Photocatalytic C-H Bond Activation of Toluene on Rutile TiO2(110)

The activation of sp(3) C-H bond over photoactive TiO2 catalysts has emerged as a promising means to realize the functionalization of hydrocarbons under mild conditions. However, a fundamental understanding of the microscopic mechanism is still unclear. In this work, we have systematically investigated the photochemistry of toluene on rutile (R)-TiO2(110) with temperature-programmed desorption (TPD) and density functional theory (DFT). The TPD results demonstrate that UV light (355 nm) efficiently facilitates the methyl C-H bond activation of toluene at 100 K, forming the stable C6H5CH2 group intermediate adsorbed on five-coordinated Ti4+ sites (Ti-5c) until around room temperature (similar to 300 K). Further DFT calculations suggest that the photocatalytic C-H bond cleavage follow a homolytic manner via the formation of active benzyl radical (C6H5CH2 center dot). Our findings provide an insightful understanding of photocatalytic hydrocarbon functionalization on TiO2 catalysts.