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

Abstract

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 Mn 3O 4 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.