On the Mechanism of Visible-Light Accelerated Methane Dry Reforming Reaction over Ni/CeO2-X Catalysts

The methane dry reforming reaction (DRM) converts methane and CO2 into syngas, a mixture of H2 and CO. When illuminated by white light, the 2Ni/CeO2-x catalyst enables conversions of both CH4 and CO2 beyond thermodynamic equilibrium, while the energy efficiency reaches 33 %. The DRM reaction is sustained in a purely photocatalytic mode without external heating when illuminated by 790 mw/cm2 of white light with CH4 and CO2 rates equaling 0.21 and 0.75 mmol/gcat*min, respectively. At a constant catalyst temperature of 400 °C, the reaction selectivity expressed as H2/CO ratio increases from 0.23 to 0.59 in light-assisted mode compared to the experiment in the dark. The theoretical analysis of Ni/CeO2-x optical properties agree with in-situ UV-Vis DRS results and show that the presence of partly reduced Ce3+ sites is crucial for extending the optical absorption of Ni/CeO2-x into the visible light range. The strong electromagnetic near field enhancement was identified as the dominant source of visible-light-induced rate acceleration and occurs mainly over nickel nanoparticles which are the active sites for methane activation. This work identifies Ni/CeO2-x photocatalyst as highly efficient for boosting methane activation by visible light illumination under mild conditions.