Ionic Nickel Embedded in Ceria with High Specific CO₂ Methanation Activity

CO₂ hydrogenation to methane is gaining increasing interest as one of the most promising ways to store intermittent renewable energy in the form of chemical fuels. Ni particles supported on CeO₂ represent a highly efficient, stable and inexpensive catalyst for this reaction. Herein, Ni-doped CeO₂ nanoparticles were tested for CO₂ methanation showing an extremely high Ni mass-specific activity and CH₄ selectivity. Operando characterization reveals that this performance is tightly associated with ionic Νi and Ce³⁺ surface sites, while formation of metallic Ni does not seem to considerably promote the reaction. Theoretical calculations confirmed the stability of interstitial ionic Ni sites on ceria surfaces and highlighted the role of Ce-O frustrated Lewis pair (FLP), Ni-O classical Lewis pair (CLP) and Ni-Ce pair sites to the activation of H₂ and CO₂ molecules. To a large extent, the theoretical predictions were validated by in situ spectroscopy under H₂ and CO₂  : H₂ gaseous environments.