Thermal Decomposition Behavior Of Polyoxometallates And Their Anchoring On The Surface Of Mesoporous Titania

Polyoxometalates (POM) are useful materials as acidic and oxidation catalysts for various reactions and have been practically applied in industry. As solid acid catalysts, especially characterized in providing a unique "pseudoliquid phase" reaction environment, POM catalysts should find more and more practical applications in green/sustainable and atomic economic reactions. In particular, owing to their changeable properties of the composition, structure and thus performance, polyoxometalates are thought as one of the most suitable materials to be artificially designed, and then more attentions are also been paid to them in theory.To realize the molecular design of polyoxometalates, the necessary prerequisite is to masterly predominate the following four levels of information: i), catalytic performance; ii), chemical and physical property; iii), molecular and bulk composition and structure; iiii), method of catalyst preparation. Thermal decomposition behavior and thermal stability are the essential physical and chemical properties, and the thermal decomposition temperature is especially an important parameter for the design and preparation of the applicable catalysts. However, the present research results, especially their decomposition temperatures, are disillusionary due to many reasons such as different determinant criterion of polyoxometalates etc. This will be unconducive for understanding and exploring the fundamental chemistry of polyoxometalates and the catalysis of the related catalysts. Besides, the practical applications of polyoxometalates have been limited due to some shorts such as their low surface area and low mechanical intensity, etc. The developed loading method-inpregnation can usually be used to improve the problems above, but it can not solve the leaching of the loaded polyoxometallates in polar solvent.We aim to explore the methods to solve the problems, and make foundations for the applications and the molecular design of polyoxometallates. The main contents are as follows:First; the thermal decomposition behavior of the polyoxometalates with Keggin structure Y_mH_mXM₁2O₄0 and Dawson structure Y_mH_mXM₁8O₆2 (X=P Si Ge, M=W Mo,Y=NH₄⁺ K⁺ Cu²+) was investigated systematically using modern thecniques shuch as X-ray diffraction and IR Spectra at different temperatures, TG-DTA etc.Their precise decomposed temperatures were obtained, and the procedure of decomposition was also explored. The determinant criterions of thermal decomposition and the factors of affecting on the thermal properties for the polyoxometalates were discussed and some new views were presented. At the same time, the main decomposition products were identified by XRD for the prepared polyoxometalates.Second; heteropoly acid (H₃PW₁2O₄0 and H₅PMo_V3O₄0) with Keggin structure was immobilized onto the surface of mesoporous TiO₂ sieves with high thermal stability and order channel through chemical bonding with amine groups which was introduced into the system during an aminosilylation procedure, resulting in strong anchoring of heteropoly anions. Thus, polyoxometalates leaching in polar solvent media was efficiently prevented. The prepared material could catalyze more effectively in photodecomposition of methyl orange and hydroxylation of benzene to phenol by molecular oxygen respectively.