Research On The Catalytic Properties Of TiO₂-SiO₂ Supported Polyoxometalates

In this paper, the Keggin-type polyoxometalates was loaded by the high specific surface area material TiO₂-SiO₂ with the impregnation method. Catalysts were characterized by FT-IR, XRD and SEM, and then synthesis of acetal（ketal） and adipic acid and photocatalytic performance were also discussed. The main contents are as follows:The environmental friendly catalyst, H₄SiW₁2O₄0/TiO₂-SiO₂ was prepared by the impregnation method. The synthesis of cyclohexanone glycol ketal was as the probe reaction and investigated the different influences on the catalytic activity of H₄SiW₁2O₄0/TiO₂-SiO₂ by the quality of the carrier TiO₂-SiO₂ ratio, load of heteropoly acid, catalyst preparation conditions of the activation time and the calcination temperature, etc. The results showed that the best condition for the preparation of the catalyst was the mass ratio of TiO₂ and SiO₂ was 1: 5, the load ratio of H₄SiW₁2O₄0 was 10 %, calcination temperature was 300 oC and the roasting time was 3.0 h. Under the condition of the molar ratio of aldehydes（ketones） and glycol（1, 2-propanediol） was 1: 1.6, the mass percent of the catalyst was 1.4 %, and the reaction time of 70 min, the yields of eight kinds acetal（ketal） were 71.6 %- 90.6 %.In order to remove aquatic organic dye contaminants utilizing the inexpensive and inexhaustible solar energy, the Keggin-type H₃PW₆Mo₆O₄0 was loaded by the specific surface area TiO₂-SiO₂ with the impregnation method. The photocatalytic degradation of methyl orange by H₃PW₆Mo₆O₄0/TiO₂-SiO₂ under simulated natural light irradiation was investigated. At the same time, the influences of the initial methyl orange concentration, the solution p H and the catalyst dosage on the photocatalytic degradation ratio of methyl orange were also examined. The results demonstratiod that initial concentration of methyl orange was 5 mg/L, and the catalyst dosage was 0.9 g/L, while the p H was 3.0. The degradation ratio of the methyl orange could reach to 98.0 % after the light irradiation time of 3.5 hours. The reaction of photocatalysis for methyl orange was the first-order kinetic model. The photodegradation of methyl viole, malachitegreen oxalate, methylene blue, fuchsin basic and methyl red were also tested, and the degradation ratio of dyes could achieve 93.2 %- 98.0 %.H₄SiW₆Mo₆O₄0/TiO₂-SiO₂ was prepared by impregnation method. The ketone condensation reaction with an alcohol as a probe was used to determine the optimal conditions for preparation of the catalyst. The conditions of catalyst were optimized by orthogonal experiment to obtaine its optimum conditions that n（TiO₂） : n（SiO₂） was 3: 1, mass ratio of m（H₄SiW₆Mo₆O₄0） : m（TiO₂-SiO₂） was 20 %, the calcined time was 3 h and activated temperature was 300 °C. The cyclohexanone was oxidated by the catalyst of H₄SiW₆Mo₆O₄0/TiO₂-SiO₂ and the oxidation of 30 % H₂O₂ to synthesis adipic acid. In this paper, the influence of the catalytic activity of the oxidation reaction by the amount of catalyst, reaction temperature, H₂O₂ dosage, reaction time and other factors were researched. Experimental results indicated that H₄SiW₆Mo₆O₄0/TiO₂-SiO₂ was a good catalyst synthesis of adipic acid. Under the condition of n（cyclohexene） : n（H₂O₂） : n（H₄SiW₆Mo₆O₄0/TiO₂-SiO₂）= 100: 979: 0.04 at 130 oC for 5 h, the yield could reach 45.9 %.