日本ゼオライト学会 刊行物 Publication of Japan Zeolite Association

ISSN: 0918–7774
一般社団法人日本ゼオライト学会 Japan Zeolite Association
〒162-0801 東京都新宿区山吹町358-5 アカデミーセンター Japan Zeolite Association Academy Center, 358-5 Yamabuki-cho, Shinju-ku, Tokyo 162-0801, Japan
Zeolite 25(2): 67-74 (2008)
doi:10.20731/zeoraito.25.2.67

解説解説

ゼオライト細孔内ナノクラスターの調製,構造,触媒特性Preparation, structure, and catalytic properties of intrazeolite nanoclusters

島根大学総合理工学部物質科学科Department of Material Science, Shimane University ◇ 〒690-8504 島根県松江市西川津町1060

受理日:2008年2月22日Accepted: February 22, 2008
発行日:2008年6月10日Published: June 10, 2008
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ゼオライト細孔内に構築されたナノクラスターのサイズ,構造,物理的機能,触媒機能を制御するためには,それらの前駆体,中間体,調製されたクラスターとゼオライト間の相互作用すなわちホスト-ゲスト相互作用をそれぞれについて明らかにする必要がある。本解説では,ゼオライト細孔内モリブデン,コバルト,モリブデン-コバルト二元系硫化物クラスター,モリブデン酸化物クラスターを中心として,その構造,触媒作用に及ぼすゼオライト組成の影響,構造-触媒特性の関係についてまとめた。ゼオライト細孔内の金属硫化物クラスターのもつ特異な構造変化についても述べた。ゼオライトの組成,カチオン,細孔構造を選ぶことにより,触媒活性種を含め種々のナノクラスターの機能を制御できる可能性がある。

Zeolites offer finely tunable environment for the preparation of nanoclusters with well defined structure, that is, the nuclearity, structure, and catalytic properties of the intrazeolite nanoclusters can be controlled simply by modifying the pore structure, composition, and cation of the host zeolite. Thus the nanoclusters encaged in zeolites are expected to provide structureactivity correlations, which are of great importance in catalyst design, as well as novel catalytic systems including bifunctional catalysis. In the present review, we focus on metal sulfide nanoclusters encapsulated in zeolite pores from the view points of the preparation, structure, and catalytic properties. We stress here the importance of the host-guest interactions of precursors, intermediates, and product nanoclusters with the host zeolite. Hexacarbonyl molybdenum Mo(CO)6 was accommodated in the supercage of faujasite zeolite, followed by sulfidation. The thermal stability and reactivity of intermediate Mo subcarbonyl species, the precursors to Mo sulfide nanoclusters, are elucidated by the interaction strength with zeolite framework oxygen, the electron density of which is strongly modified by the Al/Si ratio and counter cation. The resultant structure of Mo sulfide nanoclusters thus depends on the composition of the host zeolite; Mo dinuclear sulfide clusters with a composition of Mo2S4 are formed when the Al/Si ratio is larger than 0.25, while MoS2 nanoclusters are produced when the ratio is lower than 0.25. The Mo-Mo atomic distance of Mo2S4 is increased as the Al content increases. It has been found that the intrinsic activity of Mo2S4 is increased with decreasing Mo-Mo atomic distance. The dynamic structural transformations between Mo2S4 and Mo4S6 nanoclusters in H2-H2S/H2 treatments are described. Co2Mo2S6 nanoclusters with a thiocubane structure are successfully prepared by introducing Co(CO)3NO to Mo2S4/NaY, followed by second sulfidation. It is noteworthy that the significantly high thermal stability of Mo2S4 and Co2Mo2S6 nanoclusters is due to moderate interactions with the framework oxygen as sold ligands.

Key words: Zeolite; Nanoclusters; Molybdenum; Metal sulfides; Metal oxides; Host-guest interactions

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