Oxidation Catalyzed by Polyoxometalate-Anion-Intercalated Layred Compounds

制备了由Mg-Al、Zn-Al和Ni-Al组成的不同原子比的层状双氢氧化物（LDH），并以Mo或W作为补充原子插入金属氧酸杂多阴离子。发现在Zn/Al比为2的Zn-Al LDH层空间中插入SiW_<12>O_<40>^<4->是相当困难的。为了避免多金属氧酸盐的分解，插入时的pH值保持在4以下，此时Zn-Al LDH比Mg-Al LDH更稳定。制备了硅钨酸盐SiW_<12>O_<40>^<4->、SiW_<11>O_<39>^<8->、SiW_< 34>^<10->插层的Zn-Al LDHs，并用红外光谱对其廊空间阴离子结构进行了表征。SiW_<11 bbb_ 0 O_<39>^<8->插层化物是一种以H_2O_2为氧化剂的烯烃环氧化反应催化剂。而SiW_<12 bbb_0 O_<40>^<4->插层化合物对o_2 -醛环氧化烯烃具有较好的催化活性，但对H_2O_2环氧化反应的催化活性较差。不含多金属氧酸盐的Ni-Al LDH在烯烃与o_2 -醛的环氧化反应中表现出相当大的活性。因此，有人建议将活性金属引入LDH本身和画廊空间可能导致双功能催化的出现，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.