Selective Oxidative Dehydrogenation of Cyclohexene into 1,3-Cyclohexadiene on TiO ₂

The selective C-H bond activation remains a big challenge in hydrocarbon dehydrogenation. Herein, the selective oxidative dehydrogenation of cyclohexene (C₆H₁₀) has been investigated on a model rutile(R)-TiO₂(110) surface. In the thermal conversion process, 1,3-cyclohexadiene (1,3-C₆H₈) is produced with nearly 100% selectivity in a stepwise manner, where the initial α-sp³ C-H bond dissociation of C₆H₁₀ occurs at <300 K with the help of surface O₂^2- species. Under UV irradiation, a new reaction pathway for 1,3-C₆H₈ formation occurs via the dehydration of 2-cyclohexen-1-olate (1,2-C₆H₉O) groups, which is formed by the reaction of surface oxygen species (predominantly O₂) with a cyclohexenyl radical (C₆H₉^•) intermediate. In addition, different surface oxygen species give rise to different products in the oxidative conversion of C₆H₁₀ under UV irradiation. The findings not only elucidate the reaction mechanism of C₆H₁₀ oxidative dehydrogenation but also provide new insights for the C-H bond activation of cyclic hydrocarbons over TiO₂-based catalysts.