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

9C, 10B/2004G329

Comparative studies of reduction behavior of copper ions in CuMFI,CuAlMCM-41, and CuMCM-41 via heat treatment in vacuo
Atsushi ITADANI, Masashi TANAKA, Toshinori MORI, Haruka SHINOGI, Yasushige KURODA*,
Mahiko NAGAO
Okayama Univ., Tsushima-naka, Okayama 700-8530, Japan

XANES

EXAFS

XANES

aa

EXAFSbb

673 K

873 K

473 K

300 K

300 K

Magnitude

473 K

Absorption

300 K

Magnitude

Absorption

300 K

473 K

473 K

673 K

673 K673 K

873 K

873 K

873 K

8.96 8.98 9.00 9.02 0 1 2 3 4 5 6 8.96 8.98 9.00 9.02 0 1 2 3 4 5 6Energy / keVDistance /Energy / keVDistance /Figure 1: XANES and EXAFS spectra for (a) CuMFI and(b) CuAlMCM-41(IE).
XANES

EXAFS

a

XANES

a

EXAFS

bb

300 K

673 K

673 K

300 K
473 K

Magnitude

473 K

Absorption

473 K
300 K

Magnitude

Results and discussion
Figure 1 shows the XANES and EXAFS spectra forCuMFI and CuAlMCM-41(IE) after evacuation at varioustemperatures. For both samples evacuated at 300 K, aweak XANES band is observed at 8.978 keV, and thisband is assignable to the 1s–3d electronic transition of the2+divalent copper ion (Cu ). With increasing evacuation
temperature, two bands appear at 8.983 and 8.993 keV,which are due to the 1s–4pʌ and 1s–4pı electronic+2+transitions of Cu , respectively: the reduction of Cu to+
Cu . In the EXAFS spectra, a band due to back-scatteringfrom the nearest neighboring oxygen atoms is observed ataround 1.5 Å (no phase-shift correction) for the 300 Ktreated samples, and the intensity of the band slightly
decreases by evacuating the samples at highertemperatures. It was considered that the reduction
properties of the exchanged copper ions in these samples
are almost the same.
The XANES and EXAFS spectra of CuAlMCM-41(TI)
and CuMCM-41(TI) evacuated at various temperatures

are depicted in Fig. 2. For both samples evacuated at 300
or 473 K, the XANES band is observed at 8.978 keV; theexchanged copper ions take a divalent state. Afterevacuating these samples at above 673 K, quite prominent
features of spectra were found, compared with those for
CuMFI and CuAlMCM-41(IE); the new bands appear at8.981 and 9.005 keV (especially in CuAlMCM-41(TI)),
suggesting that the metallic copper species are formed in
CuAlMCM-41(TI) and CuMCM-41(TI). This fact issupported from the EXAFS spectra; the band at 1.5 Å isdrastically reduced in its intensity, and the first bandassigned to the metallic copper species appears newly at2.2 Å (no phase-shift correction). From these results, it2+
was found that the Cu species which were introduced byutilizing the template ion-exchange method are easily
reduced to the metallic copper and the size of formed
metal particles are different depending on the kinds ofmother MCM-41 samples.

Absorption

Introduction
Supported metal clusters inside the cages of molecularsieve hosts are expected to possess size-dependent
electronic properties and non-linear optical features. The
behavior of metal clusters in various reactions isdependent on their size and degree of homogeneous
distribution in the host matrix. Moreover, the formationof CuI species during the reduction of zeolites containing
CuII species is important for the catalytic activity, mainly
for the selective reduction of NOx[1], and for their
specific activity in N2 adsorption at room temperature[2].
Despite the intensive research in catalysis, theformation process of various kinds of metal clusters andemergence of different species during the reduction
process of metal ions confined in porous host materials is
still not well understood. Detailed understanding of thereduction process of copper ion in the samples will be
helpful in designing the other kinds of metal species inporous host materials, such as silver and gold ions, sincethese ions have the similar electronic structure in theouter shell and exhibit prominent catalytic features. In
this report, the changes in the state of copper ions in fourkinds of samples by heat treatment in vacuo have beenstudied by means of XAFS method. The samples used are
as follows; CuMFI (Si/Al=11.9), CuAlMCM-41(IE)(Si/Al=11.5), CuAlMCM-41(TI) (Si/Al=11.5), andCuMCM-41, where we used the symbols of “IE” and“TI” signifying ion-exchange and template ion-exchange.

300 K

473 K

673 K

673 K

873 K

873 K

873 K

873 K

8.96 8.98 9.00 9.02 0 1 2 3 4 5 6 8.96 8.98 9.00 9.02 0 1 2 3 4 5 6Energy / keVDistance /Energy / keVDistance /Figure 2: XANES and EXAFS spectra for (a)CuAlMCM-41(TI) and (b) CuMCM-41(TI).
Reference[1] M. Iwamoto et al., J. Chem. Soc. Chem. Commun.
1272 (1986).
[2] Y. Kuroda et al., J. Phys. Chem. B 103, 2155 (1999); Y.
Kuroda et al., Chem. Lett. 1580 (2004).
* kuroda@cc.okayama-u.ac.jp

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