Studies On The Oxidation Of Cyclohexene Over Photocatalysts

The increasing progress of chemical industry ensures substance for people' s standard of living, but at the same time it makes a mass of pollutants. The method of photocatalysis with TiO₂ catalyst is not only used in the filed of dealing with pollutants, but also has some potential in the field of chemosynthesis because it is usually employed at normal temperature and normal pressure for chemosynthesis without second pollutants. Photocatalytic speciality of TiO₂ has been widely reported, however, photic utilization and catalytic efficiency are low because of the narrow range of photo-respond, easy compoundation of photogenerated electrons and holes, and low photo-quantum efficiency of TiO₂. Furthermore, it is not easy for powder catalyst to recover, and is easy to aggregate and lose activity. Surface modification could increase photogeneration carriers' separation, enhancing photo-quantum efficiency and extending range of photo-respond. And the problem of aggregating could be solved by solidification measures.Nanoparticle TiO₂, the film of TiO₂ and Nanoparticle Fe³⁺ -TiO₂ were prepared by sol-gel and analysed by means of TEM and XRD. Epoxidations of cyclohexene at irradiation of 8W mercury lamp over the catalysts were stduied. The result was compared with oxidations of cyclohexene without irradiation and at irradiation without catalyst. As a result, cyclohexene epoxide was not yielded during the latter oxidations. Among different crystalline TiO₂ catalysts, the rutile TiO₂ catalyst can not lead to cyclohexene epoxide. The activity of intermingled catalyst was improved, and the optimal content of Fe³⁺ was observed .New phases were not found at X-ray diffraction patterns of Fe³⁺-TiO₂, so, higher activity of intermingled catalyst was caused by Fe³⁺ which became electron trap, decresed compoundation of electrons and holes and enhanced photo-quantum efficiency. Oxidations of cyclohexene at irradiation of 8-W mercury lamp with ZnO catalyst were also studied, but the results were not as good as TiO₂ catalysts beacause ZnO was easily eroded at irradiation. In addition, oxidations of cyclohexene at irradiation of 100-W mercury lamp with the aboved catalysts were investigated. The results showed that cyclohexene epoxide wasnot yielded with any one of the aboved catalysts, and that main products were CO2 and H2O.The effects of temperature^ velocity of air flow and reaction time on cyclohexene oxidation were stduied. We learned that the effect of temperature was great: cyclohexene epoxidation didn't occur under 40°C ; the yiled of cyclohexene epoxide increased a little with temperature when it was beyond 40 °C. But too high temperature was not permitted, because cyclohexene might lose much at the open system. We noticed that the yiled of cyclohexene epoxide increased with velocity of air's flow, which could not be too big because of the same reason. Although the yiled also increased with reaction time, it reached a peak, not increasing without limit.