Hybrid Polyoxotungstate/MIL-101 Materials: Synthesis, Characterization, and Catalysis of H2O2-Based Alkene Epoxidation
Hybrid Polyoxotungstate/MIL-101 Materials: Synthesis, Characterization, and Catalysis of H2O2-Based Alkene Epoxidation
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DOI：
10.1021/ic902459f
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发表时间：
2010-03-15
影响因子：
4.6
通讯作者：
Kholdeeva, Oxana A.
中科院分区：
文献类型：
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作者：
Maksimchuk, Nataliya V.;Kovalenko, Konstantin A.;Kholdeeva, Oxana A.
多金属氧钨酸盐[PW₄O₂₄]³⁻（PW₄）和[PW₁₂O₄₀]³⁻（PW₁₂）已被插入金属有机骨架MIL - 101的纳米笼中。已获得含有5 - 14 wt%多金属氧钨酸盐的杂化材料PWₓ/MIL - 101（x = 4或12），并通过元素分析、N₂吸附、傅里叶变换红外光谱、拉曼光谱和³¹P核磁共振魔角旋转光谱技术对其进行了表征。在温和的反应条件（[H₂O₂] = 0.1 - 0.2 M，50℃，乙腈）下，用过氧化氢水溶液对烯烃进行选择性氧化，评估了它们的催化性能。含有5 wt%多金属氧钨酸盐的PWₓ/MIL - 101在各种烯烃（3 - 蒈烯、柠檬烯、α - 蒎烯、环己烯、环辛烯、1 - 辛烯）的环氧化反应中表现出相当好的催化活性，其周转频率（TOF）和烯烃转化率接近均相PWₓ所达到的相应参数。对于具有芳香基团的底物（苯乙烯、顺式和反式二苯乙烯）的氧化，使用PW₁₂/MIL - 101可获得更高的烯烃转化率。此外，将PW₁₂限制在MIL - 101纳米笼内使我们能够在更高的烯烃转化率下获得更高的环氧化物选择性。杂化的PWₓ/MIL - 101材料具有抗浸出稳定性，表现为真正的多相催化剂，可通过过滤轻松回收，并在保持催化性能的情况下重复使用多次。
Polyoxotungstates [PW4O24](3-) (PW4) and [PW12O40](3-) (PW12) have been inserted into nanocages of the metal organic framework MIL-101. The hybrid materials PWx/MIL-101 (x = 4 or 12) containing 5-14 wt % of polyoxotungstate have been obtained and characterized by elemental analysis, N-2 adsorption, FT-IR, Raman, and P-31 NMR MAS spectroscopic techniques. Their catalytic performance was assessed in the selective oxidation of alkenes with aqueous hydrogen peroxide under mild reaction conditions ([H2O2] = 0.1-0.2 M, 50 degrees C, MeCN). PWx/MIL-101 enclosing 5 wt % of polyoxotungstate demonstrated fairly good catalytic activities in the epoxidation of various alkenes (3-carene, limonene, alpha-pinene, cyclohexene, cyclooctene, 1-octene), the turnover frequencies (TOF) and alkene conversions were close to the corresponding parameters achieved with homogeneous PWx. For the oxidation of substrates with aromatic groups (styrene, cis- and trans-stilbenes), a higher level of olefin conversion was attained using PW12/MIL-101. Moreover, confinement of PW12 within MIL-101 nanocages allowed us to reach higher epoxide selectivities at higher alkene conversions. The hybrid PWx/MIL-101 materials were stable to leaching, behaved as true heterogeneous catalysts, were easily recovered by filtration, and reused several times with the maintenance of the catalytic performance.