Platinum- and CuOx-Decorated TiO2 Photocatalyst for Oxidative Coupling of Methane to C2 Hydrocarbons in a Flow Reactor

Article abstract of DOI:10.1002/anie.202007557

Oxidative coupling of methane (OCM) is considered one of the most promising catalytic technologies to upgrade methane. However, C₂ products (C₂H₆/C₂H₄) from conventional methane conversion have not been produced commercially owing to competition from overoxidation and carbon accumulation at high temperatures. Herein, we report the codeposition of Pt nanoparticles and CuO_x clusters on TiO₂ (PC-50) and use of the resulting photocatalyst for OCM in a flow reactor operated at room temperature under atmospheric pressure for the first time. The optimized Cu_0.1Pt_0.5/PC-50 sample showed a highest yield of C₂ product of 6.8 μmol h^?1 at a space velocity of 2400 h^?1, more than twice the sum of the activity of Pt/PC-50 (1.07 μmol h^?1) and Cu/PC-50 (1.9 μmol h^?1), it might also be the highest among photocatalytic methane conversions reported so far under atmospheric pressure. A high C₂ selectivity of 60 % is also comparable to that attainable by conventional high-temperature (>943 K) thermal catalysis. It is proposed that Pt functions as an electron acceptor to facilitate charge separation, while holes could transfer to CuO_x to avoid deep dehydrogenation and the overoxidation of C₂ products.

Full text of DOI:10.1002/anie.202007557

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
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Accepted Article
Title: Pt and CuOx decorated TiO2 photocatalyst for oxidative coupling
of methane to C2 hydrocarbons in a flow reactor
Authors: XIYI LI, Jijia Xie, Heng Rao, Chao Wang, and Junwang Tang
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202007557
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Platinum and CuOx-Decorated TiO2 Photocatalyst for Oxidative
Coupling of Methane to C2 Hydrocarbons in a Flow Reactor
Xiyi Li, [a] Jijia Xie, [a] Heng Rao, [b, c] Chao Wang, [a] and Junwang Tang*[a]
[a]
X. Li, Dr. J. Xie, C. Wang, Prof. J. Tang
Solar Energy & Advanced Materials Research Group, Department of Chemical Engineering
University College London
Torrington Place, London, WC1E 7JE (UK)
E-mail: junwang.tang@ucl.ac.uk
[b]
[c]
Dr. H. Rao
State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry
Jilin University
2699 Qianjin Street, Changchun, 130012 (China)
Dr. H. Rao
International Center of Future Science, Jilin University
2699 Qianjin Street, Changchun, 130012 (China)
E-mail: rao@jlu.edu.cn
Supporting information for this article is given via a link at the end of the document.((Please delete this text if not appropriate))
Abstract: Oxidative coupling of methane (OCM) has been considered
as one of the most promising and attractive catalytic technology to
upgrade methane. However, C2 products (C2H6/C2H4) from
conventional methane conversion have not yielded commercially due
to the competition from overoxidation and carbon accumulation at
high temperatures. Herein, we reported the co-deposition of Pt
nanoparticles and CuOx clusters on TiO2 (PC-50), and then used the
photocatalyst to demonstrate the first successful case of
photocatalytic OCM in a flow reactor operated at room temperature
and under atmospheric pressure. The optimized Cu0.1Pt0.5/PC-50
sample showed a highest yield of C2 product of 6.8 µmol h-1, at the
space velocity of 2400 h-1, two times higher than the sum of the activity
of Pt/PC-50 (1.07 µmol h-1) and Cu/PC-50 (1.9 µmol h-1), and it might
also be the highest among photocatalytic methane conversions
reported so far under atmospheric pressure. A high selectivity of 60%
to C2 was also comparable to the benchmark work of conventional
high temperature (>943K) thermal catalysis. It is proposed that Pt
functioned as an electron acceptor facilitating charge separation,
while holes could transfer to CuOx avoiding deep dehydrogenation
and overoxidation of C2 products. This work provides a new revenue
for photocatalytic methane upgrade.
However, it is difficult to activate or convert CH4 due to its inert
nature, including high C-H bond energy (439 kJ mol-1),
symmetrical tetrahedral geometry, low polarizability (2.84 × 10-40
C2·m2·J-1).[4] The introduction of oxygen and high temperature are
thus conventionally required to overcome the thermodynamic
barriers and increase the conversion. Such reaction conditions
inevitably produce the undesired while thermodynamically
favourable products, CO2 and graphitic carbon. This subsequently
leads to the low selectivity and low yield of C2 products, bringing
about a barrier to commercialization.
Photocatalysis, employing photons operated under mild
conditions instead of thermal energy, has been regarded as a
potential economic technology to break the thermodynamic
barrier in the direct conversion of methane. Thus, the harsh
reaction condition, overoxidation and deposition of coke could be
theoretically avoided. In the past two decades, a wide range of
products has been successfully obtained through photocatalytic
methane conversion, such as methanol,[5] ethanol,[6]
ethane/ethylene,[7] benzene,[8] syngas,[9] and so on in batch
reactors, but with very moderate efficiency due to the following
major causes. Firstly, the high recombination rate of photo-
induced carriers in the intrinsic semiconductor greatly limits their
quantum efficiency, thus resulting in a low conversion. Next, the
pristine photocatalysts with unmodified interface lead to poor
selectivity because of overoxidation by the extremely oxidative
photoholes in the valence band (VB) of the photocatalyst and the
lack of active centres. More importantly, the majority of
photocatalytic methane conversion reactions were carried out in
batch reactors, which is easy to run but is theoretically hard to
avoid overoxidation as the long residence time in the batch
reactor favours the thermodynamically stable products of CO2. In
addition, such a system is also challenging for scale-up.
Under the pressure of the decreasing reserves of crude oil,
natural gas (methane) is widely accepted as an alternative for fuel
and more importantly as a fundamental building block for
chemical synthesis.[1] So far, only indirect conversion of methane
via syngas (a certain ratio of H2 and CO) process reaches feasible
commercial-scale.[2] This multi-stage process is not only energy-
intensive, operated at a high temperature with high capital cost,
but also accompanied by substantial CO2 emission. Therefore,
there are manifest financial and environmental incentives to
explore the direct transformation of methane to value-added
chemicals under moderate conditions.
Herein, the co-modification of TiO2 (PC-50) photocatalysts by
Pt nanoparticles and CuOx clusters were investigated to
overcome the major drawbacks mentioned above for
photocatalytic OCM. Furthermore, a flow system was applied to
Among various direct transformation technologies, oxidative
coupling of methane (OCM) to ethane and ethylene has been
regarded as a promising route for the valorisation of methane.[3]
1
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10.1002/anie.202007557
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manipulate the residence time of the reactants at room
temperature and atmospheric pressure. The synergy of Pt and Cu
species on PC-50 led to an increased C2 (ethane and ethylene)
yield (6.8 µmol h-1), which was ca. 3.5 times higher than the parent
semiconductor PC-50. It is also the highest yield for C2 products
among all the photocatalytic methane conversion reported under
atmospheric pressure. The C2 selectivity of 60% was comparable
to the traditional thermal catalysis operated at high temperature
(>943 K). The active species have then been investigated by X-
ray photoelectron spectroscopy (XPS), Transmission electron
microscopy (TEM), Electronic paramagnetic resonance (EPR),
Photoluminescence (PL) spectroscopy, transient photocurrent
response and in-situ EPR.
displayed no extra peaks for copper or platinum species, which
was likely because of their low amount and/or high dispersion.[10]
The anatase structure could be further supported by the Raman
spectroscopy (Figure 1b). The typical Raman peaks for anatase
TiO2 were clearly observed at 144 cm-1 (Eg), 198 cm-1(Eg), 399
cm-1(B1g), 512 cm-1(A1g) and 639 cm-1(Eg), respectively.[11] Notably,
a slight blue shift and broadening of the 144 cm-1 Raman peak
was observed after the introduction of co-catalysts, in particular
Cu0.1Pt0.5/PC-50. This could be explained as the surface strain
after surface modifications.[12]
The photoabsorption properties of the as-prepared samples
were investigated by Ultraviolet-visible diffuse reflectance
spectroscopy (UV-Vis DRS). After the introduction of CuOx
clusters, the photo absorption enhanced in the range from 200 to
320 nm (Figure 2a). This was likely because of charge transfer
between oxygen and isolated copper(II) species and the charge
transfer in clusters.[13] The absorption edge remained almost
unchanged for all of the samples, indicating the intact band
structure of PC-50 and the little contribution from CuOx absorption.
The photocatalytic activities of the as-prepared samples for
OCM were evaluated in a flow system at room temperature and
under atmospheric pressure. It has been widely reported that the
photo-induced holes at the valance band of TiO2 tended to
promote the mineralize CH4 into CO2 through deep
dehydrogenation.[14] The valence band edge of CuO and Cu2O
were around 0.75 eV and 0.99 eV more negative (vs. NHE)
compared with TiO2, respectively.[15] It indicates a potential to C2
products rather than CO2 after the introduction of copper species,
because copper species were expected to accept the photo-
induced holes from TiO2 and dramatically lower their oxidation
potential. Moreover, CuII clusters as active sites has previous
observed to selectively oxidise methane in thermal catalysis.[16,17]
The optimum content of copper was first investigated (Figure 2b).
It exhibited the volcanic trend with an increasing weight
percentage of Cu and achieved the highest C2 yield over
Cu0.1/PC-50 (1.2 µmol h-1). This was probably because excessive
amount of CuO could act as the recombination center of photo-
induced electrons and holes,[18] more discussion will be given later.
After optimised Cu amount was obtained, Pt was added to
a
c
e
b
Cu 2p
Pt 4f
d
Cu2+
Cu+
Cu2+ : Cu+ = 5:1
955
950
945
940
935
930
925
82
80
78
76
74
72
70
68
Binding energy (eV)
Binding energy (eV)
f
facilitate charge separation as
a widely known electron
acceptor.[19] In order to test the photocatalytic efficiency at a
relatively harsh condition, we increased the space velocity from
1200 h-1 to 2400 h-1 and then the samples with bimetallic co-
catalyst were investigated (Figure 2c and Figure S8). The
conversion of methane was increased compared with the pristine
TiO2 while the yield of both C2 products and CO2 increased after
the co-deposition of Pt nanoparticles and CuOx clusters. This was
due to more available separated photo-induced carriers through
the efficient transfer of electrons and holes to Pt and CuOx
clusters, respectively. It should be noted that the selectivity to C2
products firstly increased compared with selectivity to CO2 with
the increasing Pt on the Pt and CuOx co-loaded samples.
However, over-increasing Pt would cause a reduction of both yield
and selectivity to C2 products. The yield of C2 products on the
optimised sample Cu0.1Pt0.5/PC-50 was 6.8 µmol h-1, more than 2
times higher than the sum of Pt0.5/PC-50 (1.07 µmol h-1) and
Cu0.1/PC-50 (1.9 µmol h-1), indicating the importance of the
synergistic effect. Moreover, the yield of CO2 only increased by
around 20% compared with PC-50, indicating the indispensable
role of CuOx clusters in shifting selectivity to C2. Remarkably, this
yield was about four times higher than the reported production
Figure 1. a) PXRD and b) Raman spectra of Cu0.1Pt0.5/PC-50, Pt0.5/PC-50,
Cu0.1/PC-50 and PC-50; c) Cu 2p XPS spectra of Cu2.0/PC-50; d) Pt 4f XPS
spectra of Cu0.1Pt0.5/PC-50; e) HR-TEM images of Cu0.1Pt0.5/PC-50; f) EDX
elemental mappings (Ti, Cu and Pt) of Cu0.1Pt0.5/PC-50.
TiO2 has been regarded as one of the benchmark
photocatalysts due to its intrinsically high stability and activity
under UV photons. Thus commercial anatase TiO2 (PC-50) was
selected as a starting substrate. Then Pt nanoparticles and CuOx
species were introduced by photodeposition and subsequent wet
impregnation method (for more details on material synthesis see
the SI). The as-prepared sample was marked as CuxPty/PC-50,
where x and y represented the nominal weight ratio of Cu and Pt
to PC-50, respectively. Cu0.1/PC-50, Pt0.5/PC-50 and PC-50 were
the reference samples.
The crystal structures of all the as-prepared samples were
indexed to anatase TiO2 (JCPDS no. 84-1286), as shown in
Powder X-ray Diffraction (PXRD) spectra (Figure 1a). After the
introduction of Pt and Cu, the PXRD spectra remained unchanged,
indicating the stable framework. Additionally, the spectra
2
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10.1002/anie.202007557
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b.
a.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
C2H6
C2H4
PC-50
Cu0.1/PC-50
Pt0.5/PC-50
Cu0.1Pt0.5/PC-50
200
300
400
500
600
700
800
/PC-50
/PC-50
/PC-50
/PC-50
/PC-50
.4
5
.1
.2
.3
Wavelength (nm)
.0
Cu0
Cu0
Cu0
Cu0
Cu0
7
6
5
4
3
2
1
0
c.
d.
C2H6
C2H4
selectivity
8
6
4
2
0
60
50
40
30
20
10
0
1
2
3
4
5
6
7
8
PC-50
Time (h)
Pt0.5/PC-50
Cu0.1/PC-50
Cu0.1Pt0.1C/PuC0-.510Pt0.5C/PuC0-.51P0t1.0C/PuC0-.15P0t1.5C/PuC0-.15P0t2.0P/Pt0C.5-5C0u0.1/PC-50
Figure 2. a) UV-DRS spectra of Cu0.1Pt0.5/PC-50, Pt0.5/PC-50, Cu0.1/PC-50 and PC-50; b) C2 Production of photocatalytic OCM over Cux/PC-50 (x = 0.05, 0.1, 0.2,
0.3, 0.4). (Reaction condition: O2 : CH4 = 1 : 240, GHSV = 1200 h-1, 10% of CH4, 365 nm LED 20 W,40 ℃); c) C2 production and selectivity of photocatalytic OCM
over Cu0.1Pty/PC-50 (y = 0.1, 0.5, 1.0, 1.5, 2.0 wt%), Cu0.1/PC-50, PC-50, Pt0.5/PC-50 and Pt0.5Cu0.1/PC-50; (Reaction condition: O2 : CH4 = 1 : 400, GHSV = 2400
h-1, 10% of CH4, 365 nm LED 40 W, 40 ℃); d) Stability test of photocatalytic OCM over Cu0.1Pt0.5/PC-50.
rate of C2H6 and C2H4 by photocatalytic methane conversion with
an irradiation of > 300 nm over different catalysts under
atmospheric pressure (Table S2). Given that some reactions in
Table S2 were non-oxidative coupling of methane, their yields
were relatively low due to the high thermodynamic barriers.[20] The
yield of C2 products over our optimised sample was also higher
compared with the partial oxidation of methane. Furthermore, the
selectivity towards C2 products of 60% was comparable to the
traditional catalysts (e.g. Li/MgO) operated at high temperature
(>943 K).[3,21] We also calculated the apparent quantum yield
(AQE) based on the methane conversion for Cu0.1Pt0.5/PC-50 and
PC-50. The AQE of Cu0.1Pt0.5/PC-50 (0.5% at 365 nm) was nearly
two times higher than that of PC-50 (0.25% at 365 nm), indicating
the higher utilization of light energy. The further adding of Pt led
to decreased C2 selectivity and increased CO2 yield with the
highest CO2 yield reaching 11.6 µmol h-1. We believe too many Pt
nanoparticles might lead to the excessive formation of O2·-, which
was the major component for overoxidation.[22] Accordingly,
Pt0.5/PC-50 only exhibited increased yield of CO2 while the lowest
yield of C2 products compared with PC-50. This resulted in the
highest selectivity to CO2 (ca. 80%) again due to the increasing
available photo-induced electrons for O2·- generation and strong
oxidative holes at the valence band of TiO2. The preparation order
of two co-catalysts was changed to observe its effect. Another
photocatalyst Pt0.5Cu0.1/PC-50 was thus prepared. Interestingly, it
showed a decreased C2 yield (4.7 µmol h-1) compared with
Cu0.1Pt0.5/PC-50, indicating that the deposition sequence of co-
catalysts also had an important influence on the performance. The
function of Pt was believed to accept photo-induced electrons and
help charge separation. If the CuOx clusterswere firstly deposited,
some of them would block the contact between Pt particles and
TiO2, leading to reduced charge separation effect, thus lower the
conversion and yield. It was noted that the yield of C2 products
over Cu0.1/PC-50 was lower than that of PC-50, while the yield of
CO2 was similar. As proved by the XPS results later, the copper
species in our samples was mainly CuO. Its conduction band (CB)
was 0.75 eV more positive than that of TiO2. Taking into account
the more negative VB of CuO than that of TiO2, some holes
transferred from the VB of TiO2 would recombine with the
electrons from the CB of TiO2 on the CuOx clusters. This could
lead to the decreased generation of methyl radicals, which would
have a more negative effect on the coupling to C2 species than
deep oxidation to CO2 because of the second-order nature of the
coupling reaction to C2 products.[23] While some remaining highly
oxidative holes with the O2·- formed by the remaining electrons
continued to proceed the overoxidation of methane to CO2. Thus,
the yield of CO2 exhibited nearly no change while the yield of C2
products decreased after single introduction of CuOx clusters,
indicating the important role of Pt nanoparticles for the synergistic
effect. Please note in our system, only ethane, ethylene and CO2
3
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as products could be detected by our GC equipped with a
methanizer unit and a FID detector (Figure S7). Thus, the C2
selectivity mentioned above was calculated based on the
measured products. No products could be detected when the
reaction was carried out in the absence of methane or without light
irradiation (Table S1). This confirmed that it was a photocatalytic
process with CH4 as the only carbon source.
The stability of the optimised sample Cu0.1Pt0.5/PC-50 was then
tested. No decay of C2 yield except slight fluctuation could be
observed during 8 h reaction (Figure 2d). The structure of
catalysts and the chemical states of active species also remained
unchanged during the reaction (Figure S5, S6). This indicated that
Cu0.1Pt0.5/PC-50 exhibited excellent stability under photocatalytic
OCM process.
365 nm LED illumination, the intensity of Cu(II) signal was
expected to decrease if it could accept electrons to form EPR
silent Cu(I) sites.[29] However, the spectrums under the chopped
a.
b.
25000
PC-50
Pt0.5/PC-50
Cu0.1/PC-50
Cu0.1Pt0.5/PC-50
20000
15000
10000
5000
0
400
500
600
700
800
Wavelength (nm)
c.
d.
XPS was then conducted to analyse the chemical states of co-
catalysts on the optimum catalyst (Figure 1c, d; Figure S2, 3). Due
to the extremely low loading amount of copper species, no clear
Cu 2p peak could be observed on Cu0.1Pt0.5/PC-50 (Figure S3).
Thus, a sample (Cu2.0/PC-50), prepared with the same procedure
but large loading amount of copper species, was used to identify
the chemical states of Cu on PC-50 (Figure 1c). The peaks
attributed to Cu 2p3/2 and Cu 2p1/2 at around 933.4 eV and 953.9
eV, coupling with the shake up satellite peak at around 942.6 eV,
indicated the main existence of fully oxidised CuO.[24] In addition,
a small amount of Cu(I) (Cu(II) : Cu(I) = 5 : 1) could be found with
peaks at 932.2 eV and 952 eV, respectively. It was believed that
similar species were formed on the best sample, Cu0.1Pt0.5/PC-50.
Compared with PC-50 and Pt0.5/PC-50, the binding energy of Ti
2p3/2 transition shifted to lower binding energy over Cu0.1/PC-50
and Cu0.1Pt0.5/PC-50 (Figure S2). The lower binding energy
suggested the electrons probably transferred from Cu to Ti,
indicating the interaction between the co-catalysts and PC-50.[25]
XPS analysis of Pt provided the peaks at 71.2 eV and 74.6 eV,
which was assigned to metallic states.[26]
TEM and HRTEM images were provided to further investigate
the particle size and distribution of Cu0.1Pt0.5/PC-50. Some
nanoparticles were dispersed on PC-50 with diameters from 3.5
to 6 nm (Figure S4). These nanoparticles were further identified
with HRTEM (Figure 1e), in which the d-spacing of lattice fringes
could be attributed to Pt (111, 0.226 nm) and anatase TiO2 (101,
0.350 nm), respectively.[27] The copper species have not been
observed at this resolution, suggesting the existence of smaller
clusters. The Energy Dispersive X-ray (EDX) mapping showed
that Cu and Pt dispersed homogeneously (Figure 1f), in good
agreement with the XRD results.
In order to further unravel the chemical state of copper species
and the charge transfer, in-situ EPR was carried out (Figure 3a).
Compared with Pt0.5/PC-50, Cu0.1Pt0.5/PC-50 exhibited new
spectra corresponding to CuO hyperfine structure owing to I = 3/2
of Cu(II), indicating the existence of Cu(II) in the copper
species.[28] Although the existence of long-range dipolar
interactions between different Cu(II) sites resulted in the
broadening of spectral lines, the anisotropic hyperfine structure
could be found after careful analysis. g‖ = 2.395 with A‖ ≈ 100 G
was obtained, while the value for g⊥ = 2.05 could not be resolved.
These resonance parameters were in agreement with the
distorted octahedral coordination of Cu(II) ions in CuO clusters.[29]
This result suggested the existence of a high distribution of CuO
clusters, which explained the invisible copper species in HRTEM.
This result was also consistent with the Cu 2p XPS analysis. Upon
Figure 3. a) EPR spectra of Cu0.1Pt0.5/PC-50 (light on and light off) and Pt0.5/PC-
50 (light on); b) PL spectra of Cu0.1Pt0.5/PC-50, Pt0.5/PC-50, Cu0.1/PC-50 and
PC-50; c) Photocurrent of Cu0.1Pt0.5/PC-50, Pt0.5/PC-50, Cu0.1/PC-50 and PC-
50; d) The proposed photocatalytic OCM process over Cu0.1Pt0.5/PC-50.
light were almost overlapped, indicating the photo-induced
electrons were trapped by Pt rather than the CuO sites as
presented in Figure 3d. Thus, the introduction of Pt was important
to impede the charge recombination on CuOx clusters, resulting
in improved performance of Cu0.1Pt0.5/PC-50.
The facilitation of charge transfer was further investigated by PL
spectra (Figure 3b). An obvious band could be observed for the
pristine PC-50, while the PL intensity decreased notably after the
incorporation of Pt nanoparticles. This suggested the efficient
separation of photo-induced electrons and holes by Pt
nanoparticles. In the case of Cu0.1/PC-50, a photoluminescence
spectrum with fine structure was shown, which could be attributed
to the highly dispersed copper species.[30] According to the UV-
vis DRS result, it was suggested that the photoexcitation occurred
by charge transfer from oxygen to copper in the clusters.
Considering the enhanced absorption in UV region observed in
UV-vis DRS spectra and the larger enhanced emission in the PL
spectra, the photo-induced carriers in PC-50 probably
recombined in the CuOx clusters over Cu0.1/PC-50. This was also
consistent with the analysis of the band structure mentioned
above and in Figure 3d. More importantly, the PL intensity of
Cu0.1Pt0.5/PC-50 was obviously lower than that of Cu0.1/PC-50,
indicating that the photo-induced electrons in PC-50 were
transferred to Pt rather than to the CB of CuOx clusters.
The function of Pt as an electrons sink was further consolidated
by the transient photocurrent response (Figure 3c). Compared
with pristine PC-50, Pt0.5/PC-50 exhibited higher reduction
photocurrent density because of the efficient transfer of electrons
to Pt nanoparticles. While the introduction of copper species
resulted in lower photocurrent response for both Cu0.1/PC-50 and
Cu0.1Pt0.5/PC-50. As mentioned above, the valence band of CuO
or Cu2O were less positive than TiO2. This decay of photocurrent
density could be explained by the weak oxidative potential of
photo-induced holes on CuOx clusters.[15]
Based on the above characterisations and investigations, a
probable mechanism of photocatalytic OCM over Cu0.1Pt0.5/PC-50
4
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was proposed (Figure 3d). Upon light irradiation, electrons could
be excited from the VB of PC-50 to its CB and then migrated to
Pt, while holes could be transferred to the VB of CuOx clusters.
This process not only retarded the recombination of photo-
induced electrons and holes, but also lower the oxidation potential
of photo-induced holes to avoid deep dehydrogenation and
overoxidation. The C-H bond in CH4 molecules was abstracted by
the holes in the VB of CuOx clusters to form methyl radicals and
protons. The combination of methyl radicals formed the ethane
molecules and the deep dehydrogenation could lead to the
formation of ethylene. O2 could be reduced by electrons from Pt
nanoparticles to form O2·- and the protons could be removed by
O2·- to form water. The synergy effects between Pt and CuOx
clusters at reduction sites and oxidation sites respectively were
highlighted to complete the catalytic cycle.
[10]
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Acknowledgements
X. Li, J. Xie, C. Wang and J. Tang are thankful for financial support
from RS International Exchanges 2017 Cost Share Award
(IEC\NSFC\170342), UK EPSRC (EP/N009533/1), Royal
Society-Newton Advanced Fellowship grant (NA170422) and the
Leverhulme Trust (RPG-2017-122). We are also thankful for the
EPR charaterisations from Yiyun Liu. X. Li would like to
acknowledge UCL PhD studentship (GRS and CRS). H. Rao is
thankful for the 111 Project (Grant No. B17020) and also
acknowledges the financial supports from the National Natural
Science Foundation of China (Grant No. 21905106).
Keywords: OCM • methane conversion • photocatalysis • flow
reactor • C2H4/C2H6
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10.1002/anie.202007557
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Pt nanoparticles and CuOx clusters co-decorated TiO2 for photocatalytic OCM in a flow system at room temperature and atmospheric
pressure has been achieved, resulting into the highest yield rate of 6.8 µmol h-1 to C2 hydrocarbons with excellent selectivity (60%)
operated at the space velocity of 2400 h-1.
6
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