Temperature-Controlled Hydrothermal Synthesis of α-MnO2 Nanorods for Catalytic Oxidation of Cyclohexanone.

Abstract

This work describes the comparison of the catalytic performances of α-MnO2 nanorods synthesized by a facile hydrothermal approach at varying temperatures (140-200 °C). The structure and morphology of these nanorods were analyzed by XRD, N2-physisorption, NH3-TPD, Raman, SEM, HRTEM, and XPS. The prepared α-MnO2 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-MnO2 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 Mn3+/4+ 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.