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 CO 2 into syngas, a mixture of H 2 and CO. When illuminated by 790 mW cm −2 of white light, the 2Ni/CeO 2−x catalyst converts CH 4 and CO 2 beyond thermodynamic equilibrium, while the energy efficiency reaches 33%. The DRM reaction is sustained in a purely photocatalytic mode without external heating, yielding CH 4 and CO 2 rates of 0.21 and 0.75 mmol (g cat • min) −1 , respectively. Theoretical analysis of Ni/CeO 2−x optical properties agrees with in-situ UV-Vis DRS results and reveals partly reduced Ce 3+ sites crucial for extending the optical absorption of Ni/CeO 2−x into the visible light range. Two photocatalytic mechanisms are postulated to occur: the hot charge-carrier driven photocatalytic mechanism and the near-field induced resonant energy transfer, depending on the energy of photons used to stimulate the catalyst. This work identifies sub-stoichiometric Ni/CeO 2−x as highly efficient for boosting methane activation by visible light under mild conditions. • Presence of Ce 3+ is a prerequisite for visible-light absorption. • Reaction is sustained in a purely photocatalytic mode without external heating. • The DRM reaction rate and H 2 selectivity are boosted in light-assisted mode. • Electromagnetic near field enhancement energy transfer is the dominant source of visible-light-induced rate acceleration.