Syngas Production by Chemical Looping Dry Reforming of Methane over Ni-modified MoO₃/ZrO₂

We investigated supported-MoO₃ materials effective for the chemical looping dry reforming of methane (CL-DRM) to decrease the reaction temperature. Ni-modified molybdenum zirconia (Ni/MoO₃/ZrO₂) showed CL-DRM activity under isothermal reaction conditions of 650 °C, which was 100-200 °C lower than the previously reported oxide-based materials. Ni/MoO₃/ZrO₂ activity strongly depends on the MoO₃ loading amount. The optimal loading amount was 9.0 wt.% (Ni/MoO₃(9.0)/ZrO₂), wherein two-dimensional polymolybdate species were dominantly formed. Increasing the loading amount to more than 12.0 wt.% resulted in a loss of activity owing to the formation of bulk Zr(MoO₄)₂ and/or MoO₃. In situ Mo K-edge XANES studies revealed that the surface polymolybdate species serve as oxygen storage sites. The Mo⁶⁺ species were reduced to Mo⁴⁺ species by CH₄ to produce CO and H₂. The reduced Mo species reoxidized by CO₂ with the concomitant formation of CO. The developed Ni/MoO₃(9.0)/ZrO₂ was applied to the long-term CL-DRM under high concentration conditions (20 % CH₄ and 20 % CO₂) at 650 °C, with two pathways possible for converting CH₄ and CO₂ to CO and H₂ via the redox reaction of the Mo species and coke formation.