3D Gold-Modified Cerium and Cobalt Oxide Catalyst on a Graphene Aerogel for Highly Efficient Catalytic Formaldehyde Oxidation

Article abstract of DOI:10.1002/smll.201804415

A hard template method is used to prepare porous gold-doped cerium and cobalt oxide (Au-Ce_xCo_y) materials. A series of 3D Au-Ce _xCo_y/graphene aerogel (GA) composites is then fabricated by a facile heating method. The obtained catalysts possess a well-defined structure of ordered arrays of nanotubes and good performance in formaldehyde (HCHO) oxidation. The composition and surface elemental valence states of the catalysts are modulated by the Ce/Co molar ratio. The Au-Ce_xCo_y catalyst and graphene oxide sheets are well compounded within 60 s through a diamine cross-linker to form 3D Au-Ce_xCo_y/GA composites. In addition, the resulting catalyst of 3 wt% Au-Ce₃Co/GA achieves ≈55% conversion at room temperature and 100% conversion when the reaction temperature is raised at 60 °C. The synergistic effect between CeO₂ and Co₃O₄ promotes the migration of oxygen species and the activation of Au, which facilitates HCHO oxidation. The method used to prepare the 3D catalyst could be used to produce other catalytic materials with good replication of the template. In addition, these findings provide a simple method for rapid fabrication of catalyst/GA composites. The superior activity and stability of the 3D Au-Ce₃Co/GA catalyst make it potentially applicable in HCHO removal.

Full text of DOI:10.1002/smll.201804415

FULL PAPER
Catalytic Formaldehyde Oxidation
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3D Gold-Modified Cerium and Cobalt Oxide Catalyst
on a Graphene Aerogel for Highly Efficient Catalytic
Formaldehyde Oxidation
Jiafu Qu, Dongyun Chen,* Najun Li, Qingfeng Xu, Hua Li, Jinghui He, and Jianmei Lu*
treatment,[11] thermal catalytic oxida-
tion,[12] and photochemical degradation.[13]
Among these methods, the most attractive
approach to treat HCHO pollution is cata-
lytic oxidation to CO2 and H2O because
of its high removal efficiency and lack of
secondary pollution.
A hard template method is used to prepare porous gold-doped cerium and
cobalt oxide (Au-CexCoy) materials. A series of 3D Au-CexCoy/graphene aerogel
(GA) composites is then fabricated by a facile heating method. The obtained
catalysts possess a well-defined structure of ordered arrays of nanotubes
and good performance in formaldehyde (HCHO) oxidation. The composition
and surface elemental valence states of the catalysts are modulated by
the Ce/Co molar ratio. The Au-CexCoy catalyst and graphene oxide sheets
are well compounded within 60 s through a diamine cross-linker to form
3D Au-CexCoy/GA composites. In addition, the resulting catalyst of 3 wt%
Au-Ce3Co/GA achieves ≈55% conversion at room temperature and 100%
conversion when the reaction temperature is raised at 60 °C. The synergistic
effect between CeO2 and Co3O4 promotes the migration of oxygen species
and the activation of Au, which facilitates HCHO oxidation. The method used
to prepare the 3D catalyst could be used to produce other catalytic materials
with good replication of the template. In addition, these findings provide a
simple method for rapid fabrication of catalyst/GA composites. The superior
activity and stability of the 3D Au-Ce3Co/GA catalyst make it potentially
applicable in HCHO removal.
Oxide-supported noble metal catalysts
are reasonably efficient at HCHO
removal.[14,15] Various oxide-supported
noble metals have been used as catalysts
for HCHO oxidation, such as Pd/CeO2,[16]
Au/MnO2,[17]
Au/TiO2,[18]
Au/Co3O4-
CeO2,[19] Pd-Mn/Al2O3,[20] Ag/SiO2,[21] and
Au/ZrO2.[22] Some transition metal oxides
(Fe2O3, Co3O4, and MnO2) and rare earth
or composite oxides (CeO2 and LaFeO3)
have also been investigated for catalytic
oxidation of HCHO.[23–25] However, these
catalysts only show high catalytic activity
for HCHO oxidation above room tem-
perature. Comparatively, oxide-supported
noble metal catalysts show higher catalytic
activities for HCHO degradation than
other materials, possibly because of the interaction of the metal
with the support.
1. Introduction
Formaldehyde (HCHO) is the most common indoor air
pollutant emitted from building/decorative materials, unregu-
lated indoor smoking, textiles, and oil paints.[1–4] Prolonged
exposure to HCHO, even at concentrations of a few parts
per million, may lead to health disorders such as coughing,[5]
headaches,[6] nasal tumors,[7] eye and nose irritation,[8] and
cardiovascular disease.[9] Therefore, considerable effort has
been expended developing methods to treat HCHO pollution
to ensure human health. Typical existing HCHO elimination
methods include chemical and physical adsorption,[10] plasma
In recent years, porous materials have been attracting con-
siderable attention because of their controllable nanostruc-
ture, high surface area, and excellent thermal stability.[26–30]
Moreover, porous materials may possess numerous edges and
corners sites that promote the adsorption and activation of
reactants.[31] An et al. reported a simple method to synthesize
3D Pt/Co3O4 catalysts that exhibited good catalytic activity for
CO oxidation.[32] Zhou et al. synthesized CeO2 nanorods that
possessed high activity for CO oxidation because of their well-
defined reactive {001} and {110} facets.[33] Therefore, use of a
3D porous material as a catalyst for HCHO removal at room
temperature is an interesting prospect.
Graphene oxide (GO) has a 2D layer structure with surface
oxygen–containing groups and has been used in diverse fields
including catalysis, sensing, and biomedicine.[34–36] The appli-
cations of GO can be further expanded by developing com-
posites of 3D graphene aerogels (GAs) and nanoparticles.[37,38]
The oxygen-containing functional groups of GO endow it with
a strong affinity for nanoparticles, allowing nanoparticles to
be easily embedded into the graphene network.[39] In addition,
3D GAs with an open macroporous structure could be used
as a support for dispersed catalyst nanoparticles. The porous
J. Qu, Prof. D. Chen, Prof. N. Li, Prof. Q. Xu, Prof. H. Li, Prof. J. He,
Prof. J. Lu
Collaborative Innovation Center of Suzhou Nano Science and
Technology
College of Chemistry, Chemical Engineering and Materials Science
Soochow University
199 Ren’ai Road, Suzhou 215123, P.R. China
E-mail: dychen@suda.edu.cn; lujm@suda.edu.cn
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/smll.201804415.
DOI: 10.1002/smll.201804415
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Scheme 1. Schematic illustration of the fabrication of Au-CexCoy/GA.
structure of GAs could provide pathways to allow the access of
reactants to the catalyst particles.[40] Compared with powder cat-
alysts, GAs are easy to clean and recycle. These features make
3D GAs ideal support materials for use in catalysis.
The interaction between CeO2 and Co3O4 supports have been
proven to have extremely favorable effects on the migration of
oxygen species and activation of gold catalyst particles.[41] In this
article, a nanocasting method is used to prepare Au-CexCoy cat-
alysts with different ratios of CeO2 to Co3O4 as ordered arrays
of nanotubes by employing SBA-15 silica as a template. Au-
CexCoy/GA composites are then fabricated by a simple method
(Scheme 1). The catalytic activity of the obtained Au-CexCoy/GA
samples in the removal of HCHO is investigated.
TEM image of the hexagonally packed rings is displayed in
Figure S1 in the Supporting Information. The metallic gold
particles cannot be observed because of their low content and
small size. However, the presence of gold particles on the
Ce3Co support was confirmed by energy-dispersive X-ray spec-
troscopy (EDX) (Figure S2, Supporting Information) and X-ray
photoelectron spectroscopy (XPS). The Au content of the as-
prepared catalysts was estimated by inductively coupled plasma
atomic emission spectrometry and is listed in Table 1.
Microscopy images (Figure 1c) indicated that 3 wt%
Au-Ce3Co was loaded on the surface of graphene in the aerogel.
The 3D 3 wt% Au-Ce3Co/GA-50 sample possessed contin-
uous macropores and a wrinkled microstructure. The 3 wt%
Au-Ce3Co catalyst and GO sheets compounded together well
in the aerogel, as shown in the TEM image of the 3 wt%
Au-Ce3Co/GA-50 sample in Figure 1d. The ultrathin GO sheets
were observed in the aerogel, some of which were folded. Inset
in Figure 1d is a photograph of 3 wt% Au-Ce3Co/GA-50.
2. Results and Discussion
2.1. Preparation and Characterization of the Catalyst
A typical high-angle annular dark field scanning transmis-
sion electron microscopy (HAADF-STEM) image of Au-Ce3Co
is shown in Figure 2a. The elemental distribution and com-
position of Au-Ce3Co was confirmed by STEM EDX analysis.
Mapping images of Ce, Co, O, and Au elements indicated that
cobalt, cerium, and gold were uniformly distributed in 3 wt%
Au-Ce3Co. Further confirmation of the formation of 3 wt% Au-
Ce3Co was obtained from the high-resolution TEM (HRTEM)
image in Figure 2b. The HRTEM image revealed an interplanar
lattice spacing (white) of about 0.312 nm, which is consistent
with the (111) crystal facet of CeO2. The (220) crystallographic
plane of Co3O4 (lattice spacing of 0.282 nm) was also observed
clearly. Furthermore, bright diffraction rings were also observed
in the corresponding selected-area electron diffraction (SAED)
pattern (insert in Figure 2b), which also confirmed that CeO2
and Co3O4 were successfully synthesized. In addition, the
SEM EDX mapping of 3 wt% Au-Ce3Co/GA-50 is also shown
in Figure S3 in the Supporting Information; it was further
The hard template method was used to prepare the porous
Au-CexCoy materials.[42,43] Appropriate ratios of HAuCl4·4H2O,
Ce(NO3)3·6H2O, and Co(NO3)2·6H2O precursors solutions
were impregnated in the pores of 3D cubic SBA-15. The SBA-15
template was then removed by etching in NaOH solution.
The resulting catalysts were characterized by scanning elec-
tron microscopy (SEM) and transmission electron microscopy
(TEM) (Figure 1). The catalysts exhibited well-defined struc-
tures because they grew along the direction of the SBA-15 chan-
nels. A typical SEM image of the 3 wt% Au-Ce3Co catalyst is
shown in Figure 1a. The 3 wt% Au-Ce3Co catalyst possessed
a rod-like morphology, which indicates good replication of the
SBA-15 structure. The TEM image in Figure 1b shows that the
3 wt% Au-Ce3Co catalyst consists of ordered arrays of nano-
tubes. Hexagonally packed rings with a diameter of ≈10.5 nm
were observed in a cross-sectional image, further confirming
the nanotube array structure of the catalyst. A magnified
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Figure 1. a) SEM and b) TEM images of 3 wt% Au-Ce3Co. c) SEM and d) TEM images of 3 wt% Au-Ce3Co/GA-50. Insets: (c) enlarged view of 3 wt%
Au-Ce3Co/GA-50 and (d) a photograph of 3 wt% Au-Ce3Co/GA-50.
confirmed that 3 wt% Au-Ce3Co was loaded on the surface of
graphene in the aerogel.
that the pore sizes in the 3 wt% Au-CexCoy catalysts are almost
the same regardless of the ratio of Ce to Co. The pore sizes in
all catalysts are distributed between 3.0 and 4.0 nm with a peak
value at 3.8 nm. N2 absorption–desorption analyses of 3 wt%
Au-CeO2 and Au-Co3O4 were also conducted and the results
are shown in Figure S4 in the Supporting Information. It also
demonstrates the coexistence of mesoporous and nanoporous
structure.
The surface area and porous structure of 3 wt% Au-CexCoy
catalysts were performed by Brunauer–Emmett–Teller (BET)
and Barrett–Joyner–Halenda (BJH) methods using nitrogen
adsorption–desorption at 77 K; the results are presented in
Figure 3 and Table S1 in the Supporting Information. The
N2 adsorption–desorption isotherms for the catalysts were
consistent with Type-IV isotherms (Figure 3a). The narrow
hysteresis loops are typical of Type-IV isotherms, indicating
the existence of both mesoporous and nanoporous structures
in the 3 wt% Au-CexCoy catalysts.[19,41] The corresponding pore
size distributions are displayed in Figure 3b, which indicate
To further study the crystallinity and phase structure of the
catalysts, they were characterized by X-ray diffraction (XRD).
Figure 4a shows XRD patterns of the 3 wt% Au-CexCoy cata-
lysts with different Ce/Co molar ratios, and Figure 4b depicts
patterns of the 3 wt% Au-Ce3Co catalyst after composite for-
mation with GO to form 3 wt% Au-Ce3Co/GA samples with
different GA contents. The phase structures of 3 wt% Au-CeO2
and Au-Co3O4 were also characterized (Figure S5, Supporting
Information). The diffraction peaks indicated that the crystal-
line structures of CeO2 and Co3O4 were the cubic fluorite and
spinel phases, respectively. The indexed diffraction peaks were
consistent with standard values for CeO2 (JCPDS 43-1002) and
Co3O4 (JCPDS 43-1003). For cubic fluorite-structured CeO2,
the five peaks at 2θ 28.549°, 33.077°, 47.483°, 56.342°, and
59.090° were attributed to the (111), (200), (220), (311), and
(222) planes, respectively. Pure Co3O4 exhibited eight peaks
at 2θ 19.000°, 31.271°, 36.845°, 38.546°, 44.808°, 68.628°,
69.741°, and 77.338°, which were ascribed to (111), (220), (311),
(222), (400), (531), (442), and (533) reflections, respectively.
In Figure 4a, 3 wt% Au-CexCoy exhibited both the diffrac-
tion peaks of the CeO2 fluorite phase and those of the Co3O4
Table 1. Theoretical and measured Au contents of catalysts with
different Ce/Co molar ratios.
Ce/Co molar ratios
Catalysts
Au contents
Theoretical [%]
Actual [%]
0.99
1:1
1:3
1:5
3:1
3:1
3:1
3:1
5:1
Au-CeCo
Au-CeCo3
Au-CeCo5
Au-Ce3Co
Au-Ce3Co
Au-Ce3Co
Au-Ce3Co
Au-Ce5Co
3
3
3
1
2
3
4
3
0.90
0.85
0.36
0.75
1.12
1.54
1.21
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Figure 2. a) HAADF-STEM and b) HRTEM image of 3 wt% Au-Ce3Co. STEM EDX maps of c) Ce, d) Co, e) O, and f) Au. Insert: (b) SAED images of
3 wt% Au-Ce3Co.
spinel phase. The peaks broadened with decreasing Co content,
which was consistent with previous reports. The characteristic
peaks of both GO and 3 wt% Au-Ce3Co were observed for the
aerogel samples (Figure 4b). The peak from GO changed in the
aerogels because D400 reacts with GO. There were no marked
changes in the structure of 3 wt% Au-Ce3Co after combining
with GO, showing that Au-Ce3Co was loaded on the GA surface
without reaction. The intensity of the peaks from 3 wt%
Au-Ce3Co gradually weakened with decreasing Au-Ce3Co con-
tent of the aerogel.
in the catalysts. However, the high-resolution Au 4f spectrum
of 3 wt% Au-CexCoy (Figure 5a) revealed the presence of Au.
The binding energies of Au 4f7/2 were resolved into three states
at 84.0 0.2 eV, 84.7 0.2 eV, and 86.0 0.2 eV. The Au 4f7/2
signal is typically resolved into two peaks at about 84.0 0.2 eV
and 86.0 0.2 eV that are ascribed to Au0 and Au3+, respec-
tively. As for the peak at 84.7 0.2 eV, there are many reports
indicating the existence of Au+ because of the charge transfer
between Au and CeO2. Therefore, we assigned the peak at
84.7 0.2 eV to Au+.[44]
To examine the chemical composition of the composite
catalysts, XPS analysis was conducted; the results are illustrated
in Figure 5 and Figure S6 in the Supporting Information.
The survey spectra of 3 wt% Au-Ce3Co and 3 wt% Au-Ce3Co/
GA-50 (Figure S6, Supporting Information) contained the
expected peaks from Ce, Co, O, and C. No obvious Au peak
was observed in the survey spectra because of its low content
The deconvolution of the O 1s spectral region at
528.0–535.0 eV for the 3 wt% Au-CexCoy samples is shown
in Figure 5b. The O 1s spectrum could be decomposed into
two types of oxygen species centered at 529.3
0.2 eV and
531.1 0.2 eV, corresponding to lattice oxygen (O2−) and sur-
face oxygen or surface hydroxyl species (Os+OHs) in Au-CexCoy,
respectively.[45] This result indicates that surface oxygen species
Figure 3. a) N2 absorption–desorption isotherms and b) BJH pore size distributions for 3 wt% (1) Au-CeCo, (2) Au-CeCo3, (3) Au-CeCo5, (4) Au-Ce3Co,
and (5) Au-Ce5Co.
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Figure 4. XRD patterns of 3 wt% a) Au-CeCo, Au-CeCo3, Au-CeCo5, Au-Ce3Co, and Au-Ce5Co and b) 3 wt% Au-Ce3Co/GA samples with different GA
contents. “♦” and “*” refer to the crystalline phase of Co3O4 and CeO2, respectively. The “blue” and “red” line refer to the standard line of Co3O4 and
CeO2, respectively.
were present in the catalysts, which was mainly because of the
presence of both Ce3+ and Ce4+. Oxygen vacancies emerged
because of the existence of Ce3+ in the catalysts. These vacancies
can adsorb O2, which lowers the surface Gibbs energy, balances
the surface charge, and forms surface active oxygen species.
The Ce 3d spectra of the 3 wt% Au-CexCoy samples con-
tained eight peaks. The four peaks from Ce 3d3/2 at binding
energies of 917.1 0.2 eV, 907.3 0.2 eV, 903.6 0.2 eV, and
2.2. Catalytic Performance and Stability
The catalytic activity of 3 wt% Au-CexCoy with different Ce/Co
atomic ratios was investigated by determining their ability to
catalyze the oxidation of HCHO in an air atmosphere containing
50 ppm HCHO; the results are shown in Figure 6a. The concen-
tration of HCHO was monitored by a formaldehyde detector.
HCHO was fully oxidized to H2O and CO2 by all the catalysts
with different Ce/Co molar ratios as the reaction temperature was
increased. The 3 wt% Au-Ce3Co catalyst fully converted HCHO at
the lowest temperature. The activity of the catalysts first increased
and then decreased with increasing Ce/Co molar ratio. The cata-
lytic activities of 3 wt% Au/CeO2 and Au/Co3O4 are also shown in
Figure 6a; these catalysts oxidized HCHO completely at around
110 and 140 °C, respectively. In addition, the 3 wt% Au-Ce3Co
catalyst shows the highest turnover frequency (TOF) and turn-
over number (TON) of 0.39 h−1 and 0.065 (Table S2, Supporting
Information), suggesting that the catalyst has the highest activity.
To investigate the influence of Au content on HCHO conver-
sion, the activities of samples with different Au loading were
measured and are compared in Figure 6b. All the samples
‴
901.3 0.2 eV were assigned to u , u″, u′, and u; those at
898.4 0.2 eV, 889.3 0.2 eV, 885.3 0.2 eV, and 882.5 0.2 eV
‴
were ascribed to v , v″, v′, and v. The u′ and v′ signals were
assigned to Ce3+, which formed through the interaction of ceria
with the surrounding atoms.[45] This results also confirmed
the mixed valence state of Ce in the catalysts. The XPS survey
spectrum of 3 wt% Au-Ce3Co/GA-50 in Figure S6a in the Sup-
porting Information confirmed that 3 wt% Au-Ce3Co was
successfully loaded on the surface of GA. In addition, the Co
2p spectra showed two main peaks at 795.1 eV and 779.9 eV
(Figure S6b, Supporting Information). The spin-orbit splitting
energy between the two peaks was 15.2 eV, indicating that the
main phase of the catalyst surface is Co3O4.[41]
Figure 5. High-resolution XPS analysis of the Au 4f (left), O 1s (middle), and Ce 3d (right) regions for 3 wt% a) Au-CeCo, b) Au-CeCo3, c) Au-CeCo5,
d) Au-Ce3Co, and e) 3 wt% Au-Ce5Co.
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Figure 6. Catalytic activity of a) 3 wt% Au-CexCoy with different Ce/Co atomic ratios, b) Au-Ce3Co with various Au loading contents: (1) 0%, (2) 1%, (3)
2%, (4) 3%, and (5) 4%. c) HCHO oxidation by (1) 3 wt% Au-Ce3Co/GA-10, (2) 3 wt% Au-Ce3Co/GA-30, (3) 3 wt% Au-Ce3Co/GA-50, and (4) 3 wt%
Au-Ce3Co/GA-70. d) Stability of 3 wt% Au-Ce3Co/GA-50 during HCHO oxidation at 60 °C.
displayed high activity for HCHO oxidation with 100% conver-
sion achieved below 180 °C. The samples with 3 wt% Au exhib-
ited the highest activity, removing 100% of HCHO at 60 °C. The
activity of Ce3Co without Au was also measured; a temperature
as high as 180 °C was needed for 100% HCHO conversion.
Compared to the Ce3Co catalyst, the Au-Ce3Co catalysts show
the better performance for HCHO oxidation, which may be
due to the fact that the incorporation of gold make the surface
active oxygen desorb easier. In addition, increasing Au loading
content to ≈4 wt% results in a slight decrease in the catalytic
activity, which may be due to the aggregation. The catalytic per-
formance of 3 wt% Au-Ce3Co/GA with different mass ratios of
Au-Ce3Co to GO was also evaluated, as illustrated in Figure 6c.
The unsatisfactory catalytic results for the 3 wt% Au-Ce3Co/
GA-10 and Au-Ce3Co/GA-30 samples were caused by the low
contents of Au-Ce3Co in these samples. The 3 wt% Au-Ce3Co/
GA-50 and Au-Ce3Co/GA-70 achieved better performance in
HCHO oxidation, which was ascribed to the proper contents of
Au-Ce3Co and GO. The stability of 3 wt% Au-Ce3Co/GA-50 was
also measured (Figure 6d). The catalytic activity of 3 wt% Au-
Ce3Co/GA-50 was almost unchanged after being used at 60 °C
for 40 h, indicating its good stability for HCHO oxidation.
In addition, several catalysts of Au-based catalysts have been
compared in Table 2. As shown in the table, 3 wt% Au-Ce3Co/
GA-50 showed the better catalytic performance for HCHO
oxidation.[22,45,46]
synergistic effect between CeO2 and Co3O4. Moreover, oxygen is
further transferred to Au. HCHO oxidation is catalyzed by this
process because oxygen is activated and transferred to HCHO
from Au2O3.[41] The high activity of the catalyst can be attrib-
uted to the improvement of the oxygen migration rate driven by
the interaction between CeO2, Co3O4, and Au.
3. Conclusion
Porous Au-CexCoy materials were prepared using SBA-15-OH
as a hard template. The obtained Au-CexCoy materials were
ordered arrays of nanotubes with large surface area. The 3 wt%
Au-Ce3Co samples exhibited high catalytic activity, removing
100% of HCHO below 60 °C. The valence states and elemental
compositions of the catalysts strongly influenced their catalytic
performance. The 3 wt% Au-Ce3Co catalyst was then success-
fully loaded on the surface of GO to allow recycling of the
catalyst. The optimal mass ratio of 3 wt% Au-CexCoy to GO was
1:1; the HCHO conversion rate of this catalyst reached 100% at
Table 2. Activity comparison of the catalysts with the previously reported
Au-based catalysts for HCHO oxidation and T100 values (temperature for
100% conversion of HCHO).
Sample
Loading [wt%]
Cat. mass [mg]
Ref.
This work
[45]
T
100 [°C]
60
The proposed reaction mechanism for the enhanced cata-
lytic activity achieved by the 3 wt% Au-Ce3Co/GA-50 catalyst
is shown in Scheme 2. First, Ce2O3 is converted into CeO2
through interaction with O2. In the presence of Co3O4, oxygen
is continuously transferred from CeO2 to Co3O4 because of the
Au-Ce3Co/GA-50
Au/MnO2
3
2
60
100
50
90
Au/ZrO2-200
Au/Fe2O3
1
85
[22]
7.1
200
80
[46]
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Scheme 2. Schematic illustration of the reaction mechanism for HCHO removal by the 3 wt% Au-Ce3Co/GA-50 catalyst.
Subsequently, the 0.5 g SBA-15-OH was added into the above mixture
solution and evaporated at 70 °C for 6 h to remove the solvent. The
powder was heated at 300 °C for 3 h with heating rate of 5 °C min−1 in a
furnace. Finally, the product was dispersed in NaOH solution (35 mL, 2 m)
at 70 °C to remove the silica template. The obtained catalysts were
referred as Au-CexCoy (x/y indicates the Ce/Co molar ratios).
60 °C. The high activity and stability of the 3 wt% Au-Ce3Co/
GA composite catalyst increases its potential for application in
HCHO removal.
Preparation of Au-CexCoy/GA: Graphene oxide (GO) was synthesized
by a modified method using KMnO4, H3PO4, H2SO4 as the strong
oxidant.[34] And the Au-CexCoy/GA was synthesized by heating the
mixture solution. In brief, 15 mg GO was dispersed in 5 mL of deionized
water under ultrasound for 30 min to form a homogeneous solution.
Then 15 mg Au-CexCoy was added and stirred for 3 h and then 25 µL
D400 was dissolved in the mixture solution. Finally, the vessel filled with
the above mixture was immersed into oil bath and heated 90 °C for only
1 min. The formed sample was then subjected by freeze-drying treatment
and noted as Au-CexCoy/GA-50. A series of Au-CexCoy/GA with different
mass ratio of Au-CexCoy and GO were also fabricated by adjusting the
mass of Au-CexCoy, the mass ratio of Au-CexCoy was 10% (1.7 mg),
30% (6.4 mg), 70% (35 mg), and the acquired samples were named as
Au-CexCoy/GA-10, Au-CexCoy/GA-30, Au-CexCoy/GA-70, respectively.
Catalytic Oxidation of Formaldehyde: A fixed-bed reactor system
using 60 mg catalyst at atmospheric pressure was used to catalyze
HCHO oxidation. The mixed gas (50 ppm HCHO, balanced in air) was
introduced into the reactor. And the total gas flow rate was 20 mL·min−1
and the weight hourly space velocity of total gaseous reactant was
20 000 mL·h−1·g−1, and the concentrations of HCHO were analyzed by a
formaldehyde detector (formaldehyde meter, PPM-400 ST).
4. Experimental Section
Materials: EO20PO70EO20 (P123, where EO is poly-(ethylene oxide)
and PO is poly-(propylene oxide)) was purchased from Sigma-Aldrich.
Tetraethyl orthosilicate (TEOs), cerium tetranitrate, cobaltous nitrate,
hydrogen tetrachloroaurate (III) hydrate (HAuCl4·3H2O), potassium
permanganate, graphite flake, sodium hydroxide, phosphoric acid,
nitric acid, sulfuric acid, hydrochloric acid, hydrogen peroxide,
poly(oxypropylene)diamine (D400, average Mn = 400) were purchased
from Sinopharm Chemical Reagents Co., Ltd. (China). HCHO was
purchased from Messer Air Liquide, Ltd. (China).
Instrumentation: The TEM (FEI Tecnai G-20) with 200 kV acceleration
voltage, SEM (Hitachi S-4700), HAADF-STEM (FEI Tecnai F-20) were
used to observe the morphology and microstructures in the fabrication
process of Au-CexCoy/GA. XRD (X’Pert-Pro MPD) and HRTEM were
employed to analyze the crystal phase. The composition analyses of
Au-CexCoy/GA were performed in an XPS (ESCALAB 250Xi) and EDX
spectra which were obtained by a FEI Tecnai F-20 microscope. The
percentage of Au in catalysts were analyzed by inductively coupled
plasma (ICP) (ICAPTM Qc). BET surface area and pores structures
were measured by nitrogen adsorption–desorption curve using ASAP
2010 analyzer. The convention of HCHO was analyzed by formaldehyde
detector.
Preparation of SBA-15-OH: Silanol group–rich mesoporous silica
SBA-15 was synthesized by a hydrothermal method. Typically, 4.0 g of
block copolymer Pluronic P123 was dissolved in 130 mL of H2O and
20 mL of 37 wt% HCl at 38 °C under stirring. Then 8.32 g of TEOs was
added. Afterwards, the mixed solution was kept at 38 °C for 24 h under
stirring, followed by hydrothermal treatment at 110 °C for 24 h. Finally,
the as-obtained product was washed with deionized water, and dried
under vacuum at 80 °C for 12 h. For P123 template removal, 65 wt%
HNO3 (120 mL), 40 wt% H2O2 (40 mL), and the above powder (2 g)
were mixed in 1.0 L round-bottom flask and heated at 80 °C for 3 h
(CAUTION! The mixture is very corrosive and brown nitrogen oxide gas
is released °10 min after the final temperature is reached.). The released
gas was absorbed by NaOH solution. Finally, the product was filtered
and washed with water several times, whereafter, the white solid was
dried at 50 °C.
Preparation of Au-CexCoy: Porous Au-CexCoy materials were prepared
by one-step method using SBA-15-OH as a hard template. In a typical
synthesis, a certain amount of HAuCl4·4H2O (20 mmol L−1) solution was
adjusted by NaOH solution (1 mol L−1) to pH 7 and was then dispersed in
appropriate amounts of Ce(NO3)3·6H2O and Co(NO3)2·6H2O precursors
in ethanol and stirred at room temperature for 2 h. The different Ce/Co
molar ratios were obtained by a previous reported with slight modification.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
The authors gratefully acknowledge the financial support provided
by the National Key R&D Program of China (2017YFC0210901,
2017YFC0210906), National Natural Science Foundation of China
(51573122, 21722607, 21776190), Natural Science Foundation of
the Jiangsu Higher Education Institutions of China (17KJA430014,
17KJA150009), Science and Technology Program for Social Development
of Jiangsu (BE2015637), and project supported by the Priority Academic
Program Development of Jiangsu Higher Education Institutions (PAPD).
Conflict of Interest
The authors declare no conflict of interest.
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[23] Z. Fan, W. Fang, Z. Zhang, M. Chen, W. Shangguan, Catal.
Commun. 2018, 103, 10.
[24] Y. Li, Z. Fan, J. Shi, Z. Liu, W. Shangguan, Chem. Eng. J. 2014, 241,
251.
[25] R. Spinicci, M. Faticanti, P. Marini, S. De Rossi, P. Porta, J. Mol.
Catal. A: Chem. 2003, 197, 147.
[26] Y. V. Kaneti, J. Tang, R. R. Salunkhe, X. Jiang, A. Yu, C. W. Wu,
Y. Yamauchi, Adv. Mater. 2017, 29, 1604898.
Keywords
aerogels, formaldehyde oxidation, gold, metal oxides, SBA-15-like
Received: October 23, 2018
Revised: November 20, 2018
Published online:
[27] T. Sun, N. Shan, L. Xu, J. Wang, J. Chen, A. A. Zakhidov,
R. H. Baughman, Chem. Mater. 2018, 30, 1617.
[28] S. Wannakao, T. Maihom, K. Kongpatpanich, M. Probst,
J. Limtrakul, J. Phys. Chem. C 2016, 120, 19686.
[29] X. Fang, Z. Liu, M. F. Hsieh, M. Chen, P. Liu, C. Chen, N. Zheng,
ACS Nano 2012, 6, 4434.
[1] M. Böhm, M. Z. Salem, J. Srba, J. Hazard. Mater. 2012, 221–222, 68.
[2] J. Zhou, L. Qin, W. Xiao, C. Zeng, N. Li, T. Lv, H. Zhu, Appl. Catal.,
B 2017, 207, 233.
[3] B. Bai, J. Li, ACS Catal. 2014, 4, 2753.
[30] D. Gu, W. Schmidt, C. M. Pichler, H. J. Bongard, B. Spliethoff,
S. Asahina, Z. Cao, O. Terasaki, F. Schüth, Angew. Chem. 2017, 129,
11374.
[4] T. Salthammer, S. Mentese, R. Marutzky, Chem. Rev. 2010, 110, 2536.
[5] X. Sun, J. Lin, H. Guan, L. Li, L. Sun, Y. Wang, S. Miao, Y. Su,
X. Wang, Appl. Catal., B 2018, 226, 575.
[31] R. Richards, W. Li, S. Decker, C. Davidson, O. Koper, V. Zaikovski,
A. Volodin, T. Rieker, K. J. Klabunde, J. Am. Chem. Soc. 2000, 122, 4921.
[32] K. An, S. Alayoglu, N. Musselwhite, S. Plamthottam, G. Melaet,
A. E. Lindeman, G. A. Somorjai, J. Am. Chem. Soc. 2013, 135, 16689.
[33] K. Zhou, W. Xun, X. Sun, Q. Peng, Y. Li, J. Catal. 2005, 229, 206.
[34] J. Qu, D. Chen, N. Li, Q. Xu, H. Li, J. He, J. Lu, Small 2018, 14,
1800343.
[6] Z. Yan, S. Gong, L. An, L. Yue, Z. Xu, React. Kinet., Mech. Catal.
2018, 124, 293.
[7] L. Qi, B. Cheng, J. Yu, W. Ho, J. Hazard. Mater. 2016, 301, 522.
[8] W. K. Dong, P. W. Seo, G. J. Kim, S. C. Hong, Appl. Catal., B 2015,
163, 436.
[9] X. Yang, X. Yu, M. Lin, M. Ge, Y. Zhao, F. Wang, J. Mater. Chem. A
2017, 5, 13799.
[35] Y. Wang, C. Li, T. Wu, X. Ye, Carbon 2018, 129, 21.
[36] R. Li, L. M. Guiney, C. H. Chang, N. D. Mansukhani, Z. Ji, X. Wang,
Y. P. Liao, W. Jiang, B. Sun, M. C. Hersam, A. E. Nel, T. Xia, ACS
Nano 2018, 12, 1390.
[10] K. J. Lee, N. Shiratori, H. L. Gang, M. Jin, I. Mochida, S. H. Yoon,
J. Jang, Carbon 2010, 48, 4248.
[11] X. Zhu, X. Gao, R. Qin, Y. Zeng, R. Qu, C. Zheng, X. Tu, Appl. Catal.,
B. 2015, 170–171, 293.
[37] W. Han, L. Ren, L. Gong, X. Qi, Y. Liu, L. Yang, X. Wei, J. Zhong,
ACS Sustainable Chem. Eng. 2014, 2, 741.
[12] S. Rong, P. Zhang, Y. Yang, L. Zhu, J. Wang, F. Liu, ACS Catal. 2017,
7, 1057.
[38] B. Adhikari, A. Biswas, A. Banerjee, ACS Appl. Mater. Interfaces
2012, 4, 5472.
[13] Y. Feng, L. Ling, J. Nie, K. Han, X. Chen, Z. Bian, H. Li, Z. L. Wang,
ACS Nano 2017, 11, 12411.
[39] L. Xiao, D. Wu, S. Han, Y. Huang, S. Li, M. He, F. Zhang, X. Feng,
ACS Appl. Mater. Interfaces 2013, 5, 3764.
[14] B. B. Chen, X. B. Zhu, M. Crocker, Y. Wang, C. Shi, Appl. Catal., B
2014, 154–155, 73.
[40] W. Li, H. Zhang, J. Wang, W. Qiao, L. Ling, D. Long, Adv. Mater.
Interfaces, 2016, 3, 1500711.
[15] H. C. Wu, T. C. Chen, Y. C. Chen, J. F. Lee, C. S. Chen, J. Catal. 2017,
355, 87.
[41] B. Liu, Y. Liu, C. Li, W. Hu, P. Jing, Q. Wang, J. Zhang, Appl. Catal.,
B 2012, 127, 47.
[42] C. Y. Ma, Z. Mu, J. J. Li, Y. G. Jin, J. Cheng, G. Q. Lu, Z. P. Hao,
S. Z. Qiao, J. Am. Chem. Soc. 2010, 132, 2608.
[43] Y. Liu, B. Liu, Q. Wang, C. Li, W. Hu, Y. Liu, P. Jing, W. Zhao,
J. Zhang, J. Catal. 2012, 296, 65.
[44] S. Zhang, X. S. Li, B. Chen, X. Zhu, C. Shi, A. M. Zhu, ACS Catal.
2014, 4, 3481.
[45] X. Yu, J. He, D. Wang, Y. Hu, H. Tian, T. Dong, Z. He, J. Nanopart.
Res. 2012, 14, 1.
[46] C. Li, Y. Shen, M. Jia, S. Sheng, M. O. Adebajo, H. Zhu, Catal.
Commun. 2008, 9, 355.
[16] H. Tan, J. Wang, S. Yu, K. Zhou, Environ. Sci. Technol. 2015, 49, 8675.
[17] J. Chen, D. Yan, Z. Xu, X. Chen, X. Chen, W. Xu, H. Jia, J. Chen,
Environ. Sci. Technol. 2018, 52, 4728.
[18] X. Zhu, C. Jin, X. S. Li, J. L. Liu, Z. G. Sun, C. Shi, X. Li, A. M. Zhu,
ACS Catal. 2017, 7, 6514.
[19] C. Ma, D. Wang, W. Xue, B. Dou, H. Wang, Z. Hao, Environ. Sci.
Technol. 2011, 45, 3628.
[20] M. C. Álvarez-Galván, V. A. P. de LaO Shea, J. L. G. Fierro,
P. L. Arias, Catal. Commun. 2003, 4, 223.
[21] C. F. Mao, M. A. Vannice, J. Catal. 1995, 154, 230.
[22] Y. C. Hong, K. Q. Sun, K. H. Han, G. Liu, B. Q. Xu, Catal. Today
2010, 158, 415.
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2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim