Oxidation Catalyzed by Polyoxometalate-Anion-Intercalated Layred Compounds

制备了由不同原子比的Mg-Al、Zn-Al和Ni-Al组成的层状双金属氢氧化物（LDH），并以钼或钨为附加原子的杂多酸阴离子插层LDH。发现在<12><40><4->Zn/Al比为2时，SiW_2 O_3很难插入到Zn-Al LDH的层间。为避免多氧钒酸盐的分解，插入过程中pH值应控制在4以下，此时Zn-Al LDH比Mg-Al LDH更稳定。制备了硅钨酸盐插层Zn-Al LDH<12><40><4-><11><39><8-><34><10->，并通过红外光谱分析了插层空间阴离子的结构。SiW_<11>O_<39>2<8->插层催化剂对H_2O_2为氧化剂的烯烃环氧化反应具有良好的催化活性。而SiW_<12>O_<40>2<4->插层化合物对O_2-醛环氧化烯烃反应活性较好，但对H_2O_2环氧化反应活性较差。不含聚氧乙烯酸酯的Ni-Al LDH在烯烃与O_2-醛的环氧化反应中表现出很好的催化活性。因此，有人建议，活性金属引入到LDH本身和廊道空间可能会导致双功能催化剂的出现，这将应用于新的催化反应。

Layred double hydroxides (LDH) consisting of Mg-Al, Zn-Al, and Ni-Al with the atomic ratios varied were prepared, and intercalated with heteropolyoxometalate anions including Mo or W as the addenda atom. It has been found rather difficult to insert SiW_<12>O_<40>^<4-> into the layr space of Zn-Al LDH with the Zn/Al ratio of 2. However, the insertion was promoted with decreasing Al/Zn ratio, To avoid decomposition of polyoxometalate, the pH during the insertion was kept at lower than 4, where the Zn-Al LDH was more stable than the Mg-Al LDH.Zn-Al LDHs intercalated with silicotungstates SiW_<12>O_<40>^<4->, SiW_<11>O_<39>^<8->, and SiW_9O_<34>^<10-> were prepared and the structure of the anions in the gallery space was examined by infrared spectroscopy. The SiW_<11>O_<39>^<8-> intercalate proved to be a good catalyst for olefin epoxidation with H_2O_2 as oxidant. In contrast, the SiW_<12>O_<40>^<4-> intercalate was effective in epoxidizing olefins with O_2-aldehyde, although it showed poor activity in the epoxidation with H_2O_2 Substitution of V for W of the addenda atom resulted in enhancement of activity for epoxidation with O_2-aldehyde. The Ni-Al LDH with no polyoxometalate included exhibited considerable activity in olefin epoxidation with O_2-aldehyde. Thus it has been suggested that the introduction of active metals into both the LDH itself and the gallery space may lead to emergence of bifunctional catalysis, which would be applied to novel catalytic reactions.