On the mechanism of visible-light accelerated methane dry reforming reaction over Ni/CeO2−x catalysts

Abstract

The methane dry reforming reaction (DRM) converts methane and CO2 into syngas, a mixture of H2 and CO. When illuminated by 790 mW cm−2 of white light, the 2Ni/CeO2−x catalyst converts 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, yielding CH4 and CO2 rates of 0.21 and 0.75 mmol (gcat • min)−1, respectively. Theoretical analysis of Ni/CeO2−x optical properties agrees with in-situ UV-Vis DRS results and reveals partly reduced Ce3+ sites crucial for extending the optical absorption of Ni/CeO2−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/CeO2−x as highly efficient for boosting methane activation by visible light under mild conditions.