Study On Titanium Catalysts For Photoisomerization Of Norbornadiene

A series of Zn doped TiO₂ catalysts, La doped ZnO/TiO₂ composite catalysts and Ti substituted Ti-MCM-41 were prepared and characterized by XRD, BET, TEM, XPS, diffuse reflectance UV-vis spectra, FT-IR, N2 absorption-desorption. The photoisomerization reaction of norbornadiene to form quadricyclane was carried out in a photoreactor in order to study the effects of the structure of the catalysts on their catalytic activity.Zn doped TiO₂ catalysts were prepared by chemical precipitation method. The results show that the Zn dopant caused the distortion of TiO₂ lattice and the decrease in the particle size, and increase in the specific surface and hydroxyl content on the surface of the catalysts, resulting in the improvement of the TiO₂ acivity. Relatively high calcination temperature was harmful to the activity of catalysts because of the large particle size, low specific surface and hydroxyl content on the surface of catalysts compared with that at low calcination temperature. The optimal amount of the Zn dopant was 1%(wt). The conversion of norbornadiene and selectivity to quadricyclane over the 1%Zn-TiO₂ catalyst can reach 88% and 100%, respectively, after the reaction of 12 hours.The ZnO/TiO₂ composite and La doped ZnO/TiO₂ catalysts were prepared by co-precipitation method. The results show that the addition of ZnO into TiO₂ led to the formation of the mix-crystal formed from the anatase and ZnTiO3, which can improve the activity of the catalyst. There was no change in the structure of the mix-crystal of the catalyst, but, the intensity of the peak in the DR UV-vis spectra and hydroxyl content on the surface increased after depositing La into ZnO/TiO₂. Among all catalysts of La-ZnO/TiO₂, the10%La-ZnO/TiO₂ gave the highest conversion of 93.6% after the reaction of 12 hours and the selectivity to quadricyclane over all samples was 100%.MCM-41 mesoporous molecular sieves and Ti substituted Ti-MCM-41 were synthesized via an in situ hydrothermal method. The modification of the MCM-41 inner surface with titanium oxide was prepared by solution grifting method. The results suggested that framework titanium of Ti-MCM-41 zeolite had a beneficial and significant influence on the activity of the catalysts, and the specific surface area and highly order had slight effects on activity. The 92% conversion of norbornadiene and 100% selectivity to quadricyclane can be obtained over the Ti-MCM-41 catalyst with the molar ratio of Si to Ti of 30. The activity of MCM-41-TiO₂ was lower than that of Ti-MCM-41 although Ti content of MCM-TiO₂ was higher (8mol%) than that of Ti-MCM-41 because no framework titianium was formed on it.