In Situ Studies of Ru-CeO 2 –TiO 2 Catalysts for Selective CO 2 Hydrogenation to Methane: Importance of Metal ↔ Oxide–Oxide Interactions

This work investigates Ru-CeO2–TiO2 catalysts for the CO2 methanation reaction and compares their performance with that of previously studied Ru-CeO2 systems. Despite the lower Ru loading, the TiO2-containing catalysts exhibit a significantly higher activity. To understand this behavior, in situ X-ray absorption spectroscopy (XAS) was carried out at the Ru K-edge and Ce L3-edge. Unlike Ru-CeO2, which displays the reversible redox behavior of Ru, the Ru-CeO2–TiO2 catalysts show irreversible Ru reduction and a substantially higher fraction of Ce3+ species under all tested conditions (H2, CO2, H2/CO2). The stabilization of metallic Ru during methanation, together with the enhanced formation of Ce3+ promoted by TiO2 through interfacial electronic transfer, accounts for the catalyst’s high activity. Complementary in situ DRIFTS measurements reveal the formation and rapid consumption of bidentate carbonates and formates. These species act as a key intermediate in methane formation. Overall, these findings highlight the crucial role of the mixed CeO2–TiO2 oxide in tuning the surface chemistry of the catalysts by stabilizing metallic Ru, enhancing ceria reducibility, and promoting efficient reaction pathways for CO2 methanation. The manipulation of metal ↔ oxide–oxide interactions can be a very useful tool when dealing with the valorization of CO2.