Characterization of the active species in the aerobic oxidation of benzyl alcohol catalyzed by Ru/ZrO2

Abstract

Ru nanoparticles and Ru acetylacetonate were loaded onto various solid supports, including Al₂O₃, SiO₂, TiO₂, ZrO₂, and CeO₂, and tested in the catalytic oxidation of benzyl alcohol with molecular oxygen in air. Two distinct preparation methods, involving different heat treatment protocols, were employed to activate the catalysts. Among the various supports, Ru loaded onto ZrO₂ and CeO₂ exhibited particularly high activity in the formation of benzaldehyde. The catalyst Ru/ZrO₂ exhibited unique redox behavior that had not been previously observed. The catalytic activity and dispersion of Ru/ZrO₂ changed substantially depending on the Ru loading and thermal treatment temperature. In particular, high catalytic activity was obtained when the Ru loading was <0.4 wt%. Although the catalytic activity of Ru/ZrO₂ catalyst was significantly reduced when reused as it was, it could be reused without loss of activity when the recovered catalyst was thermally treated in air at 973 K prior to each reuse. The catalysts were characterized using hydrogen temperature-programmed reduction (H₂-TPR). For Ru/ZrO₂ treated below 973 K, the H₂/Ru ratio observed in the H₂-TPR exceeded two, suggesting the ZrO₂ was partially reduced with H₂ during H₂-TPR.