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

Abstract

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 (Al2O3, SiO2, TiO2, tetragonal ZrO2, monoclinic ZrO2, and CeO2), 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 ZrO2 and CeO2 were used as supports. In contrast, RuO2 remained aggregated when Al2O3, SiO2, and tetragonal ZrO2 were used, and a Ru-TiO2 solid solution was formed at 1173–1273 K when TiO2 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 ZrO2 and CeO2 demonstrated remarkably high activity in the reactions, leading to high yields of benzaldehyde, γ-valerolactone, and hydrogen; in contrast, Ru on Al2O3, SiO2, TiO2, and tetragonal ZrO2 were either less active or completely inactive in the reactions.