Photon Factory Activity Report 2004 #22 Part B (2005)
Surface and Interface

9A/2003G248

Ce LIII-edge XANES Study on Valence of alumina-supported cerium oxide
Leny YULIATI, Tadashi HATTORI, Hisao YOSHIDA*.Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.

Experimental
Alumina-supported ceria samples were prepared byimpregnation method. Alumina was a reference catalyst
donated from the Catalysis Society of Japan, JRC-ALO-8,
which spesific surface area was 163 m2g-1. Alumina
support were impregnated with an aqueous solution ofcerium nitrate (Kishida), dried at 383 K in an oven overnight and calcined at 773 K in a flow of dry air for 5 h.
CeO2 and Ce(NO3)3 sample was commercially obtainedand employed as reference compounds.
The Ce LIII-edge XANES measurement was performedat room temperature in transmission mode (Ce > 1 mol%)and fluorescence mode (Ce < 1 mol%) at the BL-9A
station of KEK-PF, Tsukuba, Japan, with a Si(111)
double-crystal monochromator. Before recording XANES
spectra, the sample was pretreated with 100 Torr oxygenfor 1 h at 773 K, followed by evacuation for 1 h at 773 K.
Then the sample was sealed with a polyethelene film in adry atmosphere.
DR UV-vis spectra were recorded at room temperature
on a JASCO V-570 equipped with an integrating sphere
covered with BaSO4. Before recording a UV-vis spectrum,
the sample was pretreated like the one before recording
the XANES spectra. Thus, the sample was transferred tothe optical cell without exposure to atmosphere by using a
specially designed in-situ cell.
Results and discussion
For analysis of XANES spectra, Ce(NO3)3 is used asCe(III) reference and CeO2 is used as Ce(IV) reference.
XANES spectra of samples with low loading of Ce on
alumina support showed the dominant peak of Ce(III),
while high loading samples showed peaks similar to CeO2.
It is suggested that in the sample of low loading, Cewould be highly dispersed on the support and mainly
exist as Ce(III), while the Ce would mainly exist asCe(IV) cation like as CeO2 at high loading samples.

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Users' Report

The results from XANES spectra are in agreement withthose from DR UV-Vis spectra. High loading samplesexhibited a large band, where the absorption edge shiftedto shorter wavelength than that for CeO2 as results ofquantum size effect, suggesting that the Ce species inhigh loading samples would be nano-sized CeO2 particles.
Samples with low loading of Ce exhibited an absorption
band at 265 nm, which was assignable to Ce(III) species.1
These similar trends were also found in silica-supported
ceria samples.1 Even though in many cases Ce4+ would bedominantly exist due to its stability, we confirm here thatthe formation of Ce3+ is possible specially at low loadingof Ce, as also reported in some literatures.2-4
The deconvolution of XANES spectra was carried out
according to the method in the previous study.1 Fig 1
showed the comparison of Ce(III) ratio between
silica-supported ceria samples and alumina-supported
ceria samples. Among samples with the same loading ofCe (< 0.1 mol%), alumina-supported ceria samples
showed higher Ce(III) ratio than silica-supported ceria
samples did. The stabilization of Ce3+ may be related tothe strong interaction between ceria and alumina, whichlead the formation of CeAlO3.2,3100
80
Ratio of Ce3+

Introduction
Cerium atom in oxides usually exists as Ce(III) orCe(IV) and the ratio of them can be determined
quantitatively by XANES spectroscopy. In the previous
study, we examined series of silica-supported cerium
oxide samples and concluded that Ce atoms would mainly
exist as Ce(III) when they are highly dispersed on silica
support.1
In the present study, series of alumina-supported
cerium oxide samples were examined by Ce LIII-edge
XANES spectroscopy in order to obtain the ratio ofCe(III) and Ce(IV), and also to compare them to thesilica-supported ceria system.

b6040a2000.01

0.1

110Ce content / mol%Fig 1. The plot of Ce3+ ratio versus Ce content. The
samples are a) the Ce/SiO2 and b) Ce/Al2O3. The ratio
was determined by curve fitting analysis of Ce
LIII-edge XANES. The data on silica-supported ceria
samples were from ref. 1.
References[1] H.Yoshida et al., Mater. Trans., 45 (2004) 2062.
[2] J. Z. Shyu et al., J. Phys. Chem., 92 (1988) 4964.
[3] A. Piras et al., Appl. Catal. B., 28 (2000) L77.
[4] G. K. DasMohapatra, Mater. Lett., 35 (1998) 120.
* h-yoshida@esi.nagoya-u.ac.jp