The effect of O-vacancies on intermediates stability and electron delocalization over MgO modified Ru/ZrO₂: Spectroscopic insights during CO₂ methanation

O-vacancies are defects commonly correlated with the production of CH₄ by CO₂ hydrogenation on reducible catalysts. Their effect on the stability of active CO_ads and its origin is, however, not commonly explored for low Ru-loaded catalysts (Ru < 0.5 wt%). Herein, we investigated two catalysts containing a comparable amount of Ru (≈ 0.4 wt%) on two different zirconia supports: ZrO₂ and ZrO₂-MgO (2.6 wt%-MgO). The rate of CH₄ formation on Ru/ZrO₂-MgO is ca. 3-fold higher than on Ru/ZrO₂. Combined results from various ex-situ and in-situ characterization techniques provide evidence supporting the correlation between methane evolution and the extended Ru-support perimeter as well as with changes in the bond strength of intermediates modulated by O-vacancies. This latter effect represents the main difference between the two catalysts since the replacement of Zr⁴⁺ by Mg²⁺ ions in the ZrO₂ lattice promotes the generation of O-vacancies, facilitating electron transfer from them to interfacial Ru sites. This not only enhances H₂ activation but also weakens the stability of adsorbed bidentate formate (b-HCOO^–_ads), which subsequently decomposes to CO_ads and then hydrogenates to CH₄ at the Ru-support perimeter.