Oxygen vacancies in Ru/TiO₂ - drivers of low-temperature CO₂ methanation assessed by multimodal operando spectroscopy

Hydrogenation of CO₂ is very attractive for transforming this greenhouse gas into valuable high energy density compounds. In this work, we developed a highly active and stable Ru/TiO₂ catalyst for CO₂ methanation prepared by a solgel method that revealed much higher activity in methanation of CO₂ (ca. 4-14 times higher turnover frequencies at 140-210°C) than state-of-the-art Ru/TiO₂ catalysts and a control sample prepared by wetness impregnation. This is attributed to a high concentration of O-vacancies, inherent to the solgel methodology, which play a dual role for 1) activation of CO₂ and 2) transfer of electrons to interfacial Ru sites as evident from operando DRIFTS and in situ EPR investigations. These results suggest that charge transfer from O-vacancies to interfacial Ru sites and subsequent electron donation from filled metal d-orbitals to antibonding orbitals of adsorbed CO are decisive factors in boosting the CO₂ methanation activity.