Chemical Looping Dry Reforming of Methane over Ni-Modified WO3/ZrO2: Cooperative Work of Dispersed Tungstate Species and Ni over the ZrO2 Surface

In this study, we successfully developed nickel (Ni)-modifiedtungstatezirconia (Ni/WO3/ZrO2) as an effective materialfor chemical looping dry reforming of methane (CL-DRM) under isothermalconditions (750 & DEG;C). The performance of Ni/WO3/ZrO2 strongly depended on the WO3 loading amount. Theoptimal amount of 10.0 wt% WO3, corresponding to low surfaceW density (<4 W atoms/nm(2)), in Ni/WO3(10)/ZrO2 resulted in the exclusive formation of dispersed tungstatespecies, such as isolated monotungstate and/or oligomeric polytungstatespecies. Increasing the loading amount to 30.0 wt% (higher surfaceW density (>4 W atoms/nm(2))) resulted in the formationofcrystalline WO3 species, diminishing the CL-DRM performanceover Ni/WO3/ZrO2. Comprehensive characterization,including in situ/operando W L-3-/L-1-, Ni K-, and Zr K-edge X-ray absorption spectroscopystudies, revealed that surface dispersed tungstate species were reducedby CH4 to yield CO and H-2, and low-valent Wspecies assignable to W-0 to W3+. The low-valentW species were reoxidized by CO2 to produce CO and regeneratethe original W6+ species. These active tungstate speciescooperatively work with Ni over ZrO2 surface to promotepartial CH4 oxidation, leading to efficient CL-DRM.