Temperature-Controlled Hydrothermal Synthesis of α-MnO Nanorods for Catalytic Oxidation of Cyclohexanone.

This work describes the comparison of the catalytic performances of α-MnO nanorods synthesized by a facile hydrothermal approach at varying temperatures (140-200 °C). The structure and morphology of these nanorods were analyzed by XRD, N-physisorption, NH-TPD, Raman, SEM, HRTEM, and XPS. The prepared α-MnO nanorods also performed exceptionally well in the catalytic oxidation of cyclohexanone to dicarboxylic acids under mild reaction conditions. The characterization results conferred that there is a significant influence of hydrothermal temperatures on the textural properties, morphology, and catalytic activity. Notably, the α-MnO nanorods obtained from 180 °C hydrothermal conditions outperformed other catalysts with 77.3 % cyclohexanone conversion and 99 % selectivity towards acid products such as adipic acid (AA), glutaric acid (GA) and succinic acid (SA). The improved catalytic activity may be attributed to the interaction of the bifunctional Mn redox metal centres and surface acidic sites. The present oxidation reaction was found to be a promising eco-benign process with high selectivity for the production of commercially significant carboxylic acids from cyclohexanone.