Preparation And Catalytic Oxidation Performance Of Polyoxometalates@Al₂O₃ Hierarchitectures Catalyst

Polyoxometalates (POMs) are a family of discrete anionic metal-oxides, such as Mo, V, W and Nb. Polyometalates have shown unrivalled structural types in their highest oxidation states, and extensive unique physicochemical properties and applications in areas as diverse as catalysis, electrochemistry, photo-chroism etc. However, POMs are highly soluble and could be easily crystallized in solution. Furthermore, the POMs anions and the counterions interactions in the crystal structures are generally weak, resulting into low lattice energies. These aforementioned disadvantages largely limit POMs application in reality. Thus, research on catalysis of POMs is mostly directed towards heterogeneous POMs-based material so as to attain good recoverability, reusability and excellent selectivity.Immobilization of POMs onto a number of substrates is one of the widely applied techniques for the preparation of various POMs-based heterogeneous catalytic material. A number of research groups have put great efforts on immobilization of POMs onto supports, such as Al2O3, SiO2, zeolite, ZrO2 and activated carbon etc. However, the reported systems do show the problems as follows:the heterogeneous catalytic material involving the electrostatic interactions between POMs and supports suffer from the weakness of the easy leaching of POMs from the support. In the case of the heterogeneous catalytic material which is based on the calcination of the POMs-support material, the POMs structures are destroyed. As a consequence, it is difficult to use the rich structural types of POMs. Thus, the study for a robust support without destruction of POMs is highly desired.In this thesis, to overcome the difficulties of the industrial application of supported polyoxometalates catalytic material as a key point, immobilizing of Dawson vacant Polyoxometalates onto spherical ?-Al2O3 successfully overcome the disadvantage of the industrial application of supported polyoxometalates catalytic material, and research POMs@Al2O3 catalytic properties, the main contents include two aspects as follows:1. A new nanocomplex catalyticmateria (P2W15@Al2O3) have been prepared through condensation between Dawson polyoxometalates and spherical y-Al2O3. The heterogeneous P2W15@Al2O3 catalyst exhibits excellent catalytic reactivity for oxidation of sulfides, and we find it facilitating to recover and recycle the catalytic material for new oxidation with highly efficient catalytic reactivity.2. Based on nanocomplex catalyticmateria (P2W15@Al2O3), by immobilizing ionic liquid onto P2W15@Al2O3 with hydroxy and prepared IL@P2W15@Al2O3 catalytic material. The heterogeneous catalytic material can overcome the difficulty that Polyoxometalates contact poorly with substrate in organic phase. When heterogeneous catalytic material was applied to oxidation of dibenzothiophene (DBT), and it shows excellent catalytic activity. Additionally, it can be recovered and reused easily with highly efficient catalytic activity in the oxidation of DBT.