Photon Factory Activity Report 2005 #23Part B (2006)
Surface and Interface

9A/2004G285

Surface Structure of Cu Species by Modified TiO2 (110) Surface with Acetic
Anhydride Acid

Wang-Jae Chun1, 2, Yuichiro Koike5, Kaoru Ijima4, Keisuke Fujikawa3, Hidenori Ashima2, Masaharu
Nomura5, Yasuhiro Iwasawa6, and Kiyotaka Asakura1
1Catalysis Research Center Hokkaido University, Sapporo 001-0021, Japan, 2CREST, JST, Saitama
332-0012, Japan, 3Department of Quantum Science and Engineering, Hokkaido University, Sapporo060-8628, Japan, 4Department of Electronic Engineering, Yamanashi University, Kofu 400-8510,
Yamanashi, Japan, 5Photon Factory, Institute of Materials Structure Science, Tsukuba 305-0801,
Japan, 6Department of Chemistry, Graduate School of Science, The University of Tokyo, Tokyo 1130081, Japan
Introduction
The control of metal-oxide interface structure is a key
technology for developing a new catalyst because themetal-oxide interface structure governs the active site
structure and chemical properties.
As an approach we have successfully prepared highly
dispersed Cu3 trimer and Cu6 prism clusters on theTiO2(110) surface using an organometallic compound.[12] In the study, we have suggested that the DPM ligands
play an important role in preventing the Cu aggregationand creating the unique clusters. From the knowledge wehave expected that if the TiO2(110) surface is covered
with an organic molecule possessing a substituent atomwhich can covalently bound to Cu, the adsorbed organic
molecule layer on the surface may provide a stable
adsorption structure for Cu and prevent the diffusion ofCu species.
In this work we report the successful preparation ofmonoatomic Cu species on the pre-modified TiO2 (110)by adopting acetic anhydride and the Cu species surface
structure determined by Polarization-dependent Total
Reflection Fluorescence XAFS (PTRF-XAFS) technique.
Experimental
TiO2(110) crystals were cleaned by Ar ion sputtering atroom temperature, followed by annealing at 1000 K untila sharp (1 × 1) LEED pattern was obtained. The cleaned
surface was modified by adsorbing acetic anhydride withsaturation coverage at room temperature. 0.18 ML Cu wasloaded to the modified surface by vacuum evaporation ofCu wire. The prepared sample was designated ashereinafter.
PTRF-XAFSCu/AcOAc/TiO2(110)measurement was carried out with an in-situ PTRF-XAFS-8
measurement chamber (a base pressure of ca. 8 x 10 Pa)
and a Canberra 19-element SSD in a fluorescence modeat BL9A. XAFS analysis was performed with REX 2000
and FEFF 8. 0.
Results and Discussion
Fig. 1(a) shows the observed Cu K-edge PTRF-EXAFS
spectra of Cu/AcOAc/TiO2(110) in three orientations withreference compounds. First, there was no difference inamplitude intensity at three orientations. Second, theenvelopes of all EXAFS oscillations damp quickly
compared to that of Cu foil. It indicated that the nearest

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Users' Reportneighbourhoods of Cu could be oxygen atoms. The curve
fitting analysis assuming Cu-O interaction showed thatthe Cu-O bond distances in all orientations weredetermined about 0.194 nm. For the [110] direction, CuTi interaction was also evaluated because the direction
corresponds to the electric vector pointing to TiO2
substrate direction. But the contribution of Cu-Ti bond
did not found. The effective coordination numbers of allorientations, N, were found in the range of 2 ~ 3. No
significant difference in the ratio of N describes that thestructure of Cu species will be a symmetrical structure.
For deriving a detailed structure, an iteration method
using FEFF
code and areal-spacemodelstructure wasemployed.
Fig.
1(b)
shows
theproposedmodelstructure.
The Cu-O
bond distance Figure1 Observed Cu K-edge PTRFwas found at EXAFS of Cu/AcOAc/TiO2 (110)(a)and the proposed model structure (b)0.196 nm. The
bond angles of the Cu-O interaction to the surface normal
were θ = 54.7 and β = 42.6 degree. The nearest Cu-Ti
bond distance found at 0.364 nm proposed that thecontribution of Cu-Ti interaction in the observed EXAFS
is negligible. These results indicate that our new approach(surface-pre-modified method) can successively block thediffusion of metal species and provide monoatomic metalspecies without elaborate chemical syntheses.
References[1] Y. Tanizawa et al., J. Phys. Chem. B 107 (2003) 12917.
[2] Y. Tanizawa et al., J. Synchrotron.Rad. 8 (2001) 508.
*wchun@cat.hokudai.ac.jp