Ag2O Nanoparticles-Doped Manganese Immobilized on Graphene Nanocomposites for Aerial Oxidation of Secondary Alcohols

Ag2O nanoparticles-doped MnO2 decorated on different percentages of highly reduced graphene oxide (HRG) nanocomposites, i.e., (X%)HRG/MnO2–(1%)Ag2O (where X = 0–7), were fabricated through straight-forward precipitation procedure, and 400 °C calcination, while upon calcination at 300 °C and 500 °C temperatures, it yielded MnCO3 and manganic trioxide (Mn2O3) composites, i.e., [(X%)HRG/MnCO3–(1%)Ag2O] and [(X%)HRG/Mn2O3–(1%)Ag2O], respectively. These nanocomposites have been found to be efficient and very effective heterogeneous catalysts for selective oxidation of secondary alcohols into their respective ketones using O2 as a sole oxidant without adding surfactants or nitrogenous bases. Moreover, a comparative catalytic study was carried out to investigate the catalytic efficiency of the synthesized nanocomposites for the aerobic oxidation of 1-phenylethanol to acetophenone as a substrate reaction. Effects of several factors were systematically studied. The as-prepared nanocomposites were characterized by TGA, XRD, SEM, EDX, HRTEM, BET, Raman, and FTIR. The catalyst with structure (5%)HRG/MnO2–(1%)Ag2O showed outstanding specific activity (16.0 mmol/g·h) with complete conversion of 1-phenylethanol and >99% acetophenone selectivity within short period (25 min). It is found that the effectiveness of the catalyst has been greatly improved after using graphene support. A broad range of alcohols have selectively transformed to desired products with 100% convertibility and no over-oxidation products have been detected. The recycling test of (5%)HRG/MnO2–(1%)Ag2O catalyst for oxidation of 1-phenylethanol suggested no obvious decrease in its performance and selectivity even after five subsequent runs