Synthesis, characterization and relative catalytic study of ZrOx-MnCO3, – MnO2or -Mn2O3 deposited on highly reduced graphene oxide nanocomposites for aerobic oxidation of secondary alcohols

Abstract

Zirconia nanoparticles doped MnCO₃ have been successfully immobilized on various percentages of highly reduced graphene oxide (HRG)[(X%)HRG/MnCO₃–(1%)ZrO_x](where, X=0–7)],via a facile and straight forward co-precipitation method. Upon calcination, the as-obtained materials have yielded different types of HRG/manganese oxide nanocomposites at different temperatures i.e.[(X%)HRG/MnO₂–(1%)ZrO_x] and [(X%)HRG/Mn₂O₃–(1%)ZrO_x]. A detail investigation was carried out to compare the catalytic performance of carbonates and oxides based nanocomposites for the selective oxidation of secondary alcohols.  For this purpose, molecular oxygen was employed as an environmentally benign oxidant under base-free conditions. The reaction conditions were optimized with different weight percentages of HRG, reaction times, calcination temperatures, catalyst dosages, and reaction temperatures using 1-phenylethanol as a substrate model. The catalytic performance of the nanocomposites was enhanced significantly due to the presence of HRG as a support material. The catalyst with (1%)HRG/MnCO₃–(1%)ZrO_x exhibited outstanding performance as well as excellent selectivity in the aerobic oxidation of 1-phenylethanol. In this case, 100% conversion in 4 min with more than 99% selectivity was achieved with excellent specific activity of 60.0 mmol.g⁻¹.h⁻¹. Moreover, catalyst can be efficiently reused 5 times without discernible decrease in its activity and selectivity. Apart from this, various other alcohols were also selectively oxidized to their corresponding carbonyls with complete conversion in short reaction times under optimal conditions without over-oxidation to the carboxylic acids.