The Two Opposite Faces of Ceria as Redox Mediator in Methane Dry Reforming

Abstract We investigate the interplay between carbon accumulation and redox-driven deactivation pathways in cerium-containing nickel (NiCe) and palladium (PdCe) bimetallic precursor materials upon eventual decomposition into a Ni- or Pd-ceria interfacial system during dry reforming of methane (DRM). By probing defined intermediate states, information from surface electronic structure, morphology, and bulk structure to track structural and chemical changes across several reaction, deactivation, and CO2 titration cycles is combined to identify how carbon accumulation, oxygen transfer, and dynamic metal–ceria interfacial interactions evolve under DRM reaction conditions. Despite their similar cerium-containing precursor architecture and surface composition, the two systems allow studying two detrimental deactivation processes. Bimetallic NiCe decomposes more readily into a Ni-ceria interface, where carbon formation is progressively suppressed. Loss of activity is a result of oxidation of Ni particles mediated by enhanced oxygen transfer from ceria. In contrast, bimetallic PdCe is much more decomposition-resistant, and the localized Pd-ceria interface exhibits high activity throughout multiple DRM cycles, even in the presence of substantial carbon deposition and filamentous carbon growth. The results demonstrate an intrinsic coupling between carbon accumulation and oxygen transfer to the metallic component, with carbon acting as a competing sink for reactive oxygen species. We emphasize the significance of dynamic interfacial structures and show that ceria-mediated oxygen transfer produces contrasting, metal-dependent catalytic outcomes. Whereas in NiCe, efficient oxygen delivery suppresses carbon accumulation, but progressively oxidizes Ni and diminishes methane activation, in PdCe, carbon generation outpaces oxygen-mediated removal, yielding a carbon-rich yet catalytically persistent surface.