mZnO and 2.0Au@mZnO samples were recorded (Figure 4a−
complexes with aromatic rings, can trigger some aerobic
oxidation.41−43 For indane oxidation, the rate of O2
•−
superoxide generation increased in the presence of 2.0Au@
mZnO as catalyst. In this process, the organic hydroperoxides
further decomposed into 1-indanol/1-indanone as the reaction
time increased. On the basis of the 2.0Au@mZnO character-
ization and the temporal variation of the product distribution
for indane oxidation, a reasonable mechanism for the catalytic
reaction is described in Scheme 2.
Scheme 2. Proposed Reaction Pathway for the Oxidation of
Indane Using 2.0Au@mZnO as Catalyst at 100 °C
Then, we investigated the effect of the size of gold
nanoparticles on the catalytic performance of the Au@mZnO
catalyst. The results show that the catalytic activity decreased
in the order 2.0Au@mZnO > 2.5Au@mZnO > 3.0Au@
mZnO; the conversion values of indane are 88.5% (2.0Au@
mZnO), 78.3% (2.5Au@mZnO), and 67.8% (3.0Au@mZnO)
(entries 7, 9, and 10, Table 1). The XPS spectra of the O 1s
peaks of 2.5Au@mZnO and 3.0Au@mZnO are shown in
Figure S7. The atomic ratios of “reactive” oxygen species in
2.5Au@mZnO and 3.0Au@mZnO were 64.5% and 43.1%,
respectively. Overall, the calculation results suggested that with
an increase in particle size the oxygen vacancies in the catalyst
are decreased, which might be the reason 2.0Au@mZnO has
the highest catalytic activity in this work.
In addition, we also studied the effect of supports on catalyst
activity. The 2.0Au@mCuO and 2.0Au@mCeO2 catalysts also
achieved remarkably high TOFs (4157 and 6302 h−1) during
the oxidation of Indane (entries 11 and 12, Table 1). The XPS
spectra of the O 1s peaks of mCeO2, 2.0Au@mCeO2, mCuO,
and 2.0Au@mCuO samples are shown in Figure S8. We found
that the gold−support interactions resulted in a large number
of oxygen defect sites in the metal oxide support. The
interactions between gold and different types of supports lead
to different concentrations of surface oxygen species in the
support. The atomic ratio of “reactive” oxygen species in
2.0Au@mCeO2 and 2.0Au@mCuO catalysts are 59% and
30.4%, which are smaller than that in the 2.0Au@mZnO
sample. Furthermore, the surface areas of 2.0Au@mCeO2 and
2.0Au@mCuO are both lower than that of the 2.0Au@mZnO
sample, which might lead to slower mass diffusion/transfer in
the catalyst process. The concentrations of “reactive” oxygen
species atoms and the surface areas of these catalysts are
summarized in Table S2. The ratio of “reactive” oxygen species
in catalyst to the surface areas of supports might affect the
catalytic performance.
Figure 4. XPS spectra of the O 1s peaks of mZnO (a) and 2.0Au@
mZnO (b). XPS spectra of the Au 4f peak of 2.0Au@mZnO (c) (0.3
wt % loading rate of Au NPs).Time−activity profile for the indane
aerobic oxidations (d). Reaction conditions: indane 5 mL, 2.0Au@
mZnO 0.01 g, 100 °C, O2 10 mL min−1, stirring speed 1000 rpm.
c). The XPS spectra of the Au 4f7/2 core levels consists of three
bands, which can be assigned to Au+ Au3+, and Au0.40
Meanwhile, the O 1s spectrum was fitted into three peaks at
529.4, 531.2, and 533.1 eV, respectively. The peak at 529.7 eV
was ascribed to lattice oxygen atoms (O2−), the peak at 531.1
−
eV was ascribed to surface oxygen species (for example, O2 ,
O22−, O− “reactive” oxygen species), and the peak at 533.1 eV
was ascribed to chemisorbed water or carbonates.33 The
concentration of “reactive” oxygen species atoms of the
2.0Au@mZnO sample was calculated by integrating the peak
areas of different oxygen species. The results reveal that the
atomic ratio of surface oxygen species in mZnO nanospheres
increases from 30% to 69% after loading of 2.0 nm Au NPs.
These results can be rationalized by assuming the existence of
Au3+, Au+, and a large number of oxygen defect sites in the
2.0Au@mZnO sample due to electron transfer between Au
NPs and mZnO nanospheres. According to the literature, the
“reactive” oxygen species from defective sites have a great
influence on the catalytic oxidation process. The high ratios of
“reactive” oxygen species in ZnO might result in the
exceptional catalytic activity of the 2.0Au@mZnO catalyst.
Figure 4d shows the variation of the product distribution
•−
detected by GC-MS. The O2
superoxide which was
generated from O2, forming collisional charge transfer
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Figure 5. Reaction kinetics plots (a, c, d) and the Arrhenius plot (b) for the indane aerobic oxidations by gold-based catalysts with O2: (a, b)
2.0Au@mZnO 0.01 g; (c) 2.0Au@mCeO2 0.01 g; (d) 2.0Au@mCuO 0.01 g. Reaction conditions: indane 5 mL, 100 °C, stirring speed 1000 rpm.
C0 is the original concentration of the substrate and Ct the concentration of substrate at time t (0.3 wt % loading rate of Au NPs).
The rate constant k is shown in Figure 5a. The indane
oxidation reaction with 2.0Au@mZnO as catalyst showed a
relatively high k value of 0.014 0.061 h−1. According to the
Arrhenius equation ln k = −Ea/RT + ln A (k, rate constant; Ea,
apparent activation energy; A, pre-exponential factor), we
plotted ln k versus 1/T, where k is calculated by linearly fitting
the concentration curve of indane within the initial 300 min of
reaction at an indicated temperature. The Ea value for the
oxidation of indane is 35.5 kJ mol−1, this extremely low value
suggesting an easily initiated reaction (Figure 5b). When
indane oxidations were catalyzed by both 2.0Au@mCeO2 and
2.0Au@mCuO, k values of 0.02 0.035 and 0.019 0.056
h−1, respectively, were obtained (Figure 5c,d). In general, the
ability to reuse and recover the catalyst after the reaction is the
best advantage of heterogeneous catalysis.2 The 2.0Au@mZnO
catalyst is very stable and can be reused more than 10 times
without remarkable loss of activity for indane oxidation, and
the corresponding conversion rate was estimated to be ∼60%
(Figure S9). Figure S10 shows the XRD pattern, TEM and
SEM images, and N2 adsorption/desorption isotherm of the
2.0Au@mZnO sample after catalysis cycling experiments. We
can clearly observe that the sizes of the gold nanoparticles and
the surface compositions of catalysts undergo no obvious
changes. In consideration of these results, it is reasonable to
confirm that the gold-based catalyst is indeed useful in practical
heterogeneous catalysis.
Table 2. Oxidation of Hydrocarbons Catalyzed by 2.0Au@
mZnO
a
a
The accurate amount of substrate was calculated by weight. TOF =
[reacted mol of substrate]/ [(total mol of metal) × (reaction time)].
The TOFs were measured after the first 2 h of reaction. Reaction
conditions unless specified otherwise: substrate 5 mL, 2.0Au@mZnO
Given these encouraging results, we also investigated some
solvent-free oxidation reactions for other hydrocarbons to
extend the application range of the 2.0Au@mZnO catalyst.
Selective oxidation of tetralin to α-tetralol and α-tetralone is an
important process in the synthetic commercial production of
α-naphthol, pharmaceuticals, and agrochemicals (entry 1,
Table 2).43,44 Diphenylmethane can be oxidized to diphenyl-
methanone with a moderate conversion of 12% in 20 h,
possibly owing to a steric hindrance effect (entry 2, Table 2).
The 2.0Au@mZnO catalyst also has great functionality in the
b
10 mg, O2 1 bar, reaction time 20 h. Reaction conditions: substrate 5
c
mmol, CH3CN 5 mL, 2.0Au@mZnO 10 mg, O2 10 bar. Reaction
conditions: substrate 5 mL, 2.0Au@mZnO 10 mg, O2 10 bar, reaction
time 20 h (0.3 wt % loading rate of Au NPs).
oxidation reaction of the large molecule fluorene with high
selectivity (entry 3, Table 2). For the oxidation of cyclohexene
it afforded a high conversion (92%), with cyclohexen-1-one
and 2-cyclohexen-1-ol as the main products (entry 4, Table 2).
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■
In summary, we successfully synthesized high-performance
gold-based catalysts by an in situ self-assembly method. We
found that the catalytic activity of gold-based catalysts and the
atomic ratio of “reactive” oxygen species in the support
increases as the gold nanoparticle size decreases. The
interactions between gold and different types of supports
lead to different concentrations of surface oxygen species in the
support. In addition, during the catalytic reaction, our catalysts
exhibit excellent thermal stability and can be subjected to long-
term high-temperature treatment at temperatures up to 500
°C. All of these results indicate that Au NPs@mMOx
nanospheres are ideal environmental catalysts for industrial
applications.
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ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b02197.
HRTEM and TEM images, N2 adsorption−desorption
isotherms, XPS spectra of O 1s peaks and XRD patterns
of 2.0Au@mZnO, 2.5Au@mZnO, 3.0Au@mZnO,
2.0Au@mCeO2, and 2.0Au@mCuO samples, recycling
runs for the indane aerobic oxidations, concentrations of
oxygen species atoms and surface areas of all catalysts,
and indane oxidation catalytic activity with other
reported catalysts (PDF)
AUTHOR INFORMATION
Corresponding Author
* E-mail for Z.-A.Q.: qiaozhenan@jlu.edu.cn.
■
ORCID
Zhen-An Qiao: 0000-0001-6064-9360
Notes
The authors declare no competing financial interest.
(16) Dong, Z.; Wu, M.; Wu, J.; Ma, Y.; Ma, Z. In Situ Synthesis of
TiO2/SnOx-Au Ternary Heterostructures Effectively Promoting
Visible-light Photocatalysis. Dalton Trans. 2015, 44, 11901.
(17) Liu, B.; Kuo, C. H.; Chen, J.; Luo, Z.; Thanneeru, S.; Li, W.;
Song, W.; Biswas, S.; Suib, S. L. Colloidal Amphiphile-templated
Growth of Highly Crystalline Mesoporous Nonsiliceous Oxides.
Angew. Chem., Int. Ed. 2015, 54, 9061−9065.
ACKNOWLEDGMENTS
■
This work was supported by the Young Thousand Talents
Program and the National Natural Science Foundation of
China (Grant Nos. 21671073, 21621001, 21671074, and
21371067), and the “111” Project of the Ministry of Education
of China (B17020).
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