The_Catalyst_Review_January_2024 - 19

Perovskite Oxide as a New Platform for Efficient Electrocatalytic Nitrogen Oxidation
Figure 1. Characterization of Sr0.9
Conversion of nitrogen into high value nitrogen
compounds such as nitrate (NO3
-) is an important
industrial process. In the case of nitrate, current
production pathways include the Haber-Bosch
and Ostwald oxidation processes which are highly
energy intensive and environmentally unfriendly.
Recently, the electrocatalytic nitrogen oxidation
reaction (NOR) has been found to be a potentially
viable alternative pathway. Unfortunately, the
kinetics of NOR process are extremely sluggish
due to low Faradaic efficiencies and NO3
- yield
rates. Herein, the authors explore the use of an
oxygen-vacancy-enriched perovskite oxide with
nonstoichiometric ratio of strontium and ruthenium
(denoted as Sr0.9
RuO3) as a NOR electrocatalyst,
which exhibits a high Faradaic efficiency (38.6%)
with a high NO3
- yield rate (17.9 μmol mg-1
h-1
These workers began by synthesizing Sr0.9
and SrRuO3 perovskite oxides with different
).
RuO3
contents of oxygen vacancies via modulating the
A-site deficiency. X-ray photoelectron spectroscopy
(XPS) measurements were then conducted to
investigate their chemical states and electronic
structures (Figure 1 a-c). To verify whether the
oxygen vacancies can promote the adsorption
of N2
molecules, N2
desorption (N2
out to verify the N2
temperature programmed
(Figure 1 f). As illustrated the Sr0.9
higher N2
to SrRuO3
of N2
XPS, EPR and N2
and activate N2
-TPD) experiments were carried
adsorption of these catalysts
RuO3
sample has
-TPD signal and larger peak area relative
, thus indicating its enhanced adsorption
. When these findings are combined with the
-TPD results, the authors suggest
that the higher amount of oxygen vacancies in
the Sr0.9
kinetics for NOR catalysis.
To verify the structural stability of the Sr0.9
RuO3 offer more active sites to adsorb
molecules, resulting in improved
RuO3
catalyst, XRD and XPS measurements of Sr0.9
were carried out before and after the NOR test.
Notably, the XRD characteristic peaks of the
Sr0.9
RuO3
RuO3
catalyst remained intact after the NOR
test). The valence state of metal elements in the
Sr0.9
RuO3
Figure 2. Characterization of Sr0.9
RuO3 perovskite oxide before and after
the NOR test. (a-c) High-resolution XPS spectra of Sr 3d, Ru 3p and O 1s,
respectively. (d) The percentages of lattice oxygen (OL), oxygen vacancy (OV),
surface oxygen (Osurf
) and adventitious oxygen (Oadv) obtained from the O 1s
XPS analysis.
RuO3 and SrRuO3
perovskite oxides. (a-c)
High-resolution XPS spectra of Sr 3d, Ru 3p and O 1s, respectively. (d) The
percentages of oxygen vacancies obtained from O 1s XPS analysis (at left axis)
and iodimetry analysis (at right axis). (e) EPR spectra. (f) N2TPD
curves.
RuO3 sample did not change after the reaction.
Moreover, the oxidation states of Ru sites and the
content of oxygen vacancies for Sr0.9
catalyst
show negligible change (Figure 2c and 2d), thus
indicating its high stability of oxygen-vacancyenriched
structures. In addition, DFT calculations
show that the oxygen-vacancy sites in Sr0.9
RuO3
oxidation to *N2
regulate the adsorption/desorption behaviors of
intermediates, where the thermodynamic barrier
of *N2
can
OH at the rate-determining
step is significantly decreased, thus resulting in
its enhanced NOR performance. Hui Z, Ziwei M,
Yunxia L, et al. (2023). Angew. Chem. Int. Ed., doi.
org/10.1002/anie. 202316097
The Catalyst Review
January 2024
19
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