Switchable Behavior of Ru–TiO2 Catalysts in HMF Conversion

5-Hydroxymethylfurfural (HMF) is a platform chemical that can be catalytically valorized into high-value-added chemicals. Despite the extensive use of titania-supported metal catalysts in HMF conversion, the specific influence of the TiO2 support on the formation of metal active sites, their dispersion, and their role in HMF conversion is not addressed sufficiently. In this work, we investigated five TiO2 supports, four anatase- and one rutile-dominant, varying in surface area and acidity, which were loaded with 1 wt % Ru using RuCl3. Characterization results revealed that the Ru environment, charge distribution, and surface features (transition from Ru–Cl to Ru–O species) varied depending on the TiO2 support used. Their catalytic performance was assessed in HMF hydrogenation. Despite identical Ru loadings, the Ru/TiO2 catalysts exhibited remarkably different catalytic activities and selectivity. High-surface-area anatase TiO2 led to the formation of smaller Ru particles and supported the conversion of HMF to 5-methylfurfural. In contrast, lower surface area anatase and rutile supports favored the formation of larger Ru particles and redirected the reaction course from 5-MF toward the hydrogenation route, yielding primarily 2,5-bis(hydroxymethyl)furan. This study revealed the switchable behavior of Ru/TiO2 catalysts and exposed the critical role of TiO2 structural and morphological features for reaction pathways in HMF valorization over Ru/TiO2. These insights provide a refined framework for the rational design of oxide-supported catalysts tailored for the selective conversion of biomass.