Mixed Co-Mn Oxide-Catalysed Selective Aerobic Oxidation of Vanillyl Alcohol to Vanillin in Base-Free Conditions.

Manganese-doped cobalt mixed oxide (MnCo-MO) catalyst was prepared by a solvothermal method. The as-prepared catalyst was characterised by X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, O2 temperature-programmed oxidation and XRD. This catalyst gave 62 % conversion with 83 % selectivity to vanillin in 2 hours for the liquid-phase air oxidation of vanillyl alcohol without using base. Three different types of metal oxides were observed in the prepared catalyst, which could be identified as Co3 O4 , Mn3 O4 and CoMn2 O4 . Among these, the tetragonal phase of CoMn2 O4 was found to be more active and selective for vanillyl alcohol oxidation than Co3 O4 and Mn3 O4 . High-resolution TEM characterisation revealed the morphology of MnCo-MO nanorods with a particle size of 10 nm. Successful recycling of the catalyst was also established in this oxidation reaction.