Preparation Of Pd / TiO 2 -SiO 2 Catalyst And Its Catalytic Oxidation Of Propylene

Propylene oxide(PO) is a kind of very important chemical feedstock in organic chemical engineering. It is widely used in the production of polyurethane, surfactant and resins. Today, propylene oxide is mainly manufactured via chlorohydr in process or Halcon process. However, the pollutions to the environments in the former process and high investments in the latter process. Gas phase propylene epoxidation for the production of PO attracts much interest for its environmental friendliness and mild operation conditions. In this work, taking the TiO2-SiO2 composite oxides as the carrier, adding some active components, such as Pd, Au, Ag, etc. MOx/TiO2-SiO2 was prepared by impregnation method. The catalytic performance of the MOx/TiO2-SiO2 was studied in the epoxidation of propylene.一、Catalysts Preparation and CharacterizationIn this paper, with sodium silicate as silicon source and titanium sulfate as titanium source. It got the catalysts after precipitation, washing, aging, drying, calcination processes. MOx/TiO2-SiO2 was prepared by impregnation method with palladium chloride, gold chloride and silver nitrate as one or more active components. A series of Pd/TiO2-SiO2 catalysts with different amount of palladium loading were also prepared at the same time.The samples were characterized using XRD, FT-IR, UV-vis, SEM, TEM and other methods. The XRD of MOx/TiO2-SiO2 catalyst showed that:after loading the active component palladium, the diffraction peak of palladium oxide appeared which showed that the palladium oxide active center in the catalyst had become a large palladium grain at this time. After loading the active components silver and gold, the diffraction peak of metal oxide didn’t appeared, which indicating the homogeneous distribution of metal oxide on the surface of the carrier. The FT-IR of MOx/TiO2-SiO2 catalyst showed that:there were no other peaks after loading the active components. The XRD of Pd/TiO2-SiO2 catalyst showed that:when the load of Pd was less than 0.1%,the diffraction peak of palladium oxide didn’t appeared, when the load of Pd was higher than 0.1%, the characteristics diffraction peaks of palladium oxide could appeared. Diffraction peak were more and more stronger as the load of Pd increased. The results showed that when the load was less than 0.1%, palladium oxide was highly dispersed, when the load was higher than 0.1%,there was a phenomenon of reunion on the palladium oxide.二、Catalytic Activity ResearchThe activity of catalysts were studied by the reaction which propylene oxide was prepared by propylene epoxidation with a trickle-bed reactor. A variety of catalysts (TiO2-SiO2, Pd/TiO2-SiO2, Ag/TiO2-SiO2, Au/TiO2-SiO2, Au-Pd/TiO2-SiO2, Ag-Pd/TiO2-SiO2) were studied for the initial selecting. From the results of the investigation, it was found that the Pd/TiO2-SiO2 catalyst has a relatively good catalytic activity on the epoxidation of propylene. Therefore, the catalytic oxidation performance of the catalyst was investigated detailedly. Effects such as palladium loading, solvent, reaction temperature, space velocity, mass ratio, reaction time and other factors on the catalyst activity were studied. The experimental results showed that:to Pd/TiO2-SiO2 catalyst, the best condition for the catalytic oxidation reaction was:the palladium loading was 0.1%, solvent was methanol, reaction temperature was 55℃, space velocity was 200h-1, mass ratio was 3. Under the best condition, the conversion of propylene was up to 53.9% and the selectivity of propylene oxide was up to 99.7%.In summary, a new kind supported catalyst was synthesized in this study, which has good selectivity to epoxidation of propylene. and has better prospects for industrial applications.