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-CeO 2 –TiO 2 catalysts for the CO 2 methanation reaction and compares their performance with that of previously studied Ru-CeO 2 systems. Despite the lower Ru loading, the TiO 2 -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 L 3 -edge. Unlike Ru-CeO 2, which displays the reversible redox behavior of Ru, the Ru-CeO 2 –TiO 2 catalysts show irreversible Ru reduction and a substantially higher fraction of Ce 3+ species under all tested conditions (H 2, CO 2, H 2 /CO 2 ). The stabilization of metallic Ru during methanation, together with the enhanced formation of Ce 3+ promoted by TiO 2 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 CeO 2 –TiO 2 oxide in tuning the surface chemistry of the catalysts by stabilizing metallic Ru, enhancing ceria reducibility, and promoting efficient reaction pathways for CO 2 methanation. The manipulation of metal ↔ oxide–oxide interactions can be a very useful tool when dealing with the valorization of CO 2 .