Hydrous ruthenium oxide supported on Co3O4 as efficient catalyst for aerobic oxidation of amines

Abstract

Ruthenium catalysts supported on various metal oxides and Co₃O₄-supported various transition metal catalysts prepared by an adsorption-precipitation method were examined for the aerobic oxidation of benzyl amine. We found that the Co₃O₄-supported ruthenium catalyst exhibited the best catalytic performance. The Co₃O₄-supported ruthenium catalyst was also effective for the aerobic oxidation of several other amines. The present catalyst could be used recyclably and be operated under solvent-free conditions. The activity of the present catalyst for the aerobic oxidation of benzyl amine depended less on the oxygen pressure, and the catalyst was also efficient even when air was used as an oxidant. The content of ruthenium and the size of Co₃O₄ particles played crucial roles in determining the catalytic performance. We have clarified that the supported hydrous ruthenium oxide (RuO₂·xH₂O) is the active species for the aerobic oxidation of benzyl amine, whereas the supported metallic ruthenium (Ru°) and supported ruthenium chloride (RuCl₃) are inactive, and the supported anhydrous ruthenium oxide (RuO₂) only exhibits a lower activity.