Solvent-Free Synthesis and Applications of Highly Dispersed Ruthenium Catalysts Prepared by Solid-Phase Mixing.

Solvent-free catalyst synthesis provides significant environmental benefits and simplifies the synthesis process. In this study, we utilized the interaction between metal oxide and support to prepare highly dispersed and active Ru catalysts using a simple, solvent-free method. Bulk ruthenium dioxide was physically mixed with six kinds of solid oxide supports (AlO, SiO, TiO, tetragonal ZrO, monoclinic ZrO, and CeO), followed by thermal treatment in air at 773-1273 K. Ru K-edge X-ray absorption fine structure analysis of the treated samples showed that atomically dispersed Ru species were obtained at 973-1073 K when monoclinic ZrO and CeO were used as supports. In contrast, RuO remained aggregated when AlO, SiO, and tetragonal ZrO were used, and a Ru-TiO solid solution was formed at 1173-1273 K when TiO was employed. The catalysts were tested in benzyl alcohol oxidation, levulinic acid hydrodeoxygenation, and ammonia decomposition. Among the different supports examined, Ru supported on monoclinic ZrO and CeO demonstrated remarkably high activity in the reactions, leading to high yields of benzaldehyde, γ-valerolactone, and hydrogen; in contrast, Ru on AlO, SiO, TiO, and tetragonal ZrO were either less active or completely inactive in the reactions.