Oxygen Transfer at Metal-Reducible Oxide Nanocatalyst Interfaces: Contrasting Carbon Growth from Ethane and Ethylene

Carbon deposition from hydrocarbon gases onto metal nanoparticles is an important process impacting materials synthesis and catalysis. Typically, light hydrocarbons may decompose on metal nanoparticles resulting in the formation of graphene layers and hydrogen gas. During hydrocarbon reforming, hydrocarbons are converted to syngas (CO and H₂), and carbon deposition is an undesirable side reaction, which can deactivate the catalyst and cause mechanical degradation. Here, aberration-corrected in situ environmental transmission electron microscopy (ETEM) was employed to investigate the atomic-level three-phase interactions occurring at the metal-support interface during the initial stages of carbon deposition from light hydrocarbons over model Ni/CeO₂ and Ni/SiO₂ catalysts. During exposure to C₂H₆, no carbon deposition took place, and localized reduction zones at the metal-CeO₂ interface demonstrated a carbon oxidation mechanism. In contrast, during exposure to C₂H₄, carbon deposition occurred and was associated with less pronounced reduction zones. The metal-support interface can catalyze the oxidative dehydrogenation of C₂H₆ and subsequently oxidize the resulting carbonaceous species. For C₂H₄, rapid dehydrogenation occurs directly on the Ni surface, which also catalyzes graphite formation. These experiments demonstrate that the ability of interfacial oxygen to inhibit carbon deposition during reforming is strongly influenced by thermodynamic and kinetic considerations, which may show significant variation among different hydrocarbon species.