Despite the challenges in determining Ru crystallite/particle size, we observe that Ru-massnormalized CO2 conversion rate increases as RuO2 crystallite size decreases in the present study. Correspondingly, CO2 conversion rate increases with Ru dispersion in Ti-doped catalysts, as evident in Fig. (a). Considering the number of Ru sites available on the catalyst surface, TOF slightly decreases with increasing Ru dispersion but remains within the same order of magnitude. These similar TOF values suggest that the specific CO2 methanation activity in Ti-doped catalysts is mostly governed by the dispersion of Ru phase (surface Ru available). In view of the literature, CO2 methanation over supported Ru catalysts is structure sensitive. In several studies, methanation activity was shown to increase with an increase of Ru particle size . However, the effect of Ru particle size on CO2 methanation activity also depends on the range of examined particle size. The activity does not keep increasing when Ru particle size is further increased across a wider range, specifically beyond 5 nm . It should also be kept in mind that changing the Ru nanoparticle size does not only affect the amount of surface-accessible Ru (dispersion), but also the amount of interfacial sites formed with the support or with specific components of the support. This could be a major parameter explaining why Ti-doped formulations are more active than Ru/SiO2 as discussed below.