Photoisomerization of Norbornadiene to Quadricyclane Using Transition Metal Doped TiO2

Metal(V, Fe, Ce, Cu, Cr)-doped TiO2 were synthesized for the photoisomerization of norbornadiene. Characterizations indicate that V and Fe are located in the substitutional sites of TiO2, Ce ions dispersed in the interstitial sites, while Cr and Cu aggregated on the surface. The order of activity is Fe-TiO2 > V-TiO2 > Cr-TiO2 > Ce-TiO2 > TiO2 > Cu-TiO2, suggesting the local structure and type of dopant are crucial. Materials with various V and Fe content were further studied. Fe ions are well dispersed in TiO2 lattice even at high metal content, whereas many separated V2O5 phases are formed. The activity of V-TiO2 changes with V content and the optimal Ti/V ratio is 15, but the activity of Fe-TiO2 is independent of the metal content. Attributed to the high dispersion, Fe-TiO2 is much more active than V-TiO2. The photoreactivity is correlated with the surface lattice oxygen, and a mechanism is proposed to explain the photoisomerization and role of Fe dopant.