Dry reforming of methane over Ca-Ni-Ce-Zr mixed oxide catalysts: Tuning the Ce/Zr ratio for balanced activity and coke resistance

A series of Ca-Ni-Ce-Zr mixed oxide catalysts with different Ce/Zr ratios were prepared by a citrate-assisted sol-gel method and investigated for dry reforming of methane. The Ce/Zr ratio strongly influenced the crystalline phase evolution, reduction state and local coordination environment of Ni species, CO 2 adsorption behavior, reducibility, catalytic activity, and carbon accumulation behavior. XRD, TEM, and HAADF-STEM–EDS analyses provided information on the crystalline structure, particle morphology, and elemental distribution of the reduced catalysts. Ni K-edge XANES/EXAFS further revealed the coexistence of metallic Ni-like and oxide-associated Ni species, with the equimolar Ce/Zr composition retaining a larger contribution from oxide-associated Ni species after reduction. In DRM at 800 °C, Ca-Ni-Ce 0.8 Zr 0.2 O δ exhibited the highest short-term activity, with CH 4 and CO 2 conversions of 92.0 and 96.2%, respectively. Descriptor-based analysis using CO 2 -TPD and H 2 -TPR suggested that this high activity was associated with favorable CO 2 adsorption behavior and strongly interacting reducible Ni-containing species. However, this high activity was also accompanied by substantial carbon deposition. In contrast, Ca-Ni-Ce 0.5 Zr 0.5 O δ showed comparable activity, with CH 4 and CO 2 conversions of 90.4 and 95.5%, respectively, while providing a more favorable activity–coke balance. A 500 h stability test confirmed that Ca–Ni–Ce 0.5 Zr 0.5 O δ maintained stable catalytic performance under prolonged DRM conditions, with only a slight increase in coke amount and a markedly decreased time-normalized coke formation rate after long-term operation. These results indicate that tuning the Ce/Zr ratio in Ca-Ni-Ce-Zr mixed oxides is an effective strategy for balancing CH 4 activation, CO 2 activation, and coke tolerance in Ni-based DRM catalysts.