Preparation, Characterization And Catalytic Properties Of The Immobilized12-Tungstophosphoric Acid Catalysts On Several Mesoporous Molecular Sieves

Phosphotungstic heteropoly acid (HPW) was a new type of catalysts, such as high catalytic activity, excellent selectivity, mild reaction conditions. However, bulk HPW used in homogeneous catalysis existed obvious disadvantages including high cost, difficult recovery, environmental pollution, equipment corrosion issues etc. Meanwhile, its catalytic activity may be not full play due to its low surface area (<10m2/g). This can be overcome by introducing HPW into suitable carriers to improve its surface area, increase the mechanical strength and thermal stability properties. Hence, the as-prepared catalysts can be recycled used in heterogeneous catalysis. On the other hand, its catalytic activity also may be improved. In addition, benzoic acid had important applications in the food industry, pharmaceutical industry, dye and fragrance industry, and its sodium salt was not only an important preservative in the food industry, but also was mordant in printing and dyeing industry.In this thesis, bulk HPW and several series of HPW-based mesporous catalysts were prepared and characterized by XRD, FT-IR, DR UV-Vis, NH3-TPD, N2adsorption-desorption, SEM, and TEM. Furthermore, the catalytic performance of the as-prepared catalysts for the oxidation of benzaldehyde to benzoic acid with aqueous hydrogen peroxide was comparatively studied. The primary conclusions in the separated parts were as follows:(1) Bulk HPW was synthesized via an improved diethyl ether extraction method and characterized by various techniques. The influence of the amount of catalyst, reaction time, and reaction temperature on benzoic acid yield was investigated. The optimized catalytic reaction was as follows:n (C6H5CHO):n (H3PW12O4o):n (H2O2)=100:0.35:350, the reaction time was5h, and the reaction temperature was80℃, The yield of benzoic acid could be up to79.2%under the conditions.(2) A series of HPW/SBA-15, HPW/MCM-41, and HPW/(M-S) catalysts were prepared by a wet impregnation method and characterized by various techniques, respectively. The results showed that HPW was finely dispersed on the surface, inside the hexagonal channels or incorporated in the pore walls of the supports to some extent. When the loading of HPW increased furthermore, bulk HPW crystals in the pores of supports would appear. On the other hand, the loading of HPW affected the structure and catalytic properties of the corresponding catalysts. The supported catalysts remained the pore structure characteristics and HPW Keggin-type structure. However, the surface areas and pore volumes decreased with the increase of HPW loadings. Meanwhile, the catalytic activity increased firstly, then decreased with the increase of HPW loading.(3) A series of HPW-SBA-15, HPW-SiO2*, and HPW-(M-S) catalysts were prepared by direct synthesis process and characterized by various techniques, respectively. The results showed that HPW was incorporated into the ordered mesoporous silica. On the other hand, although the catalysts maintained Keggin-type structure of HPW and pore structure characteristic of the carriers to a certain extent, the amount of HPW addition affected the structure and catalytic properties obviously. It was noteworthy that the35wt.%HPW-SiO2*catalyst exhibited the best catalytic properties. The yield of benzoic acid may reach up to84.7%over the HPW-SiO2*catalyst and had not obvious decrease even reuse four times.