Low-temperature catalytic oxidation of aniline to azoxybenzene over an Ag/Fe2O3 nanoparticle catalyst using H2O2 as an oxidant

Abstract

An in situ modified hydrothermal synthesis of Ag/Fe₂O₃ nanoparticles (NPs) and studies of their catalytic activity as a simple, eco-friendly and recyclable catalyst for one-pot conversion of aniline to azoxybenzene were performed. The as-synthesized nanostructured material was characterised by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), SEM-mapping, temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption isotherms (BET), Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma–atomic emission spectroscopy (ICP-AES), ultraviolet-visible spectroscopy (UV-vis) and vibrating sample magnetometer spectroscopy (VSM). The most active and recyclable catalyst with 2–5 nm diameters of the metallic Ag particles supported on 10–50 nm Fe₂O₃ nanoparticles was formed with a silver loading of 1.8 wt%. A high turnover number of ∼592 was achieved with 92% conversion of aniline and 94% selectivity towards the target product azoxybenzene under atmospheric conditions. The effects of various reaction parameters including the reaction time, temperature and substrate to H₂O₂ molar ratio were screened and studied in detail. The results reveal the role of a synergistic effect between the surface Ag nanoparticles and Fe₂O₃ nanospheres for high catalytic activity.