Enhancement in the metal efficiency of Ru/TiO₂ catalyst for guaiacol hydrogenation via hydrogen spillover in the liquid phase

Decrease in the metal dispersion of noble-metal-loaded catalysts with high metal loading is a major factor reducing noble-metal efficiency. Herein, we investigated the enhancement in metal efficiency of Ru/TiO₂ catalyst by utilizing hydrogen spillover in the liquid-phase. Ru was highly dispersed at low loadings (0.1 and 0.5 wt%), while larger nanoparticles were formed at higher loadings (1–5 wt%). The hydrogen spillover in liquid phase was activated at reaction temperature (100 °C) as the Ru dispersion decreased, which was confirmed through physical dilution experiments, hydrogen temperature-programmed-reduction, and kinetic analysis. Isotope experiment was conducted using D₂O, observing inverse kinetic isotope effect (IKIE) for the high-Ru-loading catalysts. Based on the understanding of the hydrogen spillover in the liquid phase, the low metal efficiency of high-Ru-loading catalysts resulting from low dispersion could be compensated simply by physically mixing pristine TiO₂, which played a role as new active sites when liquid-phase hydrogen spillover was activated.