Reduction of Nitro Aromatic Compounds over Ag/Al₂O₃ Nanocatalyst Prepared in Water-in-Oil Microemulsion: Effects of Water-to-Surfactant Mole Ratio and Type of Reducing Agent

Abstract

Silver nanoparticles, with controlled sizes, are synthesized by chemical reduction of silver nitrate with sodium borohydride reducing agent by microemulsion method. To obtain small and monodisperse particles, as-synthesized Ag nanoparticles are readily tuned by varying the water-to-surfactant mole ratio, ω (most crucial operating parameter), and the type of reducing agent. Superior nanoparticles are obtained at intermediate ω (ω = 3). When hydrazine hydrate is used as reducing agent, further superior nanoparticles are obtained with a calculated surface area of 9.76 × 108 mm2/g and hence are chosen for further nanocatalyst synthesis by proper deposition of the same on alumina support. The catalyst is analyzed with UV–visible spectroscopy and X-ray diffraction techniques to confirm the presence of metallic silver. The synthesized catalyst can be conveniently recovered from the reaction system, leading to easy monitoring of the catalytic reaction by spectroscopic methods. Accordingly, reduction of model nitro aromatic compounds, viz., 4-nitrophenol and 4-nitroaniline, are studied. Gradual disappearance of the peak corresponding to nitro compounds reveals the degradation of nitro compounds with time. Furthermore, the appearance and increase of new peaks with time reveal the progressive formation of respective products.