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.
Keywords: Chemical looping dry reforming of methane (CL-DRM); Ni-modified molybdenum zirconia (Ni/MoO3/ZrO2); two-dimensional polymolybdate species.
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