Mixed Zinc/Manganese on Highly Reduced Graphene Oxide: A Highly Active Nanocomposite Catalyst for Aerial Oxidation of Benzylic Alcohols

Abstract

Nanocomposites of highly reduced graphene oxide (HRG) and ZnO x nanoparticles doped manganese carbonate containing different percentages of HRG were prepared via a facile co-precipitation method.The prepared sample calcined at 300 • C yielded i.e., ZnO x (1%)-MnCO 3 /(X%)HRG (where X = 0-7), calcination at 400 • C and 500 • C, yielded different manganese oxides i.e., ZnO x (1%)-MnO 2 /(X%)HRG and ZnO x (1%)-Mn 2 O 3 /(X%)HRG respectively. The prepared catalyst were subjected to catalytic evaluation and a comparative catalytic study between carbonates and oxides for the liquid-phase aerobic oxidation of benzylic alcohols to corresponding aldehydes using molecular oxygen as an eco-friendly oxidant without adding additives or bases. The influence of various parameters such as percentage of HRG, reaction time, catalyst amount, calcination and reaction temperature was systematically examined to optimize reaction conditions using oxidation of benzyl alcohol as a substrate model. It was found that the catalytic performance is remarkably enhanced after using HRG as catalyst co-dopant for the aerobic oxidation of alcohols, possibly owing to the presence of carbon defects and oxygenated functional groups on HRG surface. The as-synthesized catalysts were characterized by SEM, EDX, XRD, Raman, TGA, BET, and FT-IR. Under optimal conditions, the catalyst with composition ZnO x (1%)-MnCO 3 /(1%)HRG calcined at 300 • C exhibited remarkable specific activity (57.1 mmol·g −1 ·h −1 ) with 100% conversion of benzyl alcohol and more than 99% product selectivity within extremely short time (7 min). The as-prepared catalyst was re-used up to five consecutive times without significant decrease in its activity and selectivity. To the best of our knowledge, the achieved specific activity is the highest so far compared to the earlier reported catalysts used for the benzyl alcohol oxidation. A wide range of substituted benzylic and aliphatic alcohols were selectively oxidized into their corresponding aldehydes with complete convertibility and selectivity in short reaction times without over-oxidation to the acids. Due to their significant low cost, superior reproducibility, excellent catalytic efficiency, the ZnO x (1%)-MnCO 3 /(X%)HRG nanocomposites possess several application prospect in other organic chemistry reactions.

Catalytic performance of the Ce-doped LaCoO3 perovskite nanoparticles

“…Selective oxidation of alcohols to carbonyl compounds over heterogeneous catalysts using molecular oxygen (aerobic oxidation) has attracted significant attentions from the viewpoint of green and sustainable chemical processes 9 – 11 . Many studies have been focused on the aerobic oxidation of alcohols using noble metal 12 , 13 and transition metal catalysts 14 , 15 with or without supports 6 , 16 . This is because they show high intrinsic advantages, in terms of effective catalytic ability, product selectivity, easy recovery and reusability.…”

Synthesis and Characterization of CoxOy–MnCO3 and CoxOy–Mn2O3 Catalysts: A Comparative Catalytic Assessment Towards the Aerial Oxidation of Various Kinds of Alcohols

“…In continuance of our present interest on the employment of several mixed metallic oxide NPs as highly effective catalysts for aerial oxidation of alcohols using O 2 molecule as an environmentally-benign oxidant without utilizing any co-oxidant or bases [32][33][34], we have reported the preparation of (X%)Co x O y -MnCO 3 (X = 0, 1, 3, 5, and 7) and thereafter calcination at 500 • C to synthesize (X%)Co x O y -Mn 2 O 3 . The as-obtained catalysts were evaluated for oxidation of a variety of alcohols to their respective carbonyls.…”

Spinel‐Type Mixed Oxides for Stable and Selective Partial Oxidation of Benzyl Alcohol

“…MnCO 3 based catalyst is more active where the surface Mn gets oxidized to γ‐MnOOH by molecular oxygen and acts as catalytic site . Mohamed and coworkers extended their studies to develop an efficient ZnO x nanoparticle doped MnCO 3 supported on highly reduced graphene composite for selective oxidation of BzOH . All the above cited reactions were performed in liquid phase which require expensive separation of catalysts and product from reaction mixture, thus making them less commercially feasible.…”