Coupling Ni exposure with interfacial oxygen on Zr-doped CeO₂ for stable dry reforming of methane

Abstract

Dry reforming of methane (DRM) co-converts CH₄ and CO₂ but is limited by Ni sintering and carbon deposition at high temperature. CeO₂-based supports with oxygen vacancies can mitigate these issues, and Zr doping further tunes defect chemistry and basicity, yet the combined roles of Zr content, Ni exposure and pore architecture in governing interfacial oxygen supply and stability remain unclear. Spherical CeO₂ with interconnected through-pores and narrow mesopores is used as a common scaffold to prepare 5Ni/Ce₁₋ₓZrₓO₂ catalysts (Zr = 0, 1, 3 and 7 mol%) at fixed Ni loading and morphology. XRD, Raman and XPS confirm homogeneous Ce₁₋ₓZrₓO₂ solid solutions and show that, within the investigated Zr range, 3 mol% Zr gives the highest Ce³⁺ fraction and defect related surface oxygen while maintaining a moderate Ni particle size. CO₂ TPD, O₂ TPD, H₂ TPR and H₂ TPD further indicate that medium strength basic sites, interfacial reducible oxygen and accessible Ni sites are best balanced at 3 mol% Zr among the studied compositions. Under DRM at 800 °C, 5Ni/Ce₀․₉₇Zr₀․₀₃O₂ shows the highest CH₄ and CO₂ conversions, the lowest apparent activation energy, an H₂/CO ratio near 1.0 and the lowest coke amount over 50 h. Post-reaction XRD, TG–DTG, Raman and SEM suggest reduced Ni sintering and a larger fraction of filamentous or weakly bound carbon. These results are consistent with the importance of the Ni–Ce–Zr–O interfacial structure in balancing Ni exposure and oxygen supply, enabling high activity with low coking.