Catalytic performances of Mn–Ni mixed hydroxide catalysts in liquid-phase benzyl alcohol oxidation using molecular oxygen

Mn–Ni mixed hydroxide was synthesized by a facile co-precipitation method and the catalytic performance in the aerobic oxidation of benzyl alcohol using molecular oxygen was examined. The Mn/Ni molar ratio played an important role and the sample with Mn/Ni molar ratio of 6:4 showed the best catalytic activity. High specific activity of 8.9 mmol/(g h) along with the benzaldehyde selectivity of 99% was achieved at 100 °C within 1 h. Characterizations of X-ray diffraction, X-ray absorption and hydrogen temperature-programmed reduction suggested that co-precipitation method afforded the formation of Mn-in-Ni(OH)2 solid solution without phase segregation. Excess amounts of Mn resulted in segregated Mn3O4 crystalline phase, which showed low surface area and poor catalytic activity. The synergistic interactions between Mn(III) and Ni(II) cations through oxygen bonding were suggested to enhance the activity of Mn–Ni mixed hydroxide catalysts for benzyl alcohol oxidation.

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► Mn–Ni mixed hydroxide catalyst is prepared by facile co-precipitation.
► A Mn-in-Ni(OH)2 solid solution is formed and shows low reduction onset.
► The prepared catalyst is active in benzyl alcohol aerobic oxidation.
► Excess Mn results in segregated Mn3O4 phase with poor activity.
► The synergistic interactions exsit between Mn(III) and Ni(II) cations.