Catalytic hydrogenation of nitrophenols and nitrotoluenes over a palladium/graphene nanocomposite
Abstract
We report a stable palladium/graphene (Pd/G) nanocomposite with differing Pd content for use in the catalytic hydrogenation of nitrophenols and nitrotoluenes. Various microscopic and spectroscopic techniques were employed to characterize the as-prepared catalysts. Catalytic hydrogenation reactions of nitrophenols were conducted in aqueous solution by adding NaBH4, while the nitrotoluene hydrogenation was carried out in methanol in the presence of H2 because of the poor solubility in water. The Pd/G hybrids exhibited much higher activity and higher stability than the commercial Pd/C. Due to the presence of a large excess of NaBH4 compared to p-nitrophenol, the kinetic data can be explained by the assumption of a pseudo-first-order reaction with regard to p-nitrophenol. The resulting high catalytic activity can be attributed to the graphene sheets’ strong dispersion effect for Pd nanoparticles and good adsorption ability for nitrobenzene derivatives via π–π stacking interactions. A plausible mechanism is proposed. Considering inductive and conjugation effects that may affect the reactions, the reactivity of nitrophenols in this study is expected to follow the order m-NP > o-NP > p-NP > 2,4-DNP > 2,4,6-TNP, which is in good agreement with the experimental results.
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