Abstract
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.
Highlights
Catalytic oxidation of alcohols into their respective carbonyls such as aldehydes and ketones is of crucial importance in synthetic chemistry [1]
X-Ray Diffraction Analysis (XRD) analysis was carried out to investigate the crystallographic structure of the as-synthesized nanocomposite catalyst
Several catalysts with changing Firstly, weight we have studied the catalyticofefficiency of pure, highly reduced graphene oxideand forexamined the aerobic oxidation of percentages
Summary
Catalytic oxidation of alcohols into their respective carbonyls such as aldehydes and ketones is of crucial importance in synthetic chemistry [1]. Huge efforts have been devoted to developing more green catalytic protocols to reduce the disadvantages of conventional oxidation approaches [6]. In the last several years, a plethora of studies have used noble metals like palladium [9], platinum [10], gold [11], and ruthenium [12] as efficient catalysts for selective alcohol oxidation. In addition to their high costs, these noble metals suffer from some drawbacks due to difficulties in synthesis, and the rarity of these precious metals make these catalysts impractical for industry [13]. The metal or metal oxide NPs-based catalysts were reported as highly effective for selective alcohol oxidation
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