Visible-Light-Mediated Methane Activation for Steam Methane Reforming under Mild Conditions: A Case Study of Rh/TiO2 Catalysts

Hot-carrier-induced molecular activation over photoexcited metal nanostructures is an important research field in solar-to-chemical energy conversion. Here, we report that visible light-illuminated TiO2-supported Rh nanoparticles could significantly enhance methane (CH4) activation in steam methane reforming at mild operating temperature (below 300 °C) with an ∼50% decrease in apparent activation energy compared to that of the pure thermal process. Femtosecond time-resolved infrared spectroscopic measurement and density functional theory calculations show an ultrafast separation of hot carriers at the Rh-TiO2 interface, resulting in the formation of an electron-deficient state of Rhδ+ at the surface for successive CH4 activation at low temperatures. Wavelength-dependent activities and kinetic isotope experiments validate that the photoexcited hot carriers in the Rh nanoparticles play a critical role in facilitating the rate-determining steps, i.e., the cleavage of the C–H bond in CH4. This study opens a promising pathway toward C–H bond activation chemistry by the construction of active nanometal photocatalysts.