Photon Factory Activity Report 2005 #23 Part B (2006)
Chemistry

7C,9A/2005G030

Investigation of active sites on manganese supported on zeolite Y for catalyticoxidation with ozone
1

Hisahiro EINAGA*1, Masafumi HARADA2
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki
305-8569, Japan2
Department of Textile and Apparel Science, Faculty of Human Life and Environment,
Nara Women’s University, Nara 630-8506, Japan

Introduction
Manganese oxide catalysts are useful for ozone
decomposition and catalytic oxidation of VOC withozone in gas streams. Oyama and his co-workers havereported that the mechanism for O3 decomposition on
manganese oxide supported on γ-Al2O3 (denoted byMnOx/Al2O3), and that the reaction proceeds through twoirreversible steps, the adsorption of ozone on the catalyst
surface and the desorption of molecular oxygen (eqs. (1)(3)), where * denotes the surface site on the catalyst [1-3].
(1)
O3 + * → O2 + O*
(2)
O* + O3 → O2 + O2*(3)
O2* → O2 + *Thus, Mn acts as the catalytic active site for oxidation
reaction by forming oxygen species active for VOCoxidation. These reactions can be applied to the oxidationof various types of organic compounds [4, 5].
Recently, we found that Mn ion-exchanged zeolite Y(denoted by MnY) showed higher activity for thecatalytic oxidation of benzene with ozone compared withsupported manganese oxide catalysts, MnOx/Al2O3 andMnOx/SiO2. However, no information has been obtainedon the catalytic active sites for the reaction. We herein
report the X-ray absorption fine structure (XAFS)
spectroscopic studies to investigate the Mn structures
supported on Y-type zeolites.
Experimental
XAFS measurements were carried out on the Photon
Factory beam line BL-7C and BL-9A. MnY was preparedby a conventional ion-exchange method from an aqueoussolution containing Mn-acetates and NaY (Zeolyst,Si/Al= 5.1). Catalyst samples were dried at 383 K andpressed into thin self-supporting wafers with 20 mmφ indiameter and set in an in situ cell with polyimide film (DuPont-Toray Co., Ltd. Kapton 200H), which wasconnected to the flow-type reaction system. XAFS
spectra were recorded at a temperature of 296 K in N2flow. Data reduction was carried out by using Rigaku
REX-2000.
Results and Discussion
Figure1 shows the Mn-K edge EXAFS Fouriertransforms for the MnY catalyst before and after heat
treatment at 723 K in N2 flow. Only the peak for Mn-O
was observed for the sample before the heat treatment,

indicating that Mn was highly dispersed in the zeolite
catalyst. On the other hand, the peak probably ascribed toMn-Mn contribution appeared after the heat treatment at
723 K, along with the decrease of the peak due to Mn-O
contribution. Thus, highly dispersed species arediminished and aggreagated species were formed. TheEXAFS spectra were unchanged after subsequent heat
treatment at 723 K in O2 flow. This catalyst showedsteady-state activity for the oxidation of benzene to COx
without the release of organic byproducts under moderatecondition (343 K). We recently reported the structuralchanges of manganese supported on alumina duringozone decomposition [6]. Therefore, further investigation
is now in progress to clarify the structures of catalytic
active sites on MnY catalyst and their changes for duringozone decomposition.

Mn-OMn-Mn

Figure1 Mn-K edge EXAFS Fourier transforms of MnY
catalyst. (solid line) as prepared; (dashed line) after heat
treatment at 723 K in N2 flow.
References[1] W. Li et al., J. Am. Chem. Soc. 120, 9041 (1998).
[2] W. Li et al., J. Am. Chem. Soc. 120, 9047 (1998).
[3] R. Radhakrishnan et al., J. Catal. 199, 282 (2001).
[4] H. Einaga et al., J. Catal. 227, 304 (2004).
[5] H. Einaga et al., Appl. Catal. B 60, 49 (2005).
[6] H. Einaga et al., Chem. Phys. Lett. 408, 377 (2005).
*h-einaga@aist.go.jp

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