Ruthenium and TiO2 rutile stabilize Ti3+ Lewis acid sites for decarboxylative CC coupling of acids with remarkably stability in hot condensed water. Display omitted •Liquid-phase ketonization of acetic acid over three catalysts of Ru on different titania supports (anatase, rutile and P25) demonstrates the outstanding effect of the support hydrophobicity on the catalyst stability.•The catalyst of Ru supported on rutile (the most hydrophobic support studied) presents the highest ketonization activity and stability.•Partially hydrophobic materials can facilitate the high temperature reactions in aqueous environments for biomass conversion, environmental remediation, artificial photosynthesis and green chemistry. Stabilization of oxygen vacancies on metal oxides (e.g. TiO2) in liquid phase is an important challenge for the utilization of these materials in artificial photosynthesis, environmental remediation and biomass conversion. To create materials with low-energy barriers for vacancies formation and high stability in aqueous environments, we have developed partially hydrophobic (contact angle ≥90°) TiO2 rutile decorated with Ru nanoparticles. Negligible catalytic activity was observed when hydrophilic (contact angle 51°) 5wt.% Ru/TiO2 anatase was utilized in hot liquid water, while amphiphilic 5wt.% Ru/TiO2 rutile (contact angle ∼90°) retained its catalytic activity. Fine-control of crystalline structure (lattice matching) of TiO2 and Ru allowed us to accelerate the rate of reaction, while the high surface hydrophobicity of the support enabled the stabilization of Ti3+ cations in aqueous and organic environments.