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

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.