Molecular Design and Structural Controlling of Heterogeneous Reaction Sites by Ship-in-bottle Synthesis

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Metal carbonyl clusters grafted on supports such as oxides and zeolites offer a great advantage in the rational preparation of metal/bimetal ensemble sites for activation of small molecules such as CH_4,CO_2 and H_2O to be effectively converted into useful chemicals. Metal clusters entrapped in zeolite micro-pores are ideal objects for the study of collective behavior and heteronuclear two-site promotion in stoichiometric and catalytic reactions of chemically modest small molecules such as CH_4,CO and CO_2.We have extended works to synthesize Rh_<6-x>Ir_x(CO)_<16>(x=0-6) and Rh_4Fe_2(CO)_<15>^<2-> inside NaY zeolite by the "ship-in-bottle" technique, and characterized the H_2-reduced bimetal ensembles by EXAFS, FTIR, and Mossbauer in CO and CH_4 atmosphere. NaY-entrapped RhIr ensembles provide selectively C_2H_6 via central C-C bond-scission in the butane hydrogenolysis, while NaY-entrapped RhFe ensembles selective towards CH_4+C_3H_8 via terminal C-C bond scission. Recently, we have succeeded to synthesize the series of Chini-type Pt clusters such as [Pt_3(CO)_6]_n^<2-> (n=3,4,5) inside NaY cages, which are characterized by FTIR, EXAFS and UV-vis. They are catalytically active for NO reaction with CO and the water gas shift reaction (CO+H_2O=CO_2+H_2) at lower temperatures, and exhibited effective photocatalysis for the latter reaction with a marked enhancement under the illumination of a Xe lamp compared with the dark reduction. The results suggest that H_2O is activated with anionic Pt carbonyl clusters inside the cages to promote the H (or OH) formation under the photo-illumination.