Abstract
In recent years, the development of green mechanochemical processes for the synthesis of new catalysts with higher catalytic efficacy and selectivity has received manifest interest. In continuation of our previous study, in which graphene oxide (GRO) and highly reduced graphene oxide (HRG) based nanocomposites were prepared and assessed, herein, we have explored a facile and solvent-less mechanochemical approach for the synthesis of N-doped graphene (NDG)/mixed metal oxide (MnCO3–ZrO2) ((X%)NDG/MnCO3–ZrO2), as the (X%)NDG/MnCO3–ZrO2 nano-composite was synthesized using physical grinding of separately synthesized NDG and pre-calcined (300 °C) MnCO3–ZrO2 via green milling method. The structures of the prepared materials were characterized in detail using X-ray powder diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Analysis (EDX), Fourier-transform infrared spectroscopy (FTIR), Raman, Thermogravimetric analysis (TGA), and N2 adsorption-desorption isotherm analysis. Besides, the obtained nanocomposites were employed as heterogeneous oxidation catalyst for the alcohol oxidation using green oxidant O2 without involving any surfactants or bases. The reaction factors were systematically studied during the oxidation of benzyl alcohol (PhCH2OH) as the model reactant to benzaldehyde (PhCHO). The NDG/MnCO3–ZrO2 exhibits premium specific activity (66.7 mmol·g−1·h−1) with 100% conversion of PhCH2OH and > 99.9% selectivity to PhCHO after only 6 min. The mechanochemically prepared NDG based nanocomposite exhibited notable improvement in the catalytic efficacy as well as the surface area compared to the pristine MnCO3–ZrO2. Under the optimal circumstances, the NDG/MnCO3–ZrO2 catalyst could selectively catalyze the aerobic oxidation of a broad array of alcohols to carbonyls with full convertibility without over-oxidized side products like acids. The NDG/MnCO3–ZrO2 catalyst were efficiently reused for six subsequent recycling reactions with a marginal decline in performance and selectivity.
Highlights
Nitrogen doping is considered as one of the essential ways of carbon functionalization
In continuation of the study of exploring effects of various carbonaceous materials on the catalytic performance, we explored the use of N-doped graphene (NDG) in which we prepared the novel (X%)NDG/ZrO2 –MnCO3 nanocomposites by mixing of separately synthesized N-doped graphene oxide (NDG) and pre-calcined ZrO2 –MnCO3 NPs using an eco-friendly mechanochemical ball milling procedure
Doped MnCO3 –(1%)ZrO2 nanocomposites, that is efficacious, low cost, and environmental-friendly and the as-prepared nanocomposites were employed for aerobic alkali-free oxidation of different kinds of alcohols with excellent effectiveness and selectivity
Summary
Nitrogen doping is considered as one of the essential ways of carbon functionalization. Incorporation of carbonaceous material along with transition metal nanoparticles have found to be much effective catalysts for the alcohol oxidation, graphene and its derivatives These catalysts have attracted extensive interest owing to their enormous potential in several applications, such as batteries, solar cells, supercapacitors, catalysis, drug delivery, sensors, hydrogen storage, electronics, and water purification [16,17]. We have displayed that zirconia acts a highly effective promoter to the MnCO3 , and the MnCO3 –(1%)ZrO2 calcined at 300 ◦ C It displayed outstanding catalytic efficacy for aerobic oxidation of alcohols using environmentally-friendly oxidant O2. In continuation of the study of exploring effects of various carbonaceous materials on the catalytic performance, we explored the use of N-doped graphene (NDG) in which we prepared the novel (X%)NDG/ZrO2 –MnCO3 nanocomposites by mixing of separately synthesized N-doped graphene oxide (NDG) and pre-calcined ZrO2 –MnCO3 NPs using an eco-friendly mechanochemical ball milling procedure. To the best of our knowledge, this is the first report of a catalytic system wherein ZrO2 –MnCO3 is doped with NDG and evaluated as an oxidation catalyst and especially, highlighting the impact of NDG in the catalytic system as a dopant
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