Preparation Of Hybrids Based On Heteropoly Acid And Investigation Of Their Catalytic Performances On Oxidation Reactions

Recently, the synthesis and application of organic-inorganic hybrid materials based on heteropolyacid have attracted wide attentions in the field of catalysis. In most cases, the hybrid materials can be endowed advantages of both the heteropolyacid and organic moieties, and always show synergistic effects. Especially, the hybrid based on heteropolyacids and ionic liquids is a kind of heterogeneous catalysts which combines the rigidness, size stability of heteropolyacids and flexility, modifiability of ionic liquids. Compared to heteropolyacids, the hybrid materials always show superior catalytic activities and reusabilities in most of catalytic reactions. Metal-organic frameworks?MOFs? are a new class of porous crystalline coordination polymers. Their inherent high specific surface areas, uniform and tunable pores endow them potential candidates in variety fields. Recently, many heteropolyacids have been immobilized in MOF materials by ion exchange method to obtain more efficiently heterogeneous catalysts. Based on above facts, two kinds of hybrids based on heteropolyacids were prepared and their catalytic activities were investigated in different oxidation reactions using H₂O₂ as oxidant. The main contents are as follows:1. A series of hybrid materials([C₄mim]₃PMo₁₂O₄₀, [C₄mim]₄PMo₁₁VO₄₀ and [C₄mim]₅PMo₁₀V₂O₄₀ based on V-substituted phosphomolybdic acids H_3+xPMo_12-xV_xO₄₀?x=0, 1, 2? and ionic liquid 1-butyl-3-methyl imidazolium bromide?[C₄mim]Br?, have been prepared by anion-exchange method. The samples were well characterized by UV-vis DRS, FT-IR and XRD methods. The catalytic performances of the samples were tested in oxidation of benzyl alcohol and the hydroxylation reaction of benzene. The results have shown that the hybrid materials exhibit much higher catalytic properties than both the corresponding moieties. In oxidation of benzyl alcohol, the hybrid [C₄mim]₄PMo₁₁VO₄₀ have shown the highest performances and 34 % of benzyl alcohol conversion can be obtained using H₂O₂, as oxidant under 80 ? after 6h reaction. The sample also exhibits good reusability and has been reused five runs without obvious decrease in catalytic activity. In the hydroxylation of benzene, the hybrid [C₄mim]₅PMo₁₀V₂O₄₀ has shown the highest performance and 21 % of benzene can be converted using H₂O₂, as oxidant under 70 ? after 6 h reaction and the selectivity of phenol is above 99 %. The sample also exhibits good reusability and has been reused five runs without much changes in catalytic activity.2. The hybrid materials H_3+xPMo_12-xV_xO₄₀/MIL-100?Fe??x=0, 1, 2? have been prepared by direct hydrothermal synthesis method using H_3+xPMo_12-xV_xO₄₀, Fe Cl3×6H2O and 1,3,5-tricarboxybenzene as raw materials. The as-prepared samples were well characterized by FT-IR, UV-vis DRS, XRD, TEM and N₂ adsorption-desorption methods. The catalytic performances of the samples were investigated for oxidation of cyclohexene and the reaction conditions have been optimized. The results have shown that H₄PMo₁₁VO₄₀/MIL-100?Fe? as catalyst, H₂O₂ as oxidant, 70 ?, 9 h, the conversion of the cyclohexene reaches 70 %, and the selectivity of 2-cyclohexen-1-one is 85 %. Moreover, the sample also exhibits good reusability and has been reused five runs without much changes in catalytic activity.