Turning to the possible CO2 methanation mechanism, direct dissociation and H-assisted dissociation of CO2 are two pathways commonly proposed for Ru-based catalysts. The former entails the dissociative CO2 adsorption into adsorbed CO and O, followed by CO hydrogenation to produce CH4 . The alternative involves the reaction of adsorbed CO2 and H to form formate species, which can be further hydrogenated into adsorbed CO and eventually into CH4 . The absence of formate species for Ru/SiO2 is consistent with a direct CO2 dissociation. The current findings also support the direct CO2 dissociation pathway for Ru/12%Ti-SiO2. Although formate species formed at the metal-support interface are known to potentially serve as the source of carbonyl species through their reaction with adsorbed hydrogen , the change in formate bands does not correlate with the evolution of CO and CH4 bands, indicating that formates might act only as spectator species. Moreover, it is clear that Ti promoter, existing in the form of anatase, modifies the CO adsorption with the provision of interfacial sites between Ru and TiO2. In the CO2 dissociative pathway, the further dissociation of adsorbed CO or hydrogenation of adsorbed CO is generally recognized as the rate-determining step over Ru-based catalysts . Importantly, this step is more favorable at the interfacial sites with lower energy barrier . The remarkable enhancement of CO adsorption at the interfacial sites over Ru/12%Ti-SiO2 catalyst thus could be the reason for the marked catalytic activity improvement.