Syngas Production by Chemical Looping Dry Reforming of Methane over Ni-modified MoO 3 /ZrO 2 .

We investigated supported-MoO 3 materials effective for the chemical looping dry reforming of methane (CL-DRM) to decrease the reaction temperature. Ni-modified molybdenum zirconia (Ni/MoO 3 /ZrO 2 ) 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/MoO 3 /ZrO 2 activity strongly depends on the MoO 3 loading amount. The optimal loading amount was 9.0 wt.% (Ni/MoO 3 (9.0)/ZrO 2 ), 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(MoO 4 ) 2 and/or MoO 3 . In situ Mo K-edge XANES studies revealed that the surface polymolybdate species serve as oxygen storage sites. The Mo 6+ species were reduced to Mo 4+ species by CH 4 to produce CO and H 2 . The reduced Mo species reoxidized by CO 2 with the concomitant formation of CO. The developed Ni/MoO 3 (9.0)/ZrO 2 was applied to the long-term CL-DRM under high concentration conditions (20 % CH 4 and 20 % CO 2 ) at 650 °C, with two pathways possible for converting CH 4 and CO 2 to CO and H 2 via the redox reaction of the Mo species and coke formation.