The high CO 2 methanation activity of Ru/TiO 2 catalysts prepared by mixing both anatase and rutile TiO 2 as a support is described, focusing on mild reaction temperature (50-200 °C). The specific catalyst design elucidated the impact of the support mixing. Pre-synthesized, monodispersed 2 nm-RuO 2 nanoparticles were used to serve as precursors for active metallic Ru responsible for the CO 2 hydrogenation reaction. Pure TiO 2 supports with different crystallinity (anatase and rutile) were either prepared in the laboratory or obtained from commercial providers, mixed, and used as supports in different ratios. The mixing was also done at different stages of the catalyst preparation, i.e. before RuO 2 deposition, before annealing or after annealing. Our study uncovers that the interaction between the RuO 2 nanoparticles and the anatase and rutile TiO 2 phase during the annealing step dictates the performance of the Ru/TiO 2 methanation catalysts. In particular, when beneficial effects of support mixing are obtained, they can be correlated with RuO 2 migration and stabilization over rutile TiO 2 through epitaxial lattice matching. Also, support mixing can help prevent the sintering of the support and the trapping of the active phase in the bulk of the sintered support. On thermally stable TiO 2 supports, however, it appears clearly that the sole presence of rutile TiO 2 support is sufficient to stabilize Ru in its most active form and to prepare a catalyst with high specific activity.