Photon Factory Activity Report 2022 #40 (2023)

BL-9C, BL-12C, AR-NW10A/2017G534, 2019G105

In situ XAFS characterization of Cr and Rh-incorporated Ceria(Cr0.19Rh0.06CeOz) during NO reduction with COSatoshi MURATSUGU*1, Satoru IKEMOTO1, Mizuki TADA1,2

Department of Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602,Japan.
2
Research Center for Materials Science (RCMS) & Integrated Research Consortium on
Chemical Science (IRCCS), Nagoya University, Furo-cho, Chikusa, Aichi 464-8602, Japan.
1

1 Introduction
The Cr and Rh-incorporated ceria (denoted as(Cr0.19Rh0.06CeOz)[1] showed an NO reduction activity
at 373 K. It afforded >99% NO conversion at 393 K
and >99% N2 selectivity at 473 K, which weresuperior to Rh0.04CeOz, Cr0.17CeOz, and CeO2,
respectively. (conditions: NO (0.5%), CO (1.0%), Ar(5.0%), and He (balance) with a total flow rate of
100 mL min−1 (GHSV = 6500 h−1)).[2] We
investigated the change in the oxidation states ofcomposed metal species in Cr0.19Rh0.06CeOz by insitu Ce LIII-edge, Cr K-edge, and Rh K-edge XAFSunder NO/CO flow and heating conditions tocomprehensively clarify the behavior of each metal
species in the NO reduction performance with CO.[2]2 Experimental
Ce LIII-edge and Cr K-edge XAFS were measured
in a transmission mode at the BL-9C station.
Ionization chambers filled with pure N2/He (70/30v/v) and pure N2 were used to monitor incident andtransmitted X-rays, respectively. Rh K-edge XAFS
was measured in a transmission mode at the AR
NW-10A station. Ionization chambers filled with pureAr and pure Kr were used to monitor incident andtransmitted X-rays, respectively.
In situ QXAFS measurements under NO flow/COflow during H2 reduction/O2 oxidation wereperformed as follows. Cr0.19Rh0.06CeOz was placedin an in situ temperature-controlled gas flow cell.
After pretreatment with N2 (100 mL min−1) at 573 Kfor 1 h, the cell temperature was decreased to 473 K
under N2 flow (100 mL min−1) for 60 min. After 10min, the QXAFS measurement was started. After 5min, the gas was changed to CO + N2 (5 + 95 mLmin−1) and the gas flow was held for 30 min. After 10min, the cell was flushed with N2 (100 mL min−1) for
20 min. Secondly, the gas was changed to NO + N2(5 + 95 mL min−1) and the gas flow was held for 30min. The gas was finally changed to N2 (100 mLmin−1), and the cell was cooled to room temperature.
3 Results and Discussion
Figure 1 (A(a), B(a), C(a)) show in situ Rh K-edge,
Ce LIII-edge, and Cr K-edge XANES spectralchanges of Cr0.19Rh0.06CeOz under CO flow.[2] The

Rh and Cr K-edge XANES spectra rapidly changed
within 5 min, suggesting that oxygen species in theCr component was consumed by the reaction withCO. On the other hand, the Ce LIII-edge XANES
spectra gradually changed over 30 min. Figure 1(A(b), B(b), C(b)) show in situ Rh K-edge, Cr K-edge,and Ce LIII-edge XANES spectral changes of
Cr0.19Rh0.06CeOz under NO flow.[2] All XANES
spectral change showed that all metal species wereoxidized, suggesting that the reduced Rh species
and Cr components and CeO2 surface were reoxidized by NO.
Together with in situ FT-IR spectral analyses of
Cr0.19Rh0.06CeOz under Co and NO treatments andkinetic analysis, Rh species acted as adsorption
sites for both NO and CO, and chromium oxides
played a role to the oxygen transfer from thecleaved NO to CO on the CeO2 surface. This effectwould promote the efficient NO reduction with CO
on Cr0.19Rh0.06CeOz at low temperature.

Figure 1. In situ (A) Rh K-edge XANES, (B) Cr Kedge XANES, and (C) Ce LIII-edge XANES spectraof Cr0.19Rh0.06CeOz (a) under CO flow and (b) underNO flow at 473 K.
References[1] S. Ikemoto et al., Phys. Chem. Chem. Phys. 21,20868-20877 (2019).
[2] S. Ikemoto et al., ACS Catal. 12, 431-441 (2021).
* smuratsugu@chem.nagoya-u.ac.jp