The Catalyst Review April 2024 - 14

Experimental
Highly Selective Methane Photooxidation to CH3OH and HCHO over an Integrated Fe2O3/WO3
Heterojunction Greatly Promoted by Iron (III) Chloride
Figure 1. CH4
Methane (CH4
), the principal component
of natural gas, is considered a potential
alternative to unsustainable fossil fuels given
the discovery of abundant CH4
in shale. Although direct CH4
to CH3
resources
conversion
OH and HCHO can achieve both
energy and environmental benefits, harsh
reaction conditions are usually required
to activate CH4
and high kinetic barrier (439 kJ mol−1
due to its inert C−H bond
).
Herein, the authors report the selective CH4
photoconversion to CH3
FeCl3
OH and HCHO in
/water solution over an integrated
Fe2O3/WO3 heterojunction under 2 MPa CH4
at ambient temperature. Under optimized
experimental conditions, a high CH3
+ HCHO yield of 15.3 mmol g−1
O3
/WO3
h−1
OH
was
achieved with a high selectivity of 97.3%.
Preparation of Fe2
by impregnation of WO3
FeCl3
·6H2
O followed by calcination at
400°C for 2 h in air. Catalytic performance
studies of CH4
in FeCl3
/water solution using H2
as
the oxidant under mechanical stirring at
ambient temperature. All CH4
oxidation
experiments were carried out in a highpressure
reactor with a 150 W xenon lamp.
The catalysts being evaluated were prepared
using different FeCl3
·6H2O/WO3
noted in Figure 1b Fe/WO3
ratios. As
presented a
similar product yield to pure WO3
without
performance enhancement. In contrast, the
Fe2
O3/WO3 heterojunction showed a total
product yield of 2.65 and 4.2 times those of
pure WO3
and Fe2
that calcination treatment was essential for
performance improvement. To clarify the
underlying reasons for the largely enhanced
CH4
conversion performance over the
Fe2O3/WO3 heterojunction, detailed energy
band profile studies were carried out. In
addition, the corresponding CH4
to CHxCl4−x
pathways on the Fe2O3
conversion
/WO3
heterojunction was simulated using DFT.
The charge density difference (CDD) was
first calculated and plotted to explore the
mechanism on the electronic level (Figure 2).
The DFT data validates the high activity and
selectivity of the Fe2
for CH4
CH3Cl and CH2
conversion to CH3
Cl2
O3/WO3 heterojunction
OH and HCHO via
in situ formed Cl effectively activated CH4
and converted it to CH3
hydrolyzed to CH3
a high CH3
hydrolysis. Moreover, the
Cl/CH2
OH and HCHO, realizing
OH + HCHO selectivity of 97.3%.
Wenhao Z, Yongqing M, Chuhong Z, et al.
(2024), ACS Catal., 14, 3606−3615
14
The Catalyst Review
April 2024
Cl, which then
O3, respectively indicating
Figure 2. (a) O 2p PDOS of Fe2
of CH4
O3 and the Fe2O3/WO3
conversion to CHxCl4−x pathways on the Fe2O3/WO3
deficiency, respectively. (g) Optimized models of the *CH2
heterojunction. (b) DFT simulations
heterojunction. (c−e)
Optimized structures of the main intermediates. (f) CDD for the *CH3
on the Fe2O3/WO3
Cl intermediates
heterojunction. Blue and yellow represent electron accumulation and
Cl2
gray, pink, brown, and green balls represent O, Fe, W, H, C, and Cl atoms, respectively.
intermediates. Red, golden,
conversion were performed
O2
was accomplished
nanosheets with
aqueous solution over catalysts prepared using different FeCl3
conversion performance characterization. Product yield histograms (a) in
·6H2O/WO3
ratios and
(b) in 1 mM FeCl3 solution over varied catalysts. Investigations on (c) different FeCl3
concentrations and ion types, (d) CH4 pressure, (e) xenon lamp operating current, (f)
H2O2 amount, and (g) reaction time. (h) Curves of product selectivity vs time. (i) Recycle
tests. Error bars represent the standard deviation of three independent measurements.

The Catalyst Review April 2024

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