Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

12C/2004G280

Characterization of the Rh/CeO2/SiO2 Catalyst for
Partial oxidation of Tar from Biomass
Tomohisa MIYAZAWA*1, Takeo KIMURA1, Jin NISHIKAWA1,Kazu OKUMURA2, Keiichi TOMISHIGE1, Kimio KUNIMORI1
1
Institute of Materials Science, Univ. of Tsukuba, Tsukuba Ibaraki 305-8573, Japan2
Department of Materials Science, Tottori Univ., Koyama-cho, Minami, Tottori 680-8552, Japan

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Rh species (Rh2O3 lattice), Rh-O (Rh2O3 lattice), and RhCe shells. And this Rh-Ce shell exhibits the interaction
between Rh and Ce. In addition, from the coordination
number of Rh-O and Rh-Rh, it is suggest that Rh wasoxidized and dispersed as two or three layers of Rh and O
atoms on the CeO2 support. From the results oftemperature-programmed reduction and oxidation
measurement, it was shown that the existence of Rh
species on CeO2 support enhanced the reducibility ofCeO2. And it can be corresponds to the higher reforming
activity of Rh/CeO2/SiO2. The result of EXAFS analysis
supports theses synergy between Rh and Ce.
8(a)63k x (k )420-2-4-6-8240468 -1
k / 10 nm

1012468 -1
k / 10 nm

1012(b)30203k x (k )Introduction
One of the promising methods of energy utilization ofbiomass is gasification to hydrogen and synthesis gas.
Biomass has been gasified at high temperature in theconventional process. Recently, our group has reported
that Rh/CeO2/SiO2 was very effective to the gasificationof biomass [1]. The performance of tar removal and thestability of Rh/CeO2/SiO2 were also much higher thanconventional methods, such as steam reforming Ni
catalyst, dolomite and or non-catalyst. We suggest thatthese high performances of Rh/CeO2/SiO2 are mainly due
to combination of high activity of reforming andcombustion caused by the synergetic effect between Rh
and CeO2. The results of temperature-programmed
reduction and oxidation support this suggestion. And in
this research, we have carried out the characterization ofRh/CeO2/SiO2 in order to confirm the interaction between
Rh and CeO2.
Experimental
The Rh/CeO2/SiO2 catalyst was prepared by incipient
wetness method using acetone solution of Rh(C5H7O2)3(Soekawa) and CeO2/SiO2 support. The loading amount ofRh was 1.2 mass%. After evaporating the acetone solvent,the catalyst was dried at 383 K for 12 h.
The catalyst was crushed and pressed to the disk (0.5mm, 10 mmφ) for EXAFS measurements. Oxide sample
was pretreated at 873 K under 30 cc/min O2 flow for 0.5 h.
Reduced sample was pretreated at 873 K under H2 flowfor 0.5 h following the same treatment of Oxide sample.
After treatment, the sample disk was transformed to themeasurement cell without exposing to air. Rh K-edge
EXAFS spectra were measured by transmission mode at
377 K. After back ground subtraction, k weighted EXAFS
functions were Fourier transformed into R space and thetwo or three-shell fitting were analyzed by curve fitting.
Results and Discussion
Fig. 1 shows the k3-weighted Rh K-edge EXAFS
oscillations for oxidized(a) and reduced(b) Rh/CeO2/SiO2.
From the fitting results of EXAFS data of reduced
catalyst, we could fit the spectrum only Rh-Rh species
and coordination number of Rh-Rh was around 12. And
the spectrum was very similar to that of Rh foil. This
result shows that almost all Rh exist as metal particles in
reduced Rh/CeO2/SiO2. And from the results of hydrogen
adsorption measurement, the size of the particles of Rh
metal was assumed about 7 nm. On the other hand, in thecase of oxidized Rh/CeO2/SiO2, we have use three-shellfitting to fit the spectrum by coordinated with longer Rh-

100-10-20-30-40
2Fig. 1. k3-weighted Rh K-edge EXAFS for Rh/CeO2/SiO2(a) Oxidized (b) Reduced
References[1] K. Tomishige, et al. Appl. Catal. A: Gen. 246 (2003) 103.
* tkmyzw@ims.tsukuba.ac.jp