Encapsulation of Ru nanoparticles: Modifying the reactivity toward CO and CO2 methanation on highly active Ru/TiO2 catalysts

[Display omitted] •COx methanation over Ru/TiO2 catalysts causes O-vacancy formation.•Ru nanoparticle charging due to electronic metal –support interactions (EMSIs).•Ru NPs partially encapsulated by TiOx upon methanation at high temperatures.•Pronounced formation of OH groups upon methanation at high temperatures.•Ru charging induced change in selectivity for CO / CO2 methanation. Aiming at a better understanding of the complex interactions between metal nanoparticles (NPs) and oxide supports, ranging from purely electronic metal-support interactions (EMSIs) to structural modifications associated with strong metal-support interactions (SMSIs), we investigated the impact of a temperature programmed reduction treatment (TPR) of a highly active Ru/TiO2 catalyst on its physical properties and its CO and CO2 methanation performance by kinetic and spectroscopic techniques, in combination with structural characterization. XP, EPR and DRIFT spectra resolved a significant shift of the Ru 3d levels to lower binding energies, the formation of O-vacancy defects and a red-shift of COad related bands, respectively, after the TPR sequence. This indicates an increase of the local charge density in the Ru NPs, due to charge transfer from O-vacancy defects to the Ru NPs. Finally, from CO adsorption and XPS measurements we conclude on a partial encapsulation of the Ru NPs by a TiOx layer.