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.