Metal Organic Framework with Tungsten Heteropoly Acid

Tungstic heteropoly acid generally refers to heteropoly acid and its salts. It is a polyoxometalate metal complex composed of central (Heteropoly) atoms (P, Si, etc.) and coordinated (multi atom W) bridged by oxygen atoms. It can be widely used in homogeneous and heterogeneous catalytic systems.

In a large number of heteropoly acids (salts), the Keggin structure heteropoly acid (salt) is the most widely studied. The tungstate heteropoly acid general formula is [XW₁₂O₄₀]^n- (X=P, Si), in which X is called the heteroatom, and W is called the coordination atom. As heteropoly acids are easily dissolved in polar solvents, the separation of catalysts and the use of cyclic use are difficult. At the same time, the specific surface area of solid POMs is usually very small (<10 m² g^-1), which restricts its catalytic performance as a solid catalyst. Therefore, supported heteropoly acid catalyst is the mainstream of tungstic heteropoly acid application. At present, most of the carriers are silica gel and activated carbon. Besides, Al₂O₃, TiO₂, MgO, MCM-41 and SBA-15 can also be used as carriers.

The metal organic framework material MIL-100 (Fe) is a Fe metal organic ligand trimer and all three formic acid (1,3,5-BTC) formed by connecting supertetrahedron as a secondary structural unit, through further supertetrahedron self-assembly extension of 3D metal with the MTN structure formed - organic complexes to space. There are two kinds of mesoporous cages in MIL-100 (Fe) with a diameter of 2.5 nm and 2.9 nm, respectively, and the opening sizes are 0.55 nm and 0.86 nm, respectively. The material has a large specific surface area and pore volume, the thermal stability of the material reaches 270 °C, and it is an excellent catalyst loading material.

Due to the confining effect of MIL-100 (Fe) mesoporous cage, the heteropoly acid after encapsulation is not easy to dissolve and drain. In addition, because the composite catalyst is carried out under the dynamic condition, the heteropoly acid in the catalyst is dispersed very evenly. Moreover, the synthesis of heteropoly acid from raw materials has the advantages of low energy consumption, high synthesis yield and low price. 

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